Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The invention relates to a closure cap made from
a polypropylene material.
Closure caps are known which comprise an end
wall and a circumferential side wall, with a gasket being
6 formed in the closure cap via a melting and a cooling
operation by applying in the closure cap an amount of
plastisol which i5 shaped therein into a gasket
configuration at an elevated temperature ad~usted after
the plastisol addition, causing the plastisol shaped into
the gasket configuration to melt completely by further
energy supply and then cooling same to form the gasket.
Such a process is known ~rom Dutch patent
applicatibn 80.033~1. In this known process a closure cap
often made by injection moulding from an olefin polymer,
in particular a high-melting polypropylene having a
melting point of approximately 165C, after having been
provided with a vinyl chloride resin plastisol, is
preheated to a temperature which must be 5-35C below the
melting point of the employed olefin polymer, e.g.,
polypropylene, preferably 5-15C,
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i.e. it must be preheated to a temperature of at least
130 C, preferably 145-160 C, followed by exposure at
this temperature in an appropriate oven to microwave energy
having a frequency which is not critical from a technical
- s point of view indeed, but is effectively 300-300,000 MHz.
Exposure to the microwave energy takes place at the moment
when the plastisol shaped into a gaske-t configuration
is completely liquid, i.e. completely molten, which means
that the resin has been completely solvated by the plasticizer.
Preheating can be appropriately carried out
in a hot air oven.
In the known process it is indicated that, in
general, a temperature of the closure cap of more than
35 C below the melting temperature thereof is probably
not suitable for the conventional plastisols. If there
is used a plastisol having a lower melting point, then
also a lower temperature of the closure cap can be maintained
in the preheating step. However, if there is started from
a closure cap made from an olefin polymer melting at a
lcwer temperature, then, conversely, the temperature range
to be maintained for the closure cap in the preheating
step must preferably be only 5-15 C, in particular 5-10 C
below the melting point of the olefin polymer. Therefore,
if the closure cap is made from, e.g., polyethylene having
a high density, then, accordingly, the temperature range
of the closure cap in the preheating step is pre~erably
120-125 C.
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In practice, it is assumed in the known process
that, e.g., after the plastisol has been added to the
closure cap, this closure cap is brought into a hot air
oven having an air temperature which is 30 C, preferably
20 C, below the melting point of the olefin polymer material
from which the closure cap has been made. For instance,
when polypropylene is used as the olefin polymer material,
the preheating step is carried out, in practice, at an
air temperature of 135-160 C for 1-10 min., e.g., an
air temperature of 155 C for approximately 3 minutes,
followed by the procedure in a microwave oven in which
the ambient temperature is likewise high enough to prevent
the preheated closure cap from sustaining heavy losses
oE heat, and which is, e.g., at least 140 C. The duration
15 of the microwave procedure depends on the energy supplied
and is not less than approximately 1 min.
The step of shaping the plastisol in the closure
cap until a gasket configuration has been obtained can
be performed in the conventional manner, preferably by
20 injecting the plastisol in liquid or semi-liquid condition
into the closure cap which is advantageously arranged
upside down, i.e. the end wall is positioned at the bottom
side, and distributing same therein by subjecting the
closure cap to a rapid rotation. There is preferably used
25 a closure cap the end wall of which is internally provided
with an inner edge, the plastisol being injected into
the annular space between the inner edge and the side
-- 4 --
wall of the closure cap.
The known process i~ suitable Eor a varlety oE
types of closure caps and container~, in particular,
however, for closure caps of bottles of threaded
construction or of the snap-on type, which caps can be
provided with an unspecified anti-theft means, however,
normally have a limited inner diameter of approximately
25-32 mm.
Various types of anti-theft means applicable in
combination with a closure cap are known, a review of
which is given in the article "Verschl~s~e f~r
Getrankeflaschen", published in Verpackings-Rundschau
10/1983, pages 10~4-1093. Among these, the type
comprising a sealing ring produced in one piece with the
close cap and connected with the side wall of the closure
cap via a number of narrow frangible brldye~ to be broken
on the first opening of the container cannot be used
within the framework of the known process. Because of the
high temperature of the closure cap to be maintained in
the preheating step and subsequently upon exposure to the
microwave energy of only 5-35C below the melting pOiIlt of
the olefin polymer material used for making the closure
cap, the narrow frangible bridges and the sealing ring,
respectively, will be softened and deformed, which results
2~ in that the whole construction becomes useless.
An object of the invention is to provide a
process for making a closure cap provided with a gasket
from a polypropylene material, which i9 further provided
with a sealing ring of the type that is integrally
connected with the closure cap, in particular with its
side wall, via a number of narrow bridges which are broken
on the first opening of the container.
Another ob~ect of the invention is to provide a
closure cap made from an olefin polymer ancl provided with
a gasket of a plastisol material, which is suitable for
~.
~g4~3
-- 5
use on a container having a wide mouth the diameter o~
which may be up to 9o mm and more.
According to one aspect of the invention there is
provided a process for making a polypropylene closure cap
for a container, said closure cap comprising an end wall
and a circumferential side wall, the end wall being thinner
by 20-50% at the position where a gasket is to be formed,
and being internally provided with an annular space bounded
by two undexcuts and within which the gasXet will be
contained, the inner undercut being tapered in cross-
section and resilient and having a width such that when the
container has been closed with the closure cap the inner
undercut rests on a paxt of the upper surface of the
container edge, in which process the gasket is formed in
the closure cap via a melting and a cooling operation by
applyiny in the closure cap an amount of plastisol which is
shaped therein into a gasket configuration at an elevated
temperature adjusted after the plastisol addition, causing
the plastisol shaped into the gasket configuration to melt
completely by further energy supply and then cooling same
to form the gasket, wherein an integral combination of the
closure cap with a sealing ring is initially formed, which
sealing ring is connected with the closure cap by means of
a number of frangible bridges capable of being broken on
the first opening of the container, and wherein the melting
operation to form the gasket is carried out by heating the
closure cap after addition of the plastisol to a
temperature of 50-llO~C and by subsequently exposing the
resulting plastisol shaped into the gasket configuration to
electromagnetic energy having a frequency of from 10 to 200
; M~lz until the plastisol has become completely molten.
The process according to the invention may start
from a closure cap of a standard grade polypropylene: it is
therefore not necessary to use a high-melting polypropyl-
`` ~Z~2~ ~3
ene material. There can also be used a normal type of
plastisol, e.g., that consisting of a microsuspension
of a vinyl chloride copolymer resin with 5% vinyl acetate
and further comprising conventional constituents, e.g.,
one or more stabilizers, plasticizers, viscosity-reducing
and/or torsion-reducing agents.
It is very advantageous to start from a closure
cap the end wall of which is internally provided with
an annular space bounded by two undercuts the outer one
of which is substantially bounded by the inner periphery
of the side wall of the closure cap, and into which annular
space a dosed amount of plastisol is injected in the conventional
manner.
Preferably, the starting point of the invention
is a closure cap the end wall of which is thinner by 20-50%
at the position where the gasket is to be formed, such
as at the position of the annular space bounded by the
undercuts mentioned before. This promotes the heat transfer
to the plastisol in the oven, such as the hot air oven
in which the preheating can be performed. Moreover, the
higher flexibility of the end wall at the relevant position
enhances the self-ventilating action of it when the contents
of the container are pasteurized.
According to a further embodiment of the process
25 of the invention the melting operation of the plastisol
disposed in situ in the closure cap is carried out by
preheating the combination of closure cap and plastisol
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to 50-110C and then exposing the resulting gasket
configuration to microwave energy having a frequency of 10-
200 MHz.
According to a preferred embodiment the melting
5 operation is carried out by heating the closure cap to
100C within 15-30 seconds after addition of the plastisol,
and completely melting the plastisol shaped into the gasket
configuration by 3-15 seconds exposure to microwave energy
having a frequency of 27.10-27.15 MHz. This frequency is
10 permitted for industrial uses throughout the whole world.
In the process according to the invention a
closure cap is obtained which comprises a homogeneous
gasket, and which is further provided with an undamaged,
undeformed sealing ring, and which closure cap may have an
15 inner diameter such that it can be applied to a container
having a wide mouth. For instance, according to the
invention a closure cap can be obtained having an inner
diameter which may be up to 90 mm or more.
The invention is particularly suitable for,
20 although not limited to, the preparation of a closure cap
with an integrally connected sealing ring, the inner side
wall of which is threaded so that this container can be
opened or closed by rotation of the closure cap, in
conjunction with corresponding provisions made at the neck
25 of the container.
Another aspect of the invention provides a
closure cap formed from an olefin polymer, comprising an
endwall, a circumferential side wall provided with a gasket
formed from a plastisol material, and a sealing ring with
30 which the container can be sealably closed in conjunction
with a locking collar disposed around the neck of the
container, which sealing ring is integrally connected with
the side wall of the closure cap via frangible bridges
capable of being broken on the first opening of the
35 container, said end wall having a wall thickness decreased
by 20-50% at the gasket and being internally provided with
an annular space bounded by two
2~'~3
undercuts and within which the gasket is contained, the
inner undercut being tapered in cross-section and resilient
and having a width such that when the container has been
closed with the closure cap the inner undercut rests on a
5 part of the upper surface of the container edge.
When the closure cap is made from a polypropylene
material, it is ensured that the diameter of the sealing
ring is large enough to provide that after the container
has been closed with the closure cap the sealing ring and
10 the bridges are not in contact with the container. When
the sealing ring and the bridges are heated during the
sealing procedure, such a contact, as will be elucidated
hereinafter, would mean that heat is dissipated via the
container so that the polypropylene material becomes
15 insufficiently plastic. On the other hand, when
dimensioning the sealing ring and the bridges with a
closure cap made from a polypropylene material, it is
ensured that in the sealing procedure
Z4~3
g
the bridges can be overstretched under the locking collar
and are malleable.
Finally the invention also relates to a process
for closing and sealing a container in which, after the
5 container has been closed, the temperature of the sealing
ring is increased and the sealing ring is deformed over
and around the locking collar towards the neck of the
container. When a closure cap according to the invention
is used which has been made from a polypropylene material,
10 the procedure followed is such that after the container
has been closed with the closure cap, the sealing ring
is subjected to a heat treatment until a sufficient plasticity
of the polypropylene material has been obtained, after
which the sealing ring is mechanically pressed agalnst
15 the neck of the container over and around the locking
collar with simultaneous overstretching and flattening
of the bridges over and under the locking collar. The
heat treatment may consist in, e.g., exposing the sealing
ring and the bridges to air having a temperature of approximate-
20 ly 400 C for approximately 2 sec. After mechanicallypinching with e.g. so-called clamps, the ring is positioned
around the container under the locking collar and the
frangible bridges are stretched and flattened. Thus it
is achieved that in spite of per se relatively tough poly-
25 propylene material the sealing ring is easily detachedat the frangible bridges on the first openiny of the container.
When the closure cap is loosened for the first time, the
-
Z~'~3
--10--
sealing ring will substantially be detached from the closure
cap via -the bridges so that, after the closure cap has
been closed again, it will always be visible that the
container has been opened.
The closure cap according to the inventlon is
the first to incorporate a combination of three properties,
namely that (a) the container closed with the closure
cap after filling can be closed in compression-proof and
vacuum-tight condition substantially without any restriction;
lO (b) the container can be closed again after opening so
that it is completely shut off from the atmosphere, and
(c) the closure of the container after the first filling
is irreversibly sealable.
Because of the fact that the closure cap according
15 to the invention can be made available with an inner diameter
which may be up to lO0 mm the possibility has been offered
for the first time to seal containers having a wide mouth
so that for the first time foodstuffs which, in practice,
are packed mainly in containers having a wide mouth, e.g.,
20 a neck diameter of 90 mm, whether or not under a partial
vacuum, can be offered to consumers in sealed condition
with a guarantee of freshness. This ensures that the date
indicating until when the product will keep, as it occurs
on containers for foodstuffs, is a practically reliable
25 date indeed. In the case of a closure without a sealing
capable of being broken irreversibly such a date is actually
a fiction.
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The invention will be further illustrated by
means of the drawing which shows an example of embodiment
of the closure cap and the method of sealing it. In the
drawing
Fig. 1 schematically shows an axial cross~section
of a container closed with the closure cap;
Fig. 2 schematically shows an axial cross-section
of a container closed with the closure cap and provided
with a sealing ring, in the pre-sealed state;
Fig. 3 shows a cross-section along the line
III-III in Fig. 2;
Fig. 4 shows, in cross-section, the assembly
of closure cap and container according to Fig. 2 during
sealing with the use of a so-called clamp; and
Fig. 5 shows a cross-section along the line
V-V in Fig. 4, without the clamp and the container.
In Fig. 1 the wall of the neck oE a container
made of glass is indicated by 1, and 2 shows the closure
cap of polypropylene. On the inside the closure cap is
provided with an annular space formed by the two circumferen-
tial undercuts 3 and 4, which annular space comprises
the gasket 5. The inner undercut 3 is crescent-shaped
and is resilient due to the outwardly decreasing thickness
of the material. The crescent-shaped construction permits
the inner undercut to rest on a part of the edge of the
neck opening of the container. As a result thereof a part
of the higher unscrewing torsion of the gasket is absorbed
-12-
and reduced by the undercut. Moreover, the crescent-shaped
undercut 3 ensures that in case of pasteurization of the
contents of the container the expanded air generated in
that process flows out between the undercut 3, which is
thereby resiliently deflicted somewhat, and the edge of
the neck whereby the deflected undercut simultaneously
causes an additional clamping force to be exerted on the
gasket and the gasket is retained in position.
Figs. 2-5 show the closure cap of polypropylene
at 10, comprising side wall 11 and sealing ring 13 which
is connected with side wall 11 via a frangible bridge
12. The neck portion of the container is shown at 14,
which neck portion 14 is provided with locking collar
17.
In the state before sealing (Fig. 2) the side
wall 11 with frangible bridges 12 and sealing ring 13
is clear of the container.
Fig. 4 shows the situation in which the frangible
bridge 12 with the sealing 13, which where previously
exposed to the action of hot air having a temperature
of 400 C for 2 sec., has been grasped by the clamp 15
moving towards the container. The frangible bridge 12
is then overskretched over and under the locking collar
17 and flattened, the sealing ring 13 also being flattened
simultaneously between the clamp 15 and the neck portion
14 of the container. Fig. 5 shows, in comparison with
Fig. 3, the deformation experienced by the frangible bridge
'` 3~;2~Z~3
-13-
12 and the sealing ring 13, which has resulted in that
the sealing ring has a diameter smaller than the largest
diameter of the locking collar 17. When the closure cap
is unscrewed, an axial shiEt of the closure cap 10 is
blocked by abutment of the sealing ring 13 against the
locking collar 17. When the unscrewing movement is continued,
the increasing force exerted by the locking collar 17
on the combination of sealing ring 13 and frangible bridge
12 will result in that the frangible bridge 12 weakened
by overstretching and flattening, which is made of the
per se tough polypropylene, is broken along the line of
fracture 16 (Fig. 5).
of course, amendments may be made to the invention
as described above and shown in the drawing without departing
from the scope of the invention.
