Field of the Invention
The present invention relates to nonwoven web and film
laminates with improved strength. More particularly, the present invention relates
to laminates for use in disposable garments and personal care products with improved
tear resistance, and to a method of manufacturing such laminates.
Background of the Invention
Industry has long recognized the benefits of combining
barrier properties of films and cloth-like attributes of nonwoven fabrics for various
medical, personal care and commercial applications. Furthermore, such web/film laminates
may also exhibit certain levels of elasticity, and when incorporating stretched
filled microporous film, breathability. Therefore, laminates have been produced
using both film and nonwoven web materials.
Lamination of films has been used to create materials which
are both impervious and somewhat cloth-like in appearance and texture. Uses for
such laminates include the outer covers for personal care products such as diapers,
training pants, incontinence garments, and feminine hygiene products. In this regard,
reference may be had to coassigned U.S. Patent No. 4,818,600 dated April 4, 1989
and U.S. Patent No. 4,725,473 dated February 16, 1988. Additionally, such materials
are particularly suited for use in protective outer wear such as coveralls, and
surgical garments and drapes. See in this regard coassigned U.S. Patent No. 4,379,102
dated April 5, 1983.
A primary purpose of the film in such laminations is to
provide barrier properties. There is also a need for such laminates to be breathable
so that they have the ability to transmit moisture vapor. Apparel made from laminates
of these breathable or microporous films are more comfortable to wear by reducing
the moisture vapor concentration and the consequent skin hydration undemeath the
Despite exhibiting many positive attributes, when used
inappropriately or when exposed to particularly stressful conditions, laminates
sometimes tear. In an attempt to create a nonwoven laminate with improved barrier
properties, improved strength and with elastic attributes, but at lower costs, laminates
have been developed in which the web fiber size has been reduced and polymer molecular
weight distribution has been narrowed (since it affects polymer mechanical properties).
For instance, it has been suggested that propylene polymers having high melt flow
rate and narrow molecular weight distribution can be used to produce fibers for
nonwoven webs and fabrics having superior barrier properties, tensile strength and
softness. For example, U.S. Patent No. 5,529. 850 to Morini et. al. describes the
preparation of crystalline polypropylene polymers having narrow molecular weight
distribution, through the use of specific di- or polyesters as intemal or extemal
electron donors in polymerization reactions accompanying a catalyst component, such
as an active magnesium halide and a titanium compound and al-alkyl compounds.
U.S. Patent Nos. 5,726,103 and 5,763,080 to Stahl et al.
describe fibers and fabrics incorporating lower melting propylene polymers in order
to achieve a relatively strong and relatively fluid impervious fabric. In particular
the Stahl patents describe propylene homopolymers and copolymers formed by metallocene
catalyst systems. Such propylene polymers exhibit generally lower melting behavior
than non-metallocene catalyzed propylene polymers. Stahl indicates that this low
melting behavior is of use in the fabrication of fibers and fabric that depend on
lower melting behavior or upon melting point differential between two fabrics to
achieve bonding. Such fibers would include chenille or tufted, core and sheath.
Stahl indicates that fabrics such as spunbond and meltblown nonwovens, when combined
in spunbond/meltblown/spunbond (SMS) fabrics will show bonding at lower temperatures,
and in particular, allow for the making of a higher melting fiber into a meltblown
and a lower melting fiber into a spunbond. In the prospective examples of the Stahl
patents, Stahl indicates that the overall strength of the fabric samples utilizing
metallocene-catalyzed polypropylene in the spunbond layers will be as high as controls
(which are unbonded SM fabrics). In a further prospective example utilizing one
metallocene-catalyzed homopolymer polypropylene "S" layer and a commercial 1100
mfr polypropylene "M" layer, the prospective fabric would have improved barrier
and filtration properties with no loss of laminated fabric strength when compared
to the control. Each of these patents do not provide for better than expected tear
strength in a film/nonwoven laminate.
U.S. Patent No. 5,723,217 to Stahl et al. describes polyolefin
fibers and their fabrics. This Stahl patent discusses fibers made from reactor grade
isotactic poly-alpha-olefin wherein polypropylene is produced by single site catalysis.
Stahl asserts that the polypropylene fibers produced will generally be stronger
or have higher tenacity than conventional polymer when drawn to a fine diameter.
Stahl also asserts that meltblown and or spunbond fabric containing the fiber will
gain extra strength but does not allude to any method for creating a breathable
film laminate with enhanced tear strength.
U.S. Patent No. 5,612,123 to Gessner et al. describes a
distribution enhanced polyolefin product. In particular this patent discusses that
improved meltspinning productivity is achieved by employing polyolefin resins having
key molecular weight distributions and rheological property parameters within predetermined
ranges. Such polyolefin filaments and the single layer spunbond fabric prepared
by the process exhibited high tenacity and tear property values. This patent also
fails to allude to a method for increasing the tear properties of a breathable film
U.S. Patent No. 5,464,688 to Timmons et al. describes nonwoven
web laminates with improved barrier properties. Such webs are formed with commercially
acceptable polymer with reduced molecular weight distribution in the meltblown layer
of an SMS.
While metallocene-catalyzed polypropylene has heretofore
been used in laminates, specifically as part of stretch bonded laminates and necked
bonded laminates, the structural components, physical attributes and bonding processes
of these laminates are markedly different from breathable film laminates. Furthermore,
tear measurement tests, such as grab tensile/ peak energy for necked bonded (NBL)
and stretch bonded laminates (SBL), as well as a single spunbond layer show a higher
peak energy value (in the machine direction) for Ziegler-Natta catalyzed polypropylene
spunbond than for metallocene-catalyzed spunbond in these laminates. One would therefore
not expect that spunbond with narrow molecular weight distribution would significantly
increase tear strength in a breathable film/nonwoven web laminate.
Therefore, despite the improvements in the nonwoven laminate
area, there exists a need for a breathable film/nonwoven web laminate which demonstrates
increased tear strength without the addition of significant cost. Further, there
exists a need for a method for producing such a laminate composite which can be
done in-line at high speeds and over a short time span. Finally, there is a need
for personal care products and other garments which utilize such laminates in their
composite constructions. It is to the provision of such composite and method that
the present invention is directed.
An object of the present invention is to provide a nonwoven
web /film laminate material which exhibits significant tear strength attributes.
A still further object is to provide a nonwoven web/film
laminate embodying the above-discussed features which utilizes relatively inexpensive
materials to increase strength properties.
A still further object is to provide an in-line process
for preparing a nonwoven web/film laminate which allows for increased tear strength
in the finished laminate.
A specific object resides in providing a material having
many of the previously identified attributes which can be advantageously used in
personal care products. The present invention relates to a film/nonwoven web laminate
including at least one nonwoven web layer having a narrow molecular weight distribution
and a film.
In one embodiment of the present invention, the film is
a stretched microporous film that includes an elastomeric resin and a film filler.
The present invention is also directed to a process for
producing a laminate including at least one nonwoven web layer having a narrow molecular
weight distribution and a film including the steps of forming a nonwoven web of
a metallocene-catalyzed polypropylene and bonding a film layer to the newly formed
nonwoven web layer within 1-30 seconds of the formation of the nonwoven web layer.
Brief Description of the Drawings
Detailed Description of the Invention
- Fig. 1 is a cross-sectional view of a material embodying the features of the
- Fig. 2 is a schematic side elevation view illustrating one manner in which the
material of the present invention can be prepared.
- Fig. 3 is a top plan view of an exemplary personal care article, in this case
a diaper, which may utilize a laminate according to the present invention.
As used herein the term "polymer" generally includes but
is not limited to, homopolymers, copolymers, such as for example, block, graft,
random and altemating 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.
As used herein the term "spunbond 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 being rapidly reduced as, for example, in U.S. Patent
4,340,563 to Appel et al., and U.S. Patent 3,692,618 to Dorschner et al., U.S. Patent
3,802,817 to Matsuki et al., U.S. Patents 3,338,992 and 3,341,394 to Kinney, U.S.
Patent 3,502,763 to Hartman, and U.S. Patent 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 average diameters (from a sample of at
least 10) larger than 7 microns, more particularly, between about 10 and 20 microns.
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, 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 U.S. Patent 3,849,241
to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous,
are generally smaller than 10 microns in average diameter, and are generally tacky
when deposited onto a collecting surface.
As used herein the term "multilayer laminate" means a laminate
wherein some of the layers are spunbond and some meltblown such as a spunbond/meltblown/spunbond
(SMS) laminate and others as disclosed in U.S. Patent 4,041,203 to Brock et al.,
U.S. Patent 5,169,706 to Collier, et al, U.S. Patent 5,145,727 to Potts et al.,
U.S. 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. Such fabrics
usually have a basis weight of from about 0.1 to 12 osy (3.4 to 400 gsm), or more
particularly from about 0.75 to about 3 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 "personal care product" means
diapers, training pants, absorbent underpants, adult incontinence products, and
feminine hygiene products.
As used herein the term "thermal point bonding" involves
passing a fabric or web of fibers to be bonded between a heated calender roll and
an anvil roll. The calender roll is usually, 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 U.S. Patent 3,855,046 to Hansen and
Pennings. 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, 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 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 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
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 term "ultrasonic bonding" means a process
performed, for example, by passing the fabric between a sonic hom and anvil roll
as illustrated in U.S. Patent 4,374,888 to Bomslaeger.
As used herein the term "composite elastic material" refers
to an elastic material which may be a multicomponent material or a multilayer material
in which one layer is elastic. These materials may be, for example, "stretch bonded"
laminates (SBL) and "neck bonded" laminates (NBL). Conventionally, "stretch bonded"
refers to an elastic member being bonded to another member while the elastic member
is extended at least about 25 percent more than of its relaxed length. "Stretch
bonded laminate" refers to a composite material having at least two layers in which
one layer is a gatherable layer and the other layer is an elastic layer. The layers
are joined together when the elastic layer is in an extended condition so that upon
relaxing the layers, the gatherable layer is gathered. Such a multilayer composite
elastic material may be stretched to the extent that the nonelastic material gathered
between the bond locations allows the elastic material to elongate. One type of
stretch bonded laminate is disclosed, for example, by U.S. Patent 4,720,415 to Vander
Wielen et al., in which multiple layers of the same polymer produced from multiple
banks of extruders are used. Other composite elastic materials are disclosed in
U.S. Patent 4,789,699 to Kieffer et al. , U.S. Patent 4,781,966 to Taylor and U.S.
Patents 4,657,802 and 4,652,487 to Morman and 4,655,760 to Morman et al.
Conventionally, "neck bonded" refers to an elastic member
being bonded to a non-elastic member while the non-elastic member is extended under
conditions reducing its width or necked. "Neck bonded laminate" refers to a composite
material having at least two layers in which one layer is a necked, non-elastic
layer and the other layer is an elastic layer. The layers are joined together when
the non-elastic layer is in an extended condition. Examples of neck-bonded laminates
are such as those described in U.S. Patents 5,226,992, 4,981,747, 4,965,122 and
5,336,545 to Morman.
As used herein, the term "compaction roll" means a set
of rollers above and below the web to compact the web as a way of treating a just
produced microfiber, particularly a spunbond web, in order to give it sufficient
integrity for further processing, but not the relatively strong bonding of secondary
bonding processes like through-air bonding, thermal bonding and ultrasonic bonding.
Compaction rolls slightly squeeze the web in order to increase its self-adherence
and thereby its integrity. As an alternative to the use of a compaction roll, a
pressured targeted air stream (hot air knife) may be used to compact a recently
formed web. As used herein, the term "hot air knife" or HAK means a process of pre-
or primarily bonding a just produced microfiber, particularly spunbond, web in order
to give it sufficient integrity, i.e. increase the stiffness of the web, for further
processing, but does not mean the relatively strong bonding of secondary bonding
processes like through air bonding, thermal bonding and ultrasonic bonding. A hot
air knife is a device which focuses a stream of heated air at a very high flow rate,
generally from about 1000 to about 10000 feet per minute (fpm) (305 to 3050 meters
per minute), or more particularly from about 3000 to 5000 feet per minute (915 to
1525 m/min.) directed at the nonwoven web immediately after its formation. The air
temperature is usually in the range of the melting point of at least one of the
polymers used in the web, generally between about 200 and 550°F (93 and 290°C)
for the thermoplastic polymers commonly used in spunbonding. The control of air
temperature, velocity, pressure, volume and other factors helps avoid damage to
the web while increasing its integrity. The HAK's focused stream of air is arranged
and directed by at least one slot of about 1/8 to 1 inches (3 to 25 mm) in width,
particularly about 3/8 inch (9.4 mm), serving as the exit for the heated air towards
the web, with the slot running in a substantially cross-machine direction over substantially
the entire width of the web. In other embodiments, there may be a plurality of slots
arranged next to each other or separated by a slight gap. The at least one slot
is usually, though not essentially, continuous, and may be comprised of, for example,
closely spaced holes. The HAK has a plenum to distribute and contain the heated
air prior to its exiting the slot. The plenum pressure of the HAK is usually between
about 1.0 and 12.0 inches of water (2 to 22 mmHg), and the HAK is positioned between
about 0.25 and 10 inches and more preferably 0.75 to 3.0 inches (19 to 76 mm) above
the forming wire. In a particular embodiment, the HAK plenum's cross sectional area
for cross-directional flow (i.e. the plenum cross sectional area in the machine
direction) is at least twice the total slot exit area. Since the foraminous wire
onto which spunbond polymer is formed generally moves at a high rate of speed, the
time of exposure of any particular part of the web to the air discharged from the
hot air knife is less than a tenth of a second and generally about a hundredth of
a second in contrast with the through air bonding process which has a much larger
dwell time. The HAK process has a great range of variability and controllability
of many factors such as air temperature, velocity, pressure, volume, slot or hole
arrangement and size, and the distance from the HAK plenum to the web. The HAK is
further described in U.S. Patent No. 5,707,468 and commonly assigned.
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 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 the density in grams/cc, multiplied by
0.00707. A lower denier indicates a finer fiber 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
.89 g/cc and multiplying by .00707. Thus, a 15 micron polypropylene fiber has a
denier of about 1.42 (152 x 0.89 x .00707 = 1.415). Outside the United
States the unit of measurement is more commonly the "tex", which is defined as the
grams per kilometer of fiber. Tex may be calculated as denier/9.
As used herein, the term "machine direction" or MD means
the direction of a fabric in the direction in which it is produced. The term "cross
machine direction" or CD means the opposite direction of the fabric, i.e. a direction
generally perpendicular to the MD.
For the purpose of this application the term "conventional"
shall refer to Ziegler-Natta catalyzed propylene homopolymers and copolymers. For
a further discussion of Ziegler-Natta catalyst reactions, one should refer to
the Encyclopedia of Polymer Science and Engineering, Volume 8, page 162,
published by John Wiley & Sons, Inc., 1987.
Referring to Figure 1, the nonwoven web/film laminate 10
of the present invention may be made from polymers which are capable of being formed
into film 15 and then bonded to a nonwoven web 20. The film may be newly formed
or pre-formed film. The nonwoven web is preferably newly formed.
Such film forming polymers include but are not limited
to extrudable thermoplastic polymers such as a polyolefin or a blend of polyolefins.
More particularly, useful polyolefins include polypropylene and polyethylene. Other
useful polymers include those described in U.S. Patent No. 4,777,073 to Sheth, assigned
to Exxon Chemical Patents Inc., such as a copolymer of polypropylene and low density
polyethylene or linear low density polyethylene. Additional polymers useful in the
present invention include flexible polyolefins. As used herein the term "flexible
polyolefin" refers to polyolefin materials containing propylene based polymer with
controlled regions of atactic polypropylene units to achieve a desired crystallinity
such as described in co-assigned U.S. Patent 5,910,136 entitled "Oriented Polymeric
Microporous Films with Flexible Polyolefins and Methods of making the Same" to Hetzler
and Jacobs; the entire contents of which are incorporated herein by reference in
its entirety. Further description of such flexible polyolefins can be found in U.S.
Patent No. 5,723,546 to Sustic and assigned to the Rexene Corporation.
Other useful polymers for the formation of film of the
present invention include elastomeric thermoplastic polymers. Such polymers include
those made from block copolymers such as polyurethanes, copolyether esters, polyamide,
polyether block copolymers, ethylene vinyl acetates (EVA), block copolymers having
the general formula A-B-A' or A-B like copoiy(styrene/ethylene-butylene), styrene-poly(ethyiene-propylene)-styrene,
poly(styrenelethylene-butylenel styrene) and the like. Specifically, the elastomeric
thermoplastic polymers indude: polyester elastomeric materials such as, for example,
those available under the trade designation HYTREL® from E. I. du Pont de Nemours
and Company; polyester block amide copolymers such as, for example, those available
in various grades under the trade designation PEBAX® from ELF Atochem Inc.
of Glen Rock, New Jersey; and polyurethane elastomeric materials such as, for example,
those available under the trademark ESTANE® from B. F. Goodrich & Co. or MORTHANE®
from Morton Thiokol Corporation.
Elastomeric polymers have been used in the past for many
applications but are somewhat limited by their intrinsic properties. These materials
have recently been joined by a new class of polymers which demonstrate high barrier,
breathability and elasticity attributes when incorporated into film. The new dass
of polymers is referred to as single site catalyzed polymers such as "metallocene"
polymers produced according to a metallocene process.
Such metallocene polymers are available from Exxon Chemical
Company of Baytown, Texas under the trade name EXXPOL® for polypropylene based
polymers and EXACT® for polyethylene based polymers. Dow Chemical Company of
Midland, Michigan has polymers commercially available under the name ENGAGE®.
More specifically, the metallocene film forming polymers may be selected from copolymers
of ethylene and 1-butene, copolymers of ethylene and 1-hexene, copolymers of ethylene
and 1-octene and combinations thereof.
The laminate film layer 15 may be a multi-layered film
which may include a core layer 16, or "B" layer, and one or more skin layers 17,
or "A" layers on either side of the core layer. Any of the polymers discussed above
are suitable for use as a core layer of a multi-layered film.
The skin layer will typically include extrudable thermoplastic
polymers and/or additives which provide specialized properties to the film 15. Thus,
the skin layer may be made from polymers which provide such properties as antimicrobial
activity, water vapor transmission, adhesion and/or antiblocking properties. The
polymers are thus chosen for the particular attributes desired. Examples of possible
polymers that may be used alone or in combination include homopolymers, copolymers
and blends of polyolefins as well as ethylene vinyl acetate (EVA), ethylene ethyl
acrylate (EEA), ethylene acrylic acid (EAA), ethylene methyl acrylate (EMA), ethylene
butyl acrylate (EBA), polyester (PET), nylon (PA), ethylene vinyl alcohol (EVOH),
polystyrene (PS), polyurethane (PU), and olefinic thermoplastic elastomers which
are multistep reactor products wherein an amorphous ethylene propylene random copolymer
is molecularly dispersed in a predominately semicrystalline high polypropylene monomer/low
ethylene monomer continuous matrix.
Suitable polymers for the "A" layer are available commercially
under the trade designation "Catalloy" from the Himont Chemical Company of Wilmington,
Delaware, and polypropylene. Specific commercial examples are Catalloy, KS 357P,
KS-084P and KS-057P. Other suitable polymers include polymers which are semi-crystalline/amorphous
or heterophasic in character. Such polymers are disclosed in European Patent Application
EP 0444671 A3 (based on Application number 91103014.6), European Patent Application
EP 0472946 A2 (based on Application number 91112955.9), European Patent Application
EP 0400333 A2 (based on Application number 90108051.5), U.S. Patent number 5,302,454
and U.S. Patent number 5,368,927. For a more detailed description of films having
core and skin layers see PCT WO 96/19346 to McCormack et al. assigned to common
assignee which is incorporated herein by reference in its entirety.
The films can be made from breathable or non-breathable
materials. Some films are made breathable by adding micropore developing filler
particles to the film during the film forming process.
As used herein, a "micropore developing filler" is meant
to include particulates and other forms of materials which can be added to a polymer
and which will not chemically interfere with or adversely affect the extruded film
made from the polymer but are able to be uniformly dispersed throughout the film.
Generally, the micropore developing fillers will be in particulate form and usually
will have somewhat of a spherical shape with average particle sizes in the range
of about 0.5 to about 8 microns. The film will usually contain at least about 30
percent of micropore developing filler based upon the total weight of the film layer.
Both organic and inorganic micropore developing fillers are contemplated to be within
the scope of the present invention provided that they do not interfere with the
film formation process, the breathability of the resultant film or its ability to
bond to a fibrous polyolefin nonwoven web.
Examples of micropore developing fillers include calcium
carbonate (CaCO3), various kinds of clay, silica (SiO2), alumina,
barium sulfate, sodium carbonate, talc, magnesium sulfate, titanium dioxide, zeolites,
aluminum sulfate, cellulose-type powders, diatomaceous earth, magnesium sulfate,
magnesium carbonate, barium carbonate, kaolin, mica, carbon, calcium oxide, magnesium
oxide, aluminum hydroxide, pulp powder, wood powder, cellulose derivative, polymer
particles, chitin and chitin derivatives. The micropore developing filler particles
may optionally be coated with a fatty acid, such as stearic acid, or a larger chain
fatty acid such as behenic acid, which may facilitate the free flow of the particles
(in bulk) and their ease of dispersion into the polymer matrix. Silica-containing
fillers may also be present in an effective amount to provide antiblocking properties.
Once the particle-filled film has been formed, it is then
either stretched or crushed to create pathways through the film. Generally, to qualify
as being "breathable" for the present invention, the resultant laminate should have
a water vapor transmission rate (WVTR) of at least about 250 g/m2/24
hours as may be measured by a test method as described below. Furthermore, the films
may be apertured. In forming the films, the films may be coextruded to increase
bonding and alleviate die lip build-up.
Processes for forming film are generally known. The film
15 can be made from either cast or blown film equipment, can be coextruded and can
be embossed if so desired. Additionally, the film 15 can be stretched or oriented
by passing the film through a film stretching unit. The stretching reduces the film
gauge or thickness from an initial gauge of 1.5-2.0 mils to an effective final gauge
of 0.5 mils or less. Generally, this stretching may take place in the CD or MD or
The nonwoven web 20 as illustrated in Figure 1, in the
laminate 10 containing the film of the present invention, may be formed from a number
of processes including, but not limited to, spunbonding and meltblowing processes.
Such nonwoven webs can for example be necked polypropylene spunbond, crimped polypropylene
spunbond, elastomeric spunbond or meltblown fabrics produced from elastomeric resins.
As used herein, the term "necked" refers to constricting in at least one dimension
by processes such as, for example, drawing or gathering.
Especially suitable fibers for forming the nonwoven web
20 include polymeric webs of narrow molecular weight distribution such as metallocene
catalyzed polypropylene spunbond, and in particular inelastic metallocene-catalyzed
polypropylene spunbond sold under the designation 3854 as available from the Exxon
Chemical Company of Baytown Texas. Single site/metallocene catalyzed polypropylene
are sold by Exxon under the trade name Achieve. In the practice of this invention,
a single nonwoven web layer may be laminated to a film layer. An example of such
is a spunbond (S)/ film (F) laminate. Alternatively, a plurality of nonwoven web
layers may also be incorporated into the laminate according to the present invention.
Examples of such materials can include, for example, SFS multilayered laminate composites.
In the process of the present invention, as illustrated
in Figure 2, filled film 15 is directed from supply roll 21 to a film stretching
unit 30 such as a machine direction orienter (MDO), which is a commercially available
device from vendors such as the Marshall and Williams Company of Providence, Rhode
Island. Such an apparatus has a plurality of stretching rollers 32 moving at progressively
faster speeds relative to the pair disposed before it. These rolls apply an amount
of stress and thereby progressively stretch filled film to a stretch length in the
machine direction of the film which the direction of travel of filled film through
the process as shown in Figure 2. The stretch rollers may be heated for better processing.
In addition, the unit may also include rolls (not shown) upstream and/or downstream
from the stretch rolls that can be used to preheat the film before stretching and/anneal
(or cool) it after stretching.
At the stretched length, a plurality of micropores form
in the film. The film is then directed out of the apparatus so that the stress is
removed in order to allow the stretched film to relax. A permanent elongation is
retained after the stretched film is allowed to relax.
Alternatively, instead of being pre-formed and supplied
by a supply roll, the film may itself be formed in-line. Such process is described
in U.S. Provisional Patent Application entitled Process for Making a Laminate of
Unaged Film and an Unaged Nonwoven Web and Products Produced Therefrom filed on
September 22, 1998, bearing Express Mail No. EL154777056US and assigned to the same
assignee, the entire contents of said application being incorporated herein by reference
in its entirety.
A fibrous nonwoven web layer is contemporaneously formed
on a conventional fibrous nonwoven web forming apparatus. As illustrated in Figure
2, a pair of spunbond machines 35 is used to form the nonwoven web layer. Alternatively
a single bank of spunbond machines may be used. The long, essentially continuous
fibers are deposited onto a forming wire as an unbonded web 19 and the unbonded
web is then sent through a pair of bonding rolls 36, 37 to bond the fibers together
and increase the tear strength of the resultant web support layer 20. One or both
of the rolls are often heated to aid in bonding. Typically, one of the rolls is
also patterned so as to impart a discrete bond pattern with a prescribed bond surface
area to the web. An example of a bond pattern which may be used would be the wire
weave pattern. The other roll is usually a smooth anvil roll but this roll may also
be patterned if desired. During the process before bonding, the spunbond web may
be compressed using a set of compaction rolls (not shown) or a hot air knife (not
Once the filled film has been sufficiently stretched and
the nonwoven web layer has been formed, the two layers are brought together and
laminated to one another using a pair of laminating rolls 38, 39 (thermal point
bonding) or other bonding means to form a breathable stretch thinned film laminate
(BSTL). As with the bonding rolls, the laminating rolls may be heated. Also, at
least one of the rolls may be patterned to create a discrete bond pattern with a
prescribed bond surface area for the resultant laminate. Generally, the maximum
bond point surface area for a given area of surface on one side of the laminate
will not exceed about 50 % of the total surface area. There are a number of discrete
bond patterns which may be used, an example of which is the C-star or Baby Objects
pattern, generally having a bond point surface area between 15 and 30 %. The time
between formation of the spunbond web and lamination of the web to the film is between
approximately 1 and 30 seconds. See for example, Brock et al., U.S. Patent No. 4,041,203,
which is incorporated by reference in its entirety. Once the laminate exits the
laminating rolls, it may be wound up into a roll for subsequent processing. Alternatively,
the laminate may continue in-line for further processing or conversion.
The process shown in Figure 2 also may be used to create
a three layer web/film laminate. The only modification to the previously described
process is to feed a supply of a second fibrous nonwoven web layer into the laminating
rolls on a side of the filled film opposite that of the other fibrous nonwoven web
layer. One or both of the nonwoven web layers may be formed directly in line as
is nonwoven web layer 20. In either event, the second roll is fed into the laminating
rolls as it is laminated to filled film in the same fashion as the first nonwoven
web layer. Such three layer laminates are particularly useful in medical and industrial
protective garment/outer workwear applications.
As has been stated previously, film/nonwoven web laminates
may be used in a wide variety of applications not the least of which includes personal
care absorbent articles such as diapers, training pants, incontinence devices and
feminine hygiene products such as sanitary napkins. An exemplary article, in this
case a diaper 50, is shown in Figure 3 of the drawings. Referring to Figure 3, most
such personal care absorbent articles include a liquid permeable top sheet or liner
52, a back sheet or outer cover 54 and an absorbent core 56 disposed between and
contained by the top sheet and back sheet. Articles such as diapers may also include
some type of fastening means such as adhesive fastening tapes 58 or mechanical hook
and loop type fasteners to maintain the garment in place on the wearer. The fastening
system may contain stretch material to form stretch ears for greater comfort.
Film/nonwoven web laminates may be used to form various
portions of the article 50 including, but not limited to, the top 52 and back sheet
54. When using the film/nonwoven web laminate as an outercover, it is usually advantageous
to place the nonwoven side facing out away from the user. In addition, in such embodiments
it may be possible to utilize the nonwoven portion of the laminate as the loop portion
of the hook and loop combination.
Other uses for the filled film and breathable film/nonwoven
web laminates according to the present invention include, but are not limited to
protective work wear such as surgical drapes and gowns, coveralls, lab coats and
other articles of clothing.
As will be explained in more detail below, a surprising
and unexpected improvement of the present invention lies in its increase in tear
strength of the produced nonwoven web/film laminate as measured through numerous
testing protocols. These improvements in tear strength are transferred to the articles
of manufacture utilizing the laminates as a structural component, such as personal
care articles and protective workwear. An advantage of the present invention lies
in that tear strength is improved using a rapid in-line process, and without the
use of relatively more expensive materials.
The present invention is further described by the examples
which follow. Such examples, however, are not to be construed as limiting in any
way either the spirit or the scope of the present invention.
A series of materials were prepared in accordance with
the previously described process including conventional Ziegler Natta catalyzed
polypropylene spunbond (designated as Z-N PP), and metallocene-catalyzed polypropylene
spunbond (designated as Met PP) as support layers. The materials utilized in the
nonwoven web/film laminate are described in the following Table 1.
Melt flow Rate
Exxon Chemical Company
Spun bond layer
24 for pellets; 30-32
of fiber/ fabric form
Natta catalyzed polypropylene
Exxon Chemical Company
Spun bond layer
35 in pellet, 45
in fiber/fabric form
50% CaCO3-50% LLDPE
Core EVA/Catalloy PP Skin
Spunbond material was introduced into the spunbond extruders.
For instance, Exxon 3854 metallocene polypropylene was introduced. The throughput
of the spunbond was approximately 0.7 grams per hole per minute (GHM). The melt
temperature for the spunbond is typically around 450 °F. The spunbond calender
and HAK settings were optimized for metallocene-catalyzed materials. The typical
calender spunbond temperature is around 310-330° F in the bonding rolls. The
HAK temperature is usually held between 220-240° F. The MDO settings on the
rolls were as follows: for the preheat 1-preheat 2 roll, the setting was at 76 %,
for the preheat 2-slow roll, the setting was at 98 %, for the slow roll-fast roll,
the setting was at 29 %, for the fast roll-anneal 1 roll, the setting was at 100.5
%, for the anneal 1- anneal 2 roll, the setting was at 100.5 %, for the anneal 2-calender
roll, the setting was at 101 %, for the calender-winder roll, the setting was at
94 %, and for the winder drum roll the setting was at 100.5 %. The settings are
expressed in percentages of the previous roll speed.
The denier of the spunbond produced was 2.0 dpf. Film was
introduced from supply rolls and laminate was made with calender temperatures at
260/220°F. The top roll temperature is the first stated. Following the lamination
of the film and spunbond layers in SF laminates, the following comparative tests
were run for the materials, the results of which are expressed in Table 2. A comparison
of data for a single layer of spunbond as well as necked bonded laminate materials
is shown in Tables 3 and 4.
Basis weight (B.W.) This test determined the mass per unit area of the textile
material by using a small 5x5 inch specimen. The measurement is typically expressed
in grams per square meter (gsm) or ounces per square yard (osy).
Hydrohead (Hydrostatic Head): A measure of the liquid barrier properties
of a fabric is the hydrohead test. The hydrohead test determines the height of water
(in centimeters) which the fabric will support before a predetermined amount of
liquid passes through. The test measures a fabric's resistance to water under static
pressure. Under controlled conditions, a specimen is subjected to water pressure
that increases at a constant rate until leakage appears on the material's lower
surface. Water pressure is measured at the hydrostatic head height reached after
the third sign of leakage. Values are recorded in millibars of pressure. When testing
meltblown material a support net is used. A fabric with a higher hydrohead reading
indicates it has a greater barrier to liquid penetration than a fabric with a lower
hydrohead. The hydrohead test is performed according to Federal Test Standard 191A,
Method 5514 using a Testest FX-3000 Hydrostatic Head Tester available from Marlo
Industries, Inc., PO Box 1071, Concord, North Carolina.
Elmendorf Tear Test (Elem.): This test measures the average force required
to propagate a tear starting from a cut slit in the specimen being tested, when
part of the specimen is held in a clamp and an adjacent part is moved by the force
of a pendulum freely falling in an arc. The specimen size is 2.5 x 4 and the test
can be conducted in the CD or MD direction. In conducting the test, one of the following
brand testers should be used. The Elmendorf Digi-tear brand Model 65-200, and Air
clamps 65-200 obtained from the Thwing-Albert Instrument Company, Philadelphia,
Pennsylvania, or the Lorentzen and Wettre brand, Model 09ED obtained from the Lorentzen
Wettre Canada Inc., of Fairfield, New Jersey, or Textest FX 3700 brand (Digital
Elmendorf) obtained from Schmid Corporation of Spartanburg, South Carolina.
Trap Tear Test (Trapezoid Tear (Trap)): The trapezoid or "trap" tear test
is a tension test applicable to both woven and nonwoven fabrics. The entire width
of the specimen is gripped between clamps, thus the test primarily measures the
bonding or interlocking and strength of individual fibers directly in the tensile
load, rather than the strength of the composite structure of the fabric as a whole.
The procedure is useful in estimating the relative ease of tearing of a fabric.
It is particularly useful in the determination of any appreciable difference in
strength between the machine and cross direction of the fabric. The test measures
the fabric resistance to tear propagation under a constant rate of extension. A
fabric cut on one edge is clamped along nonparallel sides of a trapezoidal shaped
specimen and is pulled, causing a tear propagation in the specimen perpendicular
to the load. The test can be conducted in either the MD or CD direction. In conducting
the trap tear test, an outline of a trapezoid is drawn on a 3 by 6 inch (75 by 152
mm) specimen with the longer dimension in the direction being tested, and the specimen
is cut in the shape of the trapezoid. The trapezoid has a 4 inch (102 mm) side and
a 1 inch (25 mm) side which are parallel and which are separated by 3 inches (76
mm). A small preliminary cut of 5/8 inches (15 mm) is made in the middle of the
shorter of the parallel sides. The specimen is clamped in, for example, an Instron
Model TM (a constant-rate-of -extension tester), available from the Instron Corporation,
2500 Washington St., Canton, MA 02021, or a Thwing-Albert Model INTELLECT 11 available
from the Thwing-Albert Instrument Co., 10960 Dutton Rd., Phila., PA 19154, which
have 3 inch (76 mm) long parallel clamps. The specimen is clamped along the non-parallel
sides of the trapezoid so that the fabric on the longer side is loose and the fabric
along the shorter side taut, and with the cut halfway between the clamps. A continuous
load is applied on the specimen such that the tear propagates across the speamen
width. It should be noted that the longer direction is the direction being tested
even though the tear is perpendicular to the length of the specimen. The force required
to completely tear the specimen is recorded in pounds with higher numbers indicating
a greater resistance to tearing. The test method used conforms to ASTM Standard
test D1117-14 except that the tearing load is calculated as the average of the first
and highest peaks recorded rather than the lowest and highest peaks. Five specimens
for each sample should be tested. The data presented include first and high peak
values. This procedure also conforms to Method 5136, Federal Test Methods Standards
No. 191 issued in December 1968. The difference between the ASTM and the Federal
procedure is in the final catculation of tearing load. In the ASTM procedure, tearing
load is calculated as the average of the highest and lowest peaks; in the Federal
method, the tearing load is the average of the five highest peaks recorded. Alternatively,
a Sintech Tensile Tester may be used in the procedure.
Grab Tensile (Grab): This test measures the effective tensile strength and
stretch of a material. A one square inch area is clamped at both ends of a 4 x 6
inch specimen. The specimen is pulled at a constant rate of extension to obtain
results before the point of rupture. The test is a measure of breaking strength
and elongation or strain of a fabric when subjected to unidirectional stress. This
test is known in the art and conforms to the specifications of ASTM standards D-5034-92
and D-5035-92, and INDA IST 110.1-92, using a Constant Rate of Extension Tensile
Testing Machine. This test also conforms to Method 5100 of the Federal Test Methods
Standard 191 A. The results are expressed in pounds to break and percent stretch
before breakage. Higher numbers are indicative of a stronger, more stretchable fabric.
The term "load" means the maximum/ peak load or force, expressed in units of weight,
required to break or rupture the specimen in a tensile test. The term "peak strain",
"total energy" or "peak energy" (PEN) means the total energy under a load versus
elongation curve as expressed in weight-length units. The term "elongation" or "percent
stretch" means the increase in length of a specimen during a tensile test. Values
for grab tensile strength and grab elongation are obtained using a specified width
of fabric, usually 4 inches (102 mm), clamp width and a constant rate of extension.
The sample is wider than the clamp to give results representative of effective strength
of fibers in the clamped width combined with additional strength contributed by
adjacent fibers in the fabric. The specimen is damped in, for example, an Instron
Model TM, available from the Instron Corporation, 2500 Washington St., Canton, MA
02021, or a Thwing-Albert Model INTELLECT H available from the Thwing-Albert Instrument
Co., 10960 Dutton Rd., Phila., PA 19154, which have 3 inch (76 mm) long parallel
clamps. This closely simulates fabric stress conditions in actual use. The test
can be conducted on wet or dry samples in the CD or MD directions. Alternatively,
a Sintech Tensile Tester may be used, available from Sintech Corp., 1001 Sheldon
Dr. Cary, North Carolina. Higher numbers in this test indicate a stronger, more
Standard Deviation (SD): Standard deviation as used in these examples represents
a measure of dispersion and measures the average distance between a single observation
and its mean. This is useful for understanding how variable a set of data may be.
For example, the standard deviation may be used to allow one to predict failure
rates and/or to determine how much variability is acceptable in a final product.
The Standard Deviation for each sample was calculated in accordance with the following
The use of n-1 in the denominator instead of the more natural
n was used because if n (instead of n-1) were used, a biased estimate of the population
standard deviation would result. The use of n-1 corrects for this bias with small
The formula for standard deviation is:
In the formula, "n" is the count of the number of observations.
The distance from each observation (xi) to the calculated average (x-bar)
provides the basis for measuring variability. The closer these observations are
to the average, the smaller the standard deviation. If all observations are the
same, the standard deviation would be zero. The deviations are squared due to the
average being the "fulcrum" of the data (a balance point between those observations
greater than the average and those less than the average). If these deviations were
not squared, the sum would be zero. The square root of the sum is then taken to
get the value back into the units of the original data.
Breathability Test (WVTR): A measure of the breathability of a fabric is
the water vapor transmission rate (WVTR). Circular samples measuring three inches
(7.6 cm) in diameter are cut from each of the test materials, and a control of a
piece of CELGARD® 2500 sheet from the Hoechst Celanese Corporation of Charlotte,
NC. CELGARD® 2500 sheet is a microporous polypropylene sheet. Three samples
are prepared for each material. The test dish is a number 68-1 Vapometer pan distributed
by Thwing-Albert Instrument Company of Philadelphia, PA. One hundred milliliters
of water are poured into each Vapometer pan and individual samples of the test materials
and control material are placed across the open tops of the individual pans. Screw-on
flanges are tightened to form a seal along the edges of the pan, leaving the associated
test material or control material exposed to the ambient atmosphere over a 6.5 centimeter
diameter circle having an exposed area of approximately 33.17 square centimeters.
The pans are placed in a forced air oven at 100°F (32°C) for 24 hrs. The
oven is a constant temperature oven with external air circulating through it to
prevent water vapor accumulation inside. A suitable forced air oven is, for example,
a Blue M Power-O-Matic 60 oven distributed by Blue M Electric Company of Blue Island,
Illinois. Prior to placement in the oven the pans are weighed. After 24 hours, the
pans are removed from the oven and weighed again. The preliminary test water vapor
transmission rate values are calculated as follows: Test WVTR = (grams weight loss
over 24 hours) x 315.5 g/m2/24 hours.
The relative humidity within the oven is not specifically
controlled. Under predetermined set conditions of 100°F (32°C) and ambient
relative humidity, the WVTR for the CELGARD® 2500 control has been defined
to be 5000 grams per square meter for 24 hours. Accordingly, the control sample
is run with each test and the preliminary test values are corrected to set conditions
using the following equation:
Peel Strength Test (Peel): This test determines the bond strength between
component layers of bonded or laminated fabrics. Bond strength is the tensile force
required to separate the component layers of a textile under specified conditions.
In peel or delamination testing a laminate is tested for the amount of tensile force
required to pull a film layer apart from a nonwoven web layer. Values for the peel
strength are obtained using a width of fabric sample in approximately 6 x 4 inch
specimens (6 inch in the MD direction). The plies of the specimens are manually
separated for a distance of about 2 inches along the length of the specimen. One
layer is then clamped into each jaw of a tensile testing machine, and then subjected
to a constant rate of extension. The maximum force (i.e. peak load) needed to completely
separate the component layers of the fabric is determined. Two clamps, each with
two equal sized jaws, each measuring 1 inch parallel to the direction of load application
and 4 inches perpendicular to the application of load are used. The average peak
load of a series of samples is calculated. Results are expressed in units of weight
with higher numbers indicating a stronger bonded fabric. The sample is clamped ,
for example in an Instron Model TM, 1000, 1122, or 1130 available from the Instron
Corporation, 2500 Washington St., Canton, MA 02021, or a Sintech Tensile Tester,
Sintech QAD or Sintech Testworks available from Sintech, Inc., P.O. Box 14226, Research
Triangle Park, North Carolina 27709 or a Thwing-Albert, Model INTELLECT II, available
from Thwing- Albert Instrument Company, 10960 Dutton Road, Philadelphia, PA 19154.
The sample is then pulled apart for a distance of 2 inches at 180 degrees of separation
and the average peel strength recorded in grams. A constant rate of extension is
applied of 12 ± 0.4 in./min (300 ± 10 mm/min). The center of the CD web
width of the film side of the sample is covered with a 4 inch wide masking tape
or some other suitable material in order to prevent the film from ripping apart
during the test. The masking tape is only on one side of the laminate and so does
not contribute to the peel strength of the sample. For the purposes of this test
the scatter index is the standard deviation of all of the data points collected
in the specified peel region. The peel strength is the average force, expressed
in grams, that is required to separate the bonded fabric at 180 degrees angle over
a distance of two inches.
Utilizing the inventive method, a laminate is produced
with increased tear strength. The tear strength (as expressed through various Grab
Tensile tests) is much higher than expected for film/ nonwoven web laminates incorporating
metallocene-catalyzed polypropylene rather than conventional Ziegler-Natta catalyzed
polypropylene. Specifically, the strength is much higher than expected for metallocene-catalyzed
inelastic polypropylene obtained under the designation 3854 from the Exxon Chemical
Company. This increased tear strength is especially apparent in reviewing the Peak
Energy test values for the metallocene-catalyzed laminates and comparing them to
the values for the Ziegler-Natta catalyzed polypropylene laminate materials in Table
2. These increased tear strength values are even more surprising in view of the
Peak Energy test results for the single spunbond facing samples and the facing samples
in necked bonded laminates as seen in Tables 3 and 4. In each of these materials,
the Peak Energy values were higher for the Ziegter-Natta catalyzed materials as
opposed to the metallocene-catalyzed materials.
Furthermore, use of metallocene-catalyzed polyolefins allows
for finer fiber which appears to aid in simultaneous bonding and lamination. It
is theorized that such in-line processing avoids the high crystallinity which is
present in aged or pre-formed spunbond. The resulting laminate provides improved
tear resistance properties as can be seen through various test measures. This improvement
is in deference to the higher temperatures and pressures necessary to thermally
bond metallocene catalyzed based polypropylene spunbond fabric. Five to ten degrees
higher bond temperatures are normally required for this polymer, which reduces tensile
strength. While not intended to be limited by theory, it is theorized that the spunbond
fibers are able to withstand the heat at the bond points without becoming brittle
and yet transfer enough heat to the film component. Even at the same fabric strength,
the tear resistance is higher.
Therefore, polyolefins (i.e. polypropylene) with narrow
molecular weight distribution (i.e. single site catalyst) enable production of meltspun
fibers with significantly enhanced mechanical properties despite the fibers being
more difficult to bond thermally. An in-line process utilizing these materials produces
a composite with better than expected tear strength attributes.
While the specification has been described in detail with
respect to specific embodiments thereof, it will be appreciated that those skilled
in the art, upon attaining an understanding of the foregoing, may readily conceive
of alterations to, variations of, and equivalents to these embodiments. Accordingly,
the scope of the present invention should be assessed as that of the appended claims
and any equivalents thereto.