WO1999048764A1

WO1999048764A1 - Vacuum container

Info

Publication number: WO1999048764A1
Application number: PCT/GB1999/000796
Authority: WO
Inventors: John William Culverwell; Jean-Marc Richeux
Original assignee: Crown Cork & Seal Technologies Corporation; Carnaudmetalbox Plc
Priority date: 1998-03-20
Filing date: 1999-03-16
Publication date: 1999-09-30
Also published as: AU2847499A; GB9805878D0

Abstract

A vacuum container comprising a metal can body (1) and a twist-off closure (2) of metal or plastics. The can body is necked in so that the angle between the shoulder and the cylindrical side wall of the can body is about 60° + 10°. The neck has a long cylindrical section on which threads or lugs are formed for receiving the closure. The container is capable of withstanding a vacuum of up to 507 mm Hg (20' HG).

Description

VACUUM CONTAINER

This invention relates to a vacuum container. In particular, it relates to a vacuum container comprising a metal can body which is adapted to be closed by, for example, a plastics or metal twist-off closure. Vacuum containers are known primarily in the form of glass jars which are closed by twist-off or screw cap closures. Such containers are very rigid and have thick walls which enables air to be readily expelled from the container for closing under vacuum. Thin walled metal cans have been used for gas packing in the presence of an inert gas in order to obtain a long shelf life. Such containers have been used particularly for the packaging of dried milk products, in which a metal can body is closed by a diaphragm fixed to the can body by seaming or adhesive. A separate closure has sometimes been used to cover the diaphragm to enable the can to be reclosed between dispensing of the product although once the inner diaphragm has been removed, any vacuum within the container is lost. One particular problem which arises when closing under vacuum conditions is that the apparatus required for purging the container of air must form an hermetic seal around the container whilst such extraction is taking place. This is not an issue with smooth glass jars but in order to be used for closing a metal can under vacuum conditions, annular beading which is formed on the thin can wall in order to strengthen the can cannot be used unless there is sufficient land to form a seal since this would prevent an hermetic seal from being obtained. Thus not only must the can body be strong enough to withstand vacuum conditions but it must also be capable of so doing without any reinforcing beading extending - 2 -

into the neck region.

This invention seeks to provide a thin-walled metal container which is capable of being closed either under vacuum conditions by mechanical closing methods, or by steam flow closing, for example, so as to obtain a desired vacuum within the closed container. The invention also aims to provide a container which is closed using only a simple twist-off cap or the like, in a similar manner to the well-known glass jar, without any intermediate diaphragm component or beading in the upper can side wall.

According to the present invention, there is provided a vacuum container comprising a metal can body having a base, a cylindrical side wall and a neck region comprising a shoulder joining the cylindrical side wall to a cylindrical neck part, in which the angle between the shoulder and the cylindrical side wall is 60° ± 10° and the neck includes threads or lugs for receiving a twist-off closure. The side wall may be smooth, i.e. unbeaded, at least in its upper region, so as to enable mechanical closing by vacuum apparatus to seal hermeticai ly with the can body. By providing a severe neck angle where the neck region joins the side wall, we have found that thin walled can bodies are capable of being closed under vacuum without any distortion of the can and without subsequent disturbance or breaking of the vacuum. Such can bodies for a three piece can may have a side wall which is only 0.21 mm thick, although 0.24 mm or 0.26 mm are more usual gauges and lower gauges may be used for two piece cans. - 3 -

The container is preferably able to withstand a sealing twist pressure and a vacuum of up to 507 mm Hg (20" Hg) . This is the customary closing vacuum which is imposed on a thick-walled glass jar and is necessary for a range of product types, both wet fill and dry fill and for mechanical closing.

A twist-off closure is the conventional type used for vacuum packed glass jars. The maximum external diameter of the closure is typically less than the diameter of the cylindrical side wall. This is preferred to avoid risk of breaking the vacuum by impact, for example, and for mechanical closing methods.

According to a further aspect of the present invention, there is provided a method of making a vacuum container, the method comprising: forming a metal sheet into a cylindrical can body; necking an open end of the can body so that the angle between a cylindrical part of the neck and the can body is 60° ± 10°; shaping threads or lugs onto the cylindrical part of the neck; flanging and curling the necked end of the can body; and sealing the can body with a twist-off closure under a vacuum of up to 507 mm Hg (20" Hg) .

Alternative embodiments such as steam flow closing may used, in which case the sealing step is such that a vacuum of up to 507 mm HG (20" Hg) is obtained at the end of the process. Typically, the top load requirement for a wet packed product which is closed by steam flow is 500 kg (5000N) . Packaging of aseptics is also considered to be within the scope of the present invention. In one embodiment, the can body may include an integral base. In an alternative embodiment, where the can is a so-called three-piece can, the method may further comprise flanging a second end of the can body; and seaming a base onto this second end of the can body.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which:

Figure 1 is a schematic showing side views of the progression of manufacture of a container according to the present invention; and

Figure 2 is a schematic showing the container of figure lg) with the vacuum inducing apparatus.

Figures la) to lg) show the progression of manufacture of a three piece can body 1, to which a closure 2 has been attached under vacuum. A three piece can is typically formed from a sheet metal blank which is first welded or otherwise formed into a cylindrical tube 3 (figure la) ) .

In accordance with the present invention, this tube is necked at one end and a flange formed at the opposite end (figure lb)) . Neck region 4 comprises a shoulder 5 and cylindrical neck part 6. Angle α between the shoulder 5 and cylindrical side wall 7 is approximately 60°. The angle between the shoulder and the horizontal as shown in these figures may be more usually quoted, in which case this angle is approximately 30°. Neck part 6 is long, typically about 17 mm. A screw thread 10 is formed on this long neck, using a flanging machine. Four screws or lugs may be formed on this length of neck.

A flange 11 and outward curl 12 are provided to hide the cut metal edge at the upper end of the container and a conventional can end 13 is seamed onto the lower end. a conventional can end 13 is seamed onto the lower end. Finally a cap 2 is applied under vacuum to close the upper end of the can.

Figure 2 shows an apparatus for removing air from the container 1 as closure 2 is applied. Tooling 20 comprises capper 22 and vacuum sealing ring 24. In use, the tooling is lowered over container 1 on which closure 2 has been placed. A 2 mm clearance between the diameter of closure 2 and that of can side wall 7 enables the tooling to operate and withdraw. A vacuum of typically

507 mm Hg (20" Hg) is pulled by the apparatus, extracting air and twisting the closure with capper 22 to close the can. This vacuum is achieved in the can. A vacuum sufficient to pull down the centre panel of the closure is needed for tamper evidence so that pulling 20" Hg provides a satisfactory safety margin.

The thin gauge material of the can side wall is only able to withstand hoop and twist loads because the neck angle is so severe. This design also improves dynamic load capability of the can and minimises risk of breaking the vacuum when moving in runways .

Finally, the closure, a twist-off or screw cap, is screwed onto the can to seal the container.

Example 1

500 cylinders 3 as shown in figure la) were produced from 0.255 mm, T57 tinplate having a diameter of 73 mm and a height of 150.2 mm. These cylinders were necked to 66.1 mm at 30° to the horizontal, leaving a straight neck portion 6 of 13 mm, 14 mm, 15 mm, 16 mm and 17 mm respectively (100 of each length) . These tubular can - 6-

bodies were formed into can bodies having a vacuum lug finish of four lugs for receiving a twist-off closure.

The cans were dry filled and placed in the apparatus of figure 2 with the closure on loose. A vacuum of 20" Hg was pulled and a twist load of 30 lbins (133.4 N) ± 50% applied. The cans were capable of a minimum of two years shelf life.

Claims

CLAIMS :

1. A vacuum container comprising a metal can body having a base, a cylindrical side wall and a neck region comprising a shoulder joining the cylindrical side wall to a cylindrical neck part, in which the angle between the shoulder and the cylindrical side wall is 60┬░ ┬▒ 10┬░ and the neck includes threads or lugs.

2. A vacuum container according to claim 1, in which the closed container can withstand a vacuum of up to 507 mm Hg (20" Hg) .

3. A vacuum container according to claim 1 or claim 2, in which in which the maximum external diameter of the closure is less than the diameter of the cylindrical side wall .

4. A method of making a vacuum container, the method comprising: forming a metal sheet into a cy.l indrical can body; necking an open end of the can body so that the angle between a cylindrical part of the neck and the can body is 60┬░ ┬▒ 10┬░; shaping threads or lugs onto the cylindrical part of the neck; flanging and curling the necked end of the can body; and sealing the can body with a twist-off closure under a vacuum of up to 507 mm Hg (20" Hg) . - R -

5. A method of making a vacuum container, the method comprising: forming a metal sheet into a cylindrical can body; necking an open end of the can body so that the angle between a cylindrical part of the neck and the can body is 60┬░ ┬▒ 10┬░; shaping threads or lugs onto the cylindrical part of the neck; flanging and curling the necked end of the can body; and sealing the can body with a twist-off closure so as to obtain a vacuum within the can body of up to 507 mm Hg (20" Hg) .

6. A method according to claim 5, further comprising: flanging a second end of the can body; and seaming a base onto this second end of the can body.