Note: Descriptions are shown in the official language in which they were submitted.
CONT~ rNER CLOSURES 2~7~
~ his invention relates to container closures
having a panel that includes an aperture that during use
is maintained closed, but that can be opened to allow
the removal of the contents of the container.
BAC~GROUND OF THE INVENTION
Containers such as cans and bottles are provided
with a closure that often comprises a metal panel. In
some instances it is intended that substantially the
entire closure should be removed in order to open the
container, but in other instances it is intended that
opening should be achieved by displacing part or all of
the panel, the remainder of the closure being left on
the container.
For this purpose, a line of weakness is provided
in the panel around the edges of a desired aperture in
the panel and this aperture is covered by a displaceable
tab. When the container is to be opened, the tab is
displaced, either by pulling or pushing, so as to open
the aperture. The displacement of the tab may involve
total removal of the tab, or it may be displaced into an
open hinged position.
In some constructions the line of weakness is
formed by scoring or stamping the metal or other panel
and a ring pull or other holding means is provided for
pulling the area defined by the line of weakness as a
tab from the panel when it is desired to open the
aperture.
It is intended that the scoring, stamping or
other operation that is used to form the line of
weakness should not disrupt the continuity of the
material of the closure, with the result that leakage of
the contents of the container should be incapable of
occurring through the line of weakness. However the
stamping, scoring or other operation that is used to
form the line of weakness is liable to disrupt the
continuity of any lacquer or other protective coating on
the inner face of the closure and this can lead to
corrosion.
2 Z~
In some containers, the line of weakness can
potentially allow for leakage to occur from the container.
This can be due to accidental disruption of the material of
the panel, but in some instances it is deliberate. In
particular, it is known to provide the panel with an
aperture and to provide a displaceable tab hinged to the
panel, wherein the edges of the tab overlie and are
separated from the edges of the aperture. It is then
necessary to provide a seal between the edges of the tab
and the aperture. Also, it may be desirable to apply
material that will prevent corrosion initiating at the
edges.
It is therefore known to provide a layer of
polymeric material to cover the line of weakness to seal
against corrosion and/or leakage through the line of
weakness. Conventionally the layer of polymeric material
is a layer of gelled PVC plastisol that has been formed by
applying a fluid PVC plastisol and then gelling it. The
layer may be in the form of a disc but often is in the form
of a ring covering the line of weakness.
GB 2,197,634 describes a container closure in which
the removable tab is hinged to the panel and the edges of
the tab overlie and are separated from the edges of the
aperture and defines the requirements of the PVC plastisol
that should be used. In particular, it states that it is
necessary to use a PVC plastisol that has a viscosity of
2,000 to 2,800 mPa.s at 40C when measured at a shear of
441 seconds -l. Other necessary properties are also
defined.
There are allegations that it is undesirable to
allow beverages and foodstuffs to come into contact with
PVC products, and this constitutes a potential disadvantage
to the system of GB 2,197,634 and other systems where a
gelled PVC plastisol covers the line of weakness. It would
be desirable to be able to overcome this disadvantage.
SUMMARY 0~ THE INVENTION
A container closure according to the invention
comprises a closure panel, a line of weakness in the panel
2 ~fr~
around the edges of an aperture in the panel that is
covered by a displaceable tab, and a layer of gelled
plastisol that covers the line of weakness and seals
aqainst corrosion and/or leakage through the line of
weakness and which has been formed by applying on to the
line of weakness a fluid plastisol of polymeric material
and then gelling the plastisol. In the invention, the
polymeric material of the plastisol is free of polyvinyl
chloride and the fluid plastisol has a viscosity that is
below 2,000 mPa measured at a shear of 441 seconds -1 and
40C and that is in the range 200 to 1,800 mPa at 100
seconds -1 and 43C.
DETAILED DESCRIPTION OF THE INV~NTION
Thus we have found that if an attempt is made to
deposit a layer of plastisol that is free of polyvinyl
chloride, it is not possible to obtain satisfactory results
when the material complies with the viscosity requirements
that are stated in GB 2,197,634 to be essential. Instead,
it is essential for the plastisol to have a much lower
viscosity than t~le lowest values stated as being acceptable
in GB 2,197,634. The reason for this is unclear but,
irrespective of the reason, we find that it is a fact that
satisfactory results are not achieved unless the viscosity
is much lower than suggested as being essential in GB
2,197,634.
In addition to the closure end, the invention also
includes containers fitted with the closure end and, in
particular, sealed containers containing a beverage or
foodstuff, methods in which the plastisol is lined on to
the closure and then gelled, and plastisol for use in these
methods.
The container can be a bottle, for instance of glass
or organic polymeric material, in which event the closure
can be a bottle cap. More usually, the container is a can,
in which event the closure will be a can end. The can
and/or can end could be of polymeric material but generally
both are of metal.
2~
A variety of fillings can be stored within the
container ~ut preferably the filling is a foodstuff or
beverage. P~eferably the filling is one that is packed
under pressure and so the invention is of particular
pressure when the filling is a carbonated beverage,
especially beer.
The line of weakness may be a score line or press line
that defines a tab provided with a ring pull or other means
for removal or hinging, as described above. The invention
is then primarily of use for preventing corrosion of the
inner face of the closure. Preferably however the
displaceable tab is hinged to the panel, the edges of the
tab overlie and are separated from the edges of the
aperture, and the layer of gelled plastisol seals between
the edges of the tab and the aperture. The layer of
gelled plastisol generally also extends over the edges of
the tab and the parts of the panel that surround the edges
of the tab. The plastisol will therefore prevent leakage
between the tab edges and the aperture edges, and will also
seal against corrosion initiating at the edges.
Preferably the tab is positioned on the inner face of
the closure and the closure is intended for a pressurised
container (such as beer) since the internal pressure then
forces the tab against the panel. The aperture can be
opened by pressing the tab inwardly.
It can be convenient to provide two apertures, each
with its associated tab and layer of gel plastisol, in the
closure panel, for instance as described in GB 2,197,634.
The tensile strength and elongation values of the gelled
plastisol should be selected having regard to the size of
the aperture such that it is possible to open the aperture
by the application of convenient finger or thumb pressure.
The aperture is often relatively small (typically in the
range 5 to 20mm diameter) and suitable opening forces are
typically in the range 10 to 60N. In order to obtain
these values it is then convenient for the gelled plastisol
to have a tensile strength of about 0.4 to lN/mm2 and a
2~
.
maximum elongation of about 120 to 250%. In particular,
when the closure has an aperture of 15 to 20mm, e.g.,
around 16.5m~, diameter for pouring and an aperture of 5 to
12mm, e.g., around 8mm, diameter for venting, the gelled
plastisol is preferably such that the opening force
required for the pouring aperture is about 20 to 60N
preferably 20 to 40N or 20 to 30N while the opening force
for the venting aperture is about 10 to 40N preferably 15
to 25N. The opening force is determined when there is no
counter pressure.
Although GB 2,197,634 states that it is essential for
the viscosity to have the value of above 2,000mPa at 441
sec1 and 40C in order to achieve satisfactory penetration
between the edges of the tab and the aperture, satisfactory
results are not achieved at these values when the plastisol
is free of polyvinyl chloride and, instead, the fluid
plastisol should have a viscosity of below 1,500mPa at
100s1 and 43C. Generally the viscosity under these
conditions is at least 250mPa and preferably at least
400mPa. Generally it is not more than 1,000mPa and
preferably it is not above 750mPa. The viscosity measured
at 40C and 441 sec typically is also below 1500mPa but
above 200mPa.
Plastisols for use in the invention comprise a
dispersion of thermoplastic polymeric particles in a liquid
organic plasticiser into which the particles will dissolve
on heating to form a gelled structure.
The polymeric component preferably comprises a
homopolymer or copolymer of an acrylic ester or a copolymer
of an olefin with maleic anhydride or blends of these or
blends of either or both of these with other polymers that
are free of polyvinyl chloride.
Other suitable polymers are copolymers of styrene
and/or alkyl styrene (e.g., a-methyl styrene) with
unsaturated carboxylic acid such as methacrylic acid.
Suitable maleic anhydride copolymers are those
disclosed in U.S. 4,020,966, comprising copolymers of
2~ ~ s~
normal ~-olefin and maleic anhydride in a one to one ~olar
ratio in suspension in a polyepoxide plasticiser, for
example epoxidised soy bean oil.
Suitable acrylic ester copolymers include those
described in U.S. 4,199,486 and comprise homo- or co-
polymers of methyl methacrylate as the resin, in suspension
in organic plasticisers such as phthalate plasticiers, for
example dioctylphthalate or dibutylphthalate.
Further suitable acrylate polymers are disclosed in DE
2,454,235 and DE 2,529,732, and include homo- or co-
polymers of alkyl methacrylates and alkylacrylates with
methacrylic acid esters with C2 to 10 aliphatic alcohol,
acrylic acid esters with Cl to 10 aliphatic alcohol,
styrene and/or ~-methyl styrene. Suitable alkyl acrylates
or alkyl methacrylates include methyl methacrylate,
tertiary butyl acrylate, ethyl methacrylate, N-propyl
methacrylate, isopropyl methacrylate, isobutyl
methacrylate, s-butyl methacrylate, t-butyl methacrylate or
cyclohexyl methacrylate.
Any plasticiser suitable for the particular polymer or
polymer ble~d may be used, and it should be capable of
solvating or dissolving the polymer or polymer blend when
heated and of remaining essentially compatible on cooling.
Suitable materials from which the plasticisers may be
selected include, for example, dialkyl phthalates such as
dibutyl, diisodecyl or dioctyl, diethylhexyl or octyldecyl
phthalate, alkylphthalylal~yl glycolate, such as
ethylphthalyl glycolate and butylphthalylbutyl glycolate;
dialkyl esters of alkane dicarboxylic acids such as
diisobutyladipate and dibutylsebacate, acetyltrialkyl
citrates, such as acetyltributyl citrate; tralkyl and
triaryl phosphates such as trioctyl phosphate and tricresyl
phosphate; alkyl esters of fatty acids such as
octylstearate; epoxidised trigycerides such as epoxidised
soy bean oil; polymeric polyester plasticisers such as
polymeric glycol adipate; polyesters derived from dibasic
acids and glycols for example dipropyleneglycolbenzoate,
diethyleneglycoldibenzoate, triethyleneglycoldibenzoate,
polyethyleneglycol 200 dibenzoate, polyethylene glycol 600
dibenzoate. Mixtures of the above plasticisers may also be
used.
The amount of plasticiser used in the plastisol
composition may for example be between 60 and 300
preferably 80 to 200, phr (parts by weight per 100 parts by
weight of the resin).
The non~PVC plastisols used in the invention may also
comprise filler materials such as aluminium trihydrate,
barytes, china clay, chalk, kaolin, mica flour`, wood flour
and diato~aceous earth. The amount typically is in the
range 60 to 600, often 100 to 400, phr.
The plastisol may, if desired, comprise a finely
divided suspension of particles comprising a core material
which reacts well with the plasticiser to form a suitable
seal after fluxing, and a shell material which is less
readily able to react with the plasticisèr and which
prevents contact between the plasticiser and the core
material until the plastisol is heated to flux it.
By appropriate selection of the resin component or
components, the plasticiser or plasticisers and any other
components in the plastisol it is possible to formulate a
plastisol that after gelling will give a gelled layer
having elongation and tensile strength values that are
suitable for the intended use of the composition.
Such fluid plastisols are liable to have too high a
viscosity for use in the invention and so it is generally
necessary to include a viscosity depressant. This is
normally selected from one or more volatile diluents,
emulsifiers and protective colloids. Suitable volatile
diluents include low boiling olefinic hydrocarbons such as
C10-C16 hydrocarbons. Suitable emulsifiers include salts
or esters of fatty acids, ethylene oxide condensates with
alkyl phenyls and fatty alcohols, zinc resinate and
zinc/magnesium octoate. Suitable protective colloids
include lecithin.
The amount will be selected according to the other
c:omponents in the composition and the desired viscosity at
t:he conditions of application, but is generally in the
range 5 to 100, usually 10 to 50, phr.
The compositions can contain other conventional
additives, for instance pigments such as carbon blacX and
titanium dioxide.
The formulation of the plastisol is preferably such
that, having regard to the lacquer or other surface
characteristics of the closure, the plasti~ol wets the
surface adequately, for instance forming an edge angle of
around 30 to 40.
The plastisol can be applied through a ring nozzle as
described in DE 2,421,315 or by other suitable lining
apparatus to a thickness as described in GB 2,197,634.
For further details of suitable fillers and methods of
application, reference can be made to GB 2,197,634.
After applying the fluid plastisol the closure
carrying it is then subjected to heating in order to cause
gelling and fluxing of the plastisol. This generally
requires exposure to a temperature of 150 to 250C for from
5 seconds to 10 minutes. Often the temperature is in the
range 180 to 230C and the time is often in the range ~ to
2 minutes.
The following examples illustrate the invention.
Example 1
A fluid plastisol is formulated from (in parts ~y weight)
MMA/BMA carboxylated copolymer (paste Grade) 70
MMA/BMA copolymer (Filler Grade) 30
30 Aluminium trihydrate 200
Barytes 60
Titanium dioxide 3
Diethyl hexyl phthalate 100
Volatile diluent (tetradecene) 28
35 Protective colloid (lecithin) S
Emulsifiers (blend of Zn/Mg octoate and
ethoylated nonyl phenol) 4.5
9 2~ `J~
MMA/BMA stands for copolymer of methyl methacrylate and
butyl methacrylate. This composition has a viscosity of
690mPa at 441 seconds1 and 400C and 600mPa at 100 sec and
430C.
A can end is provided with a pouring aperture about
16mm in diameter and a venting aperture about 8mm in
diameter, and each aperture has a hinged tab covering it,
of slightly larger diameter so that the edges of the tab
overlie the edges of the associated aperture, with the tab
on the side of the can end that has been coated with
lacquer and that is intended to be inside the can. The
general arrangement is described in GB 2,197,634.
The plastisol is applied as a ring around each
aperture, as described in GB 2,197,634 to give coatings
having a thickness of 0.5mm at the pouring aperture and
0.4mm at the vent ring aperture and which extend between
the adjacent edges of the associated apertures and tabs.
The lined can end is then heated to a temperature of
210C for 1 minute in order to flux and gel the plastisol.
The force required to open the pouring and venting
apertures is 30N and 17N respectively.
Example 2
Two fiuid plastisols are formulated from (parts by
weight):-
A B
Carboxylated MMA/BMA core/shell 70 70
cap alymer (Paste grade)
Carboxylated MMA/BMA conventional 30 30
cap alymer (Filler grade)
30 Diethyl hexyl phthalate loO 130
Di-iso decyl phthalate 2.5 2.5
Aluminium trihydrate 50 50
Barytes 60 60
Titanium Dioxide 3 3
35 Carbon Black 0.1 0.1
Lecithin 5 5
Zn/Mg octoate 2.5 2.5
10 2 g~ ! 6 ~
Ethoxylated monyl phenol 2 2
The compositions have the following viscosities (in
mPa):-
~ B
441 secl at 40C 909 325
100 secl at 43C 1042 407
When applied using the same conditions as described in
Example 1 (except that the fluxing was carried out at 180C
for 3 minutes) to can ends the opening forces for the two
lo apertures are as follows (in N):-
A B
Venting aperture 28 21
Pouring aperture 56 43
While the present invention has been described in relation to its
preferred embodiments, other equivalents, modifications, or variations
can achieve the same result. Equivalents, modifications and
variatlons of the present invention will be obvious to those skilled
ln the art and it ls lntended in the appended claims to cover all
such modifications variations and equlvalents as fall within the
true spirit and scope of this invention.
