[0001] The present invention relates to a method for forming nonwoven webs and an apparatus
for forming such webs.
[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 July 04, 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.
[0005] In accordance with the present invention there is provided a process for forming
a nonwoven web as claimed in claim 1.
[0006] 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.
[0007] The present invention also provides an apparatus for forming a nonwoven web as claimed
in claim 12. 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
[0008]
Figure 1 shows a schematic illustration of an exemplary process for process for producing
a nonwoven web.
Figures 2 A and 2B each show an exemplary device for applying an electrostatic charge
to the fibers.
Figure 3 shows a device for applying an electrostatic charge to the fibers, which
is included for illustrative and reference purposes only and which is not exemplary
of the present invention.
Definitions
[0009] 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.
[0010] 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.
[0011] As used herein the term "fibers" refers to both staple length fibers and continuous
fibers, also known as filaments, unless otherwise indicated.
[0012] 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.
[0013] 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. 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.
[0014] 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.
[0015] 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).
[0016] 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. Nos. 4,340,563 to Appel et al.,
3,692,618 to Dorschner et al., and
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.
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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. Patent No. 5,989,004 to Cook.
[0023] 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.
[0024] 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.
[0025] 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..
[0026] 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.
[0027] 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. The electrostatics unit
includes rows of protrusions on a first side of the electrostatics unit and rows of
protrusions 21 on a second side of the electrostatics unit. 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 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.
[0028] Shown below the electrostatic unit is an optional mechanical deflector 24 which helps
distribution of the fibers. The mechanical deflector may be replaced with a non-contacting
containing deflector, such as a non-contacting deflecting device which comprises an
air jet deflector providing discrete jets of air. The deflector is an optional attachment
below the electrostatics unit. That is, the deflector is not needed in the process
of the present invention.
[0029] 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 for removing or
reducing the charge on the web may optionally be employed such as applying an oppositely
charged field or ion cloud.
[0030] Turning to FIG. 2A, an electrostatic unit arrangement 201 embodying 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.
[0031] 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.
[0032] Turning to Figure 2B, another electrostatic unit arrangement 251 embodying 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.
[0033] 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.
[0034] FIG 3 shows an electrostatic unit arrangement 351 not embodying the present invention
but which is shown in a side view for illustrative and reference purposes. The electrostatic
unit arrangement is 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.
[0035] 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 ¼ inch (6 mm), and recessed at 1/8
inch (3 mm) in a cavity of 0.5 inch (13 mm) high x 0.25 inch (6 mm) 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.
[0036] 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.
[0037] In 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.
[0038] 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.
[0039] 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,
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.
[0040] In a further embodiment of the present invention, the electrostatics unit shown in
FIG 2B 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.
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.
[0041] 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
[0042] 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.
[0043] An electrostatic unit was prepared having emitter pins spaced apart at 0.25 inch,
and recessed at 0.125 inch (3 mm) in a cavity of 0.5 inch high (13 mm) x 0.25 inch
(6 mm) deep on a first. A 26 inch (66 cm) wide rows (24 effective inch; 61 effective
cm) of pins was prepared. The row of pins was manufactured by Tantec Inc. 630 Estes
Avenue, Schaumburg,
IL 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., P0 Box
551, Route 22 East, Salem Park, Whitehouse Station, NJ 08889.
[0044] 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.
[0045] 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 (18 mm) and 1.2 inches (30 mm) 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.
[0046] 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 (19 mm) 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 (19 mm) 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.
[0047] As a comparison, the emitter pins of the second side were replaced with a target
plate. The target plate was approximately 3 inches (76 mm) high x 26 inches (66 cm)
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 (15 mm) and 1.1 inches ( 28 mm) 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.
Table 1
|
Current for single row of emitter pins on both sides at distance (mA) |
Current for two rows of emitter pins on both sides at distance (mA) |
Current for emitter pins with target plate electrode at distance (mA) (Comparative) |
Voltage
(kV) |
0.7 in
(18 mm) |
1.2 in
(30 mm) |
0.7 in
(18 mm) |
1.2 in
(30 mm) |
0.6 in
(15 mm) |
1.1 in
(28 mm) |
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 |
[0048] 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.
[0049] The electrostatics unit described in the above Example above may be used in a process
of producing a nonwoven fabric, as shown in Figure 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.
[0050] 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.
[0051] 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..
[0052] The nonwoven web materials made by a process in accordance with 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.
[0053] 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 scope of the invention as described therein.
1. A process for forming a nonwoven web comprising :
a. providing a source (10) of fibers (12);
b. subjecting said fibers (12) to an electrostatic charge by passing said fibers (12)
through an electrostatic unit (201; 251) having a first side and a second side opposed
to each other, wherein the electrostatic unit (201; 251) has an array of protrusions
(21; 211) on both the first side and the second side of the electrostatic unit; and
c. collecting said fibers (12) on a forming surface to form a nonwoven web (32); and
characterised in that the electrostatic charge is generated between the array of protrusions (21;211) of
the first side and the array of protrusions (21;211) of the second side and the array
of protrusions (21;211) of the first side and the array of protrusions (21;211) of
the second side are opposed to one another one.
2. The process of claim 1, wherein the fibers (12) are provided by a melt spinning process
and the fibers are substantially continuous fibers.
3. The process of claim 1 or 2, wherein continuous fibers are subjected to a pneumatic
draw force in a fiber draw unit prior to being subjected to said electrostatic charge.
4. The process of claim 1, wherein the fibers (12) 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
(21;211) of the first side and the array of protrusions (21; 211) 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.
5. The process of any preceding claim, 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 (21;211)
on either side of the electrostatic unit (251).
6. The process of any preceding claim, wherein the array of protrusions (21;211) of the
first side and the array of protrusions (21;211) of the second side each comprise
an array of pins.
7. The process of any preceding claim, 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.
8. The process of claim 7, wherein the first electrostatic field is generated from a
potential on the first side of the electrostatic unit (201;251) and the second electrostatic
field is generated from a potential on second side of the electrostatic unit (201;251).
9. The process of any preceding claim, wherein the array of protrusions (21; 211) is
an array of pins which 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 any preceding claim further comprising deflecting the fibers (12) with
a defecting device (24) prior to collecting the fibers (12) on the forming surface.
11. The process of any preceding claim, wherein an electrical potential is alternated
from the protrusions (21;211) on the first side to the protrusions (21;211) on the
second side and back to the protrusions (21;211) on the first side.
12. An apparatus for forming a nonwoven web (32) comprising:
a. a source (10) of fibers (12);
b. a device for applying an electrostatic charge to said fibers (12), said device
comprising a first side and a second side opposed to each other, wherein the device
has an array of protrusions (21; 211) on the first side and the second side of an
electrostatic unit (201; 251); and
c. a forming surface for collecting said fibers (12); and characterised in that the electrostatic charge is generated between the array of protrusions (21;211) of
the first side and the array of protrusions (21;211) of the second side and the array
of protrusions (21;211) of the first side and the array of protrusions (21;211) of
the second side are opposed to one another one.
13. The apparatus of claim 12, wherein the array of protusions (21; 211) on the first
and second sides comprise an array of pins.
14. The apparatus of claim 13, 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.
15. The apparatus of claim 12, 13 or 14, wherein the source (10) of fibers (12) comprises
a spinplate which is fed with one or more polymeric materials.
16. The apparatus of any of claims 12 to 15, further comprising a fiber draw unit (14),
wherein the fiber draw unit (14) is located below the source (10) of fibers (12) and
the device for applying an electrostatic charge.
17. The apparatus of any of claims 12 to 16, further comprising a deflector (24) located
below the device for applying an electrostatic charge and above the forming surface.
18. The apparatus of any of claims 12 to 17, wherein the device for applying an electrostatic
charge comprises a series of at least two separate electrostatic charge field sections
along a length of the electrostatic unit, each charge field section having an array
of pins on either side of the device.
19. The apparatus of claim 18, 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.
1. Verfahren zur Bildung eines Vliesstoffgewebes, umfassend:
a. Bereitstellen einer Quelle (10) von Fasern (12);
b. Aussetzen der Fasern (12) einer elektrostatischen Ladung, indem die Fasern (12)
durch eine elektrostatische Einheit (201, 251) mit einer ersten Seite und einer zweiten
Seite, die einander gegenüber liegend angeordnet sind, hindurch geleitet werden, wobei
die elektrostatische Einheit (201; 251) eine Anordnung von Vorsprüngen (21; 211) sowohl
an der ersten Seite als auch der zweiten Seite der elektrostatischen Einheit aufweist;
und
c. Sammeln der Fasern (12) auf einer Formfläche zum Bilden eines Vliesstoffgewebes
(32); und dadurch gekennzeichnet, dass
die elektrostatische Ladung zwischen der Anordnung von Vorsprüngen (21; 211) der ersten
Seite und der Anordnung von Vorsprüngen (21; 211) der zweiten Seite erzeugt wird;
und die Anordnung von Vorsprüngen (21; 211) der ersten Seite und der Anordnung von
Vorsprüngen (21; 211) der zweiten Seite einander gegenüber liegend angeordnet sind.
2. Verfahren nach Anspruch 1, bei dem die Fasern (12) durch ein Schmelzspinnverfahren
bereitgestellt werden und die Fasern im Wesentlichen Endlosfasern sind.
3. Verfahren nach Anspruch 1 oder 2, bei dem Endlosfasern einer pneumatischen Ziehkraft
in einer Faserzieheinheit ausgesetzt sind, bevor sie der elektrostatischen Ladung
ausgesetzt werden.
4. Verfahren nach Anspruch 1, bei dem die Fasern (12) im Wesentlichen durch Schmelzspinnen
bereitgestellte Endlosfasern sind, die einer pneumatischen Ziehkraft in einer Faserzieheinheit
ausgesetzt sind, bevor sie der elektrostatischen Ladung ausgesetzt werden; die Anordnung
von Vorsprüngen (21; 211) der ersten Seite und die Anordnung von Vorsprüngen (21;
211) der zweiten Seite jeweils eine Anordnung von Stiften aufweist; die elektrostatische
Ladung zwischen der Anordnung von Stiften der ersten Seite und der Anordnung von Stiften
der zweiten Seite erzeugt wird, und die Anordnung von Stiften der ersten Seite und
die Anordnung von Stiften der zweiten Seite einander gegenüber liegend angeordnet
sind.
5. Verfahren nach einem vorhergehenden Anspruch, bei dem die elektrostatische Ladung
durch eine Reihe von mindestens zwei getrennten elektrostatischen Ladungsfeldem entlang
einer Länge der elektrostatischen Einheit erzeugt wird, jedes Ladungsfeld eine Anordnung
von Vorsprüngen (21; 211) an jeder Seite der elektrostatischen Einheit (251) aufweist.
6. Verfahren nach einem vorhergehenden Anspruch, bei dem die Anordnung von Vorsprüngen
(21; 211) der ersten Seite und die Anordnung von Vorsprüngen (21; 211) der zweiten
Seite jeweils eine Anordnung von Stiften umfasst.
7. Verfahren nach einem vorhergehenden Anspruch, bei dem ein erstes elektrostatisches
Ladungsfeld zwischen einer ersten Anordnung von Stiften an der ersten Seite der elektrostatischen
Einheit und einer ersten Anordnung von Stiften an der zweiten Seite der elektrostatischen
Einheit erzeugt wird; und ein zweites elektrostatisches Ladungsfeld zwischen einer
zweiten Anordnung von Stiften an der ersten Seite der elektrostatischen Einheit und
einer zweiten Anordnung von Stiften an der zweiten Seite der elektrostatischen Einheit
erzeugt wird.
8. Verfahren nach Anspruch 7, bei dem das erste elektrostatische Feld aus einem Potenzial
an der ersten Seite der elektrostatischen Einheit (201; 251) erzeugt wird, und das
zweite elektrostatische Feld aus einem Potenzial an der zweiten Seite der elektrostatischen
Einheit (201; 251) erzeugt wird.
9. Verfahren nach einem vorhergehenden Anspruch, bei dem die Anordnung von Vorsprüngen
(21; 211) eine Anordnung von Stiften ist, die innerhalb eines Hohlraums eines isolierenden
Materials ausgespart sind, so dass sich die Stifte im Wesentlichen nicht über das
isolierende Material hinaus erstrecken.
10. Verfahren nach einem vorhergehenden Anspruch, das des Weiteren das Ablenken der Fasern
(12) mit einer Ablenkvorrichtung (24) vor dem Sammeln der Fasern (12) auf der Formfläche
umfasst.
11. Verfahren nach einem vorhergehenden Anspruch, bei dem ein elektrisches Potenzial von
den Vorsprüngen (21; 211) an der ersten Seite zu den Vorsprüngen (21; 211) an der
zweiten Seite und zurück zu den Vorsprüngen (21; 211) an der ersten Seite periodisch
verändert wird.
12. Vorrichtung zur Bildung eines Vliesstoffgewebes (32), umfassend:
a. eine Quelle (10) von Fasern (12)
b. eine Vorrichtung zum Anlegen einer elektrostatischen Ladung an die Fasern (12),
wobei die Vorrichtung eine erste Seite und eine zweite Seite aufweist, die einander
gegenüber liegend angeordnet sind, wobei die Vorrichtung eine Anordnung von Vorsprüngen
(21, 211) an der ersten Seite und der zweiten Seite einer elektrostatischen Einheit
(201; 251) aufweist; und
c. eine Formfläche zum Sammeln der Fasern (12),
und
dadurch gekennzeichnet, dass die elektrostatische Ladung zwischen der Anordnung von Vorsprüngen (21; 211) der
ersten Seite und der Anordnung von Vorsprüngen (21; 211) der zweiten Seite erzeugt
wird; und die Anordnung von Vorsprüngen (21; 211) der ersten Seite und die Anordnung
von Vorsprüngen (21; 211) der zweiten Seite einander gegenüber liegend angeordnet
sind.
13. Vorrichtung nach Anspruch 12, bei der die Anordnung von Vorsprüngen (21; 211) an der
ersten und der zweiten Seite eine Anordnung von Stiften umfasst.
14. Vorrichtung nach Anspruch 13, bei der die Anordnung von Stiften der ersten Seite und
die Anordnung von Stiften der zweiten Seite innerhalb eines Hohlraums eines isolierenden
Materials ausgespart sind, so dass sich die Stifte im Wesentlichen nicht über das
isolierende Material hinaus erstrecken.
15. Vorrichtung nach Anspruch 12, 13 oder 14, bei der die Quelle (10) von Fasern (12)
eine Spinnplatte aufweist, der ein oder mehrere Polymerwerkstoffe zugeführt wird.
16. Vorrichtung nach einem der Ansprüche 12 bis 15, die des Weiteren eine Faserzieheinheit
(14) aufweist, wobei sich die Faserzieheinheit (14) unter der Quelle (10) von Fasern
(12) und der Vorrichtung zum Anlegen einer elektrostatischen Ladung befindet.
17. Vorrichtung nach einem der Ansprüche 12 bis 16, die des Weiteren eine Ablenkvorrichtung
(24) aufweist, die sich unter der Vorrichtung zum Anlegen einer elektrostatischen
Ladung und über der Formfläche befindet.
18. Vorrichtung nach einem der Ansprüche 12 bis 17, bei der die Vorrichtung zum Anlegen
einer elektrostatischen Ladung eine Reihe von mindestens zwei getrennten elektrostatischen
Ladungsfeldabschnitten entlang einer Länge der elektrostatischen Einheit aufweist,
wobei jeder Ladungsfeldabschnitt eine Anordnung von Stiften an jeder Seite der Vorrichtung
aufweist.
19. Vorrichtung nach Anspruch 18, bei der ein elektrostatisches Ladungsfeld erzeugt wird
zwischen einer ersten Anordnung von Stiften an der ersten Seite der elektrostatischen
Einheit und ersten Anordnung von Stiften an der zweiten Seite der elektrostatischen
Einheit, so eingerichtet, dass die Stifte der ersten Seite und die Stifte der zweiten
Seite einander gegenüber liegend angeordnet sind, und ein zweites elektrostatisches
Ladungsfeld erzeugt wird zwischen einer zweiten Anordnung von Stiften an der ersten
Seite der elektrostatischen Einheit und einer zweiten Anordnung von Stiften an der
zweiten Seite der elektrostatischen Einheit, so eingerichtet, dass die Stifte der
ersten Seite und die Stifte der zweiten Seite einander gegenüber liegend angeordnet
sind.
1. Procédé de formation d'un voile non-tissé comprenant :
a. la fourniture d'une source (10) de fibres (12) ;
b. le fait de soumettre lesdites fibres (12) à une charge électrostatique en faisant
passer lesdites fibres (12) au travers d'une unité électrostatique (201;251) ayant
un premier côté et un second côté opposés l'un à l'autre, où l'unité électrostatique
(201;251) comporte un réseau de protubérances (21;211) sur l'un et l'autre du premier
côté et du second côté de l'unité électrostatique ; et
c. la collecte desdites fibres (12) sur une surface de formation pour former un voile
non-tissé (32) ; et
caractérisé en ce que
la charge électrostatique est générée entre le réseau de protubérances (21;211) du
premier côté et le réseau de protubérances (21;211) du second côté, le réseau de protubérances
(21;211) du premier côté et le réseau de protubérances (21;211) du second côté étant
opposés l'un à l'autre.
2. Procédé selon la revendication 1, dans lequel les fibres (12) sont issues d'un procédé
de filage à l'état fondu et les fibres sont des fibres sensiblement continues.
3. Procédé selon la revendication 1 ou 2, dans lequel des fibres continues sont soumises
à une force d'étirage pneumatique dans une unité d'étirage de fibres avant d'être
soumises à ladite charge électrostatique.
4. Procédé selon la revendication 1, dans lequel les fibres (12) sont des fibres sensiblement
continues issues d'un filage à l'état fondu et sont soumises à une force d'étirage
pneumatique dans une unité d'étirage de fibres avant d'être soumises à ladite charge
électrostatique, le réseau de protubérances (21;211) du premier côté et le réseau
de protubérances (21; 211) du second côté comprenant chacun un réseau d'aiguilles,
la charge électrostatique est générée entre le réseau d'aiguilles du premier côté
et le réseau d'aiguilles du second côté, et le réseau d'aiguilles du premier côté
et le réseau d'aiguilles du second côté sont opposés l'un à l'autre.
5. Procédé selon l'une quelconque des revendications précédentes, dans lequel la charge
électrostatique est générée par une série d'au moins deux champs de charge électrostatique
séparés le long d'une longueur de l'unité électrostatique, chaque champ de charge
ayant un réseau de protubérances (21;211) sur l'un et l'autre côtés de l'unité électrostatique
(201;251).
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel le réseau
de protubérances (21;211) du premier côté et le réseau de protubérances (21;211) du
second côté comprennent chacun un réseau d'aiguilles.
7. Procédé selon l'une quelconque des revendications précédentes, dans lequel un premier
champ de charge électrostatique est généré entre un premier réseau d'aiguilles sur
le premier côté de l'unité électrostatique et un premier réseau d'aiguilles sur le
second côté de l'unité électrostatique, et un second champ de charge électrostatique
est généré entre un second réseau d'aiguilles sur le premier côté de l'unité électrostatique
et un second réseau d'aiguilles sur le second côté de l'unité électrostatique.
8. Procédé selon la revendication 7, dans lequel le premier champ électrostatique est
généré depuis un potentiel sur le premier côté de l'unité électrostatique (201;251)
et le second champ électrostatique est généré depuis un potentiel sur le second côté
de l'unité électrostatique (201;251).
9. Procédé selon l'une quelconque des revendications précédentes, dans lequel le réseau
de protubérances (21;211) est un réseau d'aiguilles qui sont en retrait au sein d'une
cavité ménagée dans un matériau isolant de telle sorte que les aiguilles ne s'étendent
pas essentiellement au-delà du matériau isolant.
10. Procédé selon l'une quelconque des revendications précédentes, comprenant en outre
le fléchissement des fibres (12) au moyen d'un dispositif fléchisseur (24) avant la
collecte des fibres (12) sur la surface de formation.
11. Procédé selon l'une quelconque des revendications précédentes, dans lequel un potentiel
électrique est alterné depuis les protubérances (21;211) sur le premier côté vers
les protubérances (21;211) sur le second côté et en retour vers les protubérances
(21;211) sur le premier côté.
12. Appareil pour former un voile non-tissé (32) comprenant :
a. une source (10) de fibres (12) ;
b. un dispositif pour appliquer une charge électrostatique auxdites fibres (12), ledit
dispositif comprenant un premier côté et un second côté opposés l'un à l'autre, où
le dispositif comporte un réseau de protubérances (21;211) sur le premier côté et
le second côté d'une unité électrostatique (201;251) ; et
c. une surface de formation pour collecter lesdites fibres (12) ;
et
caractérisé en ce que
la charge électrostatique est générée entre le réseau de protubérances (21;211) du
premier côté et le réseau de protubérances (21;211) du second côté, le réseau de protubérances
(21;211) du premier côté et le réseau de protubérances (21;211) du second côté étant
opposés l'un à l'autre.
13. Appareil selon la revendication 12, dans lequel le réseau de protubérances (21;211)
sur le premier et le second côtés comprend un réseau d'aiguilles.
14. Appareil selon la revendication 13, dans lequel le réseau d'aiguilles sur le premier
côté et le réseau d'aiguilles sur le second côté sont en retrait au sein d'une cavité
ménagée dans un matériau isolant de telle sorte que les aiguilles ne s'étendent pas
essentiellement au-delà du matériau isolant.
15. Appareil selon la revendication 12, 13 ou 14, dans lequel la source (10) de fibres
(12) comprend une plaque de filage qui est alimentée avec un ou plusieurs matériaux
polymères.
16. Appareil selon l'une quelconque des revendications 12 à 15, comprenant en outre une
unité d'étirage de fibres (14), où l'unité d'étirage de fibres (14) est située entre
la source (10) de fibres (12) et le dispositif d'application d'une charge électrostatique.
17. Appareil selon l'une quelconque des revendications 12 à 16, comprenant en outre un
dispositif fléchisseur (24) situé au-dessous du dispositif d'application d'une charge
électrostatique et au-dessus de la surface de formation.
18. Appareil selon l'une quelconque des revendications 12 à 17, dans lequel le dispositif
d'application d'une charge électrostatique comprend une série d'au moins deux sections
de champ de charge électrostatique séparées selon une longueur de l'unité électrostatique,
chaque section de champ de charge ayant un réseau d'aiguilles sur l'un et l'autre
côtés du dispositif.
19. Appareil selon la revendication 18, dans lequel un champ de charge électrostatique
est généré entre un premier réseau d'aiguilles sur le premier côté de l'unité électrostatique
et un premier réseau d'aiguilles sur le second côté de l'unité électrostatique agencé
de telle sorte que les aiguilles du premier côté et les aiguilles du second côté sont
opposées les unes aux autres, et un second champ de charge électrostatique est généré
entre un second réseau d'aiguilles sur le premier côté de l'unité électrostatique
et un second réseau d'aiguilles sur le second côté de l'unité électrostatique agencée
de telle sorte que les aiguilles du premier côté et les aiguilles du second côté sont
opposées les unes aux autres.