U.S. patent application number 10/694420 was filed with the patent office on 2005-04-28 for method and apparatus for production of nonwoven webs.
Invention is credited to Haynes, Bryan David, Lennon, Eric Edward.
Application Number | 20050087288 10/694420 |
Document ID | / |
Family ID | 34423338 |
Filed Date | 2005-04-28 |
United States Patent
Application |
20050087288 |
Kind Code |
A1 |
Haynes, Bryan David ; et
al. |
April 28, 2005 |
Method and apparatus for production of nonwoven webs
Abstract
The present invention provides an improved process of using
electrostatics in the formation of nonwoven webs. In the process of
the present invention, a source of fibers is provided. The fibers
and filaments are subject to an electrostatic charge which is
generated via an electrostatic unit having a first side and a
second side opposed to each other, wherein the electrostatic unit
has an array of protrusions on the first side and the second side
of the electrostatic unit. Once subject to the electrostatic
charge, the fibers are collected on a forming surface to form a
nonwoven web. The present invention also provides an apparatus for
forming a nonwoven web. The apparatus of the present invention has
a source of fibers, a device for applying an electrostatic charge
to said fibers, wherein device having a first side and a second
side opposed to each other, wherein the device has an array of
protrusions on the first side and the second side of the device;
and a forming surface for collecting said fibers.
Inventors: |
Haynes, Bryan David;
(Advance, NC) ; Lennon, Eric Edward; (Roswell,
GA) |
Correspondence
Address: |
KIMBERLY-CLARK WORLDWIDE, INC.
401 NORTH LAKE STREET
NEENAH
WI
54956
|
Family ID: |
34423338 |
Appl. No.: |
10/694420 |
Filed: |
October 27, 2003 |
Current U.S.
Class: |
156/167 ;
156/273.1; 156/379.8; 156/441; 264/103; 264/210.8; 264/465;
264/555; 425/174.8R; 425/72.2 |
Current CPC
Class: |
D04H 3/02 20130101; D01D
10/00 20130101; D01D 5/0985 20130101; D04H 3/16 20130101 |
Class at
Publication: |
156/167 ;
264/103; 264/465; 264/210.8; 264/555; 425/174.80R; 425/072.2;
156/273.1; 156/379.8; 156/441 |
International
Class: |
D04H 003/02; D04H
003/16 |
Claims
We claim:
1. A process for forming a nonwoven web comprising a. providing a
source of fibers; b. subjecting said fibers to an electrostatic
charge by passing said fibers through an electrostatic unit having
a first side and a second side opposed to each other, wherein the
electrostatic unit has an array of protrusions on both the first
side and the second side of the electrostatic unit; c. collecting
said fibers on a forming surface to form a nonwoven web.
2. The process of claim 1, wherein the electrostatic charge is
generated between the array of protrusions of the first side and
the array of protrusions of the second side and the array of
protrusions of the first side and the array of protrusions of the
second side are opposed to one another one.
3. The process of claim 2, wherein the array of protrusions of the
first side and the array of protrusions of the second side each
comprise an array of pins.
4. The process of claim 3, wherein the array of pins of the first
side and the array of pins of the second side are recessed within a
cavity of an insulating material such that the pins essentially do
not extend beyond the insulating material.
5. The process of claim 2, wherein the fibers are provided by a
melt spinning process and the fibers are substantially continuous
fibers.
6. The process of claim 2, wherein continuous fibers are subjected
to pneumatic draw force in a fiber draw unit prior to being
subjected to said electrostatic charge.
7. The process of claim 2, further comprising deflecting the fibers
with a deflecting device prior collecting the fibers on the forming
surface.
8. The process of claim 1, wherein the fibers are substantially
continuous fibers provided by melt spinning and are subjected to
pneumatic draw force in a fiber draw unit prior to being subjected
to said electrostatic charge, the array of protrusions of the first
side and the array of protrusions of the second side each comprise
an array of pins, the electrostatic charge is generated between the
array of pins of the first side and the array of pins of the second
side and the array of pins of the first side and the array of pins
of the second side are opposed to one another one.
9. The process of claim 8, wherein the array of pins of the first
side and the array of pins of the second side are recessed within a
cavity of an insulating material such that the pins essentially do
not extend beyond the insulating material.
10. The process of claim 9, further comprising deflecting the
fibers with a deflecting device prior collecting the fibers on the
forming surface.
11. The process of claim 1, wherein the electrostatic charge is
generated by a series of at least two separate electrostatic charge
fields along a length of the electrostatic unit, each charge field
having an array of protrusions on at least one of the first side or
the second side of the electrostatic unit.
12. The process of claim 11, wherein the array of protrusions of
the first side and the array of protrusions of the second side each
comprise an array of pins.
13. The process of claim 12, wherein a first charge field is
generated by the array of pins on the first side of the
electrostatic unit and a second charge field is generated by the
array of pins on the second side of the electrostatic unit.
14. The process of claim 13, wherein a first electrostatic charge
field is generated between a first array of pins on the first side
of the electrostatic unit and first array of pins on the second
side of the electrostatic unit and a second electrostatic charge
field is generated between a second array of pins on the first side
of the electrostatic unit and a second array of pins on the second
side of the electrostatic unit.
15. The process of claim 14, wherein the first electrostatic field
is generated from a potential on the first side of the
electrostatic unit and the second electrostatic field is generated
from a potential on second side of the electrostatic unit.
16. The process of claim 11, wherein the array of pins of the first
side and the array of pins of the second side are recessed within a
cavity of an insulating material such that the pins essentially do
not extend beyond the insulating material.
17. The process of claim 2, wherein an electrical potential is
alternated from the protrusions on the first side to the
protrusions on the second side and back to the protrusions on the
first side.
18. An apparatus for forming a nonwoven web comprising a. a source
of fibers; b. a device for applying an electrostatic charge to said
fibers, said device comprising a first side and a second side
opposed to each other, wherein the device has an array of
protrusions on the first side and the second side of the
electrostatic unit; c. a forming surface for collecting said
fibers.
19. The apparatus of claim 18, wherein the array of protrusions on
the first and second sides comprise an array of pins.
20. The apparatus of claim 19, the array of pins of the first side
and the array of pins of the second side are recessed within a
cavity of an insulating material such that the pins essentially do
not extend beyond the insulating material.
21. The apparatus of claim 19, wherein the source of fibers
comprises a spinplate which is feed with one or more polymeric
materials.
22. The apparatus of claim 21, further comprising a fiber draw
unit, wherein the fiber draw unit is located below the source of
fibers and the device for applying an electrostatic charge.
23. The apparatus of claim 22, further comprising a deflector
located below the device for applying an electrostatic charge and
above the forming surface.
24. The apparatus of claim 19, wherein the device for applying an
electrostatic charge comprises a series of at least two separate
electrostatic charge fields sections along a length of the
electrostatic unit, each charge field section having an array of
pins on at least one of the first side or the second side of the
device.
25. The apparatus of claim 24, wherein an electrostatic charge
field is generated between a first array of pins on the first side
of the electrostatic unit and first array of pins on the second
side of the electrostatic unit arranged such that the pins of the
first side and the pins of the second side are opposed to each
other and a second electrostatic charge field is generated between
a second array of pins on the first side of the electrostatic unit
and a second array of pins on the second side of the electrostatic
unit arranged such that the pins of the first side and the pins of
the second side are opposed to each other.
26. The nonwoven web produced by the process of claim 1.
27. The nonwoven web produced by the process of claim 8.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for forming
nonwoven webs and an apparatus for forming such webs.
BACKGROUND OF THE INVENTION
[0002] Many of the personal care products, medical care garments
and products, protective wear garments, mortuary and veterinary
products in use today are partially or wholly constructed of
nonwoven web materials. Examples of such products include, but are
not limited to, consumer and professional medical and health care
products such as surgical drapes, gowns and bandages, protective
workwear garments such as coveralls and lab coats, and infant,
child and adult personal care absorbent products such as diapers,
training pants, swimwear, incontinence garments and pads, sanitary
napkins, wipes and the like. For these applications nonwoven
fibrous webs provide tactile, comfort and aesthetic properties
which can approach those of traditional woven or knitted cloth
materials. Nonwoven web materials are also widely utilized as
filtration media for both liquid and gas or air filtration
applications since they can be formed into a filter mesh of fine
fibers having a low average pore size suitable for trapping
particulate matter while still having a low pressure drop across
the mesh.
[0003] Nonwoven web materials have a physical structure of
individual fibers or filaments which are interlaid in a generally
random manner rather than in a regular, identifiable manner as in
knitted or woven fabrics. The fibers may be continuous or
discontinuous, and are frequently produced from thermoplastic
polymer or copolymer resins from the general classes of
polyolefins, polyesters and polyamides, as well as numerous other
polymers. Blends of polymers or conjugate multicomponent fibers may
also be employed. Nonwoven fibrous webs formed by melt extrusion
processes such as spunbonding and meltblowing, as well as those
formed by dry-laying processes such as carding or air-laying of
staple fibers are well known in the art. In addition, nonwoven
fabrics may be used in composite materials in conjunction with
other nonwoven layers as in a spunbond/meltblown (SM) and
spunbond/meltblown/spunbond (SMS) laminate fabrics, and may also be
used in combination with thermoplastic films. Nonwoven fabrics may
also be bonded, embossed, treated and/or colored to impart various
desired properties, depending on end-use application.
[0004] Melt extrusion processes for spinning continuous filament
yarns and continuous filaments or fibers such as spunbond fibers,
and for spinning microfibers such as meltblown fibers, and the
associated processes for forming nonwoven webs or fabrics
therefrom, are well known in the art. Typically, fibrous nonwoven
webs such as spunbond nonwoven webs are formed with the fiber
extrusion apparatus, such as a spinneret, and fiber attenuating
apparatus, such as a fiber drawing unit (FDU), oriented in the
cross-machine direction or "CD". That is, the apparatus is oriented
at a 90 degree angle to the direction of web production. The
direction of nonwoven web production is known as the "machine
direction" or "MD". Although the fibers are laid on the forming
surface in a generally random manner, still, because the fibers
exit the CD oriented spinneret and FDU and are deposited on the
MD-moving forming surface, the resulting nonwoven webs have an
overall average fiber directionality wherein more of the fibers are
oriented in the MD than in the CD. It is widely recognized that
such properties as material tensile strength, extensibility and
material barrier, for example, are a function of the material
uniformity and the directionality of the fibers or filaments in the
web. Various attempts have been made to distribute the fibers or
filaments within the web in a controlled manner, attempts including
the use of electrostatics to impart a charge to the fibers or
filaments, the use of spreader devices to direct the fibers or
filaments in a desired orientation, the use of mechanical
deflection means for the same purpose, and reorienting the fiber
forming means. Electrostatic charging devices are known in the art.
Generally described, an electrostatic charging device may have one
or more rows of electric emitter pins or bars which produce a
corona discharge, thereby imparting an electrostatic charge to the
fibers. The fibers, once charged, will tend to repel one another
and help prevent groups of individual fibers from clumping or
"roping" together. An exemplary process for charging fibers to
produce nonwovens with improved fiber distribution is disclosed in
co-assigned PCT Pub. No. WO 02/52071 published Jul. 4, 2002.
However, it remains desired to achieve still further capability to
gain this control in a way that is consistent with costs dictated
by the disposable applications for many of these nonwovens.
SUMMARY OF THE INVENTION
[0005] The present invention provides an improved process of using
electrostatics in the formation of nonwoven webs. In the process of
the present invention, a source of fibers is provided. The fibers
and filaments are subject to an electrostatic charge which is
generated via an electrostatic unit having a first side and a
second side opposed to each other, wherein the electrostatic unit
has an array of protrusions on both the first side and the second
side of the electrostatic unit. Once subject to the electrostatic
charge, the fibers are collected on a forming surface to form a
nonwoven web.
[0006] The present invention also provides an apparatus for forming
a nonwoven web. The apparatus of the present invention has a source
of fibers, a device for applying an electrostatic charge to said
fibers, wherein the device having a first side and a second side
opposed to each other, wherein the device has an array of
protrusions on the first side and the second side of the device;
and a forming surface for collecting said fibers.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 shows a schematic illustration of an exemplary
process for process for producing a nonwoven web.
[0008] FIGS. 2 A and 2B each show an exemplary device for applying
an electrostatic charge to the fibers.
[0009] FIG. 3 shows an exemplary device for applying an
electrostatic charge to the fibers.
DEFINITIONS
[0010] As used herein and in the claims, the term "comprising" is
inclusive or open-ended and does not exclude additional unrecited
elements, compositional components, or method steps.
[0011] As used herein the term "polymer" generally includes but is
not limited to, homopolymers, copolymers, such as for example,
block, graft, random and alternating copolymers, terpolymers, etc.
and blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometrical configurations of the material. These configurations
include, but are not limited to isotactic, syndiotactic and random
symmetries.
[0012] As used herein the term "fibers" refers to both staple
length fibers and continuous fibers, also known as filaments,
unless otherwise indicated.
[0013] As used herein the term "monocomponent" fiber refers to a
fiber formed from one or more extruders using only one polymer.
This is not meant to exclude fibers formed from one polymer to
which small amounts of additives have been added for color,
anti-static properties, lubrication, hydrophilicity, etc. These
additives, e.g. titanium dioxide for color, are generally present
in an amount less than 5 weight percent and more typically about 2
weight percent.
[0014] As used herein the term "multicomponent fibers" refers to
fibers which have been formed from at least two component polymers,
or the same polymer with different properties or additives,
extruded from separate extruders but spun together to form one
fiber. Multicomponent fibers are also sometimes referred to as
conjugate fibers or bicomponent fibers. The polymers are arranged
in substantially constantly positioned distinct zones across the
cross-section of the multicomponent fibers and extend continuously
along the length of the multicomponent fibers. The configuration of
such a multicomponent fiber may be, for example, a sheath/core
arrangement wherein one polymer is surrounded by another, or may be
a side by side arrangement, an "islands-in-the-sea" arrangement, or
arranged as pie-wedge shapes or as stripes on a round, oval, or
rectangular cross-section fiber.
[0015] Multicomponent fibers are taught in, for example, U.S. Pat.
No. 5,108,820 to Kaneko et al., U.S. Pat. No. 5,336,552 to Strack
et al., and U.S. Pat. No. 5,382,400 to Pike et al. For two
component fibers, the polymers may be present in ratios of 75/25,
50/50, 25/75 or any other desired ratios.
[0016] As used herein the term "biconstituent fiber" or
"multiconstituent fiber" refers to a fiber formed from at least two
polymers, or the same polymer with different properties or
additives, extruded from the same extruder as a blend and wherein
the polymers are not arranged in substantially constantly
positioned distinct zones across the cross-section of the
multicomponent fibers. Fibers of this general type are discussed
in, for example, U.S. Pat. No. 5,108,827 to Gessner.
[0017] As used herein the term "nonwoven web" or "nonwoven
material" means a web having a structure of individual fibers or
filaments which are interlaid, but not in an identifiable manner as
in a knitted or woven fabric. Nonwoven webs have been formed from
many processes such as for example, meltblowing processes,
spunbonding processes, air-laying processes and carded web
processes. The basis weight of nonwoven fabrics is usually
expressed in grams per square meter (gsm) or ounces of material per
square yard (osy) and the fiber diameters useful are usually
expressed in microns. (Note that to convert from osy to gsm,
multiply osy by 33.91).
[0018] As used herein, the term "spunbond" or "spunbond nonwoven
web" means to a nonwoven fiber or filament material of small
diameter fibers that are formed by extruding molten thermoplastic
polymer as fibers from a plurality of capillaries of a spinneret.
The extruded fibers are cooled while being drawn by an eductive or
other well known drawing mechanism. The drawn fibers are deposited
or laid onto a forming surface in a generally random manner to form
a loosely entangled fiber web, and then the laid fiber web is
subjected to a bonding process to impart physical integrity and
dimensional stability. The production of spunbond fabrics is
disclosed, for example, in U.S. Pat. No. 4,340,563 to Appel et al.,
U.S. Pat. No. 3,692,618 to Dorschner et al., and U.S. Pat. No.
3,802,817 to Matsuki et al. Typically, spunbond fibers or filaments
have a weight-per-unit-length in excess of about 1 denier and up to
about 6 denier or higher, although both finer and heavier spunbond
fibers can be produced. In terms of fiber diameter, spunbond fibers
generally have an average diameter of larger than 7 microns, and
more particularly between about 10 and about 25 microns, and up to
about 30 microns or more.
[0019] As used herein the term "meltblown fibers" means fibers or
microfibers formed by extruding a molten thermoplastic material
through a plurality of fine, usually circular, die capillaries as
molten threads or fibers into converging high velocity gas (e.g.
air) streams which attenuate the fibers of molten thermoplastic
material to reduce their diameter. Thereafter, the meltblown fibers
are carried by the high velocity gas stream and are deposited on a
collecting surface to form a web of randomly dispersed meltblown
fibers. Such a process is disclosed, for example, in U.S. Pat. No.
3,849,241 to Buntin. Meltblown fibers may be continuous or
discontinuous, are generally smaller than 10 microns in average
diameter and are often smaller than 7 or even 5 microns in average
diameter, and are generally tacky when deposited onto a collecting
surface.
[0020] As used herein, "thermal point bonding" involves passing a
fabric or web of fibers or other sheet layer material to be bonded
between a heated calender roll and an anvil roll. The calender roll
is usually, though not always, patterned on its surface in some way
so that the entire fabric is not bonded across its entire surface.
As a result, various patterns for calender rolls have been
developed for functional as well as aesthetic reasons. One example
of a pattern has points and is the Hansen Pennings or "H&P"
pattern with about a 30% bond area with about 200 bonds/square inch
as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The
H&P pattern has square point or pin bonding areas wherein each
pin has a side dimension of 0.038 inches (0.965 mm), a spacing of
0.070 inches (1.778 mm) between pins, and a depth of bonding of
0.023 inches (0.584 mm). The resulting pattern has a bonded area of
about 29.5%. Another typical point bonding pattern is the expanded
Hansen and Pennings or "EHP" bond pattern which produces a 15% bond
area with a square pin having a side dimension of 0.037 inches
(0.94 mm), a pin spacing of 0.097 inches (2.464 mm) and a depth of
0.039 inches (0.991 mm). Other common patterns include a diamond
pattern with repeating and slightly offset diamonds and a wire
weave pattern looking as the name suggests, e.g. like a window
screen. Typically, the percent bonding area varies from around 10%
to around 30% of the area of the fabric laminate web. Thermal point
bonding imparts integrity to individual layers by bonding fibers
within the layer and/or for laminates of multiple layers, point
bonding holds the layers together to form a cohesive laminate.
[0021] As used herein, the term "protrusions" means a structure
which extends outward from another structure. The protrusions can
extend into the fiber curtain passing through the electrostatics
unit or can be recessed in a cavity such that they do not extend
into the fiber curtain, but extend from a structure with the
cavity. In the present invention, the protrusions can be rods,
bars, a wire, a loop of wire or pins.
[0022] As used herein, the term "array" means a matrix of
protrusions. The matrix can be one row of protrusions extending the
width of the cross machine direction of the process or a series of
rows.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The present invention provides an improved process of using
electrostatics in the formation of nonwoven webs. In the process of
the present invention, a source of fibers is provided. The fibers
are subject to an electrostatic charge which is generated via an
electrostatic unit having a first side and a second side opposed to
each other, wherein the electrostatic unit has an array of
protrusions on both the first side and the second side of the
electrostatic unit. Once subject to the electrostatic charge, the
fibers are collected on a forming surface to form a nonwoven
web.
[0024] The invention will be more fully described with reference to
the Figures. Turning to FIG. 1, illustrated in schematic form in
side view is an exemplary process for production of a nonwoven web
material. As illustrated, spinplate 10 receives polymer from a
conventional melt extrusion system (not shown) and forms fibers 12
which may be monocomponent, multicomponent (conjugate) or
biconstituent fibers, as described above. The spinplate has
openings (not shown) arranged in one or more rows. The spinplate
opening form a downwardly extending "curtain" or "bundle" of fibers
12 when the polymer is extruded through the spinplate. Spinplates
for extruding multicomponent continuous fibers are well known to
those of ordinary skill in the art and thus are not described here
in detail; however, an exemplary spinplate for producing
multicomponent fibers is described in U.S. Pat. No. 5,989,004 to
Cook, the entire contents of which are herein incorporated by
reference.
[0025] Polymers suitable for the present invention include the
known polymers suitable for production of nonwoven webs and
materials such as for example polyolefins, polyesters, polyamides,
polycarbonates and copolymers and blends thereof. Suitable
polyolefins include polyethylene, e.g., high density polyethylene,
medium density polyethylene, low density polyethylene and linear
low density polyethylene; polypropylene, e.g., isotactic
polypropylene, syndiotactic polypropylene, blends of isotactic
polypropylene and atactic polypropylene; polybutylene, e.g.,
poly(1-butene) and poly(2-butene); polypentene, e.g.,
poly(1-pentene) and poly(2-pentene); poly(3-methyl-1-pentene);
poly(4-methyl-1-pentene); and copolymers and blends thereof.
Suitable copolymers include random and block copolymers prepared
from two or more different unsaturated olefin monomers, such as
ethylene/propylene and ethylene/butylene copolymers. Suitable
polyamides include nylon 6, nylon 6/6, nylon 4/6, nylon 11, nylon
12, nylon 6/10, nylon 6/12, nylon 12/12, copolymers of caprolactam
and alkylene oxide diamine, and the like, as well as blends and
copolymers thereof. Suitable polyesters include polylactide and
polylactic acid polymers as well as polyethylene terephthalate,
poly-butylene terephthalate, polytetramethylene terephthalate,
polycyclohexylene-1,4-dimethylene terephthalate, and isophthalate
copolymers thereof, as well as blends thereof.
[0026] The exemplary process line in FIG. 1 also includes a quench
blower 11 positioned adjacent the curtain of fibers 12 extending
from the spinplate 10. Air from the quench air blower 11 quenches
the fibers 12 extending from the spinplate 10. The quench air can
be directed from one side of the fiber curtain 12 as shown in FIG.
1, or both sides of the fiber curtain 12. As used herein, the term
"quench" simply means reducing the temperature of the fibers using
a medium that is cooler than the fibers such as using, for example,
chilled air streams, ambient temperature air streams, or slightly
to moderately heated air streams. The process may desirably further
comprise a means (not shown) to carry away fumes produced from the
molten polymer such as a vacuum duct mounted above or otherwise
near spinplate 10.
[0027] A fiber draw unit or aspirator 14 is position below the spin
plate and the quench blower 11. The fiber draw unit or aspirator
receives the quenched curtain of fibers 12. Fiber draw units or
aspirators for use in melt spinning polymers are well known in the
art. Suitable fiber drawing units for use in the method of the
present invention include, for example, linear fiber aspirators of
the types shown in U.S. Pat. No. 3,802,817 to Matsuki et al. and
U.S. Pat. Nos. 4,340,563 and 4,405,297 to Appel et al., all herein
incorporated by reference.
[0028] Generally described, the fiber drawing unit 14 includes an
elongate vertical passage 15 through which the fibers are drawn by
aspirating air entering from the sides of the passage and flowing
downwardly through the passage. Aspirating air is supplied by a
blower (not shown). The aspirating air may be heated or unheated.
The aspirating air applies drawing forces on the fibers and pulls
the fibers through the passage of the fiber drawing unit 14 and by
the application of drawing forces attenuates the fibers, that is,
reduces the diameter of the fibers. The aspirating air also acts to
guide and pull the bundle of fibers through the attenuation chamber
of the fiber drawing unit 14. Where multicomponent fibers in a
crimpable configuration are used and where it is desired to
activate latent helical crimp in the fibers prior to fiber laydown,
the blower supplies heated aspirating air to the fiber drawing unit
14. In this respect, the heated aspirating air both attenuates the
fibers and activates the latent helical crimp, as is described in
U.S. Pat. No. 5,382,400 to Pike et al. When it is desired to
activate the latent helical crimp in the fibers at some point
following fiber laydown, the blower supplies unheated aspirating
air to fiber drawing unit 14. In this instance, heat to activate
the latent crimp may be supplied to the web at some point after
fiber laydown.
[0029] Generally, the fiber draw unit 14 includes chambers 16 which
are supplied with air for the blower not shown. The aspirating air
is directed from the chambers 16 at high velocity downward to pull
the curtain of fibers 12, thereby causing orientation of the
fibers, which often results in an increase in their strength
properties. Below the fiber draw unit 14, there is shown
electrostatics unit 18. The electrostatics unit includes rows 20 of
protrusions on a first side of the electrostatics unit 18, and rows
of protrusions 21 on a second side of the electrostatics unit 18. A
potential or voltage is applied to the protrusions on one or both
sides of the electrostatics unit via a power supply V1 or V2. The
potential can be either a negative or positive potential, however,
if a potential is applied to both sides of the electrostatics unit,
then one side must have a positive potential and the other side
must have a negative potential applied to the protrusions. This
difference in potential charge is commonly referred to as a bias.
Alternatively, one side of the electrostatic unit may be grounded
and the other side will have a potential applied to the
protrusions. When one side is grounded, it is not critical if the
potential is negative or positive. As shown in FIG. 1, the
protrusions 20 produce a corona discharge against row of
protrusions 21, resulting in an electrostatic charge being placed
on the fibers. Once charged, the fibers tend to repel one another,
thereby preventing groups of individual fibers from clumping or
"roping" together. The configuration of the electrostatics unit of
the present invention will be given in further detail below, and
can be different from that which is shown in FIG. 1. Further
possible configurations will be shown in FIG. 2 and FIG. 3.
[0030] Shown below the electrostatic unit 18 is an optional
mechanical deflector 24 which helps distribution of the fibers. The
mechanical deflector may be replaced with a non-contacting
deflector, such as the one described in U.S. patent application
Ser. No. ______, filed concurrently herewith, assigned to the
assignee of the present application (Attorney docket No. 18242) and
is hereby incorporated by reference. In this patent application,
described is a non-contacting deflecting device comprises an air
jet deflector providing discrete jets of air. The deflector is an
optional attachment below the electrostatics unit. That is, the
deflector are not needed in the process of the present
invention.
[0031] The charged filaments 12' then are directed to the forming
wire 26 moving around rolls 28, one or both of which may be driven
with a motor (not shown). A compaction device, such as air knife
30, may be used to consolidate web 32 prior to bonding nip 34
between calender rolls 36, 38 (one or both of which may be
patterned as described above) which form bonded web 40. Other
methods of bonding the resulting nonwoven web, such as through air
bonding may also be used in the process of the present invention in
place of the compaction device. If desired, a conventional means 35
for removing or reducing the charge on the web may optionally be
employed such as applying an oppositely charged field or ion
cloud.
[0032] Turning to FIG. 2A, an electrostatic unit arrangement 201
useful in the present invention is shown in a side view. The
electrostatic unit arrangement has a first array of electrodes 210
on a first side of the electrostatic unit 201 and a second array of
electrodes 220 on a second side of the electrostatic unit, wherein
the electrodes are opposed to one another. As shown, the electrode
arrays 210 and 220, each have a series of multiple bars extending
substantially along the cross-machine width of the fiber draw unit,
for example four bars 212, 214, 216 and 218 associated with the
first array of electrodes 210 and four bars 222, 224, 226, and 228
associated with the second array of electrodes, each with a
plurality of protrusions 211. The protrusions can be rods, loops,
including loops or wire or pins and are desirable emitter pins 211.
The bars in each array are held in place by an electrically
insulating material 205, which also serves to isolated the
electrostatic unit from the other equipment of the process, such as
the fiber draw unit. Each of the charge bars is attached to a power
supply 230, or is in the alternative grounded, if the pins 211 on
the other side of the electrostatic unit 201 are connected to a
power supply.
[0033] Also as is shown in FIG. 2A, the emitter pins 211 are
desirable recessed within the insulation material to prevent the
fibers from fouling the emitter pins. Fouling of the emitter pins
can be caused by the fibers catching on the emitter pins since the
pins have relatively sharp tips to better generated the
electrostatic charge.
[0034] Turning to FIG. 2B, another electrostatic unit arrangement
251 useful in the present invention is shown in a side view. The
electrostatic unit arrangement has a first array of electrodes 210
and a third array of electrodes 260 on a first side of the
electrostatic unit 201 and a second array of electrodes 220 and a
fourth array of electrodes 270 on a second side of the
electrostatic unit. As shown, the electrode arrays 210, 220, 260
and 270 each have a series of multiple bars extending substantially
along the cross-machine width of the fiber draw unit, for example
four bars 212, 214, 216 and 218 associated with the first array of
electrodes 210 and four bars 222, 224, 226, and 228 associated with
the second array of electrodes 220, four bars 262, 264, 266 and 268
associated with the third array of electrodes 260 and four bars
272, 274, 276, and 278 associated with the fourth array of
electrodes 270 each with a plurality of protrusions 211, which are
desirable emitter pins 211. The bars are held in place by an
electrically insulating material 205, which also serves to isolated
the electrostatic unit from the other equipment of the process,
such as the fiber draw unit and the electrodes of the previous
section of the electrostatic unit. Each of the charge bars is
attached to a power supply 230 or 231, or is, in the alternative,
grounded, if the pins 211 on the other side of the electrostatic
unit 201 is connected to a power supply.
[0035] As shown in FIG. 2A and FIG. 2B, the protrusions are on
either side of the electrostatic unit and are opposed to each
other. The electrostatic charge is generated between the
protrusions or emitter pins.
[0036] FIG. 3 shows yet another electrostatic unit arrangement 351
useful in the present invention shown in a side view. The
electrostatic unit arrangement such that a first section has a
first array of electrodes 310 on a first side of the electrostatic
unit 351. This array of electrodes has a series of multiple bars
extending substantially along the cross-machine width of the fiber
draw unit, for example four bars 312, 314, 316 and 318 associated
therewith, each with a plurality of protrusions 311. The bars are
connected to a power supply 330 which provides a potential or
voltage to the pins. On a second side of the electrostatic unit,
directly across from the array of electrodes 311 is a target 319,
which is shown to be grounded. In the alternative the target 319
may also be attached to a power supply, provided that a bias is
established, as is stated above. In FIG. 3, the protrusions on the
first side and the second side are offset and are not directly
opposed to one another. The bars in each array are held in place by
an electrically insulating material 305, which also serves to
isolate the electrostatic unit from the other equipment of the
process, such as the fiber draw unit. In addition, the insulation
material 305 insulates the first section of the electrostatic unit
from other sections of the electrostatic unit. In a second section
of the electrostatic unit, this section has a second array of
electrodes 320 on a second side of the electrostatic unit 351. This
array of electrodes has a series of multiple bars extending
substantially along the cross-machine width of the fiber draw unit,
for example four bars 322, 324, 326 and 328 associated therewith,
each with a plurality of protrusions 311, shown as pins 311 .The
bars are attached to a power supply 330 On the first side of the
electrostatic unit, directly across from the array of electrodes is
a target 329. Like the first section of the electrostatic unit, the
bars of the second section are held in place by an electrically
insulating material 305, which also serves to isolate the second
section of the electrostatic unit from the first section and an
optional third section. In addition, a power supply is connected to
the bars, hence the protrusions 320 and the target is shown to be
grounded, but also may be attached to a power supply. In an
optional third section of the electrostatic unit, this section has
a third array of electrodes 360 on a first side of the
electrostatic unit 351. This array of electrodes has a series of
multiple bars extending substantially along the cross-machine width
of the fiber draw unit, for example four bars 362, 364, 366 and 368
associated therewith, each with a plurality of protrusions 311. On
the second side of the electrostatic unit, directly across from the
array of electrodes is a target 369. Like the first and second
sections of the electrostatic unit, the bars of the third section
are held in place by an electrically insulating material 305, which
also serves to isolate the third section of the electrostatic unit
from the second section and an optional additional sections of the
electrostatics unit and the bars are connected to a power supply.
Additional sections can be added below the optional third section,
provided that the array of electrodes is on the opposite side of
the previous section of the electrostatics unit.
[0037] The protrusions of the present invention of the
electrostatic unit may be a pin, a rod, a wire or a looped wire.
Desirably, the protrusions are pins, most desirably emitter pins.
An exemplary emitter pin configuration usable in the present
invention is one where the emitter pins are spaced apart at 1/4
inch, and recessed at 1/8 inch in a cavity of 0.5 inch
high.times.0.25 inch deep. The actually spacing of the pins is not
critical to the present invention and can be varied to achieve the
desired corona discharge. The pins are typically arranged in rows
which can be as wide or slightly wider than the fiber draw unit.
Further, it is desirable, but not required, that the emitter pins
are recessed. It has been discovered that fouling of the pins
occurs to a lesser degree when the pins are recessed to a small
degree in the insulation material which holds the pins in place, as
compared to having the pins extend into the fiber curtain.
[0038] The protrusions can be stacked in several rows. As shown in
the figures, there are 4 rows of the pins stacked on top of each
other. This is not required, and the electrostatic unit can have a
single row of protrusions of pins or several rows, for example, any
where from 2-50 rows or more. The actual number of rows is limited
by the height available from the fiber draw unit to the forming
surface.
[0039] In the aspect of the electrostatic unit shown in FIG. 3, the
target plate is prepared from conductive material and will
typically have a height and width approximately the same as the
height and width of the protrusions or pins, whether unstacked or
stacked. Typically, the size of the target plate varies depending
on factors such as the width of the drawing slot. Generally, the
target plate is prepared from conducting steel.
[0040] Using an electrostatic unit having an array of protrusions
described above provides advantages over prior art electrostatic
units. Advantages include, the ability to create greater currents
at a given applied voltage, the ability to alternate the current
from one side of the electrostatics unit to the other, and the
ability to set the protrusions within a cavity to prevent fouling
without reducing the size of the passage of the electrostatics
unit, among others.
[0041] In addition, the present invention provides stacking of the
electrostatics generating protrusions in several different and
isolated sections, such as is shown in FIG. 2B. This allows for
longer running times before the fiber production unit must be shut
down due to fouling of the protrusions. Having stacked sections as
shown in FIG. 2B and FIG. 3, each section of the unit may be run
independent of the others. Therefore one section of the unit may be
switched off, while another section is operating. As the operation
section becomes fouled, and loses its ability to generate an
acceptable current, the operation section of the electrostatic unit
may be shut down and a different section be operated to generate
the electrostatics.
[0042] In a further embodiment of the present invention, the
electrostatics unit shown in FIG. 2B and FIG. 3 can be operated
such that the current in the first section is in the direction of
the first side to the second side of the electrostatics unit and
the current in the next section is in the direction of the second
side to the first side. For example, this can be accomplished by
grounding the protrusions of the second side of the first section
of the electrostatics unit and grounding the protrusions on the
first side in the second section of the electrostatics unit, as
shown in FIG. 2, or visa verso. In FIG. 3, the plates can be
ground. As another alternative, the protrusions on the first side
of the first section can have a negative or positive potential
applied thereto and the opposite potential applied to the
protrusions on the second side of the first section. In the next
section, of the electrostatic unit, the potential can be set
opposite that of the first section. In additional sections, if
present, the potential is set such that the current is in a
direction opposite of the previous section. This allows the fibers
in the electrostatic unit to be charged on both sides and causes
the fibers to flap back and forth from side to side, thereby
causing and improved formation of the nonwoven web.
[0043] In a even further embodiment, the polarity of the
electrostatics unit in any operating section can be reversed at
high frequency from first side to the second side and the second
side to the first side to flap fibers from the first to second side
of the electrostatic unit or the second to the first side of the
electrostatic unit. For example in FIG. 1, the potential of V1 is
switched form negative to positive at the same time the potential
of V2 is switched from positive to negative. This will also tend to
improve the formation of the resulting nonwoven web.
EXAMPLES
[0044] While the invention will be illustrated by means of
examples, the examples are only representative and not limiting on
the scope of the invention which is determined in reference to the
appended claims.
[0045] An electrostatic unit was prepared having emitter pins
spaced apart at 0.25 inch, and recessed at 0.125 inch in a cavity
of 0.5 inch high.times.0.25 inch deep on a first. A 26 inch wide
rows (24 effective inch) of pins was prepared. The row of pins was
manufactured by Tantec Inc. 630 Estes Avenue, Schaumburg, Ill.
60193. These pins were connected to a high voltage DC source
through a single 100 mega ohm resistor to measure the discharge
current via the corresponding voltage. The power supply was Model
EH3OR3, 0-30 KV, 0-3 MA, 100 watt regulated, reversible with
respect to chassis ground, but the negative voltage was applied
here although opposite charge may also be used. It was manufactured
by Glassman High Voltage, Inc., PO Box 551, Route 22 East, Salem
Park, Whitehouse Station, N.J. 08889.
[0046] On a second side of the electrostatics unit, directly
opposite the emitter of the first side are emitter pins having the
same configuration as the emitter pins of the first side. The pins
of the second side were connected to another power supply through
another 100 mega-ohm resistor. The power source was the same
Glassman power supply, but with different, positive sign, polarity
grounded rather than connected to the power supply.
[0047] The emitter pins of the first side of the unit and the
second side of the unit were set such that the emitter pins were
0.7 inch and 1.2 inches apart from one another. The current between
the emitter pins of the first side and the emitter pins of the
second side was measured from the grounded second side at various
voltages shown in Table 1.
[0048] In a second experiment, two rows of emitter pins having the
same configuration as described above, were stacked such that the
pins of the first row were approximately about 0.75 inch apart from
the pins of the second row. The second side of the electrostatics
unit also had two rows of pins such that the first row was 0.75
inch apart from the pins of the second row. The two rows of pins on
the first side were connected to a power supply and the pins on the
second side were connected to another power supply through another
100 mega-ohm resistor. The power source was the same Glassman power
supply, but with different, positive sign, polarity were grounded.
The current between the emitter pins of the first side and the
emitter pins of the second side was measured from the grounded side
at various voltages shown in Table 1.
[0049] As a comparison, the emitter pins of the second side were
replaced with a target plate. The target plate was approximately 3
inches high.times.26 inches wide and was prepared from an
electrically conducting steel plate t, while the corresponding
value of the uncoated steel resistance was close to 0.0002 ohms.
The target plate was connected to another power supply through
another 100 mega-ohm resistor. The power source was the same
Glassman power supply, but with different, positive sign, polarity.
The emitter pins of the first side of the unit and the target plate
of the unit were set such that the emitter pins were 0.6 inch and
1.1 inches away from the target. The current between the emitter
pins of the first side and the target plate of the second side was
measured from the grounded second side at various voltages shown in
Table 1.
1TABLE 1 Current for emitter Current for single Current for two
pins with target row of emitter pins rows of emitter pins plate
electrode on both sides at on both sides at at distance Voltage
distance (mA) distance (mA) (mA) (Comparative) (kV) 0.7 in 1.2 in
0.7 in 1.2 in 0.6 in 1.1 in 15 0.211 0.093 0.354 0.150 0.149 0.0 16
0.240 0.114 0.399 0.176 0.177 0.004 17 0.276 0.135 0.450 0.205
0.212 0.020 18 0.318 0.163 0.500 0.236 0.308 0.037 19 0.361 0.180
0.560 0.302 0.294 0.051 20 0.400 0.206 0.636 0.340 0.333 0.067 21
0.444 0.232 0.710 0.385 0.380 0.084 22 0.490 0.263 0.775 0.422
0.412 0.100 23 0.536 0.290 0.850 0.468 0.463 0.114 24 0.580 0.319
0.920 0.513 0.506 0.133 25 0.629 0.353 0.992 0.560 0.560 0.150
[0050] It is noted that in Table 1, the comparative example has the
target plate at a shorter distance from the emitter pins than the
Examples within the present invention. This is due to the fact that
the emitter pins of the present invention are recessed within the
cavity of the insulating material. In any event, as can be clearly
seen in Table 1, the current generated at a given voltage is
greater when emitter pins are used as the target instead of the
target plate. Further, the current generated can also be increased
by using additional rows of emitter pins on both sides of the
electrostatics device.
[0051] The electrostatics unit described in the above Example above
may be used in a process of producing a nonwoven fabric, as shown
in FIG. 1. Using the arrangement described herein, improve web
formation can be obtained using lower voltages. Further, using pins
on both sides of the electrostatics units gives the ability to
alternate the potential across in order to cause the fibers to move
side to side within the electrostatics unit.
[0052] The nonwoven web materials produced with the process of the
present invention may be used alone or may be used in a laminate
that contains at least one layer of nonwoven web and at least one
additional layer such as a woven fabric layer, an additional
nonwoven fabric layer, a foam layer or film layer. The additional
layer or layers for the laminate may be selected to impart
additional and/or complementary properties, such as liquid and/or
microbe barrier properties. The laminate structures, consequently,
are highly suitable for various uses including various
skin-contacting applications, such as protective garments, covers
for diapers, adult care products, training pants and sanitary
napkins, various drapes, surgical gowns, and the like. The layers
of the laminate can be bonded to form a unitary structure by a
bonding process known in the art to be suitable for laminate
structures, such as a thermal, ultrasonic or adhesive bonding
process or mechanical or hydraulic entanglement processes.
[0053] As an example, a breathable film can be laminated to the
nonwoven web to provide a breathable barrier laminate that exhibits
a desirable combination of useful properties, such as soft texture,
strength and barrier properties. As another example the nonwoven
web can be laminated to a non-breathable film to provide a strong,
high barrier laminate having a cloth-like texture. These laminate
structures provide desirable cloth-like textural properties,
improved strength properties and high barrier properties. Another
laminate structure highly suitable for the present invention is the
spunbond-meltblown-spunbond laminate material such as is disclosed
in U.S. Pat. No. 4,041,203 to Brock et al., which is herein
incorporated in its entirety by reference.
[0054] The nonwoven web materials made by the present invention are
highly suitable for various uses, such as for example uses
including disposable articles, e.g., protective garments,
sterilization wraps, surgical garments, and wiper cloths, and
liners, covers and other components of absorbent articles.
[0055] While the invention has been described in terms of its best
mode and other embodiments, variations and modifications will be
apparent to those of skill in the art. It is intended that the
attached claims include and cover all such variations and
modifications as do not materially depart from the broad scope of
the invention as described therein.
* * * * *