Note: Descriptions are shown in the official language in which they were submitted.
21~ X784
Docket No. CAN-65
TITLE: METHOD AND APPARATUS FOR MANUFACTURING A LIQUID-
AHSORHENT ARTICLE AND THE RESULTING PRODUCT
'THEREOF
FIELD OF THE INVENTION
The present invention relates to the art of
manufacturing structures for absorbing body exudate. More
particularly, the invention relates to a method and
apparatus for manufacturing liquid-absorbent articles by
deposition of particles suspended in fluid on a foraminous
forming member. Advantageously, the method can be used
for producing anatomically shaped, non-planar liquid
absorbent components for disposable absorbent products
such as sanitary napkins, diapers, urinary pads, adult
briefs, nursing pads, tampon pledgets and desiccants for
keeping goods dry during shipping and storage, among
others.
BACKGROUND OF THE INVENTION
Traditionally, sanitary napkins for medium to high
menstrual flow have been relatively thick and bulky
containing an absorbent core made of fluffed hydrophillic
materials such as wood pulp, rayon or cotton. These
absorbent materials are attractive because they are fairly
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Docket No. CAN-65
easy to manufacture at low cost while having, at least
theoretically, a high absorbent capacity. However, this
category of disposable absorbent products is known to
possess severe deficiencies, failing in practise to
provide the required protection against leakage and
staining. More particularly, such fibrous materials
suffer from poor fluid distribution properties and do not
have the ability to disperse fluid within the entire
available absorbent volume. As a result, the absorbed
fluid will tend to concentrate in a certain area of the
absorbent core, causing localized saturation and collapse.
This phenomenon often results in fluid leaking past the
edges of the sanitary napkin and staining the wearer's
clothes. Another disadvantage of sanitary napkins with
thick absorbent cores resides in their inability to
closely conform and follow the contour of the human body,
achieving at best an intermittent contact surface between
the fluid permeable side of the sanitary napkin and the
integument of the wearer, which results in poor gasketing,
increasing the likelihood of failures due to fluid
leakage.
To address the above-discussed problems, a growing
number of thinner and more flexible sanitary napkins have
been developed, providing better fit, comfort and
discretion, while being sufficiently absorbent to provide
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Docket No. CAN-65
effective menstrual protection. The absorbent cores used
in thin sanitary napkins include compressed sphagnum moss
material which has a large proportion of extremely tiny
pores and capillaries, having the ability to absorb a very
high quantity of liquid.
The following United States patents document the use
of sphagnum moss material for manufacturing absorbent
components for disposable absorbent products.
PATENT INVENTOR(sj DATE OF ISSUE
#
4,170,515 Lalancette et al. October 9, 1979
4,215,692 Levesque August 5, 1980
4,226,237 Levesque October 7, 1980
4,305,393 Nguyen December 15, 1981
4,473,440 Ovans September 25, 1984
4,507,122 Levesque March 26, 1985
4,618,496 Brasseur October 21, 1986
4,676,871 Cadieux et al. June 30, 1987
4,992,324 Dubs February 12, 1991
5,053,029 Yang October 1, 1991
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Docket No. CAN-65
Sphagnum moss material can be formed in a highly
cohesive sheet by using anyone of the methods disclosed in
the above-identified prior art. In sheet form, the
sphagnum moss material is convenient to handle and it can
be directly processed in high speed automatic equipment
for assembling disposable absorbent products.
More particularly, the method for producing the
sphagnum moss sheet consists of wet classifying raw peat
moss material in particulate form to retain only the
particles which are the most absorbent. The screened
fraction is sheeted on a Fourdrinier wire in the form of
a slurry and de-watered by the application of vacuum. The
thus formed sheet is dried and calendered to increase its
density to the desired level. In order to tenderize,
soften and improve the flexibility of the calendered
sphagnum moss sheet, it may be subjected to mechanical
working such as perf-embossing or micro-corrugating as
described in the United States patents 4,559,050 and
4,596,567 to Iskra issued on December 17, 1985 and June
24, 1986 respectively.
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Docket No. CAN-65
The sphagnum moss sheets manufactured by the above-
described wet laying method have a planar configuration.
Although such liquid-absorbent sheets possess a high
degree of fly=_xibi.lity and softness, hence they are
highly conforrr,able to the shape of the human anatomy,
there are lirnits to the degree of deformation the
absorbent structure can sustain. For that reason, it is
desirable to develop a method and an apparatus allowing
to manufacture sphagnum moss liquid-absorbent articles
having either a planar or a non-planar configuration, as
desired.
OHJECTB AND BT;i~TEMENT OP TH8 INVENTION
An object of this invention is to provide an improved
method for manufacturing a liquid-absorbent article from
particles susF~ended in fluid (for the purpose of this
specification '"particle" means a small amount of material
without limitations of shape. A fiber that is
characterized by a geometrical extension along a
preferential dlirect:ion will be considered a particle.
Hence, "partic:ulate matter" covers a material made of
fibers, particles having non-fibrous identity or a
combination of both).
Another olbject of the invention is an apparatus for
carrying aut the aforementioned method.
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Docket No. CAN-65
A further object of the invention is a fluid-laid
liquid-absorbent article of non-planar configuration. For
the purpose of this specification, the expression "non-
planar configuration" is intended to encompass three-
s dimensional shapes that are not flat, such as convex or
concave bodies, or shapes which have of non-uniform
thickness. An example of the later case is a sheet-like
absorbent core with thinner marginal portions by
comparison to its central area. Although the sheet-like
absorbent core may have a preferential extension along an
imaginary plane, it is considered non-planar because at
least one of its main outer surfaces is not confined
within a plane. In contrast, a sheet-like body having
parallel main faces will be characterized as planar.
As embodied and broadly described herein, the
invention provides a method for manufacturing a liquid-
absorbent article, said method comprising the steps of:
- placing a foraminous forming member in a body of
particles suspended in a fluid, such as liquid or gas;
- establishing a pressure differential across said
forming member to cause particles in said fluid to
agglomerate on said forming member into a layer of
particles;
- removing said layer of particles from said forming
member to form said liquid-absorbent article.
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Docket No. CAN-65
This method is particularly well-suited for
manufacturing absorbent cores made from sphagnum moss
material, although other particulate materials can be used
as well. In a preferred embodiment, raw sphagnum moss is
wet-classified to remove the particles that are
substantially non-absorbent, such as the extremely small
particles commonly referred to as fines, and larger
rejects such as roots and branches. The classified
fraction is then formed into an aqueous slurry having a
consistency in the range from about 0.1% to about 3.0%
solids, preferably of about 1.0%. The forming member is
an apertured surface in fluid communication with a suction
device. When the forming member is immersed in the slurry
of sphagnum moss particles and the suction device is
actuated, the resulting pressure differential causes
sphagnum moss particles to agglomerate on the surface of
the forming member into a layer of complimentary shape.
Thus, by employing a concave forming member, a cup-shaped
liquid-absorbent article will be produced. Such shape
enables the absorbent article conform well to the perineal
region of the human body.
The thickness of the sphagnum moss layer deposited on
the forming member is determined by the residence time of
the forming member in the liquid suspension and also by
the intensity of the pressure differential. Generally
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Docket No. CAN-65
speaking, an increased pressure differential will result
into a thicker layer of sphagnum moss. Likewise, a longer
residence time in the liquid suspension produces a thicker
deposit.
The present method can be put to practical use for
manufacturing tampon pledgets by employing mandrel-shaped
forming members. In one embodiment, a layer of particulate
material, preferably sphagnum moss, is caused to
agglomerate on the outer surface of the forming member,
' thus producing a hollow pellet-like mass which can be
deposited in the vaginal orifice of the user by
conventional tampon applicator structures. In a variant,
the particle agglomeration is effected within the cavity
of a forming member to provide a solid pellet-like tampon
pledget.
The method according to the invention also allows to
manufacture laminated liquid-absorbent articles by
successively depositing on the forming member layers from
different particle suspension beds. Each layer of
particles forms an individual stratum of the absorbent
structure. For instance, if a dual-layer structure is
contemplated, the forming member is first immersed in a
first particle suspension to build-up the first layer and
then transferred to a second particle suspension to form
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Docket No. CAN-65
the second layer on top of the first layer. This feature
enables to produce tampon pledgets, either hollow or of
the solid variety, having an outer liquid-permeable jacket
that prevents fragmentation and loss of structural
integrity of the inner sphagnum moss core during use of
the tampon pledget. Such protective jacket is preferably
build-up by deposition of comparatively long fibers made
of polyester, rayon, cotton or cellulose, among other
materials.
The method in accordance with the invention also
offers the possibility of manufacturing liquid-absorbent
articles of varying thickness. In one embodiment, this is
achieved by establishing a pressure differential gradient
along the surface of the forming member. For instance,
the apertures establishing a fluid path with the source of
vacuum are made comparatively large at the areas of the
forming member where a high rate of particle deposition is
required. In contrast, smaller apertures are formed in
the areas where a reduced thickness is desired. It will
be apparent that the smaller apertures create a path of
higher resistance to fluid drawn by the source of vacuum
and as a consequence the forces that urge the particles in
suspension to agglomerate against the forming member are
weaker in that region.
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Docket No. CAN-65
As embodied and broadly described herein, the
invention also provides an apparatus for manufacturing a
liquid-absorbent article, said apparatus comprising:
- a container for holding a suspension of particles
in a fluid; _
- suction means;
- a forming member capable of insertion in said
container, said forming member having an apertured surface
in a fluid-communicative relationship with said suction
means, whereby said suction means is capable of
establishing across said apertured surface a pressure
differential for causing deposition of particles in said
suspension against said apertured surface in order to form
said liquid-absorbent article.
As embodied and broadly described herein the
invention also provides a moulded, non-planar, liquid
absorbent article, said liquid-absorbent article
comprising discrete particles amalgamated into a unitary
structure, said particles forming interstices therebetween
for admitting liquid.
As embodied and broadly described herein, the
invention further provides a laminated, integral, tampon
pledget comprising:
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Docket No. CAN-65
- an absorbent core comprising discrete particles
amalgamated into a unitary structure, said particles
forming interstices therebetween for admitting liquid; and
- a jacket of fibrous material covering at least
partially said absorbent core, said jacket having a three-
dimensional structure complementary to said absorbent core
and being joined therewith in an intimate fluid-
communicative relationship, whereby body exudate delivered
to said jacket of fibrous material is capable of migrating
through said jacket toward said absorbent core.
BRIEF DESCRIPTION OF TH$ DRAWINGS
- Figure 1 is a schematic representation of an
apparatus according to the invention for manufacturing a
liquid-absorbent article, showing a forming member
immersed in a suspension of particles at the beginning of
a liquid aspiration cycle;
- Figure 2 illustrates the apparatus of Figure 1,
showing a build-up of particles on the forming member
following a period of aspiration of liquid;
- Figure 3 illustrates the forming member withdrawn
from the suspension following completion of the formation
of a layer of particles on the forming member;
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Docket No. CAN-65
- Figure 4 illustrates the forming member located in
a station for drying the formed layer of particles;
- Figure 5 illustrates the forming member located in
a station for treating the formed layer of particles with
binder;
- Figure 6 illustrates the forming member in the
process of ejecting the dried liquid-absorbent article;
- Figure 7 shows a variant of the forming member
featuring a non-planar configuration;
- Figure 8 is a plan view of a forming member in
accordance with a variant characterized by the ability of
producing a liquid-absorbent article having a non-uniform
thickness;
- Figure 8a is a vertical cross-sectional view of
forming member in accordance with a further variant
employing a dual source of vacuum for producing a liquid-
absorbent article having a non-uniform thickness.
- Figure 9 is a vertical sectional view of a mandrel-
shaped forming member for use in manufacturing tampon
pledgets in accordance with the invention;
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Docket No. CAN-65
- Figure 10 illustrates the mandrel-shaped forming
member partially immersed in a first liquid suspension
while aspiration is being applied to build-up the
absorbent core of the pledget;
- Figure 11 illustrates the build-up of particles
against the mandrel-shaped forming member after a period
of time following the actuation of the suction device; and
- Figure 12 illustrates the mandrel-shaped forming
member partially immersed in a second liquid suspension to
form an outer protective jacket on the previously formed
absorbent core;
- Figure 12a is a vertical cross-sectional view of a
dual-layer tampon pledget to which is integrated a loop-
shaped withdrawal string;
- Figure 13 is a vertical cross-sectional view of a
forming member in accordance with a variant for producing
a solid core tampon pledget;
- Figure 14 illustrates the forming member shown in
Figure 13 immersed in a liquid suspension to form the
outer protective jacket of the tampon pledget;
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Docket No. CAN-65
- Figure 15 is a vertical cross-sectional view of the
forming member of Figure 13, showing the formed protective
jacket and a withdrawal string;
- Figure 16 illustrates the forming member with the
protective jacket and the withdrawal string immersed in a
liquid suspension to form the absorbent core of the tampon
pledget;
- Figure 17 illustrates the forming member immersed
in an another liquid-suspension to completely close the
protective jacket, thus encapsulating the absorbent core;
and
- Figure 18 is a vertical cross-sectional view of the
formed tampon pledget.
DESCRIPTION OF PREFERRED EKHODIMENTB
Figure 1 of the annexed drawings schematically
illustrates an apparatus 10 for manufacturing liquid-
absorbent articles by deposition of solid particles
suspended in a liquid. More specifically, the apparatus
10 comprises a vessel 12 containing an aqueous slurry of
solid particles from which the absorbent article will be
made. In a specific example, the solid particles are
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Docket No. CAN-65
sphagnum moss. However, other materials can also be used
such as polyester fibers, rayon fibers, cotton fibers, and
cellulose fibers, among many others.
The suspension of sphagnum moss particles has a
consistency in the range from about 0.1% to about 3.0% by
weight of solids and most preferably of about 1.0%.
A forming member 14 is shown immersed in the
suspension of sphagnum moss particles. The forming member
14 comprises a container member 16 in which is mounted a
fine mesh screen 18. The container member 16 has an
opened lower extremity and an upper extremity (as viewed
in the drawings) that is closed except for an opening
communicating with a conduit 20. The screen 18 is
maintained in the container member 16 to separate the
container member 16 into a first portion adjoining the
opened lower extremity and a second portion between the
upper extremity and the screen 18.
The conduit 20 is connected to a source of vacuum
such as a pump (not shown in the drawings). When the pump
is energized, a pressure differential is established
across the screen 18 (i.e. the pressure in the first
portion that adjoins the open end of the container member
16 is higher than the pressure in the second portion
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CA 02159784 2000-09-11
between the screen 18 and the upper end of the container
member lE~) which causes aspiration of water through the
conduit 2Ø Solid particles of the suspension that are
entrained in the flow are arrested by the screen 18 and
agglomerate, as shown in Figure 2, into a layer of
uniform thickness. The particles, when agglomerating,
thereby also forming interstices for admitting liquid.
The layer of sphagnum moss particles is designated by
the reference 22.. The rate of material build-up is
determined primarily by the intensity of the pressure
differential ~icro~;s the screen 18. Generally, increased
vacuum will produce a higher rate of material deposition
on the screen 18. Of course, the final thickness of the
layer 22 is detE=_rmined by the rate of material
deposition anti al=;o by the residence time of the forming
member 14 in the su:~pension oi. sphagnum moss particles.
Once the desired sphagnum moss thickness has been
reached, the forming member 14 is withdrawn from the
vessel 12. This can be achieved by mounting the forming
member 16 to a hydraulic or pneumatic actuator (not
shown in the drawings) to displace the forming member 14
in and out oi= the vessel 12 in order to automate the
manufacturing process. It will be appreciated that a
flexible line (not. ahown in the drawings) ~is required to
connect the c~~ndu:it 20 to the source of vacuum that is
preferably a ~;tationary installation.
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Docket No. CAN-65
When the forming member 14 is withdrawn from the
suspension of sphagnum moss particles, it is desirable to
maintain the pressure differential so as to avoid the
layer of sphagnum moss particles from falling under the
effect of gravity.
At the next processing stage, as shown in Figure 4,
the forming member 14 is placed in a body of warm air such
as an oven 26. By maintaining the aspiration through the
conduit 20, warm air passes through the particulate layer
22 and causes water to evaporate. This stage is a
convenient location for treating the sphagnum moss layer
with the desired substance to impart to it desirable
properties. For example, as shown in Figure 5, the
sphagnum moss material may be treated with a binder
substance by vaporizing in the oven 26 liquid binder from
nozzle 24 to create a suspension of droplets that are
drawn within the layer 22 during the drying phase. In
addition to causing the binder droplets to penetrate
deeply within the sphagnum moss material, the air flow
also accelerates the curing time of the binder.
Treatments other than binder deposition can also be
envisaged, such as delivery of surfactant to better
develop the affinity of the sphagnum material for water,
among others.
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Docket No. CAN-65
Once the drying/curing stage has been completed, the
layer 22 is ejected from the forming member 14 by
reversing the pressure differential. This is accomplished
by switching the vacuum source to the air blowing mode, as
shown in Figure 6.
In a variant, the apparatus 10 may be used to
manufacture multi-layered absorbent articles. This is
achieved by providing several vessels containing a
suspension of different particles that form the various
layers of the final structure. By successively performing
an aspiration cycle in each vessel, a laminated structure
can be built-up. Of course, the various layers would have
to have sufficient porosity to permit liquid containing
the particles for the final layer to be admitted through
the base layers under the effect of the pressure
differential so that particles can be deposited on the
base layers.
Figure 7 illustrates a variant of the forming member.
The difference with the previously described embodiment
resides in the shape of the screen 18 which has a non-
planar configuration. This is a particularly desirable
feature because it allows to manufacture sphagnum moss
articles of a specific shape selected to fit well the
anatomy of the user. For instance, the arrangement of
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Docket No. CAN-65
Figure 7 would allow to produce a cup-shaped sphagnum moss
layer that conforms to the perineal area of the user.
Such cup-shaped absorbent structures could be advantageous
for use as absorbent cores in sanitary napkins or urinary
pads.
In a further variant shown in Figure 8, the screen
18' is constituted by a wire mesh so arranged as to create
comparatively small openings near the longitudinal end
edges of the forming member and much larger openings in
the centre. It will be apparent to those skilled in the
art that the small openings would create a path of high
resistance to fluid aspirated by the conduit and, as a
result, the forces urging the particles against the screen
18' are more intense in the centre than at the
longitudinal extremities. Consequently, the final layer
will be thicker at the centre than at the ends. This
feature enables to produce liquid absorbent articles that
are thicker at selected areas where high absorbency is
required. In a variant, as shown in Figure 8a, a non-
uniform rate of material deposition is achieved by
connecting selected zones of the forming member where a
thicker deposit is required to a source of high vacuum,
while the remaining of the forming member is subjected to
lower vacuum. In the drawing, the central portion of the
forming member 18 " is coupled to a first aspiration
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CA 02159784 2000-09-11
conduit 19 that i_s connected to a source of high vacuum
(not shown :W the drawings). On the other hand, the
peripheral portion of the forming member 18" is
subjected to a lower pressure deferential established by
a second conduit 21 leading to a source of lower vacuum
(not shown in the drawings). It will be apparent that
the resu.ltinc~ la~~er of sphagnum moss will be thicker at
the center than at the sides.
Advantageously, the present invention can also be
used for manufacturing single layered or multi-layered
tampon pledgets, a:~ shown in Figures 9 to 18. Figure 9
illustrates a f:~rming member 28 on which a tampon
pledget is build-up. The forming member 28 is a hollow,
mandrel-shape stz~u~~ture having a foraminous surface 30
that covers a portion of its length. The internal
cavity of the forming member 28 is coupled to the source
of vacuum (not ~~hown in the drawings) to create the
pressure diff'eren.tial across the foraminous surface 30.
In Figure 10, the forming member 28 is shown partially
immersed in a liquid suspension of sphagnum moss
particles to force the absorbent core 32 of the tampon
pledget. The particles, when agglomerating, thereby
also foaming interstices for admitting liquid. As
mentioned ea:=liei:~, the residence time of the forming
member 28 in the liquid suspension and the intensity of
the aspiration a:Llow the operator to control the
thickness of the core 32 for, in turn, controlling its
absorption capacity.
Docket No. CAN-65
Once the desired core thickness has been reached, the
forming member 28 is transferred to a vessel, as shown in
Figure 12, containing long fibers suspended in water in
order to form on the sphagnum moss absorbent core a
protective jacket 34 to prevent fragmentation and loss of
structural integrity of the absorbent core 32 in use. In
a preferred embodiment, the liquid suspension contains
fibers of a length in the range from about 1 cm to about
3 cm and has a consistency in the range from about 0.1% to
about 5.0% by weight of solids, more preferably of about
2.0%. The fibers are preferably selected from the group
consisting of polyester, rayon, cotton and cellulose,
among many others.
Since the jacket 34 is directly moulded by successive
fiber deposition on the absorbent core 32, it acquires a
three-dimensional shape complementary to the configuration
of the absorbent core 32. As a result, the absorbent core
32 is enclosed within a fibrous network that facilitates
the insertion of the tampon pledget in the vaginal orifice
of the user, and also prevents the sphagnum moss particles
from loosening and falling off the tampon pledget,
especially when the absorbent structure is saturated with
liquid.
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Docket No. CAN-65
When subjected to a liquid discharge, the protective
jacket 34 behaves as a transit region that initially
captures the liquid before passing it to the absorbent
core where it is permanently entrapped. As a consequence,
the porosity of the protective jacket 34, and the nature
of the bond absorbent core/jacket are important factors
that influence the liquid-absorptive properties of the
tampon pledget structure. Most preferably, the protective
jacket 34 should have a comparatively high inter-fiber
void volume to provide a high liquid acceptance rate.
Fibrous material selected from the group of polyester,
rayon, cotton and cellulose yields a porous network having
the desired properties in this regard. In addition, since
the jacket 34 is build directly over the absorbent core
32, these components are structurally united in an
intimate fluid communicative relationship, that enables a
fast fluid transfer from the jacket toward the core.
In a variant, a withdrawal string 36 may be
integrated to the tampon pledget structure, as shown in
Figure 12. This is achieved by positioning alongside the
absorbent core 32, prior the deposition of the protective
jacket 34, the withdrawal string 36. The string should be
long enough to sufficiently extend beyond the upper
boundary of the foraminous surface 30 so as to enable the
user.to conveniently grasp it when the tampon pledget is
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Docket Ho. CAH-65
inserted in the vaginal orifice. It will become apparent
that during the deposition of the fibrous material the
withdrawal string 36 becomes gradually integrated to the
protective jacket 34. To prevent the string from being
accidentally extracted from the fibrous mass forming the
protective jacket 34, one or more anchoring projections,
such as knots, may be provided on the string.
Alternatively, the string may be formed into a loop, as
shown in Figure 12a.
After the protective jacket 34 is formed on the
absorbent core 32, the mandrel-shaped forming member 28 is
withdrawn from the liquid suspension and it is then
subjected to the desired post-formation treatments such as
drying, binder deposition and hydrophilicity enhancement,
among others. Finally, the tampon pledget is extracted
from the mandrel-shaped forming member 28 by effecting a
pressure differential reversal, as discussed in connection
with the previous embodiment. It will be noted that once
the tampon pledget has been striped from the mandrel-
shaped forming member 28, a cavity remains in the
absorbent core 32. This cavity should be small, otherwise
the structural integrity of the tampon pledget may be
compromised. For this reason, a forming member having the
smallest possible diameter should be used.
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Docket No. CAN-65
The method in accordance with the invention can also
be used for manufacturing solid-core tampon pledgets, as
shown in Figures 13 to 17. The forming member 38, best
illustrated in Figure 13, is in the form of a blind sleeve
having a solid outer wall 40 and an internal cylindrical
cavity 42. The cavity 42 is delimited by a foraminous
surface, such as fine wire mesh which is radially spaced
apart from the outer wall 40 to define a surrounding fluid
passage that merges with a conduit 46 that is connected to
the source of vacuum (not shown in the drawings).
The tampon pledget formation process consists of
first aspirating fibers suspended in liquid to partially
build-up an outer protective jacket 48, as shown in
Figures 14 and 15. The forming member 38 is then removed
from the liquid suspension and a withdrawal string 50
inserted in the cavity of the protective jacket 48.
Preferably, the string is in the form of a loop which is
temporarily retained to the fibrous material of the
protective jacket 48 by a small amount of positioning
adhesive so, the free ends of the loop are left hanging
from the forming member. Next, the assembly is immersed
in the liquid suspension of sphagnum moss to form the
absorbent core 52 of the tampon pledget, as shown in
Figure 16. Contrary to the previous embodiment, the core
is solid and free of cavities. Finally, the assembly is
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Docket No. CAN-65
immersed in a liquid suspension of long fibers (the same
fibers used for making the protective jacket 48) , as shown
in Figure 17 to form a layer 54 that fully closes the
protective jacket around the absorbent core 52 for a
complete encapsulation. For ease of use, the free ends of
the withdrawal string structure can be tied into a knot,
as depicted in Figure 18.
The above description of this invention should not be
interpreted in any limiting manner since many variations
and refinements are possible without departing from the
spirit of the invention. The scope of the invention is
defined in the annexed claims and their equivalents.
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