U.S. patent application number 08/940886 was filed with the patent office on 2001-08-16 for crimped multicomponent filaments and spunbond webs made therefrom.
Invention is credited to BROWN, KURTIS L., CLARK, DARRYL F., CREAGAN, CHRISTOPHER C., MARMON, SAMUEL E., MLEZIVA, MARK M..
Application Number | 20010014395 08/940886 |
Document ID | / |
Family ID | 25475584 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014395 |
Kind Code |
A1 |
MLEZIVA, MARK M. ; et
al. |
August 16, 2001 |
CRIMPED MULTICOMPONENT FILAMENTS AND SPUNBOND WEBS MADE
THEREFROM
Abstract
Spunbond multicomponent filaments and nonwoven webs made from
the filaments are disclosed. In accordance with the present
invention, the multicomponent filaments contain a crimp enhancement
additive. Specifically, the crimp enhancement additive is added to
the polymeric component that has the slower solidification rate.
The additive enhances crimp, allows for highly crimped filaments to
be made at low fiber linear densities, improves the integrity of
unbonded webs made from the filaments, and produces webs with
improved stretch and cloth-like properties. The additive
incorporated into the filaments is a random copolymer of butylene
and propylene.
Inventors: |
MLEZIVA, MARK M.; (APPLETON,
WI) ; MARMON, SAMUEL E.; (ALPHARETTA, GA) ;
CREAGAN, CHRISTOPHER C.; (MARIETTA, GA) ; CLARK,
DARRYL F.; (ALPHARETTA, GA) ; BROWN, KURTIS L.;
(ALPHARETTA, GA) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Family ID: |
25475584 |
Appl. No.: |
08/940886 |
Filed: |
September 30, 1997 |
Current U.S.
Class: |
428/369 ;
428/370; 428/373; 428/374 |
Current CPC
Class: |
Y10T 442/637 20150401;
D01F 8/06 20130101; Y10T 442/638 20150401; Y10T 428/2929 20150115;
Y10T 442/681 20150401; D01D 5/22 20130101; Y10T 442/608 20150401;
Y10T 442/629 20150401; Y10T 428/2922 20150115; Y10T 428/2924
20150115; Y10T 442/627 20150401; Y10T 428/2931 20150115; D01D 10/02
20130101 |
Class at
Publication: |
428/369 ;
428/370; 428/373; 428/374 |
International
Class: |
D02G 003/02; D02G
001/18 |
Claims
What is claimed is:
1. A process for forming a nonwoven web comprising the steps of:
melt spinning multicomponent filaments, said filaments comprising a
first polymeric component and a second polymeric component, said
first polymeric component having a faster solidification rate than
said second polymeric component, said second polymeric component
containing a butylene-propylene copolymer; drawing said
multicomponent filaments; naturally crimping said multicomponent
filaments; and thereafter forming said multicomponent filaments
into a nonwoven web.
2. A process as defined in claim 1, wherein said second polymeric
component comprises polyethylene.
3. A process as defined in claim 1, wherein said butylene-propylene
copolymer comprises a random copolymer containing up to about 20%
by weight butylene.
4. A process as defined in claim 1, wherein said butylene-propylene
copolymer is added to said second polymeric component in an amount
up to about 10 percent by weight.
5. A process as defined in claim 1, wherein said butylene-propylene
copolymer is added to said second polymeric component in an amount
from about 0.5% to about 5% by weight.
6. A process as defined in claim 2, wherein said first polymeric
component comprises polypropylene.
7. A process as defined in claim 2, wherein said first polymeric
component comprises a material selected from the group consisting
of nylon, polyester and propylene-ethylene copolymers.
8. A process as defined in claim 1, wherein said second polymeric
component further comprises reclaimed polymers, said reclaimed
polymers comprising polypropylene, polyethylene or copolymers of
propylene and ethylene.
9. A process as defined in claim 1, wherein said multicomponent
filaments have a linear density of less than about 2 denier.
10. A process for forming a nonwoven web comprising the steps of:
melt spinning bicomponent filaments, said bicomponent filaments
comprising a first polymeric component and a second polymeric
component, said first polymeric component comprising polypropylene,
said second polymeric component comprising a mixture of
polyethylene and a butylene-propylene copolymer; drawing said
bicomponent filaments; crimping said bicomponent filaments; and
thereafter forming said bicomponent filaments into a nonwoven
web.
11. A process as defined in claim 10, wherein said bicomponent
filaments are crimped by subjecting said filaments to a flow of a
gas.
12. A process as defined in claim 10, wherein said
butylene-propylene copolymer is present in said second polymeric
component in an amount from about 0.5% to about 5% by weight.
13. A process as defined in claim 12, wherein said
butylene-propylene copolymer comprises a random copolymer
containing about 14% by weight butylene.
14. A process as defined in claim 10, wherein said second polymeric
component further comprises reclaimed polymers, said reclaimed
polymers comprising polypropylene, polyethylene or copolymers of
propylene and ethylene.
15. A process as defined in claim 14, wherein said reclaimed
polymers are present in said second polymeric component in an
amount up to about 20% by weight.
16. A process as defined in claim 10, wherein said bicomponent
filaments have a linear density of less than about 2 denier.
17. A process as defined in claim 10, wherein said crimped
bicomponent filaments contain at least 10 crimps per inch.
18. A nonwoven web comprising spunbond multicomponent crimped
filaments, said multicomponent crimped filaments being made from at
least a first polymeric component and a second polymeric component,
said first polymeric component having a faster solidification rate
than said second polymeric component, said second polymeric
component containing a butylene-propylene random copolymer.
19. A nonwoven web as defined in claim 18, wherein said second
polymeric component comprises polyethylene.
20. A nonwoven web as defined in claim 19, wherein said
butylene-propylene random copolymer is present within said second
polymeric component in an amount up to about 5% by weight.
21. A nonwoven web as defined in claim 20, wherein said first
polymeric component comprises polypropylene.
22. A nonwoven web as defined in claim 21, wherein said
butylene-propylene random copolymer contains up to about 20% by
weight butylene.
23. A nonwoven web as defined in claim 22, wherein said
multicomponent crimped filaments have a linear density of less than
about 2 denier.
24. A naturally crimped bicomponent filament comprising at least a
first polymeric component and a second polymeric component, said
first polymeric component having a faster solidification rate than
said second polymeric component, said filament containing a crimp
enhancement additive, said crimp enhancement additive being added
in an amount sufficient for said filament to have at least 10
crimps per inch, said multicomponent filament having a linear
density of less than about 2 denier.
25. A naturally crimped multicomponent filament as defined in claim
24, wherein said filament has a linear density of less than about
1.2 denier.
26. A naturally crimped multicomponent filament as defined in claim
24, wherein said second polymeric component comprises polyethylene
and wherein said crimp enhancement additive comprises a
butylene-propylene random copolymer and is contained within said
second polymeric component.
27. A naturally crimped multicomponent filament as defined in claim
26, wherein said first polymeric component comprises
polypropylene.
28. A process for improving the unbonded strength of a spunbond
nonwoven web, said process comprising the steps of: incorporating
into a first polymeric component a butylene-propylene copolymer;
melt spinning multicomponent filaments from said first polymeric
component and at least a second polymeric component; drawing said
multicomponent filaments; and thereafter forming said
multicomponent filaments into a nonwoven web wherein said
butylene-propylene copolymer is present in said web in an amount
sufficient to increase the strength of said web prior to being
thermally bonded.
29. A process as defined in claim 28, wherein said
butylene-propylene copolymer is added to said first polymeric
component in an amount from about 0.5% to about 5% by weight.
Description
FIELD OF THE INVENTION
[0001] The present invention is generally directed to spunbond
multicomponent filaments and to nonwoven webs made from the
filaments. More particularly, the present invention is directed to
incorporating an additive into one of the polymers used to make
multicomponent filaments. The additive enhances crimp, allows for
finer filaments, improves the integrity of unbonded webs made from
the filaments, enhances bonding of the filaments, and produces webs
with improved stretch and cloth-like properties. The additive
incorporated into the filaments is a butylene-propylene random
copolymer.
BACKGROUND OF THE INVENTION
[0002] Nonwoven fabrics are used to make a variety of products
which desirably have particular levels of softness, strength,
uniformity, liquid handling properties such as absorbency, and
other physical properties. Such products include towels, industrial
wipers, incontinence products, filter products, infant care
products such as baby diapers, absorbent feminine care products,
and garments such as medical apparel. These products are often made
with multiple layers of nonwoven fabrics to obtain the desired
combination of properties. For example, disposable baby diapers
made from polymeric nonwoven fabrics may include a soft and porous
liner layer which fits next to the baby's skin, an impervious outer
cover layer which is strong and soft, and one or more interior
liquid handling layers which are soft, bulky and absorbent.
[0003] Nonwoven fabrics such as the foregoing are commonly made by
melt spinning thermoplastic materials. Such fabrics are called
spunbond materials. Spunbond nonwoven polymeric webs are typically
made from thermoplastic materials by extruding the thermoplastic
material through a spinneret and drawing the extruded material into
filaments with a stream of high velocity air to form a random web
on a collecting surface.
[0004] Spunbond materials with desirable combinations of physical
properties, especially combinations of softness, strength and
absorbency, have been produced, but limitations have been
encountered. For example, for some applications, polymeric
materials such as polypropylene may have a desirable level of
strength but not a desirable level of softness. On the other hand,
materials such as polyethylene may, in some cases, have a desirable
level of softness but not a desirable level of strength.
[0005] In an effort to produce nonwoven materials having desirable
combinations of physical properties, nonwoven polymeric fabrics
made from multicomponent or bicomponent filaments and fibers have
been developed. Bicomponent or multicomponent polymeric fibers or
filaments include two or more polymeric components which remain
distinct. As used herein, filaments mean continuous strands of
material and fibers mean cut or discontinuous strands having a
definite length. The first and subsequent components of
multicomponent filaments are arranged in substantially distinct
zones across the cross-section of the filaments and extend
continuously along the length of the filaments. Typically, one
component exhibits different properties than the other so that the
filaments exhibit properties of the two components. For example,
one component may be polypropylene which is relatively strong and
the other component may be polyethylene which is relatively soft.
The end result is a strong yet soft nonwoven fabric.
[0006] To increase the bulk or fullness of the bicomponent nonwoven
webs for improved fluid management performance or for enhanced
"cloth-like" feel of the webs, the bicomponent filaments or fibers
are often crimped. Bicomponent filaments may be either mechanically
crimped or, if the appropriate polymers are used, naturally
crimped. As used herein, a naturally crimped filament is a filament
that is crimped by activating a latent crimp contained in the
filaments. For instance, in one embodiment, filaments can be
naturally crimped by subjecting the filaments to a gas, such as a
heated gas, after being drawn.
[0007] In general, it is far more preferable to construct filaments
that can be naturally crimped as opposed to having to crimp the
filaments in a separate mechanical process. Difficulties have been
experienced in the past, however, in producing filaments that will
crimp naturally to the extent required for the particular
application. Also, it has been found to be very difficult to
produce naturally crimped fine filaments, such as filaments having
a linear density of less than 2 denier. Specifically, the draw
force used to produce fine filaments usually prevents or removes
any meaningful latent crimp that may be contained in the filaments.
As such, currently a need exists for a method of producing
multicomponent filaments with enhanced natural crimp properties.
Also, a need exists for nonwoven webs made from such filaments.
SUMMARY OF THE INVENTION
[0008] The present invention recognizes and addresses the foregoing
disadvantages, and others of prior art constructions and
methods.
[0009] Accordingly, an object of the present invention is to
provide improved nonwoven fabrics and methods for making the
same.
[0010] Another object of the present invention is to provide
nonwoven polymeric fabrics including highly crimped filaments and
methods for economically making the same.
[0011] A further object of the present invention is to provide a
method for controlling the properties of a nonwoven polymeric
fabric by varying the degree of crimp of filaments and fibers used
to make the fabric.
[0012] Another object of the present invention is to provide an
improved process for naturally crimping multicomponent
filaments.
[0013] It is another object of the present invention to provide a
method for naturally crimping multicomponent filaments by adding to
one of the components of the filaments a butylene-propylene
copolymer.
[0014] Still another object of the present invention is to provide
a naturally crimped filament that has a linear density of less than
2 denier.
[0015] Another object of the present invention is to provide a
bicomponent filament made from polypropylene and polyethylene,
wherein a crimp enhancement additive has been added to the
polyethylene.
[0016] It is still another object of the present invention to
provide a process for naturally crimping multicomponent filaments
containing polypropylene and polyethylene in which a crimp
enhancement additive and reclaimed polymer has been added to the
polyethylene.
[0017] Another object of the present invention is to provide a
crimp enhancement additive that also improves the strength of
unbonded webs made from filaments containing the additive.
[0018] These and other objects of the present invention are
achieved by providing a process for forming a nonwoven web. The
process includes the steps of melt spinning multicomponent
filaments. The multicomponent filaments include a first polymeric
component and a second polymeric component. The first polymeric
component has a faster solidification rate than the second
polymeric component for providing the filaments with a latent
crimp. The second polymeric component contains a crimp enhancement
additive that is a butylene-propylene copolymer.
[0019] Once melt spun, the multicomponent filaments are drawn and
naturally crimped. Thereafter, the multicomponent crimped filaments
are formed into a nonwoven web for use in various applications.
[0020] In one embodiment, the second polymeric component can
include polyethylene. The butylene-propylene copolymer can be added
to the second polymeric component in an amount less than about 10%
by weight, and particularly from about 0.5% to about 5% by weight.
Preferably, the butylene-propylene copolymer is a random copolymer
containing less than about 20% by weight butylene, and particularly
about 14% by weight butylene.
[0021] The first polymeric component, on the other hand, in one
preferred embodiment is polypropylene. Other polymers that may be
used include nylon, polyester and copolymers of polypropylene, such
as a propylene-ethylene copolymer.
[0022] In accordance with the present invention, it has been also
discovered that the butylene-propylene copolymer also functions as
a polymer compatibilizer. In particular, it has been found that the
copolymer allows better homogeneous mixing between different
polymers. In this regard, the first polymeric component, in
accordance with the present invention, can also contain reclaim
polymer. Reclaim polymer, as used herein, are polymer scraps that
are recycled and added to the filaments. For instance, the reclaim
polymer can comprise a mixture of polyethylene, polypropylene, and
copolymers of propylene and ethylene, and can be obtained from the
trimmed edges of previously formed nonwoven webs. In the past,
difficulties were experienced in recycling reclaim polymer,
especially bicomponent reclaim polymer, and incorporating them into
filaments without adversely affecting the physical properties of
the filaments.
[0023] These and other objects of the present invention are also
achieved by providing a nonwoven web made from spunbond
multicomponent, crimped filaments. The multicomponent crimped
filaments are made from at least a first polymeric component and a
second polymeric component. In particular, the polymeric components
are selected such that the first polymeric component has a faster
solidification rate than the second polymeric component. In
accordance with the present invention, the second polymeric
component contains a crimp enhancement additive. Specifically, the
crimp enhancement additive is a butylene-propylene random
copolymer.
[0024] For instance, in one embodiment, the crimped filaments can
be bicomponent filaments which include a polypropylene component
and a polyethylene component. The butylene-propylene random
copolymer can be added to the polyethylene component in an amount
up to about 5% by weight. Preferably, the butylene-propylene random
copolymer contains about 14% by weight butylene.
[0025] Because of the addition of the crimp enhancement additive,
the multicomponent filaments can have a very low denier and still
be crimped naturally. For instance, the denier of the filaments can
be less than 2, and particularly less than about 1.2.
[0026] In this regard, the present invention is also directed to a
naturally crimped multicomponent filament that includes at least a
first polymeric component and a second polymeric component. The
first polymeric component can be, for instance, polypropylene. The
second polymeric component, on the other hand, can be, for
instance, polyethylene and can contain a crimp enhancement additive
in an amount sufficient to allow the filaments to be naturally
crimped at a denier of less than about 2 and particularly less than
about 1.2.
[0027] Other objects, features and aspects of the present invention
are discussed in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] A full and enabling disclosure of the present invention,
including the best mode thereof, to one of ordinary skill in the
art, is set forth more particularly in the remainder of the
specification, including reference to the accompanying figures, in
which:
[0029] FIG. 1 is a schematic drawing of a process line for making a
preferred embodiment of the present invention;
[0030] FIG. 2A is a schematic drawing illustrating the cross
section of a filament made according to an embodiment of the
present invention with the polymer components A and B in a
side-by-side arrangement; and
[0031] FIG. 2B is a schematic drawing illustrating the cross
section of a filament made according to an embodiment of the
present invention with the polymer components A and B in a
eccentric sheath/core arrangement.
[0032] Repeat use of reference characters in the present
specification and drawings is intended to represent same or
analogous features or elements of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0033] It is to be understood by one of ordinary skill in the art
that the present discussion is a description of exemplary
embodiments only, and is not intended as limiting the broader
aspects of the present invention, which broader aspects are
embodied in the exemplary construction.
[0034] The present invention is generally directed to
multicomponent filaments and to spunbond webs produced from the
filaments. In particular, the filaments are naturally crimped into,
for instance, a helical arrangement. Crimping the filaments
increases the bulk, the softness, and the drapability. The nonwoven
webs also have improved fluid management properties and have an
enhanced cloth-like appearance and feel.
[0035] Multicomponent filaments for use in the present invention
contain at least two polymeric components. The polymeric components
can be, for instance, in a side-by-side configuration or in an
eccentric sheath-core configuration. The polymeric components are
selected from semi-crystalline and crystalline thermoplastic
polymers which have different solidification rates with respect to
each other in order for the filaments to undergo natural crimping.
More particularly, one of the polymeric components has a faster
solidifying rate than the other polymeric component.
[0036] As used herein, the solidification rate of a polymer refers
to the rate at which a softened or melted polymer hardens and forms
a fixed structure. It is believed that the solidification rate of a
polymer is influenced by different parameters including the melting
temperature and the rate of crystallization of the polymer. For
instance, a fast solidifying polymer typically has a melting point
that is about 10.degree. C. or higher, more desirably about
20.degree. C. or higher, and most desirably about 30.degree. C. or
higher than a polymer that has a slower solidifying rate. It should
be understood, however, that both polymeric components may have
similar melting points if their crystallization rates are
measurably different.
[0037] Although unknown, it is believed that the latent
crimpability of multicomponent filaments is created in the
filaments due to the differences in the shrinkage properties
between the polymeric components. Further, it is believed that the
main cause of the shrinkage difference between polymeric components
is the incomplete crystallization of the slower solidifying polymer
during the fiber production process. For instance, during formation
of the filaments, when the fast solidifying polymer is solidified,
the slow solidifying polymer is partially solidified and does not
measurably draw any longer and thus does not further experience a
significant orienting force. In the absence of an orienting force,
the slow solidified polymer does not significantly further
crystallize while being cooled and solidified. Accordingly, the
resulting filaments possess latent crimpability, and such latent
crimpability can be activated by subjecting the filaments to a
process that allows sufficient molecular movement of the polymer
molecules of the slow solidifying polymer to facilitate further
crystallization and shrinkage.
[0038] The present invention is directed to adding a crimp
enhancement additive to the polymeric component having the slower
solidification rate in order to further slow the solidification
rate of the polymer. In this manner, the differences between the
solidification rates of both polymeric components becomes even
greater creating multicomponent filaments that have an enhanced
latent crimpability. In particular, the crimp enhancement additive
of the present invention is a random butylene-propylene
copolymer.
[0039] Besides creating multicomponent filaments that have a
greater natural crimp, it has also been discovered that the crimp
enhancement additive of the present invention provides many other
benefits and advantages. For instance, because the filaments of the
present invention have a greater degree of crimping, fabrics and
webs made from the filaments have a higher bulk and a lower
density. By being able to make lower density webs, less material is
needed to make webs of a specified thickness and the webs are thus
less expensive to produce. Besides having lower densities, the webs
have also been found to be more cloth-like, to have a softer hand,
to have more stretch, to have better recovery, and to have better
abrasion resistance.
[0040] Of particular advantage, it has also been unexpectedly
discovered that the crimp enhancement additive of the present
invention further improves the strength and integrity of unbonded
webs made from the filaments. For instance, it was discovered that
adding only 1% by weight of the additive can more than double the
unbonded strength of the web. By having greater unbonded web
integrity, the webs of the present invention may be processed at
faster speeds. In the past, in order to run at higher speeds,
unbonded spunbond webs had to be prebonded or compacted. Such steps
are not necessary when processing webs made according to the
present invention.
[0041] Besides have increased strength, spunbond webs made
according to the present invention also have dramatically reduced
web handling problems when processed at higher speeds. For
instance, the occurrences of eyebrows, flip overs and stretch marks
are significantly reduced when the crimp enhancement additive is
present within the filaments. More particularly, webs incorporating
filaments made according to the present invention have a lesser
tendency to protrude from the web but, instead, have a greater
tendency to lay down on the web surface. As such, the filaments are
less likely to penetrate the foraminous surface upon which the web
is formed, thus making it easier to remove the web from the
surface.
[0042] Another unexpected benefit to using the crimp enhancement
additive of the present invention is that the additive also
functions as polymer compatabilizer. In other words, the additive
facilitates homogeneous mixing of different polymers. Thus, the
polymeric component containing the additive can contain a mixture
of polymers if desired. For example, in one embodiment of the
present invention, the polymeric component containing the additive
of the present invention can also contain reclaim polymer, such as
polymeric scraps collected from the trimmings of previously formed
spunbond webs and particularly bicomponent webs.
[0043] A further advantage to the crimp enhancement additive of the
present invention is that the additive permits the formation of
very fine multicomponent filaments having a relatively high natural
crimp. In the past, it was very difficult to create fine filaments,
such as at less than 2 denier, that had a relatively high natural
crimp. In the past, the draw force used to produce fine fibers
usually prevented or removed any meaningful latent crimp present
within the filaments. Filaments made according to the present
invention, on the other hand, can have greater than 10 crimps per
inch at less than 2 denier, and even lower than 1.2 denier.
[0044] Besides the above-listed advantages, it has also been
discovered that the crimp enhancement additive of the present
invention improves thermal bonding between the filaments. In
particular, the crimp enhancement additive has a broad melting
point range and has a relatively low melt temperature, which
facilitates bonding.
[0045] The webs and fabrics of the present invention are
particularly useful for making various products including liquid
and gas filters, personal care articles and garment materials.
Personal care articles include infant care products such as
disposable baby diapers, child care products such as training
pants, and adult care products such as incontinence products and
feminine care products. Suitable garments include medical apparel,
work wear, and the like.
[0046] As described above, the fabric of the present invention
includes continuous multicomponent polymeric filaments comprising
at least first and second polymeric components. A preferred
embodiment of the present invention is a polymeric fabric including
continuous bicomponent filaments comprising a first polymeric
component A and a second polymeric component B. The bicomponent
filaments have a cross-section, a length, and a peripheral surface.
The first and second components A and B are arranged in
substantially distinct zones across the cross-section of the
bicomponent filaments and extend continuously along the length of
the bicomponents filaments. The second component B constitutes at
least a portion of the peripheral surface of the bicomponent
filaments continuously along the length of the bicomponent
filaments.
[0047] The first and second components A and B are arranged in
either a side-by-side arrangement as shown in FIG. 2A or an
eccentric sheath/core arrangement as shown in FIG. 2B so that the
resulting filaments exhibit a natural helical crimp. Polymer
component A is the core of the filament and polymer component B is
the sheath in the sheath/core arrangement. Methods for extruding
multicomponent polymeric filaments into such arrangements are
well-known to those of ordinary skill in the art.
[0048] A wide variety of polymers are suitable to practice the
present invention including polyolefins (such as polyethylene and
polypropylene), polyesters, polyamides, and the like. Polymer
component A and polymer component B must be selected so that the
resulting bicomponent filament is capable of developing a natural
helical crimp. Preferably, polymer component A has a faster
solidification rate than polymer component B. For instance, in one
embodiment, polymer component A can have a higher melting
temperature than polymer component B.
[0049] Preferably, polymer component A comprises polypropylene or a
random copolymer of propylene and ethylene. Besides containing
polypropylene, polymer component A can also be a nylon or a
polyester.
[0050] Polymer component B, on the other hand, preferably comprises
polyethylene or a random copolymer of propylene and ethylene.
Preferred polyethylenes include linear low density polyethylene and
high density polyethylene.
[0051] Suitable materials for preparing the multicomponent
filaments of the present invention include PD-3445 polypropylene
available from Exxon of Houston, Tex., random copolymer of
propylene and ethylene available from Exxon, ASPUN 6811A and 2553
linear low density polyethylene available from the Dow Chemical
Company of Midland, Mich., 25355 and 12350 high density
polyethylene available from the Dow Chemical Company.
[0052] When polypropylene is component A and polyethylene is
component B, the bicomponent filaments may comprise from about 20
to about 80% by weight polypropylene and from about 20 to about 80%
polyethylene. More preferably, the filaments comprise from about 40
to about 60% by weight polypropylene and from about 40 to about 60%
by weight polyethylene.
[0053] As described above, the crimp enhancement additive of the
present invention is a random copolymer of butylene and propylene
and is added to polymer component B which is preferably
polyethylene. The butylene-propylene random copolymer preferably
contains from about 5% to about 20% by weight butylene. For
instance, one commercially available product that may be used as
the crimp enhancement additive is Product No. DS4D05 marketed by
the Union Carbide Corporation of Danbury, Conn. Product No. DS4D05
is a butylene-propylene random copolymer containing 14% by weight
butylene and 86% by weight propylene. Preferably, the
butylene-propylene copolymer is a film grade polymer having an MFR
(melt flow rate) of from about 3.0 to about 15.0, and particularly
having a MFR of from about 5 to about 6.5.
[0054] In order to combine the crimp enhancement additive with
polymer component B, in one embodiment, the polymers can be dry
blended and extruded together during formation of the
multicomponent filaments. In an alternative embodiment, the crimp
enhancement additive and polymer component B which can be, for
instance, polyethylene, can be melt blended prior to being formed
into the filaments of the present invention.
[0055] In general, the crimp enhancement additive can be added to
polymeric component B in an amount less than 10% by weight. When
polymeric component B contains polyethylene, preferably the crimp
enhancement additive is added in an amount from about 0.5% to about
5% by weight based upon the total weight of polymer component B.
Should too much of the butylene-propylene random copolymer be added
to the polymer component, the resulting filaments may become too
curly and adversely interfere with the formation of a nonwoven
web.
[0056] It is believed that the butylene-propylene random copolymer,
when added to a polymer such as polyethylene, slows the
solidification rate and the crystallization rate of the polymer. In
this manner, a greater difference in solidification rates is
created between the different polymer components used to make the
filaments, thereby increasing the latent crimpability of the
filaments.
[0057] In an alternative embodiment of the present invention,
besides adding the crimp enhancement additive to polymer component
B, reclaimed and recycled polymers are also added to the polymer
component. As described above, it has been discovered that the
crimp enhancement additive of the present invention also
facilitates homogeneous mixing between polymers. Specifically, the
butylene-propylene random copolymer has been found to facilitate
mixing between polyethylene and a reclaim polymer that contains a
mixture of polyethylene and polypropylene. In this embodiment, the
reclaim polymer can be added to the polymeric component in an
amount up to about 20% by weight. Preferably, the reclaim polymer
is collected from scraps and trimmings of previously formed
nonwoven webs. Being able to recycle such polymers not only
decreases the amount of materials needed to make the nonwoven webs
of the present invention, but also limits the amount of waste that
is produced.
[0058] One process for producing multicomponent filaments and
nonwoven webs according to the present invention will now be
discussed in detail with reference to FIG. 1. The following process
is similar to the process described in U.S. Pat. No. 5,382,400 to
Pike et al., which is incorporated herein by reference in its
entirety.
[0059] Turning to FIG. 1, a process line 10 for preparing a
preferred embodiment of the present invention is disclosed. The
process line 10 is arranged to produce bicomponent continuous
filaments, but it should be understood that the present invention
comprehends nonwoven fabrics made with multicomponent filaments
having more than two components. For example, the fabric of the
present invention can be made with filaments having three or four
components.
[0060] The process line 10 includes a pair of extruders 12a and 12b
for separately extruding a polymer component A and a polymer
component B. Polymer component A is fed into the respective
extruder 12a from a first hopper 14a and polymer component B is fed
into the respective extruder 12b from a second hopper 14b. Polymer
components A and B are fed from the extruders 12a and 12b through
respective polymer conduits 16a and 16b to a spinneret 18.
[0061] Spinnerets for extruding bicomponent filaments are
well-known to those of ordinary skill in the art and thus are not
described here in detail. Generally described, the spinneret 18
includes a housing containing a spin pack which includes a
plurality of plates stacked one on top of the other with a pattern
of openings arranged to create flow paths for directing polymer
components A and B separately through the spinneret. The spinneret
18 has openings arranged in one or more rows. The spinneret
openings form a downwardly extending curtain of filaments when the
polymers are extruded through the spinneret. For the purposes of
the present invention, spinneret 18 may be arranged to form
side-by-side or eccentric sheath/core bicomponent filaments
illustrated in FIGS. 2A and 2B.
[0062] The process line 10 also includes a quench blower 20
positioned adjacent the curtain of filaments extending from the
spinneret 18. Air from the quench air blower 20 quenches the
filaments extending from the spinneret 18. The quench air can be
directed from one side of the filament curtain as shown FIG. 1, or
both sides of the filament curtain.
[0063] A fiber draw unit or aspirator 22 is positioned below the
spinneret 18 and receives the quenched filaments. Fiber draw units
or aspirators for use in melt spinning polymers are well-known as
discussed above. Suitable fiber draw units for use in the process
of the present invention include a linear fiber aspirator of the
type shown in U.S. Pat. No. 3,802,817 and educative guns of the
type shown in U.S. Pat. Nos. 3,692,618 and 3,423,266, the
disclosures of which are incorporated herein by reference.
[0064] Generally described, the fiber draw unit 22 includes an
elongate vertical passage through which the filaments are drawn by
aspirating air entering from the sides of the passage and flowing
downwardly through the passage. A heater or blower 24 supplies
aspirating air to the fiber draw unit 22. The aspirating air draws
the filaments and ambient air through the fiber draw unit.
[0065] An endless foraminous forming surface 26 is positioned below
the fiber draw unit 22 and receives the continuous filaments from
the outlet opening of the fiber draw unit. The forming surface 26
travels around guide rollers 28. A vacuum 30 positioned below the
forming surface 26 where the filaments are deposited draws the
filaments against the forming surface.
[0066] The process line 10 further includes a bonding apparatus
such as thermal point bonding rollers 34 (shown in phantom) or a
through-air bonder 36. Thermal point bonders and through-air
bonders are well-known to those skilled in the art and are not
disclosed here in detail. Generally described, the through-air
bonder 36 includes a perforated roller 38, which receives the web,
and a hood 40 surrounding the perforated roller. Lastly, the
process line 10 includes a winding roll 42 for taking up the
finished fabric.
[0067] To operate the process line 10, the hoppers 14a and 14b are
filled with the respective polymer components A and B. Polymer
components A and B are melted and extruded by the respective
extruders 12a and 12b through polymer conduits 16a and 16b and the
spinneret 18. Although the temperatures of the molten polymers vary
depending on the polymers used, when polypropylene and polyethylene
are used as components A and B respectively, the preferred
temperatures of the polymers when extruded range from about
370.degree. to about 530.degree. F. and preferably range from
400.degree. to about 450.degree. F.
[0068] As the extruded filaments extend below the spinneret 18, a
stream of air from the quench blower 20 at least partially quenches
the filaments to develop a latent helical crimp in the filaments.
The quench air preferably flows in a direction substantially
perpendicular to the length of the filaments at a temperature of
about 45.degree. to about 90.degree. F. and a velocity of from
about 100 to about 400 feet per minute.
[0069] After quenching, the filaments are drawn into the vertical
passage of the fiber draw unit 22 by a flow of a gas, such as air,
from the heater or blower 24 through the fiber draw unit. The fiber
draw unit is preferably positioned 30 to 60 inches below the bottom
of the spinneret 18. The temperature of the air supplied from the
heater or blower 24 is sufficient to activate the latent crimp. The
temperature required to activate the latent crimp of the filaments
ranges from about 60.degree. F. to a maximum temperature near the
melting point of the lower melting component which is the second
component B.
[0070] The actual temperature of the air being supplied by heater
or blower 24 generally will depend upon the linear density of the
filaments being produced. For instance, it has been discovered that
at greater than 2 denier, no heat is required at the fiber draw
unit 22 in order to naturally crimp the filaments, which is a
further advantage of the present invention. In the past, air being
supplied to the fiber draw unit 22 typically had to be heated.
Filaments finer than about 2 denier made according to the present
invention, however, generally will need to be contacted with heated
air in order to induce natural crimping.
[0071] The temperature of the air from the heater 24 can be varied
to achieve different levels of crimp. Generally, a higher air
temperature produces a higher number of crimps. The ability to
control the degree of crimp of the filaments is particularly
advantageous because it allows one to change the resulting density,
pore size distribution and drape of the fabric by simply adjusting
the temperature of the air in the fiber draw unit.
[0072] The crimped filaments are deposited through the outlet
opening of the fiber draw unit 22 onto the traveling forming
surface 26. The vacuum 20 draws the filaments against the forming
surface 26 to form an unbonded, nonwoven web of continuous
filaments. In the past, the web was then typically lightly
compressed by a compression roller and then thermal point bonded by
rollers 34 or through-air bonded in the through-air bonder 36. As
described above, however, it has been discovered that nonwoven webs
made according to the present invention have increased strength and
integrity when containing the crimp enhancement additive. As such,
very little prebonding by a compression roller or any other type of
prebonding station is necessary in process line 10 prior to feeding
the webs to a bonding station. Further, due to the increased
strength of nonbonded webs made according to the present invention,
line speeds can be increased. For instance, line speeds can range
from about 150 feet per minute to about 500 feet per minute.
[0073] In the through-air bonder 36 as shown in FIG. 1, air having
a temperature above the melting temperature of component B and
below the melting temperature of component A is directed from the
hood 40, through the web, and into the perforated roller 38. The
hot air melts the lower melting polymer component B and thereby
forms bonds between the bicomponent filaments to integrate the web.
When polypropylene and polyethylene are used as polymer components
A and B respectively, the air flowing through the through-air
bonder preferably has a temperature ranging from about 230.degree.
to about 280.degree. F. and a velocity from about 100 to about 500
feet per minute. The dwell time of the web in the through-air
bonder is preferably less than about 6 seconds. It should be
understood, however, that the parameters of the through-air bonder
depend on factors such as the type of polymers used and thickness
of the web.
[0074] Lastly, the finished web is wound onto the winding roller 42
and is ready for further treatment or use. When used to make liquid
absorbent articles, the fabric of the present invention may be
treated with conventional surface treatments or contain
conventional polymer additives to enhance the wettability of the
fabric. For example, the fabric of the present invention may be
treated with polyalkylene-oxide modified siloxanes and silanes such
as polyalkylene-oxide modified polydimethyl-siloxane as disclosed
in U.S. Pat. No. 5,057,361. Such a surface treatment enhances the
wettability of the fabric.
[0075] When through-air bonded, the fabric of the present invention
characteristically has a relatively high loft. The helical crimp of
the filaments creates an open web structure with substantial void
portions between filaments and the filaments are bonded at points
of contact. The through-air bonded web of the present invention
typically has a density of from about 0.015 g/cc to about 0.040
g/cc and a basis weight of from about 0.25 to about 5 oz. per
square yard and more preferably from about 1.0 to about 3.5 oz. per
square yard.
[0076] Filament linear density generally ranges from less than 1.0
to about 8 denier. As discussed above, the crimp enhancement
additive of the present invention allows for the production of
highly crimped, fine filaments. In the past, naturally crimped fine
filaments were difficult if not impossible to produce. According to
the present invention, filaments having a natural crimp of at least
about 10 crimps per inch can be produced at linear densities less
than 2 denier, and particularly at less than about 1.2 denier. For
most nonwoven webs, it is preferable for the filaments to have from
about 10 crimps per inch to about 25 crimps per inch. Of particular
advantage, filaments having a natural crimp in the above range can
be produced according to the present invention at a lower linear
density than what has been possible in the past.
[0077] Thermal point bonding may be conducted in accordance with
U.S. Pat. No. 3,855,046, the disclosure of which is incorporated
herein by reference. When thermal point bonded, the fabric of the
present invention exhibits a more cloth-like appearance and, for
example, is useful as an outer cover for personal care articles or
as a garment material.
[0078] Although the methods of bonding shown in FIG. 1 are thermal
point bonding and through-air bonding, it should be understood that
the fabric of the present invention may be bonded by other means
such as oven bonding, ultrasonic bonding, hydroentangling or
combinations thereof. Such bonding techniques are well-known to
those of ordinary skill in the art and are not discussed here in
detail.
[0079] Although, the preferred method of carrying out the present
invention includes contacting the multicomponent filaments with
aspirating air, the present invention encompasses other methods of
activating the latent helical crimp of the continuous filaments
before the filaments are formed into a web. For example, the
multicomponent filaments may be contacted with air after quenching
but upstream of the aspirator. In addition, the multicomponent
filaments may be contacted with air between the aspirator and the
web forming surface. Furthermore, the filaments may also be exposed
to electromagnetic energy such as microwaves or infrared
radiation.
[0080] Once produced, the nonwoven webs of the present invention
can be used in many different and various applications. For
instance, the webs can be used in filter products, in liquid
absorbent products, in personal care articles, in garments, and in
various other products.
[0081] The present invention may be better understood with
reference to the following Examples.
EXAMPLE NO. 1
[0082] The following Example was conducted in order to compare the
differences between filaments and nonwoven webs made with the crimp
enhancement additive of the present invention and filaments and
nonwoven webs constructed without the crimp enhancement
additive.
[0083] Two bicomponent spunbond fabrics were produced generally in
accordance with the process disclosed in U.S. Pat. No. 5,382,400
(Pike, et al). In both fabrics, the filaments were round in cross
section with the two components arranged in a side-by-side
configuration. One side of the filaments was made primarily of
polypropylene (Exxon 34455), while the other side was made
primarily of polyethylene (Dow 61800). In both fabrics, the
polypropylene (PP) side contained in an amount of 2% by weight an
additive composed of 50% polypropylene and 50% TiO.sub.2.
[0084] In the first fabric (Fabric A), in accordance with the
present invention, the polyethylene (PE) side contained in an
amount of 2% by weight a random copolymer of 14% butylene and 86%
propylene (Union Carbide DS4D05). The polyethylene side of the
other fabric (Fabric B), on the other hand, was 100%
polyethylene.
[0085] Both fabrics were produced at a total polymer throughput of
0.35 ghm of polymer per hole at a hole density of 48 holes per inch
of width and were through air bonded at an air temperature of
265.degree. F. Fabric A was produced at a line speed of 44 feet per
minute, while Fabric B was produced at 37 feet per minute. Line
speed was used to control basis weight, all other process
conditions remained the same. Both fabrics had a basis weight of
2.6 ounces per square yard (osy).
[0086] The fabrics were tested for tensile peak load, peak strain
and peak energy (3" strips) in both the machine direction (MD) and
cross-machine direction (CD) according to ASTM D-5035-90 and for
caliper under a load of 0.05 psi with a Starrett-type caliper
tester. Fabric density was calculated from basis weight and
caliper. Fiber crimp was rated on a subjective 1 to 5 scale with
1=no crimp and 5= very high crimp. Fiber linear density was
calculated from the diameter of the filaments (measured by
microscope) and the density of the polymer. The strength of the
unbonded web was determined by collecting a length of fabric that
had not yet entered the bonder and gently laying it on the floor.
The fabric was then slowly and gently lifted by one end until
tensile failure was noted. The length of the fabric that was lifted
at the point of tensile failure was recorded as the breaking length
of the unbonded web.
[0087] The test results are shown on the following table.
1 Properties of Fabrics A & B Fabric A Fabric B Filament Linear
Density (denier) 1.3 1.3 Filament Crimp Index 4.0 1.0 Fabric Basis
Weight (osy) 2.6 2.6 Fabric Caliper (in) 0.135 0.090 Fabric Density
(g/cc) 0.026 0.038 Unbonded Fabric Tensile 66 18 Breaking Length
(in) Bonded Fabric Tensile Properties: MD Peak Load (lb) 6.5 10.9
MD Peak Strain (%) 46 20 MD Peak Energy (in-lb) 4.7 4.4 CD Peak
Load (lb) 10.6 22.3 CD Peak Strain (%) 138 66 CD Peak Energy
(in-lb) 24 32
[0088] The results show that Fabric A, relative to Fabric B, is
composed of filaments having greater crimp and has a greater
caliper (and therefore, lower density). Fabric A further has much
greater unbonded web strength. While the tensile peak loads of
Fabric B are about twice as large as those of Fabric A, the peak
strain values of Fabric A are greater than those of Fabric B by
about the same factor. Fabric peak energies, particularly in the
machine direction, are similar.
[0089] Of particular significance, it is noted that the linear
densities of both sets of filaments were very low, at about 1.3
denier. As shown, the filaments made containing the crimp
enhancement additive of the present invention had a high natural
crimp while the filaments not containing the additive experienced
no significant crimp. As described above, in the past, it was very
difficult to create a naturally crimped filament at low linear
densities.
EXAMPLE NO. 2
[0090] The following example was conducted in order to demonstrate
the ability of the additive of the present invention to facilitate
mixing between different polymeric materials.
[0091] Polyethylene/polypropylene bicomponent filaments were
produced and formed into a spunbond nonwoven web generally in
accordance with the process described in Example 1 and disclosed in
U.S. Pat. No. 5,382,400 to Pike, et al.. The polyethylene side of
the bicomponent filaments contained 20% by weight reclaim polymer.
Specifically, the reclaim polymer was a mixture of polypropylene
and polyethylene that had been collected from the trimmings of a
previously formed nonwoven web.
[0092] In accordance with the present invention, the polyethylene
component also contained 5% by weight of the butylene/propylene
random copolymer identified in Example 1.
[0093] It was observed that by adding the butylene/propylene
copolymer of the present invention, the reclaim polymer readily
blended with the polyethylene component and produced a polymeric
material that could be spun into filaments, which, in turn, could
be naturally crimped. Further, it was discovered that filaments
with very low linear densities could be produced. For instance, at
a polymer throughput of 0.4 ghm and at a fiber draw pressure of 7.4
psi, filaments were produced having a linear density of 1.18
denier.
[0094] In the past, attempts have been made to produce bicomponent
filaments containing reclaim polymer. Absent adding the additive of
the present invention, however, it was not possible to spin the
polymer mixture into filaments.
[0095] These and other modifications and variations to the present
invention may be practiced by those of ordinary skill in the art,
without departing from the spirit and scope of the present
invention, which is more particularly set forth in the appended
claims. In addition, it should be understood that aspects of the
various embodiments may be interchanged both in whole or in part.
Furthermore, those of ordinary skill in the art will appreciate
that the foregoing description is by way of example only, and is
not intended to limit the invention so further described in such
appended claims.
* * * * *