U.S. patent application number 11/276993 was filed with the patent office on 2007-09-20 for apparatus and methods for producing split spunbond filaments.
This patent application is currently assigned to NORDSON CORPORATION. Invention is credited to Rachelle Bentley, Patrick L. Crane.
Application Number | 20070216059 11/276993 |
Document ID | / |
Family ID | 38516977 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070216059 |
Kind Code |
A1 |
Bentley; Rachelle ; et
al. |
September 20, 2007 |
APPARATUS AND METHODS FOR PRODUCING SPLIT SPUNBOND FILAMENTS
Abstract
A spunbonding apparatus capable of producing multicomponent
spunbond filaments. The spunbonding apparatus includes a
spunbonding apparatus comprises a spinneret discharging
multicomponent filaments and a filament-drawing device applying a
first force that is effective to attenuate the filaments. A force
applicator stationed between the spinneret and the filament-drawing
device is operative for applying a second force to the filaments
that promotes filament splitting. Splitting may occur before the
filaments enter the filament-drawing device, within the
filament-drawing device, and/or after discharge from the
filament-drawing device.
Inventors: |
Bentley; Rachelle; (Cumming,
GA) ; Crane; Patrick L.; (Dawsonville, GA) |
Correspondence
Address: |
MOORE & VAN ALLEN PLLC
P.O. BOX 13706
Research Triangle Park
NC
27709
US
|
Assignee: |
NORDSON CORPORATION
Westlake
OH
|
Family ID: |
38516977 |
Appl. No.: |
11/276993 |
Filed: |
March 20, 2006 |
Current U.S.
Class: |
264/172.11 ;
264/211.12; 425/131.5; 425/378.2; 425/72.2 |
Current CPC
Class: |
D01D 5/32 20130101; D01D
5/0985 20130101 |
Class at
Publication: |
264/172.11 ;
264/211.12; 425/072.2; 425/131.5; 425/378.2 |
International
Class: |
D01D 5/30 20060101
D01D005/30 |
Claims
1. A spunbonding apparatus comprising: a spinneret adapted to
discharge a plurality of multicomponent filaments that move in a
downwardly direction away from said spinneret, each of the
multicomponent filaments having at least two polymer regions; a
filament-drawing device positioned below said spinneret, said
filament-drawing device adapted to pneumatically attenuate the
multicomponent filaments; a force applicator directing an air
stream impinging the multicomponent filaments between said
spinneret and said filament-drawing device, said air stream
effective to divide at least some of the multicomponent filaments
into the at least two polymer regions to form smaller filaments;
and a collector for collecting the smaller filaments.
2. The spunbonding apparatus of claim 1 wherein said force
applicator includes an air knife directing said air stream at an
impingement angle greater than 0.degree. and less than 180.degree.
relative to the multicomponent filaments.
3. The spunbonding apparatus of claim 1 further comprising: a first
driven roller contacting the multicomponent filaments; and a second
driven roller spaced from said first driven roller, said second
driven roller contacting the multicomponent filaments, and said air
stream impinging the multicomponent filaments between said first
driven roller and said second driven roller.
4. The spunbonding apparatus of claim 3 wherein said force
applicator includes an air knife directing said air stream at the
multicomponent filaments between said first driven roller and said
second driven roller.
5. The spunbonding apparatus of claim 4 wherein said air stream
intersects the multicomponent filaments at an impingement angle
greater than 0.degree. and less than 180.degree. relative to the
multicomponent filaments between said first driven roller and said
second driven roller.
6. A spunbonding apparatus comprising: a spinneret adapted to
discharge a plurality of multicomponent filaments that move in a
downwardly direction away from said spinneret, each of the
multicomponent filaments having at least two polymer regions; a
filament-drawing device positioned below said spinneret, said
filament-drawing device adapted to pneumatically attenuate the
multicomponent filaments; a force applicator including a first
roller contacting the plurality of multicomponent filaments between
said spinneret and said filament-drawing device, said first roller
effective to divide at least some of the multicomponent filaments
into the at least two polymer regions to form smaller filaments;
and a collector for collecting the smaller filaments.
7. The spunbonding apparatus of claim 6 wherein said first roller
is driven, and said force applicator further includes a second
roller spaced from said first driven roller, said second roller
being driven and contacting the multicomponent filaments.
8. The spunbonding apparatus of claim 7 wherein said first roller
is separated from said second roller in a direction perpendicular
to the downwardly direction in which the multicomponent filaments
are moving.
9. The spunbonding apparatus of claim 7 wherein said first roller
is separated from said second roller in a direction parallel to the
downwardly direction in which the multicomponent filaments are
moving.
10. A method of forming a spunbond nonwoven web, comprising:
forming a plurality of multicomponent filaments each having at
least two polymer regions; pneumatically attenuating the
multicomponent filaments; applying a dividing force to the moving
plurality of multicomponent filaments effective for dividing the at
least two polymer regions of at least some of the filaments to
provide smaller filaments; and collecting the smaller filaments to
form the spunbond nonwoven web.
11. The method of claim 10 wherein applying the dividing force
further comprises: acting with the second force on the moving
plurality of multicomponent filaments along a line perpendicular to
the first force.
12. The method of claim 10 wherein the plurality of multicomponent
filaments travel in a downward direction, and applying the dividing
force further comprises: directing an air stream toward the
multicomponent filaments at an angle that is less than 180.degree.
and greater than 0.degree. relative to the downward direction.
13. The method of claim 10 wherein applying the dividing force
further comprises: intersecting the multicomponent filaments with
at least one roller to apply the dividing force.
14. The method of claim 10 wherein applying the dividing force
further comprises: intersecting the multicomponent filaments with a
plurality of rollers rotating at different angular velocities to
apply the dividing force.
15. The method of claim 10 wherein applying the dividing force
further comprises: intersecting the multicomponent filaments with a
plurality of rollers rotating at a uniform angular velocity to
apply the dividing force.
16. The method of claim 10 wherein the filaments are substantially
attenuated before the dividing force is applied.
17. The method of claim 16 further comprising: quenching the
filaments with a flow of cooling air before the dividing force is
applied.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to melt-spinning apparatus
and methods, and more particularly, to a spunbonding apparatus and
methods for forming slit spunbond filaments.
BACKGROUND OF THE INVENTION
[0002] Melt-spinning technologies are used for forming nonwoven
webs of meltblown and/or spunbond filaments or fibers composed of
one or more thermoplastic polymers such as polyethylene,
polypropylene, and polyester. Nonwoven webs are fashioned into many
consumer and industrial products, including disposable hygienic
articles, disposable protective apparel, fluid filtration media,
and household durables.
[0003] Spunbonding processes generally involve pumping one or more
molten thermoplastic polymers through a spin pack that distributes,
filters, combines, and finally extrudes continuous filaments of the
constituent thermoplastic polymer(s) through an array of thousands
of spinneret orifices in a spinneret. After extrusion, the spunbond
filaments are drawn or stretched by, for example, an impinging
high-velocity airflow that accelerates the filament velocity and
then quenched to cause solidification. The drawn spunbond filaments
are propelled toward a forming zone and collected on a moving
collector to form the spunbond nonwoven web.
[0004] Multicomponent spunbond filaments consist of two or more
thermoplastic polymers that have separate flow paths that are
manipulated as the molten thermoplastic polymers pass through the
spin pack. Multicomponent fibers enable a manufacturer to take
advantage of the material-specific properties of different
thermoplastic polymers simultaneously, often with synergistic
results.
[0005] Meltblown processes are formed by extruding a molten
thermoplastic polymer through a plurality of die capillaries as
molten fibers and impinging the molten fibers with high velocity
air streams that attenuate the molten fibers to reduce their
diameter. The meltblown fibers are carried by the high velocity gas
stream and are deposited on a collecting surface to form a web of
randomly dispersed meltblown fibers. Meltblown fibers, which may be
continuous or discontinuous, are generally smaller than ten microns
in average diameter and may be as small as one to five microns or
less. Spunbond filaments, which are typically in the one to three
denier range as determined by their application, are significantly
larger than meltblown filaments.
[0006] Many nonwoven web structures are currently produced using
spunbond and meltblown filaments or a composite of both filament
types. Generally, nonwoven webs of meltblown filaments include
tortuous fluid paths and may be appropriate for use as a barrier
material. However, meltblown nonwoven webs lack sufficient web
tensile strength or bonding to be used independently for products
that experience high abrasion or contact with a user's skin. To
solve that dilemma, the nonwovens industry often uses nonwoven webs
of spunbond filaments with enhanced strength and abrasion
resistance properties either in combination with meltblown nonwoven
webs or as a substitute for meltblown nonwoven webs.
[0007] Another difficulty associated with barrier materials of
meltblown filaments is that the throughput of meltblown processes
is significantly less than the throughput of spunbond processes.
Consequently, multiple beams of meltblown filaments must be
deposited to form a laminate barrier structure. Meltblown filaments
are formed from spinnerettes having between 1000 and 4000,
typically 1200 and 2000, filament outlets per meter. In contrast,
spunbond filaments are formed from spinnerettes having 4000 to 8000
filament outlets per meter. Additionally, throughput per outlet is
generally greater for spunbond processes than for meltblown
processes. However, spunbond filaments are too large in diameter
for use as, for example, a barrier material.
[0008] Multi-component spunbond filaments having an appropriate
arrangement of regions of different thermoplastic polymers (e.g., a
segmented pie arrangement or a side-by-side arrangement) may be
split to define smaller individual filaments each consisting of one
region. After these filaments are collected as a nonwoven web, the
filaments in the nonwoven web may be divided by a mechanical based
approach involving a hydroentangling (or spunlacing) process that
impinges the nonwoven web with fine water jets under high pressure
to prompt filament division along the boundaries between different
multicomponent regions. When mechanical action is used to split
multicomponent filaments, the thermoplastic polymers are selected
to bond poorly with each other to facilitate subsequent division.
Another type of multi-component spunbond filaments have an
appropriate arrangement of regions of different thermoplastic
polymers (e.g., a island in the sea arrangement) that may be
separated to define smaller individual filaments each consisting of
one region. After these filaments are collected as a nonwoven web,
the filaments in the nonwoven web may be separated by a chemical
based approach that involves wetting the nonwoven web with a
solvent that selectively dissolves the sea thermoplastic polymer in
the multi component filaments leaving the islands of the other
thermoplastic polymer as the smaller individual filaments
[0009] Among the disadvantages of these conventional processes for
splitting multicomponent spunbond filaments is that the wet
nonwoven web must be dried to remove solvent or water after
processing. This introduces an additional processing step between
web production and fashioning the nonwoven web into a consumer or
industrial product. In addition, the solvent used in chemical
processes creates a waste stream that must be either recycled or
discarded.
[0010] It would be desirable, therefore, to provide a spunbonding
apparatus and methods capable of forming smaller diameter filaments
that overcomes these and other disadvantages of conventional
apparatus and methods.
SUMMARY
[0011] In one embodiment of the present invention, a spunbonding
apparatus comprises a spinneret adapted to discharge a plurality of
multicomponent filaments that move in a downwardly direction away
from the spinneret and a filament-drawing device positioned below
the spinneret. The filament-drawing device is adapted to
pneumatically attenuate the multicomponent filaments, each of which
has at least two polymer regions. The spunbonding apparatus further
includes a force applicator effective to divide at least some of
the multicomponent filaments into the at least two polymer regions
to form smaller filaments. The force applicator may direct an air
stream to impinge the multicomponent filaments between the
spinneret and the filament-drawing device. Alternatively, the force
applicator may include a roller contacting the plurality of
multicomponent filaments. The spunbonding apparatus further
includes a collector for collecting the smaller filaments.
Splitting may occur before the filaments enter the filament-drawing
device, within the filament-drawing device, and/or after discharge
from the filament-drawing device.
[0012] In another aspect of the invention, a method of forming a
spunbond nonwoven web includes forming a plurality of
multicomponent filaments each having at least two polymer regions
and pneumatically attenuating the multicomponent filaments. The
method further includes applying a dividing force to the moving
plurality of multicomponent filaments effective for dividing the at
least two polymer regions of at least some of the filaments to
provide smaller filaments and collecting the smaller filaments to
form the spunbond nonwoven web.
[0013] Among other advantages, one benefit of a split
multicomponent filament is that the constituent regions are smaller
than traditional spunbond filaments. This provides a structure that
may be used as a substitute for traditional meltblown filaments in
forming nonwoven webs, such as nonwoven webs used as barrier
materials. The ability to produce spunbond filaments with a smaller
fiber diameter, in accordance with the present invention, also
addresses the deficiency in the throughput of traditional
meltblowing processes by providing a small filament at a greater
throughput characteristic of spunbond processes that may be used as
a substitute or replacement for meltblown filaments.
[0014] These and other objects and advantages of the present
invention shall become more apparent from the accompanying drawings
and description thereof.
BRIEF DESCRIPTION OF THE FIGURES
[0015] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and, together with a general description of the
invention given above, and the detailed description given below,
serve to explain the principles of the invention.
[0016] FIG. 1 is a diagrammatic side view of a spunbonding
apparatus in accordance with an embodiment of the invention;
[0017] FIG. 1A is a diagrammatic perspective view of a portion of
the spunbonding apparatus of FIG. 1;
[0018] FIG. 2 is a cross-sectional view of a filament discharged
from the spinneret of the spunbonding apparatus of FIG. 1;
[0019] FIG. 3 is a diagrammatic side view of a filament splitting
in accordance with the principles of the invention;
[0020] FIG. 4 is a diagrammatic perspective view of a spunbonding
apparatus in accordance with another embodiment of the
invention;
[0021] FIG. 5 is a diagrammatic side view of a filament splitting
in accordance with the principles of the invention; and
[0022] FIG. 6 is a diagrammatic perspective view of a spunbonding
apparatus in accordance with yet another embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] With reference to FIGS. 1 and 1A, a spunbonding apparatus 10
is equipped with a pair of extruders 12, 14 each coupled to receive
amounts of a solid melt-processable thermoplastic polymer from a
corresponding one of a pair of hoppers 11, 13. Extruder 12 converts
one solid melt-processable thermoplastic polymer (polymer A) into a
molten state. The molten polymer A is transferred from extruder 12
under pressure and at an elevated temperature suitable for melt
processing from the extruder 12 to at least one metering pump 16.
Extruder 14 converts another solid melt-processable thermoplastic
polymer (polymer B) into a molten state. The molten polymer B is
transferred under pressure and at an elevated temperature suitable
for melt processing from the extruder 14 to at least one metering
pump 18.
[0024] Metering pumps 16, 18 pump metered amounts of the
corresponding one of molten thermoplastic polymers through separate
distribution chambers 17, 19 extending through a die body 25 to a
spin pack 20. The spin pack 20 and die body 25 form components of a
spin beam assembly that extends in the cross-machine direction of
the apparatus 10 and, thus, defines the width (typically several
meters) of a nonwoven web 30. The spin pack 20 is heated and
supported by the surrounding die body 25.
[0025] The spin pack 20 contains flow passageway plates 38 that
cooperate for distributing and combining the two molten
thermoplastic polymers received from the distribution chambers 17,
19. Heat transferred from the die body 25 to the spin pack 20
maintains the two molten thermoplastic polymers in the flow
passageway plates 38 at a temperature suitable for melt processing
and providing an extrudable melt. The flow passageway plates 38
convey the combined thermoplastic polymers to a spinneret 22 from
which a curtain of filaments 24 is discharged from an array of
discharge openings (not shown) distributed across an outlet surface
of the spinneret 22.
[0026] Quench ducts 27, which are positioned below the spinneret 22
and flanking the spinneret 22, direct a low velocity cross flow 21
of cooling air at the descending curtain of filaments 24. The cross
flow 21 of cooling air quenches the filaments 24 by reducing the
filament temperature to accelerate solidification. A blower (not
shown) and an air chilling device or air temperature reduction
(i.e., air conditioning) device supplies a flow of cooling air to
the quench ducts 27.
[0027] A filament-drawing device 26 is also positioned below the
spinneret 22 and receives the descending curtain of quenched
filaments 24. The filaments 24 are directed into a draw jet or
filament-drawing device 26 along with entrained ambient air from
the environment above and surrounding the filament-drawing device
26. A blower (not shown) supplies process air, which may be heated,
to a supply manifold of the filament-drawing device 26. Generally,
the filament-drawing device 26 includes a vertical passage 31,
which is illustrated with an exaggerated width for clarity, defined
between manifold segments and in which the filaments 24 are
impinged by converging sheets 35a,b of high velocity process air.
The process air sheets 35a,b are introduced into the vertical
passage 31 through slots 33a,b defined in the opposite sidewalls of
the vertical passage 31. The process air sheets 35a,b are
discharged from the slots 33a,b in a downwardly direction generally
parallel to the length of the filaments 24.
[0028] Because the filaments 24 are extensible, the sheets 35a,b of
high-velocity process air apply a downward drag or pneumatic force
that creates longitudinal tension to attenuate the filaments 24.
Exemplary filament-drawing devices 26 are disclosed in U.S. Pat.
Nos. 4,340,563, 6,182,732 and 6,799,957, the disclosures of which
are hereby incorporated herein by reference in their entirety.
Other types of filament-drawing devices 26 are contemplated by the
invention as usable with the spunbonding apparatus 10.
[0029] A descending curtain of attenuated filaments 24 is
discharged from filament-drawing device 26 and propelled toward a
moving porous collector 28. The filaments 24 are deposited in a
substantially random manner as substantially flat loops on the
collector 28 to aggregately form nonwoven web 30. The width of the
nonwoven web 30 deposited on collector 28 is approximately equal to
the width of the curtain of filaments 24. The collector 28 is
traveling in a machine direction (MD) relative to the spunbonding
apparatus 10 and filament-drawing device 26.
[0030] Positioned below the collector 28 is an air management
system 32 that supplies a vacuum transferred through the collector
28 for attracting the filaments 24 onto the collector 28 and
disposing of the high-velocity process air discharged from the
filament-drawing device 26 so that filament laydown is relatively
undisturbed. Exemplary air management systems 32 are disclosed in
U.S. Pat. No. 6,499,982, the disclosure of which is hereby
incorporated by reference herein in its entirety.
[0031] Additional meltspinning apparatus (not shown) may be
provided either downstream or upstream of spunbonding apparatus 10
for depositing one or more additional spunbond and/or meltblown
nonwoven webs of either monocomponent or multicomponent filaments
either as a substrate for receiving nonwoven web 30 or onto an
exposed surface of nonwoven web 30. An example of such a multilayer
laminate in which some of the individual layers are spunbond and
some meltblown is a spunbond/meltblown/spunbond (SMS) laminate made
by sequentially depositing onto a moving forming belt first a
spunbond fabric layer, then a meltblown fabric layer and last
another spunbond layer containing filaments 24.
[0032] With continued reference to FIGS. 1 and 1A, spunbonding
apparatus 10 further includes a pair of air knives 40a,b located
generally in the open space between the spinneret 22 and the
filament-drawing device 26 and below the quench ducts 27. Air knife
40a directs a flat sheet or stream of process air, generally
indicated by reference numeral 42a, with a high velocity towards
and against the flow of filaments 24 on a downstream side of the
filaments 24. Air knife 40b directs a flat sheet or stream of
process air, generally indicated by reference numeral 42b, with a
high velocity towards and against the flow of filaments 24 on an
upstream side of the filaments 24. Downstream and upstream are
defined in relation to the machine direction and relative to the
curtain of filaments 24. The high velocity streams 42a,b of process
air from the air knives 40a,b impinge the filaments 24 and apply a
force to the filaments 24 between the spinneret 22 and
filament-drawing device 26 and before the filaments 24 enter the
filament-drawing device 26.
[0033] Each of the air knives 40a,b transforms or amplifies a
relatively low flow of compressed air to deliver the corresponding
one of the high velocity process air streams 42a,b. Air knife 40a
includes an internal air plenum (not shown) coupled by a feed
conduit 41a with a source of compressed air, such as a standard
centrifugal blower. Air knife 40a includes an outlet 44a, such as a
single elongate slot or a line of shorter aligned slots, from which
the air stream 42a is discharged. Alternatively, the outlet 44a of
air knife 40a may include a plurality of densely-spaced orifices,
or any other suitable structure for discharging the corresponding
process air stream as a high velocity stream 42. The air knife 40a
may also include a Coanda surface that defines a guide for
directing the high velocity stream discharged from the outlet 44a.
Air knife 40b has a construction identical or similar to the
construction air knife 40a and, accordingly, also includes a feed
conduit 41b and outlet 44b similar to the feed conduit 41a and
outlet 44a as described above for air knife 40a.
[0034] Suitable air knives 40a,b for use in the present are
commercially available from various vendors including but not
limited to EXAIR Corporation (Cincinnati, Ohio), which sells air
knives under the Super Air Knife trade name. The invention
contemplates that the air knives 40a,b may be replaced by multiple
air jets (not shown). The invention also contemplates that,
although two air knives 40a,b are depicted in FIG. 1, more than two
air knives, each similar or identical to air knives 40a,b or even a
single air knife, similar or identical to either of the air knives
40a,b, may be used to provide additional high velocity air streams,
similar to high velocity air streams 42a,b, that impinge the
filaments 24.
[0035] With reference to FIG. 2, the constituent thermoplastic
polymers in multicomponent filaments 24 are arranged in distinct
regions 24a,b across the cross-section of the filament 24 and are
coupled cohesively along an interface 24c along which at least two
regions 24a,b contact or otherwise confront. Regions 24a,b extend
substantially along the entire length of the filament 24 and the
filaments 24 are each substantially continuous and
uninterrupted.
[0036] The regions 24a,b may have any cross-sectional profile that
is capable of being split by an applied force. For example, the
filaments 24 may have a circular or circular eccentric side-by-side
configuration, an oval configuration, a trilobal configuration, a
triangular configuration, a dog-boned configuration, a segmented
pie or wedge configuration, or a flat ribbon-like configuration.
Advantageously, the thermoplastic polymers are immiscible to
promote splitting along the interface 24c between each set of
adjacent regions 24a,b constituted by the different polymers. The
interface 24c will define a shear line once splitting is
initiated.
[0037] The invention contemplates that additional thermoplastic
polymers may be combined with these two thermoplastic polymers in
the spin pack 20 to form multicomponent filaments 24 with more than
two constituent thermoplastic polymers and more than a single
interface, similar to interface 24c, along which splitting may
occur. After splitting is induced, these multicomponent filaments
24 may partially split in that certain regions may remain bonded
together in pairs or groups with intact, bonded interfaces.
[0038] The melt-processable thermoplastic polymers in regions 24a,b
are usually different from each other, although multicomponent
filaments 24 may comprise separate components of similar or
identical polymeric materials. The two melt-processable
thermoplastic polymers may be of different composition, or have
different melt flow rates and the same composition. The polymers in
regions 24a,b may each be selected from among any commercially
available spunbond grade of a wide range of thermoplastic polymer
resins, copolymers, and blends of thermoplastic polymer resins
including, but not limited to, polyolefins, such as polyethylene
and polypropylene, polyesters, nylons, polyamides, polyvinyl
acetate, polyvinyl chloride, polyvinyl alcohol, and cellulose
acetate. Additives such as surfactants, colorants, anti-static
agents, lubricants, flame retardants, antibacterial agents,
softeners, ultraviolet absorbers, polymer stabilizers, and the like
may also be blended with either thermoplastic polymer. Each
constituent thermoplastic polymer may be identical in base
composition and differ only in additive concentration.
[0039] With reference to FIGS. 1, 1A, 2, and 3, the air streams
42a,b from the air knives 40a,b each apply a force to the filaments
24 that is effective for weakening or breaking the cohesive force
along interface 24c of at least a portion of the filaments 24
before the filaments 24 enter into the inlet to the
filament-drawing device 26. The force applied by each of the air
streams 42a,b from air knives 40a,b, respectively, acts along a
line that differs from the line of action of the attenuation force
applied by the filament-drawing device 26. Generally, each of the
air knives 40a,b represents a force applicator operative for
applying a force along a line non-parallel or non-collinear with
the attenuation force applied to the filaments 24 by the filament
drawing device 26, which is along the length of the filaments
24.
[0040] Specifically, the air streams 42a,b are directed to impinge
the filaments 24 at an angle, .alpha., less than 180.degree. and
greater than 0.degree. to an axis 47 aligned with a direction of
motion of the filaments 24, which is along the length of the
filaments 24. As a result, the air streams 42a,b transfer momentum
to the filaments 24 to generate the force that promotes division or
splitting at the interface 24c between regions 24a,b. The
attenuation force transferred from the filament-drawing device 26
to the filaments 24 is a tensile force acting parallel to axis 47.
The operation of the filament-drawing device 26 may also encourage
splitting for filaments 24 characterized by weakened cohesion along
interface 24c.
[0041] The resolved splitting-promoting force transferred from the
air streams 42a,b to the filaments 24 has a vector component acting
along a line that is perpendicular to the line of action of the
attenuation force (i.e., axis 47). Another vector force component
of the splitting-promoting force acts parallel to the attenuation
force and, as a result, does not contribute significantly to the
filament splitting in this embodiment of the invention. If the air
stream impingement angle relative to axis 47 is equal to
90.degree., the splitting-promoting force only has a vector
component applied along a line that is perpendicular to the line of
action of the attenuation force.
[0042] Filaments 24 that experience a loss of cohesion will divide
or partition into the constituent regions 25a,b, which have a
reduced cross-sectional area. Although the invention is not so
limited, the invention contemplates that substantially all of the
filaments 24 may split along their respective interfaces 24c and
into constituent regions 25a,b before entering into the
filament-drawing device 26. However, the force applied to the
filaments 24 may weaken, but not break, the cohesive force along
the interface 24c of another portion of the filaments 24 before the
filaments 24 enter the filament drawing device 26.
[0043] The filaments 24 are stretched taut in the space between the
spinneret 22 and the filament-drawing device 26 and are
non-touching when contacted by the air steams 42a,b from the air
knives 40a,b. The impinging high velocity process air sheets 35a,b
inside the filament-drawing device 26 cause attenuation of the
filaments 24. The process air sheets 35a,b may also cause some or
all of the intact filaments 24 with reduced cohesion to split
inside the filament-drawing device 26 and/or additional attenuation
of the split filaments 24. Additional splitting may occur of intact
filaments 24 with reduced cohesion after the filaments 24 are
discharged from the filament-drawing device 26 and before the
filaments 24 impact the collector 28. The air velocity of the air
streams 35a,b to which the filaments 24 are exposed inside the
filament-drawing device 26 is adjusted to select a spinning speed
that does not cause a significant number of the filaments 24, which
are reduced in diameter by splitting induced by the air streams
42a,b from air knives 40a,b, to break during attenuation.
[0044] In use, two thermoplastic polymers are melted in extruders
12, 14 and are subsequently combined to form filaments 24.
Filaments 24 in the descending curtain extruded from spinneret 22
are attenuated by the operation of the filament-drawing device 26
and are quenched by cooling air from quench ducts 27. The air
streams 42a,b from the air knives 40a,b apply a force to the
filaments 24 before the filaments 24 enter into the
filament-drawing device 26. This force, which acts along a line
that differs from the line of action (i.e., axis 47) of the tensile
force applied by the filament-drawing device 26, is effective for
weakening or breaking the cohesive force along interface 24c of at
least a portion of the filaments 24. Filaments 24 that lose
cohesive will divide or partition into the constituent regions
25a,b, which have a reduced cross-sectional area in comparison with
the intact filament 24, before collection on collector 28.
[0045] With reference to FIG. 4 in which like reference numerals
refer to like features in FIGS. 1,1A and in an alternative
embodiment of the present invention, the air knives 40a,b (FIGS.
1,1A) may be replaced by a set of rollers 45, 46 positioned between
the spinneret 22 and the filament-drawing device 26 and beneath the
quench ducts 27. The rollers 45, 46 are arranged on opposite sides
of the curtain of filaments 24 and physically contact the
descending filaments 24 before the filaments 24 enter the
filament-drawing device 26. The rollers 45, 46 may be offset
vertically so that each of the rollers 45, 46 may be positioned
closer to the center-plane of the descending curtain of filaments
24.
[0046] The rollers 45, 46 are each driven rotationally in a
direction that opposes the downward movement of the filaments 24.
This operates to increase the mechanical drag applied to the
filaments 24 and increases the tension between the rollers 45, 46
and the filament-drawing device 26. As a result, rollers 45, 46
each represent a force applicator that is operative for applying a
tensile force acting along a line that is parallel to the line
(i.e., axis 47) of the attenuation force applied to the filaments
24 by the filament drawing device 26. The tensile force applied by
the rollers 45, 46 is effective for promoting splitting of the
filaments 24, but is believed to supply negligible attenuation
because of quenching before the filaments 24 reach rollers 45, 46.
The rollers 45, 46 may be chilled so that the curved surfaces
contacted by the filaments 24 are cooled. The invention
contemplates that only one of the rollers 45, 46 may be present or
that more than two rollers may be used to apply tension to the
filaments 24 effective to promote filament splitting.
[0047] With reference to FIG. 5, filament splitting is promoted by
the tensile force applied to the filaments 24 because of the speed
difference introduced by the rollers 45, 46. Region 70 of the
transit path for filaments 24 is defined above the control points
defined by rollers 45, 46. In region 70, the filaments 24 are
attenuated and have a first velocity. Region 72 of the transit path
for the filaments 24 is defined between rollers 45, 46 and the
filament-drawing device 26. In region 72, the filament-drawing
device 26 maintains the tension on the filaments 24 and the
filaments 24 have a second velocity greater than the first velocity
in region 72. The difference in velocity promotes splitting due to
the tensile force applied to the filaments 24 is in a direction
parallel to the direction in which the attenuation force is applied
to the filaments 24 by the filament-drawing device 26.
[0048] With reference to FIG. 6 in which like reference numerals
refer to like features in FIG. 1, and in an alternative embodiment
of the present invention, the spunbonding apparatus 10 may include
a set of rollers 48, 50, 52 positioned on one side of the
descending curtain of filaments 24 and another set of rollers 54,
56, 58 positioned on the opposite side of the descending curtain of
filaments 24. The rollers 48-58 are positioned vertically between
the spinneret 22 and the filament-drawing device 26. A portion of
the filaments 24 is threaded through rollers 48, 50, 52 and another
portion of the filaments 24 is threaded through rollers 54, 56, 58.
Rollers 48, 50, 52 and rollers 54, 56, 58 redirect the path of the
filaments 24 and, in doing so, apply a force to the filaments 24
that imparts mechanical drag that is effective to cause filament
splitting before the filaments 24 enter the filament-drawing device
26. The force applied by rollers 48 and 54 causes the majority of
the filament attenuation.
[0049] The invention contemplates that different numbers of rollers
may be included in each set of rollers. For example, each roll set
may include a set of four individual rollers about which the
filaments 24 are threaded and directed.
[0050] Each of the rollers 48-58 is capable of driven rotation
about a central axis. In one embodiment of the present invention,
rollers 50 and 56 will have a slightly faster angular velocity or
speed than rollers 48 and 54, respectively, which to create tension
in the filaments 24 and applies a tensile force that breaks the
cohesive force of the interface 24c between the filament regions
24a,b and initiate the splitting. Rollers 52 and 58 will maintain
the same speed as rollers 50 and 56, respectively, or be rotated
with a slightly faster speed than rollers 50 and 56. Although not
wishing to be bound by theory, the tension is believed to provide a
minor contribution to filament attenuation during splitting but the
split attenuated filament size should return after the tension
applied between rollers 48 and 50 and the tension applied between
rollers 54 and 56 is released. The filament-drawing device 26 is
believed to provide a minor contribution to attenuation and
operates primarily to distribute the filaments 24 across the
collector 28.
[0051] With reference to FIGS. 5 and 6, filament splitting is
promoted by the tensile force applied to the filaments 24 because
of the speed difference between roller 48 and roller 50 and the
speed difference between roller 54 and roller 56. For example, in
region 70 above the control point defined by roller 48 and between
roller 48 and the spinneret 22, the filaments 24 are attenuated and
have a first velocity. In region 72 between rollers 48 and 50, the
split-promoting tensile force is applied to the filaments 24, which
are sufficiently quenched such that significant permanent
attenuation does not occur in region 72. Filament tension is
maintained in region 72 by the downstream roller 52 and the
filament-drawing device 26. After exiting region 72, the tension
applied by rollers 48, 50 is released and the filaments 24 are
believed to reassume their split attenuated size in region 70.
Similar considerations apply to rollers 54, 56, and 58.
[0052] Alternatively and with renewed reference to FIG. 6, all
rollers 48-58 may be driven at the same angular velocity or speed
that is lower than the filament draw speed or spinning speed of the
filament-drawing device 26. In this instance, a tensile force is
applied to filaments 24 in transit between roller 52 and the
filament-drawing device 26 because the rollers 48, 50, 52 increase
the tension between roller 52 and the filament-drawing device 26.
Similarly, a tensile force is applied to filaments 24 in transit
between roller 58 and the filament-drawing device 26 because the
rollers 54, 56, 58 increase the tension between roller 58 and the
filament-drawing device 26. These tensile forces promote filament
splitting, as described with regard to FIG. 5, and act along a line
(i.e., axis 47) parallel with the attenuation force applied by the
filament-drawing device 26. Splitting may occur before the
filaments 24 enter the filament-drawing device 26, within the
filament-drawing device 26, and/or after discharge from the
filament-drawing device 26.
[0053] With continued reference to FIG. 6, optional air knives 60,
62 may be provided that generate air sheets 64, 66, respectively,
that impinge the filaments 24 in the space between the spinneret 22
and the filament-drawing device 26. Air knives 60, 62 are typically
similar in construction to air knives 40a,b. Air knife 60 supplies
a stream or sheet 64 of high velocity process air that impinges the
filaments 24 in a direction that angled relative to the direction
of motion of the filaments 24 between rollers 48 and 50. The air
sheet 64 promotes splitting of the filaments 24 to which a tensile
force is applied between rollers 48 and 50. Similarly, air knife 62
supplies a stream or sheet 66 of high velocity process air that
impinges the filaments 24 in a direction that angled relative to
the direction of motion of the filaments 24 between rollers 54 and
56. The air sheet 66 promotes splitting of the filaments 24 to
which a tensile force is applied between rollers 54 and 56.
[0054] Generally, the optional air knives 60, 62 each represent a
force applicator that is operative for applying a force along a
line non-parallel or non-collinear with the attenuation force
applied to the filaments 24 by the filament-drawing device 26,
which acts along the length of the filaments 24 (i.e., axis 47).
Specifically, the air sheets 64, 66 are directed to impinge the
filaments 24 perpendicular (i.e., 90.degree.) to the direction of
motion of the filaments 24 between rollers 48 and 50 and between
rollers 54 and 56, respectively, or at an angle, .alpha., less than
180.degree. and greater than 0.degree. to the motion direction. As
a result, the air sheets 64, 66 transfer momentum to the filaments
24 to generate the force that promotes division or splitting at the
interface 24c between regions 24a,b.
[0055] The resolved splitting-promoting force has a vector
component acting along a line that is perpendicular to the line of
action of the attenuation force, which is parallel to length of the
filament and axis 47. The resolved vector component of the force
imparted by the air sheets 64, 66 parallel to the attenuation force
does not contribute significantly to the filament splitting. If the
air sheet impingement angle is at 90.degree. to the axis 47, the
splitting-promoting force only has a vector component applied along
a line that is perpendicular to the line of action of the
attenuation force and the axis 47.
[0056] The attenuation force transferred from the rollers 50, 52,
56, 58 and the filament-drawing device 26 to the filaments 24 is a
tensile force applied along the direction of motion and directed
along the length of the filaments 24.
[0057] The attenuation force is believed to further develop the
filament splitting promoted by the air sheets 64, 66. Splitting may
occur before the filaments 24 enter the filament-drawing device 26,
within the filament-drawing device 26, and/or after discharge from
the filament-drawing device 26.
[0058] While the present invention has been illustrated by a
description of various embodiments and while these embodiments have
been described in considerable detail, it is not the intention of
the applicants to restrict or in any way limit the scope of the
appended claims to such detail. Additional advantages and
modifications will readily appear to those skilled in the art. The
invention in its broader aspects is therefore not limited to the
specific details, representative apparatus and methods, and
illustrative examples shown and described. Accordingly, departures
may be made from such details without departing from the spirit or
scope of applicants' general inventive concept. The scope of the
invention itself should only be defined by the appended claims,
wherein we claim:
* * * * *