Polyethylene closure for a container

Details Polyethylene closure for a container Polyethylene closure for a container

2000-04-18

2001-11-13

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S140000, C521S144000, C521S124000

Reexamination Certificate

active

06316511

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a polymeric closure for a container. It will be convenient to describe the invention with reference to use as a closure for bottles, in particular, wine bottles, however it should be noted that the invention may have wider application.
BACKGROUND OF THE INVENTION
Natural cork has been used as a closure for bottles containing wine and other liquids for many years. Due to its resilience, elastic properties, water impermeability and, in earlier times, low cost, cork is widely used throughout the wine industry worldwide for sealing bottles.
Availability of cork has in recent time decreased due to more widespread demand and limited supply. However, cork quality has also become a concern to wine producers as a result of undesirable reactions between the cork and the wine. Problems from cork taint are estimated to be as high as 6% of all bottled wine. One form of cork taint occurs when trichloroanisole (TCA) present in the cork migrates into the wine giving rise to “off” flavours. The costs involved have become an unacceptable burden on wine producers. Accordingly, there is a need for an inexpensive alternative to natural cork, which has no such reaction with wine.
A number of synthetic closures are presently available on the market. One type of closure comprises a substantially cylindrical polymeric body having radial resilient flanges along the length of its shank adapted to seal about the inside neck of a container, and a crown which overlies the bottle opening. Such closures are commonly used for sparkling wines. A disadvantage of such closures is that they require special corking machinery for their insertion into bottles and they cannot be utilised in an unmodified bottling operation.
Other types of polymeric closures available are generally identical in size and shape to conventional corks and can be utilised in standard bottling operations without needing to modify machinery. One group of known polymeric closures are manufactured from foamed ethylene vinylacetate (EVA) copolymer. The polymer is generally foamed with a foaming agent such as azodicarbonamide (ABFA) or ozodecarbonoxide. Other polymers have also been proposed for use for such closures. Closures made from Linear Low Density Polyethylene (LLDPE) blended with ionomers have also been disclosed.
The polymeric stoppers known in the art suffer from a number of disadvantages primarily as a result of the polymeric material from which they are made. First, the EVA polymers which have the desired flexural properties may exhibit some odour or flavour taint which may affect the contents of the bottle and EVAs which do not exhibit taint are not likely to have the desired flexural properties. The foaming agents suftable for use with EVAs similarly may demonstrate some flavour or odour taint of the contents of the bottle which they are sealing. EVAs are also prone to degradation during manufacture of a closure.
Polyvinylchlorides (PVCs) and ionomers are unsuitable as they impart undesirable taint to the wine.
LDPEs including LLDPEs although they do not impart significant undesirable tastes to the wine, do not have adequate flexural properties in particular, inadequate elastic recovery in order to form an adequate seal.
Accordingly there is a need for a polymeric closure for a container which satisfies many or most of the following performance criteria:
a) Does not impart any taint to the contents of the container, especially where such contents are wine;
b) Does not scalp any flavours from the contents of the container to any significant extent;
c) Has suitable flexural properties such that it can be adequately deformed and inserted into the opening of the container, yet will recover sufficiently to maintain a long-term fluid impermeable seal between the closure and the container
d) Can be removed in one piece from said container when desired using conventional apparatus, such as a corkscrew, without structural failure
e) Can be coloured to resemble natural cork and optionally printed upon
f) Can be used in conventional corking machinery
g) Can be mass produced cost effectively.
“Scalp” refers to the undesirable tendency of some substances to extract flavours from a liquid. it is an object of the present invention to provide a polymeric closure which meets one or more of the above performance criteria.
SUMMARY OF THE INVENTION
In one aspect of the invention there is provided a polymeric closure for a container comprising a foamed polyethylene, wherein said polyethylene has:
i) a density of between 0.910 g/cm
3
and 0.885g/cm
3
;
ii) a molecular weight distribution of 2 or less; and
iii) a melt index of between 2 and 30, more preferably between 2 and 10.
In another embodiment there is provided a polymeric closure for a container comprising a foamed polyethylene, wherein said polyethylene consists of a blend of two or more polyethylenes, each polyethylene having:
i) a density of between 0.910 g/cm
3
and 0.885 g/cm
3
;
ii) a molecular weight distribution of about 2 or less; and
iii) a melt index of between 2 and 30.
Even more preferred polyethylenes of the present invention are selected from polyethylenes having:
i) a density of between 0.900 g/cm
3
and 0.888 g/cm
3
;
ii) a molecular weight distribution of 2 or less; and
iii) a melt index between 2.2 and 3.5, or a blend of 2 or more polyethylenes having these properties.
Melt index, being the viscosity of the polymer at a specified temperature and pressure is determined by ASTM D-1238, and is a function of the molecular weight of the polymer.
The polyethylenes selected in the present invention display all the desirable characteristics for container closures, especially those used in wine bottles, namely high thermal stability and resistance to degradation during processing and storage, no off tastes or odours, no tendency to “scalp” and very good elastic recovery. The polyethylenes utilised in the present invention are superior to LDPEs or LLDPEs in that they exhibit far better elastic recovery. Commonly known LLDPEs have a hardness, Shore D, of between 55 to 58 which is too hard to mimic the properties of natural cork, whereas the selected polyethylenes have a Shore D hardness of between 20-50.
Preferably the selected polyethylenes are formed by polymerisation of comonomers using a metallocene-catalyst, alternatively known as a constrained geometry catalyst or single site catalyst. The advantage of such catalysts is that they enable the performance characteristics of the polyethylene to be far better controlled giving rise to a narrower molecular weight distribution range and a lower density range that is otherwise achievable with low density polyethylenes. The narrow molecular weight distribution of the selected polyethylenes gives rise in part to the properties desired. The molecular weight distribution (MWD) of the selected polyethylenes is calculated as
M
W
/M
N
where M
W
=weight average molecular weight; and
M
N
=number average molecular weight
Absence of high and low molecular weight species in the selected polyethylenes gives rise to decreased or eliminated taint characteristics, more controllable peak melting points, a narrower melting range, higher tensile strength and improved flexibility and elasticity. High tensile strength and elastic recovery is important for extraction of the closure form a bottle. Preferably the flexural modulus of the selected polyethylenes is generally in the range of 2 to 15 kpsi.
Furthermore, due to their saturation, i.e., absence of chemical double bonds, the selected polyethylenes have superior chemical stability when compared to other polymers.
The range of polyethylenes selected for use in the present invention are illustrated in FIG. A.
The selected polyethylenes of the present invention have physical properties defined within area (i). More preferably the selected polyethylenes have physical properties defined within area (ii).
The closure of the present invention is preferably cylindrical in shape and of similar dimensions to known cork stoppers for sealing wine bot

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