Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CLOSUR:E:S FOR C CNTAIME~RS FOR
WINE .OR WINE-BASi3D PRODUCTS
This invention relates to closures for containers
for wine or wine-based products. Traditionally such clo-
sures have been of cork, in the form of bungs or stoppersinserted into the necks of glass bottles. Cork has the
- advantages of high elasticity, resilience and softne~s,
which enable cork stoppers to be compressed to a di~meter
- less than that of the bottle neck for insertion into the
neck and then to recover elastically to such an extent as
to seal the neck effectively. The frictional charactçristics
- of cork are such that the stopper grips the neck tightly and
is not liable ~o accidental displacement but can be drawn
out when required, and the gas barrier characteristics are
such that a cork stopper of conventional size, having a
length of ~8 mm. or 44 mmO and a diameter when uncompressed
of 22 mm. (19 mm~ when compressed in a bottle necX), will
restrict ingress of oxygen into the bottle to a low figure.
Against these advantages, one must set the disadvantages
that cork, being a natural produc~, is variable in quality,
and good quality cork suitable for stoppers is relatively
expensive. Any defects in the cork may lead to deterioration
in the effectiveness of the stopper and deleterious e~fects
on the taste of the contents.
For the preservation of wine and wine-based ~ro-
ducts, it is essential that access of oxygen to the product
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should be restricted, to prevent oxidation of the flavour
constituents and of the alcohol content. To stabilise
the product against oxidation, it is normal practice for
the producer to incorporate a small proportion of free sulphur
dioxide (S02) in the product, though the amount which may
be incorporated is restricted by law. Thus a light table
wine may, for example, contain 50 parts per million of free S02.
To achieve an adequate shelf life for the wine, say one year
for a mass-produced light table wi~e, the bottle and stopper
must co-operate to restrict access of oxygen to the wine to
a total amount during that year which is less than the total
amount which can be dealt with by the S0~ in the wine. For
a wine contained in a standard 75 centilitre bottle and
incorporating 50 p.p.m. S02, it can be calculated that the
amount of oxygen which can be dealt with by the S02 in the
wine is 6.5 ml. at normal temperature and pressure.
Efforts have been made previously to produce
stoppers for wine bottles from synthetic plastics materials,
in particular polyolefins such as polyethylene. Difficulties
have been encountered, however, because these materials are
too hard and incompressible for a solid stopper to be
easily inserted into a bottle neck or to conform with
irregularities in the interior surface of the neck to pro-
duce a good seal, when inserted. It has been proposed that
such sto~pers should be made with hollow interiors or in
the form oi a closed-cell elastic foam w.th a densified
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periphery offering a smooth external surface, in order to make
the more compressible, but the relative lack of resilience
in the material still makes it difficult to achieve suffi-
cient conformity with irregularities in the neck to produce
a good seal. Further, the material has a relatively low
creep resistance so that such stoppers tend to take a perma-
nent set after insertion into a bottle neck and thereby lose
their grip in the neck after a time. The frictional character-
istics of the material are such that the stopper can then
slide out of the neck.
In our French patent application 7711990 filed
April 21st, 1977 and published November 25th, 1977 with
Serial Number 2349508 we have described and claimed a
closure for a container of a wine or a wine-based product, at
least a part of said closure intended to contact the product
being in the form of a moulded stopper of a thermoplastics
material, such as an ethylene/vinyl acetate copolymer, having
a foamed core within a liquid-impervious skin, wherein the
foamed core has been produced by blowing the thermoplastics
material with a blowing agent including a thermally decompos-
able sulphite and a water-producing compound, whereby said
foamed core contains sulphur dioxide and water enabling the
sulphur dioxide to act as an oxygen scavenger.
It is an object of the present invention to provide
closures for containers for wine or wine-based products which
will avoid the above-mentioned disadvantages, and
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. . specifically to provide closures for synthetic plastics E
' materials which can be made at relatively low cost and
which will have the advantages.of natural cork closures
as regards insertion and retention of the closures, with-
5 out the disadvantages described above.
. .' . According to the invention, there is provided
a closure'for a co'ntainer for a wine or wine-based '
product, at least the part of said closure which:is
intended to be exposed to the product being in the form
10 of a moulded stopper of.a thermoplastic material having .'~
a closed-cell foamed core'within a liquid-impervious skin,
wherein the thermoplastic material is an ethylene!vinyl
acetate copolymer with a vinyl acetate content of from
. 10/o to 25% and the deg.ree of foaming of the'moulded stopper,
.15 measured in terms of the reduction of density as'compared
' with the unfoamed material, is from 45% to 70%. '
-. Preferably the ethylene~vinyl acetate copolymer :. .
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has.a vinyl.acetate content of from 10% to 20~o.
It has been found that by selecting the material
20 and the degree of foaming in this manner the stopper can be
made to reproduce the de.sirable properties of natulal cork
as regards compressibility and resilience, so that it is
readily inserted into the neck of a.container, such as
a bottle, and conforms with any irregularities therein so
25 as to produce a good seal. The material has.a good creep
resistance so that the stopper retains its grip in the neck
and is not liable to be accidentally dislodged, Stoppers
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in accordance with the invention, when made of appropriate
conventional size, can thus be employed with existing cork
inserting machinery in bottling plants.
sy selecting the material to have a vinyl acetate
content within the specified range, it has also been found
possible to achieve satisfactory gas barrier characteristics
for restriction of ingress of oxygen into the container. In
particular, where the moulded stopper is of conventional
dimensions for a wine bottle cork, having a length between
30 mm and 50 mm and an uncompressed diameter of substantially
22 mm., it has proved possible to provide an oxygen barrier
sufficient to restrict passage of oxygen into a container in
which the closure is fitted to less than 4 ml. per annum.
The oxygen barrier can be further improved by
arranging that the cells of the foamed core contain sulphur
dioxide and water enabling the sulphur dioxide to act as
an oxygen scavenger. This can be done as described and
claimed in our above published French Patent Application
2349508, by producing the foamed core by blowing with a
blowing agent including a thermally decomposable sulphite
and a water-producing compound.
To achieve desirable frictional characteristics
and thereby facilitate handling of the closures in exist-
ing cork-inserting machinery, it is preferable to coat the
moulded stoppers with a lubricant.
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The lubricant must be insoluble in water, because
water-soluble lubricants could mix with the product in
the container and allow the stopper to slide in the neck.
It is also important that the lubricant should not migrate
-5 into the body of the stopper and thus be lost from the
surface. The preferred lubricant which is coated on to the
moulded stopper is a silicone, specifically a polymethyi - !
siloxane, which is insoluble in water and remains on the
surface of the stopper.
Specific examples of the invention will n~w be
described by way of example.
Cylindrical stoppers similar to conventional
- wine corks, having a length of 38 mm and a diameter of
22 mm, were formed from three different ethylene/vinyl
15 acetate (EVA) copolymers having vinyl acetate (VA) contents -
of 12~%, 15% and 18yoJ respectively. An injection moulding
technique was used in which the EVA copolymer was mixed -
with a blowing agent, heated, and injected into a cool mould
so as to produce in known manner a stopper having a closed-
cell foamed core within a smooth liquid-impervious skin.
The melt flow index values for the EVA copolymers were 4,
8 and 10, respectively. It is believed that the melt flow
index is not particularly relevant in this context, though
excessively fluid copolymers should be avoided because o~
difficulty of ensuring formation of the desired multiplicity
of small clo~ed cells and avoiding cell collapse in the
foaming process. The feedstock was formulated and the blp-n--
ing controlled to achieve a degree of foaming of from 50% to
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. 70% measured in terms of the reduction in density as com-pared with the unf.oamed material. The degree of foaming
has been found to be critical. Below 45% foaming the stop-
~ per is insufficiently soft and compressible, and a minimum
of 50% is usually to be preferred, whereas above 70% the
skin of.the stopper is too thin to~retain adequate strength
and oxygen barrier properties.
The blowing agent used in this series of experi-
ments was a mixture of sodium bicarbonate and sodium metabi-
sulphite, the composition of the feedstock being:
Ethylene/Vinyl acetate copolymer 96%
. . Sodium bicarbonate 1%
Sodium metabisulphite 2%
. . Pigment 1%
- 15 The sodium bicarbonate and the sodium metabi-
sulphite decompose at the temperature to which the feedstock
is heated prior to injection into the mould, to produce
carbon dioxide, water vapour and sulphur dioxide, and some
of the sulphur dioxide reacts with the sodium carbonate formed
by decomposition of the sodium bicarbonate to liberate more
carbon dioxide:-
Na2S2o5, _ Na2S03 + SO2
2NaHC03 - _ Na2C03 ~ H20 + C0
N C0 S0 _ N 0 C0
m e sodium metabisulphite ~eing present in stoichiometric
excess, the blowing gas contains sulphur dioxide, carbon di-
oxide and water vapour which expand to cause foaming of the
mixture as the feedstock enters the mould, the effect of ihe
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cool mould walls being to restrict the ~ormation of cells at
or near the sur~ace of the moulded stopper, so that it has a
closed-cell foamed core within a smooth liquid-impervious
skin. The sulphur dioxide, carbon dioxide and water produced
in the blowing process are retained in the cells.
There would be a tendency for the sulphur dioxide
to diffuse slowly out of the cells if the s~oppers were
stored in air. m ey are therefore preferably stored in a
sealed container in an atmosphere of sulphur dioxide until
they are required for use.
Stoppers made as described above were coated with
a polymethyl siloxane lubricant and'inserted into the necks
(of 19 mm.' internal diameter) of wine bottles using conventional
cork-inserting machinery, in which the stoppers are compressed
- 15 to a diameter of 15 mm. bèfore being irserted into the necks.
- The compressibility, resilience, creep resistance and frictional
characteristics'of the stoppers proued to be well suited to the
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machinery so as to enable the stoppers to be readily inserted,
and to cause them to grip the necks tightly and form effective
and lasting seals with no tendenc'y for the stoppers to slip out.
Measuremen~ were made of the rate of oxygen diffusion
through the stoppers described above, under normal atmospheric
pressure conditions. Stoppers made with the 12~% and 15y VA
copolymers showed figures of approximately 3 ml. per annum in
the firs~ year. Stoppers of the 18% VA copolymer gave an
average figure of 3.3~ ml in the first ~ear with a maximum
of 3.5 ml in that year. After the first year, there was a
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. drop to a rate of 2.5 ml per annum. These figures are
well below the.figure of 6.5 ml of oxygen which can be
dealt with by the normal content'of 50 p.p.m. free S02 in
a mass-produced light table wine, indicating that a good
shelf life could be expected. It will be understood that
most other wines and wine-based products have a better resis-
tance to oxidation so that even.bëtter.shelf lives could be
expected for such other products'from use of stoppers in '
accordance with the invention.
. 10 By contrast, stoppers made in the same manner from
' various samples of ethyléne/vinyl acetate copolymer having
- a vinyl acetate content of 28% were found to show. oxygen
diffusion rates of 6.5 ml per annum.and higher and thus to
'have an unacceptably low~oxygen barrier.
. ~hile.the blowing agent described ab.ove is designed
to produce sulphur dioxide and water in the cells to act as
an oxygen s~avenger and thus improve the oxygen barrier, it
would naturally be possible to use other conventional blowing
agents such as nitrogen, pentane, low boiling compounds such
as methylene chloride or fluorinated hydrocarbons. Alternatively
sulphur dioxide and water. can be produced in the cells by other
bl~wing agents apart from the sodlum metabisulphite and sodium
bicarbonate mentioned above'. For example, metabisulphites and
bicarbonates of other metals, particularly other alkali metals
such as potassium, may be used. The water vapour or part
thereof may be'provided by. incorporation of hydrated sodium
citrate in the blowing agen~.
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The stoppers may be moulded with a small chamfer
at each end. Alternatively they may be provided with a
flanged end or head, e.g. of spherical or part-spherical
shape, which may be moulded of the same EVA copolymer or
of a different polymer.
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