U.S. patent application number 09/489095 was filed with the patent office on 2002-08-22 for high speed method of making plastic film and nonwoven laminates.
Invention is credited to Mortellite, Robert M., Mushaben, Thomas G., Wu, Pai-Chuan.
Application Number | 20020112809 09/489095 |
Document ID | / |
Family ID | 23563822 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020112809 |
Kind Code |
A1 |
Mortellite, Robert M. ; et
al. |
August 22, 2002 |
High speed method of making plastic film and nonwoven laminates
Abstract
Laminates of thermoplastic films and nonwoven fibrous webs are
made at high speeds on the order of about 700 fpm to about 1200
fpm. Bond strengths of film and nonwoven laminates are effectively
controlled to make breathable laminates at high speeds. Air cooling
devices cause the air to flow substantially parallel to the
extruded plastic web during drawdown and provide a plurality of
cooling air vortices to effectively cool the web. Film gauge
control is also achieved by the method.
Inventors: |
Mortellite, Robert M.;
(Maineville, OH) ; Mushaben, Thomas G.;
(Cincinnati, OH) ; Wu, Pai-Chuan; (Cincinnati,
OH) |
Correspondence
Address: |
David J Josephic
Wood Herron & Evans LLP
2700 Carew Tower
441 Vine Street
Cincinnati
OH
45202-2917
US
|
Family ID: |
23563822 |
Appl. No.: |
09/489095 |
Filed: |
January 21, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09489095 |
Jan 21, 2000 |
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09395627 |
Sep 14, 1999 |
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Current U.S.
Class: |
156/163 ;
156/229; 156/244.24 |
Current CPC
Class: |
B29C 48/08 20190201;
B32B 2309/14 20130101; B29C 48/9135 20190201; B29C 2035/1658
20130101; B32B 2305/28 20130101; B32B 2307/724 20130101; B32B
38/1825 20130101; B32B 2305/20 20130101; B29C 48/914 20190201; B32B
37/153 20130101; B32B 2307/7265 20130101; B32B 2038/0028
20130101 |
Class at
Publication: |
156/163 ;
156/229; 156/244.24 |
International
Class: |
C09J 001/00 |
Claims
What is claimed is:
1. a high speed method of making a laminate of a nonwoven fibrous
sheet and a microporous thermoplastic film comprising melt blending
a thermoplastic polymer and filler particles to form a
thermoplastic polymer composition, extruding a web of said molten
thermoplastic composition from a slot die through a cooling zone
into a nip of rollers to form a film at a speed greater than about
700 fpm, and introducing a nonwoven fibrous sheet into said nip of
rollers and controlling the temperature and compressive force
between the fibrous sheet and the film at the nip to bond the
surface of the fibrous sheet to the film and to form a laminated
sheet having bond strength between the film and the fibrous sheet
of about 100 to about 600 grams/inch as measured at room
temperature.
2. The method of claim 1 wherein said bond strengths are about 200
grams/inch to about 500 grams/inch.
3. The method of claim 1 comprising the further step of applying a
stretching force to the laminate at said speed to provide a
microporous laminate.
4. The method of claim 3 wherein the stretching force is an
incremental stretching force applied across the laminated sheet to
provide a cloth-like microporous laminate having a web to film bond
strength of about 100 to about 200 grams/inch.
5. The method of claim 1 wherein said laminate is formed at a speed
of about 700 fpm to about 1200 fpm.
6. The method of claim 1 wherein the composition comprises (a)
about 30% to about 45% by weight of a linear low density
polyethylene, (b) about 1 % to about 10% by weight of a low density
polyethylene, (c) about 40% to about 60% by weight calcium
carbonate filler particles.
7. The method of claim 6 wherein said melt blended composition
consists essentially of about 41% by weight linear low density
polyethylene, about 5% by weight low density polyethylene, about
45% by weight calcium carbonate filler particles, and about 5% by
weight high density polyethylene.
8. The method of claim 7 wherein said melt blended composition
further comprises about 3% by weight titanium dioxide and about 1%
by weight antioxidant/processing aid.
9. The method of claim 1 wherein said nip of rollers comprises a
metal embossing roller and a rubber roller and the compressive
force between said rollers is controlled to form an embossed film,
directing a stream of cooling gas to flow through said zone
substantially parallel to the surface of said web to cool the web
and form a film without draw resonance.
10. The method of claim 1 wherein the melt blended composition
comprises a thermoplastic polymer containing a dispersed phase of
particles selected from the group consisting of an inorganic filler
and an organic material.
11. The method of claim 1 wherein said fibrous sheet comprises
polyolefin fibers.
12. The method of claim 1 wherein said fibers are selected from the
group consisting of polypropylene, polyethylene, polyesters,
cellulose, rayon, nylon, and blends or coextrusions of two or more
of such fibers.
13. The method of claim 1 wherein the fibrous sheet has a weight
from about 5 to about 70 gms/yd.sup.2and the microporous film has a
thickness on the order of about 0.25 to about 10 mils.
14. The method of claim 13 wherein said fibrous sheet is formed
from staple fibers or filaments.
15. The method of claim 3 wherein said incremental stretching step
is conducted at ambient temperature.
16. The method of claim 3 wherein said incremental stretching step
is conducted at elevated temperature.
17. The method of claim 1 wherein said thermoplastic composition is
a polymer selected from the group consisting of polyethylene,
polypropylene, and copolymers thereof.
18. The method of claim 1 wherein said thermoplastic composition is
an elastomeric polymer.
19. The method of claim 18 wherein said elastomeric polymer is
selected from the group consisting of poly(ethylene-butene),
poly(ethylene-hexene), poly(ethylene-octene),
poly(ethylene-propylene), poly(styrene-butadiene-styrene),
poly(styrene-isoprene-styrene),
poly(styrene-ethylene-butylene-styrene), poly(ester-ether),
poly(ether-amide), poly(ethylene-vinylacetate),
poly(ethylene-methylacryl- ate), poly(ethylene-acrylic acid),
poly(ethylene butylacrylate), polyurethane,
poly(ethylene-propylene-diene), and ethylene-propylene rubber.
20. A high speed method of making a laminate of a microporous
thermoplastic film and nonwoven fibrous sheet comprising melt
blending a composition of (a) about 30% to about 45% by weight of a
linear low density polyethylene, (b) about 1 % to about 10% by
weight of a low density polyethylene, (c) about 40% to about 60% by
weight calcium carbonate filler particles, extruding a web of said
melt blended composition and a nonwoven fibrous sheet through a
cooling zone into a nip of rollers to form a film at a speed on the
order of at least about 700 fpm to about 1200 fpm, controlling the
temperature and compressive force between the fibrous sheet and the
film at the nip to bond the surface of the fibrous sheet to form a
laminated sheet having a bond strength between the film and the
fibrous sheet of about 200 to about 500 grams/inch at about room
temperature. applying an incremental stretching force to said
laminated sheet at said speed along lines substantially and
uniformly across said laminated sheet and throughout its depth to
provide a microporous laminate having a fibrous sheet to film bond
strength of about 100 to about 200 grams/inch.
21. The method of claim 20 wherein said melt composition further
contains high density polyethylene and titanium dioxide.
22. The method of claim 21 wherein the high density polyethylene is
contained in an amount of 5% by weight and the titanium dioxide is
contained in an amount of about 3% by weight.
23. The method of claim 20 wherein said linear low density
polyethylene is selected from the group consisting of
poly(ethylene-butene), poly(ethylene-hexene),
poly(ethylene-octene), poly(ethylene-propylene),
poly(styrene-butadiene-styrene), poly(styrene-isoprene-styrene),
poly(styrene-ethylene-butylene-styrene), poly(ester-ether),
poly(ether-amide), poly(ethylene-vinylacetate),
poly(ethylene-methylacryl- ate), poly(ethylene-acrylic acid),
poly(ethylene butylacrylate), polyurethane,
poly(ethylene-propylene-diene), and ethylene-propylene rubber.
24. The method of claim 20 wherein said fibers are selected from
the group consisting of polypropylene, polyethylene, polyesters,
cellulose, rayon, nylon, and blends of coextrusions of two or more
such fibers.
25. The method of claim 24 wherein the fibrous sheet has a weight
of from about 5 to about 70 grams/yd.sup.2and the microporous film
has a thickness on the order of about 0.25 to about 10 mils.
26. The method of claim 20 wherein said incremental stretching step
is conducted at ambient temperature.
27. The method of claim 20 wherein said incremental stretching step
is conducted at an elevated temperature.
Description
RELATED APPLICATION
[0001] This application is a continuation-in-part application of
application Ser. No. 09/395,627, filed on Sep. 14, 1999, which is
incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
[0002] Methods of making plastic film and nonwoven laminates date
back many years. For example, more than thirty years ago U.S. Pat.
No. 3,484,835 (1968) issued to Trounstine, et al., and it is
directed to embossed plastic film having desirable handling
characteristics and fabricating useful articles such as diapers.
Since that time, many patents have issued in the field. U.S. Pat.
No. 5,202,173 issued on Apr. 13, 1993, for an ultra-soft
thermoplastic film which was made by incrementally stretching the
embossed film to achieve breathability. The film may include
fillers. Polymer films of polycaprolactone (PCL) and starch polymer
or polyvinyl alcohol (PVOH) upon incremental stretching also
produce breathable products, as disclosed in U.S. Pat. Nos.
5,200,247 and 5,407,979. More recently, U.S. Pat. No. 5,865,926
issued for a method of making a cloth-like microporous laminate of
a nonwoven fibrous web and thermoplastic film having air and
moisture vapor permeabilities with liquid-barrier properties.
[0003] Methods of making microporous film products have also been
known for some time. For example, U.S. Pat. No. 3,832,267, to Liu,
teaches the melt-embossing of a polyolefin film containing a
dispersed amorphous polymer phase prior to stretching or
orientation to improve gas and moisture vapor transmission of the
film. According to the Liu '267 patent, a film of crystalline
polypropylene having a dispersed amorphous polypropylene phase is
first embossed prior to biaxially drawing (stretching) to produce
an oriented imperforate film having greater permeability. The
dispersed amorphous phase serves to provide microvoids to enhance
the permeability of the otherwise imperforate film to improve
moisture vapor transmission (MVT). The embossed film is preferably
embossed and drawn sequentially.
[0004] In 1976, Schwarz published a paper which described polymer
blends and compositions to produce microporous substrates (Eckhard
C. A. Schwartz (Biax-Fiberfilm), "New Fibrillated Film Structures,
Manufacture and Uses", Pap. Synth. Conf. (TAPPI), 1976, pages
33-39). According to this paper, a film of two or more incompatible
polymers, where one polymer forms a continuous phase and a second
polymer forms a discontinuous phase, upon being stretched will
phase separate thereby leading to voids in the polymer matrix and
increasing the porosity of the film. The continuous film matrix of
a crystallizable polymer may also be filled with inorganic filler
such as clay, titanium dioxide, calcium carbonate, etc., to provide
microporosity in the stretched polymeric substrate.
[0005] Many other patents and publications disclose the phenomenon
of making microporous thermoplastic film products. For example,
European patent 141592 discloses the use of a polyolefin,
particularly ethylene vinyl acetate (EVA) containing a dispersed
polystyrene phase which, when stretched, produces a voided film
which improves the moisture vapor permeability of the film. This EP
'592 patent also discloses the sequential steps of embossing the
EVA film with thick and thin areas followed by stretching to first
provide a film having voids which, when further stretched, produces
a net-like product. U.S. Pat. Nos. 4,452,845 and 4,596,738 also
disclose stretched thermoplastic films where the dispersed phase
may be a polyethylene filled with calcium carbonate to provide the
microvoids upon stretching. Later U.S. Pat. Nos. 4,777,073;
4,814,124; and 4,921,653 disclose the same processes described by
the above-mentioned earlier publications involving the steps of
first embossing a polyolefin film containing a filler and then
stretching that film to provide a microporous product.
[0006] With reference to U.S. Pat. Nos. 4,705,812 and 4,705,813,
microporous films have been produced from a blend of linear low
density polyethylene (LLDPE) and low density polyethylene (LDPE)
with barium sulfate as the inorganic filler having an average
particle diameter of 0.1-7 microns. It is also known to modify
blends of LLDPE and LDPE with a thermoplastic rubber such as
Kraton. Other patents, such as U.S. Pat. No. 4,582,871, disclose
the use of thermoplastic styrene block tripolymers in the
production of microporous films with other incompatible polymers
such as styrene. There are other general teachings in the art such
as the disclosures in U.S. Pat. Nos. 4,472,328 and 4,921,652.
[0007] Relevant patents regarding extrusion lamination of
unstretched nonwoven webs include U.S. Pat. Nos. 2,714,571;
3,058,868; 4,522,203; 4,614,679; 4,692,368; 4,753,840 and
5,035,941. The above '868 and '368 patents disclose stretching
extruded polymeric films prior to laminating with unstretched
nonwoven fibrous webs at pressure roller nips. The '203 and '941
patents are directed to co-extruding multiple polymeric films with
unstretched nonwoven webs at pressure roller nips. The '840 patent
discloses preforming nonwoven polymeric fiber materials prior to
extrusion laminating with films to improve bonding between the
nonwoven fibers and films. More specifically, the '840 patent
discloses conventional embossing techniques to form densified and
undensified areas in nonwoven base plies prior to extrusion
lamination to improve bonding between nonwoven fibrous webs and
films by means of the densified fiber areas. The '941 patent also
teaches that unstretched nonwoven webs that are extrusion laminated
to single ply polymeric films are susceptible to pinholes caused by
fibers extending generally vertically from the plane of the fiber
substrate and, accordingly, this patent discloses using multiple
co-extruded film plies to prevent pinhole problems. Furthermore,
methods for bonding loose nonwoven fibers to polymeric film are
disclosed in U.S. Pat. Nos. 3,622,422; 4,379,197 and 4,725,473.
[0008] It has also been known to stretch nonwoven fibrous webs
using intermeshing rollers to reduce basis weight and examples of
patents in this area are U.S. Pat. Nos. 4,153,664 and 4,517,714.
The '664 patent discloses a method of incremental cross direction
(CD) or machine direction (MD) stretching nonwoven fibrous webs
using a pair of interdigitating rollers to strengthen and soften
nonwoven webs. The '664 patent also discloses an alternative
embodiment wherein the nonwoven fibrous web is laminated to the
thermoplastic film prior to intermesh stretching.
[0009] Efforts have also been made to make breathable non-woven
composite barrier fabrics which are impervious to liquids, but
which are permeable to water vapor. U.S. Pat. No. 5,409,761 is an
example of a fabrication process from the patent art. According to
this '761 patent, a nonwoven composite fabric is made by
ultrasonically bonding a microporous thermoplastic film to a layer
of nonwoven fibrous thermoplastic material. These methods and other
methods of making breathable laminates of nonwoven and
thermoplastic materials tend to involve expensive manufacturing
techniques and/or expensive raw materials. U.S. Pat. No. 5,865,926
discloses a method of making a microporous laminate of a nonwoven
web and thermoplastic film which is conducted on high-speed
production machinery on the order of about 200-500 fpm. While
methods disclosed in this '926 patent were very satisfactory for
producing cloth-like microporous laminates of a nonwoven fibrous
web and thermoplastic film, when operating machinery for producing
a laminate by extrusion lamination in excess of 500 fpm,
satisfactory bond strengths were difficult to achieve. In
particular, at high speeds, temperature control of the
thermoplastic extrudate at the nip above its softening point to
form a film laminated to the fibrous web in order to achieve
satisfactory bond strengths prior to extrusion lamination is a
significant problem.
[0010] U.S. Pat. No. 5,865,926 discloses a method of making a
microporous laminate of a nonwoven web and thermoplastic film which
is conducted on high-speed production machinery on the order of
about 200-500 fpm. While methods disclosed in this '926 patent were
satisfactory when operating machinery for producing a laminate by
extrusion lamination in excess of 500 fpm, satisfactory bond
strengths were difficult to achieve. In particular, at high speeds
of about 700-1200 fpm. Temperature control of the thermoplastic
extrudate at the nip for bonding the film to the fibrous web was
also difficult to achieve.
[0011] Notwithstanding the extensive development of the art for
making plastic films, breathable microporous films and laminates to
provide air and moisture vapor permeabilities with liquid-barrier
properties, further improvements are needed. In particular,
improvements are desired for producing microporous film products
and nonwoven laminates on high-speed production machinery without
draw resonance. Also, in extrusion lamination of film and nonwoven
webs, it has been difficult to achieve target bond levels at high
speeds while maintaining the appearance of fabric and soft
feel.
SUMMARY OF THE INVENTION
[0012] This invention is directed to a method of making a laminate
of a thermoplastic film and a nonwoven fibrous web. The method is
particularly advantageous for operating on high-speed production
machinery at speeds greater than about 700 fpm, preferably about
700-1200 fpm. It has been found that target bond levels of, for
example, 100 gms/cm (about 250 grams/inch) between the film and the
nonwoven are achieved at line speeds of 900 fpm, or more. Such bond
strengths enable the laminate to be incrementally stretched in line
at high speeds to create microporosity in a cloth-like laminate
without adverse effects on the laminate such as breakage and web
separation.
[0013] The method of this invention involves lamination by
extrusion of a microporous-formable thermoplastic film with a
nonwoven fibrous web. The microporous-formable thermoplastic
composition of the film may comprise a blend of a thermoplastic
polymer and a mechanical pore-forming agent such as an inorganic
filler (CaCO.sub.3). The pore-forming agent in the film of the
laminate is then activated upon incremental stretching to form a
microporous laminate of the fibrous web and film. This unique
method not only provides economies in manufacturing breathable
laminates, but also enables their production on high-speed
machinery on the order of about 700-1200 fpm.
[0014] The method involves melting a microporous-formable
thermoplastic composition and slot-die extruding a web of that
composition through a cooling zone into a nip of rollers with a
nonwoven fibrous web to form a laminate at a speed greater than
about 700 feet per minute (fpm). A stream of cooling gas (air) is
directed at the web during its drawdown into a film. The air flow
through the cooling zone is substantially parallel to the surface
of the web to cool the web and form a film without draw
resonance.
[0015] In the preferred form of the method, the effectiveness of
the cooling gas is enhanced by creating a plurality of vortices of
the gas as the stream moves through the zone to cool the web. The
vortices enhance the effectiveness of the cooling gas by mixing the
cooling gas and making the flow of the cooling gas turbulent in the
cooling zone. A cooling device is used to create the vortices and
make the gas stream move in different directions parallel to the
movement of the web. Alternatively, the gas stream moves primarily
in the same direction as the web movement or in a direction
opposite to the movement of the web.
[0016] In the slot die extrusion lamination of the plastic web or
film to a nonwoven fibrous web, a nonwoven fibrous web is
introduced into the nip of rollers and the lamination temperature
is controlled by the cooling gas to control target bond levels at
high speeds of extrusion lamination. For example, target bond
levels between the plastic film and the nonwoven web are achieved
at speeds in excess of about 700 fpm even up to about 1200 fpm, or
more. Target bond levels of, for example, 100 gms/cm (about 250
grams/inch) between the film and nonwoven are achieved at line
speeds on the order of 900 fpm for commercial purposes. The
compressive force between the web and the film at the nip is
controlled to bond the surface of the web to form a laminated
sheet. Furthermore, even at high line speeds the film gauge is
controlled without draw resonance. For example, a fixed film basis
weight of about 40 grams per square meter (gsm) is achieved at 900
fpm. Thus, the method of cooling eliminates draw resonance which
otherwise may normally be encountered under such conditions.
[0017] According to the invention, breathable laminates which are
permeable to air and water vapor, but are a barrier to liquid, are
produced. These breathable laminates are made from a
microporous-formable thermoplastic composition comprising a
thermoplastic polymer and filler particles. Upon slot-die extrusion
of such composition, followed by applying a stretching force to the
film at high speeds along lines substantially and uniformly across
the film and throughout its depth, a microporous film is formed.
Breathable laminates are made when a nonwoven fibrous web is
laminated to the film during the extrusion. The effectiveness of
the cooling gas is enhanced by creating a plurality of vortices of
the gas as the stream moves through the cooling zone to cool the
web during extrusion lamination. Thereafter, preferably an
incremental stretching force is applied to the film or the laminate
at high speeds substantially and uniformly across the film and
throughout its depth to provide a microporous laminate of film and
nonwoven. Tentering may also be used to stretch the laminate.
[0018] Other benefits, advantages and objectives of this invention
will be further understood with reference to the following detailed
description.
DETAILED DESCRIPTION OF THE INVENTION
[0019] It is a primary objective of this invention to produce films
laminated to nonwoven fibrous webs on high-speed production
machinery. It is the further objective of the method to produce
breathable laminated products of regular gauge without draw
resonance. It is another objective to produce such laminates having
satisfactory bond strengths while maintaining the appearance of a
fabric or cloth having suitable moisture vapor transmission rates
and air permeability while maintaining liquid-barrier
properties.
[0020] The high speed method of making a laminate of a nonwoven
fibrous web and a mircroporous thermoplastic film comprises melt
blending a thermoplastic polymer and filler particles to form a
thermoplastic polymer composition, extruding a web of said molten
thermoplastic composition from a slot die through a cooling zone
into a nip of rollers to form a film at a speed grater than about
700 fpm, and introducing a nonwoven fibrous web into said nip of
rollers and controlling the temperature and compressive force
between the web and the film at the nip to bond the surface of the
web to the film and to form a laminated sheet having a bond
strength between the film and the web of about 100 to about 600
grams/inch when measured at about room temperature. Preferably,
bond strengths are about 200 grams/inch to about 500 grams/inch to
facilitate incremental stretching at about 700-1200 fpm to provide
a microporous laminate. The incremental stretching force is applied
across the laminated sheet to provide a cloth-like microporous
laminate having a web to film bond strength of about 100 to about
200 grams/inch.
[0021] In a preferred mode, the high speed method of making a
microporous thermoplastic film involves melt blending a composition
comprising
[0022] (a) about 30% to about 45% by weight of a linear low density
polyethylene (LLDPE),
[0023] (b) about 1% to about 10% by weight of a low density
polyethylene (LDPE), and
[0024] (c) about 40% to about 60% by weight calcium carbonate
filler particles of about 0.1 to 1 micron.
[0025] The melt-blended composition is slot-die extruded as a web
through a cooling zone into a nip of rollers to form a film at
speeds in the order of about 700 to about 1200 fpm without draw
resonance. A device for directing a stream of cooling gas to flow
in the cooling zone substantially parallel to the web surface is
shown, for example, in U.S. Pat. Nos. 4,718,178 and 4,779,355. The
entire disclosure of these patents is incorporated herein by
reference as examples of devices which may be employed to provide
enhanced effectiveness of the cooling gas by creating a plurality
of vortices of the gas as the stream moves through the cooling zone
to cool the web. Thereafter, an incremental stretching force is
applied to the film at high speeds along lines substantially and
uniformly across the film and throughout its depth to provide a
microporous film.
[0026] The blend of LLDPE and LDPE within the above approximate
ranges of components enables the production of microporous film at
high speed when balanced with the prescribed amount of calcium
carbonate.
[0027] In particular, the LLDPE is present in an amount of about
30% to about 45% by weight in order to provide a sufficient amount
of matrix to carry the calcium carbonate filler particles thereby
enabling the film to be handled and stretched without pin holing
and breakage. The LDPE in an amount of about 1% to about 10% by
weight also contributes to the production of film without pin
holing and enables the high speed production without draw
resonance. The polymeric matrix is balanced with an amount of about
40% to about 60% by weight of calcium carbonate particles having an
average particle diameter of preferably about 1 micron to achieve a
sufficient moisture vapor transmission rate (MVTR) in the range of
about 1000 gms/m.sup.2/day to 4500 gms/m.sup.2/day as measured by
using the ASTM E96E method. Furthermore, the melt-blended
composition may include a triblock polymer in an amount of about 0%
to about 6% by weight to facilitate stretching in high-speed
production without breakage. Other components such as about 5% by
weight high density polyethylene (HDPE) and about 1% by weight
antioxidants/processing aids are used. An incremental stretching
force may be applied in line to the formed film under ambient
conditions or at an elevated temperature at speeds greater than
about 700 fpm along lines substantially uniformly across the film
and throughout it depth to provide a microporous film.
[0028] For instance, a nonwoven fibrous web is introduced into the
nip of rollers along with the microporous-formable thermoplastic
extrudate at 700 to 1200 fpm. The compressive force between the
fibrous web and the extrudate is controlled to bond one surface of
the web to the film and form a laminate. The laminate is then
incrementally stretched along lines substantially uniformly across
the laminate and throughout its depth to render the film
microporous. The laminate may be stretched in both the cross
direction (CD) and the machine direction (MD) to provide breathable
cloth-like liquid barriers capable of transmitting moisture vapor
and air.
A. Materials for the Method
[0029] The thermoplastic polymer for the film preferably is of the
polyolefin type and may be any of the class of thermoplastic
polyolefin polymers or copolymers that are processable into a film
or for direct lamination by melt extrusion onto the fibrous web. A
number of thermoplastic copolymers suitable in the practice of the
invention are of the normally-solid oxyalkanoyl polymers or
dialkanoyl polymers represented by poly(caprolactone) blended with
polyvinylalcohol or starch polymers that may be film-formed. The
olefin based polymers include the most common ethylene or propylene
based polymers such as polyethylene, polypropylene, and copolymers
such as ethylene vinylacetate (EVA), ethylene methyl acrylate (EMA)
and ethylene acrylic acid (EAA), or blends of such polyolefins.
Other examples of polymers suitable for use as films include
elastomeric polymers. Suitable elastomeric polymers may also be
biodegradable or environmentally degradable. Suitable elastomeric
polymers for the film include poly(ethylene-butene),
poly(ethylene-hexene), poly(ethylene-octene),
poly(ethylene-propylene), poly(styrene-butadiene-styrene),
poly(styrene-isoprene-styrene),
poly(styrene-ethylene-butylene-styrene), poly(ester-ether),
poly(ether-amide), poly(ethylene-vinylacetate),
poly(ethylene-methylacryl- ate), poly(ethylene-acrylic acid),
poly(ethylene butylacrylate), polyurethane,
poly(ethylene-propylene-diene), ethylene-propylene rubber. This new
class of rubber-like polymers may also be employed and they are
generally referred to herein as metallocene polymers or polyolefins
produced from single-cite catalysts. The most preferred catalysts
are known in the art as metallocene catalysts whereby ethylene,
propylene, styrene and other olefins may be polymerized with
butene, hexene, octene, etc., to provide elastomers suitable for
use in accordance with the principles of this invention, such as
poly(ethylene-butene), poly(ethylene-hexene),
poly(ethylene-octene), poly(ethylene-propylene), and/or polyolefin
terpolymers thereof.
[0030] The microporous-formable film composition can be achieved by
formulating a thermoplastic polymer with suitable additives and
pore-forming fillers to provide an extrudate or film for lamination
with the nonwoven web. Calcium carbonate and barium sulfate
particles are the most common fillers. Microporous-formable
compositions of polyolefins, inorganic or organic pore-forming
fillers and other additives to make microporous sheet materials are
known. This method may be done in line and provides economies in
manufacturing and/or materials over known methods of making
laminates. In addition, as developed above, microporous-formable
polymer compositions may be obtained from blends of polymers such
as a blend of an alkanoyl polymer and polyvinyl alcohol as
described in U.S. Pat. No. 5,200,247. In addition, blends of an
alkanoyl polymer, destructured starch and an ethylene copolymer may
be used as the microporous-formable polymer composition as
described in U.S. Pat. No. 5,407,979. With these polymer blends, it
is unnecessary to use pore-forming fillers to provide microporosity
upon incremental stretching. Rather, the different polymer phases
in the film themselves, when the film is stretched at ambient or
room temperature, produce microvoids.
[0031] The nonwoven fibrous web may comprise fibers of
polyethylene, polypropylene, polyesters, rayon, cellulose, nylon,
and blends of such fibers. A number of definitions have been
proposed for nonwoven fibrous webs. The fibers are usually staple
fibers or continuous filaments. As used herein "nonwoven fibrous
web" is used in its generic sense to define a generally planar
structure that is relatively flat, flexible and porous, and is
composed of staple fibers or continuous filaments. For a detailed
description of nonwovens, see "Nonwoven Fabric Primer and Reference
Sampler" by E. A. Vaughn, Association of the Nonwoven Fabrics
Industry, 3d Edition (1992).
[0032] In a preferred form, the microporous laminate employs a film
having a gauge or a thickness between about 0.25 and 10 mils and,
depending upon use, the film thickness will vary and, most
preferably, in disposable applications is the order of about 0.25
to 2 mils in thickness.
[0033] The nonwoven fibrous webs of the laminated sheet normally
have a weight of about 5 grams per square yard to 75 grams per
square yard preferably about 20 to about 40 grams per square yard.
The composite or laminate can be incrementally stretched in the
cross direction (CD) to form a CD stretched composite. Furthermore,
CD stretching may be followed by or preceded by stretching in the
machine direction (MD) to form a composite which is stretched in
both CD and MD directions. As indicated above, the microporous
films or laminates may be used in many different applications such
as baby diapers, baby training pants, catamenial pads and garments,
and the like where moisture vapor and air transmission properties,
as well as fluid barrier properties, are needed.
B. Stretchers for the Microporous-Formable Laminates
[0034] A number of different stretchers and techniques may be
employed to stretch the starting or original laminate of a nonwoven
fibrous web and microporous-formable film. These laminates of
nonwoven carded fibrous webs of staple fibers or nonwoven
spun-bonded fibrous webs may be stretched with the stretchers and
techniques described as follows:
1. Diagonal Intermeshing Stretcher
[0035] The diagonal intermeshing stretcher consists of a pair of
left hand and right hand helical gear-like elements on parallel
shafts. The shafts are disposed between two machine side plates,
the lower shaft being located in fixed bearings and the upper shaft
being located in bearings in vertically slidable members. The
slidable members are adjustable in the vertical direction by wedge
shaped elements operable by adjusting screws. Screwing the wedges
out or in will move the vertically slidable member respectively
down or up to further engage or disengage the gear-like teeth of
the upper intermeshing roll with the lower intermeshing roll.
Micrometers mounted to the side frames are operable to indicate the
depth of engagement of the teeth of the intermeshing roll.
[0036] Air cylinders are employed to hold the slidable members in
their lower engaged position firmly against the adjusting wedges to
oppose the upward force exerted by the material being stretched.
These cylinders may also be retracted to disengage the upper and
lower intermeshing rolls from each other for purposes of threading
material through the intermeshing equipment or in conjunction with
a safety circuit which would open all the machine nip points when
activated.
[0037] A drive means is typically utilized to drive the stationery
intermeshing roll. If the upper intermeshing roll is to be
disengageable for purposes of machine threading or safety, it is
preferable to use an antibacklash gearing arrangement between the
upper and lower intermeshing rolls to assure that upon reengagement
the teeth of one intermeshing roll always fall between the teeth of
the other intermeshing roll and potentially damaging physical
contact between addenda of intermeshing teeth is avoided. If the
intermeshing rolls are to remain in constant engagement, the upper
intermeshing roll typically need not be driven. Drive may be
accomplished by the driven intermeshing roll through the material
being stretched.
[0038] The intermeshing rolls closely resemble fine pitch helical
gears. In the preferred embodiment, the rolls have 5.935" diameter,
45.degree. C. helix angle, a 0.100" normal pitch, 30 diametral
pitch, 141/2.degree. pressure angle, and are basically a long
addendum topped gear. This produces a narrow, deep tooth profile
which allows up to about 0.090" of intermeshing engagement and
about 0.005" clearance on the sides of the tooth for material
thickness. The teeth are not designed to transmit rotational torque
and do not contact metal-to-metal in normal intermeshing stretching
operation.
2. Cross Direction Intermeshing Stretcher
[0039] The CD intermeshing stretching equipment is identical to the
diagonal intermeshing stretcher with differences in the design of
the intermeshing rolls and other minor areas noted below. Since the
CD intermeshing elements are capable of large engagement depths, it
is important that the equipment incorporate a means of causing the
shafts of the two intermeshing rolls to remain parallel when the
top shaft is raising or lowering. This is necessary to assure that
the teeth of one intermeshing roll always fall between the teeth of
the other intermeshing roll and potentially damaging physical
contact between intermeshing teeth is avoided. This parallel motion
is assured by a rack and gear arrangement wherein a stationary gear
rack is attached to each side frame in juxtaposition to the
vertically slidable members. A shaft traverses the side frames and
operates in a bearing in each of the vertically slidable members. A
gear resides on each end of this shaft and operates in engagement
with the racks to produce the desired parallel motion.
[0040] The drive for the CD intermeshing stretcher must operate
both upper and lower intermeshing rolls except in the case of
intermeshing stretching of materials with a relatively high
coefficient of friction. The drive need not be antibacklash,
however, because a small amount of machine direction misalignment
or drive slippage will cause no problem. The reason for this will
become evident with a description of the CD intermeshing
elements.
[0041] The CD intermeshing elements are machined from solid
material but can best be described as an alternating stack of two
different diameter disks. In the preferred embodiment, the
intermeshing disks would be 6" in diameter, 0.031" thick, and have
a full radius on their edge. The spacer disks separating the
intermeshing disks would be 51/2" in diameter and 0.069" in
thickness. Two rolls of this configuration would be able to be
intermeshed up to 0.231" leaving 0.019" clearance for material on
all sides. As with the diagonal intermeshing stretcher, this CD
intermeshing element configuration would have a 0.100" pitch.
3. Machine Direction Intermeshing Stretcher
[0042] The MD intermeshing stretching equipment is identical to the
diagonal intermeshing stretch except for the design of the
intermeshing rolls. The MD intermeshing rolls closely resemble fine
pitch spur gears.
[0043] In the preferred embodiment, the rolls have a 5.933"
diameter, 0.100" pitch, 30 Diametral pitch, 141/2.degree. pressure
angle, and are basically a long addendum, topped gear. A second
pass was taken on these rolls with the gear hob offset 0.010" to
provide a narrowed tooth with more clearance. With about 0.090" of
engagement, this configuration will have about 0.010" clearance on
the sides for material thickness.
4. Incremental Stretching Technique
[0044] The above described diagonal, CD or MD intermeshing
stretchers may be employed to produce the incrementally stretched
laminate of nonwoven fibrous web and microporous-formable film to
form the microporous laminate of this invention. The stretching
operation is usually employed on an extrusion laminate of a
nonwoven fibrous web of staple fibers or spun-bonded filaments and
microporous-formable thermoplastic film. In one of the unique
aspects of this invention a laminate of a nonwoven fibrous web of
spun-bonded filaments may be incrementally stretched to provide a
very soft fibrous finish to the laminate that looks like cloth. The
laminate of nonwoven fibrous web and microporous-formable film is
incrementally stretched using, for instance, the CD and/or MD
intermeshing stretcher with one pass through the stretcher with a
depth of roller engagement at about 0.025 inch to 0.120 inch at
speeds from about 700 fpm to 1200 fpm or faster. The results of
such incremental or intermesh stretching produces laminates that
have excellent breathability and liquid-barrier properties, yet
provide superior bond strengths and soft cloth-like textures.
[0045] The following example illustrates the method of making
laminates of this invention. In light of the example and this
further detailed description, it is apparent to a person of
ordinary skill in the art that variations thereof may be made
without departing from the scope of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] The invention is further understood with reference to the
drawings in which:
[0047] FIG. 1 is a schematic of an in line extrusion lamination and
incremental stretching apparatus for making the microporous
laminate of this invention.
[0048] FIG. 2 is a cross sectional view taken along the line 2-2 of
FIG. 1 illustrating the intermeshing rollers in diagrammatic
form.
[0049] FIG. 3 is an enlarged view of the die, cooling devices and
embossing rollers arrangement, showing the substantially parallel
air flow with vortices.
EXAMPLE
[0050] Blends of LLDPE, LDPE and HDPE having the compositions
reported in the following TABLE I were extruded to form laminates
of films and nonwovens which were then incrementally stretched to
provide microporous laminates.
1 TABLE I Formulation (by wt.): CaCO.sub.3 45 LLDPE 41 LDPE 5 HDPE
5 TiO.sub.2 3 Antioxidant/processing aid 1 Basis Weight
(gms/m.sup.2) 40 Gauge (mils) 1.2 Line Speed (fpm) 900 ACD No. 1
(cfm/foot) 68 ACD No. 2 (cfm/foot) 113 Web Stability Good, without
draw resonance
[0051] The formulation of TABLE I was extruded into laminates of
films and nonwovens employing an extrusion apparatus as shown
diagramatically in FIG. 1. The formulation of the EXAMPLE was fed
from an extruder 1 through slot die 2 to form the extrudate 6 into
the nip of a rubber roll 5 and a metal roll 4 with two air cooling
devices (ACD), ACD No. 1 and ACD No. 2, shown by numbers 3A and 3B
on the drawing. There is an incoming web of fibrous material 9 from
roller 13 which is also introduced into the nip of the rubber roll
5 and metal roll 4. In the EXAMPLE, the laminate was produced for
subsequent incremental stretching to form the microporous film. As
shown in TABLE I, a polyethylene film 6 on the order of about 1.2
mils in thickness was made at a speed of about 900 fpm, which was
taken off at roller 7. The ACDs have dimensions approximating the
web width with a sufficient manifold sized to deliver the cooling
air. These ACDs are described in more detail in the above mentioned
U.S. Pat. Nos. 4,718,178 and 4,779,355 Pat. The air velocity blown
through the nozzle of ACD 3A and against the extrudate 6 is about
4000 fpm at the exit of the nozzle, and air volume is 68 cfm per
foot. The air velocity of ACD 3B is about 6800 fpm at the exit of
the nozzle, and the air volume is 113 cfm per foot. The ACD 3A is
located about 3.7 inches (95 mm) from the die and about 1 inch (25
mm) from the web 6. The ACD 3B is located on the opposite side of
the web 6 about 11.2 inches (2.85 mm) from the die and about 0.6
inches (15 mm) from the web. The nip of the rubber roll 5 and metal
roll 4 is located about 29 inches (736 mm) from the die. The
compressive force at the nip and the ACDs are controlled such that
the laminate of the film and nonwoven is made without pin holing
and without draw resonance. The melt temperatures from the slot die
feed zone to the screw tip of extruders A and B (not shown) were
maintained to provide an extrudate temperature of about 243.degree.
C. with cooling gas from the ACDs 3A and 3B decreasing the web
temperatures to 211.degree. C. -181.degree. C. before entering the
nip to form the laminate 12.
[0052] The laminate 12 is a precursor of film and nonwoven,
typically spunbond polypropylene or polyethylene. In this EXAMPLE
the nonwoven is spunbond polypropylene. The following TABLE II
reports the results of rolls 1-5 of laminates made at about 900 fpm
under the above conditions to produce a satisfactory average bond
strength of about 256 grams/inch, within a range of about 191 to
about 324 grams/inch. Other properties are also recorded in TABLE
II.
2 TABLE II Roll 1 Roll 2 Roll 3 Roll 4 Roll 5 Average Film Basis
Wt. (gsm) 44.86 42.66 42.15 43.50 42.91 43.22 Laminate Basis Wt.
(gsm) 62.96 60.96 61.46 62.44 65.88 62.74 Bond (grams/inch) 191 324
226 299 238 256 Film Tensile Properties Break MD 1721 1522 1529
1475 1247 1499 (grams/inch) CD 1075 968 973 779 813 922 20% MD 743
786 751 785 781 769 (grams/inch) CD 639 595 588 584 592 600 40% MD
727 763 733 767 764 751 (grams/inch) CD 601 589 574 553 580 579
Elongation MD 523 488 492 476 405 477 (%) CD 606 574 571 493 495
548 Impact Strength F.sub.50 (grams) ASTM D1709 108 168 170 178 210
180
[0053] Bond strengths were measured by the following peel bond
strength method of TABLE Ill.
3TABLE III Peel Bond Strength Measurement The peel bond strength
measurement is done according to the following well-established
conventional technique: 1. A 6" strip at 1" width is cut along the
machine direction. 2. The initial peel (separation) is made by hand
to separate the precursor film and the nonwoven. 3. The precursor
film portion is attached to one jaw of the Instron tester and the
nonwoven is attached to the other jaw of the Instron tester. 4. The
Instron is set at 12"/min of cross head speed for peeling the
precursor film and the nonwoven. 5. The force (grams) of peel is
recorded while peeling the 1" strip.
[0054] As shown schematically in FIG. 1, where the incoming
laminate 12 at ambient temperature was passed through temperature
controlled rollers 20 and 21 before CD and MD incremental
stretching rollers ( 10 and 11, and 10"and 11"), the temperatures
and the depths of engagements can be controlled. In brief, moisture
vapor transmission rates (MVTRs) for the microporous film and
nonwoven laminates on the order of about 1200-2400 gms/m.sup.2/day
(ASTM E96E) were achieved.
[0055] It has been found that laminates having bond strengths on
the order of about 100 grams/inch to about 600 grams/inch of peel
strength are necessary for intermeshing to provide a cloth-like
mircroporous composite. Preferably, the bond strengths before CD
and MD intermeshing stretching are about 200 grams/inch to about
500 grams/inch. The measured peel strength at the high end of about
600 grams/inch may vary depending upon the nonwoven used, its type
(spunbonded polypropylene and/or spunbonded polyethylene), or its
weight of about 15 gsm or 50 gsm. A satisfactory precursor having
the preferred peel bond strengths of between about 200 grams/inch
and 500 grams/inch will produce a cloth-like microporous composite
using CD and MD intermeshing rollers have peel bond strengths
between about 100 grams/inch to about 200 grams/inch. In summary,
in order to provide breathable composites having the desired
breathability and bond strength between the film and the nonwoven,
it is essential to control the bond strength in the film extrusion
lamination section. When satisfactory bond strengths are achieved,
one can successfully stretch the laminate, preferably by
incremental stretching in the CD and MD directions, to produce a
soft, non-delaminatable, moisture vapor permeable and cloth-like
microporous composite. If satisfactory bond strengths are not
achieved, the laminate will either delaminate easily, break during
formation, or adverse pinholing will result.
[0056] The MVTR of the microporous laminate can also be controlled
by the web temperature during the stretching. When the laminate is
heated to different temperatures before CD stretching, different
MVTRs can result. The embossed laminate was made with a metal
embossing roller having a rectangular engraving of CD and MD lines
with about 165-300 lines per inch. This pattern is disclosed, for
example, in U.S. Pat. No. 4,376,147 which is incorporated herein by
reference.
[0057] This micro pattern provides a matte finish to the film of
the laminate but is undetectable to the naked eye.
[0058] FIG. 3 is an enlarged schematic of the die 2, ACDs 3A,3B and
embossing rollers arrangement showing the air flows 30 on both
sides of the web substantially parallel to the web surface with a
plurality of vortices on both sides of the web. A slight offset of
cooling devices 3A and 3B has been shown to provide cooling;
however, different arrangements may be used.
[0059] It has been found that ACDs of the type illustrated which
provide a substantially parallel cooling air flow with vortices
over the web surface efficiently cool the web. Surprisingly, web
draw resonance which one may normally encounter in prior techniques
has been eliminated or controlled at high speeds of about 700-1200
fpm of the web. Furthermore, when laminates of film and nonwoven
are made, the bond strengths are very effectively achieved at
targets which have not been possible with other known methods of
cooling while at the same time maintaining film gauge controls,
even at web high speeds.
[0060] In view of the above detailed description, it will be
understood that variations will occur in employing the principles
of this invention depending upon materials and conditions, as will
be understood by those of ordinary skill in the art.
* * * * *