Note: Descriptions are shown in the official language in which they were submitted.
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LAMINATION OF BREATHABLE FILM USING
A RUBBER-COVERED ANVIL ROLL
FIELD OF INVENTION
The present invention relates to a prc~ess for laminating
breathable film using an anvil roll covered with a soft
material. The invention further concerns the product produced
thereby.
BACKGROUND OF THE INVENTION
The present invention relates to a breathable
film/nonwoven laminate having improved toughness (elongation)
and greater retention of barrier properties. The present
invention also relates to the process of producing the same
usi.~.g an anvil roll covered with a soft material.
Laminate materials have a wide variety of uses,
especially in the areas of absorbent articles and disposable
items. As used herein, the term "absorbent articles" refers
to devices which absorb and contain body exudates and, more
specifically, refers to devices that are placed against or in
proximity to the body of the wearer to absorb and contain the
various exudates discharged from the body. The term
"absorbent articles" is intended to include diapers, training
pants, incontinence devices and the like. The term
"disposable" is used herein to describe absorbent articles not
intended to be laundered or otherwise restored or reused as an
absorbent article.
Film/nonwoven laminates may be produced using thermal
point bonding. Traditionally thermal point bonding entails
passing the webs that are to be bonded together through the
nip of two steel rolls. Generally, one of the steel rolls is
engraved, or embossed, with a pattern. This roll is known as
the "pattern roll." The non-engraved roll is known as the
"anvil roll." During the lamination process, the pattern on
the pattern roll is imparted to the laminated web. Use of
steel anvil rolls tends to result in severe deformation of the
nonwoven fibers, resulting in a weak laminate.
A need, therefore, exists for a method of producing a
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film/nonwoven laminate having improved toughness without
causing severe deformation to the nonwoven fibers.
SUI~iARY OF THE INVENTION
It has now been found that lamination of breathable film
using an anvil roll covered with a soft material produces
laminates without the severe deformation of the nonwoven web
that often results from using two steel rolls. The reduced
deformation of the nonwoven web results in a laminate with
improved tensile properties and improved laminate elongation.
Greater laminate elongation is important because it indicates
a tougher material, i.e., one that is able to withstand
pulling longer before breaking. The process of the present
invention also maintains film integrity throughout the entire
~5 bonding procedure.
The lamination process of the present invention =equires
a patter.~. roll, an energy source and an anvil roll that is
covered with a soft material that deforms under nip pressure
but that also has adequate operational life.
Laminate materials produced according to the present
invention may be used in personal care absorbent articles and
in surgical gowns and d~Yapes and other forms of protective
apparel such as lab coats and workwear. Film/nonwoven
laminates produced according to the present invention are
especially useful in the outer coverings of personal care
absorbent articles, particularly diapers.
The foregoing and other features and advantages of the
present invention will become apparent from the following
detailed description of the presently preferred embodiments,
when read in conjunction with the accompanying examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary perspective view of a
film/nonwoven laminate constructed in accordance with the
present invention.
FIG. 2 is a schematic side view of the lamination process
of the present invention.
FIG. 3 is a partially cut-away top view of an exemplary
disposable garment which may utilize the laminate produced
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according to he present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to lamination of
breathable film and nonwoven webs using an 3nvi1 roll covered
with a soft material.
Referring now to the drawings wherein like reference
numerals represent the same or equivalent structure and, in
particular, to FIG. 1 of the drawings, there is illustrated a
film/nonwoven laminate 10 produced according to the present
invention. The laminate 10 includes a fibrous nonwoven web 12
and a polymeric film 14 bonded thereto.
The fibrous nonwoven web 12 may be, for example, necked
polypropylene spunbond, crimped polypropylene spunbond, bonded
carded webs, elastomeric spunbond or meltblown fabrics
produced from elastomeric resins. Fibrous nonwoven webs can
impart additional properties such as a softer, more cloth-like
feel to polymeric film. A more cloth-like feel is
particularly advantageous when the film is being used as a
barrier layer in, for example, outer covers for personal care
absorbent articles, surgical gowns and drapes, lab cats and
other forms of protective apparel.
The manufacture of fibrous non-woven webs is known. Such
webs may be formed from a number of processes including, but
not limited to, spunbonding and meltblowing processes.
Meltblown fibers are fibers formed by extruding a molten
thermoalastic material through a plurality of fine, usually
circular, capillaries of a meltblowing die as molten threads
or filaments into converging high-velocity, usually hot, gas
(e.g., air) streams which are flowing in the same direction as
the extruded filaments or threads of the molten thermoplastic
material so that the extruded filaments or threads are
attenuated, i.e., drawn or extended, to reduce their diameter.
The threads or filaments may be attenuated to microfiber
diameter which means the threads or filaments have an average
diameter not greater than about 75 microns (um), generally
from about 0.5 microns to about 50 microns, and more
particularly from about 2 microns to about 40 microns.
Thereafter, the meltblown fibers are carried by the high-
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velocity gas stream and are deposited on a collecting surface
to form a web of randomly disbursed meltblown fibers. The
meltblown process is well-known and is described, in various
patents and publications, including NRL Report 4364,
"Manufacture of Super-Fine Organic Fibers" by B.A. Wendt, E.L.
Boone and D.D. Fluharty; NRL Report 5265, "An Improved Device
for the Formation of Super-Fine Thermoplastic Fibers" by K.D.
Lawrence, R.T. Lukas and J.A. Young; U.S. Patent No. 3,676,242
to Prentice; and U.S. Patent No. 3,849,241 to Buntin et al.
The foregoing references are incorporated herein in by
reference in their entirety. 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.
Preferably the fibrous nonwoven web is polypropylene
spunbond. Spunbonded fibers are small diameter fibers that
are formed by extruding a molten thermoplastic material as
filaments from a plurality of fine, usually circular,
capillaries of a spinneret with the diameter of the extr~.:ded
filaments then being rapidly reduced as by, for example, non-
eductive or eductive fluid-drawing or other well-known
spunbonding mechanisms. The production of spunbonded non-
woven webs is illustrated in patents such as, for example,
U.S. Patent No. 4,340,563 to Appe1 et al.; U.S. Patent No.
3,802,817 to Matsuki et al.; U.S. Patent No. 3,692,618 to
Dorschner et al; U.S. Patent No. 3,542,615 to Dobo; U.S.
Patent No. 3,502,763 to Hartman; U.S. Patent No. 3,502,538 to
Peterson; U.S. Patent Nos. 3,341,394 and 3,338,992 to Kinney;
U.S. Patent No. 3,276,944 to Levy; and Canadian Patent No.
803,714 to Harmon. The disclosures of these patents are
herein incorporated by reference in their entirety.
Spunbonded fibers generally are not tacky when deposited onto
a collecting surface. Spunbonded fibers generally are
continuous and have average diameters (from a sample of at
least 10) larger than 7 microns and, more particularly, from
about 10 microns to about 20 microns.
For the film 14 that is laminated to the nonwoven web
12, a wide variety of thermoplastic films are useful. Such
films include, but are not limited to, polypropylene and/or
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polyethylene-based polyolefins in mono- or coex- executions.
Polypropylene films are preferred for lamination to
polypropylene spunbond.
A process for forming polymeric film 14 is shown in FIG.
2 of the drawings. Referring now to that figure, polymeric
film 14 is formed from an extrusion film apparatus 20 such as
a cast or blown unit. Typically, the apparatus 20 includes an
extruder 22. The polymeric material is prepared in a mixer 24
and directed to the extruder 22. The film 14 is extruded into
a pair of nip rollers 26, 28 one of which may be patterned so
as to impart an embossed pattern to the newly formed film 14.
From the extrusion film apparatus 20, film 14 is directed
to a film stretching unit 30 such as a machine direction
orienter which is commercially available from vendors such as
The Marshall and Williams Company of Providence, Rhode Island.
Such an a_~paratus 30 has a plurality of stretching rollers 32
that move at progressively faster speeds relative to the pair
~.;soosed befcre it. These rollers 32 apply an amount of
stress and thereby progressively stretch fil:r. 14 to a second
length in the machine direction of the film, which is the
direction of travel of film 14 through the process as shown in
FIG, 2. The stretch rollers 32 may be heated for better
processing. Film stretching unit 30 may also include rollers
(not shown) upstream and/or downstream from the stretch
rollers 32 that can be used to preheat the film 14 before
orienting it and/or to cool the film 14 after stretching it.
Preferably, the second, or stretched, length is from
about two to about six times, more preferably from about three
times to about four times, the original length of the film 14
prior to stretching.
Film 14 is then directed out of stretching unit 30 so that the
stress is removed and the film 14 is allowed to relax. Preferably,
a permanent elongation length of from about 1.5 times the original
length is retained after the stretched film is allowed to relax.
Lamination reinforces and protects the film. During the
laminating process, the film 14 is attached to the nonwoven web
12 to form a laminate 10.
Referring again to FIG. 2, there is also illustrated a
side view of the lamination process of the present invention.
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A conventional fibrous nonwoven web-forming apparatus 40, such
as a pair of spunbond machines, is used to form the fibrous
nonwoven web 12. The long, essentially continuous fibers 42
are deposited onto a forming wire 44 as an unbonded web 46.
The unbonded web 46 is then sent through a pair of bonding
rolls 48, 50 to bond the fibers together and increase the tear
strength of the resultant web 12. One or both of the rolls
48, 50 are often heated to aid bonding. Typically, one of the
rolls 48, 50 is also patterned so as to impart a discrete bond
pattern with a prescribed bond surface area to the web 12.
The other roll is usually a smooth anvil roll, but this roll
also may be patterned if desired. As used herein, the term
"smooth" means that the roll is not patterned.
Once the film 14 has been sufficiently stretched and the
Fibrous nonwoven web 12 has been formed, the two layers are
brought Together and laminated using thermal point bonding.
Thermal point bonding involves passing the film 14 and the
fibrous nonwoven web 12 through the nip formed between a pair
of rolls 52, 54. As with t~~.e bonding rolls 48, 50 at least
2C one of the laminating rolls is patterned to create a disc~~~a
bond pattern upon the resultant laminate 10. If desired,
bonding rolls 48, 50 may be omitted or used for light
compaction and the laminating nip between rolls 52, 54 may
serve to simultaneously bond the nonwoven web 12, as well as
form the laminate 10. Generally, the maximum bond point
surface area for a given area of surface on one side of the
laminate 10 will not exceed about 50% of the total surface
area. Any of a number of discrete bond patterns may be used.
Examples are disclosed in U.S. Patent No. 4,041,203 to Brook
et al., which is incorporated herein by reference. The
pattern roll 52 is a metal roll, preferably steel.
During lamination, the film is oriented against the non-
engraved roll 54, which is also known as the anvil roll. Such
orientation assists force distribution and prevents damage to
the film during the bonding process.
The anvil roll 54 is also made of metal, again preferably
steel. The anvil roll 54, however, is covered with a soft
material that deforms under nip pressure but that also has an
adequate operational life. The soft material generally has a
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surface roughness (Ra) of about 5 to about 250. Surface
roughness is measured with a surface roughness tester such as,
for example, the Surftest 211 produced by MTI Corporation.
The soft material must be softer and more conformable than
steel, such as rubber. Rubber-containing compounds may also
be useful such as, for example, a silicone rubber compound
with a Shore-A hardness of about 80-95. Preferably, a sleeve
(not shown) slides over the metal anvil roll 54 to provide the
soft, conformable surface. The sleeve deforms under the nip
pressure of lamination thereby creating a larger area over
which a constant nipping force is distributed. This, in turn,
results in a lower pressure required for lamination. The
pressure used during lamination according to the present
invention is from about 170 to about 230 psi (11.95-16.17
kg/cm2), depending on the relative softness of the sleeve
covering the anvil roll 54. The lower pressure, while enough
to laminate the incoming film 14 and nonwoven web 12,
eliminates the severe deformation of the nonwoven web 12 that
generally occurs during lamination. The resulting laminate 10
also shows improved tensile properties and laminate
elongat,;on, thus i:~dicating a tougher laminate material.
Preferably, the energy source used to assist lamination
is vn~rared heaters. Other sources, such as a hot air knife,
may also be used. The temperature on the pattern roll 52 is
between about 230°F (110°C) and about 260°F
(126.67°C). The
anvil roll 54 picks up heat and runs at about 150°F (65.57°C)
during steady state processing.
Once the laminate 10 exists, it may be wound up into a
roll 58 for subsequent processing. Alternatively, the
laminate 10 may continue in line for further processing or
conversion.
The process shown in FIG. 2 may also be used to create a
three layer laminate. The only modification to the previously
described process is to feed a supply 60 of a second fibrous
nonwoven web 12a into the pattern roll 52 and the anvil roll
54 on the side of the film 14 opposite that of the other
nonwoven web 12. One or both of the nonwoven webs 12 and 12a
may be formed directly in line, as illustrated with nonwoven
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web 12 in FIG. 2. Alternatively, one or both of the nonwoven
webs 12 and 12a may be in the form of a pre-formed roll 62 as
illustrated in FIG. 2 by nonwoven web 12a. In any event, the
second nonwoven web 12a is fed between the nip of the pattern
roll 52 and the anvil roll 54 and is laminated to film 14 in
the same manner as the first fibrous nonwoven web 12.
As previously stated, the laminate 10 produced according
to the present invention may be used in a wide variety of
applications including personal care absorbent articles such
as diapers, training pants, incontinence garments, surgical
gowns and drapes and protective apparel such as lab coats and
other workwear. A disposable garment 70, in this case a
diaper, is shown in FIG. 3. Although a diaper is shown in
rIG. 3, it will be understood that use of the laminate 10
produced according to the present invention is not limited to
such articles and may also be used in a wide variety of
applications. Referring again to FIG. 3, the disposable
garment 70 includes a liauid permeable top sheet or liner 72,.
a back sheet or outer cover 74 and an absorbent core 76
disposed between and contained by the liner 72 and the outer
ccver 74. Disposable garment 70 may also include some type of
fastening means 78 such as adhesive fastening tapes or
mechanical hook and loop type fasteners and stretch region 80.
Laminate 10 may be used to form various portions of
disposable garment 70 including, but not limited to, liner 72,
outer cover 74 and stretch region 80. Preferably, laminate 10
is used to form the outer cover 74 of disposable garment 70.
The advantages and other characteristics of the present
invention are best illustrated by the following examples. It
should be understood that the following examples are
illustrative and are not limiting.
Two sets of film/spunbond laminates were produced using
rubber and steel anvil rolls. The laminates bonded with the
rubber anvil roll displayed greater elongation compared to the
laminates bonded with the steel anvil roll. An analysis of
the resultant laminates by a scanning electron microscope
indicated that the increase in elongation in the material
laminated with the rubber anvil roll is due to the fact that
the spunbond fibers in the area of the bond points in those
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materials were flattened and indented into the film rather
than fused into the film as shown in the samples bonded with
the steel anvil roll.
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