U.S. patent application number 09/740741 was filed with the patent office on 2002-06-20 for process for manufacturing a toothbrush.
Invention is credited to Morawski, Linda Mary.
Application Number | 20020074698 09/740741 |
Document ID | / |
Family ID | 24977857 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020074698 |
Kind Code |
A1 |
Morawski, Linda Mary |
June 20, 2002 |
Process for manufacturing a toothbrush
Abstract
A process for manufacturing hollow handled toothbrushes is
disclosed. The process includes; a) providing a toothbrush mold
having a head portion, a base portion, a toothbrush cavity located
between said head and end portions and having walls, an injection
port for molten plastic, and a gas injection port, wherein the gas
injection port is positioned in the end of the base portion of the
mold so that gas is injected into the mold cavity substantially
centrally thereof and in a direction parallel to the longitudinal
axis of the mold; b) injecting a predetermined amount of a molten
plastic into the mold cavity to partially fill the cavity; and c)
injecting at least one gas through the gas injection port into the
cavity to direct the molten plastic against the walls of the mold
cavity.
Inventors: |
Morawski, Linda Mary;
(Norton, MA) |
Correspondence
Address: |
Philip S. Johnson, Esq.
Johnson & Johnson
One Johnson & Johnson Plaza
New Brunswick
NJ
08933-7003
US
|
Family ID: |
24977857 |
Appl. No.: |
09/740741 |
Filed: |
December 19, 2000 |
Current U.S.
Class: |
264/572 ;
264/243; 264/85 |
Current CPC
Class: |
B29C 2045/1728 20130101;
B29L 2031/425 20130101; B29C 45/1704 20130101 |
Class at
Publication: |
264/572 ; 264/85;
264/243 |
International
Class: |
B29D 022/00 |
Claims
We claim:
1. A process for manufacturing a toothbrush comprising: a)
providing a toothbrush mold having a head portion, a base portion,
a toothbrush cavity located between said head portion and said base
portion and having walls, an injection port for injecting molten
plastic, and a gas injection port for injection at least one gas,
wherein the gas injection port is positioned in the end of the base
portion of the mold so that gas is injected into the mold cavity
substantially centrally thereof and in a direction parallel to the
longitudinal axis of the mold; b) injecting a predetermined amount
of a molten plastic into the mold cavity to partially fill the
cavity; and c) injecting said at least one gas through the gas
injection port to direct the molten plastic into contact with the
walls of the mold cavity.
2. The process of claim 1 wherein the injection port for the molten
plastic is positioned near the base portion of the mold,
perpendicular to the lengthwise direction of the toothbrush
mold.
3. The process of claim 1 wherein the injection port for the molten
plastic is positioned in the center of the end of the base portion
of the mold.
4. The process of claim 1 wherein the molten plastic is selected
from the group consisting of cellulose acetate propionate, nylon,
polyethylene, polypropylene, polycarbonate, and poly(ethylene
terephthalate) and mixtures thereof.
5. The process of claim 1 wherein the amount of molten plastic
injected into the mold ranges from about 10% to about 90% of the
total volume of the mold cavity.
6. The process of claim 1 wherein the amount of molten plastic
injected into the mold ranges from about 20% to about 80% of the
total volume of the mold cavity.
7. The process of claim 1 wherein the gas is selected from the
group consisting of air, carbon dioxide, nitrogen, and mixtures
thereof.
8. The process of claim 7 wherein the gas is injected at a pressure
ranging from about 340 kPa to about 4000 kPa.
9. The process of claim 8 wherein the gas is injected at a pressure
ranging from about 700 kPa to about 2800 kPa.
10. The process of claim 9 wherein the gas in injected at a
pressure ranging from about 1375 kPa to about 2400 kPa.
Description
FIELD OF THE INVENTION
[0001] This patent relates to an improved process for manufacturing
a toothbrush. More specifically, the patent relates to a process
for manufacturing hollow handled toothbrushes. The process utilizes
a gas which is injected from a specific location in a toothbrush
mold to assist in blowing a molten plastic therethrough. The
injection of the gas in a specific location results in a more
efficient process for manufacturing hollow handled
toothbrushes.
DESCRIPTION OF THE PRIOR ART
[0002] Toothbrushes are typically manufactured using an injection
molding process. The injection molding process is characterized by
providing a mold in the shape of the toothbrush and injecting
molten plastic through a hot channel nozzle into the mold. The
toothbrush is then cooled and ejected from the mold.
[0003] Toothbrushes may be difficult to handle for several reasons.
Children may have difficulty handling toothbrushes due to the size
of the child's hands. People with arthritis also sometimes have
difficulty handling toothbrushes, due to difficulty in flexing the
joints in their hands. Handicapped people may also have difficulty
handling toothbrushes. There has been a recent trend to provide
toothbrushes with relatively large cross section handles to make
handling the toothbrush easier. Additionally, the larger cross
section handles on the toothbrushes may be better for the user from
an ergonomics point of view.
[0004] The manufacture of toothbrushes with larger cross section
handles has several drawbacks. Firstly, the toothbrush is more
expensive due to the use of more plastic to make the toothbrush.
Secondly, the cost of manufacture is increased because the time to
cool the toothbrush increases. The increase in cooling time is due
to the increased amount of hot plastic and the larger cross section
of the toothbrush. Accordingly, there is a need for a more
efficient process for making toothbrushes with larger cross section
handles.
[0005] European Patent No. EP 668140 discloses the use of air
assist technology to make toothbrushes with large cross section
handles. In the process, molten plastic is injected near the base
of the toothbrush handle, perpendicular to the lengthwise direction
of the toothbrush mold to partially fill the toothbrush mold. A hot
needle is then inserted into the molten plastic, also near the base
of the toothbrush handle and also perpendicular to the lengthwise
direction of the toothbrush mold. A gas is blown through the needle
to press the molten plastic against the walls of the toothbrush
mold. The disclosed process may be modified to inject a separate,
less expensive polymer in place of the gas, in which case there is
produced a solid handle in which the interior portions are made
from said separate polymer. In either case, the process is
completed by injecting a small amount of plastic to close the hole
left by the needle.
[0006] European Patent No. EP 721832 also discloses the use of air
assist technology to make toothbrushes with large cross section
handles. In the disclosed process, molten plastic is injected near
the head of the toothbrush mold, perpendicular to the lengthwise
direction of the toothbrush mold to partially fill the toothbrush
mold. A hot needle is then inserted into the molten plastic, also
near the head of the toothbrush, and also perpendicular to the
lengthwise direction of the toothbrush mold. A gas is then blown
through the needle to press the molten plastic against the walls of
the toothbrush mold. The process includes transferring the hollow
handled brush to a second mold and injecting a separate plastic to
fill the toothbrush handle.
[0007] We have found that gas injected just above the base of the
toothbrush handle, perpendicular to the lengthwise direction of the
toothbrush mold, as taught in European Patent No. EP 668140, may
result in inadequate hollowing of the toothbrush handle, i.e., some
portions of the previously injected polymer remain as a "mound"
near the gas injection point and are not uniformly distributed
against the walls of the mold. Additionally, it may be difficult to
control the flow of the gas sufficiently to prevent hollowing of
the toothbrush neck. Depending on the inherent strength of the
polymer being used, it may be desirable to avoid formation of neck
portions which are hollow.
[0008] We have also found that the gas injected near the neck of
the toothbrush, perpendicular to the lengthwise direction of the
toothbrush mold, as taught in European Patent No. EP 721832, may
result in inadequate hollowing of the toothbrush handle.
Additionally, the process is likely to lead to a hollowing of the
toothbrush neck.
[0009] Therefore, despite the disclosure of the references, there
is a continuing need for a more efficient process for making
toothbrushes with large cross section handles.
SUMMARY OF THE INVENTION
[0010] The present invention provides a process for manufacturing a
toothbrush including: a) providing a toothbrush mold having a head
portion, a base portion, a toothbrush cavity located between said
head portion and said base portion and having walls, an injection
port for injecting molten plastic, and a gas injection port for
injecting a gas, wherein the gas injection port is positioned in
the end of the base portion of the mold so that gas is injected
into the mold cavity substantially centrally thereof and in a
direction parallel to the longitudinal axis of the mold; b)
injecting a predetermined amount of a molten plastic into the
cavity to partially fill the mold cavity; and c) injecting a gas
(or a mixture of gases) through the gas injection port to direct,
or force, the molten plastic into contact with the walls of the
mold cavity, thereby forming a toothbrush having at least some
portions which are hollow.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0011] The present invention utilizes an injection molding
apparatus in the manufacture of toothbrushes with hollow handles.
Injection molding machines are well known in the art. Any such
machine may be utilized in the present invention. The present
invention is herein described with respect to FIGS. 1, 2, and 3 of
the appended drawings. The key to the present invention is the
location of the gas injection port. In order to control the gas
assist process of manufacturing toothbrushes at least portions of
which are hollow and in which the amount of plastic utilized is
minimized, the gas injection port (5) must be positioned in the
base end (3) of the toothbrush mold (1) such that gas flows into
the mold cavity substantially centrally thereof.
[0012] The molten plastic injection port may be positioned anywhere
on the toothbrush mold, provided it communicates with the mold
cavity. Preferably, however, molten plastic injection port (6) is
located near base portion (3) of mold 1 as illustrated in FIG. 3.
More preferably, molten plastic injection port (6) is located in
the center of the end (3a) of base portion (3) as illustrated in
FIGS. 1 and 2. Even more preferably, the port through which the
molten plastic is injected is located concentrically around gas
injection port (5) in end (3a) of base portion (3) as illustrated
in FIG. 1.
[0013] The toothbrush may be made of any well known plastic such
as, but not limited to, cellulose acetate propionate, nylon,
polyethylene, polypropylene, polycarbonate, poly(ethylene
terephthalate) or the like. Mixtures of two or more such plastics
may be used. The plastic is heated above its melting point and
injected through the molten plastic injection port into toothbrush
cavity (7) in toothbrush mold (1). The amount of plastic injected
will depend on the size of the toothbrush and the desired thickness
of the toothbrush walls. The amount of plastic injected will be
less than the total volume of the toothbrush cavity (7) in the
toothbrush mold. The amount of plastic injected may range from
about 10% to about 90%, preferably from about 20% to about 80% of
the total volume of the toothbrush cavity (7), more preferably from
about 50% to about 80% of the total volume of cavity (7). It will
be understood that lesser amounts of plastic may be used if
desired.
[0014] Mold 1 includes a gate (not illustrated in the drawings)
positioned at the point where molten plastic injection port (6)
joins the body of the mold cavity. Various types of such gates and
their specific orientation in the mold apparatus are well known in
the art. Such gates allow the molten plastic to flow into the
toothbrush mold. There are several types of known gates that may be
utilized. One type of gate that is useful is an edge gate. An edge
gate is shaped like a slot, and has a length ranging from 1 mm to
10 mm, preferably from 5 mm to 7 mm. Although useful, the edge gate
may result in excess polymer flowing into the toothbrush mold after
the gas has been injected.
[0015] A second and preferred type of gate is a point gate. A point
gate is circular in shape.
[0016] The diameter of the gate may range from 1 mm to 10 mm,
preferably from 2 mm to 5 mm, even more preferably from 2 mm to 4
mm. An annular gate is particularly preferred. The annular gate
contains both outer and inner tubes. The outer diameter of the
outer tube of the annular gate may range from 1 mm to 10 mm,
preferably from 2 mm to 5 mm, preferably from 2 mm to 4 mm. The
diameter of the inner tube of the annular gate may range from about
0.1 mm to 9 mm, preferably from about 0.5 mm to 5 mm. Typically,
the outer tube is utilized to inject the molten plastic, while the
inner tube is utilized to inject the gas.
[0017] During the molding operation, at least one gas is injected
through gas injection port (5) into cavity (7) to push the molten
plastic towards the head portion (2) of the mold and to bring the
molten plastic into contact with walls (8) of cavity (7). The gas
may be any inert gas, including, but not limited to, air, carbon
dioxide, nitrogen, and mixtures thereof The pressure at which the
gas is injected may be controlled, so that, if desired, the neck of
the toothbrush is left solid. The pressure at which the gas is
injected will depend on the type of plastic utilized, the size of
the cavity, and the desired thickness of the toothbrush wall.
Typically, the gas is injected at pressures ranging from about 340
kPa to about 4000 kPa, preferably from about 700 kPa to about 2800
kPa, more preferably from about 1375 kPa to about 2400 kPa. The
pressure of the injected gas may be gradually increased during the
gas injection stage, i.e., the initial injection gas pressure may
be relatively low, but during the course of the gas injection, the
pressure of the gas is increased. The pressure of the gas may be
increased uniformly or step-wise throughout the molding cycle.
[0018] The gas injection may begin after the molten plastic
injection is completed. Alternatively, the gas injection may begin
during the molten plastic injection. For example, the gas injection
may begin at any time after from about 10% to about 100%,
preferably from about 30% to about 90%, more preferably from about
50% to about 80% of the total molten plastic injection has been
completed.
[0019] The toothbrush is then cooled and released from the mold. In
order to further reduce the toothbrush manufacturing cycle time,
the gas utilized for the gas injection may be cooled, so as to
begin the cooling process. Conventional cooling techniques, such
as, but not limited to cool water lines around or in the toothbrush
molds and blown air may be utilized to complete the cooling
process.
[0020] The toothbrush may be finished by utilizing conventional
techniques to secure bristles or bristle tufts to the head of the
toothbrush. The bristles may be stapled into the head of the
toothbrush or fused into or onto the head of the toothbrush. The
handle of the toothbrush may be overmolded with materials such as
thermoplastic elastomers or rubber. If desired, the overmolding
process may be carried out during the above described molding
operation. Alternatively, the toothbrush may be transferred to a
separate mold for the overmolding process.
[0021] Several examples are set forth below to further illustrate
the nature of the invention and the manner of carrying it out.
However, the invention should not be considered as being limited to
the details thereof
EXAMPLES OF REDUCTION TO PRACTICE
Example 1
Gas Flow Perpendicular to the Lengthwise Direction of the
Toothbrush Mold
[0022] An injection molding machine designed such that the
toothbrush mold was injected with molten plastic near the base
portion of the toothbrush mold, perpendicular to the lengthwise
direction of the toothbrush mold, and the gas was injected at the
center of the end of the base portion of the toothbrush mold,
parallel to the lengthwise direction of the toothbrush mold, was
used in this Example 1. The location of the gas injection port in
the center of the end portion of the mold helped ensure that the
gas was injected into the central region of the mold cavity. Molten
polypropylene (9 grams /75 percent by volume of the capacity of the
mold cavity) was injected into the mold. Nitrogen gas was then
injected into the mold cavity for about 2 to 3 seconds. The
pressure of the gas at the start of the gas injection cycle was
about 1724 kPa/second. The gas injection pressure was uniformly
increased throughout the gas injection cycle. The pressure of the
gas at the end of the cycle was about 2070 kPa/second. The
toothbrush was cooled and removed from the mold.
Results:
[0023] The toothbrush was cut in half along the lengthwise
direction of the handle. 15 Although most of the handle was hollow;
a mound of residual plastic was seen near the bottom of the handle
where the molten plastic was injected. Additionally, the thickness
of the wall of the toothbrush was not uniform. The cycle time to
produce a solid toothbrush in this mold is typically 32 seconds.
When this mold is used to produce a toothbrush having hollow
portions as set forth in this Example 1, the process cycle time was
reduced to about 24 seconds. The amount of plastic needed to
produce a solid toothbrush in this mold is typically 12 grams. The
amount of plastic needed to produce a hollow toothbrush according
to this Example 1 was about 9 grams.
Example 2
Gas Flow From the Center of the Base End of the Toothbrush Mold
[0024] The injection molding machine described in Example 1 was
modified such that the toothbrush mold was injected with molten
plastic at the center of the end of the base portion of the
toothbrush mold, parallel to the lengthwise direction of the
toothbrush mold. The gas injection port remained located in the
center of the end of the base portion of the toothbrush mold.
Molten polypropylene (9 grams /75 percent of the capacity of the
mold by volume) was injected into the mold. Nitrogen gas at an
initial pressure of 1724 kPa was fed into the molten plastic for 3
seconds, with the pressure at the end of the cycle being 2070
kPa/second. The toothbrush was cooled and removed from the
mold.
Results
[0025] The toothbrush made according to Example 2 was cut in half
along the lengthwise direction of the handle. The handle was
hollow, and the mound of residual plastic observed in the
toothbrush of Example 1 was eliminated. The process of this Example
2 reduced the cycle time to 20 seconds. The amount of plastic
utilized to make the toothbrush utilizing the apparatus and process
of this Example 2 was 9 grams. The wall of the toothbrush had a
substantially uniform thickness.
* * * * *