Note: Descriptions are shown in the official language in which they were submitted.
CA 02281968 1999-09-16
J
AIR KNIFE APPARATUS FOR REMOVING
AN AIRLAID ARTICLE FROM A DEPOSITION CAVITY
This application is a division of Application Ser.
s No. 2,017,453, filed May 24, 1990.
The present invention relates to an air knife
apparatus for the removal of an airlaid article of fibrous
materials from a deposition cavity. More specifically, the
present invention permits different types of fibrous
materials to be formed into an absorbent core for product
such as a sanitary napkin, diaper or the like.
BACKGROUND OF THE INVENTION
The ongoing research into the chemistry of
~s absorbent materials, particularly fibrous materials such as
cellulose, has yielded significant gains in the affectivity
of absorbent products. Improvements in the absorptivity,
fluid retention and other characteristics which affect user
comfort, such as decreased stiffness, have all been
zo realized. Additionally, it has been found that certain
absorptive materials may be treated online to render them
hydrophobic or fluid repellent to some extent. Most
absorbent products have at least one major surface which is
exposed to a fluid flow or a collection of fluid.
2s Hydrophobic materials may be combined with absorbent
materials to provide a structure which absorbs and retains
fluids, while preventing exudation of the retained fluids
from the lateral sides of the pad, or by providing a layer
which prevents the fluid from completely traversing the pad
3o from the absorbing major surface to another surface.
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Along with advanced materials and improved absorbent
article structures comes the concomitant need for advanced
manufacturing techniques. This is particularly true regarding
items such as sanitary napkins, disposable diapers, wound
dressing$ and the like, which are produced in necessarily
extremely high volumes. In many instances, the materials which
comprise such absorbent articles are manufactured in sheet form.
In other instances, the materials may be in pellets or randomly
sized pieces, however, they are usually not initially comprised
of individual fibers. Accordingly, apparatus and methods have
been developed whereby the starting materials are ground or
otherwise physically impacted to render the material into a
fibrous state, this process is known as "defiberizing". For
example, wood pulp may be defiberized in a conventional
hammermill, disk mill or lickerin. The defiberized material is
then readily formed into absorbent articles having a high level
of consistency.
It has been found that an efficient way of handling,
defiberized material for mass producing absorbent articles is by
creating an air-entrained stream of the defiberized material.
Using this technique, the material may be efficiently transported
and handled in high speed production machinery. Air-entrained
defiberized material may be formed into absorbent pads or the
like by passing the airstream through a foraminous surface; if
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the foramen are of the proper size, the defiberized material is
deposited thereon, this process is know as "airlaying". Most
typically, apparatus may be constructed which comprises an air
entrainment system which delivers a stream of fibers to a
rotating drum. Disposed on the periphery of the drum are a
series of foraminous cavities or molds, usually substantially in
the shape of the desired article. In certain cases, however, the
periphery is a continuous foraminous surface, allowing the
production of a continuous airlaid sheet. Fibers are then
airlaid on the foraminous surface; in some instances, if the
cavity is overfilled, the excess is removed by passing the cavity
in close proximity of a rotating brush, a process known as
"scarfing". By regulating the internal pressure of the drum,
relative to the pressure of the air-entrained stream, the density
of the deposited fibers can be controlled. Additionally, in
certain apparatus a positive pressure is created in portions of
the drum, allowing the airlaid articles to be ejected for further
processing.
An air-drum type apparatus for forming fibrous pads
from a sheet of fibrous material is disclosed in U.S. Patent No.
4,005,957--Savich. The apparatus described therein consists of a
means for defiberizing a sheet of fibrous material and providing
a stream of air-entrained fibers to a rotating drum. A series of
foraminous cavities are disposed on the periphery of the drum,
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into which the air-entrained fibers are introduced, producing an
airlaid article in the shape of the recess. Savich teaches the
forming of the article in a curved recess and ejecting the
airlaid article onto a flat vacuum conveyer, thereby providing an
article,, with one curved side and one flat side. The pressure
differential between the vacuum conveyor and the rotating drum is
sufficient to compress the airlaid article into an article having
a relatively greater basis weight.
Another example of airlaying apparatus is presented in
U.S. Patent 4,598,441--Stemmler, which discloses apparatus for
the manufacture of absorbent pads shaped to fit the body. As
discussed above, it is sometimes desireable to produce absorbent
articles comprised of two or more materials. Stemmler teaches
the use of what is'essentially a series of two separate,
identical forming machines connected by a transfer wheel. An
air-entrained fiber stream is created from a cellulose web using
separate apparatus attached to each machine. The first machine
has a hollow drum having recesses into which a stream of air-
entrained fibers is carried. The air-entrained fibers are
deposited to form a first component layer of the absorbent
article. The first layer of the article is then transferred to
the second machine where the second layer of the article has been
formed using a second stream of fibers. The two layers are
pressed together by a transfer drum which transports the
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resulting two-layer article to be further compressed and ejected.
Thus, Stemmler teaches the formation of a two layer article, each
layer of which may be comprised of a different fibrous material.
The reference teaches the placing of a first airlaid layer and a
second a,irlaid layer of substantially the same shape and surface
area atop one another, and compressing the layers to form an
absorbent article.
An apparatus which incorporates apparatus for
defiberizing a web of compressed material and forming the
resulting fluff into absorbent pads is disclosed in U.S. Patent
4,674,966--Johnson, et al. (Johnson I). A hammermill creates
fluff, which is drawn by a vacuum shroud through insert molds
which form the fluff into a desired shape. The molds are arrayed
on a circular drum; any overfill is removed and recycled as each
mold exits the drum. The molds illustrated are straight-sided
and have a foraminous bottom surface, beneath which is disposed
structure for controlling the airstream carrying the fibers.
The use of multiple streams of air-entrained fibers is
taught by British Patent Application No. 2,191,793. The
disclosure is primarily directed toward splitting streams of air-
entrained fibers in a clump free manner. Such split streams are
used to form absorbent articles having a central core of super
absorbent, overlaid by a larger layer of fibers. It is important
to keep the materials used for deposition free of clumps or other
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irregularities in order to assure a consistent product and an
uninterrupted, continuous manufacturing process. The British
reference teaches the use of two separate drum-type airlaying
apparatus. In one of the airlaying drums, the air-entrained
fibers a,re mixed with a superabsorbent prior to deposition in
order to form the superabsorbent core. Separate pad layers
produced by each airlaying apparatus are joined by compressing
one atop the other using conveyor belts and other transfer
apparatus external to the airlaying machines.
U.S. Patent 4,592,708--Feist discloses apparatus for
making airlaid articles of non-uniform thickness. The device
disclosed therein is a drum-type airlaying apparatus for making
discrete absorbent fibrous articles of airlaid matter. Feist
utilizes a rotating deposition drum having a plurality of article
formation cavities disposed in circumferentially spaced relation
about the periphery of the deposition drum. Each of the cavities
has a foraminous bottom wall. By providing means for directing
air-entrained fibers toward the~periphery of the drum and means
for vacuum drawing the entrainment air through the foraminous
bottom walls and exhausting it from the apparatus, discrete
absorbent articles are obtained. The improvement provided by
Feist consists of directing the stream of fibers substantially
radially toward the drum, thus assuring deposition on the bottom
of the forming cavity. Feist also teaches exhausting the
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entrainment air through substantially empty additional cavities
disposed upstream from the cavity into which the fibers are being
deposited.
In addition to airlaying apparatus generally, the
control of the impinging air-entrained stream of fibers has been
usefully exploited. It has been found that ; +- ; ~ oa~; e,. ~..
regulate the deposition of airlaid fibers by regulating open area
of the foraminous deposition surface and, concurrently or
separately, regulating the pressure and/or velocity at or near
the point of deposition. In this regard, it has been found that
a variety of screens or baffles may be used to achieve certain
useful conditions when such apparatus are placed beneath the
foraminous deposition surface, that is, when the deposition
surface is disposed between the impinging airstream and the
regulating apparatus.
For example, U.S. Patent 4,388,056--Lee et al.
discloses apparatus for continuously making an airlaid fibrous
web having a patterned basis weight distribution. The contoured
web produced has alternately spaced relatively high basis weight
and relatively low basis weight regions. Lee et al. teaches the
use of air flow modulating means which can be adjusted to produce
a range of pressure differentials across the foraminous bottom
surface of the recess into which air-entrained fibers are
introduced.
CA 02281968 1999-09-16
Also, West German Patent DE 3 5 08 344 Al discloses a
web forming assembly for use in a drum-type airlaying apparatus.
A series of apertures are disposed along the bottom surface of
the assembly, which is contoured to produce a pad having a
central,~ortion of a somewhat greater thickness than the
remainder of the article formed. The cavities in the deposition
drum are subdivided into a number of zones, each zone having a
separate, regulated vacuum line. The device disclosed permits
the production of airlaid articles of unifona quality having a
varying thickness.
An apparatus and process having airflow regulating
means is disclosed in U.S. Patent No. 4,666,647--Enloe et al.
(Enloe I). The improvement of Enloe I lies providing apparatus
for the formation of laid fibrous articles having a non-stepwise
gradation in basis weight. Enloe I teaches the use of a concave
forming surface bounded by angled walls, whereby the laid fibrous
article is readily removable from a foraminous forming surface.
As shown in Figures 2 and 3 of Enloe I, the foramen are located
on both the bottom and the sides of the recess into which the
air-entrained fibers are laid.
Similarly, U.S. Patent 4,761,258--Enloe (Enloe II)
discloses apparatus for forming of airlaid fibrous webs. The
webs disclosed have tailored absorbency zones, wherein certain
areas have a higher basis weight, and therefore a higher
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absorbency. Enloe II teaches depositing air-entrained fibers on
a foraminous web forming structure. A gas flow regulating means
using apertures provides a selected pattern of gas flow resulting
in a web forming assembly which creates a desired distribution of
fiber b~.sis weight across the formed web.
Finally, European Patent Application No. 35300626.0
discloses methods and improved apparatus for making discrete
airlaid absorbent articles. A drum-type apparatus is disclosed,
having a series of cavities which have foraminous bottom walls.
As shown in Figure 2, the foraminous bottom wall is preferably a
contoured mesh structure, having a relatively uniform
distribution of the foramen. The airlaid articles are then
further processed after deposition. The articles are compacted a
predetermined amount and then ejected, the compaction means is
shown as comprising a lugged wheel in gear-like engagement with
the cavities of the airlaying drum.
Also known in the art is the separation of fluff
components. For example, U.S. Patent 4,625,552--Johnson (Johnson
II) discloses an instrument for separating out any one or more of
the components of any given sample of fluff. As pointed out by
the reference, "fluff" is a collection of wood pulp fibers which,
if recycled, during a production process may also include bits of
reclamation waste, such as plastic or other materials. Although
Johnson II is primarily directed toward testing apparatus for
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determining the composition of a sample of fluff, one of ordinary
skill is also taught how to construct apparatus which can
separate out any one or more of the components of the fluff. To
accomplish this result, fluff is agitated by compressed air and
loose fibers are separated and drawn through a sieve by a vacuum,
while the non-fiber portions of the fluff are left in an
agitation chamber. The fibers are caught in a sieve, while.the
highly defiberized, broken fibers are caught later downstream in
a filter.
Thus, although several variations of airlaying
apparatus and deposition control are known, it would be
desireable to provide apparatus capable of continuously
depositing two or more materials in selected areas of a product.
At present, such constructions are limited to placing a first
layer atop a second layer and compacting the resulting assembly.
Such a construction is not preferred, however. In the case of
many absorbent articles, such as those combining absorbent and
repellent fibers. It would be further desireable that apparatus
be constructed which required only a reduced the cost and
complexity of the airlaying equipment, while still allowing two
or more materials to be continuously deposited. Finally, such
apparatus would ideally be flexible to the extent that the
characteristics of the product and the geometry of the areas in
which materials are selectively deposited may be easily changed.
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SUMMARY OF THE INVENTION
Accordingly, it has now been found that apparatus for
forming fibrous articles having at least two distinct portions of
fibrous materials may be constructed. Such apparatus comprises a
first mill and a second mill for defiberizing two distinct
materials. The defiberized materials are then air-entrained and
transported to first and second airlaying locations. The
airlaying locations are located so as to be in communication with
airlaying apparatus. In a most preferred embodiment, the
airlaying apparatus comprises first and second forming chambers
in communication with a duct means carrying first and second air
entrained fibers or other material to be deposited. A cavity
transport device having an interior section in which a vacuum is
created is also provided; most preferably this device will be of
the rotating drum type. Disposed upon the periphery of the
transport device are a plurality of deposition cavities, at least
a portion of each of the deposition cavities has a foraminous
surface. Disposed in the interior section of the cavity transport
means, is a vacuum chamber, in communication with at least a
portion of the foraminous surface of a deposition cavity. The
system utilizes air handling apparatus to create controlled
pressure differentials between the airlaying locations and the
interior section of the cavity transport means. In operation the
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first defiberized material is deposited in at least a portion of
a deposition cavity and the second defiberized material is
deposited in at least a portion of a deposition cavity resulting
in an article having at least two distinct portions of fibrous
materials. After the article is formed it is removed, most
preferably by a carefully controlled stream of compressed air
while simultaneously being transferred to a vacuum belt or drum.
In certain embodiments, the apparatus described is also
provided with environmental control equipment to regulate the
temperature and humidity within the duct means, this is important
when one of the fibers being deposited is hydrophobic, in order
to ensure proper defiberization and prevent agglomeration
throughout the system. Also provided in certain embodiments is
scarfing equipment for removing airlaid material extending beyond
the boundaries of the deposition cavity, prior to the ejection of
the fibrous article.
In the present invention, the separation between the
layers of different materials is largely maintained by the novel
basket screen mold disclosed. By carefully controlling the
positive and negative pressures beneath the foraminous bottom
surface of the basket, it has been found that a first material
may be airlaid in a defined area and retained there while a
second material is airlaid in another defined area. The basket
screen mold and related apparatus provide a series of baffles
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underneath the mold for controlling the airflow and a portion
of "honeycomb" material which reduces the turbulence and helps
eliminate side currents which may lead to undesirable
clumping.
Methods for producing airlaid articles of two or more
clearly defined layers or portions are also provided.
According to a broad aspect of the present invention
there is provided an air knife apparatus for removing an
airlaid article from a deposition cavity wherein a knife-like
to air curtain is provided by forcing compressed air into a
chamber, the chamber having a thin, adjustable slot through
which the knife-like air curtain is formed, the slot being
multi-axis adjustable and being directed lift the leading edge
of the article to effect smooth transfer of the whole article
from the deposition cavity to a transfer apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial diagrammatic view of the
preferred airlaying apparatus of the present invention.
Figure 2 is a partial diagrammatic view of a deposition
2o chamber and airlaying drum made in accordance with the present
invention.
Figure 3 is a cross-sectional view, taken along line 3-
3 in Figure 2 of a portion of a preferred deposition chamber.
Figure 4 is a cross-sectional view of the improved mold
cavity and screen found in prior art airlaying apparatus.
Figure 5A-5C depict the process of the present
invention using a cross-sectional view of the improved mold
cavity and screen of the present invention.
Figure 6 is a cross-sectional view taken along line 6-6
of Figure 5A which depicts the structural elements disposed
beneath the mold cavity and screen of the present invention.
Figure 7 is a partially broken away view of an
airlaying device depicting the fibrous object removal
apparatus of the present invention.
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Figure 8 is a perspective view of the improved mold
cavity and screen of the present invention.
DETAILED DESCRIPTION
As discussed above, it is known in the art to use a
forming chamber that deposits defiberized material into a molding
cavity in either a flat or contoured configuration. However; the
system of the present invention delivers multiple defiberized
materials and/or particulate components into different zones of
the same molding cavity for the production of an improved
sanitary protection product, sanitary napkin, diaper and the
like.
The apparatus and methods of the present invention
allow the deposition of two or more materials in a manner such
that the resulting product is not limited to being formed from
two "layers" of different material. Instead, the capability is
provided to selectively deposit fibers of different
characteristics in a variety of depths and configurations. Most
preferably, a "cup" of hydrophobic fibers is disposed on one side
and along the edge of a central "core" of absorbent fibers. When
the absorbent core is placed against the body, such a
construction will absorb fluids through the core, but the
hydrophobic "cap" will prevent flowthrough or exudation from the
front surface and lateral sides of the article. These novel
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improvements of the present invention mainly relate airlaying
apparatus of the type of using auxiliary defiberizers and fiber
or particle metering devices that deliver different materials to
specific locations along the forming drum. The resulting process
is known~,as "selective placement".
Referring to Figure 1, there is illustrated a
diagrammatic representation of a preferred apparatus for
practicing the present invention. Certain details, such as
electrical and vacuum lines, have been omitted in order to
simplify the description. Those of ordinary skill are well
versed in such aspects of airlaying and similar apparatus. A
first type wood pulp or other fibrous material il is defiberized
in a conventional hammermill, disk mill or lickerin 12, and fed
into an air-entrained stream moving in an air duct 15. The air-
entrained stream of a first defiberized material moves to a first
forming chamber 16 which is preferably directly adjacent to a
molding cavity 17. The molding cavity 17 is preferably one of a
plurality of such cavities disposed on the periphery of the
deposition drum 21 of a rotating drum-type airlaying device.
However, other airlaying apparatus may be substituted quite
readily. For example, an enclosed conveyor carrying mold
cavities which has a sufficient interior vacuum could also be
used. As will be further understood by those of ordinary skill,
the feeding of defiberized materials to the deposition drum 21 is
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accomplished either by directly feeding the materials to a
forming chamber from the underside of a mill or by conveyance
through duct work.
A vacuum source 18 directs the defiberized materials
into the~,molding cavities 17 along the periphery of the rotating
deposition drum 21.
As shown, a duct 22 connects a first forming chamber 16
to the vacuum source 18. In some versions of this device,
deposited materials overfill the molding cavity 17 slightly and
are scarfed and recirculated back into the forming chamber. The
fabricated absorbent cores are then deposited onto a transfer
drum, discussed below, and become available for further
processing into a finished product. The construction of vacuum
sources and the other equipment disclosed herein is generally
known to those of ordinary skill: further elaboration being
unnecessary at this junction.
Also depicted in Figure 1 is a second defiberizing and
air-entrained system. A second fibrous material 31 is
defiberized by a second hammermill 32 or similar apparatus. The
defiberized second material is transported via a duct 35 to a
second forming chamber 20, disposed at a fixed location on the
deposition drum 21. The equipment described relating to the
second fibrous deposition may be of the conventional type
described above. Moreover, other equipment or materials may be
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substituted. For example, it may be desired to deposit a foam or
other material, rather than a second fibrous material.
It is understood by those of ordinary skill that
although in a most preferred embodiment a hydrophobic layer of
fibrous materials will be airlaid first, followed by a layer of
absorbent material, the present apparatus is not limited to the
manufacture of this type of construction. The present invention
permits the formation of an article having two or more layers,
portions or sections which are comprised of materials having
different characteristics. Advantageously, the present invention
facilitates the production of such articles at a high rate of
speed and further permits the layers to be clearly demarcated.
One aspect of the present invention comprises a novel
enhancement to a molded core production system as described
immediately above. The system of the present invention uses one
or more auxiliary formation chambers along the main formation
drum for specialty absorbent core production. The absorbent
cores produced have fibers of two or more types selectively
placed in distinct areas of the article. Referring again to
Figure 1, there is illustrated a preferred system for pulp
delivery. A specially designed scrub chute 13 located under the
first mill 12 transitions the selected materials out of the mill
and into an air stream 14 in a uniform manner which substantially
reduces the agglomeration of the fibers. The defiberized air-
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entrained material is then transported via conventional ductwork
15 to an airlaying apparatus. A contoured formation chamber 16
of specific geometry deposits the individual fibers into the mold
cavity 17: the details of the formation chamber 16 are discussed
below. ~A specially designed mold, also discussed below, channels
the defiberized fibers into selected locations within the
confines of the mold cavity 17. A neutral zone 19 located after
the first formation chamber 16 is provided to isolate the stages
of the deposition processes.
Specialty materials, most preferably a repellent or
hydrophobic pulp, are preferably defiberized in a screenless
hammermill 12 which is rotating between about 5,000 to about
7,000 RPM, most preferably about 6,000 RPM, with a peripheral tip
velocity of about 13,600 ft/m to about 19,000 ft/m most
preferably about 16,900 ft/m. However, other defiberizing
apparatus may be used. To prevent clumps forming at the
defiberizer, it has been found that throughput should be less
than about 40 lbs/hr/in. of hammermill width. Material which has
been defiberized and influenced by the vacuum from the auxiliary
vacuum source 18 is now transported into the scrub chute 13 and
mixed with conditioned air 14, preferably with a relative
humidity (RH) between about 50% RH to about 75% RH, and most
preferably about 65% RH. The humidity requirement is critical to
the transportation of repellent fibers, due to the moisture
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resistance of such fibers relative to conventional absorbent
pulp. A high static charge is developed in the defiberization
and transportation of these fibers; humidified air reduces
agglomeration and increases fiber deposition uniformity.
Therefore, the air quality within the entrainment apparatus must
be controlled. The fibers, once treated with humidified air, are
transported through conventional ductwork, preferably at a
velocity of about 3,000 to about 15,000 ft/min, and most
preferably about 6,000 ft/min. It will be understood, however,
that velocity is dependent upon both materials and the position
within the system. The velocity will vary widely throughout the
system, but will be within a specified range. In other
embodiments or for the purposes of making products having other
than a repellent fiber layer, the relative humidity may be less
critical, although it may still be controlled to some degree.
The defiberized, humidified repellent fiber material
then enters the formation chamber 16 which is contoured to
efficiently deposit the transported fibers into the open mold
cavities 17. The exact curvature of the formation chamber
depends upon the materials being deposited and the conditions
under which the deposition takes place. By varying the velocity,
pressure and angle of impingement, those of ordinary skill will
be able to achieve the results contemplated herein with a minimal
amount of experimentation. Further details of the formation
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chamber 16 are discussed below with reference to Figure 2.
Forming pressures in the forming chamber 16 preferably range from
about -3"H20 to about -15"HZO and most preferably the pressure is
about -10"H20. Differential pressures through the mold cavity
preferably range from about -17"HZO to about -60"H20 and most
preferably is about -41"H20. Fibers deposit themselves into
select locations within the cavity due to the chambering of. the
mold and the corresponding baffling located under the mold cavity
17, which is discussed in greater detail below. The deposition
uniformity is controlled by the precise control of material
infeed, humidity control, air transportation velocity control,
and forming chamber geometry. The mold cavities 17 move through
the formation chamber 16 and pass into the neutral zone 19 where
a pressure differential through the mold preferably between about
-25"H20 and about -45"HZO is placed across the mold, with the
neutral chamber preferably having a pressure of about 0"H20 to
about -5"H20. This neutral zone 19 separates the deposition
chambers 16,20 and preferably has a length from about 10% to 500%
and most preferably about 100% of the pitch length of the mold
cavity 17.
The mold cavity 17 then moves through the neutral zone
19 into the next deposition zone 20 where it is processed by
depositing air-entrained defiberized material in the conventional
manner. Ultimately, a complete molded core is transferred out of
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the mold cavity 17 and out of the vicinity of the airlaying
apparatus for further processing. As discussed above, those of
ordinary skill will readily appreciate the variations of the
process described. For example, the "cup" of fibers which is
formed can be filled with a hydrophilic foam, rather than
absorbent fibers, therefore the second deposition chamber 20
would be of a somewhat different design.
Referring now to Figure 2, there is illustrated a
preferred embodiment of a formation chamber 16 for use in the
present invention. As explained above with reference to Figure
1, a stream of air 14, carrying fibers or other materials to be
deposited within a mold cavity, is conveyed in a duct 15 to the
forming chamber 16. An elbow 162 with a rectangular cross-
section is located just prior to the formation chamber 16. The
radius of curvature of the elbow is on the opposite side of the
duct from empty molds entering the formation chamber 16. The
action of the elbow 162 on the conveyed materials is to
concentrate the materials toward the straight wall 164 resulting
in a rapid deposition of the material into the mold cavity 17.
The side walls of the elbow 162, the interconnecting duct 170 and
the forming chamber 16 are preferably the same distance apart;
the distance is most preferably substantially the width of the
mold cavities 17.
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As a mold cavity 1? enters the forming chamber 16 at
the intersection with the deposition drum 21, air is drawn
through the mold cavity 17 into the vacuum chamber 23. As shown
in Figure 3, the vacuum chamber 23 is connected to a vacuum
source,l8 (not shown) via duct 22. A foraminous surface in the
mold cavity 17 traps the conveyed air-entrained material.
Referring again to Figure 2, as the mold cavity 17 continues to
rotate from j~~ through ~f, less and less air is drawn through the
mold, due to build-up of depcsited material on the foraminous
surface of the mold cavity 17. The average amount of air flow
through the deposition drum 21, as a function of ~J, is determined
by testing the cross-sectional area, A,, of the forming chamber
which continually decreases with the angle ~l to maintain air
velocity (at least about 3000 ft/min) in the forming chamber.
The suction chamber 23, as shown in Figure 3, is
disposed on the inside of the deposition drum 21, and extends
from ~i to ~3f, as shown in Figure 2. The width of the suction
chamber 23 is substantially the width of the flow passages in the
mold cavities 17, as shown in Figure 3.
In conventional forming chambers, poor control of air
velocity (magnitude and direction) causes vortices within the
chamber, which may agglomerate fibers into low density clumps.
Edges within the chambers cause buildup of low density clumps
which erratically break loose and fall into the mold cavities.
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These low density clumps lower the integrity of the absorbent
product, increasing wet collapse and reducing wicking--all of
which are undesirable characteristics. Moreover, due to poor air
velocity control (magnitude and direction), conventional forming
chambers use about twice the forming air volume as the chamber 16
of the present invention. Therefore, the present invention
requires smaller vacuum sources, air conditioners and dust.
collectors, resulting in greater energy efficiency and more
economical operation.
Another advantage of the distribution chamber of the
present invention are that molds are filled rapidly since most of
the material is deposited early in the molding cycle. Since the
design eliminates air recirculation and edges within the chamber
which may cause agglomeration, clumps and uneven filling of the
mold cavities is substantially eliminated. The design minimizes
the amount of air necessary for conveying and molding, however,
the material is deposited with high kinetic energy onto the
screen, resulting in a higher density product, thereby enhancing
the integrity of the molded product.
The present invention also provides novel means for
selectively placing fibers and other materials within the core of
an absorbent product, such as a sanitary napkin. The invention
permits multiple layers, strips, rings and other geometric shapes
of fibers arid particles to be placed in a mold cavity and be
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CA 02281968 1999-09-16
built up, one on top of the other, or side by side, until the
mold cavity is filled. This allows specialized materials to be
placed and used optimally within the core of an absorbent
product.
As depicted in Figure 4, in conventional molding
processes, air and entrained material 200 is pulled by vacuum
through a flat or two dimensional screen 210. The material. is
deposited on the screen, filling the mold cavity 212. The molds
themselves are preferably attached to a rotating drum, the
1~ rotating molding drum either rotates clockwise or
counterclockwise, depending on the requirement to have the shaped
side of the molded product up or down after transfer out of the
molding drum.
In the present invention, as shown in Figures 5A-5C, a
15 three dimensional screen 220 is used and air-entrained material
200 flows through both the bottom and the sides of the screen
basket, as illustrated by the arrows. The area under the
improved screen 200 is divided into two or more independent
suction chambers. As illustrated, the area under the screen is
20 divided into an annular chamber 230, which encircles the
perimeter of the area of the molded object. A second chamber 232
is located beneath the central portion of the mold cavity; most
preferably this is the location where absorbent material will be
selectively deposited. When a vacuum source is applied to a
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CA 02281968 1999-09-16
particular suction chamber, preferably at the bottom and/or sides
of the mold, air and entrained fibers are selectively pulled to a
section of the screen and the material in the air is deposited on
that section of screen. As will be apparent to those of ordinary
skill, a suction chamber may be routed to any portion of the
screen, resulting in the deposition of material anywhere in the
surface of a shaped screen. In the example shown in Figure,5,
suction is applied to a first chamber 230, resulting in a buildup
of a first material in the mold in the areas above the chamber
230 to which a vacuum is applied. Most preferably, the first
material will be a hydrophobic fibrous material. When sufficient
amounts of a first material have been deposited, the mold is
exposed to continued vacuum in chamber 230 and a positive
pressure is applied to another chamber 232. This causes any
material inadvertently deposited in the area above the other
chamber 232, to be moved to the area above the first chamber 230,
thus providing a clearly defined layer of material disposed only
on those portions of the screen 220 disposed above a first
chamber 230. Suction is then applied to both chambers 230,232.
The suction in the first chamber 230 retains the first material
in its position. A second material is then deposited in the area
above the other chamber 232.
By referring to Figures 5A-5C one of ordinary skill can
appreciate the novel process of the present invention. As shown
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CA 02281968 1999-09-16
by the arrows of Figure 5A, a first air-entrained material is
placed in specified areas of the mold by opening those areas to a
vacuum. A seal 233 is used to separate other portions of the
deposition cavity from the vacuum source. As a result, in a
preferred embodiment depicted in Figure 5B, a portion of the
deposition cavity is filled with a first air-entrained material.
In the preferred embodiment depicted, a "ring" of hydrophobic
material has been airlaid around the perimeter of the deposition
cavity.
A second airlaid material is next added to the article,
as shown in Figure 5C. As shown by the arrows, the air-entrained
stream is placed in communication with the vacuum source through
substantially all the area of the forming cavity. The airflow
through the previously airlaid first material keeps that material
in place, while the unfilled area is now filled. Thus, in a most
preferred embodiment, when the condition shown in Figure 5C is
reached, the article is substantially complete in terms of
airlaying and may be removed from further processing.
Referring now to Figure 8, there is illustrated a
perspective view of a section of the deposition drum showing a
typical embodiment of a three dimensional screen 220 made in
accordance with certain aspects of the present invention. It can
be observed that the foraminous surface of the three dimensional
screen 220 covers both the bottom surface and a portion of the
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CA 02281968 1999-09-16
side walls, as explained above. Additional details of the
airlaying methods of the present invention are discussed both
above and below. However, one of ordinary skill will immediately
realize that numerous variations of the apparatus and methods of
the present invention can be used in combinations to produce an
immediate variety of products, all containing two or more
distinct materials.
To place pulps, fibers and other materials within the
mold and maintain their placement, it is important to control the
airflow through the mold cavity as it enters and leaves a
particular forming chamber. In the present invention, as shown
in Figure 6, this is accomplished by a plurality of axial
partitions 250 placed beneath the forming screen 220 and
extending to and forming the inner sealing surface between the
mold cavity 17 and the vacuum chamber 176. In certain
embodiments the axial partitions 250 may be comprised of a
honeycomb material which has a plurality of axial passages formed
therethrough.
The advantages of the basket screen molding of the
present invention are that two or more materials may be deposited
in selected locations within a molded core and actively removed
from all other areas, allowing materials of different properties
to be segregated and used optimally. Thus, sharp delineation
27
CA 02281968 1999-09-16
between the materials which was heretofore impossible is
achieved.
To eject formed articles from the mold cavities 17
while avoiding the separation of different layers of formed
materials and keeping the article from deforming or separating as
it exits the deposition drum 21 to transfer drum 310, apparatus
for ejecting a formed article using a precisely controlled stream
of air is provided, as illustrated in Figure 7.
The present invention provides apparatus to feed
compressed air 312 into a chamber 314 in which the pressure is
distributed evenly (equalized). The air is then forced through a
thin adjustable slot 316 providing a knife-like air curtain as
shown by the arrow at 318. Preferably, multi-axis adjustment is
provided and the slot opening can be varied from about 0 to about
0.03125 inches. By multi-axis adjustment, it is understood that
it may be desireable to precisely direct the stream of air by
moving the apparatus along one or more linear axes relative to
the molding cavity 17 and/or pivot the apparatus about one or
more axes of rotation. The multi-axis adjustment may be provided
in many practical ways, well known to those-of ordinary skill.
For example, certain axes of adjustment may be built into the
mounting bracket 320 which affixes the removal apparatus to the
deposition drum structure or into the apparatus itself.
Preferably, the air knife is operated at a pressure of about 4-20
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CA 02281968 1999-09-16
psi, and most preferably at 12 psi. It has been found that the
high velocities created by higher pressures tend to dislodge the
fibers of which the article is formed.
The apparatus depicted in Figure 7 provides a smooth
transfer of molded articles onto a vacuum transport device such
as a conveyor belt or drum, etc. As depicted, the most preferred
transfer device is a transfer drum 310. The air knife depicted
in Figure 7 allows articles formed from two or more distinct
layers of fibers to be efficiently removed from the basket molds
of the present invention. It has been found that the vacuum
transfer drum does not always withdraw the formed article
effectively. This is due to fiber entanglement with the sides of
the mold cavity, which creates a greater resistance to article
removal. The air knife of the present invention thus lifts the
leading edge of the article and ensures that it and the rest of
the article are transferred smoothly out of the mold.
Although certain embodiments of the present invention
have been described with particularity, the invention is by no
means limited to the embodiments described. As numerous
variations will be immediately apparent to_those of ordinary
skill, reference should be made to the appended claims to
determine the scope of the invention.
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