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, more particularly to a personal grooming implement having a two
component head wherein the head comprises two or more segments, at least one
of
which is connected to an adjacent segment essentially only by an elastomer
which is
fused to the adjacent head segments.
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 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.
WO 92/17092, WO 92/17093 and WO 96/02165 disclose toothbrushes having
resiliently flexible, bristle-bearing heads, the heads, in certain embodiments
being in
the form of two or more segments which are flexibly and resiliently linked to
each.
Gaps between the segments can be wholly or partially filled with an elastomer.
In
brushes of this type of construction the bond between the elastomer and the
body can
be subject to great stress, repeatedly applied through frequent use. In most
of the
embodiments, the segments are linked to each other by hinges or spines of the
same
material as the brush body. In practice, such hinges or spines can cause
difficulties
in conventional injection moulding operations since the hinge or spine is
subject to
fracturing. Further, the presence of non-elastic links in flexible joints can
lead to
permanent deformation of the joint through repeated flexing, as a result of
plastic
flow within the non-elastic link. WO 92/17092 discloses some embodiments in
which the gap between adjacent head segments is closed by a diaphragm of an
elastomeric material. It is not clear in any of these embodiments, however,
how the
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2
closure is made or whether it is intended that the diaphragm will
substantially
contribute to the structural integrity of the brush head.
It has now been found that a sufficiently strong bond can be made between
elastomer
and the material of the brush body that even a flexible head, which is subject
to
many cycles of repeat flexure throughout its use, can be constructed that
relies
principally on the elastomer for holding the head segments together.
It is accordingly an object of this invention to provide a segmented head for
a
personal grooming implement, such as a toothbrush, which relies principally on
the
elastomer for holding the head segments together.
It is a further object of this invention to provide a segmented head for a
personal
grooming implement which can flex resiliently and which has good long-term
durability.
It is yet a further object of this invention to provide a segmented head for a
personal
grooming implement which is suitable for short cycle time injection moulding.
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 at one end
of
the handle a head comprising two or more segments, at least one of the
segments
comprising a grooming means, the segments being made from material having a
modulus of elasticity of at least 500 MPa, the head being characterised in
that at
least one of the segments is joined to an adjacent segment or to the handle by
a
connecting means consisting essentially of an elastomer having a modulus of
elasticity of less than 500 MPa, the elastomer being connected to the adjacent
segments and/or to the handle so that the elastomer can be stretched to about
120%
of its unstressed length without separation of the elastomer from the head
segments.
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
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J
bristles, combing teeth, polishing materials, rubber massage pads and the
like. In
preferred embodiments heroin 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 detachab(y 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
continuos with the handle. In a preferred embodiment the handle and first head
segment is a single piece farmed by injection moulding. Preferably the handle
and
all of the head segments are formed within a single mould by injection
moulding. In
any case the handle has a longitudinal axis extending between its two ends.
This
axis also defines the longitudinal axis of tire head which is co-extensive
with the axis
of the handle. Preferably the head is of generally flattened construction
having a pair
of opposing faces and the head also has a transverse axis lying orthogonal to
the
longitudinal axis and generally paralle;; to the opposed 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 prefe ~ed. Suitable poly-
propylenes include the material 'Polypropylene PM 1600' (marketed by TMhell),
having a modulus of elasticity (ISO 178) of 1500 MPa and Apryl 3400 MA7 from
Elf Atochem. Preferably, a foaming agent such as Hydrocerol HP20DP from
Boehringer-Mannheim is mixed with 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 poly-
propylene. T'he foaming agent assists the flow of the polypropylene during
moulding. 'the handle itsolf 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 two or more segments, one of which may be coextensive with
the handle. Preferably them are two, 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
can
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have any suitable spatial relationship to each other such as being in layers
or
arranged, for example, in quadrants of the brush head. Preferably. the
segments are
disposed in longitudinal sequence along the head so that a longitudinal line
drawn
from the handle end of the head to the free 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 one
or
more additional head segments arranged in longitudinal sequence towards the
free
end of the head. Preferably also, the segments are a monolayer so that any
line
drawn through the head perpendicular to its two opposed faces will generally
pass
through only one sort of material. 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 a connecting
means. The connecting means can take any form which is suitable for the
implement in its intended function. The connecting means can, for example, be
adhesive, plastic links which are integral with or detachably connected to the
head
segments, or metal links. It is an essential feature of the invention,
however, that at
least one of the segments is joined to an adjacent segment or to the handle by
a
connecting means consisting essentially of an elastomer having a modulus of
elasticity of less than 500 MPa, the elastomer being connected to the adjacent
segments and/or to the handle so that the elastomer can be stretched to about
I20%
of its unstressed length without separation of the elastomer from the head
segments.
By "consisting essentially of an elastomer" herein is meant that the elastomer
is the
sole mechanical link between the one segment and the adjacent segment or
handle.
By sole mechanical link, what is meant is that there are no continuous, non-
eiastomeric 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
andlor handle such that their removal would not materially alter the strength
of
connection. Connecting means between other segments can comprise an elastomer
in addition to other mechanical connections such as plastic links, provided
that at
least one connecting means consists essentially of, or even only of an
elastomer.
There can be from one to several connecting means which consist essentially of
an
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elastomer. Preferably, in a multi-segmented head. the connecting means between
' each adjacent pair of segments consists essentially of an elastomer. In
highly
preferred embodiments herein the head has a top face and a bottom face and the
connecting means extend transversely across the head and from the top face to
the
bottom face. For example, in a head comprising four segments, longitudinally
sequenced along the head, with the first segment being co-extensive with the
handle,
there are three such connecting means. The bands of elastomer 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 non-
linear
and take the form of chevrons or waves whose apex points towards the free end
of
the head.
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. It has
surprisingly been found that strongest fusion of the elastomer to the segments
and/or
handle is obtained when a relatively high injection temperature is employed.
Preferably the elastomer is injected at a temperature in the range from about
245°C
to about 270°C, more preferably in the range from about 250°C to
about 260°C. The
injection temperature is the temperature at which the elastomer enters the
mould. In
a typical injection moulding setup involving a screw-feed injection cylinder
this may
not be the same as the temperature of the elastomer in the cylinder.
Preferably a
lower temperature is employed in the cylinder, of around 210°C to about
220°C, to
reduce the possibility of burning or thermal degradation of the elastomer,
heating to
the final injection temperature being provided via a hot runner between the
cylinder
nozzle and the final injection point.
Other preferred conditions for the elastomer injection step include:
a) An injection pressure in the range of from about 30 to about 80 MPa,
preferably from about 40 to about 70 MPa, more preferably from about 50 to
about 60 MPa and an elastomer injection time of less than one second,
preferably less than about 0.8s. Short injection times facilitate the
elastomer
reaching all the flexible joint areas at the desired temperature.
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6
b) A holding pressure. after the elastomer has been fully injected, in the
range of
from about ~ to about 15 MF'a, preferably from about 8 to about 12 MPa, held
for between about 2 to about ~ seconds.
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 elastomers for use herein have a
modulus
of elasticity of less than about 300 MPa, especially preferred are
thermoplastic
elastomers with a hardness of about 3C) Shore A to 74 Shore D, polyolefin
types .such
as styrene-ethylene-butylene-styrene (SEBS) are preferred, for exanrpIe those
based
on Kraton~ G, but other classes of elastomer. such as polyurethanes and
TM
polyamides, can also be used. An exemplary elastomer is 'PTS Thermoflex: 75'
(marketed by Plastic Technologic Service, Germany), having a rnodulus of
elasticity
(ISO 178) of 100 MPa and a hardness (150 868) of 80 Shore A. Elastomers
TM TM 'I'M
PL1'?291, PL12292, and PL1'2'?9 3 (marketed by Multibase, Saint Laurent Du
font,
France) are also suitable for use herein. Ln 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 aptionally be mixed with a suitable plasticiser
or
foasrring 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. More than
one
type of elastomer can be used within the impiernent as a whole. This may be
appropriate, for example when it is desired to modify the head flexibility
progressively along its length:;. One way of achieving this is to use a soft
elastomer
as the connecting means between the pair of segments closest to the free end
of the
head and a hard elastomer as the connecting means between the pair of segments
closest to the handle end of the head.
The elastomer is connected to the adjacent segments and/or to the handle so
that the
elastomer can be stretched to about l2tl%, preferably to about 150%, more
preferably to about 200% of its unstressed length without separation of the
elastomer
from the head segments. This makes the p:~esent invention particularly
suitable for
constructing flexible head toothbrushes as will be described further herein.
Preferably at least about 50%, more preferably at least about 75%, especially
about
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100% of the interfacial area between the elastomer and the head segment or
handle,
in any one elastomer / segment interface is connected to the segments to the
extent
described above.
By "without separation of the elastomer from the head segments" herein is
meant
that the elastomer does not become completely detached from the head segments.
Since even partial loss of attachment of the elastomer to the head segment or
handle
can compromise the function and/or integrity of the implement, it is preferred
that
even partial detachment is avoided. In preferred embodiments, the elastomer
will
become detached over less than about 30%, preferably less than about 15%, more
preferably less than about S% of the connected interfacial area between
elastomer
and head segment or handle when the elastomer is stretched to at least about
120%.
preferably to about 150%, more preferably to about 200% of its unstressed
length.
The above results should hold true whether the elastomer is stretched by
linear
deflection, bending or torsional movements of a segment relative to the
adjacent
segment or handle. Since, for some geometries of segment-segment or segment-
handle connections, or for bending or torsional movements of one segment
relative
to its neighbour, there will be varying extents of elastomer stretching across
an
interface, care is required in measuring partial detachment. In such cases of
differential elastomer extension, at each point on any one interface to be
measured,
the stretching should be measured along a line drawn through the elastomer
which is
perpendicular to the interface at the point where separation is to be
determined.
when the implement is in its rest, unstressed state. In bending or torsional
modes it
may be that this line will deviate from the perpendicular as one segment is
moved
relative to the other.
Over its lifetime, an implement having a resiliently flexible head, as
described
herein, may be subjected to stretching of the elastomer by e.g. bending of the
head,
many thousands of times. Preferably then, the elastomer-segment bond is able
to
withstand repeated extension and relaxation of the elastomer, to the extent
described
above, and back to the rest state through at least 10,000, preferably at least
25.000.
more preferably 75,000 extension-relaxation cycles.
In highly preferred embodiments herein the head comprises at least one
longitudinal
groove which connects transversely disposed bands of elastomer and permits the
elastomer 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
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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 present invention is particularly suitable for the manufacture of
implements
having a resiliently flexible head. By "resiliently flexible" is meant herein
that when
a 3 Newton force is applied to one end of the head, the other end being held
fixed,
the end to which the force is applied will deflect through an angle of at
least 2° and,
when the 3 Newton force is removed, the head will return to its original
position
without the application of external force. The end of the head which is to be
held
fixed is defined by the line which is perpendicular to the axis along which
bending
takes place and which touches the first point to comprise a grooming means,
such as
a row of toothbrush bristles. The end of the head where the force is to be
applied is
the opposite end of the head at the furthest point away along the bending
axis. The
angle through which the head bends when a 3 Newton force is applied as above
is
referred to herein as the flex angle. The flex angle can conveniently be
measured by
measuring the vertical displacement (y) of the free end of the head under a 3
Newton
force and the distance y and the distance between the clamping point and the
application of the force (x), the flex angle being derived by the relationship
tan(flex
angle] = ylx. In preferred embodiments the flex angle is at least 3°,
more preferably
at least 5° and it can be as high as 15° or more.
In preferred embodiments herein. the implement comprises a grooming means on
only one face of the head and that face is concavelv shaped. In these
embodiments
the head preferably has a flex angle such that the concave face is able to
bend to the
extent that the face can become convex. In its rest state, the face of the
head
comprising the grooming means can be concave along either its longitudinal or
transverse axis. Where the face is concave along the longitudinal axis, 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 1 ~ to 250 mm, especially
from
2~ to 150 mm.
In use. toothbrushes according to this invention can be used for cleaning the
teeth by
an entirely conventional tooth brushing hand action, preferably in a manner
recommended by dental health authorities. The implement can also be an
electrically driven toothbrush.
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The invention will now be described by way of example only, with reference to
the
accompanying drawings in which:
Fig. 1 is a perspective view of a toothbrush according to the invention. Some
of the
bristles are omitted for the sake of clarity.
Fig. 2 is a partial side view of the head of a toothbrush according to the
invention.
Fig. 3 is a plan view of the bottom face of the head of a brush according to
the
mventlon.
Fig. 4 is a schematic showing the measurement of the flex angle.
Referring to Fig. l, a toothbrush 1 has a resiliently flexible, flattened head
2, having
a top face 3 and bottom face 4 which are substantially parallel to each other,
and an
elongated polypropylene handle 5. The head comprises four polypropylene
segments 6, the first of which is continuous with handle 5. The segments are
connected only by bands of a SEBS elastomer 7 having a hardness of 60 Shore A.
The segments 6 are longitudinally sequenced along a longitudinal axis A-A. The
bands of elastomer 7 extend across the transverse axis of the head B-B and
from the
top face 3 to the bottom face 4. Tufts of bristles 8 extend from top face 3.
In
practice, the brush has bristles extending from each of the four segments. Top
face 3
is slightly concave, along the longitudinal axis A-A, having a radius of
curvature of
about 7~ mm. The bands of elastomer afford 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. The handle comprises
further
regions 9 of the same elastomer to form a functional and attractive grip. The
toothbrush is made by sequential injection moulding of first the polypropylene
to
form the handle 5 and segments 6 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.
Referring to Fig. 2, a toothbrush head 2 having a free end 10 and handle end
11 is
formed integrally at one end of a handle 5. The head includes five segments 6
which
are longitudinally sequenced along the head. The segments are flexibly
connected
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by bands of elastomer 7 and the segment nearest the handle end 11 is flexibly
connected to the handle 5 only by a band of elastomer. The bands of elastomer
7
extend completely across the transverse axis of the head and taper from the
top to the
bottom face. Along the top face the bands of elastomer have a width of about
1.2
mm and along the bottom face the bands of elastomer have a width of about 0.8
mm.
Tufts of bristles 8 extend from the top face of the head. The toothbrush is
made by
sequential injection moulding and subsequent tufting as described above.
Referring to Fig. 3, a toothbrush head 2 is formed integrally at one end of a
handle 5.
The head includes four segments 6, one of which is continuous with handle ~.
The
segments are connected only by bands of a SEBS elastomer 7 having a hardness
of
60 Shore A and which have a wave profile across the transverse axis of the
head. A
longitudinal groove 12 extends along the bottom face of the head and the
handle,
connecting the bands of elastomer so that they can all be formed from a single
elastomer injection point. The top face, not visible in the figure, comprises
a
grooming means.
Fig. 4 illustrates the measurement of the flex angle. The head 2 is clamped 13
against the first row of bristles 14 at the end which is attached to the
handle ~ and a 3
Newton force (F) is applied to the opposite end. The dashed lines show the
original
position of the brush head before the force is applied. The vertical
displacement (y)
of the free end of the head under the force F is measured and the flex angle
is
derived from the distance y and the distance between the clamping point and
the
application of the force (x) by the relationship tan(flex angle) = ylx.
