Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
PLASTIC BARRIER CLOSURE AND METHOD OF FABRICATION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a plastic closure (or cap) for
containers such as glass bottles and PET bottles. The closure provides
barrier against transmission of gases such as carbon dioxide and oxygen
and also exhibits a reduced tendency to "scalp" flavor components from
the packaged product. Methods of fabricating such a closure are also
described.
Description of Related Art
Plastic closures for packaging containers, including glass and
plastic bottles, have been commercially available for a number of years.
The most common examples of the plastic caps are internally threaded to
allow them to be screwed onto the neck of PET bottles used to package a
variety of beverages including carbonated soft drinks. The most common
caps for carbonated soft drinks comprise an outer shell of molded
polypropylene with a liner material usually made from an ethylene vinyl
acetate polymer compound. The shell is fabricated either by injection
molding or compression molding. The liner is installed using one of two
methods: 1 ) "pick and place" where a pre-molded disk of material is
mechanically placed into the shell and, 2) "in-shell molding" where a small
mass of melted material is deposited in the shell and then molded in place
by a plunger. The cap liner functions as a mechanical gasket or seal that
will prevent the leakage of carbon dioxide gas from the cap. These caps
are referred to as "two-piece" caps.
More recently, another kind of cap design has been introduced to
the market. Referred to as "one-piece" or "linerless" caps, these are
injection-molded or compression-molded caps that are made from a single
polymer, most commonly HDPE. Examples of such closures are
described in the following patents, which are incorporated by reference:
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USP 3,948,405, USP 4,526,284, USP 4,739,893, and USP 5,743,420.
Through a proper combination of geometric design and material, these
caps can provide adequate mechanical seal against C02 leakage, for
example, from a carbonated beverage.
Although cap designs as described above can provide good
mechanical seal against gas leakage, they are not effective in preventing
permeation of gas through the wall of the cap because the polyolefin
polymers typically used have relatively poor gas barrier properties. For
some packaging applications, a better barrier against gas permeation is
desired.
A number of approaches to plastic closures with improved barrier
have been described in the prior art. One approach is to replace the liner
used in a two-piece cap with a liner formed from a barrier material. EP
62340 teaches the use of a multilayer structure where at least one layer
provides a barrier against gas permeation and at least one other layer
functions as the mechanical seal layer. JP - 07137754 describes a
closure comprising a multilayer liner with a barrier layer and a seal layer,
with the closure body molded over the liner. EP 926078 describes a
sealing liner consisting essentially of alternating layers of matrix material
and barrier material. In both EP 62340 and EP 926078, the liners
described function both as a mechanical seal against gas leakage and as
a barrier layer against permeation of gas. An alternative approach to a
barrier closure as disclosed in EP 233414 is to coat a conventional plastic
cap (presumably one-piece or two-piece) with a coating of "vapour
impermeable material" which is cured to form a solid and is permanently
adhered to the cap.
Another concept for a barrier cap is to produce a cap of linerless
design from a material that exhibits good barrier properties rather than
from HDPE, which is preferred. Most common barrier polymers, however,
tend to be stiff and hard making it difficult to achieve a good mechanical
seal against gas leakage.
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BRIEF SUMMARY OF THE INVENTION
The present invention provides for a plastic closure (or cap) for a
container, particularly a container having an externally threaded neck
through which the container can be filled or emptied, such as bottles and
the like. The neck of the container or opening of the container is a tubular
member connected to the container at one end and open at the opposing
end (top edge or rim). The rim has an inner edge and an outer edge. The
tubular member has an inside surface and an outside surface. Preferably,
there are threads on the outside surface, the threads extending between
the top edge and a location between the top edge and the bottom of the
member. Preferably, the closure is secured on (or screwed onto) the
bottles as treads on the inside of the closure engage threads on the
outside of the bottle opening. Other means for securing the closure to the
bottle may be employed.
The closure exhibits good barrier against the transmission of gases
and reduced tendency to absorb flavor components from the packaged
product. The closure comprises a body and a barrier layer.
The body comprises
a A disc-shaped top wall having an inside surface that is
disposed so as to contact or nearly contact the rim of the
container neck when engaged on the neck,
b A cylindrical side wall attached to and extending from the top
wall;
c A means for securing the body with the neck; the means
preferably comprising internal threads in the cylindrical side
wall that engage corresponding threads on the outside
surface of the neck; and
d A seal disposed so as to provide a good mechanical seal
against leakage of gas when the closure is installed on the
container.
The seal comprises at least one sealing member that is attached to
and extends from the inside surface of the top wall, is concentric with the
cylindrical side, and is disposed so as to continuously contact the neck of
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the container (top of rim, inner or outer edge of rim, or side wall of neck)
when the body is engaged with the neck.
Alternatively, the seal may comprise
An outer sealing member that is attached to and
extends from the inside surface of the top wall and is
disposed between the inside surface of the cylindrical
side wall and the outside edge of the bottle opening
so as to continuously contact the top outside edge of
rim of the container neck when the body is engaged
with the neck; and
ii An inner sealing member concentric with the outer
sealing member and extending from the inside
surface of the top wall of the body so as to
continuously contact the inner edge of the rim when
the body is engaged with the neck.
The body is made of molded plastic, most preferably HDPE.
The barrier layer, which is incorporated into the top wall of the
body, is selected from materials known to provide a good barrier against
permeation of gas and also exhibit a low tendency to absorb flavor
components from the packaged product. The barrier material can be any
of a number of barrier polymers including EVOH, nylon, and polyester
(including 2GT, 3GT and blends of 2GT and 3GT polyester). Amorphous
nylon or 3GT polyester is preferred. The barrier layer can also be metallic
such as aluminum.
An alternative embodiment comprises a body with a seal that has a
single sealing member that is attached to and extends from the inside
surface of the top wall and is disposed so as to continuously contact the
outside edge of the container rim when the body is engaged with the neck
of the container. When only an outer sealing member is employed as the
seal, the barrier material preferably contacts the rim of the container with
the closure is engaged with the container neck.
The barrier layer is incorporated into the body of the cap by one of
two methods:
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a. a melted mass of the barrier polymer is deposited in the
pre-molded cap body and then molded into place by
mechanical means. This method is referred to as "in-shell
molding".
b. The barrier layer is formed in a separate step and then
installed into the pre-molded cap body. This method is
referred to as "pick and place."
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1. is a vertical sectional view showing a closure in
accordance with the invention being applied to the neck of a container.
Figure 2. is a vertical sectional view showing a closure in
accordance with the invention, installed on a container, where an inner
concentric ring provides mechanical seal.
Figure 3. is a vertical sectional view showing a closure in
accordance with the invention, installed on a container, where an outer
concentric ring provides mechanical seal and the barrier layer functions as
a positive stop.
Figure 4. is a vertical sectional view showing a closure in
accordance with the invention, installed on a container, with an alternate
configuration to Figure 3 where an outer concentric ring provides
mechanical seal and the barrier layer functions as a positive stop.
DETAILED DESCRIPTION
The present invention provides for a generally cylindrical plastic
closure for sealing the open end of a container neck (or cap) in a way that
provides superior barrier to the transmission of gas and a reduced
tendency to absorb flavor components from product packaged in the
sealed container. Such a closure is especially useful as a cap on glass
bottles and PET bottles such as are used for carbonated soft drinks, beer
and other beverages. The closure may optionally include a guarantee ring
or tamper-evident strip. This closure comprises a body that is bottle-cap
shaped (i.e., having a generally disc-shaped top wall with a cylindrical or
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tubular side member essentially perpendicular to and extending from the
top wall) and a barrier layer incorporated into the top wall of the closure.
The body of the closure, as will be more clearly understood from
reference to the figures that are part of the disclosure of this
specification,
has a means for securing the closure to the container and a means for
providing a mechanical seal when the closure is secured to the container.
The means for securing the closure is typically internal threads that
engage with external threads on the neck of the container, as is depicted
in Figure 1. While the closure of the present invention has been
described as utilizing a threaded engagement with the container neck, it is
understood that the attendant benefits may be realized with other means
for securing such as if a crown or Snap-On type closure design is utilized.
The means for providing a mechanical seal preferably conmprises
one or more sealing members attached to the inside top of the closure
and extending therefrom so as to contact the neck of the container when
the the closure is secured to the container.
Figures 1 and 2 depict a closure in accordance with the invention
being applied to the neck of a container. The body 1 of the closure
comprises a top wall 2, an internally threaded sidewall 3, and a seal 4.
The seal may consist of an inner concentric ring 4a, an outer concentric
ring 4b, or both. The seal extends downwardly from an inner surface of
the top wall and is disposed to engage the neck of the container so as to
provide a good mechanical seal against leakage of gas when the closure
is screwed onto the bottle. It will be appreciated that the body 1 of the
closure may also be of a different configuration. The prior art contains
many designs for such plastic closures where a section or sections of the
body of the closure are disposed to engage the neck of a container to
affect a good mechanical seal against gas leakage. The seal can be
disposed to engage the neck of the container on the rim 7 or on the inside
wall 8 or on the outside wall 9. This class of closure is referred to as
"one-piece" or "linerless."
The body can be made from any number of plastic materials
including polyolefins, such as high-density polyethylene (HDPE), low-
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density polyethylene (LDPE) and polypropylene (PP), nylon, polyvinyl
chloride, polycarbonate, polystyrene, and polyester. In general,
thermoplastic polymers are preferred although thermoset polymers can be
used. For many packaging applications, and in particular for packaging
carbonated soft drinks, HDPE is the preferred material of construction for
the body. HDPE exhibits a combination of mechanical properties (in
particular, flexural modulus and hardness) well suited to produce an
effective mechanical seal against a container rim. For packaging
applications involving a hot-fill or retort process, depending on pressure
and temperature, HDPE may not offer adequate thermal resistance as a
body material. In these applications, materials exhibiting higher thermal
resistance than HDPE, such as polypropylene or nylon, may be preferred.
The body can be produced using common thermoplastic processing
methods such as compression molding and injection molding.
The barrier layer 5 of the closure can be made from any number of
common barrier materials including amorphous nylon, semicrystalline
nylon, ethylene vinyl alcohol (EVOH), polyvinylidene chloride (PVDC),
polyester (PE), including 2GT, 3GT and blends of 2GT and 3GT polyester,
and polyacrylonitrile. The barrier layer can also be made of metal, such as
aluminum, but, in general, a plastic barrier material is preferred. The
barrier layer of the closure functions to prevent permeation of gasses such
as carbon dioxide and oxygen through the closure. It also may exhibit a
reduced tendency to absorb, or "scalp", flavor components from the
packaged product or impart undesired components to the product. A
preferred material for the barrier layer is amorphous nylon such as
Selar~PA from E. 1. du Pont de Nemours and Company. For liquid
packaging, among the common barrier materials, amorphous nylon
provides the best combination of gas barrier properties and non-scalping
performance. Another preferred material is 3GT polyester, which offers
good barrier properties and ease of processing. In particular, 3GT can be
processed at lower melt temperatures than the other common barrier
polymers.
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The barrier layer can be incorporated into the closure body by
various methods including the following.
1 ) A melted mass of the barrier material is deposited on the inside
surface of the top wall of a pre-formed body and then molded in
place by an actuated plunger to form the finished barrier layer.
This process is referred to as "in-shell molding." The melted
material may be conventional polymer melt or the melted material
may be foamed using chemical or physical blowing agents. The
amount of barrier material deposited is controlled so that the
finished dimensions of the barrier layer are maintained within
acceptable limits. The face of the molding plunger is designed to
give the desired contour to the exposed surface of the barrier layer.
In Figure 2, the barrier layer 5 is flat. In Figures 3 and 4, the barrier
layer 5 is contoured so as to provide a raised area that serves as a
stop for the container rim 7. The plunger diameter is sized slightly
smaller than the smallest diameter of the innermost seal ring of the
body so that there is minimum clearance between the plunger and
the seal ring as the plunger compresses the melted barrier material
into the body. Equipment that utilizes this in-shell molding process
is commercially available from companies including Sacmi and
Oberburg Engineering AG. The barrier layer 5 is retained in the
body 1 of the closure by direct adhesion to the body, by mechanical
retention, or both. To achieve mechanical retention, the closure
body 1 is preferably designed with an undercut 6 at the root of the
seal ring 4b as illustrated in Figures. 3 and 4, such that the barrier
layer 5 will have a outer diameter somewhat larger than the inside
minimum diameter of the sealing ring 4b.
2) The barrier layer 5 may be formed in a separate process, and then
installed into the preformed body 1 by mechanical means to
produce the finished closure. This process is referred to as the
"pick and place" process. The barrier layer 5 is retained in the body
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1 by mechanical retention.
As illustrated in Figures 3 and 4, the body 1 is designed with an
undercut 6 at the root of the seal ring 4b, thus creating an
interference fit between the preformed barrier layer 5 and the body
1. The preformed barrier layer must be sufficiently flexible to
survive the installation process without cracking. This method of
installation is especially suited for metallic barrier layers and
thermoset plastic barrier layers but can also be used if the barrier
layer is formed from a thermoplastic material.
An alternative method for preparing a plastic barrier cap of the
present design is by use of a coextrusion injection molding process. In
this process, two extruders are used to produce molten material; one
extruder for the body material, and a second extruder for the barrier
material. The molten materials are introduced either simultaneously or
sequentially into a mold cavity to form the finished plastic cap. The
equipment and tooling used in this process tend to be more complicated
and costly than the equipment and tooling used in either the "in-shell
molding" process or the "pick and place" process.
The benefits of the present invention are most attendant if the gas
barrier properties of the barrier layer material are at least one order of
magnitude higher than the body material, preferable at least two orders of
magnitude higher. For example, one preferred embodiment of the
invention comprises a HDPE body and an amorphous nylon barrier layer:
amorphous nylon exhibits a C02 barrier about 100x higher than HDPE.
In one embodiment of this invention, as illustrated in Figure 2, the
seal in the body 1 comprises only the inner concentric seal member 4a
extending down from the top wall 2 disposed to engage the inner edge 7a
of the rim of the neck of the container when the closure is installed on the
container. Alternatively, the inner concentric seal ring 4a could be
disposed to engage the inside wall 8 of the neck of the container. The
inner seal member 4a provides the mechanical seal against gas leakage
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and the barrier layer 5 provides the primary barrier against gas
permeation.
In a preferred embodiment of this invention, as illustrated in
Figures. 3 and 4, the seal in the body 1 comprises only the outer
concentric sealing member 4b extending down from the top wall 2
disposed to engage the outer edge 7b of the rim of the neck of the
container when the cap is screwed unto the container. Alternatively, the
outer concentric sealing member 4b could be disposed to engage the
outer wall 9 of the neck of the container. The barrier layer 5 is
incorporated in the body 1 of the cap and preferably is designed to contact
the rim top edge 7 (Figure 3) of the bottle or the rim inner edge 7a (Figure
4) when the cap is secured to the neck preferably by being screwed on
using the proscribed installation torque, typically 14 to 18 inch-pounds for
a 28-mm cap. The design of the barrier layer may have a bead 7c (Figure
3) that contacts the rim top edge 7 or may have a taper (Figure 4) so that
the barrier contacts only the inner edge 7a. In this embodiment, the
barrier layer 5 functions as a positive stop as the closure is installed on
the container. The outer seal member 4b of the body 1 provides the
primary mechanical seal against gas leakage and the barrier layer 5
provides secondary mechanical seal and functions as the primary barrier
against gas permeation. In this preferred embodiment, when the closure is
properly installed on the container, the packaged product will have no
direct contact with the body material, and the optimum gas barrier and
non-scalping performance will be achieved.
It is recognized that the materials used in the fabrication of both the
body and the barrier liner may optionally be modified with other materials
as are commonly used in the caps and closures industry. These modifiers
may include pigments, slip agents, and oxygen scavengers, among
others.
While a common utility of the present invention is for closures for
PET bottles, it is recognized these closures may be used on any kind of
container having a generally cylindrical neck, e.g., bottles or cans made
from glass, plastic, or metal.
