BANDES EN PLASTIQUE ET ARTICLE HYGIENIQUE

PLASTICS TAPES AND A SANITARY ARTICLE

Abrégé français

Couche ou autre article absorbant possédant des bandes de fermeture constituées par un matériau plastique, tel qu'un copolymère de propylène ou de polypropylène. Ces bandes possèdent chacune un ou deux bords arrondis par l'application de chaleur afin de les rendre moins coupantes. Ceci permet de limiter les risques d'irritation pour un enfant en bas âge ou un autre utilisateur, ainsi que de blessure occasionnée à toute personne venant en contact avec les bandes.

Abrégé anglais

Disclosed are flexible plastic tapes each having at least one rounded
edge, a method for forming the rounded edge by the application of heat, and
an absorbent article provided with such tapes. The edges are rounded to
reduce their sharpness in order to reduce the risk of irritation or injury to
a
wearer of the absorbent article and/or to any person coming into contact with
the tapes. The tapes have a thickness not greater than that at which the edge
would be sharp if it were not rounded. The tapes are relatively stiff and
formed from a plastic material such as polypropylene or polypropylene
copolymer.

Revendications

7
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE ARE CLAIMED ARE DEFINED AS FOLLOWS:
1. A flexible plastic tape having an adhesive coating covering at least a
portion of the tape, the tape being formed using plastic material, the tape
having at least one edge, wherein the edge is rounded as viewed in a cross-
section taken through the edge and wherein the tape has, at most, a
thickness equivalent to the thickness of a sharp edge.
2. The tape according to claim 1, wherein the thickness thereof is less
than 500 µm.
3. The tape according to claim 2, wherein the thickness thereof is less
than 200 µm.
4. The tape according to claim 3, wherein the thickness thereof is less
than 150 µm.
5. The tape according to claim 1, wherein the thickness thereof is of the
order of 100 µm.
6. The tape according to any one of claims 1 to 5, wherein both edges
which have been cut are rounded as aforesaid.
7. The tape according to any one of claims 1 to 6, wherein the plastic
material essentially consists of polypropylene.
8. The tape according to any one of claims 1 to 6, wherein the plastic
material essentially consists of a copolymer of propylene and a further
material the inclusion of which increases the softness of the tape.
9. The tape according to claim 8, wherein the plastic material is a


8
propylene/ethylene copolymer.
10. The tape according to claim 9, wherein the plastic material comprises
up to 10% by weight of ethylene.
11. The tape according to any one of claims 8 to 10, wherein the
copolymer is a random copolymer.
12. A method of rounding at least one edge of a flexible tape having an
adhesive coating covering at least a portion of the tape, the tape being
formed
using a plastic material, the tape having at least one edge, wherein the edge
is rounded as viewed in a cross-section taken through the edge wherein the
tape has, at, most, a thickness equivalent to the thickness of a sharp edge,
the method comprising the step of applying heat to the tape edge to be
rounded.
13. The method according to claim 12, wherein heat is applied by
contacting the edge to be rounded with a heated surface.
14. The method according to claim 12, wherein the edge is formed in a
rounded condition by cutting the tape from a sheet of the plastic material
using a heated cutter.
15. The method according to claim 12, wherein heat is applied by directing
hot air at the edge to be rounded.
16. The method according to any one of claims 12 to 15, wherein the tape
edge to be rounded is subjected to a temperature which lies in a range from
20 °C below to 50 °C above the crystalline melting point of the
plastic
material, where the plastic material is highly crystalline, or the softening
point
of the plastic material, where the plastic material has a low crystallinity.


9
17. A tape when formed according to the method of any one of claims 12
to 16.
18. An absorbent article which comprises a fluid-absorbing body portion
and at least one tape as claimed in any one of claims 1 to 11, for securing
the
article in place on a user.
19. The absorbent article according to claim 18, wherein the article is a
diaper.
20. The article according to claim 19, wherein a pair of the tapes is
provided.

Description

CA 02228455 2000-11-02
1
PLASTICS TAPES HAVING ROUNDED CROSS SECTION AND
METHODS FOR MAKING SUCH TAPES
Field of the Invention
This invention relates to flexible plastics tapes, and to sanitary articles
provided with such tapes. In particular the invention relates to diapers
provided with such tapes.
Background of the Invention
It is conventional to use flexible plastics tapes for holding a diaper in
place. This is so with diapers for infants, though such tapes are also used
for
adult diapers. In its unused condition the diaper has a pair of tapes, one on
each side, the tapes being secured to the rest of the diaper by, for example,
heat sealing. The tapes have free end portions which are coated with
adhesive, the adhesive surface each being covered prior to use with a
backing film. At the time of use, the backing films are removed and the tapes
adhered to the portion of the diaper which is then adjacent to them, the tape
connections then being located adjacent either side of the waist of the infant
or other user.
In order to provide adequate strength for the tapes, it is normal to use
a strong, relatively stiff plastics material, such as polypropylene, in the
form
of solid tapes produced, for example, by extrusion. The term "solid" here is
used to mean that the material of the tape is present throughout its cross-
section, as opposed, for example, to tapes formed of matted fibres. The
tapes are cut with a blade from a roll of material. Normally what is done is
to
start with a roll whose width is equal to the desired length of the tapes, and
cut it into lengths equal to the desired tape width. However, the tapes are
quite thin. They might be as much as 500 ~m in thickness, but would
normally be less than 200 Vim, and typically about 100 ~m or 150 ~,m.
They might be as little as 20 or 25 ~m in thickness. These values exclude
the adhesive coating. As a result of their thinness the edges of the
polypropylene tape are very sharp. The phenomenon is akin to that

CA 02228455 2001-06-19
2
encountered with paper. There is therefore a risk of the person putting the
diaper on the infant being cut by the tapes. Furthermore, it is found that
movement by the infant after the diaper is pus: on can result in the tapes
coming into contact with the infant's skin, which can be the cause of the
irritation.
The problem is one which is known in the art, but the only solution
proposed hitherto, as far as the present applicants are aware, is that
described in EP-A-379850, which involves cutting the initial plastic material
in a wave shape. This requires a specially constructed, and somewhat
complex, cutting apparatus.
It is an object of an aspect of the present invention to provide tapes in
which the above problem is avoided or mitigated in a simple and effective
manner, and a sanitary article, for example a diaper, using such tapes.
Summar~i of the Invention
In accordance with one embodiment of i:he present invention, there
is provided a flexible plastic tape having an adhesive coating covering at
least a portion of the tape, the tape being formed using plastic material, the
tape having at least one edge, wherein the edge is rounded as viewed in a
cross-section taken through the edge and wherein the tape has, at most, a
thickness equivalent to the thickness of a sharp edge.
In accordance with another embodiment of the present invention there
is provided a method of rounding at least one edge of a flexible tape having
an adhesive coating covering at least a portions of the tape, the tape being
formed using a plastic material, the tape having at least one edge, wherein
the edge is rounded as viewed in a cross-section taken through the edge
wherein the tape has, at, most, a thickness equivalent to the thickness of a
sharp edge, the method comprising the step of applying heat to the tape
edge to be rounded.
The tape typically has a thickness of less; than 500 Vim, more typically
less than 200 Vim, still more typically less than 150 Vim, and most typically
of
the order of 100 ~,m.
The invention further provides a sanitary article, for example a diaper,

CA 02228455 2000-11-02
2a
which comprises a fluid-absorbing body portion and at least one tape as just
defined.
Brief Description of the Drawings
Fig. 1 shows the edge of a polypropylene plastic film, of a type
conventionally used for diapers, before treatment with hot air at 350 deg. C.
Fig. 2 shows the film from Fig. 1 after treatment with a hot air at 350
deg. C.
Detailed Description of the Invention

CA 02228455 1998-O1-30
WO 97/06764 PCT/LTS96/13144
3
The invention will now be described in more detail,
During diaper assembling, closure tapes are cut from a roll by a
cutting device, and conveyed to a point at which they are fixed in
place on the diaper. According to the present invention, at least one
S edge, and preferably both edges of the tapes have their sharpness
reduced. One way of doing this is to arrange for the tapes to contact
hot metallic surfaces during the above mentioned conveying process,
so that they are softened or partially melted and thereby assume a
curved shape as viewed in cross-section. Alternatively, and this is
preferred, the hot metallic surfaces are formed by the cutting device
' itself, which is kept at the desired elevated temperature.
One point to note is that where rounding is achieved by contact
with a hot surface, the plastics material of the tape must have a
sufficiently low elongational viscosity to avoid the occurrence of
lagging, a phenomenon in which the hot surface pulls filaments of
material outwardly thereof and gives rise to an irregular surface. A
low viscosity, and/or the maintenance of the material at a sufficiently
high temperature for a sufficient length of time, also assists in
ensuring that surface tension effects are able to produce the desired
rounding of the edge.
Still more preferably, however, the rounding of the edges is
achieved by directing hot air at the edges of the tape. For example, it
has been found that air at 350 °C will produce the desired effect on a
conventional polypropylene tape of a type normally used on diapers.
' 25 In general it is desirable that only a very small portion of the
tape should be modified by heat in that way, e.g. a region up to
0.5 mm from the edge of the tape, whose overall width is in the
region of 30 mm. This is desirable both for aesthetic reasons, and to

CA 02228455 2000-11-02
4
avoid adversely affecting the functional characteristics of the main
part of the tape.
Where rounding is achieved by contact with a hot surface, -the
temperature of the hot surface with which the tape is contacted can
5 be different depending on the polymer nature and structure, on the
crystallinity fraction and on the process speed and so on the time of
contact. Similar considerations apply where hot air is used to achieve
rounding.
In the case of highly crystalline polymers, for example
10 homopolymer polypropylene, it is useful to work in a range between
20 °C below and 50 °C above its crystalline melting point.
In the case of polymers with lower crystailinity (e.g.
propyiene/ethylene copolymers) it is more meaningful to refer to the
softening point of the polymer !e.g. determined by the ring and ball
15 method according to ASTM E28-67) and work in a similar range
around it.
In a preferred embodiment the tape material is a polypropylene
copolymer containing up to 10% of ethylene. This makes the material
intrinsically softer, which itself helps in partially reducing the
20 sharpness of the edges. Moreover this lowers the softening point and
makes easier the application of the present invention. In a more
preferred embodiment this copolymer is a random copolymer. These
materials have a limited heat-shrinkability which helps the curving of
edges without giving macroscopic distortion to the tape, helping the
25 formation of rounded edges also in the Zones which do not reach a
level of temperature sufficient for softening or melting. For example,
MOPLEN*EP2 C30F is a random polypropylene copolymer containing
2% by weight of ethylene, and is available from HIMONT. * At 100 °C
* = Trade-mark

CA 02228455 2000-11-02
5
- it shrinks about 3%. Depending on the tape structure and process
conditions, this level of shrinkage can be useful in the present
invention.
In any case the degree of heat-shrinkage can be tailored to the
5 desired level by properly formulating the polymer. For example, by
blending the above mentioned polypropylene with the compatible
hydrogenated hydrocarbon resin ARKON * P-125 available from
ARAKAWA CO., it is possible to modify the behaviour as follows:
°~ of resin in PP % of heat-shrinkage at 100 °C
10 0~ 3%
5%
10% 16%
20% 31 %
30% 4.4%
15 In this way it is possible to choose the optimum level of heat
shrinkability useful in the particular application or process concerned.
However, the invention can also be applied even where the
plastics material has not significant heat shrinkability. In that case,
however, the temperature at which the edges are treated needs to be
20 sufficient to cause melting of the material, thus permitting surface
tension to cause the necessary rounding.
The invention is further illustrated in Figures 1 and 2 of the
accompanying drawings. These are photomicrographs showing the
edge of a polypropylene plastics film, of a type conventionally used for
25 diapers, respectively before and after treatment with hot air at
350 °G. The film on which the treatment was carried out was coated
on the side facing away from view with a layer of adhesive. In Figure
2 the layer can be seen quite clearly. In Figure 1 a broken line has
* = Trade-mark

CA 02228455 1998-O1-30
WO 97/06764 PCT/LTS96/13144
6
been added to mark the boundary between the adhesive and the
plastics material. Comparison of the two Figures clearly shows the
rounding which is achieved. It is also noteworthy that it is found that
the process does not adversely affect the adhesive.

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