Note: Descriptions are shown in the official language in which they were submitted.
W~ 91/1~369 PCT/C~91/00022
Screw Cap with Warranty Ring
The invention concerns a screw cap for closure of a container
opening, according to the preamble of Claim 1. These types of
screw caps perform a warranty function, in that initial removal
of the cap is displayed through a tearing-away of the warranty
strip. The retention elements, on initial screwing-on of the
cap, engage under the container bead and can, howe~er, no
longer slide over the bead on initial unscrewing, so that the
warranty strip tears away
There are already numerous different versions of retention
elements known. Thus, inwardly protruding tongues or also beads
are used, for example, which block the warranty strip when
unscrewing for the first time. Shaping of the entire wall of
the warranty strip, in cross section, in such a way that it
forms numerous inward pointing indentations is also known, as
is described, for example, in EP-A-337 0~6.
A problem with all related screw caps of comparable design is
that the retention elements on the one hand must possess
sufficient flexibility in order that screwing on of the cap is
possible, and that on the other hand they must be solid and
stiff enough to bring about a tearing-away of the warranty
strip when unscrewing. Finally, the entire arrangement must
also be easily ejectable from an injection molding tool with
axially opening parts, since undercuttings are only permitted
to a limited extent.
21~.9~
It is therefore a purpose of the invention to create a screw
cap of the type mentioned in the introduction, with which the
retention elements permit themselves to be slid over the
container bead without excessive expansion of the warranty
strip, whereby reliable blocking of the warranty strip is
ensured as soon as the screw cap has reached its final
position. This purpose is solved with a screw cap according to
the invention, which exhibits the features of Claim 1.
The wedges, which taper in the direction of screwing on, offer
only slight resistance to the screwing-on movement. The
slipping behaviour in the closure direction is of particular
advantage, whilst the recoiling faces of the wedges have a
blocking effect in the direction of unscrewing. Since the
wedges are positioned upon the inner wall, they additionally
stiffen the warranty strip, whereby the ability to tamper with
the strip is greatly reduced~
Both the side flanks of the wedge are preferably inclined
relative to the inner wall. In the case of the lower side flank
which is aligned towards the lower edge of the warranty strip,
this causes a centralising of the strip during screwing-on, and
a gentle expansion over the container bead. ~n the case of the
side flank aligned towards the cap base, the inclination causes
easier ejection from the injection molding tool.
The side flanks of the wedge oriented towards the cap base are
inclined at an angle relative to a plane running a right angles
to the middle axis of the screw cap with particular advantage.
With that, the inclined position of the side flanks can
correspond approximately to that of the helix angle of the
pitch of the cap thread. This configuration has the result that
the side flanks will not engage with a sudden spring action
under the bead, but will rather slide beneath the bead in
accordance with the chosen inclination.
Further advantages can be achieved if material beads which
protrude above the wedge surface are arranged on the side
flanks of the wedges oriented towards the cap base. As opposed
to the rest of the wedge body/ these edge beads are relatively
flexible and can easily bend backwards on initial screwing-on
of the cap. In spite of that, they increase the engagement
depth of the entire retention element.
The shape and number of wedges is in each case adjusted to the
specific relationships, respectively other dimensions of the
screw cap. Preferably, however, the wedge extends over at least
half of the total height of the warranty strip. Good stiffening
of the warranty strip is achieved through this axial expansion
of the retention elements. The ma~imum wedge thickness can be
at least the same or greater than the thickness of the rest of
the warranty strip. The spacing between the individual wedges
should be such that the individual wedges can achieve optimum
effect and that a certain circumEerential elasticity can still
be maintained. The spacing between the individual wedges should
for this reason at least correspond to the total length of a
wedge.
The material beads on the side flank of the wedges, as
mentioned above, are formed with particular advantage
immediately on ejection from the tool, without the need for a
negative bead shape on a tool component. The side flanks of the
wedge oriented towards the cap base must merely be inclined in
such a way that the material beads form themselves through
-- 4 --
squeezing of the material when the inner tool part which forms
the inner wall of the warranty strip retracts away from the
wedge, with the plastic material being in a condition which is
not yet fully solidified. According to the chosen inclination,
a somewhat larger or smaller material deformation of the
material can be achieved.
~n embodiment of the invention is portrayed in the drawings and
will be more closely described in the following. Namely:
igure 1 a cross-section through a screw cap placed upon a
container opening, with the features of the
invention.
igure 2 a view of the screw cap from below, according to
figure 1
igure 3 a cxoss-section through the warranty strip in a
greatly enlarged scale, and
igure 4 a plan view of a wedge in the axial direction of the
screw cap.
Figures 1 and 2 show the screw cap enlarged several times. It
comprises, in a known way, an approximately cylindrical cap
side wall 2 with an internal thread 4. On the cap base 3, an
inner seal is arranged which can, however, have another desired
configuration or which can be replaced by a seal insert r for
example. On the lower edge of the cap 6 a one piece warranty
strip 1 is arranged on numerous tear-off connecting ribs 7.
-- 5 --
Numerous wedges 9, which taper in the screwing-on direction A,
are positioned upon the inner wall 8 of the warranty strip at
regular intervals. After the initial screwing-on of the cap~
these wedges serve as retention elements which engage under a
surrounding container bead 17 on a container opening 15r The
container opening is provided with an external thread 16 and
the screw caps are screwed onto the container in a known way
with the aid of special screwing-on devices.
As can be observed in figure 2, eight wedges 9 can, for
example, be arranged at regular intervals in the line of the
circumference. In the case of closure caps for mineral water
bottles, this number has shown itself to be of particular
advantage. Naturally, either more or fewer wedges can be
arranged, depending on the total circumference of the warranty
strip. In certain cases it would be even conceivable for the
wedges to be arranged at irregular intervals. Details of the
wedge configuration can be observed in figures 3 and 4.
Accordingly here, the individual wedges have an angle Alpha,
which ensures gentle engagement. The wedge surfaces 14 can be
shaped either flat or curved. The wedge face 12 runs preferably
radially outwards, but could however be inclined.
The upper side flank 10, oriented towards the cap base 3, is
inclined at an angle Gamma to the inner wall of the warranty
strip. This inclined position of less than 90 ensures axial
ejection from the inside of the tool mold inspite of the
undercutting formed by the side flank 10. The lower side flank
11 is inclined at a somewhat more acute angle Delta, so that
the wedges slide easily over the container bead.
~ Q ~
The upper side flanks 10 do not run parallel to the lower edge
6 of the cap, but at the angle seta, inclined to a plane
running at rightangles to the middle axis of the cap. This
angle can approximately correspond to the helix angle of the
pitch of the internal thread 4, thus approx. 2 degrees 30
minutes. The side flank 10 slides in this way beneath the
container bead 17 in a particularly gentle way.
A material bead 13, which protrudes over the wedge surface, can
be arranged in the transitional area between the side flank 10
and the wedge surface 14. This bead improves the retention
properties of the wedgel but is not absolutely necessary. The
bead 13 can be created without a special negative shape on the
tool through correct choice of the angle Gamma. During
retraction of the inner tool component, with a molding compound
in a relatively plastic condition, squeezing of the material
will occur in accordance with the dimensions of the wedge, and
this will result in a useable bead. The screw cap is
manufactured from a known plastic material such as, for
example, Polyethylene or Polypropylene.
