U.S. patent application number 11/140058 was filed with the patent office on 2006-12-28 for toothbrush.
This patent application is currently assigned to GlaxoSmithKline Consumer Healthcare GmbH & Co. KG. Invention is credited to Matthias Georgi, Hans Kraemer.
Application Number | 20060288510 11/140058 |
Document ID | / |
Family ID | 34082117 |
Filed Date | 2006-12-28 |
United States Patent
Application |
20060288510 |
Kind Code |
A1 |
Georgi; Matthias ; et
al. |
December 28, 2006 |
Toothbrush
Abstract
A toothbrush made partly of a hard plastic material and partly
of an elastomeric material, characterized in that at least part of
the elastomeric material comprises an inner core (23) of a first
soft elastomeric material wholly or partly enclosed within an outer
flexible skin (24) of a second polymer material having different
physical characteristics to the inner core polymer. Processes for
making such a toothbrush are also described.
Inventors: |
Georgi; Matthias; (Buehl
(Baden), DE) ; Kraemer; Hans; (Buehl (Baden),
DE) |
Correspondence
Address: |
GLAXOSMITHKLINE;Corporate Intellectual Property - UW2220
P.O. Box 1539
King of Prussia
PA
19406-0939
US
|
Assignee: |
GlaxoSmithKline Consumer Healthcare
GmbH & Co. KG
|
Family ID: |
34082117 |
Appl. No.: |
11/140058 |
Filed: |
May 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10924047 |
Aug 23, 2004 |
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11140058 |
May 27, 2005 |
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09959173 |
Jan 30, 2002 |
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PCT/EP00/03728 |
Apr 20, 2000 |
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10924047 |
Aug 23, 2004 |
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Current U.S.
Class: |
15/167.1 ;
15/143.1 |
Current CPC
Class: |
A46B 5/007 20130101;
A46B 5/0029 20130101; A46B 5/0062 20130101; A46B 5/026 20130101;
B29C 45/1676 20130101; A46B 5/00 20130101; A46B 2200/1066 20130101;
A46B 5/02 20130101; B29L 2031/425 20130101; B29K 2221/003 20130101;
B29C 45/1642 20130101 |
Class at
Publication: |
015/167.1 ;
015/143.1 |
International
Class: |
A46B 9/04 20060101
A46B009/04; A46B 5/02 20060101 A46B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 22, 1999 |
GB |
9909101.9 |
Claims
1-25. (canceled)
26. A toothbrush comprising a handle, a head on which are mounted
bristles, with optionally a neck region between the head and
handle, the toothbrush being made partly of a hard plastic material
and having at least one part made of an elastomeric material,
wherein; at least part of the at least one elastomeric material
part comprises an inner core of an elastomeric material wholly or
partly enclosed within an outer flexible skin of the same
elastomeric material comprising the same monomer units as the core
but having different physical characteristics to the inner core
material.
27. A toothbrush according to claim 48 wherein the core comprises a
foamed elastomeric material and the skin comprises the same
elastomeric material in a non-foamed state.
28. A toothbrush according to claim 48 wherein the core comprises a
foamed elastomeric material and the skin comprises the same
elastomeric material in a foamed state having different void
characteristics to the inner core material.
29. A toothbrush according to claim 50 wherein the skin comprises
the same elastomeric material in a foamed state having a lower
number of gas bubbles per unit volume than the core.
30. A toothbrush according to claim 48 wherein the elastomeric
material of the core comprises a foamed elastomeric material having
a hardness of Shore A 5 to 30, and the outer skin comprises a non
foamed elastomeric material or an elastomeric material less foamed
than the material of the core having a hardness of Shore A 65.+-.5,
the thickness of the outer skin being in the range 100 microns-1.5
mm.
31. A toothbrush according to claim 52 wherein the elastomer part
of the toothbrush has a thickness of 3 mm-1.5 cm.
32. A toothbrush according to claim 48 wherein the elastomeric
material of the core and skin is selected from the group of
compounds based on styrenic block copolymers such as
styrene-ethylene-butadiene-styrene (SEBS) copolymers, polyblends
based on EPDM/PP, polyacrylate/PP blends, thermoplastic
polyurethanes, thermoplastic copolyesters, natural or synthetic
latex type elastomers, polychloroprenes, natural rubber and
polyurethane foams.
33. A toothbrush according to claim 48 when made by a process in
which: a hard plastic part of the toothbrush is made in a first
stage by a process of injection moulding in the form of a skeleton
of the hard plastic material having one or more cavity therein
corresponding to the intended position(s) and dimensions of the
elastomeric material part(s), then; this skeleton is enclosed in a
mould having at least one cavity therein corresponding to the
intended position of an elastomer part, then the skin material is
injected into the cavity, then the core material is injected into
the cavity to form the core and to fill and inflate the skin.
34. A toothbrush according to claim 55 wherein the skin material is
injected into the mould cavity in an amount comprising 20-30% of
the total cavity volume then the core material is injected into the
cavity to form the core and to fill and inflate the skin.
35. A toothbrush according to claim 55 wherein the core comprises
an elastomer material which includes a foaming agent and the
quantity of such core material injected into the cavity is such
that the combined volume of skin and core materials fills ca.
50-70% of the cavity and the expansion of the core material as
foaming occurs then causes sufficient expansion that the core and
skin materials fill the cavity.
36. A toothbrush according to claim 48 when made in a process in
which: a hard plastic part of the toothbrush is made in a first
stage by a process of injection moulding in the form of a skeleton
of the hard plastic material having one or more cavity therein
corresponding to the intended position(s) and dimensions of the
elastomeric material part(s), then; this skeleton is enclosed in a
mould having at least one cavity therein, bounded by a wall,
corresponding to the intended position of an elastomer part, then
an elastomer material having incorporated therein a foaming agent
is injected into the mould and outer parts of the elastomer
material injected into the mould are arranged to cool more rapidly
so as to foam less to result in an outer skin in a non foamed state
or in a less foamed state than the inner core parts of the material
further away from the walls of the mould cavity.
Description
[0001] This invention relates to toothbrushes, in particular to
toothbrushes made of two construction materials being a hard
plastic and a softer elastomeric material.
[0002] Such toothbrushes are known. For example EP 0 336 641 A
discloses a toothbrush having elastomeric material grip-enhancing
pads on its handle. WO 92/17092 discloses a toothbrush having
elastomeric material parts forming a flexible link between its head
and its handle. WO 92/017093 discloses a toothbrush having
elastomeric material parts in its head, thereby modifying the
flexibility at its head. DE 3923495 A discloses a toothbrush having
elastomeric material inserts in cut-outs between the handle and
neck region, also to modify flexibility. EP 0310482 discloses a
toothbrush having elastomeric material parts around its head as a
soft buffer to absorb impact forces between the head and the mouth
of the user. EP 0371293 A discloses a toothbrush having elastomeric
material parts in its neck. WO 94/05183 discloses a toothbrush
having elastomeric material parts in one, two or three places in
its handle, neck and head. Other parts of the head, handle and neck
region of the above-mentioned toothbrushes are made of hard plastic
materials. The above-mentioned disclosures are only examples of
many in the literature. Two component toothbrushes of this type
have been made and sold commercially for many years, for example
the applicant's Dr BEST.TM. and AQUAFRESH.TM. range of
toothbrushes.
[0003] The above-mentioned two component toothbrushes are made by a
process of injection moulding in which the hard plastic parts are
first injection moulded to form a frame or skeleton having cavities
which define the position, size and shape of the elastomeric
material parts to be formed therein, and in which cavities the
elastomeric material parts are subsequently formed by a second
injection moulding of fluid elastomeric material. Such a process is
described for example in WO 94/05183.
[0004] A problem with known two-component toothbrushes of this type
is that the elastomeric materials which are used need to be
relatively soft, for example to enable them to fulfil their
function of forming soft grip handles, flexible links or soft
buffers. Soft elastomeric materials are relatively vulnerable to
physical damage during use, e.g. due to impact with and abrasion
from tooth surfaces or other surfaces. Soft elastomeric material s
tend to be absorbent, and consequently when such toothbrushes are
used, especially when they are exposed to detergents, soaps or
toothpastes, moisture and dirt etc, their elastomeric material
parts can absorb these substances. As a consequence these
elastomeric material parts can deteriorate, become discoloured or
dirty, and such absorbed substances can be difficult to remove by
cleaning.
[0005] It is an object of this invention to offer a solution to
this problem.
[0006] According to this invention a toothbrush is provided
comprising a handle, a head on which are mounted bristles, with
optionally a neck region between the head and handle, the
toothbrush being made partly of a hard plastic material and having
at least one part made of an elastomeric material, characterised in
that at least part of the at least one elastomeric material part
comprises an inner core of a soft elastomeric material wholly or
partly enclosed within an outer flexible skin of a polymer material
having different physical characteristics to the inner core
material.
[0007] The term "elastomeric" material as used herein includes
natural and synthetic elastomeric materials which have a semi-rigid
rubbery nature, i.e. being soft and resilient to the touch,
deforming under hand pressure and springing, preferably rapidly,
back to substantially or exactly its original shape on release of
the hand pressure. The term also includes polymers which are not
inherently of a rubbery nature but which are rendered rubbery in
nature by for example foaming or other treatment.
[0008] By "soft" herein is meant deforming under the pressure of
the hand, particularly under pressures applied during normal use of
the toothbrush in brushing the users teeth.
[0009] The outer skin should be a flexible skin, so that the
elastomeric core material can deform as pressure is applied to the
outer skin and transmitted to the core elastomeric material via the
skin. It is desirable that the outer polymer skin binds with,
preferably has good bonding characteristics to, the hard plastic
material of the toothbrush.
[0010] The physical characteristics of the inner core and the skin
polymer may differ in various ways. The skin may be a polymer
material which is harder than the soft core elastomeric material.
Additionally or alternatively the skin material may be a polymer
material which is more resistant to physical damage or penetration
by absorption of substances than the core elastomeric material as
mentioned above. Additionally or alternatively the skin polymer
material may have better surface properties than the core
elastomeric material, e.g. having better tactile properties or
being more easy to print upon than the core elastomeric material.
Additionally or alternatively the core and skin may differ in
quality, e.g. the inner core elastomeric material being a
relatively cheap, low quality recycled elastomeric material and the
outer skin material may be a higher quality, e.g. non-recycled
polymer. For example there may be an inner core of a less dense, or
soft or easily damaged or absorbent elastomeric material and an
outer skin of a material which is denser or relatively less soft or
more resistant to damage or less absorbent. The inner core
elastomeric material may be a cheap elastomeric material, e.g. a
recycled low quality e.g. easily damaged, elastomeric material, and
the outer skin may be a thin skin of an expensive polymer of high
quality or having desirable surface properties high quality. In
this way the superior surface properties of the more expensive
polymer may be enjoyed whilst minimising the quantity used.
[0011] By means of the invention the elastomeric material parts of
the toothbrush may benefit from the softness of the core
elastomeric material, e.g. in providing a comfortable grip, in
forming a flexible region in the toothbrush, or in providing a soft
buffer around the head, whilst the outer skin can provide a coating
having advantageous properties, e.g. of physical resistance,
resistance to absorption of substances, hand-feel, or of printing
onto its surface. The outer skin can enhance the bonding of the
elastomeric material and hard plastic parts of the toothbrush as
this bonding can be made between the outer skin and the hard
plastic parts, and a polymer material may be selected for the outer
skin which has better bonding characteristics with the hard plastic
material than the core elastomeric material.
[0012] In the toothbrush of this invention the elastomeric material
part(s) may be in any or all of the parts where elastomeric
material is at present used in two-component toothbrushes of the
state of the art. For example the elastomeric material part(s) may
comprise a pad on the grip handle, a flexibility modifying region,
for example in the handle, neck or head or between the handle and
neck or the neck and the head, or a soft buffer around the head.
The elastomeric material part is preferably a pad on the grip
handle. The toothbrush of the invention may also incorporate parts
which are made of conventional elastomeric material, i.e. of soft
elastomeric material throughout without the less soft coating
skin.
[0013] The outer skin and inner core elastomeric material polymers
should preferably be compatible to encourage bonding between them.
The outer skin and inner core materials may be inherently
compatible, or alternatively they may be of materials which are
modified to be compatible with each other.
[0014] The outer skin polymer may be an elastomeric or non
elastomeric material.
[0015] For example the inner core material and the skin material
may comprise the same polymer, i.e. including the same monomeric
units, but including different additives or quantities of additives
to give the core and skin materials such different physical
characteristics.
[0016] For example the core and outer skin may comprise the same
polymer, i.e. both being an elastomeric material and comprising the
same monomer units, but being different grades of the same polymer.
For example such different grades may differ in their relative
density, softness, resistance to damage or ability to absorb
environmental substances or other characteristics.
[0017] The core and outer skin may be different polymers, i.e.
comprising different monomer units or different combinations of
monomer units.
[0018] In a preferred embodiment the core comprises a foamed
elastomeric material. With such a core the outer skin may be an
elastomeric material or a non-elastomeric material. If the skin in
this embodiment is an elastomeric material it may be the same
elastomeric material as the core but in a different grade, e.g.
harder, more resistant or higher quality than the core. Such an
elastomeric skin, whether or not it is the same elastomeric
material as the core, may be a non-foamed elastomeric material, or
it may be a foamed elastomeric material having different
characteristics, e.g. different void characteristics, to the inner
core material so as to give the outer skin different properties to
the inner core, e.g. so as to make the outer skin more dense, less
soft and/or more resistant to penetration or absorbency than the
inner polymer. For example a higher number of gas bubbles per unit
volume in such a foamed polymer can result in a softer polymer than
a lower number of gas bubbles per unit volume. For example the
difference in void characteristics may comprise the skin having a
lower number of gas bubbles per unit volume than the core.
[0019] Suitable elastomeric materials for use as the core polymer
include thermoplastic elastomer ("TPE") materials, for example
compounds based on styrenic block copolymers such as
styrene-ethylene-butadiene-styrene (SEBS) copolymers, e.g. the
material Thermolast-K.TM. (available from Gummiwerk Kraiburg GmbH
& Co, Germany), polyblends based on EPDM/PP such as the
material Sarlink.TM. (available from DSM Thermoplastic Elastomers
NL), or polyacrylate/PP blends such as the material Pacrel.TM.
(available from Optatech Corporation, Suomi), thermoplastic
polyurethanes such as Desmopan.TM. (available from Bayer AG,
Germany), thermoplastic copolyesters such as Hytrel.TM. (available
from Du Pont De Nemours, USA) natural or synthetic latex type
elastomers such as Baystal S.TM. or Baypren Latex.TM. (available
from Polymer Latex, DE), polychloroprenes such as Baypren.TM.
(available from Bayer AG, DE), natural rubber and foamed polymers
such as polyurethane foams. Preferably such core polymers are used
in a foamed form, e.g. incorporating a dispersion of gas bubbles in
their structure.
[0020] A core of a foamed material such as a foamed elastomeric
material may be formed in situ in an injection mould cavity by
incorporating into the elastomeric material, such as a known TPE
material, a foaming agent, such as the known foaming agents
Exocerol AB40E.TM. or Hydrocerol.TM., typically at 1-2.5 weight %,
typically 2% of the former or 1.5% of the latter. These foaming
agents generate a gas on heating to elevated temperatures,
typically those used for injection moulding, and if such a foaming
agent is included in the elastomeric material, then when it is
injected in a heated state into the mould, the foaming agent will
form bubbles within the elastomeric material, resulting in a
foam.
[0021] Suitable polymers for the outer polymer skin include the
above-mentioned elastomeric materials in non-foamed or other grades
of foaming e.g. having a lower number of gas bubbles per unit
volume than the core. This may be achieved by using an elastomeric
material without a foaming agent, or with less foaming agent than
the core material, or a different foaming agent than the core which
generates less gas bubbles. Other suitable polymers for the skin
include the above-mentioned elastomeric materials with different
hardness, resistance etc. to the core, and inherently harder
polymers different to such elastomers, e.g. polypropylenes,
polyamides (such as Nylon.TM.), polyurethanes etc. Preferred
polymers for the outer skin are those which bind with the hard
plastic material of the toothbrush. For example the polymer for the
outer skin may be chemically similar to the hard plastic material
of the toothbrush. A suitable combination of inner and outer
polymers is an inner core of a thermoplastic elastomer and an outer
skin of the same thermoplastic elastomer in a less soft grade,
preferably being a thermoplastic elastomer which binds to the hard
plastic material. Thermolast-K.TM. is such an elastomer, and is
known for use in two-component toothbrushes where it is bonded to
the hard plastic material of the toothbrush.
[0022] Suitably if the inner elastomeric polymer is a relatively
soft elastomer and the outer skin is a relatively less soft
polymer, e.g. a foamed elastomer core and a non foamed or less
foamed elastomer skin, the inner core polymer may have a hardness
of ca. Shore A 5 to 30 preferably ca. 20-20, and the outer skin may
have a hardness of ca. Shore A 65.+-.5. The thickness of the outer
skin may vary from application to application but typically a
thickness of 100 microns to 1.5 mm may be used. It will be
appreciated by those skilled in the art that the shape and size of
a toothbrush will inevitably impose dimensional constraints, for
example only a relatively thin outer skin may be possible in some
parts of the toothbrush where only a relatively thin mass of the
elastomeric parts may be used.
[0023] Suitably the elastomeric part(s) of the toothbrush may
comprise part(s) of a grip handle in which the elastomer is of
sufficient thickness, i.e. from their outer surface to the hard
plastic internal skeleton, that the elastomer parts resiliently
deform under the pressure of a gripping hand, so that the grip
handle has a soft hand feel. For example the elastomer parts of the
toothbrush may have a thickness of 3 mm-1.5 cm, e.g. 5 mm-1.0 cm. A
suitable grip handle having thick elastomer regions of this type is
known for example from WO 97/29663 the contents of which are
included herein by reference.
[0024] The hard plastics material of the other parts of the
toothbrush may be made of any plastics material which is used at
present in the manufacture of toothbrushes, particularly in the
manufacture of two component toothbrushes which incorporate parts
of elastomeric material, and in which the elastomeric parts and
plastics parts are bonded together. Suitable hard plastics include
polypropylenes such as Polypropylenes P 1600.TM. (Shell) and Apryl
3400 MA1 from Elf Atochem, Novolene 1100 HX.TM. (BASF), and
polyamides such as Ultramil B3.TM. (BASF). Polypropylenes for
example bond readily with Thermolast-K.TM.. Such hard plastics
materials typically have a hardness Shire R 80-100.
[0025] The hard plastic parts of the toothbrush may be made in a
first stage by a conventional process of injection moulding as is
common in the art and has long been used for making toothbrushes.
In this first stage the hard plastic part(s) of the toothbrush are
made, typically in the form of a "skeleton" or "frame" of the
plastics material is made, having one or more cavities therein
corresponding to the intended position(s) and dimensions of the
elastomeric material part(s).
[0026] The elastomer parts may then be made in a second stage by
containing the so plastic material part(s) in a second mould having
one or more cavities therein corresponding to the intended position
of the elastomeric material part(s), then forming the elastomer
part(s) by injection of the fluid elastomeric material into the one
or more cavities. Such a process is for example described in WO
94/05183. Suitable conditions of temperature and pressure etc. for
the injection moulding process to achieve a bond between the
plastic material skeleton and the elastomer material injected into
the mould are known in the art, for example as used currently to
make two-component toothbrushes.
[0027] The elastomer parts of the present invention, having an
inner core and an outer skin, may be formed by the known injection
moulding process of "sandwich moulding" also called the "skin/core"
method, in which the elastomeric material part(s) is/are formed by
an injection moulding process in which at least two materials being
the materials of the skin and core are injected into a mould cavity
simultaneously or successively in such a way that the injected
polymer is in the form of an inner core and an outer skin. This
process is known from the technical literature. Suitable processes
and moulding equipment for such a sandwich moulding process are for
example disclosed in U.S. Pat. No. 5,789,033 and U.S. Pat. No.
5,798,069, the contents of which are incorporated herein by way of
reference. In sandwich moulding, a core is introduced into an outer
skin component. This process takes place in two or three stages.
First the material of the outer skin is injected into the mould
cavity to partially fill the cavity with a mass of the material of
the outer skin, and then the core component is injected into the
mass of introduced skin material to fill and "inflate" the skin
material. To finish off, a closure can be produced with the first,
i.e. the skin component near the sprue (the point in the cavity at
which the materials are injected). This prevents the core material
remaining on the surface and at the same time cleans the system for
the next shot of polymer to be injected into the mould. U.S. Pat.
No. 5,789,033 and U.S. Pat. No. 5,798,069 disclose sandwich
moulding processes in which opposed gating injection is used, i.e.
the core and skin materials are injected into the mould cavity via
respective separate injection nozzles. Sandwich moulding processes
are also known in which a single nozzle is used to inject both skin
and core materials. Hot runner injection moulding equipment is
generally preferred for the sandwich moulding process.
[0028] Suitable injection moulding machinery for sandwich injection
moulding is available from inter alia Mannesman Demag (Germany).
The operating conditions, e.g. temperature, pressure, flow rate
etc. conditions of the sandwich moulding process are preferably
selected such that the elastomer part outer skin material bonds to
the plastic material of the toothbrush, "skeleton" or "frame"
referred to above. Such conditions can be determined by practice in
the art.
[0029] For example in a sandwich moulding process suitable for
making the toothbrush of the present invention a skeleton or frame
may be made as described above and this skeleton or frame may be
enclosed in a second mould having cavities therein corresponding to
the intended position of the elastomer parts, then the skin
material, e.g. a material such as those described above, for
example an elastomeric material, may be injected into the cavity,
typically in an amount comprising ca 20-30% of the total cavity
volume. Then the core material, e.g. a material such as those
described above, for example an elastomeric material, e.g. the same
elastomeric material as the skin material and containing a foaming
agent may be injected into the cavity to form the core, and the
core material fills and inflates the skin. Suitably if the core
material includes a foaming agent expansion of the core material
within the mould may occur as a result of the temperature of the
mould. If the core material is a foaming elastomer, e.g. includes a
foaming agent, then a quantity of such a core material may be
injected into the cavity such that the combined volume of skin and
core materials fills ca. 50-70%, e.g 60% of the cavity, and the
expansion of the core material as foaming occurs may then cause
sufficient expansion that the core and skin materials fill the
cavity.
[0030] Alternatively the elastomer parts of the present invention,
having an inner core and an outer skin, may be formed by an
injection moulding process that employs internal foaming of an
injected elastomer material to generate both skin and core. For
example an elastomer material such as those described above may
have incorporated into it a foaming agent, such as those described
above. These foaming agents generate a gas on heating to elevated
temperatures, typically those used for injection moulding, and if
such a foaming agent is included in the elastomeric material, then
when it is injected in a heated state into the mould, the foaming
agent will form bubbles within the elastomeric material, resulting
in a foam. However an injection mould for a toothbrush is normally
made of a heat conducting metal and will normal include cooling
fluid channels in its metal mould blocks to rapidly cool the
toothbrush formed therein. Consequently the outer parts of the
moulded elastomer being in contact with the metal mould cavity
surfaces can be arranged to cool more rapidly so as to foam less,
resulting in an outer skin in a non foamed state or in a less
foamed state than the inner core parts of the material further away
from the metal walls of the mould cavity.
[0031] Accordingly this invention further provides an injection
moulding process for malting a toothbrush comprising hard plastic
and elastomeric material parts, in which a hard plastic material
"skeleton" or "frame" is provided having one or more cavities
therein corresponding to the intended position of the elastomeric
part(s), this skeleton or frame is located within a mould having
one or more cavities corresponding to the intended position of the
elastomeric parts, and the elastomeric part(s) are formed within
the said mould cavities by an injection process which forms an
inner core of a soft elastomeric material wholly or partly enclosed
within an outer skin of a second polymer material. The injection
process is preferably a sandwich moulding or foaming process.
[0032] The invention further provides a mould suitable for use in
such an injection moulding process, having cavities therein
corresponding to the intended position of the elastomeric parts,
and provided with means to carry out a sandwich moulding process
therein. The mould is suitably provided with injection ports to
facilitate a sandwich moulding process.
[0033] The invention further provides a mould suitable for use in
such an injection moulding process, having cavities therein
corresponding to the intended position of the elastomeric parts,
suitable for injecting an elastomeric material which includes an
internal foaming agent therein.
[0034] The invention will now be described by way of example only,
referring to:
[0035] FIG. 1 which shows a toothbrush according to this
invention.
[0036] FIG. 2 which shows an enlarged cross section through part of
the toothbrush of FIG. 1.
[0037] FIG. 3 which shows an enlarged cross section through an
alternative construction of part of the toothbrush of FIG. 1.
[0038] FIG. 4 which shows the sandwich moulding process used for
making a toothbrush of FIG. 1.
[0039] Referring to FIG. 1 a toothbrush is shown in longitudinal
section, comprising a handle 1, a head 2 on which are mounted
bristles 3, and a neck region 4 between the handle 1 and head 2.
The toothbrush of FIG. 1 is made partly of a hard polypropylene
material, which is in the form of a frame 5 having cavities 6
therein, and partly of parts 7, 8, 9, 10, 11, 12 which comprise an
elastomeric material. The cavities 6 are in positions which
correspond to the positions of the elastomeric material parts
7-12.
[0040] Part 7 is a grip pad on the handle 1. Part 8 is a flexible
link between the handle 1 and neck 4 of the toothbrush comprising
an aperture in the hard plastic material which is occupied by the
elastomeric material. Part 9 is a flexible link in the toothbrush
neck 4, part 10 is a flexible link between the head 2 and neck 4 of
the toothbrush 2 comprising apertures in the hard plastic material
of the neck which are occupied by the elastomeric material. Parts
11 are flexible links in the head 2 of the toothbrush, each
comprising a widthways extending groove being occupied by the
elastomeric material. Part 12 is a soft buffer around the head 2,
comprising a projecting rim around the head 2.
[0041] Each of parts 7-12 comprises an elastomeric core made of a
soft thermoplastic elastomeric material of hardness Shore A ca 5;
and an outer enclosing skin of a less soft grade of the same
thermoplastic elastomeric material. Two alternative structures of
the elastomeric material parts 7-12 are shown in FIGS. 2 and 3.
[0042] Referring to FIG. 2, a cross section through the part 7 of
the toothbrush of FIG. 1 which is circled in FIG. 1 is shown,
although sections through other elastomeric parts shown in FIG. 1
would be identical. FIG. 2 shows part 21 of the plastic material of
the toothbrush. The elastomeric material part 22 comprises a core
23 of a first soft elastomeric material polymer material and an
outer skin 24 of a second polymer. The second polymer of the outer
skin 24 is a flexible polymer which is harder and less permeable
than the elastomeric material of the core. At the interface 25
between the elastomeric material part 22 and the plastic material
21 the outer polymer skin 24 is bonded to the plastic material 21.
The elastomeric material parts 7-12 are formed by a process of
sandwich moulding.
[0043] Referring to FIG. 3, a cross section through the part 7 of
the toothbrush of FIG. 1 which is circled in FIG. 1 is shown,
although sections through other elastomeric parts shown in FIG. 1
would be identical. FIG. 3 shows part 31 of the plastic material of
the toothbrush. The elastomeric material part 32 is a soft foamed
thermoplastic elastomeric material, i.e. within which there are
numerous internal bubbles 33. As is shown in FIG. 3 the extent of
foaming decreases towards the outer surface 34 of the elastomeric
material part 32, and the part 35 of the elastomeric material part
32 immediately adjacent to the outer surface 34 is essentially
non-foamed. Consequently the outer parts 35 of the polymer layer
are less soft than the inner core part closer to the plastic parts
31. At the interface 36 between the elastomeric material part 32
and the hard plastic material part 31 these parts are bonded
together.
[0044] The elastomeric material part 32 has been formed by
positioning the hard plastic parts 31 in the cavity of a injection
mould (not shown), and injecting an elastomeric material which
includes a foaming agent into the cavity under known conditions
such that the elastomeric material and plastic parts bond. At the
temperature of the mould the foaming agent generates gas bubbles
33, but the metal walls of the mould (not shown) are a good heat
conductor and the outer layers 35 of the injected elastomeric
material rapidly cool down immediately after the elastomeric
material is injected in so that less foaming occurs in these
layers. The plastic material part 31 is not as good a heat
conductor as the metal injection mould (not shown) in which the
elastomeric material part 32 has been formed, consequently bubbles
33 are formed in the parts of the elastomeric material 32 adjacent
to the plastic parts 31.
[0045] The thickness of the elastomeric material part, e.g. the
distance from the outer surface 34 to the plastic part 31 may be
typically 3 mm-1.5 cm.
[0046] Referring to FIG. 4A, part of an injection mould 40 is shown
overall, being a two part mould having two halves 41, 42 with a
split line A-A, and defining a mould cavity 43 between the two
halves 41, 42. There is an injection gate 44, of a known type
suitable for sandwich moulding. The mould 40 encloses a hard
plastic part 45 of a toothbrush handle which has previously been
made in a separate first stage injection moulding process. The part
45 shown is part of the grip handle of the toothbrush, wth a neck
46 extending therefrom, but the head is not shown. Part of the
cavity 43 is also defined by a cavity in the handle part 45.
[0047] Referring to FIG. 4B a first material 47 has been injected
into the cavity 43 via gate 44. The material 47 is a thermoplastic
elastomer such as Thermolast-K.TM., and the quantity injected is
sufficient to fill ca. 20-30% of the cavity 43. The moulding
conditions are such that the the material 47 is injected in a hot
fluid state, but cools slightly in the cavity 43 to increase its
viscosity.
[0048] Referring to FIG. 4C, a second material 48 has been injected
into the cavity 43, in a way such that the material 48 flows into
the centre of the mass of first material 47, to inflate the mass of
material 47 so that the material 47 surrounds the inner core of
material 47. The second material 48 is typically a thermoplastic
elastomer such as Thermolast-K.TM. but including a foaming agent
such as Exocerol AB40E.TM. or Hydrocerol.TM., typically at 1-2.5
weight %, typically 2% of the former or 1.5% of the latter. The
quantity of second material 48 injected is such that the combined
first and second material 47, 48 occupy ca. 60% of the cavity 43.
The second material 48 is of a lower viscosity than the first
material 47 in the cavity 43.
[0049] Referring to FIG. 4D, the second material 48 has foamed
under the hot conditions inside the cavity 43, and the second
material 48 has consequently expanded within the skin of first
material 47 so that the mass of combined first and second material
fills cavity 43. The small residual hole (not shown) in the skin 47
where the second material has penetrated into the core of first
material 47 has been closed by a small injection of first material
47 through gate 44.
[0050] The conditions inside the cavity 43 are such that the first
material 47 bonds to the plastic material part 45. Suitable
conditions to achieve bonding are known in the art, e.g in
conventional toothbrush manufacturing processes.
[0051] In FIG. 4 the sandwich moulding process shown uses a single
gate 44, but it will be understood that further gates (not shown)
may be provided to inject first and second materials into other
parts of the toothbrush. It will also be appreciated that the
process shown in FIG. 4 may be adapted for use with opposed gate
techniques, although id materials 47, 48 are injected from sides of
the cavity 43 on opposite sides of the handle 45, it will be
necessary to provide some communication channels either through or
around the part 45 to enable the core to be injected. In the manner
described.
* * * * *