Note: Descriptions are shown in the official language in which they were submitted.
CA 02308848 2000-OS-02
17256.5
PCT/EP98/06954 Translation of Application as
amended on December 31, 1999
MONOFILAMENT AND METHOD FOR PRODUCING BRISTLES AND
INTERDENTAL CLEANERS AND BRISTLES AND INTERDENTAL
CLEANERS MADE FROM SUCH MONOFILAMENTS
The invention relates to a monofilament with reduced
secondary binding forces of at least two polymers commonly
extruded in regular geometric relationship with substantially
axially extending border surfaces for producing bristles or
interdental cleaners, which are substantially axially
slittable by the action of mechanical forces. The invention
also relates to a method for producing bristles or
interdental cleaners from such monofilaments as well as to
brush-ware with such bristles and to interdental cleaners.
Bristles for brushware of random types, e.g. personal hygiene
and tooth-brushes, household brushes, industrial brushes,
paint brushes, etc., are nowadays mainly produced from
polymers, in that the polymer melt is extruded to continuous
monofilaments, the monofilaments are stretched and optionally
stabilized. The bristles are then produced from such
monofilaments by cutting to the desired length. As a rule,
the monofilaments, like the bristles, have a circular
cylindrical cross-section. For special applications bristles
with a different cross-section are known, e.g. an oval or
CA 02308848 2000-OS-02
2
polygonal cross-section. The monofilaments is then extruded
with a corresponding profile.
In many cases it is desirable to use bristles in a fibrous,
particularly fine fibrous structure at the use end. This e.g.
applies for brushware intended for the application of media
to surfaces or the like, e.g, paint brushes. Even if a fleecy
structure is sought, the bristle must be of a fine fibrous
nature. Of late in the dental sector it has been found that
conventional bristles of toothbrushes have an inadequate
cleaning action, because they do not penetrate the fine
cracks of the tooth surface and instead slide over the same.
Much the same applies for the cleaning action in the
interdental space.
In order to obtain a highly fibrous structure, proposals have
already been made for extruding the monofilament from polymer
blends. During the extrusion and subsequent stretching of the
monofilament, the polymer molecules are oriented in the
longitudinal direction of the monofilament. The primary
binding forces acting in the longitudinal direction ensure a
high tensile strength. The longitudinal orientation of the
molecules also effects the desired flexural elasticity. In
monofilaments made from a single polymer, the so-called
secondary binding forces, namely the forces transversely to
the molecular extension, are adequate in order to prevent a
unraveling or cleaving of the monofilament or bristle. In the
case of monofilaments from two different, blended polymers,
between the molecular chains of the polymers during
CA 02308848 2000-OS-02
3
stretching sliding zones occur, in which the secondary
binding forces are reduced. Such a monofilament or a bristle
produced therefrom can be unraveled by the action of
mechanical forces using knife-like tools. The resulting flags
have a very irregular shape, irregular cross-sections and
frayed circumferential surfaces. In a larger bundle of such
bristles admittedly a fleecy and good absorbing structure is
obtained, but the flags have uncontrolled strength
characteristics. They tear out, break off or wrap round. Such
unraveled bristles are consequently unsatisfactory and are
even unusable for many applications. For hygienic reasons
their use in toothbrushes is risky.
The same disadvantages are encountered in a known bristle
structure (W097/14830) which has a core and an envelope,
which are produced by the coextrusion of two different
polymers. The core material is mechanically or chemically
removed at the use-side end of the bristle in order to form a
deep pocket, which is intended to receive a dentifrice or
paint. In addition, a discription is given of flags which are
obtained by the unraveling of the envelope material to the
extent that it projects over the core. This unraveling takes
place in conventional manner by cutting with knives. The
bristles obtained show the same irregular structure.
Particularly for toothbrushes, bristles have already been
proposed which comprise a plurality of this fibers, similar
to textile fibers, and an envelope enveloping the fibers (DE
94 08 268 U1). The envelope and fibers can be coextruded as a
CA 02308848 2000-OS-02
4
filament. After cutting to the bristle length, the envelope
is removed at the use-side end of the bristle by mechanical
working or cutting, so that the fibers are free over a short
length. Quite apart from the complicated production of such
bristles, they can only be used to a limited extent. It is
particularly disadvantageous that there is a sudden change in
the bending behavior at transition from the fibers to the
envelope. If such bristles are used in applicators, there can
be damage to the surface due to the hard transition. The same
applies when such bristles are used in toothbrushes in
connection with the action on the teeth and gums. In
addition, the fibers are bending-limp, so that they do not or
do not adequately penetrate deeper cavities, intendental
spaces etc. In the case of permanent stressing, the fibers
also easily break off at the edge of the envelope.
W096/39117 discloses an intendental cleaner made from
monofilaments which are co-extruded in defined geometric
relationship. Each monofilament comprises at least two
polymer components leading to reduced secondary binding
forces at the borders between neighboring monofilaments. The
secondary forces are reduced through the action of axial
tensile forces to produce a multi-fibered fleecy structure
similar to that of dental floss.
Conventional textile fibers (US-A-3117362) are produced
having glossy, sharp-cornered structures by co-extruding
various polymers, each of which has a suitable cross
sectional shape, which bond to each other at their bordering
CA 02308848 2000-OS-02
surfaces and which are separated through introduction of a
solvent which dissolves one of the polymers.
The problem of the invention is to propose a monofilament of
at least two commonly extruded polymers, which is suitable
for producing slitted bristles or interdental cleaners with
reproducible strength characteristics and flags or slits
which are definable according to number, shape and
dimensioning. The invention is also directed at a method for
the production of bristles or interdental cleaners from such
monofilaments .
A monofilament solving this problem and having the features
of the precharacterizing part of claim 1 is characterized in
accordance with the invention in that the border surfaces are
border layers having reduced secondary binding forces,
wherein the monofilament comprises a matrix of polymers whose
physical and chemical properties define the properties of the
bristle or interdental cleaner, wherein the second polymer is
a thin layer imbedded into the matrix as a border
layer.
As a result of the geometry of the boundary layers it is
possible to forecast in what way the monofilament for example
for an interdental cleaner or the bristle produced from the
monofilament by cutting to length will be disintegrated or
split by the action of mechanical forces. The slits or flags
occur precisely with the predetermined contour given by the
extrudate geometry. As the boundary layers extend in the
CA 02308848 2000-OS-02
6
longitudinal direction of the monofilament, over their entire
length a single flag has the same shape and same cross-
section. Thus, all the flags have the same strength
characteristics, in particular an identical bending behavior
and identical tensile strength. However, it is possible by
appropriately defining the geometry to produce flags with
different cross-sections. As the monofilament or bristle,
under the action of mechanical forces, exclusively and
precisely splits at the boundary layers, the flags form edges
on the facing surfaces depending on the cross-section which
assist the cleaning action. A bristle split in this way is
consequently more effective at its circumferential surface
than conventional spreading of the bristle flags. The
congruent shapes prevent excessive spreading of the bristles.
Each bristle acquires in a densely packed bundle a
monofilament-like shape again and the full effect of the
flags only results from the axial or radial pressure. Thus,
media can be well absorbed and delivered on application by
pressure action.
This makes it possible to produce bristles, whose flags have
the desired characteristics of conventional bristles. During
splitting no or few fine parts are formed, so that there is
no need for an extensive cleaning of the bristle. Definitely
flagged and definitely slit monofilaments for interdental
cleaners are obtained, with which the proceeding of splitting
or slitting can be avoided.
CA 02308848 2000-OS-02
7
The polymer of the matrix as well as of the thin layers can
also be a copolymer or a polymer blend. These aforementioned
advantages are achieved in a particularly optimum form if the
thin layers comprise at least partly the polymer of the
matrix. In this case the polymer or the bristle tears at the
weakest point when force is exerted, namely roughly in the
center of the thin layers, but the adhesiveness of the part
of the matrix polymer in the thin layer at the resulting,
neighboring flags is adequate to avoid the formation of fine
parts.
Preferably the thin layers have a thickness of a few Vim.
Practical extrusion tests have revealed that such thin layers
can be coextruded with the polymer of the matrix.
The two polymers can be present in roughly equal parts in the
thin layers.
The specific definition of the geometry is determined by the
desired characteristics of the bristle and interdental
cleaner. Thus, the thin layers in the matrix can extend to
the circumference of the monofilament, so that the
monofilament can be split or slit with a relatively limited
force action.
It is possible instead of this for the thin layers to
terminate in the matrix at the distance from the monofilament
circumference. In this case a somewhat greater force action
is required, but it is advantageous that the resulting flags,
CA 02308848 2000-OS-02
8
also in the edge region, comprise the matrix material, i.e.
have the same wear characteristics as the envelope of the
bristle or the flags.
Optionally the monofilament matrix can have a third polymer
incorporated into said matrix and which is mainly used for
influencing the strength characteristics of the resulting
flags.
As is normally the case with bristles, the monofilament can
be circular, but can also have a non-circular cross-section.
Particular mention is made of polygonal cross-sections, which
are more effective in their cleaning action than circular
cross-sections.
In this case the thin layers can run out to the corners of
the polygonal cross-section, so as to give relatively sharp
edges with an edge angle smaller than 90°.
Instead the thin layers can also run out to the surfaces of
the polygonal cross-section and it is then possible to obtain
edges with an angle of approximately 90°.
According to a preferred development the matrix comprises a
polyamide and the thin layers a polyolefine, particularly
polypropylene or polyethylene. This material pairing has at
the interfaces adequately high secondary binding forces in
order to prevent an untimely tearing or unraveling during the
CA 02308848 2000-OS-02
9
processing and use of the bristles. However, the polymer
union tears in the case of a strong, planned force action.
The method according to the invention for producing bristles
from the aforementioned monofilament comprises the following
steps: coextruding the at least two polymers to a
monofilament, stretching and optionally stabilizing the
monofilament, cutting the monofilament to bristles of the
desired length, splitting the bristles at their use ends
along the boundary layers on a limited length by the action
of mechanical forces transversely to the axis of the bristle.
Another method suitable for producing bristles as well as
interdental cleaners from the aforementioned monofilament
comprises the following steps: coextruding the at least two
polymers to a monofilament, slitting, following extrusion,
stretching and optically stabilizing, the monofilament along
the boundary layers on a locally limited length for forming
short slits by the action of mechanical forces transversely
to the axis of the monofilament. With the method in
accordance with the invention, crack-like slits can be formed
in the monofilament envelope and these can be used for
receiving media. In the case of toothbrushes or interdental
cleaners these are more particularly dentifrices or dental or
antibacterial preparations. As a result of the slitting
action, the monofilaments envelope has an increased
roughness.
Interdental cleaners of arbitrary length can be manufactured
from the monofilament described above. The same measure can
CA 02308848 2000-OS-02
- 10
naturally be carried out on the bristle cut to length from
the monofilament. The location of slitting and the extension
of the slits can be matched to the bristle length, in order
to either prevent or encourage in planned manner a split ting
of the bristle end. For example, only the bristle end may be
split. The slits made on the envelope can be used for the
further splitting of the bristle following the wearing away
of the flags. As a function of the nature and number of
incorporated layers, a corresponding number of flags is
formed at the use end of the bristle.
For processing monofilaments into interdental cleaners of
arbitrary length, a variation of the method provides for
compressing the monofilament in its axial direction during or
after the action of the mechanical forces. Thereby the
lengthwise slitted areas and the strips limiting the slits
respectively are rendered bulged.
The mechanical forces are preferably applied to a greater
part of the circumference of the monofilament or bristle to
ensure that an action takes place on all the boundary layers
of the polymers.
The slitting of the monofilament or the splitting of the
bristles preferably takes place by impact forces. Instead of
this, it is also possible to use squeezing or torsional
forces. These forces can be applied to the cut to length
bristle or also simultaneously to groups of bristles, e.g.
CA 02308848 2000-OS-02
~ 11
bristle bundles, before or after the fixing thereof to the
bristle carrier of the brush.
Preferably the bristles are rounded at their use-side ends.
This can take place before and/or after splitting. In
accordance with a further preferred embodiment of the method,
the several ends obtained after splitting are provided with a
marking optically indicating the usable length. This
indicates to the user that the bristle has become worn up to
the marking, i.e. following the wearing of the split ends the
use characteristics suddenly change, because then the much
more bending-stiff cross-section of the complete bristle
comes into action. The split ends also become ever shorter
and consequently mechanically more aggressive. Such an
indication is particularly appropriate in the case of
toothbrushes, personal hygiene brushes, etc.
The invention is described in greater detail hereinafter
relative to embodiments and the attached drawings, wherein
show:
Figs. 1 to 5 Different cross-sections of a monofilament.
Fig. 6 A view of a bristle with a split, use-side end.
Fig. 7 A bristle or interdental cleaner with a slit
envelope.
CA 02308848 2000-OS-02
- 12
Fig. 8 A further form of the cross-section of a
monoffilament.
Fig. 9 A view of an interdental cleaner in an
alternative form.
The monofilament 1 according to fig. 1 has a circular cross-
section and is produced by coextrusion of at least two
polymers. It comprises a matrix 2 of a polymer determining
the characteristics of the bristle and thin layers 3
incorporated in a geometrical shape, in this case in the
shape of a cross and which comprise a different polymer or a
blend thereof with the polymer of matrix 2. The secondary
binding forces, i.e. binding forces at right angles to the
longitudinal extension of the monofilament, are reduced in
the regions of the thin layers 3 or the borders of the matrix
2. In the represented embodiment the thin layers 3 run out at
the circumferential surface 4 of the monofilament, but can
also terminate at a short distance therefrom.
The polymer for matrix 2 can in particular be polyamide (PA),
whereas the thin layers 3 e. g. comprise a PA/PP of PA/PE
polymer blend.
In the embodiment according to fig. 2 the thin layers 3 are
incorporated in the form of a three-armed star into the
matrix 2, whilst fig. 3 shows a monofilament 1 with a
polygonal, namely triangular cross-section. In this
embodiment the incorporating thin layers, which extend
CA 02308848 2000-OS-02
- 13
outwards from the center here, run out in the corners of the
polygon. They can a naturally also terminate on the surfaces
between the corners.
In the embodiment according to fig. 4 with matrix 2 of the
monofilament 1 is extruded a further polymer from among the
several possible polymers in such a way that it is fully
incorporated into the matrix. For example, these can be
thread-like structures 5, which following the production of
the bristle or the splitting or slitting thereof influence
the bending behavior or strength of the resulting flags.
Fig. 5 shows a flat, rectangular monofilament 1, in which the
thin layers 3 are applied in grid or raster-like manner, so
that from the monofilament can be produced a plurality of
substantially rectangular flags. Finally, figure 8
illustrates a cross section through a monofilament with which
the matrix 2 comprises four equal outer portions having
circular segment cross sections and a central core which are
bordered by correspondingly disposed thin layers 3.
Fig. 6 diagrammatically shows a bristle 6, produced by
cutting a monofilament e.g. of fig. 2 to length, which is
split on its use-side end by the action of mechanical forces,
so that individual flags 7 are obtained, whose shape
corresponds to that of the monofilament areas forming the
matrix 2. The same number of flags are formed as the matrix 2
is divided up by thin layers 3. The usable length of the
CA 02308848 2000-OS-02
14
flags can be optically marked by a transverse line shown in
Fig. 6.
In the embodiment of fig. 7, the mechanical forces are
applied to the circumferential surface of a monofilament with
identical spacings or to a bristles at a distance from the
use-side end. Through the thickness of the layers and the
magnitude of the force and/or the frequency of its
application, it is possible to ensure that the envelope of
the monofilament or the bristle 6 only tears over a locally
limited length and that slits 8, 9 and 10 are formed. These
slits are roughly in a row, namely in the areas formed by the
thin layers 3. In this variant the slits tear at the bristle
end, accompanied by the formation of flags. The flags
constantly re-form as the bristle wear increases.
The monofilament according to fig. 7 can be used with a
random length as interdental cleaner (dental floss). The
slits can receive dentifrice, antiseptics or
antibacterizides. In the case of a interdental cleaner it is
recommendable to axially upset the monofilament as shown in
fig. 9 so that the matrix strips 10 delimiting the slits 9
are bulged outwardly.
With all the embodiments specified the matrix polymer can be
dyed with different colors in the various cross-section parts
2 delimited by the thin layers 3.
