WO2000058169A1

WO2000058169A1 - Plastic closure

Info

Publication number: WO2000058169A1
Application number: PCT/GB2000/001013
Authority: WO
Inventors: Robert Cecil Mcfadyen
Original assignee: Reckitt Benckiser (Australia) Pty Limited; Reckitt Benckiser (Uk) Limited
Priority date: 1999-03-25
Filing date: 2000-03-24
Publication date: 2000-10-05
Also published as: GB9906789D0; AU3440200A; GB2348193A; GB0007147D0

Abstract

In this invention there is disclosed an integrally moulded plastic closure (10) which is substantially cylindrical in shape, closed by a top wall (11) about which downwardly depends an outer curved wall (12) to form an opening dimensioned to accept a neck finish of a container, the curved outer wall (12) including a means to engage a corresponding portion on a container and affix it thereto. The closure (10) is characterised by having on an inner surface (13) of the top wall (11) a downwardly depending inner wall (14) which is concentric with the threaded outer wall (12) of the closure (10), the inner wall (14) having in section a radius of curvature towards the outer wall (12) and an inwardly curving skirt (15) on a lower end thereof, the inner wall (14) having sufficient flexibility so as to sealingly engage an inner surface of the neck finish of a container to be sealed in a region below a stress concentration point thereof.

Description

Plastic Closure

Field of the Invention

This invention relates to screw cap and press fit closures, in particular to such closures which are formed from plastic and incorporate an integral sealing means.

Background to the Invention

One problem that occurs in the packaging art is that of incompatibility between a liquid composition and a container in which it is sealed. The incompatibility may arise between the liquid composition and the container, the liquid composition and the closure, or the liquid composition the container and the closure. The compatibility is particularly acute when the container and closure is formed from synthetic plastics materials and the liquid composition includes non-aqueous solvents, or other substances that attack the plastics material. By "attack" is meant to chemically react to cause undesirable physical changes in the plastics materials. Such undesirable changes may include swelling of the plastic, stress cracking, increased permeability of the plastic so as to cause loss of liquid contents or failure of the closure to maintain a seal. One particular problem that results in stress cracking is so-called "hoop stress".

There are a variety of screw cap closures and press fit closures known in the art that may be formed from synthetic plastics materials. One type of closure that is used is that which incorporates an integral sealing means. The advantage of such closures is that they are moulded as a single composition thereby avoiding the additional cost and effort required to produce and fit a separate sealing means.

In seeking to address the problem of incompatibility between liquid compositions, containers and closures, where the containers and closures are formed from synthetic plastics materials, the present inventors have sought to provide a closure that incorporates an integral sealing means.

Accordingly, the present invention consists in an integrally moulded plastic closure which is substantially cylindrical in shape, closed by a top wall about which downwardly depends an outer curved wall to form an opening dimensioned to accept a neck finish of a container, the curved outer wall including on an inner surface thereof a means to engage a corresponding portion on a container and affix it thereto, characterised in that on an inner surface of the top portion, there is a downwardly depending outwardly curving inner wall which is concentric with the outer wall of the closure, the inner wall having an inwardly curving skirt on a lower end thereof, the inner wall having sufficient flexibility so as to be adapted to sealingly engage an inner surface of the neck finish of a container to be sealed in a region below a stress concentration point thereof, the length of the inner wall, as measured orthogonally from where the inner wall depends from the inner surface of the top wall to the lowest point thereof, being in the range of from 2 to 4 mm, preferably about 3mm. The means to engage a corresponding portion on a container and affix it thereto will generally comprise a threaded portion on the inner surface of the curved outer wall. A container for use with the closures of the invention will include a correspondingly threaded portion.

Alternatively, the means to engage a corresponding portion on a container and affix it thereto may comprise a press fit, push fit or snap on type arrangement. In general terms, such an embodiment includes a recess in the inner surface of the curved outer wall. A container for use with such a closure includes a ledge on the wall forming the neck finish. In use, the ledge and recess engage so as to cause the closure to affix to the container.

In the region in which the inner wall sealingly engages the inner surface of the neck finish, it is preferred that the skirt makes sealing contact with the neck finish. This sealing contact will generally occur by virtue of a flattening or a distortion of the skirt when the closure is affixed to a container. To facilitate the flattening or distortion of the skirt, it is desirable that the skirt be appropriately dimensioned with a requisite degree of flexibility. In particular, it is preferred that the skirt has a wall thickness in the range of from 0.2 to 0.5 mm in a portion thereof that affects the seal with the container. Most preferably, the wall thickness if 0.3mm in the portion that affects the seal with the container. It is important that the dimensional stability of the skirt is preserved during the moulding process to form the closure. This ensures that the closure not only seals adequately but that stresses are minimised when the closure is sealed on a container. One construction of the skirt that is useful in assisting in the preservation of dimensional stability is to cause the skirt to taper towards its lower edge. This makes it easier to remove the closure from the mould thereby reducing any distortion in the dimensions of the skirt.

To ensure that the sealing contact between the inner wall and the neck finish minimises stress, particularly hoop stress, the length of the inner wall, as measured orthogonally from where the inner wall depends from the inner surface of the top wall to the lowest point thereof, is in the range of from 2 to 4 mm, most preferably about 3mm. Generally these dimensions will ensure that the region of contact between the inner wall and the container will be below the stress concentration point of the container.

In the closure of the invention the inner wall in section curves towards the outer wall. This radius of curvature of the inner wall is such that a portion thereof is biased towards the inner surface of the neck finish of the container when the closure is in place on the container. Preferably the extent of curvature is sufficient so that the horizontal distance as determined between a point on the inner wall where it downwardly depends from the inner surface of the top wall closest to the outer wall - and a point at which a line extending orthogonally from the inner surface of the top wall and tangentially to a point on the inner wall which is closest to the inner surface of the outer wall intersects the inner surface of the top wall is in the range of 0.2 to 1.00 mm, preferably about 0.5mm.

The closures of the invention may be used with a wide variety of containers. Preferred containers are those formed from plastic which have a tendency to undergo stress cracking in use, particularly as a result of incompatibility between the liquid contents thereof and the plastic material from which the container is formed.

Particularly preferred containers are those that are so-designed as to ensure that the stress concentration point in the neck finish is above the region of contact of the closures of the invention. Especially preferred are containers in which the wall of the neck finish in an upper region thereof is shaped in a manner such that an inner surface thereof has a vertically extending radius of curvature, preferably a compound radius of curvature. In this way, stress is minimised in the neck finish of the container.

Accordingly in a second aspect, the present invention further consists in a plastic container having a neck finish which includes a wall having a means to engage a closure so as to affix it thereto, characterised in that the wall in an upper region is shaped on an inner surface so as to have a vertically extending radius of curvature, preferably a compound radius of curvature. The containers of the invention preferably comprise a neck finish, the wall of which has an upper edge with a surface which is orthogonal to the wall. This upper edge co-operates with the inner surface of a top wall of a closure. When used with the closures of this invention, the upper edge will cooperate with the region of the inner surface which lies between the inner wall and the outer wall.

The containers and closures of the invention are particularly useful for containing liquids that attack the plastic from which they are formed.

Accordingly in a third aspect, the present invention still further consists in a package comprising a plastic container having a neck finish which includes a wall having a means to engage a closure so as to affix it thereto, the wall in an upper region being shaped on an inner surface so as to have a vertically extending radius of curvature, an integrally moulded plastic closure which is substantially cylindrical in shape, closed by a top wall about which downwardly depends an outer curved wall to form an opening dimensioned to accept a neck finish of a container, the curved outer wall on an inner surface thereof including a means to engage a corresponding portion on a container and affix it thereto, the inner surface of the top wall having a downwardly depending outwardly curving inner wall which is concentric with the threaded outer wall of the closure, the inner wall having an inwardly curving skirt on a lower end thereof, the inner wall having sufficient flexibility so as to be adapted to sealingly engage an inner surface of the neck finish of a container to be sealed in a region below a stress concentration point thereof, the length of the inner wall, as measured orthogonally from where the inner wall depends from the inner surface of the top wall to the lowest point thereof, being in the range of from 2 to 4mm, preferably about 3mm, and a liquid which attacks the plastic.

In order to better understand the nature of this invention, an example will now be described with reference to the following drawings in which:

Figure 1 is an sectional view of a closure of the invention showing a typical neck finish of a container in place; and

Figure 2 is a side elevational view of the closure of figure 1, and

Figure 3 is a top plan view of the closure of figure 1.

The closure 10 is an integrally moulded plastic closure formed from polypropylene. It will of course be appreciated that the closure could be moulded from a variety of plastics materials including high density polyethylene and low density polyethylene. Closure 10 is generally cylindrical in shape and comprises a circular top wall 11 from which downwardly depends an outer wall 12. This outer wall 12 slopes slightly outwardly and is curved in a plane about the circular top wall 11.

In order to accept a screw thread 18 of a neck finish 19 of a container, outer wall 12 includes a thread 16 on an inner surface 17.

On an inner surface 13 of the top wall 11 is an inner wall 14 which depends downwardly therefrom. Inner wall 14 is disposed concentrically to the outer wall 12.

The inner wall 14 has a skirt 15 in a lower region thereof. Whilst overall the inner wall 14 has, in section, a radius of curvature towards outer wall 12, the skirt 15 curves inwardly, that is, away from the outer wall. In figure 1 it is apparent that the skirt 15, when the closure is in place on a container, seals against a portion 20 of an upper inner wall of the neck finish of the container.

On the outer wall 12 there are disposed a plurality of ribs 21. These ribs extend generally about the longitudinal axis of the closure. By providing ribs arrayed in this way, gripping of the closure is made easier. This assists both application and removal of the closure.

As is best seen in figure 3, the top wall 11 has embossed therein a design of a tree. It will be readily apparent to a person skilled in the art that a wide range of designs may be incorporated into the closures of the invention. It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS :

1. An integrally moulded plastic closure which is substantially cylindrical in shape, closed by a top wall about which downwardly depends an outer curved wall to form an opening dimensioned to accept a neck finish of a container, the curved outer wall including on an inner surface thereof a means to engage a corresponding portion on a container and affix it thereto characterised in that on an inner surface of the top portion, there is a downwardly depending outwardly curving inner wall which is concentric with the outer wall of the closure, the inner wall having inwardly curving skirt on a lower end thereof, the inner wall having sufficient flexibility so as to be adapted to sealingly engage an inner surface of the neck finish of a container to be sealed in a region below a stress concentration point thereof - the length of the inner wall, as measured orthogonally from where the inner wall depends from the inner surface of the top wall to the lowest point thereof, being in the range of from 2 to 4mm, preferably about 3mm.

2. A closure as claimed in claim 1 wherein the means to engage a corresponding portion on a container and affix it thereto comprises a threaded portion on the inner surface of the curved outer wall .

3. A closure as claimed in claim 1 wherein the means to engage a corresponding portion on a container and affix it thereto comprises a recess in the inner surface of the curved outer wall.

4. A closure as claimed in any one of claims 1 to 3 wherein in the region in which the inner wall sealingly engages the inner surface of the neck finish, the skirt makes sealing contact with the neck finish.

5. A closure as claimed in claim 4 wherein the skirt is appropriately dimensioned such that the skirt flattens or distorts so as to make sealing contact with the neck finish.

6. A closure as claimed in claim 5 wherein the skirt is appropriately dimensioned such that the skirt flattens or distorts so as to make sealing contact with the neck finish.

7. A closure as claimed in any one of claims 1 to 6 wherein the skirt tapers towards its lower edge.

8. A closure as claimed in any one of claims 1 to 7 wherein the radius of curvature of the inner wall is such that a portion thereof is biased towards the inner surface of the neck finish of the container when the closure is in place on a container.

9. A closure as claimed in claim 8 wherein the radius of curvature is sufficient so that the horizontal distance as determined between a point on the inner wall where it downwardly depends from the inner surface of the top wall closest to the outer wall and a point at which a line extending orthogonally from the inner surface of the top wall and tangentially to a point on the inner wall which is closest to the inner surface of the outer wall intersects the inner surface of the top wall is in the range of 0.2 to 1.0mm, preferably about 0.5mm.

10. A plastic container having a neck finish which includes a wall having a means to engage a closure so as to affix it thereto, characterised in that the wall in an upper region is shaped on an inner surface so as to have a vertically extending radius of curvature, preferably a compound radius of curvature.

11. A container as in claim 10 wherein the means to engage a closure so as to affix it thereto comprises a ledge on the wall forming the neck finish.

12. A container as in claim 10 wherein the means to engage a closure so as to affix it thereto comprises a threaded portion on the wall forming the neck finish.

13. A container as in any one of claims 10 to 12 wherein the neck finish, includes a wall which has an upper edge with a surface which is orthogonal to the wall, the upper edge co-operating with the inner surface of a top wall of a closure.

14. A package comprising a plastic container having a neck finish which includes a wall having a means to engage a closure so as to affix it thereto, the wall in an upper region being shaped on an inner surface so as to have a vertically extending radius of curvature, an integrally moulded plastic closure which is substantially cylindrical in shape, closed by a top wall about which downwardly depends an outer curved wall to form an opening dimensioned to accept a neck finish of a container, the curved outer wall on an inner surface thereof including a means to engage a corresponding portion on a container and affix it thereto, the inner surface of the top wall having a downwardly depending outwardly curving inner wall which is concentric with the threaded outer wall of the closure, the inner wall having an inwardly curving skirt on a lower end thereof, the inner wall having sufficient flexibility so as to be adapted to sealingly engage an inner surface of the neck finish of a container to be sealed in a region below a stress concentration point thereof, the length of the inner wall, as measured orthogonally from where the inner wall depends from the inner surface of the top wall to the lowest point thereof, being in the range of from 2 to 4mm, preferably about 3mm, and a liquid which attacks the plastic.