Note: Descriptions are shown in the official language in which they were submitted.
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A GROOMING IMPLEMENT
Field of the Invention
The present invention relates to a personal grooming implement, such as a
toothbrush,
comprising a segmented, articulating head attached at one end to a handle, the
segments
being disposed longitudinally along the head and jointed to each other by an
elastomer
which is preferably fused to each segment. The joint nearest the free end of
the head has
a groove on its upper surface to improve its flexibility relative to the other
joints, thus
providing for more uniform bending of the head.
Background of the Invention
The configuration of human teeth requires that the ideal bristle contour for
toothbrushes
for brushing the buccal or outside surfaces of teeth be concave and that the
ideal bristle
contour for brushing the lingual or inside surfaces of teeth be convex. Most
commercial
brushes have a single piece head which is of comparable thickness to the
handle and
which is relatively rigid and of a fixed curvature or configuration.
A further drawback of conventional brushes is that pressing the brush
sufficiently hard
against the teeth to get good cleaning risks damaging or discomforting the
softer,
adjacent gums. To a certain extent this can be solved by modifying the
configuration of
the brush, or by varying bristle hardness or length, though again, a single
configuration
cannot be optimum for all circumstances.
Recently, there has been considerable interest in providing brushes with a
degree of
flexibility in the head. The means for achieving this has generally been to
provide for
one or more articulating joints, often partially or wholly filled with
elastomer in order to
modify the flexibility of the joint or to prevent the ingress of toothpaste.
Illustrative of
the art are WO 92/17092, WO 92/17093, WO 96/02165, WO 97/07707, WO 97/20484,
WO 97/24048, WO 97/25899, WO 97/25900, WO 98/07349, WO 98/12948,
WO 98/27846 and WO 98/27847.
One of the difficulties encountered in making an articulated, multi-segment
head in
which the joints between segments are longitudinally disposed along the head,
is in
controlling the relative flexibility of the joints between segments such that
the head
bends in a uniform curve. In practice, unless special steps are taken, there
is a tendency
for most bending to occur at the joint nearest the handle. WO 97/25900,
referenced
above, recognises this problem and discloses as a solution that integral
hinges between
the segments nearer to the handle are desirably less flexible than those which
are more
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remote from it. This approach cannot be adopted however for brushes such as
those
described in WO 98/27846, also referenced above, where there are no hinges
between
segments and the elastomer is relied upon for bonding segments together.
Decreasing
the amount of elastomer used can put at risk the overall integrity of the
brush head.
Furthermore, unless the head thickness is also reduced, which may make it
impractical to
insert bristle tufts, the removal of elastomer creates voids which may fill up
with
toothpaste and make the brush unsightly or unhygienic. WO 98/27847 discloses
the use
of elastomers of different hardness as a means of controlling individual joint
flexibility,
in particular the use of a softer elastomer at the tip joint. The use of
multiple elastomer
types has the disadvantage however of complicating the manufacturing
procedure.
It has now been found that removal of elastomer from the head surface which
carries the
bristles or other personal grooming means, is surprisingly efficient at
improving the
flexibility of the brush in the direction of bending of the head away from the
face bearing
the grooming means. Consequently, the flexibility of the tip joint can be
improved
relative to other joints whilst keeping to a minimum the amount of elastomer
removed.
It is accordingly an object of this invention to provide a multi-segmented
head for a
personal grooming implement, such as a toothbrush, which provides uniform
bending of
the head way from the bristles or the like whilst retaining high strength and
minimising
dirt build-up.
Summary of the Invention
According to the present invention there is provided a personal grooming
implement, the
implement comprising a handle having two ends, and an articulated head
connected to
one end of the handle, the head having handle and tip ends, upper and lower
faces and
comprising three or more segments, the handle end being connected to the
handle, the
segments being spaced along a longitudinal axis defined by the handle and tip
ends of the
head and being joined to adjacent segments by joints made of an elastomer
which extend
transversely across the head, whereby each segment can articulate relative to
neighbouring segments, at least one of the segments comprising a grooming
means on an
upper face thereof, the elastomer in each joint extending to the lower face of
the head,
characterised in that, in the joint nearest the tip end of the head, the
elastomer only
partially fills the joint such that there remains a groove in the upper face
of the head, the
remaining joints being completely filled with elastomer or partially filled
such that
grooves on the upper surface are of lesser depth than that of the tip joint,
the flexibility of
the tip joint being thereby increased relative to remaining joints.
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The head of the implement can bend uniformly away from the grooming means, yet
at
the same time employing sufficient elastomer to maintain head integrity and
resilience
over a long period and avoiding deep voids which might accumulate dirt.
Detailed Description of the Invention
The personal grooming implement of this invention can be any implement of the
type
that has a sufficiently elongated handle for the user to grip and, disposed at
one end of
the handle, a segmented head comprising a grooming means. The implement can,
for
example be a toothbrush, hairbrush or a massaging implement. More especially,
it is a
toothbrush.
At least one of the head segments comprises a grooming means. Preferably, each
segment comprises a grooming means. The grooming means can take the form of
bristles, combing teeth, polishing materials, rubber massage pads and the
like. In
preferred embodiments herein the implement is a toothbrush wherein the
grooming
means comprises a plurality of bristles extending from the segments of the
head.
The head can be detachably connected to the handle, for example to permit
replacement
of the head when bristles become worn, in which case the head has a point of
attachment
for the handle. Alternatively, a first head segment can be continuous with the
handle. In
a preferred embodiment the handle and a first head segment are a single piece
formed by
injection moulding. Preferably the handle and all of the head segments are
formed
within a single mould by injection moulding. The head is of generally
flattened
construction having opposed upper and lower faces and the head also has a
transverse
axis lying orthogonal to the longitudinal axis and generally parallel to the
opposed upper
and lower faces. References to transverse or longitudinal herein refer to
directions which
are respectively parallel to these transverse and longitudinal axes, unless
indicated
otherwise.
The head and handle are generally made of relatively non-compressible
materials,
preferably with a modulus of elasticity of at least about 500 MPa, more
preferably at
least about 1000 MPa, which are conventional in the manufacture of
toothbrushes,
especially plastics materials. Suitable plastics materials include, for
example,
polyamides and polypropylenes. Polypropylene is preferred. Suitable
polypropylenes
include the material 'Polypropylene PM 1600' (marketed by Shell), having a
modulus of
elasticity (ISO 178) of 1500 MPa and Apryl 3400 MA1 from Elf Atochem.
Preferably, a
foaming agent such as Hydrocerol HP20DP from Boehringer-Mannheim is mixed with
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the polypropylene at a level of from about 1% to about 3%, preferably from
about 1.5%
to about 2.5%, by weight of the polypropylene. The foaming agent assists the
flow of the
polypropylene during moulding. The handle itself is generally rigid and may be
of a
shape which is conventional in the manufacture of toothbrushes. Optionally,
the handle
may comprise a neck portion which is more flexible than the rest of the
handle.
The head comprises three or more segments, one of which may be coextensive
with the
handle. Preferably there are three or four segments, more preferably four.
Many more
than this increases the manufacturing complexity and, in a toothbrush where
bristle tufts
are inserted only into the head segments, makes it difficult to achieve a
sufficiently high
tuft density on the brush head. The head segments are disposed in longitudinal
sequence
along the head so that a longitudinal line drawn from the handle to the tip
end of the head
passes through the first head segment then the second head segment and so on.
More
especially, there is a first head segment which is connected to or continuous
with the
handle and two or more additional head segments arranged in longitudinal
sequence
towards the tip or free end of the head. In general, each head segment will be
made of
the same material which will preferably be the same material as the handle so
that they
can all be made in a single injection moulding step.
In the finished implement, all the head segments are connected by joints
comprising an
elastomer. Elastomers are well known in the art of injection moulding. The
term
"elastomer" herein refers to a material which is both elastically compressible
and
elastically extensible. For the purposes of this invention, suitable
elastomers have a
modulus of elasticity of less than 500 MPa. Preferred eiastomers for use
herein have a
modulus of elasticity of less than about 300 MPa, especially preferred are
thermoplastic
elastomers with a hardness of about 30 Shore A to 74 Shore D', polyolefin
types such as
styrene-ethylene-butylene-styrene (SEBS) are preferred, for example those
based on
Kraton~ G, but other classes of elastomer, such as polyurethanes and
polyamides, can
also be used. An exemplary elastomer is 'PTS Thermoflex 75' (marketed by
Plastic
Technologie Service, Germany), having a modulus of elasticity (ISO 178) of 100
MPa
and a hardness (ISO 868) of 80 Shore A. Elastomers PL12291, PL12292, and
PL12293
(marketed by Multibase, Saint Laurent Du Pont, France) are also suitable for
use herein.
In general, choosing the elastomer so that is based upon the same chemical
class of
polymers as material of the head segments assists in fusing the elastomer to
the head
segments. For example, when the head segments are made from polypropylene, the
elastomer is preferably based upon a polyolefin. The elastomers can optionally
be mixed
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with a suitable plasticiser or foaming agent to make them more compressible.
The colour
of the elastomer material can be the same as that of the head segments, or it
may be
different thereby achieving a distinctive striped or otherwise patterned
appearance.
The elastomer can be connected to the head segments and/or handle by any
suitable
means, such as by adhesive or by thermal fusion. The elastomer is preferably
incorporated into the implement of the present invention by injection
moulding, such that
the elastomer becomes fused to the head segments and/or handle. Preferred
injection
moulding conditions and bonding strengths are described in WO 98/27846 and
WO 98/27847.
In highly preferred embodiments herein the head comprises at least one
longitudinal
groove which connects the transverse elastomer joints and permits the
elastamer to flow
from one band to the other during an injection moulding process. In an
implement with a
co-moulded handle, this longitudinal groove can extend along the handle so
that the same
elastomer injection point in the mould that is customarily used for supplying
elastomer to
form handle grips can also be used to inject the elastomer for the segment
connecting
means of the head. Normally the groove will not extend through the full depth
of the
handle or head at all points, though it can do so where desired, for instance
to provide
opposed grip points on top and bottom surfaces of the handle.
The joints between segments can be strengthened by integral hinges, preferably
as
described in WO 97/25900, it is preferred however that the elastomer is
essentially the
only means connecting the segments, by which is meant that the elastomer is
the sole
mechanical link between one segment and the next. By sole mechanical link,
what is
meant is that there are no continuous, non-elastomeric links such as bridges
or springs
connecting the segments. The elastomer may, however, have other materials
dispersed
within it, such as flecks of metal or pigments which might be used, for
example, to
provide a distinctive appearance or modify the properties of the elastomer.
These
additional materials will generally make a negligible contribution to the
mechanical
connection between the segments and/or handle such that their removal would
not
materially alter the strength of connection.
The head has upper and lower faces and the elastomer joints extend
transversely across
the head and between the faces. The elastomer jointing extends essentially all
the way to
the lower face of the head so that preferably it is flush with the head
segments. It is to be
recognised however that a small, functionally inconsequential degree of
shrinkage may
occur. In the transverse direction, though partial elastomer filling of the
joints can be
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effected, the elastomer preferably extends the full width of the head in order
to avoid
exposed edges of the segments.
It is an essential feature of the invention that in the joint nearest the tip
end of the head
(the tip joint), the elastomer only partially fills the joint such that there
remains a groove
in the upper face of the head. This can of course be arranged by suitable
construction of
the mould for the preferred injection moulding process. The remaining joints
can be
completely filled with elastomer or partially filled, provided that other
grooves on the
upper surface are of lesser depth than that of the tip joint, the flexibility
of the tip joint
being thereby increased relative to remaining joints, especially for bending
of the head
away from the upper face.
The depth of groove in the tip joint is suitably from about 5 to about 20%,
preferably
from about 7 to about 18%, more preferably from about 10 to about 15% of the
depth of
the head, which is the distance between the upper and lower faces. For a
typical
toothbrush head the absolute depth of the groove is generally in the range
from about 0.3
to about 1.5 mm, preferably from about 0.5 to about 1 mm, more especially
about 0.7
mm.
In one embodiment according to the invention the head comprises three
segments, of
which one is integrally connected to the handle, there being two joints, the
joint nearest
the handle being wholly filled with elastomer. In a preferred embodiment the
head
comprises four segments, of which one is integrally connected to the handle.
There are
three joints, a first joint nearest the handle, a second joint and a tip
joint. The elastomer
can wholly fill the first and second joints, preferably there are grooves in
the upper
surface of the head at the second and tip joints, the groove of the tip joint
being deeper
than that of the second joint. A suitable groove depth for the second joint is
from about 3
to about 12%, preferably from about 5 to about 10%, more preferably from about
6 to
about 9% of the depth of the head. The absolute depth of the groove in the
second joint
is generally in the range from about 0.2 to about 1 mm, preferably from about
0.3 to
about 0.6 mm, more especially about 0.4 mm, for a typical toothbrush head.
The elastomer joints can vary in thickness, either from one band to the next
or even
across the width or along the depth of the band. Suitably, their thickness,
measured
along the longitudinal axis, is in the range from about 0.1 mm to about 10 mm,
preferably from about 0.3 mm to about 5 mm, more preferably from about 0.5 mm
to
about 3 mm. The bands of elastomer can be linear or non-linear. Preferably
they are
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non-linear and take the fonm of chevrons or waves whose apices point towards
the free
end of the head.
In preferred embodiments herein, the upper face of the head has a concave
profile along
the longitudinal axis of the head, though the radius of curvature may vary
along the
length of the head. The radius of curvature is preferably from 10 to S00 mm,
more
preferably from 15 to 250 mm, especially from 25 to 150 mm.
The invention will now be described by way of example only, with reference to
the
accompanying drawings in which:
Fig. 1 is a longitudinal, vertical cross-section through the centre of the
head of a
toothbrush according to the invention; bristles are omitted for the sake of
clarity.
Fig. 2 is a plan view of the lower face of the head of a toothbrush according
to the
invention.
Referring to the figures, a toothbrush head 1 has an upper face 2 and lower
face 3 which
are substantially parallel to each other and about S mm apart. The head has a
handle end
4 and tip end 5, the handle end being integrally formed with an elongated
polypropylene
handle 6. The head comprises four longitudinally spaced, polypropylene
segments 7, the
first of which is continuous with handle 6. The segments are connected only by
bands of
a SEBS elastomer 8, having a hardness of 60 Shore A, which extend transversely
across
the head and between the upper face 2 and lower face 3. A longitudinal groove
9 extends
along the bottom face of the head and the handle, connecting the bands of
elastomer so
that they can all be foamed from a single elastomer injection point. The bands
of
elastomer are of generally uniform thickness along the longitudinal direction
but broaden
forwards and outwards at .the lower face to provide improved keying of the
elastomer to
the polypropylene segments. The upper face of the head includes tuft holes 10
which for
tufting with bristles. In preferred embodiments, the brush head has bristles
extending
from each of the four segments. Upper face 2 is slightly concave along the
longitudinal
axis, having a radius of curvature of about 145 mm. The bands of elastomer 8
form the
joints between segments 7 allowing them to articulate relative to each other,
affording
sufficient flexibility to the brush head that it can bend along the
longitudinal axis until
the top face becomes convex. In doing so the elastomer is stretched along the
top face.
The elastomer on this face can stretch to more than 200% of its unstressed
length without
any observable loss of attachment of the elastomer to the segments. The head
is able to
repeatedly flex to this extent and back to the rest state through 75,000
cycles, without any
detachment of the elastomer from the head segments.
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In order to improve the uniformity of bending, the joint between the third and
tip
segments is not completely filled with elastomer, such that there is a groove
11 which
has a depth of about 0.7 mm, in order to improve the flexibility of the joint.
There is also
a shallower groove 12, about 0.4 mm deep between the second and third
segments, the
joint between the first and second segments being wholly filled with
elastomer.
The toothbrush is made by sequential injection moulding of first the
polypropylene to
form the handle 6 and segments 7 and then in a second step the elastomer is
injected at a
temperature of 255°C, thereby becoming fused to the polypropylene.
After the brush has
cooled the bristle tufts are inserted by the stapling technique into pre-
formed tuft holes
10.
