Note: Descriptions are shown in the official language in which they were submitted.
CA 02249327 2004-06-22
MECHANICAL AND INTERNAL SOFTENING FOR NONWOVEN WEB
BACKGROUND OF THE INVENTION
This invention relates to the field of nonwoven fabrics or webs and their
manufacture. More particularly, it relates to such nonwoven fabrics which are
comprised of
at least one layer of staple fibers or filaments or continuous filaments. Such
fibers are
1 o commonly comprised of thermoplastic polymers such as polyamides,
polyesters, polyethers
and polyolefins such as polypropylene, polyethylene, polybutylene and
copolymers and
blends thereof.
Uses for such microfibrous webs are in such personal care products as diapers,
training pants, feminine hygiene products and adult incontinence products,
infection control
15 Products like surgical drapes, gowns and sterilization wraps, and in
various clothing
applications. The softness of the web is an important factor in such
applications as the
web may be in contact with a wearer for an extended period of time.
Various methods to increase the softness of a nonwoven web are known in the
art.
These methods include wash softening, mechanical stretching, and topical
treatment of the
2 o web with softening chemicals.
The technique of wash softening the nonwoven web is a time consuming, batch
process which does not lend itself to the requirements of industrial
production. In addition,
large volumes of water from the washing process must be handled, either by
recycling or
disposal, and the web must be dried. Drying a nonwoven web is an energy
consuming
2 5 process which is somewhat difficult to control in a commercial setting,
sometimes resulting
in remelted, glazed or otherwise damaged webs.
CA 02249327 1998-09-18
WO 97140778 PCTIUS97/06701
Mechanical softening alone by stretching does not provide the degree of
softness
being sought for some applications. Topical treatments also do not provide the
degree of
softness sought for some applications and have additional manufacturing
constraints.
Treatments to increase the softness of a nonwoven web involving both
mechanical
s and chemical means are described in US Patent 5,413,811 to Fitting et al.
This patent
describes topical chemical treatments and mechanical stretching to produce a
softer web by
wetting a nonwoven web having a starting, unstretched width and a starting cup
crush value,
with an aqueous solution of softening chemicals, necking the saturated
nonwoven web to a
second width of between about 50 and 95 percent of its starting, unstretched
width, and
to drying the nonwoven web at a temperature and time sufficient to remove at
least 95 percent
of the moisture from the nonwoven web.
While this method produces a very soft web, a simpler method would be
desirable as
it would have fewer steps and therefore fewer opportunities for error in
manufacturing. It
would also be preferable to avoid a topical treatment of the web as this is a
relatively messy
15 step in the process.
Internal, as contrasted with topical, additives for webs for the purpose, for
example,
of increasing the repellence of a fabric, are known in the art. These usually
involve the use
of a fluorocarbon additive which migrates or "blooms" to the surface of a web
after fiber
formation. Examples of such additives may be found in US Patent 5,178,931 to
Perkins et
2o al. and US Patent 5,482,765 to Bradley et al.
There remains a need for a web which is produced by a softening process or
treatment procedure which avoids topical treatments and yet is sufficiently
soft for garment
applications. This process must be relatively rapid, when compared to wash
softening,
clean in comparison to topical treating, and suited to large scale commercial
manufacturing.
CA 02249327 2004-06-22
Accordingly, this invention seeks to provide a microfibrous web which avoids
topical treatment chemicals, can be produced in a continuous industrial
production
operation, and which is soft enough for garment applications.
The objects of this invention are achieved by a web which has been spun from a
mixture of thermoplastic polymer and an internal softening additive in an
amount up to about
3 weight percent, and which has been mechanically treated to increase
softness. The web
has a final cup crush value which is less than 50 percent of the starting cup
crush value and
the drop in cup crush value is greater than the sum of the drop in cup crush
values from the
treatments individually.
According to one aspect of the present invention there is provided a nonwoven
web
comprising a polymer and between a positive amount and about 3 weight percent
of an
internal softening agent having a formula consisting essentially of:
CH3
I
f li-Oj
CH3
wherein n is from 3 to about 1,000, and which web has been mechanically
softened wherein
the web has a cup crush value which is less than 50 percent of a cup crush
value of the same
fabric without said internal additive and said mechanical softening.
According to a further aspect of the present inveniton there is provided a
nonwoven
web comprising a polymer and between a positive amount and about 3 weight
percent of a
siloxane softening agent having a formula consisting essentially of:
CH3
I
f ii-Oj
CH3
wherein n is from 3 to about 1000, and which web has been neck stretched to a
second width
of between about 50 and 95 percent of its starting, first, unstretched width
and un-necked is to
a third width of between about 80 and 150 percent of its starting, unstretched
width and which
has a cup crush value which is less than 50 percent of a cup crush value of
the same fabric
without said internal additive and said mechanical softening.
In other aspects of the present invention there are provided garments,
personal care
products, infection control products and medical gowns comprising the nonwoven
webs
defined above.
CA 02249327 2004-06-22
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illustration of an apparatus which may be utilized to
neck-
stretch the fabric of the invention. Figure 2 is an illustration of an
apparatus which may be
used to un-neck the fabric of the invention.
As used herein the term "nonwoven fabric or web" means a web having a
structure
of individual fibers or threads which are interlaid, but not in an
identifiable manner as in a
knitted fabric. Nonwoven fabrics or webs have been formed from many processes
such as
for example, meltblowing processes, spunbonding processes, and bonded carded
web
processes. The basis weight of nonwoven fabrics is usually expressed in ounces
of material
3a
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WO 97/40778 PCT/US97/06701
per square yard (osy) or grams per square meter (gsm) and the fiber diameters
useful are
usually expressed in microns. (Note that to convert from osy to gsm, multiply
osy by 33.91 ).
As used herein the term "microfibers" means small diameter fibers having an
average diameter not greater than about 75 microns, for example, having an
average
diameter of from about 0.5 microns to about 50 microns, or more particularly,
microfibers
may have an average diameter of from about 2 microns to about 40 microns.
Another
frequently used expression of fiber diameter is denier, which is defined as
grams per 9000
meters of a fiber and may be calculated as fiber diameter in microns squared,
multiplied by
to the density in gramslcc, multiplied by 0.00707. A lower denier indicates a
finer Fber and a
higher denier indicates a thicker or heavier fiber. For example, the diameter
of a
polypropylene fiber given as 15 microns may be converted to denier by
squaring, multiplying
the result by 0.89 g/cc and multiplying by 0.00707. Thus, a 15 micron
polypropylene fiber
has a denier of about 1.42, (152 x 0.89 x 0.00707 = 1.415). Outside the United
States the
1 s unit of measurement is more commonly the "tex", which is def ned as the
grams per
kilometer of fiber and which may be calculated as denierl9.
As used herein the term "spunbonded fibers" refers to small diameter fibers
which
are formed by extruding molten thermoplastic material as filaments from a
plurality of fine,
usually circular capillaries of a spinneret with the diameter of the extruded
filaments then
2 o being rapidly reduced as by, for example, in US Patent no. 4,340,563 to
Appel et al., and US
Patent no. 3,692,618 to Dorschner et al., US Patent no. 3,802,817 to Matsuki
et al., US
Patent nos. 3,338,992 and 3,341,394 to Kinney, US Patent no. 3,502,703 to
Hartman, and
US Patent no. 3,542,615 to Dobo et al. Spunbond fibers are generally not tacky
when they
are deposited onto a collecting surface. Spunbond fibers are generally
continuous and have
25 average diameters (from a sample of at least 10) larger than 7 microns,
more particularly,
between about 10 and 20 microns.
CA 02249327 2004-06-22
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
which attenuate the filaments of molten thermoplastic material to reduce their
diameter,
s which may 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 US
Patent no. 3,849,241 to Butin. Meltblown fibers are microfibers which may be
continuous or
discontinuous, are generally smaller than 10 microns in average diameter, and
are generally
1 o tacky when deposited onto a collecting surface.
As used herein, the term °coform" means a process in which at least two
meltblown
dieheads are arranged around a central chute through which other materials are
added to
the web while it is forming. Such other materials may be pulp, superabsorbent
particles,
cellulose or staple fibers, for example. Coform processes are shown in
commonly assigned
i5 US Patents 4,818,464 to Lau and 4,100,324 to Anderson et al. Webs produced
by the
coform process are generally refered to as coform materials.
As used herein °multilayer laminate" means a laminate wherein some of
the layers
are spunbond and some meltblown such as a spunbondlmeltblown/spunbond (SMS)
laminate and others as disGosed in U.S. Patent 4,041,203 to Brock et al., U.S.
Patent
2 0 5,169,706 to Collier, et al, US Patent 5,145,727 to Potts et al., US
Patent 5,178,931 to
Perkins et al. and U.S. Patent 5,188,885 to Timmons et al. Such a laminate may
be made
by sequentially depositing onto a moving forming belt first a spunbond fabric
layer, then a
meltblown fabric layer and last another spunbond layer and then bonding the
laminate in a
manner described below. Alternatively, the fabric layers may be made
individually, collected
2 s in rolls, and combined in a separate bonding step. Such fabrics usually
have a basis weight
of from about 0.1 to 12 osy (6 to 400 gsm), or more particularly from about
0.75 to about 3
CA 02249327 2004-06-22
osy. Multilayer laminates may also have various numbers of meltblown layers or
multiple
spunbond layers in many different configurations and may include other
materials like films
(F) or coform materials, e.g. SMMS, SM, SFS, etc.
As used herein the term "polymer" generally indudes but is not limited to,
s homopolymers, copolymers, such as for example, block, graft, random and
aitemating
copolymers, terpolymers, etc. and blends and modifications thereof.
Furthermore, unless
otherwise spedfically 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.
i o As used herein, the term "machine direction" or MD means the length of a
fabric in
the direction in which it is produced. The term "cross machine direction" or
CD means the
width of fabric, i.e, a direction generally perpendicular to the MD.
As used herein the term "monocomponent" fiber refers to a fiber formed from
one or
more extruders using only one polymer. This is not meant to exclude fibers
formed from
i s one polymer to which small amounts of additives have been added for color,
anti-static
properties, lubrication, hydrophilicity, etc. These additives, e.g. titanium
dioxide for
color, are generally present in an amount less than 5 weight percent and more
typically
about 2 weight percent.
As used herein the term "conjugate fibers" refers to fibers which have been
formed
2o from at least two polymers usually extruded from separate extruders but
spun together to
form one fiber. Conjugate fibers are also sometimes referred to as
multicomponent or
bicomponent fibers. The polymers are usually different from each other though
conjugate
fibers may be monocomponent fibers. The polymers are arranged in substantially
constantly positioned distinct zones across the cross-section of the conjugate
fibers and
2 s extend continuously along the length of the conjugate fibers. The
configuration of such a
conjugate fiber may be, for example, a sheath/core arrangement wherein one
polymer is
CA 02249327 2004-06-22
surrounded by another or may be a side by side arrangement, a pie arrangement
or an
"islands-in-the-sea" arrangement. Conjugate fibers are taught in US Patent
5,108,820 to
Kaneko et al., US Patent 4,795,668 to Krueger et al. and US Patent 5,336,552
to Strack et
al. Conjugate fibers are also taught in US Patent 5,382,400 to Pike et al. and
may be used
s to produce crimp in the fibers by using the differential rates of expansion
and contraction of
the,two (or more) polymers. Crimped fibers may also be produced by mechanical
means
and ~y the process of German Patent DT 25 13 251 A1. For two component fibers,
the
polymers may be present in ratios of 75/25, 50/50, 25175 or any other desired
ratios. The
fibers may also have shapes such as those described in US Patents 5,277,976 to
Hogle et
to al., US Patent 5,466,410 to Hilfs and 5,069,970 and 5,057,368 to Largman et
al., which
describe fibers with unconventional shapes.
As used herein the term "blend" means a mixture of two or more polymers while
the
term "alloy" means a sub-class of blends wherein the components are immiscible
but have
been compatibilized.
1 s As used herein, "ultrasonic bonding" means a process performed, for
example, by
passing the fabric between a sonic horn and anvil roll as illustrated in US
Patent 4,374,888
to Bomslaeger.
As used herein "thermal point bonding" involves passing a fabric or web of
fibers to
be bonded befinreen a heated calender roll and an anvil roll. The calender
roll is usually,
2o though not always, patterned in some way so that the entire fabric is not
bonded across its
entire surface, and the anvil roll is usually flat. As a result, various
patterns for calender rolls
have been developed for functional as well as aesthetic reasons. One example
of a pattern ,
has points and is the Hansen Pennings or "H&P" pattern with about a 30% bond
area with
about 200 bonds/square inch as taught in US Patent 3,855,046 to Hansen and
Pennings.
2s The H&P pattern has square point or pin bonding areas wherein each pin has
a side
dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches (1.778 mm)
between pins,
* Trade-mark
CA 02249327 1998-09-18
WO 97140778 PCT/US97/06701
and a depth of bonding of 0.023 inches (0.584 mm). The resulting pattern has a
bonded
area of about 29.5%. Another typical point bonding pattern is the expanded
Hansen
Pennings or "EHP" bond pattern which produces a 15% bond area with a square
pin having
a side dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches
{2.464 mm) and
s a depth of 0.039 inches (0.991 mm). Another typical point bonding pattern
designated
"714" has square pin bonding areas wherein each pin has a side dimension of
0.023 inches,
a spacing of 0.062 inches (1.575 mm) between pins, and a depth of bonding of
0.033 inches
(0.838 mm). The resulting pattern has a bonded area of about 15%. Yet another
common
pattern is the C-Star pattern which has a bond area of about 16.9%. The C-Star
pattern has
1 o a cross-directional bar or "corduroy" design interrupted by shooting
stars. Other common
patterns include a diamond pattern with repeating and slightly offset diamonds
with about a
16% bond area and a wire weave pattern looking as the name suggests, e.g. like
a window
screen, with about a 19% bond area. Typically, the percent bonding area varies
from
around 10% to around 30% of the area of the fabric laminate web. As is well
known in the
15 art, the spot bonding holds the laminate layers together as well as imparts
integrity to each
individual layer by bonding filaments and/or fibers within each layer.
As used herein, the terms "necking" or "neck stretching" interchangeably refer
to a
method of elongating a nonwoven fabric, generally in the machine direction, to
reduce its
width in a controlled manner to a desired amount. The controlled stretching
may take place
2 o under cool, room temperature or greater temperatures and is limited to an
increase in
overall dimension in the direction being stretched up to the elongation
required to break the
fabric, which in most cases is about 1.2 to 1.4 times. When relaxed, the web
retracts toward
its original dimensions. Such a process is disclosed, for example, in US
Patent 4,443,513 to
Meitner and Notheis, US Patents 4,965,122, 4,981,747 and 5,114,781 to Morman
and US
2s Patent 5,244,482 to Hassenboehler Jr. et al.
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WO 97/40778 PCT/US97/06701
As used herein the term "neck softening" means neck stretching carried out
without
the addition of heat, i.e. at ambient temperature, to the material as it is
stretched in the
machine direction. In neck stretching or softening, a fabric is referred to,
for example, as
being stretched by 20%. This means it is stretched in the machine direction
until its width is
80% of its original unstretched width.
As used herein, the term "neckable material" means any material which can be
necked.
As used herein, the term "necked material" refers to any material which has
been
constricted in at least one dimension by processes such as, for example,
drawing or
1 o gathering.
As used herein the term "un-necking" means a process applied to a reversibly
necked material to extend it by the application of a stretching force in a
direction generally
perpendicular to the direction of the original stretching force which causes
it to recover to
within at least about 50 percent of its reversibly necked dimensions upon
release of the
15 stretching force.
As used herein, the term "wash softened" refers to the feel of a material that
has
been softened by washing in a conventional home-type washing machine.
As used herein, the terms "elastic" and "elastomeric" when referring to a
fiber, film or
fabric mean a material which upon application of a biasing force, is
stretchable to a
2o stretched, biased length which is at least about 150 percent, or one and a
half times, its
relaxed, unstretched length, and which will recover at least 50 percent of its
elongation upon
release of the stretching, biasing force.
As used herein the term "recover" refers to a contraction of a stretched
material
upon termination of a biasing force following stretching of the material by
application of the
2 s biasing force. For example, if a material having a relaxed, unbiased
length of one (1 ) inch
was elongated 50 percent by stretching to a length of one and one half (1.5)
inches the
CA 02249327 2004-06-22
material would have a stretched length that is 150 percent of its relaxed
length. If this
exemplary stretched material contracted, that is recovered to a length of one
and one tenth
(1.1 ) inches after release of the biasing and stretching force, the material
would have
recovered 80 percent (0.4 inch) of its elongation.
s As used herein, the term "garment" means any type of non-medically oriented
apparel which may be wom. This includes industrial workwear, and coveralls,
undergarments, pants, shirts, jackets, gloves, socks, and the like.
As used herein, the term "infection control product" means medically oriented
items
such as surgical gowns and drapes, face masks, head coverings like bouffant
caps, surgical
1 o caps and hoods, footwear like shoe coverings, boot covers and slippers,
wound dressings,
bandages, sterilization wraps, wipers, garments like lab coats, coveralls,
aprons and jackets,
patient bedding, stretcher and bassinet sheets, and the like.
As used herein, the term "personal care product' means diapers, training
pants,
absorbent underpants, adult incontinence products, and feminine hygiene
products.
TEST METHODS
Cup Crush: The softness of a nonwoven fabric may be measured according to the
"cup crush" test. The cup crush test evaluates fabric stiffness by measuring
the peak load
(also called the "cup crush") required for a 4.5 cm diameter hemispherically
shaped foot to
crush a 23 cm by 23 cm piece of fabric shaped into an approximately 6.5 cm
diameter by
6.5 cm tall inverted cup while the cup shaped fabric is surrounded by an
approximately 6.5
cm diameter cylinder to maintain a uniform deformation of the cup shaped
fabric. An
average of 10 readings is used. The foot and the cup are aligned to avoid
contact between
2 s the cup walls and the foot which could affect the readings. The peak load
is measured while
the foot is descending at a rate of about 0.25 inches per second (380 mm per
minute) anti is
to
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WO 97/40778 PCT/US97/06701
measured in grams. The cup crush test also yields a value for the total energy
required to
crush a sample (the "crush energy") which is the energy from the start of the
test to the peak
load point, i.e. the area under the curve formed by the load in grams on one
axis and the
distance the foot travels in millimeters on the other. Crush energy is
therefore reported in
s gm-mm. Lower cup crush values indicate a softer fabric. A suitable device
for measuring
cup crush is a model FTD-G-500 load cell (500 gram range) available from the
Schaevitz
Company, Pennsauken, NJ.
The values reported in the Tables herein are cup crush load values.
zo DETAILED DESCRIPTION OF THE INVENTION
The object of the invention is achieved by a web of thermoplastic polymer
fibers
where the polymer used to form the web has an additive to enhance softening
and the
formed web is mechanically softened.
A number of softening chemicals are known in the art and generally include
silicone
i5 in some form. Examples of silicone containing compounds are shown in US
Patent
4,923,914 to Nohr and MacDonald for the purpose of increasing wettability of a
web.
Another suitable silicone containing compound is an ultra high molecular
weight polymer
available in solid pellet form as a family of polymers sold under the
designation Dow
Corning~ MB50 Silicone Masterbatch polymer. One particular Dow Corning~ MB50
2o Silicone Masterbatch polymer has about 50 percent silicone content and an
organic resin of
a 12 melt index polypropylene and is designated Dow Corning~ MB50-001 Silicone
Masterbatch polymer. The family of Dow Corning~ MB50 Silicone Masterbatch
polymers is
available from the Dow Corning Corporation of Midland, MI.
11
CA 02249327 2004-06-22
The preferred additive for the practice of this invention is of a particular
class of
siloxanes having the general formula:
CH3
s -(-Si-O-)~
I
CH3
wherein n is from 3 to about 1000.
1 o One commercial source of a siloxane suitable for the practice of this
invention is Uow
Coming Corporation of Midland, MI, which marketsthe siloxane under the trade-
mark f 2000
fluid. Other sources include General Electric, PPG Industries, Inc.,
Goldschmidt and OSi.
In order to practice this invention, the additive must be thoroughly mixed
with the
thermoplastic polymer. The mixture may be produced by compounding the
ingredients in,
15 for example, a 30 or 60 mm twin screw extruder. Any other method known to
those skilled
in the art of compounding polymers as effective may also be used. In the
following
Examples having internal additives, the mixture was produced by mixing the
polymer,
generally polypropylene, with each additive at a predetermined level in a twin
screw
extruder. The resulting polymer mixture was then dry blended with neat polymer
in order to
2 o reach the percentage of additive mentioned in each Example.
The inventors have found for siloxane additves that amounts should be below 3
weight percent since amounts above this level have a negative effect on
bonding. They
have also found that the siloxane additive tends to migrate or bloom to the
surface of the
fiber, providing a degree of lubrication. The bulk softening and surface
lubricity provided by
25 the siloxane additive combined with mechanical softening results in a
surprisingly softer and
more drapable fabric in a commercially acceptable continuous process. The
practice \of this
invention results in a fabric having a cup crush of at least 50% below a
fabric produced
without the combination of internal additive and mechanical treatment of this
invention.
12
CA 02249327 2004-06-22
Mechanical treatment of a web may be carried out by a number of different
methods
such as micro-creping, cold embossing, beater bar treatment, neckstretching,
un-necking,
passing through a nip, and combinations thereof. Other methods known in the
art may also
be used. The objective is to loosen or break a sufficient number of interfiber
bonds to
produce a softer web.
Turning to Figure 1, in one embodiment of the present invention the neckable
material 12 may be a multilayer material having, for example, at least one
layer of
spunbonded web joined to at least one layer of meltblown web, bonded carded
web or other
suitable material. For example, the neckable material 12 may be multilayer
material having
to a first layer of spunbonded polypropylene having a basis weight from about
0.2 to about :3
ounces per square yard (osy), a layer of meitblown polypropylene having a
basis weight
from about 0.2 to about 4 osy, and a second layer of spunbonded polypropylene
having a
basis weight of about 0.2 to about 8 osy.
Alternatively, the neckabie material 12 may be single layer of material such
as, for
1 ~ example, a spunbonded web having a basis weight of from about 0.2 to about
10 osy or a
meltblown web having a basis weight of from about 0.2 to about 8 osy.
The neckable material 12 may also be a composite or coformed material made of
a
mixture of two or more different fibers or a mixture of fibers and
particulates. Such mixtures
may be formed by adding fibers andlor particulates to a gas stream in which
meltblown
2 o fibers are carried so that an intimate entangled commingling of meltblown
fibers and other
materials, e.g., wood pulp, staple fibers or particulates such as, for
example,
superabsorbent materials,occurs prior to collection of the fibers upon a
collecting device to
form a coherent web of randomly dispersed meltblown fibers and other materials
such as
disclosed in US Pat. No. 4,100,324 to Anderson et al.
25 If the neckable material 12 is a nonwoven web of fibers, the fibers should
be joined
by interfiber bonding to fomn a coherent web structure which is able to
withstand necking.
13
CA 02249327 2004-06-22
Interfiber bonding may be produced by entanglement between individual
meltblown fibers.
The fiber entangling is inherent in the meltblown process but may be generated
or increased
by processes such as, for example, hydraulic entangling or needlepunching.
Alternatively
and/or additionally a bonding agent may be used to increase the desired
bonding or bonding
may be accomplished by ultrasonic, print or thermal point bonding.
After passing through the nip 16 of the driven roller arrangement 18, the
neckable
material 12 passes over a series of steam cans 28-38 in a series of reverse S
loops. The
steam cans 28-38 typically have an outside diameter of about 24 inches
although other
sized cans may be used. The contact time or residence time of the neckable
material on the
1 o steam cans to effect heat treatment will vary depending on factors such
as, for example,
steam can temperature, and type and/or basis weight of material. For example,
a necked
web of polypropylene may be passed over a series of steam cans heated to a
measured
temperature from room temperature to about 150 °C (302 °F) for a
contact time of about 1
to about 300 seconds to effect heat treatment. More particularly, the
temperature may
1 s range from about 100 °C to about 135 °C. and the residence
time may range from about 2
to about 50 seconds.
Because the peripheral linear speed of the drive rollers 20 and 22 is
controlled to be
lower than the peripheral linear speed of the steam cans 28-38, the neckable
material 12 is
tensioned between the steam cans 28-38 and the drive rollers 20 and 22. By
adjusting the
2 o difference in the speeds of the rollers, the neckable material 12 is
tensioned so that it necks
a desired amount from a first, starting, un-necked width to a second width and
is maintained
in such necked condition while passing over the heated steam cans 28-38. This
action
imparts memory of the necked condition to the neckable material 12. The
peripheral linear
speed of the rollers of the idler roller arrangement 42 may be maintained at a
higher speed
2 s than the steam cans 28-38 so that the necked material 12 is further
stretched and also
19
CA 02249327 1998-09-18
WO 97/40778 PCT/US97/06701
cooled in the necked condition on its way to the un-neckng step of Figure 2.
This completes
formation of the reversibly necked material 44.
The reversibly necked material 44 can be extended to a third width which is
about its
original, pre-necked dimensions upon application of a stretching force in a
generally cross-
s machine direction. Un-necking of a fabric is accomplished through the use of
commercially
available devices such as Tenter frames which grab the edges of the fabric and
pull it to the
desired width, and which are shown in Figure 2. In the practice of this type
of un-necking
device, the reversibly necked material 44 is passed to the unnecking assembly
56,
comprising a Tenter frame, which is known to those skilled in the art. Figure
2 shows a
1 o Tenter frame in which a chain 58 having a plurality of clips 60 attached
to the chain links
and spaced along the chain 58, and a chain 62 having clips 60 similarly spaced
therealong. The chains 58 and 62 are actuated by gears 64 which are driven by
a motor
65 (not shown). The chains 58 and 62 are not parallel, rather they diverge
(from a top
view) in the downstream direction (indicated by arrow 65A). As the material 44
is approaches the assembly 56 the open clips 60 automatically and sequentially
close and
grip the edge of the laminate. As the chains 58 and 62 advance, the material
44 is
stretched as the chain paths diverge. As the clips 60 reach the end of the top
of the chain
run, the clips automatically open, releasing the stretched fabric 44. The
material can then
recover to within at least about 50 percent of its reversibly necked
dimensions upon release
20 of the stretching force. The finished formed fabric 44 may be wound onto a
roll (not
shown) for uptake and storage.
An absolute cup crush load value of about 70 grams or less is considered
desirably
soft for the purposes of this invention. Fabrics processed according to this
invention have a
final cup crush load value of at least 50 percent less than the starting cup
crush value of
2s such a fabric, i.e., the final cup crush load value is no more than 50% of
the starting cup
crush load value. In addition, the various treatment methods discussed herein,
including the
CA 02249327 2004-06-22
instant invention, are not as effective on lighter basis weight fabrics since
they already have
low cup crush values by virtue of their thinness and inherent conformability.
Basis weights
above about 1 osy (34 gsm) are the ones most affected by the treatment methods
discussed below and are the predominate area of applicability of the
invention.
s The inventors further believe that a web treated with an internal softener
and
mechanical treatment as described herein would also benefit from a topical
treatment if
desired. For example, the topical treatments as described in US Patent
5,413,811 to Fitting
et al. would probably function to lower the web cup crush still further. In
Fitting, the
softening chemicals are added in an amount of between 0.1 and 10 weight
percent of the
1 o nonwoven web prior to mechanical softening . These chemicals may be any of
those
commonly known to those skilled in the art as being useful for softening
textiles. Softeners
may be silicone, anionic, nonionic or cationic though cationic softeners are
preferred.
Anionic softeners are generally chemical compounds such as sulfated oils like
castor, olive and soybean, sulfated synthetic fatty esters, such as glyceryl
trioleate, and
1 s sulfated fatty alcohols of high molecular weight.
Nonionic softeners are highly compatible with other finishing agents and are
generally compounds such as glycols, glycerin, sorbitol and urea. Compounds of
fatty acids
Like polyglycol esters of high molecular weight saturated fatty acids such as
palmitic and
stearic acids are other examples.
2o Cationic softeners are generally long chain amides, imidazolines, and
quarternary
nitrogen compounds. One suitable cationic softener is -a tallow based
quartemary
ammonium compound sold under the trade-marK Varisoft~. Textile softeners are
discussed
in Textile LaunderincLTechnolocry (1979), Riggs, C.L., and Sherill, J, C. (p.
71-74), the
magazine .American D rLestuff Reporter ~, September 1973 (p. 24-26) and the
magazine
2 s Textile World , December 1973 (p. 45-46).
16
CA 02249327 2004-06-22
The following examples show the effect of various treatment methods on the cup
crush values of nonwoven material. Note that because of the standard deviation
of the cup
crush test, each data point represents the measurement of at least five
individual fabrics.
Note also that only Example 8 has examples of the invention.
EXAMPLE 1
A nonwoven spunbond-meltblown-spunbond (SMS) laminate was made generally
according to US patent 4,041,203 in which the layers were sequentially
deposited onto a
1 o moving forming wire. The layers were respectively 0.5 - 0.5 - 0.5 osy (17 -
17 -17 gsm) for
a 1.5 osy (51 gsm) total basis weight for the laminate. The polymers used to
produce the
* *
layers were respectively, PF-304 available from the Himont Corporation, 37956
available
from the Exxon Chemical Company, and PF-304. The laminate was thermally point
bonded
to produce a coherent nonwoven web.
In this example the laminates were washed in a conventional home-type washing
machine. The wash cycle was 30 minutes long and used warm water and 1/2 cup of
Tide~
detergent. In the samples which were washed more than once, more detergent was
added
after each wash and the next wash cycle begun without drying between cycles.
After alf of
the wash cycles were completed, each sample was put into a conventional home-
type dryer
2 0 on the low setting for 30 minutes. The SMS laminates were then tested for
cup crush values
and the results are reported in Table 1.
* Trade-mark
17
CA 02249327 1998-09-18
WO 97/40778 PCT/US97/06701
TABLE 1
Sample Control Sample % chance
1.5 osy SMS 205 same NA
1.5 osy SMS washed 1 time 205 70 -66
1.5 osy SMS washed 5 times 205 50 -76
The results clearly show the dramatic increase in softness attributable to
mechanical
softening through washing alone. Not only does washing result in a great
decrease in the
1 o cup crush value in percentage terms, but the absolute value of the cup
crush indicates a
very soft fabric.
Washing is, unfortunately, a very water, labor, and energy intensive method
for
softening a nonwoven fabric. Washing is a batch process which is not well
suited to the
continuous production of large volumes of fabric.
EXAMPLE 2
A nonwoven spunbond-meltblown-spunbond (SMS) laminate was made generally
according to US patent 4,041,203 in which the layers were sequentially
deposited onto a
2o moving forming wire. The layers were respectively 0.55 - 0.5 - 0.55 osy (19
-17 -19 gsm) for
a 1.6 osy (54 gsm) total basis weight for the laminate. The polymers used to
produce the
layers were the same as in Example 1 above. The laminate was thermally point
bonded to
produce a coherent nonwoven web.
In this example, the laminates were neck softened to a width of 80% of the
starting,
2 s unstretched width (i.e., by 20%). The SMS laminates were then tested for
cup crush values
and the results are reported in Table 2.
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CA 02249327 1998-09-18
WO 97/40778 PCT/US97/06701
TABLE 2
Sample Control Sample % chance
1.6 osy SMS, not neck softened 295 same NA
1.6 osy SMS, 20% neck softened 295 243 -18
The results show that neck softening can reduce the cup crush of a nonwoven
fabric
by a significant amount.
Io EXAMPLE 3
A nonwoven spunbond-meltblown-spunbond (SMS) laminate the same as that of
Example 2 was used for this example.
In this example, the laminates were neck stretched by the percent of the
starting,
unstretched width as shown in Table 3 and at between 230 and 250 °F
(110 and 121°C).
The SMS laminates were then tested for cup crush values and the results are
shown in
Table 3.
TABLE 3
necking Control Sample % chance
2 0 0 180 same NA
180 140 -22
180 120 -33
180 116 -36
180 105 -42
2 5 50 180 94 -48
29
CA 02249327 2004-06-22
The results show that neck stretching can decrease the cup crush in amounts
roughly proportional to the amount of neck stretching. The absolute cup crush
values,
however, were far above the results of mechanical washing alone.
EXAMPLE 4
A nonwoven spunbond-meltblown-spunbond (SMS) laminate the same as Example
1 was used for this example.
In this example, the laminates were topically treated with two softening
chemicals.
to The chemicals were Y-12230 which is a polyalkyleneoxide modified
polydimethyl siloxane
and is commercially available from OSi (formerly a division of Union Carbide
Corp.) of
Danbury-, Connecticut, and Triton~ X-405, an alkylaryl polyether alcohol,
available from the
Rohm & Haas Company of Philadelphia, PA. The chemicals were mixed with water
to
produce an aqueous solution containing the weight percent of the chemical as
shown in
Table 4. The treatment was applied to the webs by the "dip and squeeze" method
described above, though alternatives like spraying would also function. The
SMS laminates
were then tested for cup crush values and the results are reported in Table 4.
TABLE 4
Sample Control Sam le % chance
1.5 osy SMS, not treated 205 same NA
1.5 osy SMS, 0.5% Y-12230 205 179 -13
1.5 osy SMS, 0.3% Triton~ X-405 205 161 -21
* Trade-mark
CA 02249327 2004-06-22
The results show that certain topical chemical treatments alone can reduce the
cup
crush of a nonwoven fabric by about 15 to 20%.
EXAMPLE 5
A nonwoven spunbond-meltblown-spunbond (SMS) laminate the same as Example
2 was used for this example.
In this example, the laminates were neck stretched by 30% at a temperature of
230°F (110°C) and then treated with three different softening
chemicals. In the Table ;5:.
1 o the first two lines show the results for the base fabric without neck
stretching (N.S.) or
treatment and for only neckstretching, respectively. The chemicals used were Y-
12230,
Triton4 X-405, and Ultralube~, a proprietary surfactant hydrocarbon blend,
which is
available from MFG Chemical and Supply, Inc. of Dalton GA. The chemicals were
mixed
with water to produce an aqueous solution containing the weight percent of the
chemical as
i s shown in Table 5. The treatment was applied to the webs by the "dip and
squeeze" method
described above, though alternatives like spraying would also function. The
SMS laminates
were then tested for cup crush values and the results are reported in Table 5.
TABLE 5
Sample Control Sample % chance
Not N.S., not treated 226 same NA
30% N.S., not treated 226 114 -50
30% N.S. then 1.0% Y-12230 226 119 -47
2s 30% N.S. then 1.0% Triton~ X-405 226 143 -37
30% N.S. then 1.0% Ultralube~ 226 156 -31
21
CA 02249327 2004-06-22
The results show that neck stretching followed by certain topical chemical
treatments
can reduce the cup crush of a nonwoven fabric up to about 50%. The absolute
cup crush
values, however, were far above the results of mechanical washing alone.
s
EXAMPLE 6
A nonwoven spunbond-meltblown-spunbond (SMS) laminate the same as Example
1 was used for this example.
to In this example, the laminates were treated with three different topical
softening
chemicals and then neck stretched by 30%, except for the final sample which
was neck
stretched by 40%, at a temperature of about 245°F (118°C). In
the Table 6 ~, the first line
shows the results for the base fabric without neck stretching or treatment.
The topical softening chemicals used were Y-12230, Triton~ X-405, and
Varisoft0
15 137 which is available from Sherex Chemical Co. of Dublin, OH. Varisoft is
a
dihydrogenated tallow dimethyi ammonium methyl sulfate and has CAS number
68002-58-
4. Hexanol is used as a co-surfactant for the Y-12230 and is driven off during
the drying of
the nonwoven so that it does not remain in any effective amount in the
finished product.
The chemicals were mixed with water to produce an aqueous solution containing
the weight
2 o percent of the chemical as shown in Table 6. The treatment was applied to
the webs by the
"dip and squeeze" method described above, though alternatives like spraying
would also
function. The SMS laminates were then tested for cup crush values and the
results are
reported in Table 5.
22
CA 02249327 2004-06-22
TABLE 6
Sample Control Sam le % chance
Not treated, not N.S. 226 same NA
s 30% N.S. with 0.5 % Y-12230 226 112 -50
30% N.S. with 0.3% Triton~ X-405226 110 -52
30% N.S. with 1.0% Varisoft 226 102 -55
40% N.S. with 1.0% Varisoft,
0.5% Y-12230, and
io 0.5% hexanol (1.6 osy SMS) 226 72 -68
The results show that topical treatment with certain chemicals followed by
neck
stretching can reduce the cup crush of a nonwoven fabric up to about 70%,
yielding an
absolute cup crush value in the range of washed fabrics.
is
EXAMPLE 7
A nonwoven spunbond-meltblown-spunbond (SMS) laminate the same as Example
2 was used for this example.
2o In this example, the laminates were neck stretched in the amounts shown, at
a
temperature of about 230 to 250°F (110 to 121 °C) and then un-
necked to a width about
20% greater than their original width according to the procedure described
above. In the
Tabfe 7 , the first line shows the results for the base fabric without neck
stretching,
treatment or un-necking. '
2s The topical treatment for those webs having treatment was applied to the
webs by
the "dip and squeeze" method described above, though alternatives like
spraying would also
23
CA 02249327 1998-09-18
WO 97/40778 PCT/US97/06701
function. The SMS laminates were then tested for cup crush values and the
results are
reported in Table 7.
TABLE 7
Sample Control Sa- mple % chance
Not treated, not N.S. 180 same NA
30% N.S. 180 95 -47
40% N.S. 180 86 -52
io 40% N.S. with 1.0% Varisoft,
0.5% Y-12230, and 0.5% hexanol 180 51 -72
The results show that topical treatment with certain chemicals followed by
neck
stretching and un-necking can reduce the cup crush of a nonwoven fabric about
70%,
yielding an absolute cup crush value in the range of washed fabrics. This
fabric and process
are further described in US Patent 5,413,811 to Fitting et al.
EXAMPLE 8
2 o A spunbond fabric was made having a basis weight of 1.2 osy (41 gsm) from
a
polypropylene polymer commercially available from Exxon Chemical and known as
ESCORENE~ PD-3445 polypropylene. The siloxane additive 200~ fluid was mixed
with the
polymer prior to extrusion in amounts as shown in Table 8. The fabric was spun
at 430 °F
(221 °C) at a rate of approximately 0.6 grams/holelminute. The fabric
was bonded by
thermal calendering at a pattern roll temperature of 280 °F (
138°C) using an expanded
Hansen Pennings pattern with a 15% bond area as taught in US Patent 3,855,046
to
24
CA 02249327 1998-09-18
WO 97/40778 PCT/US97/06701
Hansen and Pennings. Some of the samples were necksoftened by the amount shown
in
Table 8 at ambient temperature and then un-necked to approximately their pre-
necksoftened width. The samples were then tested for cup crush and the results
are
reported in Table 8.
TABLE 8
Sample Control Sample % chance
No additive, no N.S. 149 149 NA
l0 3% additive, no N.S. 149 115 -23
0% additive, 50 % N.S. 149 105 -30
3% additive, 20% N.S. 149 94 -37
3% additive, 45% N.S. 149 68 -54
3% additive, 53% N.S. 149 61 -59
The results show that internal treatment with certain chemicals followed by
neck
stretching and un-necking can reduce the cup crush of a nonwoven fabric about
60%,
yielding an absolute cup crush value in the range of washed fabrics. The
inventors believe
that this result will occur with SMS laminates as well.
2o The above example shows that a nonwoven fabric comparable in softness to a
washed fabric can be produced through internal chemical and mechanical
treatment in a
continuous, commercially feasible operation. The resulting fabric, though
soft, retains a
sufficient amount of its original properties e.g.: strength, to be of use in a
number of useful
products. The internal treatment used in this invention is relatively simple
to carry out in a
manufacturing setting as it involves blending one additional ingredient into
the polymer mix.
CA 02249327 2004-06-22
The topical treatment of Example 7, while quite effective, is a relatively
messy process
involving additional equipment and process steps.
Although only a few exemplary embodiments of this invention have been
described in detail above, those skilled in the art will readily appreciate
that many
modifications are possible in the exemplary embodiments without materially
departing
from the novel teachings and advantages of this invention. Accordingly, all
such
modifications are intended to be included within the scope of this invention
as defined in
the following claims. In the claims, means plus function claims are intended
to cover the
structures described herein as performing the recited function and not only
structural
to equivalents but also equivalent structures. Thus although a nail and a
screw may not be
structural equivalents in that a nail employs a cylindrical surface to secure
wooden parts
together, whereas a screw employs a helical surface, in the environment of
fastening
wooden parts, a nail and a screw may be equivalent structures.
26
