阅读说明：本技术 多层电池隔板和其制作方法 (Multilayer battery separator and method of making same ) 是由 蒂莫西·斯科特·林茨 理查德·A·克莱斯 威廉·A·Iii·基弗 于 2018-04-27 设计创作，主要内容包括：描述了一种适用作电池隔板的纤维性结构。所述纤维性结构可包括多个板层或层。每个板层或层用于提供屏障功能和吸收功能,使得所述多层纤维性结构适用作电池隔板,例如碱性电池隔板。(A fibrous structure suitable for use as a battery separator is described. The fibrous structure may comprise a plurality of plies or layers. Each ply or layer is used to provide a barrier function and an absorbent function, making the multilayer fibrous structure suitable for use as a battery separator, such as an alkaline battery separator.)

1. An alkaline battery separator comprising:

about 65 wt% to up to 100 wt% nanofibrillated cellulose based fibers;

0 wt% to about 35 wt% of alkali resistant polymeric fiber; and

0 wt% to about 10 wt% of a cationic strength additive.

2. The alkaline battery separator of claim 1 wherein the battery separator comprises

About 65 wt% to about 85 wt% nanofibrillated cellulose based fiber,

about 15 to about 35 weight percent of an alkali resistant polymeric fiber, and

about 2 wt% to about 7 wt% of a cationic strength additive.

3. The alkaline battery separator according to claim 1 comprising a first sheet layer and a second sheet layer in a face-to-face relationship with each other, wherein said first sheet layer and said second sheet layer each independently comprise

About 65 wt% to at most 100 wt% nanofibrillated cellulose based fibers,

0 to about 35 weight percent of an alkali resistant polymeric fiber, and

0 wt% to about 10 wt% of a cationic strength additive.

4. The alkaline battery separator according to claim 1, wherein said nanofibrillated cellulose-based fibers comprise at least one of nanofibrillated synthetic cellulose fibers and nanofibrillated mercerized cotton cellulose fibers.

5. The alkaline battery separator of claim 1, wherein the nanofibrillated cellulose-based fibers have

A Shore-Ruigler scale of from about 83 to about 97, and

canadian standard freeness of from about 12 to about 20.

6. The alkaline battery separator of claim 1, wherein the alkaline resistant polymeric fibers comprise polyvinyl alcohol fibers.

7. The alkaline battery separator of claim 1 wherein the alkaline resistant polymeric fibers have

A length of about 4mm to about 9mm, and

a denier of about 1.5dpf to about 5.0 dpf.

8. The alkaline battery separator of claim 1, wherein the cationic strength additive comprises a cationic starch.

9. The alkaline battery separator of claim 8, wherein the cationic starch comprises potato starch.

10. The alkaline battery separator according to claim 1 wherein

The nanofibrillated cellulose based fibres comprise at least one of nanofibrillated synthetic cellulose fibres and nanofibrillated mercerized cotton cellulose fibres,

the alkali-resistant polymeric fibers comprise polyvinyl alcohol fibers, and

the cationic strength additive comprises a cationic starch.

11. The alkaline battery separator of claim 10 wherein

The nanofibrillated cellulose-based fiber has a schopper-riegler scale freeness of from about 83 to about 97, and a canadian standard freeness of from about 12 to about 20, and

the polyvinyl alcohol fibers have a length of about 4mm to about 9mm, and a denier of about 1.5dpf to about 5.0 dpf.

12. A method of making an alkaline battery separator, the method comprising:

forming a first ply; and

forming a second ply in a face-to-face relationship with the first ply,

wherein the first ply and the second ply each independently comprise

About 65 wt% to at most 100 wt% nanofibrillated cellulose based fibers,

0 to about 35 weight percent of an alkali resistant polymeric fiber, and

0 wt% to about 10 wt% of a cationic strength additive.

13. The method of claim 12, wherein the first ply and the second ply each independently comprise

About 65 wt% to about 85 wt% nanofibrillated cellulose based fiber,

about 15 to about 35 weight percent of an alkali resistant polymeric fiber, and

about 2 wt% to about 7 wt% of a cationic strength additive.

14. The method of claim 12, further comprising making at least one furnish having a solids content of about 1 to about 8 wt%, wherein the first ply and the second ply are formed from the at least one furnish.

15. The method of claim 14, further comprising drying the first layer of furnish and the second layer of furnish to form the first ply and the second ply, respectively.

16. The method of claim 14, further comprising drying the first layer of furnish and the second layer of furnish such that the alkali-resistant polymeric fibers sinter or fuse with adjacent fibers based on nanofibrillated cellulose.

17. The method of claim 14, wherein forming the first ply and the second ply comprises

Depositing a first layer of the at least one furnish on a forming surface;

depositing a second layer of the at least one furnish on the first layer of furnish; and

drying the first layer of furnish and the second layer of furnish to form the first ply and the second ply, respectively.

18. The method of claim 17, wherein said first sheet layer and said second sheet layer each comprise about 50 wt% of said alkaline cell separator.

19. The method of claim 14, wherein

The nanofibrillated cellulose based fibres comprise at least one of nanofibrillated synthetic cellulose fibres and nanofibrillated mercerized cotton cellulose fibres,

the alkali-resistant polymeric fibers comprise polyvinyl alcohol fibers, and

the cationic strength additive comprises a cationic starch.

20. The method of claim 19, wherein

The nanofibrillated cellulose-based fiber has a schopper-riegler scale freeness of from about 83 to about 97, and a canadian standard freeness of from about 12 to about 20, and

the polyvinyl alcohol fibers have a length of about 4mm to about 9mm, and a denier of about 1.5dpf to about 5.0 dpf.

Technical Field

The present disclosure generally relates to fibrous structures comprising at least one ply or layer. More particularly, the present disclosure relates generally to multilayer fibrous structures that may be used in various applications (e.g., as battery separators).

Background

Alkaline cells typically include a very thin multifunctional separator between their anode and cathode. The separator allows hydroxyl (OH)^-) The ions pass freely between the anode and cathode compartments so that chemical reactions can be produced that generate the current of the cell, while physical separation can be maintained between the anode and cathode.

Battery separators are typically configured as a two-layer structure, with one layer being an absorbing layer and the other layer being a barrier layer. The absorbent layer provides the required electrolyte absorbency, which is necessary for high energy capacity. The barrier layer serves to prevent dendritic growth between the anode and cathode, which can lead to subsequent cell shorting. It is also generally desirable that the battery separator be alkali resistant and not readily undergo chemical shrinkage in use of more than about 2% to prevent shorting of the battery.

In view of these various requirements, there is a continuing need for battery separators that provide enhanced functionality, thereby improving battery performance.

Disclosure of Invention

In one aspect, the present disclosure is directed to a multi-ply fibrous structure comprising a plurality of plies, such as at least two plies, wherein each ply comprises a first type of fiber, and optionally at least one of a second type of fiber and a strength additive.

In another aspect, the present disclosure is directed to a multi-ply fibrous structure comprising a plurality of plies, such as at least two plies, wherein each ply is configured to provide a barrier function and an absorbent function such that the multi-ply fibrous structure is suitable for use as a battery separator, such as an alkaline battery separator.

In another aspect, the present disclosure is directed to a method of making a multi-ply fibrous structure comprising a plurality of plies, such as at least two plies, wherein at least two plies of the multi-ply fibrous structure comprise a plurality of types of fibers (e.g., a first type of fiber and a second type of fiber), and optionally a strength additive. The method includes forming a first layer of furnish, and applying a second layer of furnish over (i.e., on) the first layer of furnish, wherein the furnish includes a plurality of types of fibers and optionally a strength additive. By layering the furnish in this manner, the resulting multi-ply fibrous structure is substantially free of defects, such as pinholes.

In each of the above aspects, and in other aspects contemplated thereby, the first type of fibers may be nanofibrillated fibers, such as nanofibrillated synthetic cellulosic fibers or nanofibrillated mercerized cotton fibers. The second type of fibers may be polymeric fibers, such as alkali resistant fibers, for example polyvinyl alcohol. The strength additive may be a charged strength additive, such as cationic starch. The relative amounts of the various components can be varied as needed to achieve the desired balance of properties.

Although various aspects of the present disclosure may be discussed primarily in connection with the use of a multi-layered fibrous structure as a battery separator (e.g., an alkaline battery separator), the multi-layered fibrous structure may be used in myriad other applications. For example, the multilayer fibrous structures described herein and contemplated thereby may be used in other technologies, such as separators for other energy storage devices (such as lithium ion batteries, solar cells, and supercapacitors).

Drawings

Fig. 1 schematically depicts a cross-sectional view of an example multi-layer fibrous structure according to one aspect of the present disclosure; and

fig. 2 schematically depicts an example method of making the multi-layer fibrous structure of fig. 1, according to another aspect of the present disclosure.

Various features, aspects, and advantages of the embodiments will become more apparent from the following detailed description and drawings, in which like numerals represent like components throughout the drawings and text. The various features described are not necessarily drawn to scale, emphasis instead being placed upon illustrating particular features relating to some embodiments.

Detailed Description

Briefly described, the present disclosure is directed to fibrous structures, such as multi-ply fibrous structures comprising a plurality of plies (e.g., at least two plies). Each ply comprises a plurality of fibers formed into a thin, flexible, porous sheet-like structure.

In one embodiment, at least two plies of the multi-ply fibrous structure each independently comprise (and are typically formed from): a plurality of fiber types, e.g., a first type of fiber and a second type of fiber. The at least two plies may also each independently include a strength additive and optionally other components. In another embodiment, the second type of fibers may be omitted such that at least two plies of the multi-ply fibrous structure each independently include (and are typically formed from) the first type of fibers.

In some examples, the at least two plies may generally have the same composition. In other examples, the composition of one or more plies may be different from one or more other plies.

At least two plies of the multi-ply fibrous structure are each operable to provide a barrier function and an absorbent function, and the multi-ply fibrous structure is therefore suitable for use as a battery separator, such as an alkaline battery separator. Because each of the at least two plies provides a multi-functional benefit, the multi-layered fibrous structure exhibits superior performance as a battery separator (e.g., an alkaline battery separator) as compared to prior art battery separators in which each ply provides only a single benefit (absorbent or barrier). Furthermore, the potential for cell failure is greatly reduced since the multilayer fibrous structure can be formed using a wet-laid process that minimizes the formation of through-web defects, which provide the primary path for dendritic growth.

Turning now to the drawings, fig. 1 schematically illustrates a cross-sectional view of an example multi-ply fibrous structure 100, in accordance with various aspects of the present disclosure. The multi-ply fibrous structure comprises a first ply or layer 102 and a second ply or layer 104, each of the first ply or layer 102 and the second ply or layer 104 having a substantially flat sheet-like configuration (such that the multi-ply fibrous structure 100 likewise has a substantially flat sheet-like configuration). First ply 102 has a first side or surface 106 defining a first outer (i.e., exterior) surface 106 of multi-ply fibrous structure 100, and a second side or surface 108 (i.e., interior or interior surface) opposite first side or surface 106. The second ply 104 has a first side or surface 110 defining a second outer (i.e., exterior) surface 110 of the multi-ply fibrous structure 100, and a second side or surface 112 (i.e., interior or interior surface) opposite the first side or surface 110. The interior surface 108 of the first ply 102 and the interior surface 112 of the second ply 104 are in facing contacting relationship with each other within the multilayer fibrous structure 100.

First and second plies 102, 104 typically each comprise (i.e., are at least partially formed from) a plurality of fibers (only some of which are schematically shown in fig. 1).

In one exemplary embodiment shown in fig. 1, at least one of first ply 102 and second ply 104 each comprise (i.e., are each formed, at least in part, from): a blend (i.e., mixture or combination) of fibers including a first type of fiber 114 (i.e., a plurality of fibers 114 of the first fiber type) (schematically illustrated as narrower wavy lines), and a second type of fiber 116 (i.e., a plurality of fibers 116 of the second fiber type) (schematically illustrated as wider straight lines). At least one of the first ply 102 and the second ply 104 may further include a strength additive 118 (shown schematically as a solid dot). The first type of fibers 114, the second type of fibers 116, and the optional strength additive 120 (as well as any other components present in the respective layers 102, 104) may generally be selected to collectively provide the desired characteristics for a particular end use. For example, when the multi-layered fibrous structure 100 is intended for use as an alkaline battery separator, the first type of fibers 114, the second type of fibers 116, and the optional strength additive 120 (as well as any other components present in the respective layers 102, 104) and their relative amounts can be selected to provide the necessary barrier and absorption properties, shrink resistance, alkali resistance, and the like. In some cases, the plies or layers 102, 104 may generally have the same composition of fibers 114, 116 and/or strength additive 118. In other instances, the composition of the fibers 114, 116 and/or strength additive 118 of one ply or layer 102, 104 may be different than the composition of the fibers 114, 116 and/or strength additive 118 of another ply or layer 102, 104.

In another exemplary embodiment (not shown), the second type of fibers 116 may be omitted such that the fibers of the first and second plies 102, 104 each comprise the first type of fibers 114 (i.e., the plurality of fibers 114 of the first fiber type). As described above, the first ply 102 and the second ply 104 may each independently further include a strength additive 118. The first type of fibers 114 and optional strength additive 118 (as well as any other components present in the respective layers 102, 104) and their relative amounts can generally be selected to provide the desired characteristics for a particular end use. For example, when the multi-layered fibrous structure 100 is intended for use as an alkaline battery separator, the fibers 114 and optional strength additive 118 (as well as any other components present in the respective layers 102, 104) may be selected to collectively provide the necessary barrier and absorption characteristics, shrinkage resistance, alkali resistance, and the like. In some cases, the plies or layers 102, 104 may generally have the same composition of fibers 114 and optional strength additives 118. In other instances, the composition of the fibers 114 and optional strength additive 118 of one ply or layer 102, 104 may be different than the composition of the fibers 114 and optional strength additive 118 of the other ply or layer 102, 104.

The first type of fibers 114 may generally comprise cellulose-based fibers, such as regenerated (i.e., synthetic/crystalline) cellulose fibers or refined (e.g., treated) cellulose fibers. The first type of fibers 114 (e.g., synthetic cellulosic fibers or refined cellulosic fibers) can be fibrillated (i.e., mechanically processed or refined to increase the surface area of the fibers and create a branched fibrous structure), and more particularlyCan be nanofibrillated such that the diameter of the fiber (e.g., nanofiber diameter) is about 10^-8To about 10^-10And m is selected. The resulting nanofibrillated cellulose-based fibers may have a pulp degree on the Schopper-Riegler (Schopper-Riegler) scale (° SR) of about 83 to about 97 (e.g., about 90), and a CSF (canadian standard freeness) of about 12 to about 20 (e.g., about 16).

The first type of fibers 114 (e.g., cellulose-based fibers) may be provided having a length of about 4mm to about 8mm, such as about 5mm to about 7mm, such as about 6 mm. Additionally or alternatively, the first type of fibers 114 (e.g., cellulose-based fibers) may be provided having a denier of about 1.4dTex to about 2.0dTex, such as about 1.6dTex to about 1.8dTex, such as about 1.7 dTex.

One synthetic cellulosic fiber that may be suitable for forming a multi-ply fibrous structure (e.g., as the first type of fiber 114) is lyocell, e.g., lyocell(commercially available from lanjing), which may be provided as having a length of about 6mm and a titer of about 1.7 dTex. Examples of cellulose-based fibers that may be suitably refined are mercerized cotton fibers (also known as "pearl" or "pearl" cotton fibers), such as GP225HL-M available from Georgia Pacific corporation (Georgia Pacific), which may be provided having a length of about 6mm and a denier of about 1.7 dTex. However, other fibers may be suitable.

The second type of fibers 116 may generally comprise polymeric fibers. When the multi-layered fibrous structure 100 is intended for use as a battery separator (e.g., an alkaline battery separator), the polymeric fibers can generally be alkali resistant (i.e., such that the polymeric fibers can be considered alkali resistant polymeric fibers). Alkali resistance can be measured, for example, by placing 2g of the fiber in 100ml of 40% KOH and allowing it to stand on a hot plate at 71 ℃ for 2 weeks. The sample can then be cooled to ambient temperature and decanted to remove excess KOH. The remaining fibers can then be dried in a convection oven at 100 ℃ until there is no longer any weight loss, and then reweighed. If the weight loss is less than 2%, the fiber is considered alkali resistant. For the sheet sample, a 3in. × 2.5in. sample (measured with a digital micrometer) may be placed in 400ml 40% KOH for 5 minutes at room temperature. After a residence time of 5 minutes, the sample can be removed and the remaining KOH solution poured off. The wet sample can then be re-measured using a digital micrometer. A sample is considered alkali resistant if the material shrinkage is less than or equal to 2% in both dimensions. While not wishing to be bound by theory, it is believed that the use of alkali resistant polymeric fibers may generally serve to stabilize the multi-ply fibrous structure from chemical shrinkage when subjected to a potassium hydroxide solution in a battery, and may enhance wet strength properties (e.g., wrinkle resistance/pleatability) (e.g., as measured by the double tensile test according to t.a.p.p.i. test method T-494), stiffness, and burst strength.

In addition, suitable alkali resistant fibers may have a dissolution temperature of at least about 100 ℃, e.g., from about 100 ℃ to about 200 ℃, as measured by ASTM 2503-07, depending on the process used to form the multi-layer fibrous structure. (e.g., if the dissolution temperature is too low, the fibers may undesirably dissolve during formation of the multi-ply fibrous structure.)

In one example, the second type of fibers 116 (e.g., alkali resistant polymeric fibers) can include (i.e., be formed at least in part from) an ethylene-based polymer such as polyvinyl alcohol (PVOH). An example of a PVOH fiber (or PVOH-based fiber) that may be suitable for use in the present disclosure is Poval, which is commercially available from cola (Kuraray)^TM. However, a myriad of other PVOH fibers or any other suitable polymeric fibers may be used. The second type of fiber (e.g., PVOH) can have a length of about 4mm to about 9mm and a denier of about 1.5dpf to about 5.0 dpf. However, other fiber types and sizes may be used depending on the particular application.

Any strength additive 118 may be used as desired to meet the requirements of a particular end use. Examples of strength additives that may be suitable include, but are not limited to, epichlorohydrin, melamine, urea formaldehyde, polyimines, cationic starch, polyacrylamide derivatives, binder fibers, vinyl/vinylidene chloride, or any combination thereof. In one particular example, when the multi-layered fibrous structure 100 is used as an alkaline battery separator, it may be desirable for the strength additive to be alkali resistant. In this case, suitable strength additives may be charged, for example cationically charged. One example of an alkali-resistant, cationic strength additive that may be suitable for use in the present disclosure is a cationic starch, such as Solvitose PLV potato starch, commercially available from Everest (the Netherlands). However, myriad other strength additives may be suitable.

Each of the individual layers or plies (e.g., plies 102, 104) of the multi-ply fibrous structure 100 may have the same composition or may differ in composition from one another.

Where a blend of fiber types is used (e.g., as shown in fig. 1), the relative amounts of the first type of fibers 114 and the second type of fibers 116 may vary for each application. For example, the first ply 102 and the second ply 104 may each independently include about 65 wt% to up to 100 wt% of the first type of fibers 114 and 0 wt% to about 35 wt% of the second type of fibers 116. The first ply 102 and the second ply 104 may each further independently include 0 to about 10 wt% of a strength additive 118.

In one example, the first ply 102 and the second ply 104 may each independently include about 70 wt% to about 88 wt% of the first type of fibers 114 and about 12 wt% to about 25 wt% of the second type of fibers 116. The first ply 102 and the second ply 104 may each, independently, further include about 3 wt% to about 8 wt% of a strength additive 118.

In another example, the first ply 102 and the second ply 104 may each independently include about 65 wt% to about 85 wt% of the first type of fibers 114 and about 15 wt% to about 35 wt% of the second type of fibers 116. The first ply 102 and the second ply 104 may each, independently, further include about 2 wt% to about 7 wt% of a strength additive 118.

In yet another example, the first ply 102 and the second ply 104 may each independently include about 75 wt% to about 80 wt% of the first type of fibers 114 and about 15 wt% to about 20 wt% of the second type of fibers 116. The first ply 102 and the second ply 104 may each, independently, further include about 3 wt% to about 6 wt% of a strength additive 118. Other possibilities are contemplated.

Where only one fiber type is used (e.g., a first type of fiber 114, such as nanofibrillated synthetic cellulose or nanofibrillated mercerized cotton), for example where the second type of fiber 116 is omitted as described above, the first ply 102 and the second ply 104 may each independently include from about 90 wt% to up to 100 wt% of the fiber 114 (e.g., the first type of fiber 114) and from 0 wt% to about 10 wt% of the strength additive 118. In one example, the first ply 102 and the second ply 104 may each independently include about 92 wt% to about 97 wt% fibers 114 (e.g., the first type of fibers 114) and about 3 wt% to about 8 wt% of the strength additive 118. In yet another example, the first ply 102 and the second ply 104 may each independently include about 96 wt% of the fibers 114 (e.g., the first type of fibers 114) and about 4 wt% of the strength additive 118. Other possible compositions are contemplated.

Each of the individual layers or plies (e.g., plies 102, 104) of the multi-ply fibrous structure 100 may have any suitable basis weight as desired for a particular application. The basis weight of a fibrous structure or material (as contemplated herein) is typically expressed in terms of weight per unit area, for example in grams per square meter (gsm) or ounces per square foot (osf) (1osf 305gsm) or lbs./2880ft²Expressed and measured according to t.a.p.p.i. test method T-410 or a.s.t.m.d-646.

When the multi-ply fibrous structure 100 is used as a battery separator, such as an alkaline battery separator, each of the individual plies or plies (e.g., plies 102, 104) of the multi-ply fibrous structure 100 independently can have a basis weight of from about 8gsm to about 16gsm, such as from about 10gsm to about 14gsm, such as about 12 gsm. Such exemplary basis weights may also be suitable for other applications, and other basis weights may be used as desired. In some embodiments, the first ply 102 and the second ply 104 may each have about the same basis weight, such that each ply 102, 104 is about half the weight of the multi-ply fibrous structure 100. In other embodiments, the basis weights of the first ply 102 and the second ply 104 may be different.

The multi-ply fibrous structure 100 likewise may have any suitable total basis weight as desired for a particular application. For example, when the multi-ply fibrous structure 100 is used as a battery separator, such as an alkaline battery separator, the multi-ply fibrous structure 100 can have a basis weight of from about 16gsm to about 32gsm, such as from about 20gsm to about 28gsm, such as about 24 gsm. Such exemplary basis weights may also be suitable for other applications, and other basis weights may be used as desired.

The multi-ply fibrous structure 100 likewise can have any suitable (dry) caliper (measured according to TAPPI T-411om-97 at a base pressure of 7.3psi using an electronic caliper micro-meter 3.3 model 49-62 (manufactured by TMI) "caliper (calipers)") as required by the particular application. For example, when the multi-layered fibrous structure 100 is used as a battery separator, such as an alkaline battery separator, the multi-layered fibrous structure 100 can have a thickness of less than about 5000 μ, such as from about 2000 μ to about 4000 μ. Such exemplary thicknesses may also be suitable for other applications, and other thicknesses may be used as desired.

The multi-ply fibrous structure 100 may also have any suitable absorbency (as measured by IST 10.1-92) as desired for a particular application. For example, when the multi-ply fibrous structure 100 is used as a battery separator, such as an alkaline battery separator, the multi-ply fibrous structure 100 can have an absorbent capacity of at least about 100gsm, such as at least about 125gsm, at least about 150gsm, at least about 175gsm, at least about 200gsm, at least about 225gsm, at least about 250gsm, at least about 275gsm, or at least about 300 gsm. Such exemplary absorption amounts may also be suitable for other applications, and other absorption amounts may be used as desired.

The multi-layer fibrous structure 100 may likewise have any suitable wet ionic resistance (as measured by ASTM D7148-13) as desired for a particular application. For example, when the multi-layered fibrous structure 100 is used as a battery separator, such as an alkaline battery separator, the multi-layered fibrous structure 100 can have a wet ionic resistance of less than about 65m Ω -cm²E.g. about 0m omega-cm²To about 50m Ω -cm²。

It is contemplated that the multi-ply fibrous structure 100 may include additional plies (not shown). Such layers may be selected to provide additional functions such as barrier properties, absorption, dimensional stability, stiffness, tensile strength, puncture/burst resistance, wicking rate, or any combination thereof. Numerous other possibilities are hereby envisaged.

Fig. 2 schematically illustrates an example method 200 of forming a multi-layer fibrous structure (such as the multi-layer fibrous structure 100 described above) according to various aspects of the present disclosure.

As shown in fig. 2, the first type of fibers 114 may optionally be combined with the second type of fibers 116 and/or strength additives 118 (such as those described above in connection with fig. 1) in a container 220. Various examples of types of fibers 114, 116 and strength additives 118 that may be suitable, as well as their relative amounts, are provided above and are not repeated here for the sake of brevity.

Water 222 may be added to the fibers 114 (or fiber blend 114, 116) and optional strength additive 118 to form a furnish 224 having from about 1 wt% to about 8 wt% solids. As will be understood by those skilled in the art, the furnish may include other components such as, for example, processing aids (e.g., surfactants, defoamers, filter aids, retention aids, dispersants, etc.), biocides, and the like.

A first layer 226 of the furnish 224 may be deposited on a forming surface (e.g., a moving belt or forming wire) 228 to form a first ply or layer 102 of the multi-ply fibrous structure 100 to be formed. As outlined above, the first layer 226 of the furnish 224 may generally be deposited in an amount such that the resulting dry weight is from about 8gsm to about 16gsm, for example from about 10gsm to about 14gsm, for example about 12 gsm.

A second layer 230 of the furnish 224 may then be deposited onto the first ply or layer 226 of the furnish. As outlined above, the second layer 230 of the furnish 224 may generally be deposited in an amount such that the resulting dry weight is from about 8gsm to about 16gsm, for example from about 10gsm to about 14gsm, for example about 12 gsm.

As will be understood by those skilled in the art, at the basis weights described above, the presence of pinholes or other defects in wet laid webs is common. However, by applying the second layer of furnish 230 over the first layer of furnish 226, any defects in the first layer may be covered or overlaid, and any defects that would otherwise be present in the second layer or ply may be covered or overlaid by the first layer or ply. The resulting multi-ply fibrous structure 100 is highly likely to be free of (through-web) defects because there is little or no likelihood that a defect in the first ply will coincide with (i.e., register with) a defect in the second ply.

This presents a significant advantage when used as a battery separator over typical battery separator constructions in which one layer of the bi-layer structure provides the barrier function and the other layer provides the absorbency. For example, if the barrier layer of a conventional prior art battery separator is damaged, dendrites are likely to pass through the absorber layer. In sharp contrast, for the present design, where each layer of the two-layer structure provides both barrier and absorption functions, adjacent coincident layers can be used to provide a barrier function even if one layer is destroyed.

Returning to FIG. 2, if desired, the resulting two ply web may be compressed or pressed by passing the web through a pair of nip rollers (not shown). The web can then be dried in dryer 232 at a temperature selected so that the PVOH fibers sinter or fuse (by melting or bonding) in the nanofiber interstices and form welds/bonds at those points, rather than melting and flowing the PVOH (to form a film). When dry, the first layer 226 of the furnish 224 becomes the first or ply 102 of the multi-ply fibrous structure 100 and the second layer 230 of the furnish 224 becomes the second or ply 104 of the multi-ply fibrous structure 100. The two plies or layers 102, 104 are joined to one another by a forming process.

The resulting multi-layered fibrous structure 100 may be calendered (not shown) to reduce thickness and increase volume, if desired, for additional KOH electrolyte loading in the cell.

It should be understood that one or more steps or stages of the example process may be replaced with other steps or stages. Further, it will be understood that one or more steps or stages of the example processes may be formed on-line or may be formed off-line, batch, or continuously. Additional steps or stages may be added, and steps or stages may be omitted. Accordingly, the example processes described herein should not be construed as limiting in any way.

Example 1

Forming a multi-ply fibrous structure substantially as described above in connection with fig. 1 and 2, wherein the first ply and the second ply each comprise about 78 wt% of nanofibrillated synthetic fibers (e.g., lyocell fibers, such as) About 18 wt.% PVOH fiber, and about 4 wt.% cationic starch.

Various properties of the multilayer fibrous structure were evaluated. Two samples were tested. The results are averaged and compared to the target value. The results are presented in tables 1-3.

TABLE 1

TABLE 2

TABLE 3

Example 2

A multi-ply fibrous structure is formed substantially as described above in connection with figures 1 and 2, in which the first and second plies each comprise about 74 wt% of mercerized cotton fibers (Georgia Pacific225HL-M) (refined in mineral processing water), about 20 wt% of PVOH fibers, and about 6 wt% of cationic starch.

Various properties of the multilayer fibrous structure were evaluated. Four samples were tested. The results are averaged and compared to the target value. The results are presented in tables 4-6.

TABLE 4

TABLE 5

TABLE 6

Example 3

A multi-ply fibrous structure is formed substantially as described above in connection with figures 1 and 2, wherein the first ply and the second ply each comprise about 74 wt% of mercerized cotton fibers (Georgia Pacific225HL-M) (refined in municipal water), about 20 wt% of PVOH fibers, and about 6 wt% of cationic starch.

Various properties of the multilayer fibrous structure were evaluated. Three samples were tested. The results are averaged and compared to the target value. The results are presented in tables 7-9.

TABLE 7

TABLE 8

TABLE 9

Example 4

A multi-ply fibrous structure is formed substantially as described above in connection with figures 1 and 2, wherein the first ply and the second ply each comprise about 74 wt% of mercerized cotton fibers (Georgia Pacific225HL-M) (refined in municipal water for 105 minutes), about 20 wt% of PVOH fibers, and about 6 wt% of cationic starch.

Various properties of the multilayer fibrous structure were evaluated. Three samples were tested. The results are averaged and compared to the target value. The results are presented in tables 10-12.

Watch 10

TABLE 11

TABLE 12

Example 5

A multi-ply fibrous structure is formed substantially as described above in connection with figures 1 and 2, wherein the first ply and the second ply each comprise about 74 wt% of mercerized cotton fibers (Georgia Pacific225HL-M) (77 minutes of refining in GRI DI water), about 20 wt% of PVOH fibers, and about 6 wt% of cationic starch.

Various properties of the multilayer fibrous structure were evaluated. Three samples were tested. The results are averaged and compared to the target value. The results are presented in tables 13-15.

Watch 13

TABLE 14

Watch 15

Example 6

A weight loss study was conducted on a multi-ply fibrous structure formed substantially as described above in connection with fig. 1 and 2, wherein the first ply and the second ply each comprised about 74 wt% of mercerized cotton fibers (Georgia Pacific225HL-M) or nanofibrillated synthetic fibers (Tencel), about 20 wt% of PVOH fibers, and about 6 wt% of cationic starch.

For this purpose, 2.00g of the original fiber type (Tencel or mercerized cotton) were placed in 60g of 40 wt% KOH solution in a 100ml beaker. The samples were placed on a flat plate dryer at a fixed temperature of 71 ℃ and 40% RH for 2 weeks. After 2 weeks, the beaker was taken out of the flat plate dryer and cooled to room temperature. The 40% KOH solution was decanted and the beaker with the fiber bundle was placed in a convection oven at 190 ℃ for 72 hours. The dried fiber was weighed on a balance to the nearest hundredth of a gram. The results are presented in table 16.

TABLE 16

The results indicate that battery separators formed using Tencel fibers may exhibit greater weight loss than battery separators formed using mercerized cotton. Thus, battery separators formed from mercerized cotton can be used in a greater number of applications.

The following additional test methods were used to test the materials, the results of which are set forth in the table above:

tensile strength: t.a.p.p.i. test method T-494, "tensile fracture properties of paper and paperboard" was used to test the mechanical strength of the exemplary materials and was measured for Machine Direction (MD) tensile strength (stress) using an Instron test machine and reported in lb. In this test, a sample (dimensions: 10in. × 1in. (25.4mm × 25.4 mm)) is stretched at a predetermined rate (1in/min./(25.4mm/min.)) until fracture.

Rigidity: t.a.p.p.i. test method T-543, "stiffness of paper", reported in milligrams, uses a Gurley type stiffness tester.

Wet burst strength: ASTM D774-97.

Air permeability (via Textech digital instrument): ASTM D737.

Gurley air resistance was tested according to t.a.p.p.i. test method T-460, which is hereby incorporated by reference. The instrument used for this test is a Gurley densitometer model 4159. For testing, the sample was inserted and fixed in a densitometer. The cylinder gradient was raised to the 100cc (100ml) line and then allowed to descend under its own weight. The time in seconds for 100cc of air to pass through the sample was recorded. The results are reported in seconds per 100cc, which is the time required for 100 cubic centimeters of air to pass through the structure.

Wet shrinkage: the dimensions of the approximately 3 inch (machine direction) by 2.5 inch (cross direction) samples were measured in the dry state using a digital caliper. The sample was then immersed in a 40% KOH solution for 5 minutes. The sample was then removed from the KOH solution and suspended vertically on a ring rack for 5 minutes by clamps to decant excess/surface KOH. The sample was then re-measured in two dimensions using a digital caliper. The% wet shrinkage was calculated based on the pre-soak and post-soak dimensional measurements for each of the two sample sizes.

Wicking rate: AATCC test method 197.

Average flow pore diameter: the test was performed according to ASTM E-1294 "standard test method for pore size characteristics of membrane filters using an automatic liquid porosimeter" using the automatic bubble point method according to ASTM F316 (using a capillary flow porosimeter). This measurement can be used to help determine the barrier properties of the structure.

The results of the above evaluations generally indicate that the experimental multi-layer fibrous structure is suitable for use as an alkaline battery separator. Notably, the absorption values indicate that the multilayer fibrous structure can exhibit superior performance relative to currently available battery separators.

The components of the apparatus shown are not limited to the specific embodiments described herein, but rather, features illustrated or described as part of one embodiment may be used on or in conjunction with other embodiments to yield yet a further embodiment. It is contemplated that the apparatus will include such modifications and variations. Further, steps described in the methods may be used independently and separately from other steps described herein.

By way of example and not limitation, various other embodiments of fibrous structures according to the present disclosure may have one or more layers (or plies) and may include:

(a) nanofibrillated cellulose-based fibers, and optionally, a strength additive;

(b) nanofibrillated cellulose-based fibers, alkali-resistant polymeric fibers and optionally strength additives;

(c) from about 65 wt% to up to 100 wt% nanofibrillated cellulose based fibers, from 0 wt% to about 35 wt% polymeric fibers, and optionally a strength additive;

(d) from about 65 wt% to up to 100 wt% nanofibrillated cellulose based fibers, from 0 wt% to about 35 wt% polyvinyl alcohol fibers, and from 0 wt% to about 10 wt% cationic strength additive;

(e) nanofibrils compounded into cellulose fibers, and optionally a strength additive;

(f) nanofibrils combined into cellulose fibers, alkali resistant polymeric fibers and optionally strength additives;

(g) from about 65 wt% to up to 100 wt% nanofibrillar composite cellulosic fibers, from 0 wt% to about 35 wt% polymeric fibers, and optionally a strength additive;

(h) from about 65 wt% to up to 100 wt% nanofibrillar synthetic cellulosic fibers, from 0 wt% to about 35 wt% polyvinyl alcohol fibers, and from 0 wt% to about 10 wt% cationic strength additive;

(i) nanofibrillated mercerized cotton fibers, and optionally a strength additive;

(j) nanofibrillated mercerized cotton fibers, alkali resistant polymeric fibers, and optionally strength additives;

(k) from about 65 wt% up to 100 wt% nanofibrillated mercerized cotton fibers, from 0 wt% to about 35 wt% polymeric fibers, and optionally a strength additive;

(l) From about 65% up to 100% by weight of mercerized cotton cellulose fibers, from 0% to about 35% by weight of polyvinyl alcohol fibers, and from 0% to about 10% by weight of a cationic strength additive, or

(m) countless variations thereof.

Any of such structures can be used in a variety of applications, such as for use as battery separators (e.g., alkaline battery separators).

Likewise, by way of example and not limitation, various other embodiments of methods of making fibrous structures according to the present disclosure may include:

(a) forming a first ply; and forming a second ply in a face-to-face relationship with the first ply, wherein the first ply and the second ply each comprise nanofibrillated cellulose-based fibers, and optionally at least one of polyvinyl alcohol fibers and a strength additive, and the first ply and the second ply each comprise about 50 wt% of the multi-layer fibrous structure;

(b) forming a furnish including nanofibrillated cellulose-based fibers, and optionally at least one of polyvinyl alcohol fibers and a strength additive; forming a first layer of furnish; forming a second layer of furnish such that the second layer of furnish covers the first layer of furnish; and drying the first layer of furnish and the second layer of furnish;

(c) applying a first layer of a furnish to a forming wire, the furnish comprising nanofibrillated cellulose-based fibers having a schopper-riegler scale freeness of about 83 to about 97 and a canadian standard freeness of about 12 to about 20, polyvinyl alcohol fibers having a length of about 4mm to about 9mm, and a denier of about 1.5dpf to about 5.0dpf, and an optional strength additive; applying a second layer of furnish to the first layer of furnish; and drying the first layer of furnish and the second layer of furnish;

(d) forming a furnish having a solids content of about 1 to about 8 wt%, the solids content comprising about 65 wt% to up to 100 wt% of nanofibrillated cellulose-based fibers, 0 wt% to about 35 wt% polyvinyl alcohol fibers, and 0 wt% to about 10 wt% of a cationic strength additive; depositing a first layer of the furnish onto a moving belt (or other forming surface); depositing a second layer of the furnish onto the first layer of the furnish; and drying the first layer of furnish and the second layer of furnish;

(e) forming a furnish having a solids content of about 1 to about 8 wt%, the solids content comprising about 65 wt% to about 85 wt% nanofibrillated cellulose-based fibers, about 15 wt% to about 35 wt% polyvinyl alcohol fibers, and about 2 wt% to about 7 wt% cationic starch; forming a first layer of furnish; forming a second layer of furnish covering the first layer of furnish; and drying the first layer of furnish and the second layer of furnish such that the polyvinyl alcohol fibers sinter or fuse with adjacent nanofibrillated cellulose-based fibers;

(f) forming a first ply; and forming a second ply in a face-to-face relationship with the first ply, wherein the first ply and the second ply each comprise nanofibrillar combined cellulosic fibers, and optionally at least one of polyvinyl alcohol fibers and a strength additive, and wherein the first ply and the second ply each comprise about 50 wt% of the multi-ply fibrous structure;

(g) forming a furnish including nanofibrillated cellulose-based fibers, and optionally at least one of polyvinyl alcohol fibers and a strength additive; forming a first layer of furnish; forming a second layer of furnish such that the second layer of furnish covers the first layer of furnish; and drying the first layer of furnish and the second layer of furnish;

(h) applying a first layer of a furnish to a forming wire, the furnish comprising nanofibrillar composite cellulosic fibers having a schopper-riegler scale freeness of from about 83 to about 97 and a canadian standard freeness of from about 12 to about 20, polyvinyl alcohol fibers having a length of from about 4mm to about 9mm, and a denier of from about 1.5dpf to about 5.0dpf, and optionally a strength additive; applying a second layer of furnish to the first layer of furnish; and drying the first layer of furnish and the second layer of furnish;

(i) forming a furnish having a solids content of about 1 to about 8 wt%, the solids content comprising about 65 wt% to up to 100 wt% nanofibrillar combined cellulosic fibers, 0 wt% to about 35 wt% polyvinyl alcohol fibers, and 0 wt% to about 10 wt% cationic strength additive; depositing a first layer of the furnish onto a moving belt (or other forming surface); depositing a second layer of the furnish onto the first layer of the furnish; drying the first layer of furnish and the second layer of furnish;

(j) forming a furnish having a solids content of about 1 to about 8 wt%, the solids content comprising about 65 wt% to about 85 wt% nanofibrillar synthetic cellulosic fibers, about 15 wt% to about 35 wt% polyvinyl alcohol fibers, and about 2 wt% to about 7 wt% cationic starch; forming a first layer of furnish; forming a second layer of furnish covering the first layer of furnish; drying the first layer of furnish and the second layer of furnish such that the polyvinyl alcohol fibers are sintered or fused with adjacent nanofibrillar composite cellulosic fibers;

(k) forming a first ply; and forming a second ply in a face-to-face relationship with the first ply, wherein the first ply and the second ply each comprise nanofibrillated mercerized cotton fibers, and optionally at least one of polyvinyl alcohol fibers and strength additives, and wherein the first ply and the second ply each comprise about 50 wt% of the multi-ply fibrous structure;

(l) Forming a furnish including nanofibrillated mercerized cotton fibers, and optionally at least one of polyvinyl alcohol fibers and strength additives; forming a first layer of furnish; forming a second layer of furnish such that the second layer of furnish covers the first layer of furnish; and drying the first layer of furnish and the second layer of furnish;

(m) applying a first layer of furnish to the forming wire, the furnish comprising nanofibrillated mercerized cotton fibers having a schopper-riegler scale freeness of from about 83 to about 97 and a canadian standard freeness of from about 12 to about 20, polyvinyl alcohol fibers having a length of from about 4mm to about 9mm, and a denier of from about 1.5dpf to about 5.0dpf, and optional strength additives; applying a second layer of furnish to the first layer of furnish; and drying the first layer of furnish and the second layer of furnish;

(n) forming a furnish having a solids content of from about 1 to about 8 wt%, the solids content comprising from about 65 wt% to up to 100 wt% nanofibrillated mercerized cotton fibers, from 0 wt% to about 35 wt% polyvinyl alcohol fibers, and from 0 wt% to about 10 wt% cationic strength additive; depositing a first layer of the furnish onto a moving belt (or other forming surface); depositing a second layer of the furnish onto the first layer of the furnish; drying the first layer of furnish and the second layer of furnish;

(o) forming a furnish having a solids content of about 1 to about 8 wt%, the solids content comprising about 65 wt% to about 85 wt% nanofibrillated mercerized cotton fibers, about 15 wt% to about 35 wt% polyvinyl alcohol fibers, and about 2 wt% to about 7 wt% cationic starch; forming a first layer of furnish; forming a second layer of furnish covering the first layer of furnish; drying the first layer of furnish and the second layer of furnish such that the polyvinyl alcohol fibers sinter or fuse with adjacent nanofibrillated mercerized cotton fibers; or

(p) innumerable variations thereof.

While the apparatus and methods have been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the intended scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings herein without departing from the essential scope thereof.

In this specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings. The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Furthermore, references to "one embodiment," "some embodiments," "an embodiment," etc., are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term such as "about" is not to be limited to the precise value specified. In some cases, the approximation class language may correspond to the precision of the instrument used to measure the value. Terms such as "first," "second," "upper," "lower," and the like are used to identify one element from another and are not meant to refer to a particular order or number of elements unless otherwise specified.

As used herein, the terms "may" and "may be" indicate a likelihood of occurrence within a set of circumstances; possession of a specified property, characteristic or function; and/or identify another verb by expressing one or more of a capability, skill or possibility associated with the identified verb. Thus, usage of "may" and "may be" indicates that the modified term is clearly appropriate, capable, or suitable for the indicated capability, function, or usage, while taking into account that in some cases the modified term may sometimes not be appropriate, capable, or suitable. For example, in some cases, an event or capability may be expected, while in other cases, an event or capability may not occur — this distinction is made by the terms "may" and "may be".

As used in the claims, the word "comprising" and grammatical variations thereof is also logically directed to and includes varying and varying degrees of phrase such as, for example and without limitation, "consisting essentially of and" consisting of. Where necessary, ranges are provided and include all subranges therebetween. It is expected that variations in these ranges will themselves initiate practitioners of ordinary skill in the art and, to the extent not already dedicated to the public, those variations are covered by the appended claims.

Advances in science and technology may enable equivalents and alternatives that are not currently contemplated due to imprecision of language; such variations are intended to be covered by the appended claims. This written description uses examples to disclose the method, machine, and computer-readable medium, including the best mode, and also to enable any person skilled in the art to practice these, including making and using any devices or systems and performing any incorporated methods. The patentable scope thereof is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.