Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED THERMOPLASTIC HYDROPHILIC ADHESIVE COMPOSITIONS
FOR ATTACHMENT ON DRY AND WET SURFACES AND WITH INCREASED
WATER ADHESION STABILITY
Field of the Invention
The present invention relates to thermoplastic adhesive compositions
having an increased adhesion capability and stability on moist or wet
surfaces,
even when in contact with high amounts of aqueous fluids, particularly on
moist
or wet skin. In particular the present invention relates to adhesive
compositions
which can be employed as topical adhesives for attachment to the skin
preferably
in the area where absorption of bodily liquids is desired, particularly for
the
adhesion of sanitary napkins, pantiliners, adult incontinence products or
sweat
pads. The adhesive compositions provide secure attachment and increased
adhesion stability on moist or wet surfaces, and, when employed as topical
adhesives for attachment to skin, are also pleasing to the skin upon
application,
yet cause no discomfort upon removal.
Background of the invention
The present invention relates to adhesive compositions which are
particularly useful for adhesion on moist or wet surfaces, where they provide
an
increased adhesion capability and stability. Particularly, the adhesive
compositions of the present invention are suitable as topical adhesives for
attachment to the skin, for example in absorbent articles for absorption of
body
fluids, such as to attach sanitary napkins or pantiliners in the genital
region. Also
incontinence devices which are worn e.g. in the genital region or perspiration
pads which are worn in the arm pit region of a person can suitably employ the
adhesive compositions of the present invention in order to be directly adhered
to
the wearer's skin.
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Adhesive compositions for attachment to the skin have been generally
disclosed in for example US statutory invention registration H1602 or
WO 96/33683 and WO 95/16424. The latter discloses sanitary articles having a
topical adhesive which is applied on the wearer facing side of a sanitary
napkin
along the entire periphery. WO 96/13238 discloses a topical adhesive which is
described in terms of frequency dependency. EP 638303 discloses the use of a
topical adhesive on side cuffs of sanitary napkins in order to keep the cuffs
in an
upright position. Swiss publication CH 643730 discloses the use of a very long
sanitary napkin having chamfered outer edges with a topical adhesive at the
four
corners of the outer edges in order to provide a topical adhesive area well
outside
the region of pubic hair growth.
However all of these disclosures typically disclose a product which is
designed to be utilised in combination with an undergarment and hence the
degree of adhesion actually provided is very low and is not designed to
withstand
any excessive stress or force. Moreover the adhesive is only discussed in
general terms or concentrates on the area of application of the adhesive to
the
article. The nature of adhesive per se other than the basic physical
requirements
such as pressure sensitivity are not discussed in particular with reference to
the
chemical composition or the adhesive criteria.
The prior art in the general field of adhesives for attachment to the skin is
particularly developed in the field of articles such as band-aids, plasters
and
bandages. These articles are however typically applied in an emergency
situation, where for example, a cut into the skin of the wearer has occurred.
In
this context, performance aspects of the article such as easy application and
use
of the product, comfortable wear as well as painless removal, and discreteness
are subordinate to other criteria such as sterility, healing support, and
mechanical
protection of the wound. Also such wound covering absorbent articles are
mostly
adhered to the skin where prior to application of the absorbent article bodily
hair
can be removed or where little hair grows.
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In order to provide in all possible situations the desired level of adhesion
of
such bandages, the prior art typically discloses the utilisation of certain
adhesives
having very high adhesive and cohesive strengths such as rubber based
adhesives, comprising natural rubber or synthetic rubbers, and acrylics. In
order
to achieve the desired level of adhesive force upon application, and also an
acceptable adhesion stability in presence of moist or wet skin, these
adhesives
are formulated so as to provide a very high level of initial adhesion, and are
also
very hard, i.e., in rheological terms, have a high elastic modulus G'. This
implies
these adhesives are not comfortable and skin friendly, but rather aggressive,
and
cause a substantial level of pain upon removal.
On the contrary, for application on the skin, and in particular for
application
in absorbent articles to be directly, adhered to the wearer's skin, it is
important
that the adhesive has a skin compatible composition and is not harsh or
aggressive towards the skin or cause skin irritation or inflammation. Also it
is
preferred if the adhesive is compliant with the skin of the wearer such that
maximum skin surface contact between the adhesive and the skin is achieved. In
this way a sufficient level of adhesion can be achieved even with adhesives
having a non aggressive adhesive strength. Moreover, it is also desirable to
provide an adhesive such that the absorbent article can be readily removed
from
the wearer, without the wearer experiencing any unacceptable pain level. This
is
particularly important under circumstances, where the article is removed and
reapplication of the article once or even a number of times is required, for
example to allow for urination and/or to ensure the application of such
articles on
sensitive skin and wearer groups such as infants. However, on the other hand
the
desired level of adhesion, albeit painless should of course also be maintained
during such multiple applications of the article.
The problem of achieving the desired adhesion level is further exacerbated
under wet skin conditions. Typically, during the placement of the article the
skin
has a physiological level of moistness which varies among individuals, and can
also by very high.
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The currently available adhesives often do not immediately strongly adhere
to wet skin and may need to be held in place until sufficient minimum adhesion
occurs. Moreover, the overall adhesive ability of such adhesives tends to be
significantly reduced on wet skin surfaces per se, so that the article will
typically
not remain attached to the skin during wear if any force or stress is exerted
onto
the article, for example by the movement of the wearer.
Moist and wet skin however is not just a problem which is prevalent at the
article application stage as a significant amount of moisture is also
generated
during the use of the article by the wearer by perspiration and from bodily
fluids,
which can also come in contact, even in large amounts, with the adhesive. With
currently available adhesives the adhesive strength is reduced under such
circumstances to such an extent that the article will often become detached
spontaneously or under exertion of even minimal force or stress during wear.
More in general, effective adhesion capability and adhesion stability on wet
or moist surfaces, either at the application stage, or with respect to
moisture or
liquid getting in contact with the adhesive during its use, are desirable in
adhesive
composition also for different uses besides the preferred application in
articles,
typically absorbent articles, intended to be kept in contact with the skin.
Among the adhesives known in the art as topical adhesives for attachment
to dry and wet skin there are adhesives of the hydrocolloid type typically
comprising a hydrophobic polymeric matrix, e.g. , constituted by a synthetic
rubber, preferably polyisobutylene, in which water soluble or water swellable
hydrocolloids, such as for example particles of pectin, gelatin, or
carboxymethylcellulose, are dispersed. In adhesive compositions of this type,
the
hydrophobic polymeric matrix provides the adhesive properties in dry
conditions,
while the dispersed hydrocolloid particles absorb aqueous fluids and render
the
adhesive, at least to a certain extent, capable of adhering to moist surfaces,
typically moist skin. Absorption is however not very efficient, since the
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hydrocolloid particles are surrounded by and often enclosed into a hydrophobic
matrix.
An increase of the hydrocolloid content in order to enhance the liquid
absorption capacity and to facilitate the access of liquids to the absorbent
particles, on the other hand, can also cause the hydrocolloid adhesives to
break
down upon exposure to relatively large amounts of fluids, for example when
they
are employed for attachment to the skin of articles intended for absorption of
body fluids, e.g. incontinence devices, where they typically also act as skin
barriers, i.e. providing a seal against liquid leakage. Upon contact with
relatively
large amounts of fluids, in fact, the swelling of the hydrocolloid particles
may
cause the adhesive composition to lose its integrity. This results in a loss
of the
barrier effect, and also, very often, in residues remaining on the skin upon
removal of the article. In addition, hydrocolloid adhesives are typically
rather hard
and not very pleasant to the skin, and may also cause pain upon removal. This
is
due to the particular structure of the hydrocolloid adhesives, in which the
inclusion of a hydrocolloid incompatible disperse phase into a hydrophobic
rubbery continuous matrix causes the resulting material to be harder, i.e., in
theological terms, having higher elastic modulus G' and storage modulus G",
which, in turn, render the initial adhesion to the skin more difficult, and
the
removal painful.
Other known adhesive compositions that are particularly useful as topical
adhesives for attachment to the skin are those having a substantially gel-like
structure, and are preferably gels. They typically comprise as a prevailing
component a plasticiser which is a material liquid at room temperature, and a
macromolecular or polymeric component forming, in the preferred embodiments,
a three dimensional network caused by physical or chemical links between the
molecules. Such adhesive compositions can be classified according to the
nature
of the main component, i.e. usually the plasticiser. Hydrophobic compositions,
also known as oil-gels, are those in which the plasticiser is typically an oil
or
blend of oils of vegetable or mineral origin and the polymer is usually a
synthetic
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hydrophobic polymer, preferably an elastomer, soluble or swellable in oil(s).
Hydrophilic compositions, also known as hydrogels, are those in which
typically
the plasticiser is water/glycerol/glycols and the like and/or mixtures
thereof, and
the polymeric phase is of synthetic (e.g. polyacrylics) or natural (e.g.
natural
gums) origin. Mixed phase compositions are also known, in which both
hydrophobic and hydrophilic components, possibly in both plasticisers and
polymers, form two or more separate phases.
The gel and gel-like adhesive compositions can be suitably formulated in
order to have rheological and physical characteristics which render them soft
and
pleasant to the skin, provide firm adhesion also on skin surface with hairs,
with
low pain level upon removal. However, they can still be improved in their
adhesion characteristics on moist or wet surfaces, typically moist or wet
skin, and
particularly also in the presence of a significant amount of moisture or
liquid
generated during the use of the adhesive, i.e. during the time the adhesive is
actually adhered to the surface, e.g. the skin.
The above mentioned oil-gel type adhesives are in fact not capable of
absorbing moisture or aqueous liquid due to their chemical nature, and
therefore
their adhesion on moist or wet surfaces is limited if none at all. Once they
are
adhered to a surface, e.g. the skin, they cannot withstand the presence or the
build up (e.g. by sweating) of even relatively small amounts of moisture or
liquid
generated during the use, and loose their adhesion capacity to a substantial
extent, to the point they can spontaneously detach from the surface.
Hydrogel type adhesives on the other hand have typically a very high liquid
absorption capacity, and while they are effective in presence of limited
amounts
of moisture or liquid on the surface when they are adhered, or generated
during
the use, since they can absorb such limited amounts of moisture or aqueous
liquid still maintaining an acceptable level of adhesion onto the surface,
their high
absorption capacity can constitute a disadvantage in presence of substantial
amounts of moisture or liquid. They in fact tend to absorb water to such an
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extent, that they dramatically change their rheology and loose their adhesion
capability very quickly after contact with such high amounts of moisture or
aqueous liquid.
Mixed phase adhesive compositions are typically harder than both oil-gels
and hydrogels, and since they comprise a hydrophobic phase and a hydrophilic
phase, they basically have the drawbacks of both oil-gels and hydrogels as
described above. Moreover, if the hydrophilic phase is the disperse phase,
they
tend to behave like hydrocolloid adhesives upon absorption increasing the
phase
separation owing to the absorption into the disperse hydrophilic phase, with
risk
of loss of integrity as explained above.
Examples of gel or gel-like adhesives are disclosed in the prior art.
US 4,699,146 discloses hydrophilic elastomeric pressure sensitive
adhesives suitable for use with ostomy devices, bandages, ulcer pads, sanitary
napkins, diapers, and athletic padding. The adhesive comprises at least an
irradiation cross linked organic polymer and an adhesive plasticizes.
GB 2115431 discloses adhesives for bandages, wounds or burn dressings,
EKG adhesives, sanitary napkins, diapers and ulcer pads. The adhesive
comprises an irradiation cross linked organic polymer such as
polyvinylpyrrolidone and an adhesive plasticizes.
Adhesion to wet skin is addressed for example in WO 98/03208 which
discloses medical pressure sensitive adhesives which can adhere to dry or wet
skin and which comprise a mixed phase composition comprising a mixture of
hydrophilic (meth)acrylate copolymer containing tertiary ammo groups, a
hydrophobic (meth)acrylate copolymer containing carboxyl groups, carboxylic
acids and a crosslinking system. However this document does not discuss
adhesion after exposure to excess liquid.
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Moreover gel-like adhesives, particularly hydrogels, need to be crosslinked
in order to achieve their three dimensional network, and typically this
crosslinking
step occurs after application of the not crosslinked composition over a
suitable
substrate, hence implying a rather complex process for the formation of
articles
comprising said adhesives.
In addition hydrogel adhesives, owing to their capability to exchange water
with the environment, lose or acquire it depending on the external conditions,
and
therefore can substantially change their theology and hence their adhesive
behaviour. As a consequence, hydrogel adhesives need to be stored in water-
and moisture-proof packages.
Hence there still exists a need for an adhesive composition having an
increased adhesion capability and stability on moist or wet surfaces,
particularly
on moist or wet skin, and more particularly in the presence of significant
amounts
of moisture or liquid, independently of whether this is upon direct
application of
the article to the moist or wet surface, e.g. skin, or when moisture or liquid
is
generated on the surface or in any case contacts the adhesive during its use.
In
particular it is an objective of the present invention to provide an adhesive
which
is liquid stable particularly to water and aqueous fluids and more
particularly to
body fluids such as menses, urine, or sweat in its use as topical adhesive for
skin
attachment, such that the adhesion properties will not be significantly
affected by
the presence of said fluids over the period of use of an article for the
absorption
of body fluids comprising the adhesive of the present invention.
It is another object of the present invention to provide an adhesive
composition having the above characteristics and which is also particularly
suitable in the use as a topical adhesive for skin attachment for the secure
attachment and painless removal from the skin, particularly for use on
sensitive
skin of an infant and/or of the genitalia.
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It is still another object of the present invention to provide an adhesive
composition which is moisture vapour permeable, while also preferably being
capable of providing a seal against liquid leakage, which is particularly
desired in
the preferred use as topical adhesive for attachment of articles to the skin,
particularly disposable absorbent articles, where the adhesive can therefore
act
as skin barrier.
It is a further object of the present invention to provide an adhesive
composition that also exhibits an ability to adhere to a surface, e.g. skin,
upon
reapplication, particularly multiple reapplication for example when an
article, e.g.
an absorbent article, comprising the adhesive is removed for urination
purposes
or is misplaced, whilst still allowing painless removal.
An additional object of the present invention is to provide an adhesive
composition which provides flexibility, stretchability and contractability so
that it is
able to adapt to the contours of the surface where it has to be applied, and
particularly of the body during all bodily movements and hence be comfortable
for
the wearer of the article comprising the adhesive composition, whilst still
having
sufficient adhesive capacity to ensure secure attachment during use.
It has now been surprisingly found that the above drawbacks of the known
adhesives, typically employed as topical adhesives for attachment to the skin,
can be substantially alleviated by providing the adhesive compositions defined
hereinafter. The adhesive compositions have an increased adhesion capability
and stability on moist or wet surfaces, particularly on moist or wet skin. In
their
preferred use as topical adhesives for skin they provide a secure attachment,
and
yet cause no discomfort upon removal and maintain their adhesive strength over
the period of use even under exposure to excess liquids.
The adhesive compositions are also simple to produce and to incorporate
into articles, namely by means of direct coating, e.g. by means of known hot
melt
coating techniques, onto a suitable substrate or directly onto the article.
They are
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also substantially stable both in storage and during use, and do not
necessitate a
particular packaging.
All the above mentioned advantages are achieved by the adhesive
composition of the present invention, which is provided by suitably
formulating a
thermoplastic polymeric matrix which is at the same time homogeneous and
intrinsically hydrophilic, and preferably also moisture vapour permeable, as
will
be described hereinafter.
Summary of the Invention
The present invention relates to an adhesive composition comprising a
thermoplastic hydrophilic homogeneous polymeric matrix having an elastic
modulus at a temperature of 37°C, G'37, and a viscous modulus at a
temperature
of 37°C, G"3~. The thermoplastic hydrophilic homogeneous polymeric
matrix has:
a maximum liquid absorption capacity in 24 hours, measured according to the
Liquid Absorption Test described herein, of from 0.02 g/g to 5 g/g, preferably
of
from 0.05 g/g to 3 g/g, more preferably of from 0.1 g/g to 2.0 g/g;
a liquid absorption rate, measured according to the Liquid Absorption Test
described herein, such that the liquid absorption capacity at 1 min is at
least 15%,
preferably at least 20%, more preferably at least 25%, of said maximum liquid
absorption capacity in 24 hours;
an elastic modulus G'37 (1 rad/s) in the range 100 Pa to 500.000 Pa,
preferably
1.000 Pa to 100.000 Pa, more preferably 3.000 Pa to 70.000 Pa;
an viscous modulus G"37 (1 rad/s) in the range 50 Pa to 200.000 Pa, preferably
300 Pa to 50.000 Pa, more preferably 500 Pa to 30.000 Pa;
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the ratio G'37 (100 rad/s) / G'37 (1 rad/s) not greater than 20, preferably
not grater
than 15, more preferably not greater than 10.
Detailed Description of the Invention
By saying "homogeneous" polymeric matrix it is herein intended a polymeric
composition constituted by a single phase, hence where no phase separation
between a continuous phase and a disperse phase is present, at least at a
macroscopically detectable level, i.e., at an order of magnitude of at least
about
1 ,um. Of course, at the sub-micronic and intramolecular level, different
phases
can be present, for example in the single molecules of the components of the
composition, where e.g. typically different phases, or domains, such as those
comprised in a thermoplastic block copolymer, may exist, without influencing
the
homogeneous nature of the matrix as described above.
By saying "thermoplastic hydrophilic" homogeneous polymeric matrix it is
herein intended a thermoplastic polymeric composition which, in addition to
being
homogeneous as explained above, is also inherently hydrophilic, i.e. its
hydrophilicity id achieved by the selection of the components of the
homogeneous matrix, as will be explained in the following description, in
contrast,
for example, to hydrocolloid or mixed phase adhesive compositions as explained
in the Background of the Invention, where hydrophilicity is provided by the
inclusion in the matrix of a macroscopically separate hydrophilic phase or
component.
Preferably, the thermoplastic hydrophilic homogeneous polymeric matrix of
the present invention is also capable of forming a continuous layer that does
not
allow the flow of moisture vapour through open pores or apertures in the
material,
but does transfer substantial amounts of moisture vapour through the
continuous
layer by absorbing water on one side of the layer where the moisture vapour
concentration is higher, and desorbing or evaporating it on the opposite side
of
the layer where the moisture vapour concentration is lower. Generally, a
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thermoplastic hydrophilic polymeric composition having the above described
characteristics of moisture vapour permeability can be also identified as a
"monolithic composition", as it is known in the art, and a moisture vapour
permeable, typically liquid impermeable layer made therefrom is known as a
"monolithic layer". This definition is also applicable to the thermoplastic
hydrophilic homogeneous polymeric matrix of the present invention, which is
therefore preferably a monolithic matrix.
The terms "breathable" and "breathability" are intended herein to correspond
to "moisture vapour permeable" or "water vapour permeable", and "moisture
vapour permeability" or "water vapour permeability", referred to "monolithic
compositions" and "monolithic layers or films" as defined herein. "Moisture
vapour" and "water vapour" are also considered to be equivalent.
Although the adhesive compositions according to the present invention can
be utilized in various articles and for different uses, as will be explained
hereinafter, where an increased adhesion capability and stability on moist or
wet
surfaces is desired, in a particularly preferred embodiment of the present
invention they can be used as topical adhesives for attachment of articles to
the
skin of a wearer, particularly disposable absorbent articles intended for
absorption of bodily liquids, such as sanitary napkins, pantiliners, adult
incontinence products or sweat pads, to be attached to the wearer's skin.
Therefore the adhesive compositions of the present invention will be herein
described, unless otherwise stated, with reference to their preferred use as
topical adhesives for skin attachment of this type of articles.
Detailed analysis of the sequence of common situations occurring from the
application of absorbent articles to the time of removal of such articles has
shown
that specific adhesive characteristics need to be preferably satisfied in
order to
achieve the desired performance objectives, in particular secure initial
attachment, secure sustained attachment during use and painless removal after
wear. The characteristics which have been considered in this context are the
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elastic modulus describing the elastic behaviour of the material and the
viscous
modulus which describes the viscous behaviour of the adhesive material.
The viscous behaviour of the adhesive can be interpreted to represent an
indication of the ability of the adhesive to quickly attach and securely
adhere to a
particular surface. The elastic behaviour can be interpreted as an indication
of the
"hardness" behaviour of the adhesive and of its ability to withstand removal.
Its
value is also important for good initial attachment. Their combination is
believed
to be an indicator of the required force upon removal. The relation between
elastic and viscous modulus is considered to be an indication on which
fraction of
the removal energy will be dissipated within the adhesive and which fraction
is
available to trigger the actual removal.
In order to provide adhesives for secure initial and prolonged attachment
and easy/painless removal the relation between the elastic modulus and the
viscous modulus as well as their dynamic behaviour is also of importance.
The adhesive composition of the present invention has an elastic modulus
at a temperature of 37°C, G'3~~ and a viscous modulus at a temperature
of 37°C,
G.~s7.
According to the present invention, the adhesive compositions comprise a
thermoplastic hydrophilic polymeric matrix which is homogeneous, has a
selected
rheology, as will be described herein, and a selected behaviour towards water,
and in general aqueous fluids, and moisture, expressed in terms of a suitable
combination of maximum liquid absorption capacity in 24 hours and liquid
absorption rate of the thermoplastic hydrophilic homogeneous polymeric matrix,
both the maximum liquid absorption capacity and the liquid absorption rate
evaluated according to the Liquid Absorption Test described herein. It has in
fact
been discovered that not only the absolute ability of the adhesive
compositions of
the present invention to absorb liquid, particularly water and aqueous fluids,
represented by the maximum liquid absorption capacity, is important, but also
the
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rate at which this absorption occurs in order to provide the adhesive
composition
with the advantages described herein.
Even though adhesives for human skin, typically with hairs, and mucous
tissues,can be classified as pressure sensitive adhesives , it is understood
that
the topical adhesive compositions could only with difficulty be considered
typical
pressure sensitive adhesives (referred to as PSA hereinafter) on the basis of
the
most characteristic theological behaviour identifying such materials.
In fact as the person skilled in the art of adhesives knows, the most
characteristic feature that distinguishes a PSA from other substances that can
temporarily adhere objects (e.g. like water between two glass plates) is the
fact
that their theological parameters and especially the Elastic Modulus G' vary
greatly with the frequency of applied stresses. More in particular, G' of PSA
can
increase over some orders of magnitude, while the frequency of applied
stresses
varies from typical bonding frequency to typical debonding frequency, i.e. 1
rad/s
to 100 rad/s as indicated below.
This increase of G' with frequency indicates that the adhesive has a high
level of hardening in the range of frequencies representing the use
conditions.
The hardening of the adhesive macroscopically causes the recording of very
high
peel force for removal and, most importantly for skin adhesives, the
occurrence of
high level of pain upon removal. It is in fact known that the physiological
pain
sensation upon removal of a skin adhesive increases more than proportionally
with the increase of G' of the adhesive in the region of frequencies typical
of
removal conditions. Therefore the adhesive composition of the present
invention
shall have a relatively limited increase of the elastic modulus G' with
frequency,
as will be explained below.
As indicated above adhesive compositions of the present invention,
particularly useful as topical adhesives for skin attachment, have theological
characteristics which are measured at a reference temperature of 37°C
(as usual
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body temperature of humans) and in a range of frequencies. It has been found
that upon application of a disposable absorbent article with an adhesive the
adhesive contact is formed at a low frequency, while debonding happens at the
speed of removing the article. This speed is expressed as a frequency of
100 rad/s, while the low frequency of forming the adhesive bond has been found
to be on the order of 1 rad/s. Therefore, the frequency range for use
according to
the present invention is between 1 and 100 rad/s.
In order to provide good conditions of bonding, i.e. at a frequency of about 1
rad/sec, the absolute values of the elastic modulus should not be too high,
otherwise the adhesive is too hard and it is not able to intimately join or
mold to
the surface to which it is expected to adhere. It is also important to have a
relatively low absolute value of G" in order to have good cohesion while the
material remains soft and capable of gently adhering to skin.
It is also well known that an indicator for the cohesiveness of an adhesive
material is the ratio G"37 (100 rad/s) / G'37 (1 radls) = tan (~).
Accordingly, the
thermoplastic hydrophilic homogeneous polymeric matrix comprised in the
adhesive compositions of the present invention preferably has a tan (o) at 1
rad/s
and 37°C not greater than 2, preferably not greater than 1.5, and more
preferably
not greater than 1.3.
According to the present invention, the following set of rheological
characteristics shall be satisfied for the thermoplastic hydrophilic
homogeneous
polymeric matrix comprised in the adhesive composition of the present
invention:
an elastic modulus G'37 (1 rad/s) in the range 100 Pa to 500.000 Pa,
preferably
1.000 Pa to 100.000 Pa, more preferably 3.000 Pa to 70.000 Pa;
a viscous modulus G"s7 (1 rad/s) in the range 50 Pa to 200.000 Pa, preferably
300 Pa to 50.000 Pa, more preferably 500 Pa to 30.000 Pa;
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the ratio G'37 (100 rad/s) / G's~ (1 rad/s) not greater than 20, preferably
not grater
than 15, more preferably not greater than 10.
Differently from the adhesive compositions of the prior art, the adhesive
compositions of the present invention comprise a thermoplastic polymeric
matrix
which is homogeneous, and intrinsically hydrophilic, i.e., hydrophilic per se,
rather
than, e.g. being provided with a certain degree of hydrophilicity by means of
the
addition of a macroscopically dispersed hydrophilic component such as in the
hydrocolloid adhesives.
The thermoplastic hydrophilic homogeneous polymeric matrix comprised in
the adhesive compositions of the present invention has a maximum liquid
absorption capacity in 24 hours, evaluated according to the Liquid Absorption
Test described herein, of from 0.02 g/g to 5 g/g, preferably of from 0.05 g/g
to
3 g/g, more preferably of from 0.1 g/g to 2.0 glg.
The thermoplastic hydrophilic homogeneous polymeric matrix comprised in
the adhesive compositions of the present invention also has a liquid
absorption
rate, evaluated according to the Liquid Absorption Test described herein, such
that the liquid absorption capacity at 1 min is at least 15%, preferably at
least
20%, more preferably at least 25%, of said maximum liquid absorption capacity
in
24 hours.
Accordingly, the adhesive compositions of the present invention are capable
of absorbing a relatively limited amount of liquid, typically water or aqueous
fluids,
at a rather high rate, and as a result such adhesives are capable of
effectively
adhering to wet and moist surfaces, for example moist or wet skin, and owing
to
the combination of relatively limited liquid absorption capacity, measured as
maximum liquid absorption capacity in 24 hours, and high liquid absorption
rate,
they maintain their adhesive strength also in the presence of excess liquid or
high
moisture levels, irrespectively of whether the moisture or liquid is already
present
on the surface at the time adhesion is achieved, or is generated directly at
the
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surface, or alternatively comes in direct contact with the adhesive during the
time
the adhesive is adhered to the surface, e.g., during the wearing time of a
disposable absorbent article adhered to the wearer's skin by means of the
adhesive composition of the present invention.
This is different, for example, to the behaviour of hydrogel type adhesives,
which instead absorb very rapidly so large amounts of liquid that they
substantially loose their adhesive strength quickly.
According to the present invention, the thermoplastic hydrophilic
homogeneous polymeric matrix comprised in the adhesive composition at least
comprises a first polar cohesive thermoplastic polymer, or blend of polar
cohesive
thermoplastic polymers, at least a second polar adhesive thermoplastic
polymer,
or blend of polar adhesive thermoplastic polymers, a compatible plasticises,
or
blend of compatible plasticisers, and optionally a tackifying resin, or blend
of
tackifying resins.
As intended herein, by "polar" thermoplastic polymer it is meant a
thermoplastic polymer having a high polar character.
The polar character of a thermoplastic polymer is a measure of its
hydrophilicity, i.e. of its affinity for water, and can be measured by means
of a
suitable polarity parameter. A suitable polarity parameter for a given
substance
can be selected among a number of parameters which are well known in the
scientific literature, and are measurable according to known methods. A
suitable
polarity parameter can be for example the so called Hildebrand solubility
parameter H.
According to the present invention, a thermoplastic polymer comprised as
the first cohesive thermoplastic polymer or as the second adhesive
thermoplastic
polymer in the thermoplastic hydrophilic homogeneous polymeric matrix is also
polar, i.e. has a high polar character, if it has a value for the Hildebrand
solubility
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1~
parameter H of at least 18 MPa'~2. In case the thermoplastic polymer has, at
an
intramolecular level, separate phases, such as for example the domains in a
thermoplastic block copolymer typically selectable as a first polar cohesive
thermoplastic polymer, having different values of the Hildebrand solubility
parameter, the highest of said different values, i.e., the most polar phase in
the
copolymer structure, has to be taken into consideration for the selection of
the
thermoplastic polymer.
The first polar thermoplastic polymer, comprised in the thermoplastic
hydrophilic homogeneous polymeric matrix, is also cohesive, i.e., has a high
degree of internal cohesion. According to the present invention, a cohesive
thermoplastic polymer is defined as having a Melt Flow Index (MFI), measured
according to the ASTM D 1238 test method, of less than 2500, preferably of
less
than 2000, more preferably of less than 1000.
According to a preferred embodiment of the present invention, said first
polar cohesive thermoplastic polymer, or at least one polymer of said blend of
polar cohesive thermoplastic polymer, is selected among thermoplastic
elastomers. More preferably, in a blend of polar cohesive thermoplastic
polymers,
all such polymers are polar cohesive thermoplastic elastomers.
The second polar adhesive thermoplastic polymer of the thermoplastic
hydrophilic homogeneous polymeric matrix comprised in the adhesive
composition of the present invention can be suitably selected among those
polymers which are well known in the field of thermoplastic adhesive
compositions, and which are also polar, according to the definition provided
above. Such polar adhesive thermoplastic polymers can be selected among
those being adhesive per se, i.e., by being pressure sensitive as such, or
alternatively among those which can be readily rendered adhesive, or
tackified,
by means of the addition of a suitable tackifying resin or resins, as it is
known in
the art.
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According to a particularly preferred embodiment of the present invention,
the first polar cohesive thermoplastic polymer, or at least one polymer in the
blend of polar cohesive thermoplastic polymers, in addition to being polar,
also
has the capability of effectively absorb liquid, typically water or more in
general
aqueous fluids. Even more preferably, all polar cohesive thermoplastic
polymers
in such a blend have the preferred liquid absorption capacity. Preferably,
also the
second polar adhesive thermoplastic polymer, or at least one polymer in the
blend of polar adhesive thermoplastic polymers, and more preferably all of
them,
is/are selected in order to also have the capability of absorbing liquid,
typically
water or more in general aqueous fluids.
According to the present invention, said liquid absorption capacity for the
first polar cohesive and/or for the second polar adhesive thermoplastic
polymer or
respective blends of thermoplastic polymers is expressed in terms of maximum
liquid absorbent capacity in 24 hours, evaluated according to the Liquid
absorption Test described herein.
Preferably, the liquid absorption capacity for said first polar cohesive
thermoplastic polymer or polymers, and/or for said second polar adhesive
thermoplastic polymer or polymers, consists in a maximum liquid absorption
capacity in 24 hours of at least 0.01 g/g, more preferably of at least 0.02
g/g,
most preferably of at least 0.05 g/g, wherein the liquid absorption capacity
is
evaluated according to the Liquid Absorption Test described herein.
Of course polar cohesive thermoplastic polymer or polymers and/or polar
adhesive thermoplastic polymer or polymers which do not have the preferred
liquid absorption capacity, i.e. which although polar do not absorb liquid, or
in any
case have a maximum liquid absorption capacity in 24 hours of less than 0.01
g/g
according to the Liquid Absorption Test, can be comprised in the thermoplastic
hydrophilic homogeneous polymeric matrix comprised in the adhesive
composition of the present invention, but preferably they should overall
constitute
not more than 70%, more preferably not more than 60%, even more preferably
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not more than 50%, of the total weight of said polar cohesive thermoplastic
polymer or polymers and of said polar adhesive thermoplastic polymer or
polymers.
Conversely, the thermoplastic hydrophilic homogeneous polymeric matrix
comprised in the adhesive composition of the present invention can comprise
polar cohesive thermoplastic polymer or polymers and/or polar adhesive
thermoplastic polymer or polymers, which is/are soluble or dispersible in
liquid,
namely in the saline solution containing 0.9% by weight of sodium chloride in
water which is used in the Liquid Absorption Test. In this case, as will be
explained in the test method description, the liquid absorption capacity of a
liquid
soluble or dispersible thermoplastic polymer will be considered infinite, and
therefore satisfying the preferred condition of the maximum liquid absorption
capacity explained above for the first and the second thermoplastic polymer or
polymers. However, according to the present invention, and as will be
explained
more in detail hereinafter, it is preferred that the thermoplastic hydrophilic
homogeneous polymeric matrix overall comprises not more than 25%, more
preferably not more than 15%, most preferably not more than 10%, by weight of
said matrix, of one or more components which are soluble or dispersible in a
saline solution containing 0.9% by weight of sodium chloride in water.
According to the present invention, the first polar cohesive thermoplastic
polymer, or blend of polar cohesive thermoplastic polymers, comprised in the
thermoplastic hydrophilic homogeneous polymeric matrix can be selected from
the group consisting of: polyurethanes; polyether- polyester- and
polyetherester-amide block copolymers; ionomers; polyesters and copolyesters;
polyetherester block copolymers; polyamides and copolyamides; polyethylene
vinylacetate with vinylacetate content of at least 28%; polyethylene acrylic
and
methacrylic esters copolymers; polyethylene acrylic acid copolymers;
polyethylene vinyl alcohol copolymers; styrenic block copolymers and
polyolefins
polarly modified by insertion or grafting of, or by copolymerization with,
highly
polar groups/monomers, such as e.g. malefic or succinic anhydride, carbon
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monoxide, sulphonic groups, etc.; and blends thereof. Preferred examples of
such polarly modified styrenic block copolymers and polyolefins are styrene-
ethylene-butylene-malefic anhydride copolymers and copolymers or terpolymers
of ethylene with typical polar comonomers such as (meth)acrylic acid, acrylic
esters, vinyl esters, malefic anhydride, glycidyl methacrylate, and
combinations
thereof.
Preferred polar cohesive thermoplastic polymers are thermoplastic
elastomers selected from the group consisting of: polyurethanes; polyether-
polyester- and polyetherester-amide block copolymers; ionomers; polyetherester
block copolymers; styrene-ethylene-butylene-malefic anhydride copolymers; and
blends thereof.
Particularly preferred polar cohesive thermoplastic polymers according to
the present invention are selected from the group consisting of:
polyurethanes;
polyether- polyester- and polyetherester-amide block copolymers; ionomers;
polyetherester block copolymers; and blends thereof, which also have the
preferred maximum liquid absorption capacity.
According to the present invention, the second polar adhesive thermoplastic
polymer, or blend of polar adhesive thermoplastic polymers, comprised in the
thermoplastic hydrophilic homogeneous polymeric matrix can be selected among
the group consisting of: sulfonated polyesters; thermoplastic polyacrylates;
polyvinyl pyrrolidone and its copolymers such as polyvinyl pyrrolidone vinyl
acetate copolymer; polyvinyl ethers; polyvinyl alcohol; polyethylene oxide;
polyketones; and blends thereof.
Preferred polar adhesive thermoplastic polymers are selected from the
group consisting of: sulfonated polyesters; thermoplastic polyacrylates;
polyvinyl
pyrrolidone and its copolymers; polyvinyl ethers; and blends thereof.
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The thermoplastic hydrophilic homogeneous polymeric matrix comprised in
the adhesive compositions of the present invention further comprises a
compatible plasticises, or a blend of compatible plasticisers, as will be
explained
hereinbelow.
The first and second thermoplastic polymers (or blend of thermoplastic
polymers) as mentioned above, comprised in the thermoplastic hydrophilic
homogeneous polymeric matrix comprised in the adhesive compositions of the
present invention, can be typically highly viscous in the molten state at the
process conditions that are typical of the known formation processes, e.g. an
extrusion process involving a high power screw extruder. For example they may
have a viscosity higher than 5000 poise at a temperature of 20°C above
the DSC
(Differential Scanning Calorimetry) melting point, which is the temperature
identified as that corresponding to the DSC peak, or corresponding to the
highest
DSC peak in case of a mixture of polymers showing more than one peak, and at
a frequency of 1 rad/sec.
The thermoplastic hydrophilic homogeneous polymeric matrix comprised in
the adhesive compositions of the present invention, comprising the first and
second thermoplastic polymers or blends of thermoplastic polymers, can
therefore still be highly viscous in the molten state at the process
conditions.
According to the present invention, and as disclosed in our patent
applications WO 99/64077 or WO 99/64505, the viscosity of the thermoplastic
hydrophilic homogeneous polymeric matrix comprised in the adhesive
compositions of the present invention can be adjusted by including in the
thermoplastic hydrophilic homogeneous polymeric matrix a suitable plasticises,
or
blend of suitable plasticisers, that is compatible with the first and second
thermoplastic polymers and that lowers the viscosity of the thermoplastic
hydrophilic homogeneous polymeric matrix in the molten state at the process
conditions.
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Suitable hot melt coating processes are in fact preferred to process the
compositions, as explained in the above mentioned patent applications
WO 99/64077 and WO 99/64505. This implies that the viscosity in the
thermoplastic hydrophilic homogeneous polymeric matrix at the process
conditions has to be adjusted to a suitable low level.
In such a case, the thermoplastic hydrophilic homogeneous polymeric
matrix of this preferred embodiment of the present invention comprises a
suitable
plasticises or blend of plasticisers such that it preferably has the following
complex viscosities (rl*):
poise < rl* < 4000 poise, preferably 10 poise < rl* < 2000 poise, more
preferably 10 poise < rl* < 1000 poise, at a frequency of 1 rad/s, and rl* <
2000
pose, preferably rl* < 1000 poise, more preferably rl* < 500 poise, at a
frequency
of 1000 rad/s, said complex viscosities (rl*) at a process temperature (T)
comprised between 110°C and 210°C, preferably between
130°C and 180°C,
more preferably between 140°C and 170°C, wherein rl* represents
the complex
viscosity of the thermoplastic hydrophilic homogenous polymeric matrix of the
present invention. According to the present invention the complex viscosity
rl* of
the thermoplastic hydrophilic homogenous polymeric matrix is measured using a
RDA-II Rheometer available from Rheometrics Co. (US).
According to this preferred embodiment of the present invention the
thermoplastic hydrophilic homogeneous polymeric matrix having the complex
viscosity described above allows for a layer to be coated onto a substrate
using
typical coating conditions and apparatuses known in the art for the coating of
low
viscosity hot melt compositions in a layer having a required thickness onto a
substrate, while also keeping the advantageous characteristics of the
preferred
thermoplastic hydrophilic homogeneous polymeric matrix of the present
invention
in providing an adhesive composition having the beneficial characteristics
described herein.
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The plasticises or blend of plasticisers comprised in the thermoplastic
hydrophilic homogenous polymeric matrix has the primary object of adjusting
the
theological characteristics of the adhesive compositions of the present
invention,
i.e., in addition to the suitable modification of the melt viscosity at the
process
conditions, as explained above, the plasticises or blend of plasticisers
modifies
the theological parameters of the matrix such as the theological moduli G' and
G"
in order to help develop and optimize the desired adhesion characteristics in
the
adhesive composition of the present invention.
Suitable compatible plasticisers comprised in the thermoplastic hydrophilic
homogeneous polymeric matrix according to this preferred embodiment of the
present invention include citric acid esters, tartaric acid esters, benzoic
acid
esters, sucrose esters, tri-mellitates, sorbitol, urea, epoxidized vegetal
oils,
polymerised vegetal oils, castor oil and its derivatives, phthalates, liquid
polyesters, liquid polyamides, glycolates, aromatic sulfonamides, polyhydric
alcohols and their esters, glycerol and its esters, pentaerythritol and its
esters,
glycols and polyglycols and their esters and ethers, polyethylene glycol-
polypropylene glycol block copolymers, sorbitan esters, phosphates, lactic
acid
and its esters, mono- and dicarboxylic fatty acids (C$-C22) and their esters,
esters
of mono- and dicarboxylic fatty acids (C$-C22) hydrophilically modified by
insertion
in the molecular chain of 1 to 40 moles of ethylene oxide and/or of propylene
oxide per mole of base ester, polyethers and their derivatives, and blends
thereof.
According to a particularly preferred embodiment of the present invention
particularly preferred plasticisers are hydrophilic plasticisers such as
citric acid
esters, aromatic sulfonamides, benzoates, glycols and polyglycols and their
esters, glycerol and its esters, and blends thereof, some of them as disclosed
in
our application WO 99/64505. Said particularly preferred hydrophilic
plasticisers
have a particularly high polar character and provide the further advantage
that
they do not impair, and possibly can even contribute to, the moisture vapour
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permeability of a resulting layer of the adhesive composition of the present
invention formed from the thermoplastic hydrophilic homogeneous polymeric
matrix comprising said first and second thermoplastic polymers and said
suitable
compatible plasticiser or blend of plasticisers.
The particularly preferred hydrophilic plasticiser or blend of plasticisers
can
also typically adjust the hydrophilicity of the thermoplastic hydrophilic
homogeneous polymeric matrix comprised in the adhesive composition of the
present invention, in order to help provide the matrix with the desired level
of
maximum liquid absorption capacity and liquid absorption rate.
Optionally, and preferably, a tackifying resin or alternatively a blend of
tackifying resins can be included in the thermoplastic hydrophilic homogeneous
polymeric matrix comprised in the adhesive composition of the present
invention.
A tackifying resin, or blend of tackifying resins, is preferably included in
order to
help provide the desired level of tackiness in the adhesive composition of the
present invention. Specifically, the addition of a tackifying resin, or of a
blend of
tackifying resins, is meant to further enhance and control the tackiness level
of
the thermoplastic hydrophilic homogeneous polymeric matrix already provided by
a second thermoplastic polymer which is intrinsically adhesive, i.e., with
pressure
sensitive characteristics. Alternatively, the addition of a tackifying resin
or blend
of tackifying resins actually provides with tackiness a second thermoplastic
adhesive polymer which is not pressure sensitive as such, but is alternatively
selected among those which can be readily rendered adhesive, or tackified, by
means of the addition of a suitable tackifying resin or blend of resins, as
explained hereinabove.
Suitable tackifying resins can be selected among rosins and rosin esters,
aromatic and aliphatic-aromatic resins, terpene and terpene-phenolic resins,
aromatic acrylic resins, and blends thereof, as disclosed for example in our
patent applications WO 99/64077 or WO 99/64505. Preferred are rosins and
rosin esters, and aromatic acrylic resins. Particularly preferred are for
example
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the tackifying resins produced by Eastman and available under the codes
Res A-2690, Res A-2691, Res A-2682, Res A-2683, Res A-2698, which have a
high polar character, as disclosed in our patent application WO 02/14417.
Preferably the thermoplastic hydrophilic homogeneous polymeric matrix
comprised in the adhesive composition of the present invention comprises from
1 % to 50%, preferably from 3% to 40%, more preferably from 5% to 25%, by
weight of said matrix, of the first polar cohesive thermoplastic polymer; from
1
to 80%, preferably from 3% to 60%, more preferably from 5% to 50%, by weight
of said matrix, of the second adhesive thermoplastic polymer; from 5% to 85%,
preferably from 7% to 75%, more preferably from 10% to 60%, by weight of said
matrix, of a compatible plasticises, or blend of compatible plasticisers; and
from
0% to 45%, preferably from 5% to 35%, more preferably from 10% to 30%, by
weight of said matrix, of a tackifying resin, or blend of tackifying resins.
The thermoplastic hydrophilic homogeneous polymeric matrix comprised in
the adhesive composition of the present invention may in addition comprise
additional optional components to further improve the processability of the
compositions and also the mechanical characteristics as well as other
characteristics as resistance to ageing by light and oxygen, visual appearance
etc., of the layers formed from such thermoplastic hydrophilic homogeneous
polymeric matrix. Such other optional components may include anti-oxidants,
UV-stabilizers, surfactants, dyes, and mixtures thereof, which may be present
within the thermoplastic hydrophilic homogeneous polymeric matrix at a level
of
up to 10% by weight of the matrix.
Furthermore, solid filler compounds can also be optionally dispersed into the
thermoplastic hydrophilic homogeneous polymeric matrix, such as for example
silica, Zn oxide, calcium carbonate, zeolites, pigments, laponite, etc.
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Although not particularly preferred, known absorbent gelling materials in
particle or in fibre form can be also optionally dispersed into the
thermoplastic
hydrophilic homogeneous polymeric matrix.
Active agents, i.e. compounds which are capable of releasing an active
substance, e.g. to the skin, such as for example a cosmetic or pharmaceutical
substance, a perfume, etc. can also be optionally included in the
thermoplastic
hydrophilic homogeneous polymeric matrix.
While not particularly preferred, the thermoplastic hydrophilic homogeneous
polymeric matrix comprised in the adhesive composition of the present
invention
can comprise one or more components which are soluble or dispersible typically
in water or aqueous fluids. For example a plasticiser can be soluble or
dispersible
in water or aqueous fluids. According to the present invention, it is
preferred that
the thermoplastic hydrophilic homogeneous polymeric matrix comprises not more
than 25%, more preferably not more than 15%, most preferably not more than
10%, by weight of said matrix, of one or more components which are soluble or
dispersible in a saline solution containing 0.9% by weight of sodium chloride
in
water. A component is considered to be soluble or dispersible when it is
soluble
or dispersible in said saline solution in a concentration of at least 0.3% by
weight.
An adhesive composition according to the present invention comprising the
thermoplastic hydrophilic homogeneous polymeric matrix can be manufactured
with any known process that will typically comprise the steps of providing at
least
the first polar cohesive thermoplastic polymer, or blend of polar cohesive
thermoplastic polymers, the second polar adhesive thermoplastic polymer, or
blend of polar adhesive thermoplastic polymers, and the compatible plasticiser
or
blend of compatible plasticisers, and optionally the tackifying resin or blend
of
tackifying resins and any further additional components as explained above,
possibly comprising components to be dispersed into the matrix, and not
actually
being part of the thermoplastic hydrophilic homogeneous polymeric matrix,
melting the components and compounding them, e.g. with a known suitable mixer
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to form the adhesive composition, i.e. the thermoplastic hydrophilic
homogeneous polymeric matrix plus optionally further components, in the molten
state for subsequent process steps.
A process for making a layer of the adhesive composition according to the
present invention typically comprises the steps of providing said composition,
heating it to make it flowable, and forming said composition in the molten,
semi-molten, or plastic state onto a substrate in a layer having the desired
thickness, e.g. preferably with a hot melt coating process, as explained
above.
Alternatively, solvent or emulsion systems can be created and used to
process the thermoplastic hydrophilic homogeneous polymeric matrix comprised
in the adhesive composition of the present invention, either as an
intermediate or
final step in making said adhesive compositions, or composite structures
comprising a layer of said adhesive composition coated onto a selected
substrate, or articles comprising said adhesive compositions or said
structures.
Typical materials for said substrate include nonwoven materials, wovens,
open celled thermoplastic foams, closed-cell thermoplastic foams, composites
of
open celled foams and stretch nonwoven, and films.
According to a preferred embodiment of the present invention, the adhesive
composition comprising the thermoplastic hydrophilic homogeneous polymeric
matrix can be formed into a continuous layer which is moisture vapour
permeable, while being capable of providing a liquid barrier. This increases
the
wearer's comfort in the use of the adhesive composition as a topical adhesive
for
skin attachment, wherein at the same time the adhesive composition also acts
as
a skin barrier and provides a seal effect against liquid leakage, which is
particularly useful when the adhesive composition is incorporated into a
disposable article for the absorption of body fluids, intended to be attached
directly to the wearer's skin. Moisture permeability and liquid barrier are
also
preferred in other uses of the adhesive composition of the present invention,
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different from the incorporation into absorbent articles, as will be explained
hereinbelow.
According to the present invention a moisture vapour permeable, liquid
impervious continuous layer can be formed from the adhesive composition of the
present invention, for example by laying with a known method said adhesive
composition onto a suitable substrate, which is typically also moisture vapour
permeable. The adhesive compositions of the present invention preferably have
a
moisture vapour transmission rate of at least 200 g/ma 24h, more preferably of
at
least 300 g/ma 24h, even more preferably of at least 500 g/ma 24h, with a
thickness of said layer or film of at least 20 Vim, said water vapour
transmission
rate measured according to the ASTM E-96B "Upright Cup" Method.
According to the present invention, typically continuous layers can be
formed from the adhesive compositions described so far which have a thickness
of from about 5,~m to about 2500,um and above, said layers being typically
used
in combination with different substrates, such as for example in a composite
laminated structure comprising a nonwoven fibrous substrate.
The adhesive compositions of the present invention can be used in a
number of different articles and structures, as will be explained hereinbelow.
Articles comprisindthe adhesive composition
In a preferred embodiment herein, the present invention is directed to
Personal Care products, capable of adhering to the wearer's s skin, which
contain an adhesive composition according to the present invention having the
characteristics described above.
For the purpose of the present invention, personal care products means
products, disposable or reusable, which are designed to be worn by a human in
contact or close proximity to the body in order to achieve a function directed
to
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the person's heatlh, well-being, comfort or pleasure, and thus require
temporary
adhesion to the body.
A first type of such articles includes disposable, human waste management
devices such as urine, menstrual and faecal management devices.
Disposable Waste-Management Devices
Urine, menstrual or faecal management devices herein include bags having
an aperture and a flange surrounding the aperture for adhesive attachment to
the
urogenital area and/or the perianal area of a wearer. Any faecal, menstrual or
urine management device known in the art can be provided with an adhesive
composition according to the present invention. Such devices are described for
example in WO 99/00084 and WO 99/00085.
The urine, menstrual or faecal management devices herein also include
devices designed to be attached to artificial apertures in the body, such as
ostomy/colostomy devices.
The bag as used in such articles is a flexible receptacle for the containment
of urine, menstrual and excreted faecal matter.
The bag is designed to safely contain any entrapped material, typically it
will
be liquid impermeable, yet it may be breathable. The bag is designed of
sufficient
strength to withstand rupture in use, also when pressure on the bag is exerted
in
typical wearing conditions, such as sitting.
The bag may contain absorbent material. The absorbent material may
comprise any absorbent material which is capable of absorbing and retaining
liquids. The absorbent material may comprise a wide variety of liquid-
absorbent
materials commonly used in disposable diapers and other absorbent articles
such
as comminuted wood pulp, which is generally referred to as airfelt.
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_ __31
The human waste management device, in particular urine/menstrual
management devices according to the present invention, may also comprise an
additional acquisition layer. The acquisition layer is typically secured to
the inner
surface of bag. However, the acquisition layer may also be secured to the
flange,
or both the flange and the inner surface of bag. The acquisition layer is
preferably
positioned such that it separates the genitalia of the wearer from coming into
direct contact with the absorbent material. The acquisition layer is fluid
pervious
allowing urine/menses to readily pass through so that it may be absorbed by
absorbent material.
The bag is provided with an aperture whereby excreted matter is received
from the body prior to storage within the bag cavity. The aperture is
surrounded
by a flange and may be provided in any shape or size, such as circular,
oblong,
heart shaped and may be symmetrical or asymmetrical, preferably the aperture
has an oblong configuration either in the longitudinal or in the transversal
direction or in both directions, e.g. the contours of the aperture are in the
shape
of two ellipses with the respective main axes being substantially
perpendicular.
The flange comprises a garment facing surface and a wearer facing surface.
In a preferred embodiment these are two large, substantially flat surfaces,
however, the flange may also comprise projections designed to fit the perineal
or
coccygeal area of the wearer.
The flange should be made of soft, flexible and malleable material to allow
easy placement of the flange to the perianal area. Typical materials include
nonwoven materials, wovens, open celled thermoplastic foams, closed-cell
thermoplastic foams, composites of open celled foams and stretch nonwoven,
and films.
The adhesive composition of the present invention can be applied to the
wearer facing surface of the flange by any means known in the art such as slot
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coating, spiral, or bead application or printing. Typically the adhesive is
applied at
a basis weight of from 10 glm2 to 2500 g/m2, more preferably from 100 g/m2 to
2000 g/m2 most preferably from 200 g/m2 to 1500 g/m2 depending on the end use
envisioned. For example, for faecal management devices to be used for babies
the amount of adhesive may be less than for faecal management devices
designed for active adult incontinence sufferers.
Disposable Absorbent Articles
Another type of personal care articles herein include disposable absorbent
articles such as diapers, sanitary napkins or catamenials, pantiliners,
tampons,
perspiration pads. Absorbent articles are articles containing an absorbent
core,
and can be made by any of the ways usual in the art. The application of the
adhesive composition of the present invention to the wearer facing surface,
typically the topsheet surface of an absorbent article, should not cause major
problems to those skilled in the art since it can be provided by any well
known
techniques commonly used to apply adhesives. Most preferably the adhesive is
provided in a pattern of small incremental areas such as dots or similar.
This invention can be used beneficially on disposable absorbent articles
which are applied directly to the skin of a user. The article usually exhibits
absorbency for bodily fluids, the protection of the user's garments from
soiling, is
comfortable to the user, and is easy to produce and to package.
Other Personal Care Products
According to the present invention the adhesive composition herein may
also find application to other personal care products. The adhesives may for
example find utility to adhere functional articles which adhere to the skin
such as
cosmetic or pharmaceutical delivery articles which provide a substance to the
skin such as skin treatment substances, cream, lotions, hormones, vitamins,
deodorants, drugs; cosmetic or pharmaceutical delivery articles provide a
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33
substance to emanate away from the skin such as insecticides, inhalation
drugs,
perfumes, etc.; functional articles which are not necessarily attached to the
skin,
but which require a high residence time on the skin such as decorative
cosmetics, (lipstick, eye shadow, stage make-up) and cleaning articles (hand
cleaners, face masks and hygienic pore cleansers). Such articles are
preferably
non-absorbent for bodily liquids.
The adhesive may also in addition find application to attach articles to the
skin such as protective articles such as genital-, knee-, or elbow-protectors
or
bandages; clothing such as bras, surgical gowns, or parts of garments during
fitting at a tailor; nasal plasters; prosthesis such as breast replacements or
wigs;
cold wraps e.g. to provide pain relief from bruises and to reduce swelling;
thermal
wraps comprising thermal cells as disclosed for example in WO 97/36968 and
WO 97/49361 to provide relief of temporary and chronic pain such as neck wraps
as disclosed in for example US 5728146, knee wraps exemplified in
WO 97/01311, and back wraps as disclosed for example in US 5741318; hearing
aids; protective face masks (for the reduction or prevention of inhalation of
noxious substances); anti-snoring patches, ornamental articles such as
jewellery,
earrings, guises, tattoos; goggles or other eye wear, tapes, bandages,
dressings
of general utility, wound healing and wound management devices; and
biomedical skin electrodes such as ECG, EMG, EEG, TENS electrosurgery,
defibrillation, EMS and electrodes for facial/beauty applications; and
fixation
products and/or devices intended to affix patient catheters, tubing leadwires
cables, etc.
Other Articles
The adhesive compositions of the present invention can also find use in
articles which do not involve attachment to human skin, such as for example
wallpapers, carpets, adhesive tapes, etc.
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Examples.
The present invention will be illustrated with the following examples. All
compositions in all examples herein are given in percent by weight, unless
otherwise stated.
Example 1
A thermoplastic hydrophilic adhesive composition was prepared by melt
compounding between 140°C and 160°C in a heated blender for hot
melts, type
COMER 3000, available from Fratelli Erba s.r.l., Italy, the ingredients below:
Eastman AQ 14000 52%
(adhesive sulfopolyester available from Eastman)
Pebax 2533 SA 10%
(poly-ether amide available from Atofina)
Eastman A 2683 21
(tackifying resin available from Eastman )
Benzoflex 9-88 SG 16%
(di-propylene glycol di-benzoate plasticizer available
from Velsicol)
Irganox B 225 1 %
(antioxidant available from Ciba-Geigy)
The composition does not contain any ingredient soluble or dispersible in
the physiological saline solution used as test liquid for maximum liquid
absorption
capacity and liquid absorption rate.
The composition, tested for liquid absorption capacity and liquid absorption
rate according to the method described herein, had a maximum liquid absorption
capacity in 24 hours of 0.62 g/g. In the first 60 seconds of immersion in the
test
liquid, the composition absorbs 0.26 g/g i.e. 42% of its maximum liquid
absorption
capacity in 24 hours.
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The theological parameters of the composition at 37°C and at the
frequencies of 1 rad/s or of 100 rad/s were measured by using a rheometer RDA
II, available from Rheometrics, and were found to be:
G'37, 1 rad/s = 2.02 105 Pa
G"3~, 1 rad/s = 7.66 ~ 104 Pa
(G'3~, 100 rad/s / G'37, 1 radls) = 3.02
Example 2
A thermoplastic hydrophilic adhesive composition was prepared in a similar
way as in Example 1, except that the compounded ingredients were the
following:
H RJ 10127 10
/
(adhesive acrylic esters copolymer available from
Schenectady)
Pebax 2533 SA 15%
(poly-ether amide available from Atofina)
Eastman A 2683 20%
(taclcifying resin available from Eastman )
Uniplex 280 20%
(sucrose benzoate plasticizes available from Unitex
)
Benzoflex 9-88 SG 25%
(di-propylene glycol di-benzoate plasticizes available
from Velsicol)
Tri-ethyl citrate 9%
(plasticizes available from Aldrich)
Irganox B 225 1 %
(antioxidant available from Ciba-Geigy)
The composition contains 9% by weight of tri-ethyl citrate which is an
ingredient soluble in the physiological saline solution used as test liquid
for liquid
absorption capacity and liquid absorption rate. Therefore when tested for
liquid
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absorption capacity and liquid absorption rate, according to the Liquid
Absorption
Test method described herein, the reference initial weight of the "dry" film
before
contact with the test liquid was considered to be 91 % of the actually
measured
weights of the dry films in the tested samples, represented by the term ~Sdry
~ -
NWd,y ;] in the formula of the Liquid Absorption Test. Under such testing
conditions, the composition showed a maximum liquid absorption capacity in
24 hours of 0.48 g/g. In the first 60 seconds of immersion in the test liquid,
the
composition absorbs 0.28 g/g i.e. 58% of its maximum liquid absorption
capacity
in 24 hours.
The theological parameters of the composition at 37°C were found
to be:
G'37, 1 rad/s = 1.3~ 104 Pa
G"37, 1 rad/s = 4.4~ 103 Pa
(G'37, 100 rad/s / G'37, 1 rad/s) = 3.42
Example 3
A thermoplastic hydrophilic adhesive composition was prepared in a similar
way as in Example 1 and 2, except that the compounded ingredients were the
following:
PVPNA S630 10%
(adhesive copolymer available from ISP)
Hytrel 8171 15%
(poly-ether ester available from Du Pont)
Eastman A 2683 20%
(taclcifying resin available from Eastman )
Uniplex 280 20%
(sucrose benzoate plasticizes available from Unitex )
Poly-ethylene glycol di-benzoate 25%
(plasticizes available from Aldrich)
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Tri-ethyl citrate 9%
(plasticizer available from Aldrich)
Irganox B 225 1%
(antioxidant available from Ciba-Geigy)
The composition contains 9% by weight of tri-ethyl citrate and 10% by
weight of PVPNA copolymer which are both ingredients soluble in the
physiological saline solution used as test liquid for liquid absorption
capacity and
liquid absorption rate. Therefore when tested for liquid absorption capacity
and
liquid absorption rate, according to the Liquid Absorption Test method
described
herein, the reference initial weight of the "dry" film before contact with the
test
liquid was considered to be 81 % of the actually measured weights of the dry
films
in the tested samples, represented by the term [Sd,y ; - NWd,y ;] in the
formula of
the Liquid Absorption Test. Under such testing conditions, the composition
showed a maximum liquid absorption capacity in 24 hours of 0.83 g/g. In the
first
60 seconds of immersion in the test liquid, the composition absorbs 0.54 g/g
i.e.
65% of its maximum liquid absorption capacity in 24 hours.
The rheological parameters of the composition at 37°C were found
to be:
G'37, 1 rad/s = 5.04 104 Pa
G"37, 1 rad/s = 3.86 ~ 103 Pa
(G'37, 100 rad/s / G'3~, 1 rad/s) = 6.23
Example 4
A thermoplastic hydrophilic adhesive composition was prepared in a similar
way as in Examples 1 to 3, except that the compounded ingredients were the
following:
PVPNA S630 10%
(adhesive copolymer available from ISP)
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Hytrel 8171 7.5%
(poly-ether ester available from Du Pont)
Elvax 40-W 7.5%
(EVA copolymer, containing 40 % by weight of vinyl acetate,
available from Du Pont)
Eastman A 2683 20%
(tackifying resin available from Eastman )
Uniplex 280 20%
(sucrose benzoate plasticizer available from Unitex )
Poly-ethylene glycol di-benzoate 25%
(plasticizer available from Aldrich)
Tri-ethyl citrate 9%
(plasticizer available from Aldrich)
Irganox B 225 1
(antioxidant available from Ciba-Geigy)
The composition contains 9% by weight of tri-ethyl citrate and 10% by
weight of PVPNA copolymer which are ingredients soluble in the physiological
saline solution used as test liquid for liquid absorption capacity and liquid
absorption rate. Therefore when tested for liquid absorption capacity and
liquid
absorption rate, according to the Liquid Absorption Test method described
herein, the reference initial weight of the "dry" film before contact with the
test
liquid was considered to be 81 % of the actually measured weights of the dry
films
in the tested samples, represented by the term [Sd,y ; - NWd,y ~] in the
formula of
the Liquid Absorption Test. Under such testing conditions, the composition
showed a maximum liquid absorption capacity in 24 hours of 0.78 g/g. In the
first
60 seconds of immersion in the test liquid, the composition absorbs 0.49 g/g
i.e.
63% of its maximum liquid absorption capacity in 24 hours.
The theological parameters of the composition at 37°C were found
to be:
G'37, 1 radls = 1.2~ 104 Pa
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G"37, 1 rad/s = 1.1 ~ 104 Pa
(G'37, 100 rad/s / G'37, 1 rad/s) = 8.4
Test Method
Liquid Absorption Test.
The Liquid Absorption Test measures the maximum liquid absorption
capacity in 24 hours and the liquid absorption rate of the thermoplastic
hydrophilic homogeneous polymeric matrix comprised in the adhesive
composition of the present invention, as well as the maximum liquid absorption
capacity in 24 hours of the first polar cohesive thermoplastic polymer or
polymers
and of the second polar adhesive thermoplastic polymer or polymers comprised
in the matrix according to the present invention.
Apparatuses:
- Balance: analytical, capable of reading 0.001 g
- Oven: capable of maintaining uniform temperatures of 80°C ~
3°C
- Climatized room at 23°C; 50% R.H. (Relative Humidity)
Preparation of the film
The composition (i.e. the thermoplastic hydrophilic homogeneous polymeric
matrix, as defined herein) or the pure polymer under test is extruded from the
molten state onto siliconized paper in the form of a film having a thickness
of
about 150,~m. The film is then let to cool down to room conditions.
Alternatively, the components of the composition under test, or the pure
polymer under test, are/is dissolved in tetrahydrofurane (THF) or any other
suitable solvent at a concentration of 30% solid by weight for the
composition,
and of 10% solid by weight for the pure polymer, owing to the higher viscosity
of
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its solution. The solution is coated onto siliconized paper using a Mayer Bar
500
available from RI< Print-Coat Instruments.
The solution coated onto the siliconized paper is dried in the oven at
80°C ~
3°C for 30 minutes in order to completely evaporate the solvent. This
results in a
final film from the composition solution having the desired thickness of 150
Vim.
The film obtained from the pure polymer solution has a thickness of about
50,~m,
therefore the coating and drying process is repeated two more times on the
same
film in order to have a final film with the desired thickness of 150,um.
Preparation of the samples
The film is then laid and adhered onto a non absorbing, pure polypropylene
spunbonded nonwoven, having a nominal basis weight of 8 g/m2 and available
from the Company Linotec under the commercial code A08AJ0. Circular samples
having an area of 10 cm2 are cut using a circular cutter Model 230/10
available
from James H. Heal Ltd. Samples are conditioned at 23°C, 50% R.H. for
12 hours before testing. The test is performed at 23°C and 50% R.H.
A physiological solution is prepared by dissolving 0.9% by weight of NaCI
available from Aldrich in distilled water.
Ten samples for each composition or pure polymer are tested in parallel.
Each conditioned sample is placed in a container and completely immersed into
g of the above physiological solution at a temperature of 23°C. At
fixed time
intervals of 1 minute, 5 minutes, 30 minutes, 90 minutes, and 24 hours, the
samples are removed from the solution one at a time, and after all surface
water
is wiped off with a dry cloth they are immediately weighed to the nearest
0.001 g.
For intermediate times, the samples, after weighing, are placed again in the
liquid
and weighed again at the next time interval following the same procedure.
In parallel, samples made of the nonwoven alone, having the same shape
and area as the ones used in combination with the film and conditioned as
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explained above, are tested in the same way to detect the liquid possibly
retained, e.g. by capillarity, by the nonwoven.
All conditioned samples under test are also always weighed before contact
with liquid.
Each point of the absorption curve is obtained by the average value of the
ten samples used.
For each time interval the absorbed liquid at time "t", expressed as g/g of
composition or polymer, is calculated as follows:
Absorbed liquid = { [ Swet t - nlWwet t ~ / [ Sdry i - nlWdry i ~ - 1 ~
where:
Swet t = weight of the wet samples (film + nonwoven) after t minutes of
soaking
NWwet t = weight of the pure nonwoven sample after t minutes of soaking
Sd~, ; = initial weight of the conditioned sample (film + non woven) before
contact
with the liquid
NWd,y ; = initial weight of the pure conditioned nonwoven sample before
contact
with liquid
The maximum liquid absorbent capacity in 24 hours is represented by the
highest value obtained in the five measurements at the respective time
intervals.
The liquid absorption rate corresponds to the percentage of the maximum
absorption capacity in 24 hours represented by the liquid absorption capacity
at
1 minute.
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To note that, because the compositions according to the present invention
may contain certain amounts (i.e. overall not more than 25%, preferably not
more
that 15% and more preferably not more than 10% of the thermoplastic
hydrophilic
homogeneous polymeric matrix) of ingredients which are soluble or dispersible
into the test liquid, the parameter Sd,y; in the above formula, for the part
referred
to the weight of the film of the composition, is calculated with reference to
the
sole weight fraction of the composition which does not include the ingredient
or
ingredients which is/are known or suspected to be soluble or dispersible in
the
test liquid.
To note also, that in the above test the absorption capacity of a pure
polymer which is soluble or dispersible in the test liquid would be considered
to
be infinite. Compositions totally made of components which are soluble or
dispersible in the test liquid, on the other hand, are not within the scope of
the
present invention. A polymer is considered to be soluble or dispersible when
it is
soluble or dispersible in the test liquid in a concentration of at least 0.3%
by
weight.
