Note: Descriptions are shown in the official language in which they were submitted.
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NONWOVEN FIBROUS STRUCTURE COMPRISING A MULTIFILAMENT FIBER
FIELD OF THE INVENTION
The present invention relates to nonwoven fibrous structures, more
particularly to
nonwoven fibrous structures comprising multifilament fibers, methods for
making such
fibrous structures and sanitary tissue products employing such fibrous
structures.
BACKGROUND OF THE INVENTION
Unlike woven fibrous structure, such as textiles, nonwoven fibrous structures
have
not employed multifilament fibers. Nonwoven fibrous structures have
conventionally
been made of monofilament fibers. Wood pulp fibers, staple synthetic fibers,
continuous
polymeric fibers all have been used in their monofilament form to produce
fibrous
structures. No multifilament fibers have been used in the past in nonwoven
fibrous
structures.
Accordingly, there is a need for nonwoven fibrous structures comprising
multifilament fibers, methods for making such fibrous structures and sanitary
tissue
products comprising such fibrous structures.
SUMMARY OF THE INVENTION
The present invention fulfills the needs described above by providing a
fibrous
structure comprising a multifilament fiber, a method for making such a fibrous
structure
and a sanitary tissue product comprising such a fibrous structure.
In one example of the present invention, a nonwoven fibrous structure
comprising
a multifilament fiber is provided.
In another example of the present invention, a nonwoven fibrous structure
comprising a fiber and/or a multifilament fiber wherein the fiber and/or the
multifilament
fiber is associated with an ingredient (other than the fiber or multifilament
itself) and/or
characteristic present in the fibrous structure, is provided.
In yet another example of the present invention, a method for making a
nonwoven
fibrous structure, the method comprising the steps of incorporating a fiber
and/or
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multifilament fiber into a fibrous structure wherein the fiber and/or
multifilament fiber is
associated with an ingredient and/or characteristic of the fibrous structure
such that a
consumer is able to determine by looking at the fiber and/or the multifilament
fiber that
the fibrous structure and/or sanitary tissue product comprising such fibrous
structure
contains a certain ingredient and/or exhibits a certain characteristic, is
provided.
In another example of the present invention, a method for making a nonwoven
fibrous structure comprising a multifilament fiber, wherein the method
comprises forming
a nonwoven fibrous structure from a fibrous slurry and/or fibrous composition
comprising
a multifilament fiber, is provided.
A fibrous slurry as used herein means a mixture of multifilaments and/or
monofilaments. Such mixtures of multifilaments and/or monofilaments may be
used in
wet laid process or an air laid process
In yet another example of the present invention, a single- or multi-ply
sanitary
tissue product comprising a nonwoven fibrous structure according to the
present
invention, is provided.
Accordingly, the present invention provides nonwoven fibrous structures
comprising a multifilament fiber, methods for making such a fibrous structure,
and
sanitary tissue products comprising such a fibrous structure.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic representation of a multifilament fiber in accordance
with the
present invention;
Fig. 2 is a schematic representation of a fibrous structure in accordance with
the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
"Multifilament fiber" as used herein means a fiber that comprises two or more
monofilaments that are substantially unbonded, but physically associated with
one another
to form a unitary structure. Nonlimiting examples of suitable multifilament
fibers may be
derived from yarns (continuous strands of twisted monofilaments) or from tow
(an
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untwisted bundle of continuous filaments) most preferably by cutting such
yarns or tow
into papermaking length. The dispersion energy from the papermaking operation
is
insufficient to separate the multifilament fibers. Groups of fibers with
substantial
bonding among the filaments, including but not limited to such as nits,
shives, and flakes,
are not multifilament fibers but rather are termed herein "bonded-
multifilament fibers".
The multifilament fiber may exhibit a length of at least about 1 mm. The
multifilament fiber may exhibit any shape, for example it may be substantially
cylindrical
in shape. The multifilament fiber may exhibit an average effective diameter
that is at least
1.2 times and/or at least 1.4 times and/or at least 1.5 times and/or at least
2 times and/or at
least 10 times the average effective diameter of any monofilaments within a
fibrous
structure. Effective diameter means the calculated diameter based on the
diameter of a
circle having the same area as the area of the filament or multifilament in
question. In one
example, the multifilament fiber exhibits a length of less than about 12.70 cm
(5 inches)
and/or less than about 10.16 cm (4 inches) and/or less than about 7.62 cm (3
inches)
and/or less than about 5.08 cm (2 inches) and/or less than about 2.54 cm (1
inch).
In one example, the multifilament fiber of the present invention exhibits an
average effective diameter of at least about 30 microns and/or at least about
100 microns
and/or at least about 500 microns.
The multifilament fibers of the present invention may comprise natural fibers,
non-naturally occurring fibers, such as spun cellulose fibers and/or spun
starch fibers,
and/or other synthetic fibers, such as polymeric fibers including but not
limited to nylon
fibers, polyester fibers, polyolefin fibers and combinations thereof.
In one example, at least one type of multifilament fiber of the present
invention is
different in color than the other types of multifilament fibers and the
monofilament fibers
comprising the fibrous structure of the present invention. Preferably the
color difference
is sufficient to render the multifilament fiber visually discernible.
As shown in Fig. 1, a multifilament fiber 10, which is in the form of a cut
yarn,
comprises two or more monofilaments 12. In this example of a multifilament
fiber, the
multifilament fiber 10 is in the form of sheaves characterized by frayed ends
14, which
are present on at least one end 16 of the multifilament fiber 10.
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A multifilament fiber may be a bonded multifilament fiber and/or a non-bonded
multifilament fiber.
"Bonded multifilament fiber" is an assembly of monofilaments that are
physically
attached to one another directly or indirectly (such as via a bonding agent),
to form a
bonded multifilament fiber. Nonlimiting examples of bonded multifilament
fibers include
flakes, nit and shives.
"Non-bonded multifilament fiber" is an assembly of monofilaments that are in
contact with one another at at least one point along their lengths but are not
physically
attached to one another. Nonlimiting examples of non-bonded multifilament
fibers
include yarn (monofilaments twisted about one another along their lengths) and
tow
(monofilaments not twisted about one another along their lengths).
In one example, the multifilament fibers of the present invention are used in
the
fibrous structures of the present invention in the form of cut yarn and/or cut
tow that
exhibit suitable lengths for inclusion in the fibrous structures of the
present invention.
"Monofilament Fiber" as used herein means an elongate particulate having an
apparent length greatly exceeding its apparent width, i.e. a length to
diameter ratio of at
least about 10. More specifically, as used herein, "fiber" refers to
papermaking fibers.
The present invention contemplates the use of a variety of papermaking fibers,
such as,
for example, natural fibers or synthetic fibers, or any other suitable fibers,
and any
combination thereof. Papermaking fibers useful in the present invention
include
cellulosic fibers commonly known as wood pulp fibers. Applicable wood pulps
include
chemical pulps, such as Kraft, sulfite, and sulfate pulps, as well as
mechanical pulps
including, for example, groundwood, thermomechanical pulp and chemically
modified
thermomechanical pulp. Chemical pulps, however, may be preferred since they
impart a
superior tactile sense of softness to tissue sheets made therefrom. Pulps
derived from both
deciduous trees (hereinafter, also referred to as "hardwood") and coniferous
trees
(hereinafter, also referred to as "softwood") may be utilized. The hardwood
and softwood
fibers can be blended, or alternatively, can be deposited in layers to provide
a stratified
web. U.S. Pat. No. 4,300,981 and U.S. Pat. No. 3,994,771 are incorporated
herein by
reference for the purpose of disclosing layering of hardwood and softwood
fibers. Also
applicable to the present invention are fibers derived from recycled paper,
which may
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contain any or all of the above categories as well as other non-fibrous
materials such as
fillers and adhesives used to facilitate the original papermaking.
In addition to the various wood pulp fibers, other cellulosic fibers such as
cotton
linters, rayon, and bagasse can be used in this invention. Synthetic fibers
and/or non-
5 naturally occurring fibers, such as polymeric fibers, can also be used.
Elastomeric
polymers, polypropylene, polyethylene, polyester, polyolefin, and nylon, can
be used. The
polymeric fibers can be produced by spunbond processes, meltblown processes,
and other
suitable methods known in the art.
An embryonic fibrous web can be typically prepared from an aqueous dispersion
of papermaking fibers, though dispersions in liquids other than water can be
used. The
fibers are dispersed in the carrier liquid to have a consistency of from about
0.1 to about
0.3 percent. It is believed that the present invention can also be applicable
to moist
forming operations where the fibers are dispersed in a carrier liquid to have
a consistency
of less than about 50% and/or less than about 10%.
"Fibrous structure" as used herein means a structure that comprises one or
more
multifilament fibers. In one example, a fibrous structure according to the
present
invention means an orderly arrangement of multifilament fibers alone or in
combination
with monofilament fibers within a structure in order to perform a function.
Nonlimiting
examples of fibrous structures of the present invention include composite
materials
(including reinforced plastics and reinforced cement), paper, fabrics
(including woven,
knitted, and non-woven), and absorbent pads (for example for diapers or
feminine hygiene
products). A bag of loose fibers is not a fibrous structure in accordance with
the present
invention.
"Nonwoven" or "Nonwoven fibrous structure" as used herein means a web that is
produced by a process other than knitting or some other woven process. A
nonwoven
fibrous structure is a web that comprises a plurality of fiber and/or
monofilaments and/or
multi-filaments that is produced by a process other than knitting or some
other woven
process.
Nonlimiting examples of processes for making nonwoven fibrous structures
include known wet-laid papermaking processes and air-laid papermaking
processes. Such
processes typically include steps of preparing a fiber composition in the form
of a
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suspension in a medium, either wet, more specifically aqueous medium, or dry,
more
specifically gaseous, i.e. with air as medium. The aqueous medium used for wet-
laid
processes is oftentimes referred to as a fiber slurry. The fibrous suspension
is then used
to deposit a plurality of fibers onto a forming wire or belt such that an
embryonic fibrous
structure is formed, after which drying and/or bonding the fibers together
results in a
fibrous structure. Further processing the fibrous structure may be carried out
such that a
finished fibrous structure is formed. For example, in typical papermaking
processes, the
finished fibrous structure is the fibrous structure that is wound on the reel
at the end of
papermaking, and may subsequently be converted into a finished product, e.g. a
sanitary
tissue product.
The fibrous structures of the present invention may be homogeneous or may be
layered. If layered, the fibrous structures may comprise at least two and/or
at least three
and/or at least four and/or at least five layers.
"Sanitary tissue product" as used herein means a soft, low density (i.e. <
about
0.15 g/cm3) web useful as a wiping implement for post-urinary and post-bowel
movement
cleaning (toilet tissue), for otorhinolaryngological discharges (facial
tissue), and multi-
functional absorbent and cleaning uses (absorbent towels). The sanitary tissue
product
may be convolutedly wound upon itself about a core or without a core to form a
roll of
sanitary tissue product.
In one example, the sanitary tissue product of the present invention comprises
a
fibrous structure according to the present invention.
"Basis Weight" as used herein is the weight per unit area of a sample reported
in
lbs/3000 ft2 or g/m2 . Basis weight is measured by preparing one or more
samples of a
certain area (m2 ) and weighing the sample(s) of a fibrous structure according
to the
present invention and/or a paper product comprising such fibrous structure on
a top
loading balance with a minimum resolution of 0.01 g. The balance is protected
from air
drafts and other disturbances using a draft shield. Weights are recorded when
the
readings on the balance become constant. The average weight (g) is calculated
and the
average area of the samples (m) . The basis weight (g/m2) is calculated by
dividing the
average weight (g) by the average area of the samples (m).
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"Machine Direction" or "MD" as used herein means the direction parallel to the
flow of the fibrous structure through the papermaking machine and/or product
manufacturing equipment.
"Cross Machine Direction" or "CD" as used herein means the direction
perpendicular to the machine direction in the same plane of the fibrous
structure and/or
paper product comprising the fibrous structure.
"Ply" or "Plies" as used herein means an individual fibrous structure
optionally to
be disposed in a substantially contiguous, face-to-face relationship with
other plies,
forming a multiple ply fibrous structure. It is also contemplated that a
single fibrous
structure can effectively form two "plies" or multiple "plies", for example,
by being
folded on itself.
As used herein, the articles "a" and "an" when used herein, for example, "an
anionic surfactant" or "a fiber" is understood to mean one or more of the
material that is
claimed or described.
All percentages and ratios are calculated by weight unless otherwise
indicated.
All percentages and ratios are calculated based on the total composition
unless otherwise
indicated.
Unless otherwise noted, all component or composition levels are in reference
to
the active level of that component or composition, and are exclusive of
impurities, for
example, residual solvents or by-products, which may be present in
commercially
available sources.
Fibrous Structure
The fibrous structures of the present invention comprise one or more fibers
and/or
one or more multifilament fibers.
When present, the fibrous structure may comprise at least about 0.1 % by
weight,
on a dry fibrous structure basis of a multifilament fiber. In one example, the
fibrous
structure may comprise at least about 0.1% and/or at least about 0.2% and/or
at least
about 0.4 % and/or at least about 1% to about 25 % and/or to about 10 % and/or
to about
5 % and/or to about 2.5 % by weight, on a dry fibrous structure basis of a
multifilament
fiber.
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In addition to the multifilament fiber, the fibrous structures of the present
invention may comprise one or more monofilament fibers. In addition to the
multifilament fiber and monofilament fibers, if any, the fibrous structures of
the present
invention may comprise any suitable ingredients known in the art. Nonlimiting
examples
of suitable ingredients that may be included in the fibrous structures include
permanent
and/or temporary wet strength resins, dry strength resins, softening agents,
wetting agents,
lint resisting agents, absorbency-enhancing agents, immobilizing agents,
especially in
combination with emollient lotion compositions, antiviral agents including
organic acids,
antibacterial agents, polyol polyesters, antimigration agents, polyhydroxy
plasticizers,
opacifying agents and mixtures thereof. Such ingredients, when present in the
fibrous
structure of the present invention, may be present at any level based on the
dry weight of
the fibrous structure. Typically, such ingredients, when present, may be
present at a level
of from about 0.001 to about 50% and/or from about 0.001 to about 20% and/or
from
about 0.01 to about 5% and/or from about 0.03 to about 3% and/or from about
0.1 to
about 1.0% by weight, on a dry fibrous structure basis.
The fibrous structures of the present invention may be of any type, including
but
not limited to, conventionally felt-pressed fibrous structures; pattern
densified fibrous
structures; and high-bulk, uncompacted fibrous structures. The fibrous
structures may be
creped or uncreped and/or through-dried or conventionally dried. The sanitary
tissue
products made therefrom may be of a single-ply or multi-ply construction.
The fibrous structures of the present invention and/or sanitary tissue
products
comprising such fibrous structures may have a basis weight of between about 10
g/m2 to
about 120 g/m2 and/or from about 14 g/m2 to about 80 g/m2 and/or from about 20
g/m2 to
about 60 g/m2.
The fibrous structures of the present invention and/or sanitary tissue
products
comprising such fibrous structures may have a total dry tensile strength of
greater than
about 59 g/cm (150 g/in) and/or from about 78 g/cm (200 g/in) to about 394
g/cm (1000
g/in) and/or from about 98 g/cm (250 g/in) to about 335 g/cm (850 g/in).
The fibrous structures of the present invention and/or sanitary tissue
products
comprising such fibrous structures may have a density of about 0.60 g/cc or
less and/or
about 0.30 g/cc or less and/or from about 0.04 g/cc to about 0.20 g/cc.
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As shown in Fig. 2, a fibrous structure 20 comprises a multifilament fiber 10
comprised of two or more monofilaments 12. The fibrous structure 20 also
comprises one
or more monofilaments 12 which are not associated with other monofilaments 12
to form
a multifilament 10.
In one example, a multifilament fiber 10 can be used within a fibrous
structure 20
to convey to a consumer of the fibrous structure 20 and/or sanitary tissue
product
comprising such fibrous structure 20 that the fibrous structure 20 exhibits a
certain
property or characteristic. In other words, the multifilament fiber 10 may
function as a
visual cue to inform a consumer that the fibrous structure contains or does
not contain a
particular ingredient (other than the fact that a multifilament fiber is
present) and/or that
the fibrous structure exhibits a certain property/characteristic such as
softness.
In another example, a fibrous structure may comprise a fiber that provides a
visual
cue that is associated with the presence of a certain ingredient (other than
the fact that a
certain fiber is present) and/or characteristic (i.e., certain property) is
provided. The fiber
may be noticeable to a consumer of the fibrous structure by being colored, of
a different
size, of a different shape, of a different length, different texture from
other fibers within
the fibrous structure.
In one example, the fibrous structure of the present invention is a nonwoven
fibrous structure.
Method for Making a Fibrous Structure
A fibrous structure comprising a multifilament fiber may be made by any
suitable
method known in the art. In one example, a method for making a fibrous
structure
comprising a multifilament fiber comprises the step of forming a fibrous
slurry and/or
fibrous composition comprising a multifilament fiber and depositing the
fibrous slurry
and/or fibrous composition onto a forming belt such that a fibrous structure
is formed.
Nonlimiting Examples
Example 1
This Example illustrates a process for making a multi-ply sanitary tissue
product
(i.e., a bathroom tissue) according to the present invention using a through-
air dried
process.
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An aqueous slurry of Northern Softwood Kraft (NSK) of about 3% consistency is
made up using a conventional pulper and is passed through a stock pipe toward
the
headbox of the Fourdrinier. A dispersion of Parez 750C (available from Kemira
Corporation of Kennesaw, GA) wet strength resin about 1% in concentration is
mixed
5 with this stock in an amount sufficient to deliver a total of about 3 lb of
resin per ton of
finished paper product. Distribution of the Parez 750C is aided by an in-line
mixer.
This wet strength resin treated stock is diluted at the inlet of a first fan-
pump with
recycled white water to a consistency of about 0.2%.
An aqueous slurry of acacia fibers (from Riau Andalan - Indonesia) of about 3%
10 by weight is made up using a conventional repulper. After the acacia fibers
are added to
the pulper, green cotton thread (spun cotton of 2 ply of 120 X 120 denier) cut
to a length
of 1/4" is added to the pulper in an amount to equal to about 1% of the final
sheet weight.
The pulping intensity is controlled to fibrillate the multifilament threads at
the ends, but
leaving the majority of the filament shaft intact. The frayed ends will add to
the
attractiveness of the finished product as well as improve the anchoring of the
multifilaments in the structure. The acacia & cotton thread slurry passes to
the second
fan pump where it is diluted with white water to a consistency of about 0.2%.
The slurries of NSK and acacia/thread are directed into a multi-channeled
headbox
suitably equipped with layering leaves to maintain the streams as separate
layers until
discharged onto a traveling Fourdrinier wire. A three-chambered headbox is
used. The
acacia/thread slurry containing 70% of the dry weight of the ultimate paper is
directed to
the chambers leading to the two outer layers while the NSK slurry comprising
30% of the
dry weight of the ultimate paper is directed to the chamber leading to the
center layer. The
NSK and acacia/thread slurries are combined at the discharge of the headbox
into a
composite slurry.
The composite slurry is discharged onto the traveling Fourdrinier wire and is
dewatered assisted by a deflector and vacuum boxes. The embryonic wet web is
transferred from the Fourdrinier wire, at a fiber consistency of about 17% by
weight at the
point of transfer, to a patterned drying fabric. The drying fabric is designed
to yield a
pattern-densified tissue with discontinuous low-density deflected areas
arranged within a
continuous network of high density (knuckle) areas. This drying fabric is
formed by
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casting an impervious resin surface onto a fiber mesh supporting fabric. The
supporting
fabric is a 48 x 52 filament, dual layer mesh. The thickness of the resin cast
is about 12
mil above the supporting fabric. The knuckle area is about 40% and the open
cells remain
at a frequency of about 400 per square inch. The open cells are generally
elliptical in
shape with the longer direction disposed in the machine direction and having
an aspect
ratio of 0.866.
Further de-watering is accomplished by vacuum assisted drainage until the web
has a fiber consistency of about 22% by weight. While remaining in contact
with the
patterned forming fabric, the patterned web is pre-dried by air blow-through
pre-dryer to a
fiber consistency of about 58% by weight.
The semi-dry web is then adhered to the surface of a Yankee dryer with a
sprayed
creping adhesive comprising a 0.250% aqueous solution of polyvinyl alcohol.
The creping
adhesive is delivered to the Yankee surface at a rate of 0.1% adhesive solids
based on the
dry weight of the web.
The fiber consistency is increased to about 98% before the is dry creped from
the
Yankee with a doctor blade. The doctor blade has a bevel angle of about 20
and is
positioned with respect to the Yankee dryer to provide an impact angle of
about 76 . The
Yankee dryer is operated at a temperature of about 350 F (177 C) and a speed
of about
800 fpm (feet per minute) (about 244 meters per minute). The paper is wound in
a roll
using a surface driven reel drum having a surface speed of about 680 fpm
(about 207
meters per minute), thus resulting in a crepe of about 15%.
After the doctor blade, the web is calendered across all its width with a
steel to
rubber calendar roll to achieve the caliper desired in the product. Resulting
fibrous
structure has a basis weight of about 20 g/m2; a 1-ply total dry tensile
between 250 and
about 300 g/in, a 1-ply initial total wet tensile between about 30 and about
35 g/in and a
1-ply caliper of about 0.018 inches. Resulting fibrous structure is then plied
together with
a like sheet to form a two-ply, creped, pattern densified fibrous structure so
that the
Yankee-contacting surface, which is the flatter surface, of each ply faces
inward while the
non-Yankee contacting surface face outward. The plies are minimally tacked
together
using about i/2" wide stripe of hot melt adhesive to prevent the plies from
easily
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separating. The resulting two-ply fibrous structure has a) a total basis
weight of about 40
g/m2 and a caliper of about 0.028 inches.
The cotton threads provide an attractive and prominent visual signal to
consumers
that a certain ingredient (not merely that a cotton thread is present) and/or
a certain
property is present in the fibrous structure.
Example 2
Example 1 is repeated except that the chopped cotton thread is replaced with
denim pulp. The denim pulp is made from recovered scraps from the manufacture
of
clothing articles such as jeans using denim fabric. It is processed by an
entirely
mechanical process using a refiner until the fibers are chopped to
satisfactory
papermaking lengths. Some of the denim filaments retain their multifilament
character.
The denim pulp is added to the pulper with the acacia fibers. Otherwise the
practice of
Example 1 is repeated. The denim pulp multifilaments provide an attractive and
prominent visual signal to consumers that a certain ingredient (not merely
that a denim
pulp multifilament is present) and/or a certain property is present in the
fibrous structure.
Example 3
Example 1 is repeated except that the chopped cotton thread is replaced with
green
dyed polyester tow. The tow is 200 ends of 2 dpf polyester chopped to. Some of
the tow
bundles their multifilament character. The denim pulp is added to the pulper
with the
acacia fibers and the time and intensity of the pulping is moderated so that
most of the
tow bundles retain a multifilament character. The ends of the chopped tow
segments
tend to feather outward creating a sheave appearance. This adds to their
appearance in
the finished product as well as helping to anchor the tow in the fibrous
structure.
Otherwise the practice of Example 1 is repeated. The polyester tow
multifilaments
provide an attractive and prominent visual signal to consumers that a certain
ingredient
(not merely that a polyester tow multifilament is present) and/or a certain
property is
present in the fibrous structure.
All documents cited in the Detailed Description of the Invention 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 invention. To
the extent that
any meaning or definition of a term in this written document conflicts with
any meaning
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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.
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".
While particular embodiments of the present invention 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
invention.
It is therefore intended to cover in the appended claims all such changes and
modifications that are within the scope of this invention.
