U.S. patent application number 14/268071 was filed with the patent office on 2015-11-05 for hydrophobic treatment on hydrophilic nonwoven.
This patent application is currently assigned to Kimberly-Clark Worldwide, Inc.. The applicant listed for this patent is Kimberly-Clark Worldwide, Inc.. Invention is credited to Marsha R Forthofer, Karen Meloy Goeders.
Application Number | 20150315749 14/268071 |
Document ID | / |
Family ID | 54354853 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150315749 |
Kind Code |
A1 |
Goeders; Karen Meloy ; et
al. |
November 5, 2015 |
HYDROPHOBIC TREATMENT ON HYDROPHILIC NONWOVEN
Abstract
A liquid-impermeable barrier material includes a hydrophilic
nonwoven web having two surfaces, the nonwoven web including
fibers; and a hydrophobic composition disposed on a surface,
wherein the barrier material is breathable. The barrier material
exhibits a positive hydrohead value. The hydrophobic composition
can include a hydrophobic component selected from the group
consisting of fluorinated polymers, perfluorinated polymers, and
mixtures thereof. The barrier material can include a hydrophilic
surface opposite the surface having the hydrophobic composition.
The nonwoven web can include tissue, cellulose, or other suitable
material. A barrier material has a hydrophobic surface and includes
a hydrophilic nonwoven substrate treated with a composition
including a hydrophobic component and water.
Inventors: |
Goeders; Karen Meloy;
(Plymouth, MN) ; Forthofer; Marsha R; (Woodstock,
GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kimberly-Clark Worldwide, Inc. |
Neenah |
WI |
US |
|
|
Assignee: |
Kimberly-Clark Worldwide,
Inc.
Neenah
WI
|
Family ID: |
54354853 |
Appl. No.: |
14/268071 |
Filed: |
May 2, 2014 |
Current U.S.
Class: |
428/421 |
Current CPC
Class: |
D21H 27/002 20130101;
D21H 19/44 20130101; Y10T 428/3154 20150401; D21H 19/64 20130101;
D21H 21/16 20130101; D21H 21/52 20130101; D21H 19/12 20130101 |
International
Class: |
D21H 21/16 20060101
D21H021/16; D21H 19/12 20060101 D21H019/12 |
Claims
1. A liquid-impermeable barrier material comprising: a hydrophilic
nonwoven web having two surfaces, the nonwoven web including
fibers; and a hydrophobic composition disposed on a surface,
wherein the barrier material is breathable.
2. The barrier material of claim 1, wherein the barrier material
exhibits a positive hydrohead value.
3. The barrier material of claim 1, wherein the hydrophobic
composition includes a hydrophobic component selected from the
group consisting of fluorinated polymers, perfluorinated polymers,
and mixtures thereof.
4. The barrier material of claim 1, wherein the barrier material
includes a hydrophilic surface opposite the surface having the
hydrophobic composition.
5. The barrier material of claim 1, wherein the nonwoven web
includes tissue.
6. The barrier material of claim 1, wherein the nonwoven web
includes cellulose.
7. The barrier material of claim 1, wherein the hydrophobic
composition is a film-like structure between a portion of the
fibers.
8. A barrier material having a hydrophobic surface, the barrier
material comprising: a hydrophilic nonwoven substrate treated with
a composition including a hydrophobic component and water.
9. The barrier material of claim 8, wherein the barrier material
includes a hydrophilic surface opposite the hydrophobic
surface.
10. The barrier material of claim 8, wherein the hydrophobic
component is selected from the group consisting of fluorinated
polymers, perfluorinated polymers, and mixtures thereof.
11. The barrier material of claim 8, the composition further
comprising nano-structured particles.
12. The barrier material of claim 11, wherein the nano-structured
particles are selected from the group consisting of fumed silica,
hydrophobic titania, zinc oxide, nanoclay, and mixtures
thereof.
13. The barrier material of claim 8, the composition further
comprising a surfactant, wherein the surfactant is selected from
nonionic, cationic, and anionic surfactants.
14. The barrier material of claim 8, wherein the hydrophobic
component is a water-dispersible hydrophobic polymer.
15. The barrier material of claim 14, wherein the water-dispersible
hydrophobic polymer includes a comonomer selected from acrylic
monomers, acrylic precursors, and the like.
16. The barrier material of claim 8, the composition further
comprising a stabilizing agent selected from the group consisting
of long chain fatty acids, long chain fatty acid salts,
ethylene-acrylic acid, ethylene-methacrylic acid copolymers,
sulfonic acid, acetic acid, and the like.
17. The barrier material of claim 8, the composition further
comprising a filler selected from the group consisting of milled
glass, calcium carbonate, aluminum trihydrate, talc, antimony
trioxide, fly ash, clays, and the like.
18. The barrier material of claim 8, wherein the nonwoven substrate
is a tissue product.
Description
BACKGROUND
[0001] The present disclosure relates to hydrophilic, breathable
materials that exhibit hydrophobic properties when treated with
certain compositions. Currently, hydrophobic, breathable materials
are generally made using hydrophobic polymeric films. Such
materials tend to be hydrophobic throughout the thickness of the
material, which might not be desired in many cases. Such materials
also tend to be less cost effective. Although various formulated
dispersions capable of coating a surface to make that surface
hydrophobic exist, these tend not to be water-based. These tend to
require the use of organic solvents.
[0002] Disposable absorbent products (e.g., diapers, feminine
hygiene products, incontinence products, etc.) are subjected to one
or more liquid insults, such as of water, urine, menses, or blood,
during use. Many commercially available diapers allow water vapor
to pass through the diaper and into the environment to lessen the
amount of moisture held against the skin and reduce the chance of
skin irritation and rash due to skin overhydration. To allow the
passage of vapor through the diaper and into the environment while
holding liquid, a "breathable" outer cover is often employed that
is formed from a nonwoven web laminated to a film.
SUMMARY
[0003] As a result, a new material is needed that is both
cost-effective and does not rely on organic solvents. For a
multitude of safety, health, economic, and environmental issues, it
is also important that the dispersion be fully aqueous-based when
regarding commercial scale production, as this will decrease
concerns associated with the use of organic solvents. The present
disclosure relates to the use of a hydrophobic chemistry applied to
a hydrophilic fibrous material to create liquid barrier properties
in an otherwise wettable nonwoven by creating a film-like structure
between the fibers. This yields a hydrophilic substrate that acts
like a film while still being air permeable and exceeding the
breathability seen in standard breathable outer cover films.
[0004] The present disclosure provides a liquid-impermeable barrier
material including a hydrophilic nonwoven web having two surfaces,
the nonwoven web including fibers; and a hydrophobic composition
disposed on a surface, wherein the barrier material is breathable.
The barrier material exhibits a positive hydrohead value. The
hydrophobic composition can include a hydrophobic component
selected from the group consisting of fluorinated polymers,
perfluorinated polymers, and mixtures thereof. The barrier material
can include a hydrophilic surface opposite the surface having the
hydrophobic composition. The nonwoven web can include tissue,
cellulose, or other suitable material.
[0005] The present disclosure also provides a barrier material
having a hydrophobic surface, the barrier material including a
hydrophilic nonwoven substrate treated with a composition including
a hydrophobic component and water.
BRIEF DESCRIPTION OF THE FIGURES
[0006] The foregoing and other features and aspects of the present
disclosure and the manner of attaining them will become more
apparent, and the disclosure itself will be better understood by
reference to the following description, appended claims and
accompanying drawings, where:
[0007] FIG. 1 illustrates the contact angle exhibited by various
hydrophobic treatments;
[0008] FIG. 2 illustrates the roll off angle exhibited by the
various hydrophobic treatments of FIG. 1;
[0009] FIG. 3 illustrates the hydrohead values exhibited by a
hydrophilic HYDROKNIT brand towel with various hydrophobic
treatments;
[0010] FIG. 4 illustrates scanning electron microscope micrographs
of hydrophilic HYDROKNIT brand towels with various hydrophobic
treatments;
[0011] FIG. 5 illustrates scanning electron microscope micrographs
of SMS with various hydrophobic treatments; and
[0012] FIG. 6 illustrates a scanning electron microscope micrograph
of TABCW (through air dried bonded carded web) fibers with UIC III
hydrophobic treatment.
[0013] Repeat use of reference characters in the present
specification and drawings is intended to represent the same or
analogous features or elements of the present disclosure. The
drawings are representational and are not necessarily drawn to
scale. Certain proportions thereof might be exaggerated, while
others might be minimized.
DETAILED DESCRIPTION
[0014] All percentages are by weight of the total composition
unless specifically stated otherwise. All ratios are weight ratios
unless specifically stated otherwise.
[0015] The term "hydrophobic," as used herein, refers to the
property of a surface to repel water with a water contact angle
from about 90.degree. to about 120.degree..
[0016] The term "hydrophilic," as used herein, refers to surfaces
with water contact angles well below 90.degree..
[0017] As used herein, the term "breathability" refers to the water
vapor transmission rate (WVTR) of an area of film. Breathability is
measured in grams of water per square meter per day. For purposes
of the present disclosure, a film is "breathable" if it has a WVTR
of at least 800 grams per square meter per 24 hours as calculated
using the MOCON test method, which is described in detail
below.
[0018] Various methods can significantly increase the water vapor
transmission rate ("WVTR") of a film, which is the rate at which
water vapor permeates through a material as measured in units of
grams per meter squared per 24 hours (g/m.sup.2/24 hrs). For
example, the film can exhibit a WVTR of about 500 grams/m.sup.2-24
hours or more, in some aspects about 1,000 grams/m.sup.2-24 hours
or more, in some aspects about 2,000 grams/m.sup.2-24 hours or
more, and in some aspects, from about 3,000 to about 15,000
grams/m.sup.2-24 hours. The high void volume can also lower the
density of the film. For example, the film can have a density of
about 1.4 grams per cubic centimeter ("g/cm.sup.3") or less, in
some aspects about 1.1 g/cm.sup.3 or less, in some aspects from
about 0.4 g/cm.sup.3 to about 1.0 g/cm.sup.3, and in some aspects,
from about 0.5 g/cm.sup.3 to about 0.95 g/cm.sup.3.
[0019] As used herein, the term "nonwoven web" or "nonwoven fabric"
means a web having a structure of individual fibers or threads that
are interlaid, but not in an identifiable manner as in a knitted
web. Nonwoven webs have been formed from many processes, such as,
for example, meltblowing processes, spunbonding processes,
air-laying processes, coforming processes and bonded carded web
processes. The basis weight of nonwoven webs is usually expressed
in ounces of material per square yard (osy) or grams per square
meter (gsm) and the fiber diameters are usually expressed in
microns, or in the case of staple fibers, denier. It is noted that
to convert from osy to gsm, multiply osy by 33.91.
[0020] As used herein the term "spunbond fibers" refers to small
diameter fibers of molecularly oriented polymeric material.
Spunbond fibers can be formed by extruding molten thermoplastic
material as fibers from a plurality of fine, usually circular
capillaries of a spinneret with the diameter of the extruded fibers
then being rapidly reduced as in, for example, U.S. Pat. No.
4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner
et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos.
3,338,992 and 3,341,394 to Kinney, U.S. Pat. No. 3,502,763 to
Hartman, U.S. Pat. No. 3,542,615 to Dobo et al, and U.S. Pat. No.
5,382,400 to Pike et al. Spunbond fibers are generally not tacky
when they are deposited onto a collecting surface and are generally
continuous. Spunbond fibers are often about 10 microns or greater
in diameter. However, fine fiber spunbond webs (having an average
fiber diameter less than about 10 microns) can be achieved by
various methods including, but not limited to, those described in
commonly assigned U.S. Pat. No. 6,200,669 to Marmon et al. and U.S.
Pat. No. 5,759,926 to Pike et al.
[0021] Meltblown nonwoven webs are prepared from meltblown fibers.
As used herein the term "meltblown fibers" means fibers formed by
extruding a molten thermoplastic material through a plurality of
fine, usually circular, die capillaries as molten threads or
filaments into converging high velocity, usually hot, gas (e.g.
air) streams that attenuate the filaments of molten thermoplastic
material to reduce their diameter, which can be to microfiber
diameter. Thereafter, the meltblown fibers are carried by the high
velocity gas stream and are deposited on a collecting surface to
form a web of randomly dispersed meltblown fibers. Such a process
is disclosed, for example, in U.S. Pat. No. 3,849,241 to Buntin.
Meltblown fibers are microfibers that can be continuous or
discontinuous, are generally smaller than 10 microns in average
diameter (using a sample size of at least 10), and are generally
tacky when deposited onto a collecting surface.
[0022] As used herein, the term "polymer" generally includes, but
is not limited to, homopolymers, copolymers, such as for example,
block, graft, random and alternating copolymers, terpolymers, etc.
and blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometrical configurations of the molecule. These configurations
include, but are not limited to isotactic, syndiotactic and random
symmetries.
[0023] As used herein, the term "multicomponent fibers" refers to
fibers or filaments that have been formed from at least two
polymers extruded from separate extruders but spun together to form
one fiber. Multicomponent fibers are also sometimes referred to as
"conjugate" or "bicomponent" fibers or filaments. The term
"bicomponent" means that there are two polymeric components making
up the fibers. The polymers are usually different from each other,
although conjugate fibers can be prepared from the same polymer, if
the polymer in each component is different from one another in some
physical property, such as, for example, melting point, glass
transition temperature or the softening point. In all cases, the
polymers are arranged in substantially constantly positioned
distinct zones across the cross-section of the multicomponent
fibers or filaments and extend continuously along the length of the
multicomponent fibers or filaments. The configuration of such a
multicomponent fiber can be, for example, a sheath/core
arrangement, wherein one polymer is surrounded by another, a
side-by-side arrangement, a pie arrangement or an
"islands-in-the-sea" arrangement. Multicomponent fibers are taught
in U.S. Pat. No. 5,108,820 to Kaneko et al.; U.S. Pat. No.
5,336,552 to Strack et al.; and U.S. Pat. No. 5,382,400 to Pike et
al. For two component fibers or filaments, the polymers can be
present in ratios of 75/25, 50/50, 25/75 or any other desired
ratios.
[0024] As used herein, the term "multiconstituent fibers" refers to
fibers that have been formed from at least two polymers extruded
from the same extruder as a blend or mixture. Multiconstituent
fibers do not have the various polymer components arranged in
relatively constantly positioned distinct zones across the
cross-sectional area of the fiber and the various polymers are
usually not continuous along the entire length of the fiber,
instead usually forming fibrils or protofibrils that start and end
at random. Fibers of this general type are discussed in, for
example, U.S. Pat. Nos. 5,108,827 and 5,294,482 to Gessner.
[0025] As used herein, the term "substantially continuous fibers"
is intended to mean fiber that have a length that is greater that
the length of staple fibers. The term is intended to include fibers
that are continuous, such as spunbond fibers, and fibers that are
not continuous, but have a defined length greater than about 150
millimeters.
[0026] As used herein, the term "staple fibers" means fibers that
have a fiber length generally in the range of about 0.5 to about
150 millimeters. Staple fibers can be cellulosic fibers or
non-cellulosic fibers. Some examples of suitable non-cellulosic
fibers that can be used include, but are not limited to, polyolefin
fibers, polyester fibers, nylon fibers, polyvinyl acetate fibers,
and mixtures thereof. Cellulosic staple fibers include for example,
pulp, thermomechanical pulp, synthetic cellulosic fibers, modified
cellulosic fibers, and the like. Cellulosic fibers can be obtained
from secondary or recycled sources. Some examples of suitable
cellulosic fiber sources include virgin wood fibers, such as
thermomechanical, bleached and unbleached softwood and hardwood
pulps. Secondary or recycled cellulosic fibers can be obtained from
office waste, newsprint, brown paper stock, paperboard scrap, etc.,
can also be used. Further, vegetable fibers, such as abaca, flax,
milkweed, cotton, modified cotton, cotton linters, can also be used
as the cellulosic fibers. In addition, synthetic cellulosic fibers
such as, for example, rayon and viscose rayon can be used. Modified
cellulosic fibers are generally are composed of derivatives of
cellulose formed by substitution of appropriate radicals (e.g.,
carboxyl, alkyl, acetate, nitrate, etc.) for hydroxyl groups along
the carbon chain.
[0027] As used herein, the term "pulp" refers to fibers from
natural sources such as woody and non-woody plants. Woody plants
include, for example, deciduous and coniferous trees. Non-woody
plants include, for example, cotton, flax, esparto grass, milkweed,
straw, jute, hemp, and bagasse.
[0028] As used herein, "tissue products" are meant to include
facial tissue, bath tissue, towels, hankies, napkins and the like.
The present disclosure is useful with tissue products and tissue
paper in general, including but not limited to conventionally
felt-pressed tissue paper, high bulk pattern densified tissue
paper, and high bulk, uncompacted tissue paper.
[0029] The present disclosure relates to a surface of a hydrophilic
substrate, or the substrate itself, exhibiting hydrophobic
characteristics when treated with certain compositions. The
hydrophobicity can be applied either over the entire surface,
patterned throughout or on the substrate material, and/or directly
penetrated through the z-directional thickness of the substrate
material.
[0030] Materials such as diaper outercover spunbond-film laminate
or surgical gown SMS are currently used to prevent liquid from
penetrating through the material and onto the user or into the
user's environment. These materials use film or meltblown as the
barrier materials to prevent fluid penetration. Many hydrophilic
materials are currently used in various applications, the materials
including those such as coform and HYDROKNIT brand towel for wipes
as well as cellulosic tissues for facial and bath tissues. These
materials are absorptive and thus not useful as barriers to fluids.
Tissue-based materials tend to be less expensive than polymeric
laminates and films.
[0031] There is interest in using naturally hydrophilic materials
in new ways. For example, a surface wet wipe made of a cellulosic
basesheet such as coform or airlaid that can maintain dryness on
one side while being wet on the other can offer hand protection to
the user. A tissue that has a barrier to fluid on one side could
allow a one-ply bath tissue to perform like a multi-ply bath tissue
by reducing fluid wet through or could allow a facial tissue to
better protect the user by reducing the amount of fluid that
penetrates through the tissue to the user's hand. Additionally,
when considering alternative and possibly lower cost or lower tier
diaper outer cover options, there is a need to consider ways to
create barriers to liquid on otherwise hydrophilic materials like
HYDROKNIT brand towel and tissue substrates.
[0032] The development described here is the use of a hydrophobic
chemistry applied to a hydrophilic nonwoven material to create
liquid barrier properties to an otherwise wettable nonwoven by way
of creating a film-like structure between the nonwoven fibers.
Hydrophobic Component
[0033] The hydrophobic component is a hydrophobic polymer that is
dispersible in water to form the basic elements of the hydrophobic
properties of the present disclosure. In general, a hydrophobic
component of this disclosure can include, but is not limited to,
fluorinated or perfluorinated polymers. However, due to low degree
of water dispersibility, the fluorinated or perfluorinated polymer
can need to be modified by introducing a comonomer onto their
molecular structure. Suitable comonomers include, but are not
limited to, ethylenically unsaturated monomers including functional
groups that are capable of being ionized in water. One example is
ethylenically unsaturated carboxylic acid, such as acrylic acid.
The amount of the comonomer within the hydrophobic component is
determined by balancing two properties: hydrophobicity and water
dispersibility. One example of the hydrophobic component of this
disclosure is a commercially available modified perfluorinated
polymer compound available from DuPont as a water-based product
under the trade name CAPSTONE STC-100. Due to its low surface
energy, the polymer contributes to the hydrophobicity.
Additionally, the polymer molecules can be modified to contain
groups, such as amines, that can become charged upon pH reduction
and alter the dynamics of hydrophobicity within the liquid
dispersion. In such a case, the polymer can stabilize in water
through partial interaction. Surfactants that are introduced into
the composition can also behave as dispersants of the polymer,
thereby also altering some of the hydrophobic mechanics.
[0034] The solid components of the present disclosure can be
present in an amount from about 1.0% to about 3.0%, by weight of
the solution. Such an amount is suitable for spray applications
where higher concentrations of polymer can lead to either
viscoelastic behavior, resulting in either clogging of the spray
nozzle or incomplete atomization and fiber formation, or dramatic
increases in dispersion viscosity and thus nozzle clogging. It
should be noted that this range is not fixed and that it is a
function of the materials being utilized and the procedure used to
prepare the dispersion. When a higher amount of the polymer is
used, the surface structure is less desirable as it lacks the
proper texture to be hydrophobic. When a lower amount of the
polymer is used, the binding is less desirable as the coating
behaves more so as a removable powder coating.
Non-Organic Solvent
[0035] The formulation used in treating the surface of the present
disclosure eliminates the use of an organic solvent by carefully
selecting the appropriate combination of elements to impart the
hydrophobic characteristics. Preferably, the non-organic solvent is
water. Any type of water can be used; however, demineralized or
distilled water can be opted for use during the manufacturing
process for enhanced capabilities. The use of water helps to reduce
the safety concerns associated with making commercial scale
formulations including organic solvents. For example, due to the
high volatility and flammability of most organic solvents,
eliminating such use in the composition reduces production safety
hazards. Additionally, production costs can be lowered with the
elimination of ventilation and fire prevention equipment
necessitated by organic solvents. Raw material costs can be reduced
in addition to the transportation of such materials as an added
advantage to utilizing the non-organic solvent formulation to
arrive at the present disclosure.
[0036] Additionally, because water is considered a natural
resource, surfaces treated with solvents including water as its
base can be considered healthier and better for the environment.
The formulation used to treat the surface of the present disclosure
includes greater than about 95%, greater than about 98%, or about
99% water, by weight of the dispersion composition.
Other Ingredients
Binders
[0037] The hydrophobic polymers within the formulation of the
present disclosure play a dual role in acting both as a hydrophobic
component and a binder. Polymers such as Dupont's CAPSTONE STC-100
promote adhesion, as compared to the fluorinated polymer alone, so
that an additional binder within the composition is not necessary.
If a water-dispersible hydrophobic polymer is used wherein an
additional binder is needed, it is preferred that the binder is
selected from water-dispersible acrylics, polyurethane dispersions,
acrylic copolymers, or acrylic polymer precursors (which can cross
link after the coating is cured).
[0038] The amount of the binder present within the formulation of
the present disclosure can vary. A binder can be included in an
effective amount of up to about 2.0% by weight of the total
dispersion composition.
Stabilizing Agent
[0039] The formulation within the present disclosure can be
additionally treated with a stabilizing agent to promote the
formation of a stable dispersion when other ingredients are added
to it. The stabilizing agent can be a surfactant, a polymer, or
mixtures thereof. If a polymer acts as a stabilizing agent, it is
preferred that the polymer differ from the hydrophobic component
used within the base composition previously described.
[0040] Additional stabilizing agents can include, but are not
limited to, cationic surfactants such as quaternary amines; anionic
surfactants such as sulfonates, carboxylates, and phosphates; or
nonionic surfactants such as block copolymers containing ethylene
oxide and silicone surfactants. The surfactants can be either
external or internal. External surfactants do not become chemically
reacted into the base polymer during dispersion preparation.
Examples of external surfactants useful herein include, but are not
limited to, salts of dodecyl benzene sulfonic acid and lauryl
sulfonic acid salt. Internal surfactants are surfactants that do
become chemically reacted into the base polymer during dispersion
preparation. An example of an internal surfactant useful herein
includes 2,2-dimethylol propionic acid and its salts.
[0041] In some aspects, the stabilizing agent used within the
composition to treat the surface of the present disclosure can be
used in an amount ranging from greater than zero to about 60%, by
of the hydrophobic component. For example, long chain fatty acids
or salts thereof can be used from about 0.5% to about 10% by weight
based on the amount of hydrophobic component. In other aspects,
ethylene-acrylic acid or ethylene-methacrylic acid copolymers can
be used in an amount up to about 80%, by weight based of
hydrophobic component. In yet other aspects, sulfonic acid salts
can be used in an amount from about 0.01% to about 60% by weight
based on the weight of the hydrophobic component. Other mild acids,
such as those in the carboxylic acid family (e.g., formic acid),
can also be included in order to further stabilize the dispersion.
In an aspect that includes formic acid, the formic acid can be
present in amount that is determined by the desired pH of the
dispersion wherein the pH is less than about 6.
Additional Fillers
[0042] The composition used to treat the surface of the present
disclosure can further include one or more fillers. The composition
can include from about 0.01 to about 600 parts, by weight of the
hydrophobic component, for example, polyolefin and the stabilizing
agent. In certain aspects, the filler loading in the composition
can be from about 0.01 to about 200 parts by the weight of the
hydrophobic component, for example, polyolefin, and the stabilizing
agent. It is preferred that such filler material, if used, be
hydrophilic. The filler material can include conventional fillers
such as milled glass, calcium carbonate, aluminum trihydrate, talc,
antimony trioxide, fly ash, clays (such as bentonite or kaolin
clays for example), or other known fillers. Untreated clays and
talc are usually hydrophilic by nature.
Substrate
[0043] The substrate of the present disclosure can be treated such
that it is superhydrophobic throughout the z-directional thickness
of the material and is controlled in such a way that only certain
areas of the material are superhydrophobic. Such treatment can be
designed to control which areas of the material can or cannot be
penetrated by wetness, thereby controlling where liquid can
flow.
[0044] Suitable substrates of the present disclosure can include a
nonwoven fabric, woven fabric, knit fabric, or laminates of these
materials. The substrate can also be a tissue or towel, as
described herein. Materials and processes suitable for forming such
substrate are generally well known to those skilled in the art. For
instance, some examples of nonwoven fabrics that can be used in the
present disclosure include, but are not limited to, spunbonded
webs, meltblown webs, bonded carded webs, air-laid webs, coform
webs, spunlace nonwoven web, hydraulically entangled webs, and the
like. In each case, at least one of the fibers used to prepare the
nonwoven fabric is a thermoplastic material containing fiber. In
addition, nonwoven fabrics can be a combination of thermoplastic
fibers and natural fibers, such as, for example, cellulosic fibers
(softwood pulp, hardwood pulp, thermomechanical pulp, etc.).
Generally, from the standpoint of cost and desired properties, the
substrate of the present disclosure is a hydrophilic nonwoven
fabric.
[0045] If desired, the nonwoven fabric can also be bonded using
techniques well known in the art to improve the durability,
strength, hand, aesthetics, texture, and/or other properties of the
fabric. For instance, the nonwoven fabric can be thermally (e.g.,
pattern bonded, through-air dried), ultrasonically, adhesively
and/or mechanically (e.g. needled) bonded. For instance, various
pattern bonding techniques are described in U.S. Pat. No. 3,855,046
to Hansen; U.S. Pat. No. 5,620,779 to Levy, et al.; U.S. Pat. No.
5,962,112 to Haynes, et al.; U.S. Pat. No. 6,093,665 to Sayovitz,
et al.; U.S. Design Pat. No. 428,267 to Romano, et al.; and U.S.
Design Pat. No. 390,708 to Brown.
[0046] The nonwoven fabric can be bonded by continuous seams or
patterns. As additional examples, the nonwoven fabric can be bonded
along the periphery of the sheet or simply across the width or
cross-direction (CD) of the web adjacent the edges. Other bond
techniques, such as a combination of thermal bonding and latex
impregnation, can also be used. Alternatively and/or additionally,
a resin, latex or adhesive can be applied to the nonwoven fabric
by, for example, spraying or printing, and dried to provide the
desired bonding. Still other suitable bonding techniques are
described in U.S. Pat. No. 5,284,703 to Everhart, et al., U.S. Pat.
No. 6,103,061 to Anderson, et al., and U.S. Pat. No. 6,197,404 to
Varona.
[0047] In another aspect, the substrate of the present disclosure
is formed from a spunbonded web containing monocomponent and/or
multicomponent fibers. Multicomponent fibers are fibers that have
been formed from at least two polymer components. Such fibers are
usually extruded from separate extruders but spun together to form
one fiber. The polymers of the respective components are usually
different from each other although multicomponent fibers can
include separate components of similar or identical polymeric
materials. The individual components are typically arranged in
substantially constantly positioned distinct zones across the
cross-section of the fiber and extend substantially along the
entire length of the fiber. The configuration of such fibers can
be, for example, a side-by-side arrangement, a pie arrangement, or
any other arrangement.
[0048] When used, multicomponent fibers can also be splittable. In
fabricating multicomponent fibers that are splittable, the
individual segments that collectively form the unitary
multicomponent fiber are contiguous along the longitudinal
direction of the multicomponent fiber in a manner such that one or
more segments form part of the outer surface of the unitary
multicomponent fiber. In other words, one or more segments are
exposed along the outer perimeter of the multicomponent fiber. For
example, splittable multicomponent fibers and methods for making
such fibers are described in U.S. Pat. No. 5,935,883 to Pike and
U.S. Pat. No. 6,200,669 to Marmon, et al.
[0049] The substrate of the present disclosure can also contain a
coform material. The term "coform material" generally refers to
composite materials including a mixture or stabilized matrix of
thermoplastic fibers and a second non-thermoplastic material. As an
example, coform materials can be made by a process in which at
least one meltblown die head is arranged near a chute through which
other materials are added to the web while it is forming. Such
other materials can include, but are not limited to, fibrous
organic materials such as woody or non-woody pulp such as cotton,
rayon, recycled paper, pulp fluff and also superabsorbent
particles, inorganic absorbent materials, treated polymeric staple
fibers and the like. Some examples of such coform materials are
disclosed in U.S. Pat. No. 4,100,324 to Anderson, et al.; U.S. Pat.
No. 5,284,703 to Everhart, et al.; and U.S. Pat. No. 5,350,624 to
Georger, et al.
[0050] Additionally, the substrate can also be formed from a
material that is imparted with texture one or more surfaces. For
instances, in some aspects, the substrate can be formed from a
dual-textured spunbond or meltblown material, such as described in
U.S. Pat. No. 4,659,609 to Lamers, et al. and U.S. Pat. No.
4,833,003 to Win, et al.
[0051] In one particular aspect of the present disclosure, the
substrate is formed from a hydroentangled nonwoven fabric.
Hydroentangling processes and hydroentangled composite webs
containing various combinations of different fibers are known in
the art. A typical hydroentangling process utilizes high pressure
jet streams of water to entangle fibers and/or filaments to form a
highly entangled consolidated fibrous structure, e.g., a nonwoven
fabric. Hydroentangled nonwoven fabrics of staple length fibers and
continuous filaments are disclosed, for example, in U.S. Pat. No.
3,494,821 to Evans and U.S. Pat. No. 4,144,370. Hydroentangled
composite nonwoven fabrics of a continuous filament nonwoven web
and a pulp layer are disclosed, for example, in U.S. Pat. No.
5,284,703 to Everhart, et al. and U.S. Pat. No. 6,315,864 to
Anderson, et al.
[0052] Of these nonwoven fabrics, hydroentangled nonwoven webs with
staple fibers entangled with thermoplastic fibers is especially
suited as the substrate. In one particular example of a
hydroentangled nonwoven web, the staple fibers are hydraulically
entangled with substantially continuous thermoplastic fibers. The
staple can be cellulosic staple fiber, non-cellulosic stable fibers
or a mixture thereof. Suitable non-cellulosic staple fibers
includes thermoplastic staple fibers, such as polyolefin staple
fibers, polyester staple fibers, nylon staple fibers, polyvinyl
acetate staple fibers, and the like or mixtures thereof. Suitable
cellulosic staple fibers include for example, pulp,
thermomechanical pulp, synthetic cellulosic fibers, modified
cellulosic fibers, and the like. Cellulosic fibers can be obtained
from secondary or recycled sources. Some examples of suitable
cellulosic fiber sources include virgin wood fibers, such as
thermomechanical, bleached and unbleached softwood and hardwood
pulps. Secondary or recycled cellulosic fibers can be obtained from
office waste, newsprint, brown paper stock, paperboard scrap, etc.,
can also be used. Further, vegetable fibers, such as abaca, flax,
milkweed, cotton, modified cotton, cotton linters, can also be used
as the cellulosic fibers. In addition, synthetic cellulosic fibers
such as, for example, rayon and viscose rayon can be used. Modified
cellulosic fibers are generally are composed of derivatives of
cellulose formed by substitution of appropriate radicals (e.g.,
carboxyl, alkyl, acetate, nitrate, etc.) for hydroxyl groups along
the carbon chain.
[0053] One particularly suitable hydroentangled nonwoven web is a
nonwoven web composite of polypropylene spunbond fibers, which are
substantially continuous fibers, having pulp fibers hydraulically
entangled with the spunbond fibers. Another particularly suitable
hydroentangled nonwoven web is a nonwoven web composite of
polypropylene spunbond fibers having a mixture of cellulosic and
non-cellulosic staple fibers hydraulically entangled with the
spunbond fibers.
[0054] The substrate of the present disclosure can be prepared
solely from thermoplastic fibers or can contain both thermoplastic
fibers and non-thermoplastic fibers. Generally, when the substrate
contains both thermoplastic fibers and non-thermoplastic fibers,
the thermoplastic fibers make up from about 10% to about 90%, by
weight of the substrate. In a particular aspect, the substrate
contains between about 10% and about 30%, by weight, thermoplastic
fibers.
[0055] Generally, a nonwoven substrate will have a basis weight in
the range of about 17 gsm (grams per square meter) to about 200
gsm, more typically, between about 33 gsm to about 200 gsm. The
actual basis weight can be higher than 200 gsm, but for many
applications, the basis weight will be in the 33 gsm to 150 gsm
range.
[0056] The thermoplastic materials or fibers making-up at least a
portion of the substrate can essentially be any thermoplastic
polymer. Suitable thermoplastic polymers include polyolefins,
polyesters, polyamides, polyurethanes, polyvinylchloride,
polytetrafluoroethylene, polystyrene, polyethylene terephthalate,
biodegradable polymers such as polylactic acid and copolymers and
blends thereof. Suitable polyolef ins include polyethylene, e.g.,
high density polyethylene, medium density polyethylene, low density
polyethylene and linear low density polyethylene; polypropylene,
e.g., isotactic polypropylene, syndiotactic polypropylene, blends
of isotactic polypropylene and atactic polypropylene, and blends
thereof; polybutylene, e.g., poly(l-butene) and poly(2-butene);
polypentene, e.g., poly(l-pentene) and poly(2-pentene);
poly(3-methyl-1-pentene); poly(4-methyl 1-pentene); and copolymers
and blends thereof. Suitable copolymers include random and block
copolymers prepared from two or more different unsaturated olefin
monomers, such as ethylene/propylene and ethylene/butylene
copolymers. Suitable polyamides include nylon 6, nylon 6/6, nylon
4/6, nylon 11, nylon 12, nylon 6/10, nylon 6/12, nylon 12/12,
copolymers of caprolactam and alkylene oxide diamine, and the like,
as well as blends and copolymers thereof. Suitable polyesters
include polyethylene terephthalate, polytrimethylene terephthalate,
polybutylene terephthalate, polytetramethylene terephthalate,
polycyclohexylene-1,4-dimethylene terephthalate, and isophthalate
copolymers thereof, as well as blends thereof. These thermoplastic
polymers can be used to prepare both substantially continuous
fibers and staple fibers, in accordance with the present
disclosure.
[0057] In another aspect, the substrate can be a tissue product.
The tissue product can be of a homogenous or multi-layered
construction, and tissue products made therefrom can be of a
single-ply or multi-ply construction. The tissue product desirably
has a basis weight of about 10 g/m2 to about 65 g/m2, and density
of about 0.6 g/cc or less. More desirably, the basis weight will be
about 40 g/m2 or less and the density will be about 0.3 g/cc or
less. Most desirably, the density will be about 0.04 g/cc to about
0.2 g/cc. Unless otherwise specified, all amounts and weights
relative to the paper are on a dry basis. Tensile strengths in the
machine direction can be in the range of from about 100 to about
5,000 grams per inch of width. Tensile strengths in the
cross-machine direction are from about 50 grams to about 2,500
grams per inch of width. Absorbency is typically from about 5 grams
of water per gram of fiber to about 9 grams of water per gram of
fiber.
[0058] Conventionally pressed tissue products and methods for
making such products are well known in the art. Tissue products are
typically made by depositing a papermaking furnish on a foraminous
forming wire, often referred to in the art as a Fourdrinier wire.
Once the furnish is deposited on the forming wire, it is referred
to as a web. The web is dewatered by pressing the web and drying at
elevated temperature. The particular techniques and typical
equipment for making webs according to the process just described
are well known to those skilled in the art. In a typical process, a
low consistency pulp furnish is provided from a pressurized
headbox, which has an opening for delivering a thin deposit of pulp
furnish onto the Fourdrinier wire to form a wet web. The web is
then typically dewatered to a fiber consistency of from about 7% to
about 25% (total web weight basis) by vacuum dewatering and further
dried by pressing operations wherein the web is subjected to
pressure developed by opposing mechanical members, for example,
cylindrical rolls. The dewatered web is then further pressed and
dried by a steam drum apparatus known in the art as a Yankee dryer.
Pressure can be developed at the Yankee dryer by mechanical means
such as an opposing cylindrical drum pressing against the web.
Multiple Yankee dryer drums can be employed, whereby additional
pressing is optionally incurred between the drums. The formed
sheets are considered to be compacted because the entire web is
subjected to substantial mechanical compressional forces while the
fibers are moist and are then dried while in a compressed
state.
[0059] One particular aspect of the present disclosure utilizes an
uncreped through-air-drying technique to form the tissue product.
Through-air-drying can increase the bulk and softness of the web.
Examples of such a technique are disclosed in U.S. Pat. No.
5,048,589 to Cook, et al.; U.S. Pat. No. 5,399,412 to Sudall, et
al.; U.S. Pat. No. 5,510,001 to Hermans, et al.; U.S. Pat. No.
5,591,309 to Ruqowski, et al.; U.S. Pat. No. 6,017,417 to Wendt, et
al., and U.S. Pat. No. 6,432,270 to Liu, et al. Uncreped
through-air-drying generally involves the steps of: (1) forming a
furnish of cellulosic fibers, water, and optionally, other
additives; (2) depositing the furnish on a traveling foraminous
belt, thereby forming a fibrous web on top of the traveling
foraminous belt; (3) subjecting the fibrous web to
through-air-drying to remove the water from the fibrous web; and
(4) removing the dried fibrous web from the traveling foraminous
belt.
Manufacture
[0060] Conventional scalable methods, such as spraying, can be used
to apply a hydrophobic coating on a surface. In one aspect, a
hydrophilic nano-structured filler (Nanomer.RTM. PGV nanoclay from
Sigma Aldrich), which is a bentonite clay without organic
modification, is used. As a hydrophobic component, a 20 wt. %
dispersion of a fluorinated acrylic co-polymer (PMC) in water is
used, as obtained from DuPont (trade name is CAPSTONE STC-100). The
hydrophilic nanoclay is added to water and is sonicated until a
stable suspension is produced. Sonication can be done by utilizing
a probe sonicator at room temperature (Sonics.RTM., 750 W, High
Intensity Ultrasonic Processor, 13 mm diameter tip at 30%
amplitude). At these settings, it can take from about 15 to about
30 min for a stable 15.5 g nanoclay-water suspension to form. The
concentration of the nanoclay in water is kept below 2 wt. % of
total suspension to prevent the formation of a gel, which renders
the dispersion too viscous to spray. After placing the stable
clay-water suspension under mechanical mixing at room temperature,
the aqueous PMC dispersion is added drop-wise to the suspension to
produce the final dispersion for spray. In such aspect, the
concentrations of each component in the final dispersion for
producing a superhydrophobic coating will be as follows: 95.5 wt. %
water, 2.8% PMC, 1.7% nanoclay or 97.5 wt. % water, 1.25% PMC,
1.25% nanoclay. Coatings can be applied by spray onto cellulosic
substrates at a distance of about 15 to about 25 cm using an
airbrush atomizer (Paasche VL siphon feed, 0.55 mm spray nozzle)
either by hand or by mounting the device onto an industrial fluid
dispensing robot (EFD, Ultra TT Series). EFD nozzles with air
assist can also be utilized as this achieves extremely fine mists
during spray application. The smallest nozzle diameter suggested
for the EFD dispensing system is about 0.35 mm. The air fans assist
in shaping the spray cone into an oval shape, which is useful for
producing a continuous uniform coating on a linearly moving
substrate. For the airbrush, operation relies on pressurized air
passing through the nozzle in order to siphon-feed the particle
dispersion and also to facilitate fluid atomization at the nozzle
exit. The pressure drop applied across the sprayer can vary from
about 2.1 to about 3.4 bar, depending on conditions.
[0061] Some technical difficulties are typically encountered when
spraying water-based dispersions: The first major problem is
insufficient evaporation of the fluid during atomization and a high
degree of wetting of the dispersion onto the coated substrate, both
resulting in non-uniform coatings due to contact line pinning and
the so called "coffee-stain effect" when the water eventually
evaporates. The second major challenge is the relatively large
surface tension of water when compared with other solvents used for
spray coating. Water, due to its high surface tension, tends to
form non-uniform films in spray applications, thus requiring great
care to ensure that a uniform coating is attained. It was observed
that the best approach for applying the aqueous dispersions of the
present disclosure was to produce extremely fine droplets during
atomization, and to apply only very thin coatings, so as not to
saturate the substrate and re-orient hydrogen bonding within the
substrate that, after drying, would cause cellulosic substrates
(e.g. paper towel) to become stiff.
[0062] In another aspect, the coatings are spray cast first on a
substrate, such as standard paperboard or other cellulosic
substrate; multiple spray passes are used to achieve different
coating thicknesses. The sprayed films are then subjected to drying
in an oven at about 80.degree. C. for about 30 min to remove all
excess water. The size of the substrate can be approximately, but
not limited to about 7.5 cm.times.9 cm. Once dried, the coatings
are characterized for wettability (i.e., hydrophobic vs.
hydrophilic). The substrates can be weighed on a microbalance
(Sartorius.RTM. LE26P) before and after coating and drying in order
to determine the minimum level of coating required to induce
hydrophobicity. This "minimum coating" does not strictly mean that
the sample will resist penetration by liquids, but rather that a
water droplet will bead on the surface and roll off unimpeded.
Liquid repellency of substrates before and after coating can be
characterized by a hydrostatic pressure setup that determines
liquid penetration pressures (in cm of liquid).
Performance Characterization
[0063] Contact angle values can be obtained by a backlit optical
image setup utilizing a CCD camera. For dynamic contact angle
hysteresis measurements (which designate the self-cleaning
property), the CCD camera can be replaced by a high-speed camera,
such as Redlake.TM. Motion Pro, in order to accurately capture
advancing and receding contact angle values. The lower the
difference between advancing and receding contact angles (i.e.
contact angle hysteresis), the more self-cleaning the surface is.
Liquid penetration pressure can be determined by increasing the
hydrostatic column pressure until liquid penetrates the sample in
accordance with ASTM F903-10. Liquid penetration can be recorded by
an optical image setup utilizing a CCD camera.
MOCON Water Vapor Transmission Rate Test:
[0064] A suitable technique for determining the water vapor
transmission rate (WVTR) value of a material is the test procedure
standardized by INDA (Association of the Nonwoven Fabrics
Industry), number IST-70.4-99, entitled "Standard Test Method For
Water Vapor Transmission Rate Through Nonwoven And Plastic Film
Using A Guard Film And Vapor Pressure Sensor," which is
incorporated by reference herein. The INDA procedure provides for
the determination of WVTR, the permeance of the film to water vapor
and, for homogeneous materials, water vapor permeability
coefficient.
[0065] The INDA test method is well known and will not be set forth
in detail herein. However, the test procedure is summarized as
follows. A dry chamber is separated from a wet chamber of known
temperature and humidity by a permanent guard film and the sample
material to be tested. The purpose of the guard film is to define a
definite air gap and to quiet or still the air in the air gap while
the air gap is characterized. The dry chamber, guard film, and the
wet chamber make up a diffusion cell in which the test film is
sealed. The sample holder is known as the PERMATRAN-W.RTM. model
100K manufactured by Modern Controls, Inc. (MOCON) (Minneapolis,
Minn.), USA. A first test is made of the WVTR of the guard film and
air gap between an evaporator assembly that generates 100 percent
relative humidity. Water vapor diffuses through the air gap and the
guard film and then mixes with a dry gas flow that is proportional
to water vapor concentration. The electrical signal is routed to a
computer for processing. The computer calculates the transmission
rate of the air gap and guard film and stores the value for further
use.
[0066] The transmission rate of the guard film and air gap is
stored in the computer as CalC. The sample material is then sealed
in the test cell. Again, water vapor diffuses through the air gap
to the guard film and the test material and then mixes with a dry
gas flow that sweeps the test material. Also, again, this mixture
is carried to the vapor sensor. The computer then calculates the
transmission rate of the combination of the air gap, the guard
film, and the test material.
[0067] This information is then used to calculate the transmission
rate at which moisture is transmitted through the test material
according to the equation:
TR.sup.-l.sub.test material=TR.sup.-1.sub.test
material,guardfilm,airgap-TR.sup.-1.sub.guardfilm,airgap
The calculation of the WVTR uses the formula:
WVTR=F.rho..sub.sat(T)RH/Ap.sub.sat(T)(1-RH)
where: F=the flow of water vapor in cc/min, .rho..sub.sat(T)=the
density of water in saturated air at temperature T, RH=the relative
humidity at specified locations in the cell, A=the cross sectional
area of the cell, and p.sub.sat(T)=the saturation vapor pressure of
water vapor at temperature T.
Examples
[0068] The following are provided for exemplary purposes to
facilitate understanding of the disclosure and should not be
construed to limit the disclosure to the examples.
[0069] Hydrophobic chemistries having similar contact angles (using
5 microliters of DI water) in the range of 125-140 degrees and
similar roll-off angles (the angle to which the material needs to
be tilted for the drop to roll off the material) in the range of 40
to 50 degrees were spray applied to one side of an otherwise
untreated HYDROKNIT brand towel at similar add-on levels (1 gsm and
5 gsm) (see FIGS. 1 and 2). The materials were assessed for barrier
properties using the standard K-C hydrohead test with water. The
hydrohead refers to the amount of hydrostatic pressure that a
sample can support before water breaks through the sample. The
standard test is done in the lab on an instrument such as the
TEXTTEST FX 3000 HYDROTESTER III. One side of the sample is placed
face down onto a surface of water and clamped into place. The
sample size for the tests described herein was 100 cm2. A button is
pressed to start the test. Water is forced upward from below,
pressing against the sample. The pressure is increased at a
constant rate (1 mbar/sec) until the water breaks through the
substrate in 3 distinct places. In some cases the material can
"flood," meaning the water comes in from all sides at once and
clearly the seal is broken. If this happens, the test is also
stopped. Once the operator notices water breaking through the
substrate in 3 distinct places, the operator presses the "stop"
button and the pressure in mbar is read off of the instrument.
[0070] Additional information related to hydrohead testing can be
found at www.youtube.com/watch?v=HwQA4tg99ds and at
www.ipstesting.com/AATCC127/tabid/196/Default.aspx.
[0071] Results illustrated in FIG. 3 show that, although the
hydrophobicity properties are similar, the treatments did not yield
the same hydrohead result. The Unidyne TGKC03, a fluorinated
methylacrylate co-polymer treatment commercially available from
Daikin Industries, Ltd., did not provide any barrier to fluid (zero
hydrohead that is the same as control HYDROKNIT brand towel).
Developmental formulations (UIC III and UIC V) were assessed and
shown to provide improved barrier performance as measured by
hydrohead. These treatments were 1) DuPont Capstone STC-100, a
fluorinated co-polymer, in water and 2) DuPont Capstone STC-100, a
fluorinated co-polymer, plus hydrophilic bentonite nanoclay from
Sigma-Aldrich. A HYDROKNIT brand towel, originally a hydrophilic
substrate with no hydrohead, gains a significant amount of
hydrohead or barrier property once coated with a film-forming
polymer (Capstone ST-100.) This is not seen with Daikin TG KC03
(bars absent). These showed hydrohead ranging from approximately 5
mbar to 17 mbar, as illustrated in FIG. 3.
[0072] Micrograph images of the treated HYDROKNIT brand towel (see
FIG. 4) as well as SMS (see FIG. 5) treated with the chemistries
showed the Capstone STC-100 polymer forms a film between the
nonwoven fibers thus creating film-like areas in the material that
enhance barrier properties. Additionally, the film-forming
treatment provides air permeability results that would not be
possible with a film having the same barrier properties. The SEM
images of the UIC III and Daikin TG KC03 coatings show differences
at the chemistry-substrate interface. The SEM images are better
quality of the SMS substrate but it is believed that the film
forming property also occurs on the HYDROKNIT brand towel. FIG. 6
shows TABCW (through air dried bonded carded web) fibers with UIC
III hydrophobic treatment. This SEM micrograph is a more zoomed in
image than those of FIGS. 4 and 5. FIG. 6 demonstrates the
film-forming nature of the treatment. The film spread between the
fibers is evident in FIG. 6.
[0073] Diaper outer cover material, typically has its breathability
measured in Mocons. For this work, however, a more sensitive and
aggressive air permeability test used an Air Permeability Tester
FX-3300. The instrument is calibrated before the test. The sample
is clamped into place and air blows from the lower test head to the
upper test head. The area of the sample is 38 cm.sup.2. An
adjustment knob is turned until the instrument indicates the sample
is in range. The air permeability is read off of the digital
display in CFM (cubic feet per minute). An example of such an air
tester can be found at
www.manufacturingsolutionscenter.org/air-permeability-us-standard.html.
[0074] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0075] All documents cited in the Detailed Description are, in
relevant part, incorporated herein by reference; the citation of
any document is not to be construed as an admission that it is
prior art with respect to the present disclosure. To the extent
that any meaning or definition of a term in this written document
conflicts with any meaning or definition of the term in a document
incorporated by reference, the meaning or definition assigned to
the term in this written document shall govern.
[0076] While particular aspects of the present disclosure have been
illustrated and described, it would be obvious to those skilled in
the art that various other changes and modifications can be made
without departing from the spirit and scope of the disclosure. It
is therefore intended to cover in the appended claims all such
changes and modifications that are within the scope of this
disclosure.
* * * * *
References