US20200340155A1

US20200340155A1 - Nonwoven sheets comprising surface enhanced pulp fibers, surgical gowns and surgical drapes incorporating such nonwoven sheets, and methods of making the same

Info

Publication number: US20200340155A1
Application number: US16/853,305
Authority: US
Inventors: Harshad Pande; Rod TIBBOLES
Original assignee: Domtar Paper Co LLC
Current assignee: Domtar Paper Co LLC
Priority date: 2019-04-23
Filing date: 2020-04-20
Publication date: 2020-10-29
Also published as: WO2020219390A1

Abstract

A nonwoven sheet can comprise a plurality of cellulosic pulp fibers and a plurality of synthetic polymeric fibers. The cellulosic pulp fibers can include a plurality of cedar pulp fibers that have a length weighted average fiber length of at least 1.0 millimeters (mm), optionally between 1.5 and 2.0 mm, and an average hydrodynamic specific surface area of at least 4.5 square meters per gram (m2/g), optionally at least 5 m2/g. The cellulosic pulp fibers can also include a plurality of softwood pulp fibers that, optionally, are NBSK pulp fibers and do not include cedar pulp fibers. The synthetic polymeric fibers can comprise polyester fibers.

Description

CROSS-REFERENCED TO RELATED APPLICATIONS

This application claims priority to and the benefit of U.S. Provisional Application No. 62/837,431, filed Apr. 23, 2019, U.S. Provisional Application No. 62/840,125, filed Apr. 29, 2019, and U.S. Provisional Application No. 62/883,223, filed Aug. 6, 2019. The contents of the foregoing applications are incorporated herein by reference in their respective entireties.

FIELD OF INVENTION

The present invention relates generally to nonwoven sheets and articles incorporating the same, and more particularly but without limitation to nonwoven sheets comprising surface enhanced pulp fibers.

BACKGROUND

Nonwoven sheets can comprise both cellulosic pulp fibers and synthetic polymeric fibers. Such nonwovens are used in a wide variety of applications, such as in medical and scientific apparel, wipes, cloths, and the like. For some applications, such as surgical gowns and surgical drapes, the nonwoven sheet preferably has a high air permeability and drapability for comfort while impeding the flow of liquids (e.g., bodily fluids) therethrough to protect a wearer. The drapability and combination of air permeability and liquid resistance that a nonwoven sheet can achieve depends, at least in part, on the morphological characteristics of the nonwoven's fibers.
Typically, cellulosic pulp fibers included in such nonwoven sheets are not fibrillated or are lightly fibrillated (e.g., have an average hydrodynamic specific surface area that is about 2 square meters per gram), at least in part because highly fibrillated pulp fibers may comprise a large amount of fines. Fines can be detrimental in the hydroentangling process used to make some nonwovens (e.g., spunlace nonwovens) and can adversely affect barrier properties; as such, highly fibrillated pulp fibers are generally considered undesirable for such nonwovens. Additionally, some fiber grades, such as northern bleached softwood kraft (NBSK) pulp fibers, may provide poor drapability and thus are also generally considered undesirable for these nonwovens. However, pulps having non-fibrillated or lightly refined fibers that tend to impart a more desirable drapability and/or combination of air permeability and liquid resistance for a nonwoven sheet are typically more expensive to produce and/or process, while fibers of pulps that have lower production and/or processing costs may not provide the same level of performance.

SUMMARY

As such, there is a need in the art for nonwoven sheets that can provide a drapability and/or a combination of air permeability and liquid resistance that is comparable to or better than that of conventional nonwoven sheets incorporating fibers of expensive-to-produce pulps, but that can be made at lower cost. The present nonwoven sheets address this need in the art by incorporating a combination of softwood pulp fibers, such as NBSK pulp fibers, surface enhanced pulp fibers (SEPF) that are highly fibrillated (e.g., have a length weighted average fiber length of at least 1.0 mm and an average hydrodynamic specific surface area of at least 4.5 m²/g, for cedar pulp fibers), and a plurality of synthetic polymeric fibers, such as polyester fibers.
The SEPF can be cedar pulp fibers, which have a high collapsibility that promotes air permeability and liquid resistance. While cedar pulp fibers can be relatively expensive to make, due at least in part to the unique fiber morphology of cedar SEPF, a nonwoven sheet can achieve comparable air permeability and liquid resistance using a combination of less expensive softwood pulp fibers that do not include cedar pulp fibers (e.g., NBSK pulp fibers) and cedar SEPF than an otherwise similar nonwoven sheet in which all of the cellulosic pulp fibers are cedar pulp fibers. And, unlike highly fibrillated pulp fibers made using conventional processes, the SEPF can be made via a mechanical refining process in which one or more refiners expend a large amount of energy, utilize refiner elements having a fine bar pattern, and/or operate at a low specific edge load (SEL), which can mitigate fine production and thereby facilitate hydroentangling and promote desirable nonwoven barrier properties. The combination of non-cedar softwood pulp fibers and cedar SEPF can also yield better nonwoven drapability than if the cellulosic pulp fibers only included the non-cedar softwood pulp fibers. Such nonwoven sheets incorporating SEPF may be particularly suitable for articles such as surgical gowns and surgical drapes.
Some of the present nonwoven sheets comprise a plurality of cellulosic pulp fibers and a plurality of synthetic polymeric fibers. The cellulosic pulp fibers, in some nonwoven sheets, comprise a plurality of cedar pulp fibers and a plurality of other softwood pulp fibers. The other softwood pulp fibers, in some nonwoven sheets, do not include cedar pulp fibers. In some nonwoven sheets, at least 50% of the fibers of the nonwoven sheet, by weight, are the cellulosic pulp fibers. The nonwoven sheet, in some embodiments, is a spunlace nonwoven.
Some of the present methods of making a nonwoven sheet comprise depositing a plurality of fibers onto a moving surface to form a nonwoven web precursor. The fibers, in some methods, include a plurality of cellulosic pulp fibers and a plurality of synthetic polymeric fibers. The cellulosic pulp fibers, in some methods, comprise a plurality of cedar pulp fibers and a plurality of softwood pulp fibers that, optionally, do not include cedar pulp fibers. In some methods, depositing the fibers is performed such that at least 50% of the fibers of the nonwoven precursor web, by weight, are the cellulosic pulp fibers. In some methods, depositing the fibers comprises depositing the synthetic polymeric fibers onto a moving surface and depositing a pulp sheet comprising the cellulosic pulp fibers onto the synthetic polymeric fibers. Some methods comprise directing one or more jets of water onto the nonwoven precursor web and, optionally, drying the nonwoven precursor web. In some methods, the nonwoven precursor web is substantially free of water before the water jet(s) are directed onto the nonwoven precursor web.
In some embodiments, the cedar pulp fibers have a length weighted average fiber length of at least 1.0 millimeters (mm), optionally between 1.0 mm and 2.2 mm or between 1.5 mm and 2.0 mm, and an average hydrodynamic specific surface area of at least 4.5 square meters per gram (m²/g), optionally at least 5.0 m²/g. The cedar pulp fibers, in some embodiments, have a length weighted fines value that is less than or equal to 30%, when fibers having a length of 0.20 mm or less are classified as fines. The softwood pulp fibers, in some embodiments, are northern bleached softwood kraft (NBSK) pulp fibers. In some embodiments, the synthetic polymeric fibers are polyester fibers. In some embodiments, between 1% and 20%, optionally between 1% and 10%, of the cellulosic pulp fibers, by weight, are the cedar pulp fibers and/or between 80% and 99%, optionally between 90% and 99%, of the cellulosic pulp fibers are the softwood pulp fibers.
Some of the present articles can comprise a surgical gown or a surgical drape. Some surgical gowns comprise a torso portion, two sleeves coupled to the torso portion, and a neck hole defined at an upper end of the torso portion such that, when the surgical gown is worn, the neck hole is configured to receive a neck of a wearer and each of the sleeves is configured to receive a respective one of the arms of the wearer. Some surgical gowns can comprise any of the present nonwoven sheets.
The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are “coupled” may be unitary with each other. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The term “substantially” is defined as largely but not necessarily wholly what is specified—and includes what is specified; e.g., a composition substantially free of water can have no water or can have a low amount of water (e.g., less than 10% of the composition, by weight, can be water)—as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially” and “approximately” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent.
The terms “comprise” and any form thereof such as “comprises” and “comprising,” “have” and any form thereof such as “has” and “having,” and “include” and any form thereof such as “includes” and “including” are open-ended linking verbs. As a result, a product or system that “comprises,” “has,” or “includes” one or more elements possesses those one or more elements, but is not limited to possessing only those elements. Likewise, a method that “comprises,” “has,” or “includes” one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps.
Any embodiment of any of the products, systems, and methods can consist of or consist essentially of—rather than comprise/include/have—any of the described steps, elements, and/or features. Thus, in any of the claims, the term “consisting of” or “consisting essentially of” can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb.
Further, a device or system that is configured in a certain way is configured in at least that way, but it can also be configured in other ways than those specifically described.
The feature or features of one embodiment may be applied to other embodiments, even though not described or illustrated, unless expressly prohibited by this disclosure or the nature of the embodiments.
Some details associated with the embodiments described above and others are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings illustrate by way of example and not limitation. For the sake of brevity and clarity, every feature of a given structure is not always labeled in every figure in which that structure appears. Identical reference numbers do not necessarily indicate an identical structure. Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers.

FIG. 1A is a top view of an embodiment of the present nonwoven sheets.

FIG. 1B is a sectional view of the nonwoven sheet of FIG. 1A taken along line 1B-1B.

FIG. 2 is a schematic front view of a surgical gown that can incorporate one or more of the present nonwoven sheets.

FIG. 3 is a schematic of a system that can be used to make some of the present nonwoven sheets, the system including a refining unit and a nonwoven manufacturing system.

FIG. 4A is a first embodiment of a refining unit that can be used in the system of FIG. 3 to make SEPF, the refining unit comprising a single mechanical refiner through which pulp fibers can be recirculated.

FIG. 4B is a second embodiment of a refining unit that can be used in the system of FIG. 3 to make SEPF, the refining unit comprising a first mechanical refiner and a second mechanical refiner through which pulp fibers can be recirculated.

FIG. 5 is a schematic, sectional view of refining elements that can be used in each of the refiner(s) in the refining units of FIGS. 4A and 4B, each of the refining elements having a plurality of bars and grooves.

FIG. 6 is a schematic of a nonwoven manufacturing system that can be used in the system of FIG. 3, the nonwoven manufacturing system configured to hydroentangle softwood pulp fibers, SEPF, and synthetic polymeric fibers.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B, shown is an embodiment 10 of the present nonwoven sheets. Nonwoven sheet 10 can have a composition that facilitates air permeability and impedes the flow of liquids through the sheet, rendering the sheet suitable for use in, for example, surgical gowns and drapes. To illustrate, nonwoven sheet 10 can comprise fibers 14 that include cellulosic pulp fibers 18 and synthetic fibers 22. Cellulosic pulp fibers 18 can comprise softwood pulp fibers 26 (e.g., originating from spruce, pine, fir, hemlock, redwood, and/or the like) and a plurality of highly fibrillated pulp fibers 30, referred to herein as “surface enhanced pulp fibers” (SEPF), that can be softwood pulp fibers, hardwood pulp fibers (e.g., originating from oak, gum, maple, poplar, Eucalyptus, aspen, birch, and/or the like), or non-wood pulp fibers (e.g., originating from kenaf, hemp, straws, bagasse, and/or the like). Preferably, SEPF 30 are softwood pulp fibers, particularly cedar pulp fibers. Cedar pulp fibers can have high collapsibility, which may promote air permeability while impeding the ingress of liquids through the sheet.
Softwood pulp fibers 26 can be unrefined or lightly fibrillated (compared to SEPF 30) (e.g., the softwood pulp fibers can have an average hydrodynamic specific surface area that is less than any one of, or between any two of, 3 square meters per gram (m²/g), 2 m²/g, 1 m²/g, or less (e.g., less than 2 m²/g)). SEPF 30 can have higher surface areas compared to conventionally-refined pulp fibers and can be made in a manner (described below) that mitigates reductions in fiber length and the production of fines. For example, SEPF 30 can have a length weighted average fiber length that is greater than or equal to any one of, or between any two of, 0.20 millimeters (mm), 0.30 mm, 0.40 mm, 0.50 mm, 0.60 mm, 0.70 mm, 0.80 mm, 0.90 mm, 1.0 mm, 1.5 mm, 2.0 mm, or larger (e.g., when cedar, greater than or equal to 1.0 mm, such as between 1.0 mm and 2.0 or 2.2 mm, or between 1.5 mm and 2.0 or 2.2 mm), and an average hydrodynamic specific surface area that is greater than or equal to any one of, or between any two of, 4.5 m²/g, 5 m²/g, 6 m²/g, 7 m²/g, 8 m²/g, 9 m²/g, 10 m²/g, 12 m²/g, 14 m²/g, 16 m²/g, 18 m²/g, 20 m²/g, or larger (e.g., for cedar, at least 4.5 or 5.0 m²/g). And, SEPF 30 can have a length weighted fines value that is less than or equal to any one of, or between any two of, 40%, 35%, 30%, 25%, 20%, or less (e.g., less than or equal to 30%), when fibers having a length of 0.20 mm are classified as fines. Optionally, the number of SEPF 30 can be at least 12,000 per milligram on an oven-dry basis (e.g., based on a sample of the SEPF that is dried in an oven set at 105° C. for 24 hours). A description of SEPF and processes by which SEPF can be made are set forth in further detail in U.S. patent application Ser. No. 13/836,760, filed Mar. 15, 2013, and published as Pub. No. US 2014/0057105 on Feb. 27, 2014, which is hereby incorporated by reference. Softwood pulp fibers 26 and SEPF 30 can be of any suitable grade, e.g., those pulp fibers can originate from a chemical process (e.g., a kraft process), a mechanical process, a thermomechanical process, a chemi-thermomechanical process, and/or the like, and can be bleached or unbleached. For example, softwood pulp fibers 26 can be northern bleached softwood kraft (NBSK) pulp fibers.
Incorporating both softwood pulp fibers 26, which can be non-cedar pulp fibers (e.g., NBSK pulp fibers), and cedar SEPF 30 can reduce the cost of producing nonwoven sheet 10 while providing a comparable or better drapability and/or combination of air permeability and liquid resistance, compared to conventional nonwoven sheets in which all of the cellulosic pulp fibers are cedar pulp fibers. Pulps having cedar fibers—which may have good collapsibility—can be more expensive to produce than other pulps such as NBSK pulps, which typically comprise pine, spruce, and/or larch pulp fibers. For example, chips used to make cedar pulp can have a low packing density which can reduce productivity and the cost of chemicals and/or bleaching when making cedar pulp may be relatively high. Due at least in part to the unique characteristics of cedar SEPF 30, incorporating softwood pulp fibers 26 can reduce the amount of cedar SEPF required to achieve desired performance. To illustrate, by weight, less than or equal to any one of, or between any two of, 20%, 18%, 16%, 14%, 12%, 10%, 8%, 6%, 4%, 2% or less (e.g., between 1% and 20% or between 1% and 10%) of cellulosic pulp fibers 18 can be SEPF 30 and greater than or equal to any one of, or between any two of, 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, or more (e.g., between 80% and 99% or between 90% and 99%) of the cellulosic pulp fibers can be softwood pulp fibers 26. The comparatively large surface area and low fines content of SEPF 30 can promote nonwoven sheet 10's barrier properties—e.g., promoting liquid resistance while maintaining good air permeability—for use in articles such as surgical gowns and surgical drapes in which these barrier properties are desirable. The relatively low fines content of SEPF 30 can also mitigate poor hydroentangling (described below) attributable to fines, a challenge that rendered conventional highly fibrillated pulp fibers undesirable in conventional nonwovens. And the combination of SEPF 30 with non-cedar softwood pulp fibers 26 (e.g., NBSK fibers) can yield a desirable drapability for nonwoven sheet 10, something that may not be achievable if the cellulosic fibers included the non-cedar softwood pulp fibers alone.
Synthetic fibers 22 can comprise any suitable polymeric fibers, such as, for example, polyester, polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, nylon, polycarbonate, and/or polysulfone fibers; as shown, the synthetic fibers are polyester fibers. And in some embodiments, synthetic fibers 22 can comprise fibers derived from cellulose, such as viscose and/or lyocell.
Nonwoven sheet 10 can comprise any suitable proportion of cellulosic pulp fibers 18 and synthetic fibers 22. For example, at least a majority of the fibers of nonwoven sheet 10 can be cellulosic pulp fibers 18, e.g., by weight, greater than or equal to any one of, or between any two of, 50%, 60%, 70%, 80%, 90%, or more of the fibers of the nonwoven sheet can be the cellulosic pulp fibers and less than or equal to, or between any two of, 50%, 40%, 30%, 20%, 10%, or less of the fibers of the nonwoven sheet can be the synthetic fibers. The combination of cellulosic pulp fibers 18 and synthetic fibers 22 can promote nonwoven sheet 10's air permeability and resistance to liquids.
A wide variety of articles, such as, for example, surgical gowns and surgical drapes, can incorporate at least a portion of nonwoven sheet 10. Referring to FIG. 2, shown is a surgical gown 34 having a torso portion 38, two sleeves 42 coupled to the torso portion, and a neck hole 46 defined at an upper end of the torso portion such that, when the surgical gown is worn, the wearer's neck can be received through the neck hole and each of the wearer's arms can be received in a respective one of the sleeves. Surgical gown 34 can comprise one or more of the present nonwoven sheets (e.g., 10). For example, at least one of (up to and including each of) torso portions 38 and sleeves 42 can comprise at least a portion of nonwoven sheet 10. The relatively high air permeability of nonwoven sheet 10 can promote comfort, and the nonwoven sheet can function as a barrier to impede the flow of liquids (e.g., bodily fluids) through the gown and to the wearer. These advantages can also be beneficial for surgical drapes, among other articles. For example, while nonwoven sheet 10 is, as shown, incorporated into a surgical gown, in other embodiments the nonwoven sheet can be used to make articles such as clean room apparel, masks, gloves, sheets, cloths, and/or the like.
Nonwoven sheet 10 can be made in any suitable process; for example, the nonwoven sheet can be a spunlace nonwoven. Referring to FIG. 3, shown is a system 50 that can be used to perform some of the present methods of making a nonwoven sheet (e.g., 10). While some methods are described with reference to system 50, system 50 is not limiting on those methods, which can be performed using any suitable system.
Some methods include a step of making the SEPF (e.g., 30) in a refining unit (e.g., 54). To make the SEPF, a first pulp feed comprising SEPF precursor pulp fibers (e.g., 58)—which can be any of the cellulosic fiber types discussed above (e.g., softwood or cedar pulp fibers)—can be refined using one or more mechanical refiners (e.g., 62 a and/or 62 b) (FIGS. 4A and 4B). Referring additionally to FIG. 5, each of the refiner(s) can comprise at least two refining elements (e.g., 66), each including a plurality of bars (e.g., 70) that extend outwardly from a surface (e.g., 74) of the refining element and define a plurality of grooves (e.g., 78). For example, each of the refiner(s) can be a disk refiner (e.g., a single-disk refiner, a double-disk refiner, or a multi-disk refiner) (e.g., in which the refining elements are refiner plates) or a conical refiner (e.g., in which the refining elements are conical refiner fillings).
The first pulp feed can be refined at least by, for each of the refiner(s), introducing the first pulp feed between the refining elements and rotating at least one, optionally each, of the refining elements. The bars can thereby impart compression and shearing forces on the SEPF precursor pulp fibers to increase the fibrillation, and thus the average hydrodynamic specific surface area, thereof. To facilitate a high degree of fibrillation while mitigating undesired reductions in fiber length, each of the refining elements can have a fine bar pattern and, optionally, the refiner(s) can be operated at a low intensity (e.g., at a low specific edge load (SEL)), compared to conventional refining processes. For example, for each of the refining elements, each of the bars can have a width (e.g., 80) that is less than or equal to any one of, or between any two of, 1.4 millimeters (mm), 1.3 mm, 1.2 mm, 1.1 mm, 1.0 mm, 0.9 mm, 0.8 mm, or less (e.g., less than or equal to 1.4 mm, 1.3 mm, or 1.0 mm) and each of the grooves can have a width (e.g., 84) that is less than or equal to any one of, or between any two of, 2.5 mm, 2.3 mm, 2.1 mm, 1.9 mm, 1.7 mm, 1.5 mm 1.3 mm, or less (e.g., less than or equal to 2.5 mm, 1.6 mm, or 1.3 mm). For cedar SEPF precursor pulp fibers, the bar width is preferably less than or equal to 1.4 mm or 1.3 mm and the groove width is preferably less than or equal to 2.5 mm or 2.4 mm. And, refining the first pulp feed can be performed such that each of the refiner(s) operates at a SEL that is less than or equal to any one of, or between any two of, 1.5 Watt-seconds per meter (W·s/m), 1.0 W·s/m, 0.50 W·s/m, 0.45 W·s/m, 0.40 W·s/m, 0.35 W·s/m, 0.30 W·s/m, 0.25 W·s/m, 0.20 W·s/m, 0.15 W·s/m, 0.10 W·s/m, or less (e.g., less than or equal to 0.45 W·s/m, at least for cedar SEPF precursor pulp fibers).
The first pulp feed can be refined using a large amount of refining energy, compared to conventional processes, to achieve a high degree of fibrillation. For example, refining the first pulp feed can be performed such that, per ton of fiber in the first pulp feed, the refiner(s) consume greater than or equal to any one of, or between any two of, 300 kilowatt-hours (kWh), 400 kWh, 500 kWh, 600 kWh, 700 kWh, 800 kWh, 900 kWh, 1,000 kWh, or more (e.g., greater than or equal to 300 kWh or 600 kWh per ton of fiber in the first pulp feed). The refining energy expended can depend at least in part on the type of pulp fibers in the first pulp feed and the desired degree of fibrillation. Without limitation, when the SEPF precursor pulp fibers are hardwood pulp fibers, the refining energy can be between 300 kWh and 600 kWh per ton of fiber and when the SEPF precursor pulp fibers are softwood pulp fibers (e.g., cedar pulp fibers), the refining energy can be at least 600 kWh per ton of fiber (e.g., because softwood pulp fibers, which are typically longer than hardwood pulp fibers, may be subjected to more refining than hardwood pulp fibers before fiber shortening and fines production adversely affects fiber quality).
Such refining energies can be reached in any suitable manner. For example, each of the refiner(s) can consume, per ton of fiber in the first pulp feed, less than or equal to any one of, or between any two of, 110 kWh, 100 kWh, 90 kWh, 80 kWh, 70 kWh, 60 kWh, 50 kWh, 40 kWh, 30 kWh, or less each time the first pulp feed is passed through the refiner. To reach the total desired refining energy, the first pulp feed can be recirculated through at least one of the refiner(s) and/or passed through multiple refiners such that the cumulative energy consumed by the refiner(s) reaches the desired level (e.g., at least 300 kWh or at least 600 kWh per ton of fiber). Referring to FIG. 4A, for example, the one or more refiners can consist of a single refiner (e.g., 62 a) (e.g., where, for each of the refiner's refining elements, each of the bars has a width that is less than or equal to 1.4 mm or 1.3 mm and each of the grooves has a width that is less than or equal to 2.5 mm or 2.4 mm) and the first pulp feed can be passed through the refiner a plurality of times (e.g., greater than or equal to any one of, or between any two of, 2, 6, 10, 14, 18, 22, 26, or more times) until the refiner consumes the desired refining energy. Alternatively, and referring to FIG. 4B, the one or more refiners can comprise one or more first refiners (e.g., 62 a) (e.g., a single first refiner) and one or more second refiners (e.g., 62 b) such that the first pulp feed passes through multiple refiners. Each of the first refiner(s) can be configured to fibrillate the first pulp fibers with less refinement than the second refiner(s). For example, for each of the first refiner(s), each of the bars can have a width that is greater than or equal to 1.0 mm, each of the grooves can have a width that is greater than or equal 1.6 mm, and the first refiner can operate at a SEL between 0.2 and 0.45 W·s/m. The first pulp feed can be introduced into the second refiner(s) after passing through the first refiner(s) and, for each of the second refiner(s), each of the bars can have a width that is less than or equal to 1.0 mm, each of the grooves can have a width that is less than or equal to 1.6 mm, and the second refiner can operate at a SEL between 0.1 and 0.2 W·s/m. The first pulp feed can be recirculated through at least one of the second refiner(s) (e.g., as described with respect to FIG. 4A). In other embodiments, the first and second refiners can provide a similar level of refinement (e.g., each can have the same bar width, such as less than or equal to 1.4 mm or 1.3 mm, and groove width, such as less than or equal to 2.5 mm or 2.4 mm, and/or operate at the same SELs).
The first pulp feed can have any suitable consistency to promote runnability in the refining unit. For example, the first pulp feed can be a slurry in which less than or equal to any one of, or between any two of, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less of the slurry, by weight, is the SEPF precursor pulp fibers.
Such high-energy refining (e.g., at least 300 kWh or 600 kWh per ton of fiber) performed using refining elements having a fine bar pattern (e.g., any of those described above) and/or at low intensity (e.g., at a SEL between 0.1 and 0.45 W·s/m) can yield larger increases in the average hydrodynamic specific area of the SEPF precursor pulp fibers than conventional refining processes while mitigating reductions in fiber length. For example, the first pulp feed can be refined such that the average hydrodynamic specific surface area of the SEPF precursor pulp fibers increases by at least 300% (e.g., at least 700%) while the length weighted average fiber length of the SEPF precursor pulp fibers decreases by less than 30%. The resulting SEPF can thereby have any of the above-described length weighted average fiber lengths and average hydrodynamic specific surface areas.
Some methods include a step of combining the refined first pulp feed and a second pulp feed comprising softwood pulp fibers (e.g., 26) that are unrefined or lightly fibrillated (e.g., any of those described above) (e.g., non-cedar, NBSK pulp fibers) to produce a third pulp feed that comprises both of the cellulosic pulp fibers (e.g., 18). The refined first pulp feed and second pulp feed can be combined such that at least a majority of the cellulosic pulp fibers in the third pulp feed are unrefined or lightly fibrillated. For example, the refined first pulp feed and the second pulp feed can be combined such that less than or equal to any one of, or between any two of, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less (e.g., between 1% and 10% or between 1% and 20%) of the pulp fibers of the third pulp feed, by weight, are the SEPF and/or greater than or equal to any one of, or between any two of, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 99%, or more (e.g., between 80% and 99% or between 90% and 99%) of the pulp fibers of the third pulp feed, by weight, are the softwood pulp fibers. As a result, a nonwoven sheet incorporating the cellulosic pulp fibers can comprise those proportions of softwood pulp fibers and SEPF and, as set forth above, can thereby achieve a suitable combination of air permeability and liquid resistance.
The third pulp feed can be prepared for delivery to a nonwoven manufacturing system (e.g., 82) where the cellulosic pulp fibers can be used to make the nonwoven sheet. For example, the third pulp feed can be dried (e.g., by draining, pressing, and/or heating the third pulp feed) (e.g., in a Fourdrinier machine) to form one or more cellulosic sheets (e.g., 84) (e.g., one or more pulp sheets) comprising the cellulosic pulp fibers. Substantially all of the moisture of the third pulp feed can be removed when it is dried, e.g., such that less than or equal to any one of, or between any two of, 15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, or less (e.g., less than or equal to 15% or 10%) of the cellulosic sheet(s), by weight, is liquid. The cellulosic sheet(s) can be baled and/or at least some of the cellulosic sheet(s) can be wound into a roll.
Referring additionally to FIG. 6, the cellulosic pulp fibers and a plurality of synthetic fibers (e.g., 22) (e.g., any of the synthetic fibers described above) can be used to make the nonwoven sheet in the nonwoven manufacturing system. Some methods include a step of depositing the fibers (e.g., 14) (e.g., the cellulosic and synthetic fibers) onto a moving surface (e.g., 86), such as a moving surface of a foraminous carrier belt (e.g., 90) or of one or more drums, to form a nonwoven precursor web (e.g., 94). The fibers can be deposited and used to form the nonwoven precursor web in any suitable manner, such as by airlaying, carding, or wetlaying the fibers, and such that the nonwoven precursor web, and thus the nonwoven sheet resulting therefrom, has any of the above-described proportions of cellulosic pulp fibers and synthetic fibers (e.g., such that at least a majority of the fibers are the cellulosic pulp fibers). To illustrate, the fibers can be deposited such that the nonwoven precursor web comprises two or more layers, at least one of which includes the cellulosic pulp fibers and at least one of which includes the synthetic fibers. To do so, the synthetic fibers can be deposited onto the moving surface (e.g., using an apertured drum 98) to form a layer of the synthetic fibers thereon and each of the cellulosic sheet(s) (e.g., each of the pulp sheet(s)) can be deposited onto the synthetic fiber layer (e.g., such that the cellulosic sheet(s) define one of the nonwoven precursor web's layers). In other embodiments, the cellulosic sheet(s) can be broken apart and the cellulosic pulp fibers of the broken-apart sheet(s) can be deposited onto the moving surface to form a cellulosic pulp fiber layer. The cellulosic sheet(s) and/or polymeric fibers can be wetted prior to the below-described bonding process (e.g., before and/or while being deposited). In other embodiments, the order in which the synthetic fibers and cellulosic pulp fibers are deposited onto the moving surface can be reversed (e.g., by depositing the cellulosic pulp fibers on the moving surface and thereafter depositing the synthetic fibers onto the cellulosic pulp fibers, such as when using a drum system) or (e.g., when the cellulosic sheet(s) are broken apart) the cellulosic pulp fibers and synthetic fibers (e.g., polyester fibers) can be deposited after mixing the fibers (e.g., such that the nonwoven precursor web comprises a single layer of the mixed fibers).
The nonwoven precursor web can, but need not, be compacted (e.g., to remove air pockets from the nonwoven precursor web). For example, the nonwoven precursor web can be pressed between two moving belts (e.g., 90 and 102), at least one of which can, but need not, be the carrier belt onto which the fibers are deposited. In other embodiments, however, the nonwoven precursor web can be compacted in any suitable manner (e.g., by pressing the nonwoven precursor web with two or more pressing elements).
The fibers of the nonwoven precursor web can be bonded by hydroentanglement, e.g., by directing one or more jets of water (e.g., 106), such as, for example, greater than or equal to any one of, or between any two of, one, two, three, four, five, six, seven, eight, nine, ten, or more jets of water, onto the nonwoven precursor web using one or more injectors (e.g., 110). For each of the jet(s) of water, the portion of the nonwoven precursor web onto which the jet is directed can be supported by a surface such as a belt (e.g., the foraminous carrier belt onto which the fibers are deposited or another carrier belt) and/or a roller (e.g., 114). To illustrate, a first water jet can be directed onto a portion of the nonwoven precursor web that is disposed on carrier web 90 (optionally, while that portion is being compacted), the nonwoven precursor web can be passed partially around each of one or more rollers (e.g., 114), and, for each of the roller(s), an additional water jet can be directed onto the portion of the nonwoven precursor web being passed partially around the roller. At least one of the surface(s) supporting the nonwoven precursor web can be configured to facilitate removal of the water from the nonwoven precursor web (e.g., to prevent oversaturation thereof); for example, each of the supporting surface(s) can be a mesh or apertured such that a vacuum can draw water from the nonwoven precursor web through the supporting surface during hydroentanglement. And, hydroentanglement can be performed such that at least one jet of water is directed onto each of opposing first and second surfaces (e.g., 118 a and 118 b) of the nonwoven precursor web, which can facilitate uniform entanglement. In other embodiments, however, the jet(s) of water can be directed onto only one of the nonwoven precursor web's surfaces (e.g., onto a surface defined by a layer of the cellulosic pulp fibers).
The injector(s) can operate at a relatively high pressure to achieve hydroentanglement. For example, a pressure of each of the jet(s) of water (e.g., at the injector) can be greater than or equal to any one of, or between any two of, 100 pounds per square inch (psi), 400 psi, 700 psi, 1,000 psi, 1,300 psi, 1,600 psi, 1,900 psi, 2,200 psi, 2,500 psi, or higher. When multiple jets of water are used, the jets can have the same or different pressures. For example, the first jet can have a comparatively low pressure (e.g., to pre-wet the nonwoven precursor web and facilitate removal of air pockets) while subsequent downstream jets can have a pressure that is higher than that of the first jet. In other embodiments, however, the jets can have the same pressure.
In conventional hydroentangling processes, highly fibrillated pulp fibers are generally considered undesirable because such pulp fibers can comprise a large amount of fines that can impede fiber entanglement. The SEPF, due at least in part to the unique process by which they are made, can comprise a relatively low amount of fines, compared to pulp fibers that have been highly fibrillated using conventional refining techniques. As such, hydroentanglement of the SEPF with the softwood and synthetic fibers may not suffer from the same detrimental effects that may result when hydroentangling conventional, highly fibrillated pulp fibers. In this manner, the nonwoven sheet can have a combination of air permeability and liquid resistance that is comparable to or better than that of an otherwise similar nonwoven sheet in which all of the cellulosic pulp fibers are unrefined or lightly refined cedar pulp fibers, at a lower cost (e.g., due to the use of softwood pulp fibers, such as NBSK pulp fibers, that are less expensive to produce in conjunction with the SEPF).
Some methods include a step of drying the nonwoven precursor web in a drying unit (e.g., 122). The nonwoven precursor web can be dried in any suitable manner, such as, for example, by passing the nonwoven precursor web partially around each of one or more rollers (e.g., 126) (each, optionally, comprising a vacuum to draw water from the nonwoven precursor web), heating the nonwoven precursor web, and/or directing a gas (e.g., air) onto the nonwoven precursor web. All or almost all of the water can be removed from the nonwoven precursor web during the drying, e.g., such that less than or equal to any one of, or between any two of, 15%, 13%, 11%, 9%, 7%, 5%, 3%, 1%, or less (e.g., less than or equal to 10%) of the nonwoven sheet, by weight, is water. The resulting nonwoven sheet can thereafter be used in the production a variety of articles, such as, for example, a surgical gown or a surgical drape, where the nonwoven sheet's combination of air permeability and liquid resistance may be desirable.
The above specification and examples provide a complete description of the structure and use of illustrative embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the products, systems, and methods are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, elements may be omitted or combined as a unitary structure, and/or connections may be substituted. To illustrate, while some methods can include a step of producing the SEPF and combining the SEPF with the softwood pulp fibers, in other embodiments the SEPF and softwood pulp fibers can be provided (e.g., such that the refining and combining steps need not be performed). Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and/or functions, and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.
The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

Claims

1. A nonwoven sheet comprising:

a plurality of cellulosic pulp fibers comprising:

a plurality of cedar pulp fibers that have a length weighted average fiber length of at least 1.0 millimeters (mm) and an average hydrodynamic specific surface area of at least 4.5 square meters per gram (m²/g); and

a plurality of softwood pulp fibers that do not include cedar pulp fibers; and

a plurality of synthetic polymeric fibers.

2. The nonwoven sheet of claim 1, wherein the softwood pulp fibers are northern bleached softwood kraft (NBSK) pulp fibers.

3. The nonwoven sheet of claim 1, wherein by weight:

between 1% and 20% of the cellulosic pulp fibers are the cedar pulp fibers; and

between 80% and 99% of the cellulosic pulp fibers are the softwood pulp fibers.

4. The nonwoven sheet of claim 3, wherein the length weighted average fiber length of the cedar pulp fibers is between 1.0 mm and 2.2 mm.

5. The nonwoven sheet of claim 4, wherein the length weighted average fiber length of the cedar pulp fibers is between 1.5 mm and 2.0 mm.

6. The nonwoven sheet of claim 4, wherein the average hydrodynamic specific surface area of the cedar pulp fibers is at least 5.0 m²/g.

7. The nonwoven sheet of claim 7, wherein the cedar pulp fibers have a length weighted fines value that is less than or equal to 30%, when pulp fibers having a length of 0.20 mm or less are classified as fines.

8. The nonwoven sheet of claim 8, wherein the nonwoven sheet is a spunlace nonwoven.

9. A method of making a nonwoven sheet, the method comprising:

directing one or more jets of water onto a nonwoven precursor web comprising a plurality of fibers, the fibers including:

a plurality of cellulosic pulp fibers that comprise:

a plurality of softwood pulp fibers that do not include cedar pulp fibers; and

a plurality of synthetic polymeric fibers; and

drying the nonwoven precursor web.

10. The method of claim 9, wherein the softwood pulp fibers are northern bleached softwood kraft (NBSK) pulp fibers.

11. The method of claim 9, wherein by weight:

between 1% and 20% of the cellulosic pulp fibers are the cedar pulp fibers; and

between 80% and 99% of the cellulosic pulp fibers are the softwood pulp fibers.

12. The method of claim 11, wherein the length weighted average fiber length of the cedar pulp fibers is between 1.5 mm and 2.0 mm.

13. The method of claim 9, wherein the average hydrodynamic specific surface area of the cedar pulp fibers is at least 5.0 m²/g.

14. The method of claim 9, wherein the cedar pulp fibers have a length weighted fines value that is less than or equal to 30%, when pulp fibers having a length of 0.20 mm or less are classified as fines.

15. The method of claim 9, comprising forming the nonwoven precursor web at least by:

depositing the synthetic polymeric fibers onto a moving surface; and

depositing a pulp sheet comprising the cellulosic pulp fibers onto the synthetic polymeric fibers.

16. The method of claim 9, wherein the length weighted average fiber length of the cedar pulp fibers is between 1.5 mm and 2.0 mm.

17. The nonwoven sheet of claim 1, wherein the length weighted average fiber length of the cedar pulp fibers is between 1.0 mm and 2.2 mm.

18. The nonwoven sheet of claim 1, wherein the average hydrodynamic specific surface area of the cedar pulp fibers is at least 5.0 m²/g.

19. The nonwoven sheet of claim 1, wherein the cedar pulp fibers have a length weighted fines value that is less than or equal to 30%, when pulp fibers having a length of 0.20 mm or less are classified as fines.

20. The nonwoven sheet of claim 1, wherein the nonwoven sheet is a spunlace nonwoven.