Note: Descriptions are shown in the official language in which they were submitted.
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A DRY LAID STRUCTURE COMPRISING PARTICULATE MATERIAL
The present invention relates to dry laid fibrous structures
preferably intended for absorbing aqueous fluids and/or for providing
odour control. The structures comprise a dry laid fibrous web and a
particulate material distributed in the web and are bonded by a
thermoplastic polymeric material distributed therein; they are particularly
suitable for use in disposable absorbent articles.
Fibrous structures, particularly fibrous structures for absorbing
liquids are manufactured for many uses, for example they are
incorporated into absorbent articles such as disposable diapers,
incontinent pads and catamenial napkins as fluid absorption or fluid
transmission and/or diffusion elements, for example as absorbent cores
that are intended to absorb and retain body fluids. Fibrous structures,
and more specifically fibrous structures used in absorbent articles as fluid
absorption or fluid transmission andlor diffusion elements, usually
comprise a multiplicity of components so as to improve their specific
performances; for example, absorbent structures that comprise fibres
and a particulate material, such as an absorbent geNing material in
particle form, are known in the art. Further components can be also
included to provide the structure with added benefits.
Dry laying and, more specifically, air laying processes are widely
used to produce webs from dry fibres) which can in turn be used e.g. as
structures for absorbing fluids. Particularly, dry laying refers to the
formation of carded webs, i.e., webs in which the fibres are oriented
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(carded) in a given direction, whereas the air laying process refers to the
formation of webs with a completely random fibre orientation; the
properties of such air laid webs are therefore somewhat isotropic. The
fibrous webs produced by dry laying processes are soft, flexible and
porous, and are particularly suitable for use as liquid absorbent structures
in absorbent articles, such as disposable diapers, sanitary napkins,
incontinent pads, and wipes.
Methods for incorporating further components e.g. in particle form
in a dry laid fibrous web are also known in the art; particularly, in US
Patent No. 4,765,780 a process and apparatus is described for forming
air laid fibrous webs having a multiplicity of components, such as a two
layer absorbent core with one layer having an absorbent gelling material
in particle form homogeneously blended therein, the other layer being
substantially free of absorbent gelling material particles. Similar
techniques can be used for incorporating in a dry laid fibrous web
different types of components, e.g. an odour control means in particle
form in order to provide the absorbent structure constituted by the dry
laid fibrous web with the further benefit of odour control.
The dry laid manufacturing process generally comprises a web
formation and layering step and a web bonding and stabilizing step; in
dry laying processes in fact the fibres, that can be of any type, e.g.
cellulosic, synthetic, or any combination thereof, are formed or
condensed into a web. Further components that are not in fibre form
can also be incorporated in the fibrous web, e.g. a particulate material.
The resulting web lacks integrity after formation, and must therefore be
stabilized. Different techniques for bonding and stabilizing a dry formed
web are known in the art, i.e. mechanical, thermal and chemical bonding
processes. Bonding a web structure by means of a chemical is one of
the most common methods of bonding in the nonwoven industry, and
consists in the application of a chemical binder to the web and in the
curing of the binder. The most widely used chemical is latex, since it is
cheap, versatile, easy to apply, and very effective as a binder. Several
methods are known to apply the latex binder to the fibrous web, while
spray bonding and print bonding are particularly preferred for fibrous
webs intended to be used in absorbent articles.
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European application EP=A-592 001 describes a nonwoven fabric
f bonded by means of e.g. a latex binder, comprising "particles" or
"globules" of a thermoplastic composition arranged in a discontinuous
pattern onto at least one of its surfaces, and with an odour control
material in powder form affixed to the thermoplastic "particles" or
"globules" on the surface of the nonwoven fabric. All the odour control
material is affixed to the thermoplastic "particles" in this case and is
present only onto the surface of the nonwoven structure.
In European application EP-A-463 716 a dry laid absorbent
structure is described that comprises a fibrous web with an absorbent
gelling material therein and is stabilized by application of a latex coating
to at least a surface of the web.
Thermal bonding process is also widely used in order to bond a
dry laid web; such a web comprises fusible fibres such as bicomponent
fibres as the sole component fibre, or as a mixture with non fusible
fibres, e.g. natural fibres. They are successively caused to melt by heat
treatment so as to bond the web structure.
Thin) layered absorbent structures described in International
applications WO 94/01069 and WO 95/17868 comprise typically two
outer independently formed fibrous layers, typically air laid . cellulose
tissue layers, and an intemediate layer comprising particles of absorbent
gelling material and particles of thermoplastic polymeric material, the two
fibrous layers being bonded by the melting of the thermoplastic particles.
The fibrous layers are themselves already formed and bonded when the
layered structure is manufactured, and therefore constitute two distinct
and separate layers joined to form the layered structure, with the
particulate material distributed only between the fibrous layers.
Both chemical and thermal bonding processes, and their possible
combination as well, suffer of certain disadvantages if applied to dry laid
' structures comprising a particulate material therein, especially when the
particulate material incorporated in the dry laid structure is concentrated
preferably intermediate the thickness of the web, therefore forming a
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region of the web in which the fibres constitute a lower percentage. In
such cases a latex composition can hardly penetrate the thickness of the
web in order to reach the particles, unless it is used in such an amount
that it will impair the performances of the entire structure and, possibly,
will cause negative interactions with the particulate material. On the
other hand the use of meltable fibres, e.g. bicomponent fibres, with
subsequent thermal treatment does not solve the problem since fibres
may not be distributed among the particles in such an amount to perform
an effective bonding action; moreover, owing to the different nature of
fibres as compared to particulate material, a homogeneous distribution of
fibres among particulate material is rather difficult to achieve when the
particulate material constitute the higher percentage of the mixture.
Heat meltable fibres such as bicomponent fibres are also rather
expensive.
It is therefore an object of the present invention to provide a dry
laid fibrous structure, preferably an air laid fibrous structure which
comprises a dry laid fibrous web and a particulate material and has good
integrity combined with softness. The dry laid fibrous structure of the
present invention can be used as absorbent structure for absorbing
fluids, preferably with the further capability of controlling odours which
are related to the absorbed fluids.
It has surprisingly been found that a thermoplastic polymeric
material in finely divided form, preferably in particle or powder form, can
be effectively distributed among the particulate materials and at least
partially among the fibres of the dry laid web. The subsequent thermal
treatment melts the thermoplastic polymeric material and therefore
creates a framework of discrete bonding points within the web, i.e.
among the fibres and the particulate material where the thermoplastic
polymeric material in finely divided form has been distributed, without
substantially modifying the effectiveness of the particulate material itself
owing to the very small dimension of the thermoptastic particles. The
use of thermoplastic polymeric material in finely divided form can be also
combined with a traditional latex bonding, e.g. the thermoplastic powder
performs the bonding preferably of the inner portion of the dry laid web,
while the application of a reduced amount of latex stabilizes the outer
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surfaces of the dry laid web. Alternatively, the dry laid web can be
entirely bonded by means of thermoplastic polymeric material in finely
divided form dispersed uniformly within the whole web and then caused
to melt by thermal treatment.
' SUMMARY OF THE INVFNTinN
The present invention relates to a dry laid fibrous structure; the
dry laid fibrous structure comprises a dry laid fibrous web having a first
surface and a second surface aligned approximately opposite to the first
surface and a particulate material distributed in the web. The dry laid
fibrous structure further comprises a thermoplastic polymeric material in
finely divided form distributed therein in order to bond the particulate
material to the fibres of the dry laid fibrous web.
While the specification concludes with claims particularly pointing
out and distinctly claiming the present invention, it is believed that the
present invention will be better understood from the following
description in conjunction with the following drawings:
FIG. 1 is a schematic, fragmentary side elevational view of an
apparatus for making a fibrous structure according to the present
invention;
F1G. 2 is an enlarged, cross-sectional view of a fibrous structure
according to the present invention;
FIG. 3 is a schematic, fragmentary side elevational view of an
apparatus for making an alternate embodiment of a fibrous structure
according to the present invention;
FIG. 4 is an enlarged, cross-sectional view of an alternate
embodiment of a fibrous structure according to the present invention.
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The present inventionrelates to a dry laid fibrous structure
preferably intended for absorbing aqueous fluids and/or for providing
odour control. The structure is constituted by a dry laid fibrous web
comprising a particulate material and is bonded by a thermoplastic
polymeric material distributed therein in finely divided form. In a
preferred embodiment, the structures of the present invention are
incorporated into absorbent articles, preferably as absorbent structures
that are intended to absorb and retain the various body fluids.
Absorbent articles, and more specifically disposable absorbent articles,
refer to articles such as sanitary napkins, disposable diapers, incontinent
pads, that are worn by a user adjacent to the body and are intended to
absorb and contain the various body fluids that are discharged from the
body (e.g., vaginal discharges, menses, sweat, and/or urine and which
is intended to be discarded after a single use.
The term "use", as used herein, refers to the period of time that
starts when the absorbent article is actually put in contact with the
anatomy of the user.
In a preferred embodiment of the present invention the dry laid
fibrous structures according to the present invention can constitute
integrally the absorbent core of a disposable absorbent article, or they
can be comprised therein as part of the absorbent core, or in any case
they can constitute an element of a disposable absorbent article, e.g.
intended for absorption of body fluids, or for odour control, or for both.
Disposable absorbent articles, such as for example sanitary
napkins, pantiliners, incontinent pads, or diapers, typically comprise a
fluid pervious topsheet, a fluid impervious backsheet, that can optionally
be water vapour and/or gas pervious, and an absorbent core comprised
therebetween.
The dry laid fibrous structures of the present invention comprise a
particulate material distributed in the web that is typically capable of
performing absorption of aqueous fluids and/or control of the odours,
e.g. those odours associated with the absorbed fluids. Preferably the
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particulate material comprises an absorbent gelling material and an odour
control means, both in particle form.
The fibrous structures of the present invention can be made using
conventional equipment designed for dry laying processes, and although
the invention is described hereinbelow with particular reference to air laid
structures, it should be understood that other dry laying processes, e.g.
carding, are also applicable.
The invention will be described as an air laid fibrous structure
which is capable of providing absorption of aqueous fluids, particularly
body fluids, and control of the odours associated with the absorbed
fluids) being intended to be incorporated as absorbent structure in a
disposable absorbent article, e.g. a sanitary napkin.
FIG. 1 is a simplified schematic illustration of a preferred
embodiment for the manufacture of the fibrous structure of the present
invention. In accordance with this embodiment, the air forming system,
indicated generally by the numeral 10, includes a distributor unit 12
disposed transversely above a continuous forming screen 14 mounted on
rollers 16 and driven by a suitable motor (not shown), and vacuum
means or suction box 18 is positioned beneath the screen. In a
conventional air forming system, upstream of the distributor unit is a
defibrator or feeder (not shown), such as a hammermill or Rando-Feeder,
where bales, taps or the like are defiberized, and further the fibres may
be cleaned and/or blended if necessary or desired depending largely on
the type of fibres used, the blend of fibres used, and the end product
sought. For example, wood pulp fibres can be blended with synthetic
fibres and applied as a blend by a single distributor, or different fibres
can be each conveyed by a different distributor to the screen to form
separate plies or layers.
The porous forming screen 14 is essentially coextensive with the
distributors, and the suction box 18 beneath the screen draws the air
stream downwardly and conveys the fibres to the surface of the screen
thereby forming plies or a loose web 22. At this stage in the process,
the web exhibits little integrity, and the vacuum means retains the loose,
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fibrous web on the screen. The web 22 has a first surface 6 that faces
the distributor and a second surface 8, opposite to surface 6, that faces
the forming screen 14.
It should be understood that the system may be modified to
control the composition and thickness of the end product. For example,
the distributor unit can comprise a plurality of individual distributors, and
although FIG. 1 shows schematically two distributors at 12A and 12B,
this number of distributors and particular arrangement can be altered or
varied depending on such factors as machine speed, capacity, type of
fibres, and end product desired.
Web 22 formed on screen 14 has incorporated therein a
particulate material. In a preferred embodiment the particulate material
comprises a mixture of an absorbent gelling material and of an odour
control means, both in particle or powder form. In a preferred
embodiment as shown in FIG. 1, a dosing unit or feed hopper 24,
containing the particulate material is positioned in the middle of the
distributor unit, i.e. between distributors 12A and 12B. In the
embodiment of FIG. 1 the dosing unit 24 receives the different
particulate materials from supply containers 25 and 26, which
respectively contain the absorbent gelling material and the odour control
means in particle form. The dosing unit 24 preferably provides the
particulate material in a homogeneous mixture.
A thermoplastic polymeric material in finely divided form,
preferably in powder form, is also added to the fibrous web 22; in a
preferred embodiment the thermoplastic polymeric material in powder
form is supplied to the dosing unit 24 from the container 27, and is
homogeneously mixed with the particulate material coming from the
containers 25 and 26.
In this manner, the particulate material comprising the
thermoplastic polymeric material in powder form are deposited between
plies of fibres laid by each distributor. That is, the particulate material
and the thermoplastic polymeric material are discharged from hopper 24
onto the moving layer of fibres laid down by distributor 12A, and the ply
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of fibres laid down by distributor 128 is laid over the particulate material.
It should be understood, however, that the plies are relatively porous,
and therefore the particulate material and the thermoplastic polymeric
material tend to distribute somewhat within adjacent plies. Therefore
the resulting fibrous web 22 comprises the particulate material and the
thermoplastic polymeric material concentrated intermediate the thickness
of the web, forming a region of the web 22 in which the fibres
constitute a lower percentage as compared to the particulate material
and the thermoplastic polymeric material. Where desired, the particulate
material may be blended with the fibres in one or more distributors, such
as in distributor 12A or 12B, thereby forming a web with particulate
material intermixed with one or more fibrous plies of the web. It is
however preferred that the particulate material with the thermoplastic
polymeric material is distributed within the thickness of the web 22,
intermediate the first and second surfaces 6, 8.
The web 22 condensed on forming wire 14 has very little integrity
and requires stabilization. In the embodiment shown in FIG. 1 the web is
subjected to a first stabilization step by means of thermal treatment at a
bonding station 28. The particulate material and the fibres of the web
22 that are comprised among the particulate material and, at least
partially, in the two plies, are bonded together by the application of heat
and, optionally, of moderate pressure to melt the thermoplastic polymeric
material in powder form mixed with the particulate material constituted
by the absorbent gelling material and by the odour control means.
The bond among the particulate material and the fibres is
generated by the melting of the individual particles of thermoplastic
polymeric material in powder form; as it melts, the thermoplastic
polymeric material forms "bridges" connecting directly the particulate
material and the fibres.
The overall surface area of the bond points represents a small
fraction of the surface area of the particulate material and of the fibres
' that are involved in the bonding, the characteristics of which thus remain
almost unchanged. Since the thermoplastic polymeric material in the
preferred powder form can be homogeneously distributed among the
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particulate material and the fibres comprised therein it can therefore
provide the web 22 with an effective bonding within the portion
interested by the distribution of the thermoplastic polymeric material
itself: in the embodiment of the present invention achieved by the
apparatus of FiG. 1 this corresponds to the region of the web 22 mainly
constituted by the particulate material with a lesser percentage of fibres,
intermediate the first and second surfaces 6 and 8.
The absorbent gelling material, which is preferably distributed in
the form of particles, may be made of inorganic or organic substances
such as cross-linked polymers, all known from the prior art.
The odour control means can be any suitable odour control agent
known in the art, or any mixture thereof, for example it can be
constituted by particles of zeolite and silica.
The average dimensions of the particulate material, given as a
weighted average of the smallest dimensions of the individual particles,
can be between 50 microns and 1500 microns, preferably between 100
microns and 800 microns.
The thermoplastic polymeric material in finely divided form, e.g. in
form of powder has the purpose of bonding the particulate material and,
at least partially, the fibres of the dry laid absorbent structure together
by melting and forming discrete, spaced-apart bond points among the
particles and the fibres. The thermoplastic polymeric material can also
be used in other finely divided forms, e.g. in form of fibrils.
As explained above, the bridges which form these bond points can
involve the particulate material and the fibres of the web 22.
The quantity of thermoplastic polymeric material in finely divided
form incorporated in the web 22 can be between 5 g/m2 and 180 g/m2.
The thermoplastic polymeric material in finely divided form can
preferably be melted at such a temperature that it does not interfere with
the characteristics of the other components of the absorbent structure,
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i.e. the fibres and the particulate material, which comprises the
absorbent gelling material and the odour control means in the preferred
embodiment. Therefore, the thermoplastic polymeric material must have
fluidity characteristics such as to enable the necessary bonds to be
formed rapidly.
These preferred characteristics can be achieved by a thermoplastic
polymeric material in finely divided form having a melt flow index
(M.F.I.), evaluated by the ASTM method D 1238-85 under conditions
190/2.16, of at least 25 g/10 min, preferably at feast 40 g/10 min, and
even more preferably at least 60 g/10 min.
If the fibres of the dry formed fibrous structure are short cellulose
fibres, it is preferable to use a thermoplastic polymeric material
composed of powder of high-density polyethylene with maximum
dimensions of the particles of about 400 microns, characterized by a
melt flow index of about 50 g/10 min, in a quantity between 12 g/m2
and 90 g/m2
According to the embodiment of the present invention illustrated
in FIG. 1 the web 22 can be further bonded on one, or preferably both
surfaces 6 and 8 by means of the application of a latex composition.
The web 22 can be first passed between compression rollers (not
shown), which may be heated, to densify the web, but this step is
optional. This densification step can enhance the penetration of the
latex into the web, and the degree or percent of densification can vary
depending on such factors as the amount of odour control particles,
basis weight of the web, the desired degree of penetration of the latex
into the web, and the end product sought.
After the bonding station 28 and the (optional) compression rollers
the web is transported to a suitable dispensing means 30, such as a
spray nozzle, doctor blade, roller applicator, or the like, where a latex
binder is applied to the first surface 6 of the web 22. A vacuum applied
by a suction box 7 9 positioned beneath the dispensing means and the
screen 14 helps to draw the latex into the web. The dispensing means
or applicator is essentially coextensive with the width of the web, and
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preferably a substantially uniform coating is applied to the web surface.
However, the latex may be applied as a non uniform, random or pattern
coating, and because the latex is water-based, it will diffuse throughout
the web and function as a binder when cured.
The latex when cured imparts integrity to the web, and therefore
some penetration of the latex is required. The extent or degree of
penetration of the latex into the web is controlled by controlling the
amount of latex applied and by controlling the vacuum applied to the
web in that the vacuum helps to draw the latex into the web. Such
extent or degree of penetration can be limited to the surface of the web
22, since the portion of the web 22 comprising the particulate material
which is intermediate the surfaces 6 and 8 is already bonded by the
thermoplastic polymeric material, and therefore any possible negative
interference between the latex composition and the particulate material
is avoided. The amount of the latex composition is also kept to such an
extent that it does not impair the absorbency and softness
characteristics of the fibrous web 22.
The latex is usually applied as an aqueous emulsion, and can be a
thermosetting plastic. In order to activate the latex, the latex emulsion
contains a suitable curing agent or cross-linking agent, and after the web
is coated, the latex is cured to effect cross-linking. Most typically,
curing is accomplished by passing the coated web through a hot air oven
or through an air drier 32, and the temperature typically ranges from
about 100 °C to 260 °C, but this depends upon the specific type
of
latex resin used, upon the curing agent or cross-linking agent, upon the
amount of latex, the thickness of the web, the degree of vacuum, and
the machine speed.
It is desirable to coat the second surface 8 of the web 22 with
latex as well, and this is readily accomplished by the dispensing means
36 as the web 22 is conveyed on the second screen 34 operating about
pulleys 191, 192, 193, and 194. The second dispensing means 36
includes a suction box 37. This second latex coating is likewise cured
by passing the web through a second oven 38 within about the same
temperature range.
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The resulting absorbent -structure 40 exiting from the last oven
now exhibits sufficient integrity and can be cut, rolled, packaged, etc.
The absorbent structure 40 made in accordance with the
foregoing process is illustrated in FIG. 2. The absorbent structure 40
comprises randomly distributed fibres 46, such as wood pulp fibres, and
particulate material 42 is distributed in the absorbent structure. The
thermoplastic polymeric material 48 in powder form is distributed mainly
among the particulate material 42 and performs the bonding of the
particulate material and of at least part of the fibres of the absorbent
structure 40, i.e. those fibres that enter in contact with the
thermoplastic polymeric material. It will be observed that the particulate
material is more concentrated in the middle zone of the absorbent
structure, but some particles migrate to other sections of the absorbent
structure. Both first and second surfaces 6 and 8 of the absorbent web
22 bear a latex coating 50, indicated in the drawing by a shading, which
has penetrated or impregnated the absorbent structure to some degree
and has partially coated some of the fibres. As explained above, the
penetration is controlled so as not to impair the characteristics of the
particulate material.
The fibrous structure of the present invention is soft yet strong
and absorbent, exhibiting a relatively high tensile strength. It can be
desirable for preferred absorbent fibrous structures of this type to have
relatively low bulk, because a more dense absorbent structure, when
compared to similar structures containing no latex and of about equal
absorptive capacity but of higher bulk, can be thinner yet highly
absorbent and consequently less bulky. A reduction in bulk, which
means a reduction in volume the absorbent fibrous structure is
occupying, without sacrificing significantly other desired properties is
important from the standpoint of manufacturing, storage and packaging.
' Hence, for products of the present invention the basis weight can range
from about 50 g/m2 to 600 g/m2, and preferably from about 75 g/m2 to
400 g/m2, and more preferably from about 250 g/m2 to 350 g/m2.
There can be manufacturing constraints in producing an absorbent
structure having a basis weight lower than about 50 g/m2 in that such
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an absorbent structure may lack desired strength. When the basis
weight exceeds the upper limit, the product may be too stiff and
therefore not useful for most applications.
Any of a variety of fibres, including a blend or admixture, can be
used in the fibrous structure of this invention. The fibres may be
cellulosic, modified cellufosic, or synthetic, and include such fibres as
wood pulp, rayon, cotton, cellulose acetate, polyester, polyethylene,
polypropylene, nylon, and the like. A fibrous structure comprising
cellulosic fibres such as wood pulp fibres is particularly useful as an
absorbent structure in such products as sanitary napkins, disposable
diapers or wipes because the cellulose is liquid absorbent and therefore
enhances the overall absorbency of the structure. Products of this type,
i.e., fibrous structures that are also absorbent, also advantageously use a
blend of cellulosic and synthetic fibres, typically comprising about 65
to 95% by weight of cellulosic fibres, and more preferably up to about
20% by weight of the synthetic fibres. The synthetic fibres, which can
be provided in any length including staple length, can improve the
strength of the structure. They can also be treated to make them
hydrophilic, in order not to decrease the absorbent capacity of the
preferred absorbent fibrous structure.
Preferred fibrous structures described so far comprise hydrophilic
fibres that are substantially absorbent towards aqueous fluids, said
structures being useful as absorbent structures in disposable absorbent
articles. Dry laid fibrous structures according to the present invention
can also comprise hydrophobic fibres only, e.g. synthetic fibres. Such
structures can comprise for example as particulate material an odour
control means only, being therefore capable of odour control without
absorbing and retaining liquid. Such type of structures can be comprised
in disposable absorbent articles as a liquid receiving and transmitting
layer, e.g. as an acquisition layer comprised between the topsheet and
the absorbent core, which is capable of acquiring body fluid quickly and
of transmitting it to the absorbent core, performing at the same time an
odour control action towards the fluid. A structure according to the
present invention comprising hydrophobic synthetic fibres only can also
be useful in different applications, e.g. as a filter medium.
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Thus, the type of fibres' and the particular blend can be varied
depending upon the end product. In addition to the foregoing uses, the
absorbent structures of this invention can be suitably used for
incontinent pads, diaper core, diaper insert, and for surgical and wound
bandages, providing absorbent capacity and/or odour control.
The absorbent gelling material, which preferably constitutes at
least part of the particulate material comprised in the dry laid absorbent
structure of the present invention, may comprise anyone of the well
known materials (sometimes referred to as "super-sorbers") that are
becoming broadly used in absorbent articles. AGM's are materials which
have fluid-absorbing properties. Such materials form hydrogels on
contact with water (e.g., with urine, blood, and the like). One highly
preferred type of hydrogel-forming, absorbent gelling material is based on
polyacids, especially polyacrylic acid. Hydrogel-forming polymeric
materials of this type are those which, upon contact with fluids (i.e.,
liquids) such as water or body fluids, imbibe such fluids and thereby
form hydrogels. These preferred absorbent gelling materials will
generally comprise substantially water-insoluble, slightly cross-linked,
partially neutralized, hydrogel-forming polymer materials prepared from
poiymerizable, unsaturated, acid-containing monomers. In such materials,
the polymeric component formed from unsaturated, acid-containing
monomers may comprise the entire gelling agent or may be grafted onto
other types of polymer moieties such as starch or cellulose. Acrylic acid
grafted starch materials are of this latter type. Thus, the preferred
absorbent gelling materials include hydrolyzed acrylonitrile grafted starch,
acrylic acid grafted starch, polyacryiates, malefic anhydride-based
copolymers and combinations thereof. Especially preferred absorbent
gelling materials are the polyacrylates and acrylic acid grafted starch.
The odour control means preferably included in the fibrous
structure of the present invention can comprise a wide variety of odour
control agents, in order to control unpleasant odours, e.g. those odours
associated with the absorbed fluids when the fibrous structure is a fluid
absorbent structure.
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In their preferred use as absorbent cores in disposable absorbent
articles the absorbent structure ~ of the present invention are intended to
absorb body fluids.
Various body fluids contain malodorous chemical compounds
including acyclic and cyclic amines, aldehydes, fatty acids, and sulfur
containing compounds such as sulfides. For example vaginal discharges
and used sanitary napkins can contain many malodorous chemical
compounds, for example, trimethylamine, pyridine, furaldehyde,
isovaleric acid, and methyl mercaptan. The particular malodorous
compounds which will be absorbed by various absorbent articles will
vary depending upon the person who is wearing the absorbent article
and the type of body fluid absorbed, i.e., urine, menstrual fluid, vaginal
discharges, perspiration, milk, etc. For feminine pads, such as sanitary
napkins or pantiliners, the length of time the article is worn, the quantity
of fluid which is absorbed and the exposure of the pad to different body
fluids will determine which odours can be emitted by the absorbent
article.
Any suitable odour-control agent known in the art can be
incorporated in the dry laid fibrous structures of the present invention, to
provide the structure with the benefit of odour control, e.g. towards
those odours associated with absorbed body fluids when the dry laid
fibrous structure is an absorbent structure preferably incorporated into
disposable absorbent articles.
Suitable odour-control agents that can be employed in the practice
of the present invention can be for example water-soluble antibacterial
compounds. Such compounds include, for example, halogenated
phenylene compounds (U.S. Patent 3,093,546), periodic acids (U.S.
Patent 3,804,0941, various copper compounds, especially copper
acetate (U.S. Patent 4,385,632), various Quaternary ammonium salts,
which are well known for their antibacterial properties, e.g. cetyl
pyridinium chloride, and the like. Alternatively, antibacterial compounds
can be used conjointly with various particulate materials which, in use
and in the presence of moisture, release the antibacterial agent. Zeolite
materials, such as zeolites which are bactericidal by virtue of having
absorbed therein and thereon various bactericidal cations such as copper,
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silver and zinc, can be advantageously used in the practice of this
invention (U.S. Patent 4,525;4101. In a preferred mode, the odour
control agent is a water-insoluble particulate odour absorbing material
such as chlorophyll particles, activated carbon granules, charcoal, ion
exchange resin (Japanese 87019865), activated alumina, and absorbent
zeolite materials, including the well known "molecular sieve" zeolites of
the type A and X and the zeolite materials marketed under the trade
name ABSCENTS by the Union Carbide Corporation and UOP, and which
are typically available as a white powder in the 3-5 micron particle size
range.
In a known mode, the odour-control agent can be a
water-insoluble particulate odour-absorbing material such as chlorophyll
particles) activated carbon granules, charcoal, ion exchange resin
(Japanese 87019865), activated alumina, and absorbent zeolite
materials, including the well known "molecular sieve" zeolites of the type
A and X and the zeolite materials marketed under the trade name
ABSCENTS by the Union Carbide Corporation and UOP, and which are
typically available as a white powder in the 3-5 micron particle size
range.
The odour-control agents used in the present invention can also
comprise other compounds such as cyclodextrin, chelating agents,
parabens, chitin, pH buffered materials, silica gel, clays, diatomaceous
earth, polystyrene derivatives, starches, and the like. For example,
chelating agents as those described in European Applications
EP 96109178.2 and EP 96109179.0, both applications filed on 7 June
1996, are particularly preferred. Some partially neutralized hydrogel
forming absorbent gelling materials, such as polyacrylate gelling material
and acrylate grafted starch gelling material can be also used, preferably
in combination with other odour-control agents.
Further odour control agents can comprise acidic compounds such
as ascorbic acid, stearic acid, boric acid, mafeic acid polymers, malonic
acid, malefic acid, polyacrylic acid and monopotassium phosphate, or
basic compounds such as inorganic salts of carbonates, bicarbonate,
phosphate, biphosphate, sulfate, bisulfate, borate, and mixtures thereof,
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as those described in US 5037412, or as the combination of boric acid
and sodium tetraborate described in International application
WO 94/25077.
It is to be understood that the odour-control means that can be
preferably employed in the practice of the present invention is not,
simply, the odour-control agent, per se, added to the fibrous structure.
Rather, the odour-control means comprises any combination of
odour-control agents and, optionally, of other materials such as binders.
Agglomerates of different odour control agents, e.g. with a binder, can
therefore also be used, such as for example an agglomerate of zeolite
and silica in particle form, as that described in European application
EP 96109175.8, filed on 7 June 1996. The odour-control agent, on the
other hand, is the specific odour-control compound.
Preferably, odour control agents are used in the present invention
in particulate form. Particularly preferred are odour control means
comprising zeolite, silica, preferably in form of silica gel, absorbent
gelling material, and combinations thereof, such as the odour control
means described in International application WO 95/26207, and in
European applications EP 96109177.4, EP 96109173.3,
EP 96109174.1, EP 96109176.6.
For example, a preferred odour control means ca.n be a
combination of particles of silica gel, zeolite and absorbent gelling
material. The weight ratio of absorbent gelling material to silica to
zeolite is preferably in the range of from 1:5:1 to 1:1:5, preferably from
1:3:1 to 1:1:3, most preferably from 1:1:1 to 1:1.5:1.5.
It has been found that the odour control material can be
incorporated into the fibrous structures according to the present
invention in an amount that ranges from 20 g/m2 to 400 g/m2,
preferably from 100 g/m2 to 300 g/m2, more preferably from 150 g/m2
to 250 g/m2, with reference to the total surface area of the fibrous
structure. Preferably the fibrous structures of the present invention can
comprise from 20% to 80% by weight of the odour control means. The
weight of the odour control means that can be actually used in various
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fibrous structures intended for different uses can be readily determined
by the skilled person bearing in- mind the size and the type of the fibrous
structure, and its intended use.
The latex is applied as an aqueous emulsion or dispersion, which
typically contains about 45% to 65% solids, and these materials are
readily available from several manufacturers. Because the latex
emulsions are water miscible, they may be further diluted, if desired,
before being applied to the web. Also, these latex compositions are
thermosetting, and in order to effect cross-linking, they contain a small
amount of a suitable cross-linking agent which are well known chemical
agents for this purpose, such as N-methylolacrylamide. Any type of
latex known in the art which is suitable for fibrous structures of the
present invention can be used, provided that it preferably does not
generate detectable odours, especially after curing, since this could be
unpleasant for a user and, moreover, could exhaust at least partially a
preferred odour control capacity of the fibrous structure well before its
intended use. Latices available are classified by chemical family, and
those particularly useful include vinyl acetate and acrylic ester
copolymers, ethylene vinyl acetate copolymers, styrene butadiene
carboxylate copolymers, and polyacrylonitriles, and sold, for example,
under the trade names of Airbond, Airflex and Vinac of Air Products,
Inc., Hycar and Geon of Goodrich Chemical Co., and Fulatex of H. B.
Fuller Company. The amount of latex used in the absorbent structure
cannot be so high as to substantially impair or obscure the effective
odour control capacity of the odour control means, and also the
absorbent properties of the hydrophilic fibres, or as to impart a stiffness
to the structure as to render it impractical. It has been found that the
latex may range from about 5% to 30% by weight of the structure, and
preferably from about 10% to 20% by weight.
Fibrous structures made according to the present invention exhibit
a good integrity due to the binding performed by the thermoplastic
polymeric material comprised within the structure in finely divided form
~ and, optionally, to the latex coating, and yet have preferably either a
remarkable absorbent capacity or an odour control capability, or more
preferably both of them, since the particulate material comprised in the
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fibrous web is affected by the binding means, i.e. by the thermoplastic
polymeric material in finely divided form and, possibly, by the latex
coating, only to a minimum extent. In case a latex binder is used the
depth of penetration of the latex into the fibrous web can controlled by
the vacuum applied by means of the suction boxes positioned in
correspondence with the dispensing means, and by the choice of the
amount to be applied to the web.
Fig. 3 shows a simplified, schematic illustration of an apparatus
for making an alternate preferred embodiment of a dry laid fibrous
structure 59 according to the present invention) for example an
absorbent structure, which structure is in turn illustrated in FIG. 4.
The apparatus of FIG. 3 is similar to the apparatus illustrated in
FIG. 1 ( and same numerals indicate corresponding parts, but in this case
the latex applying and curing section is missing, since the whole bonding
of the structure is performed by the thermoplastic polymeric material in
finely divided form incorporated in the web.
As can be seen from FIG. 3 the thermoplastic polymeric material,
preferably in powder form, contained in the container 27 is supplied both
to the feeder 24 and to the distributors 12A and 12B. The thermoplastic
polymeric material is therefore homogeneously mixed with the particulate
material and with the fibres that form the fibrous plies as well.
During the subsequent bonding stage performed at the binding
station 28 the whole dry laid structure 59 is thermally stabilized in its
entire thickness by the melting of the powder of the thermoplastic
polymeric material that bonds both the particulate material comprised
intermediate the first and second surfaces 6 and 8, and the fibres of the
web 22.
Referring to FIG. 4, the dry laid absorbent structure 59 comprises
fibres 60 and particulate material 61 constituted by a mixture of an
absorbent gelling material and of an odour control means interspersed in
the web, but more concentrated in the middle of the thickness of the
web 22. The thermoplastic polymeric material 63 in powder form is
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homogeneously distributed within the whole fibrous web forming the dry
laid absorbent structure 59.
In further alternate embodiments of the present invention either
the absorbent gelling material or the odour control means can be
included in the absorbent structure in a form different from the
particulate form, e.g. fibrous absorbent gelling materials can be used, or
odour control means in form of a solution sprayed onto the absorbent
structure can be incorporated, provided that a particulate material is
comprised in the absorbent structure. For example, a suitable solution
could be sprayed onto the first fibrous ply laid down by the distributor
12A in the apparatus illustrated in F1G. 1, or onto the first surface 6 of
the web 22 of FIG. 3, instead of, or in combination with, the odour
control means in particle form distributed by the hopper 24 within the
web 22.
In a further alternate embodiment of the present invention, not
illustrated, a latex coating could be applied also to the first ply of the
fibrous web, and subsequently cured, before the application of the
particulate material, onto the surface where the particulate material is to
be distributed.
One of the plies of the fibrous web, for example the second ply of
the web of FIG. 3, can also, in another alternate embodiment, be
substituted by a nonwoven layer, or by a polymeric film. In this latter
case the polymeric film should be applied to the web after the bonding
station 28, in order to avoid that the temperature in the bonding station
can possibly melt the polymeric film. A structure of this type could
constitute an absorbent element of a disposable absorbent article having
an impervious layer incorporated therein.
