Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: METHOD AND ME~NS FOR FOR~ING LINES OF
WEAK~ESS IN CLOSURE CAPS AND SI~ILAR
ARTICLES USING A LASER_B~AM
BACKGROUND OF THE INVENTION
The present invention relates to the use of a laser
beam in the manufacture of closure caps and similar articles
where a line of weakness~is incorporated in the article
during manufacture. More particularly, the method and means
covers the use of a laser beam for providing lines of weakness
which define tear strips or other portions of closure caps
which are removed by the user incident to opening the container
and which are almost universally used in manufacturing tamper-
evident molded plastic closure caps.
There are a large number of differing molded plastic
closure caps which use one form or another of ~ line of
weakness to provide tamper indicating properties. Presently
these caps are formed in one or multi-stage molding processes
where the lines of weakness are formed during the molding process
itself. While this has resulted in satisfactory caps, such
molds are relatively complicated since they require additional
parts for forming the lines. These additional mold parts
require means for moving them during the molding operation to
permit the completed caps to be stripped from the molds without
damage. These characteristics reduce manufacturing speed and
occasionally produce unacceptable articles and also result in
excPss mold wear since there often is a metal to metal contact
resulting from the line forming action within the mold.
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In the method and means of ~he present invention, the
caps are first molded in simplified molds which form the
necessary caps without the formation of the lines of weakness.
Thereafter the caps are transferred to a laser station where
the laser beam melts or cuts the necessary lines of weakness
in closure caps to complete tlleir manufacture. The result is
a simplified high speed cap manufacturing operation which
requires only simple molds which operate indefinitely without
excessive mold wear.
Examples of closure caps including lines of weakness
are found in many prior caps including, for example, the caps
described in issued United States patents No. 3,913,771, dated
October 21, 1975 and No. 4,299,328, dated November 10, 1981.
Accordingly, an object of the present invention is
to provide an improved method and means for manufacturing
molded plastic closure caps and similar articles which incorporate
lines of weakness or perforated lines.
Another object of the present invention is to provide
a method and means of employing laser beams in forming lines
of weakness in molded plastic articles such as closure caps
and the like.
Another object of the pr~sent invention is to provide
an improved laser method and means for use in closure cap
manufacture.
Other and further objects of the present invention
will become apparent upon an understanding of the illustrative
embodiments about to be described or will be indicated in the
appended claims, and various advantages not referred to
herein will occur to one skilled in the art upon employment
of the invention in practice.
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BRIEF DESCRIPTION OF THE DRAWINGS
A preferred embodiment of the invention has been
chosen for purposes of illustration and description and is
shown in the accompanying drawings, forming a part of the
specification, wherein:
FIG. l is a diagramatic illustration of the method
and means of the present invention employing a laser beam in
manufacturing closure caps and the like.
FIG. 2 is a horizontal sectional view taken along line
2-2 on FIG. 3.
FIG. 3 is a vertical sectional view of a molded plastic
closure cap including a line of weakness formed using a laser
beam in accordance with the method and means of the invention.
FIG. 4 is an enlarged fragmentary sectional view of
a portion of a closure cap skirt having varying thickness for
forming an interrupted line of weakness using a laser beam.
DESCRIPTION OF THE PR~FERRED EMBODIMENT
In this invention, laser beams are employed for the
purpose of burning or melting plastic and thereby forming very
thin cut lines or interrupted lines7 or in some cases grooves
which extend only partially through the articles. In each
case these laser beams are forming what are known as lines of
weakness which facilitat-e a tearing-off or a rupturing of
certain portions of closure caps and the like for tamper evident
portions.
For example, in the drawing, a molded plastic closure
cap l is illustrated havin~7 an upper sealing cap portion 2,
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with threads 3, for fastening it to a container mouth. A
tamper indicating ring 4 is provided which extends downwardly
from the bottom of the cap skirt and which includes a bead 5
for locking engagement with a cooperating bead on the container.
A line of weakness 6 is provided between the cap portion 2
and the tamper indicating ring 4. The line 6 comprises a
relatively thin slit interrupted by a number of connecting
bridges 7 which hold the ring 4 in place. When the closure cap 1
is purposely removed or is removed by an unauthorized person,
the ring 4 remains locked to the container so that it is torn
free of the closure at the line 6 thereby indicating that the
cap top portion 2 has been completely or partially removed.
Such lines of weakness are also employed on a number of closure
caps which have a rip tab which is removed during the cap
opening and where the line of weakness facilitates the removal
of the tear strip by the package user. The laser method and
means of the present invention is used to form such lines of
weakness in a manner which will now be more fully described.
There are a number of laser devices which are
commercially available and which generate laser beams which
are beams of high intensity coherent light which is essentially
monochromatic or having a single wave length. Thi.s
characteristic permits the light energy of the laser beam to
be focused at the surface of the closure caps into a very
small contact area as small as a few thousandths of an inch or
less. The lasers are available in a wide range of power or
heat producing energy and may have an output power from a
fraction of a watt to several hundred watts depending upon the
particular application.
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Laser beams for forming lines of weakness in
accordance with the present invention use a relatively sharp
focus to concentrate the beam energy over the width required
for the line of weakness.
Since plastic materials are poor ~hermal conductors
or insulators, heating action at the surface of the plastic is
localized and remains high for the area defining the width of
the line of weakness. The temperature of the plastic in this
localized area rises above the melting point providing the
necessary cutting action. A satisfactory melting or cutting
action is therefore obtained with the typical closure materials
such as polyethylene, polystyrene or polypropylene or other
moldable plastics having thermo-plastic charac~eristics.
FIG. 1 illustrates diagramatically a line forming
appa~atus 8 such as might be used in accordance with the present
invention for forming the line of weakness 6 in a closure cap l
as illustrated in FIG. 3. The closure caps are mounted on a
suitable spindle 9, probably in a multi-spindle machine and the
caps are presented to the laser beam cutting station 10. At
the station lO the cap l is rotated while being exposed to the
laser beam ll generated by a laser, 12. The beam 11 is
focused by a suitable focusing means, shown as a focusing lens 13
in FIG. 1, to strike the moving surface of the closure cap l
at the desired position. In the formation of a line of weakness 6
of the type illustrated in FIG. 4, a single revolution at a
relatively low speed may be employed with the beam 11 being
turned on and off at pre-set intervals to form the necessary
number of bridges which detachable connect the ring to the
closure cap. The control of the beam may be by means of an
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electro-mechanical or electronic s~itching device coordinated
with the means 1~ for rotating the cap.
Alternatively, more than one turn of the cap may be
used where a complete cut is done or where the line of weakness
may extend only partially through the plastic cap material.
Other controls may be used in the form of sensing devices such
as an electronic counter illustrated at 15 in FIG. 1.
Another means for forming an intermittent or interrupted
line of weakness results from the shaping of the molded plastic
article. In the case of a closure cap, for example as
illustrated in ~IG. 4, the cap sidewall or skirt 16 is molded
with portions of differing thickness 17 and 18. In this case
the intensity of the laser beam 19 is adjusted for providing
sufficient heating to melt or cut completely through the thinner
portions 17 of the cap skirt 16 while cutting an equivalent
distance into the thicker portions 18 therPby leaving plastic
bridges 19 along the line of weakness 20.
It will be seen that an improved method and means has
been described for the manufacture o~ closure caps and similar
articles in which the previously difficult operation of forming
lines of weakness in the molding process has been replaced by
an efficient and simplified laser cutting process. The
improved laser process insures a more accurate production of
lines of weakness and also eliminates the need for complicated
dies and the need for dies which include parts subject to
significant wear.
As various changes may be made in the form, construction
and arrangement of the parts herein without departing from the
spirit and scope of the invPntion and without sacrificing
any of its advantages, it ;s to be understood that all matter
herein is to be interpreted as illustrative and not in a
limiting sense.
