GB1564403A

GB1564403A - Method and apparatus for heat sealing metal foil closures to containers

Info

Publication number: GB1564403A
Application number: GB48265/75A
Authority: GB
Original assignee: TI Fords Ltd
Current assignee: TI Fords Ltd
Priority date: 1976-11-24
Filing date: 1976-11-24
Publication date: 1980-04-10

Description

(54) METHOD AND APPARATUS FOR HEAT SEALING METAL FOIL CLOSURES TO CONTAINERS (71) We, TI FORDS LIMITED, formerly, Fords (Finsbury) Limited, a British Company, of Chantry Avenue, Kempston, Bedford, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method and apparatus for sealing the mouths of containers with metal foil closures, such as metal foil caps, discs or diaphragms. More particularly, although not exclusively, the invention relates to a method and apparatus for sealing glass bottles, tumblers, jars and other glass containers with metal foil closures.

Containers made from thermoplastic materials, such as polyethylene, may be hermetically sealed by applying a cap or disc made from a lamination of aluminium foil and a thermoplastic film. The film may be bonded to the container by the application of sufficient heat and pressure to produce a weld between the two materials. Some types of container material, for example polystyrene, are more effectively sealed if the aluminium closure is coated on the container side with a suitable heat sealing lacquer coating. Various high melting-point waxes have also been employed for this purpose.

The most convenient method of applying the heat is by means of an electrically heated metal platen which is brought into contact with the aluminium cap. Heat is transferred to the cap mainly by conduction through the aluminium foil. The contact time, the temperature of the platen and the pressure between cap and container may be adjusted so that any surface irregularities of the container mouth are melted down, thus producing a uniformly satisfactory seal around the whole periphery of the container mouth. Typical polyethylene containers having a mouth diameter of 50mm may be heat sealed with a platen temperature of 160or, a vertical load of 5K-gf and a contact time of approximately one second.

The closure may be in the form of a cap with a cylindrical or tapered skirt portion to provide a location on the container prior to the heat sealing step. Alternatively, the location may be provided by a recess in an otherwise flat diaphragm closure, the recess fitting into the opening of the container mouth, or, if other means of location can be provided, a flat diaphragm type of closure may be used.

Glass containers which are required to be sealed in a leak proof or hermetic manner have commonly been provided with a mouth opening having an external or internal screw thread to receive a threaded closure and provided with a resilient gasket to effect the seal. Alternatively, a strong metal cap with a resilient gasket has been crimped over a flange or bead formed on the outer periphery of the container mouth.

A much cheaper closure which would also be tamper proof could be provided if a coated aluminium or other metal foil cap, disc or diaphragm, as discussed above, could be heat sealed to a glass container.

There would be a further advantage in that glass drinking tumblers, mugs or cups could be used as containers for food products and, when empty, have an attractive secondary use in the home.

There are a number of films, heat activated adhesives and waxes (referred to hereafter generally as thermoplastic materials) which may be coated onto aluminium foil and which will adhere to glass by'heat sealing. One such material is marketed under the trade mark "Surlyn".

Attempts to heat seal such a closure to glass by the hot platen method described for plastics containers have not hitherto been successful because the rims of glass containers and the hot surfaces of platens are never accurately flat. Hence, the heat seals are only effected on the high points of the container rims and very rarely is a complete seal obtained around the whole periphery of the container mouth.

Interposing a thin resilient layer, such as a heat resisting silicone rubber, between the hot platen and the closure will ensure uniform contact around the container rim but these resilient materials are poor conductors of heat and therefore much higher platen temperatures are required with an unacceptably long contact time for use on a high speed production line.

Other methods of heat sealing the closures have been tried, as disclosed in patent specifications Nos. 1,135,943, 1,231,208 and 1,373,595, which require the use of high frequency induction heating whilst resiliently pressing the closure into contact with the container. The serious disadvantages of this method lie in the high cost of the high frequency generator, the very low power efficiency and vulnerability of the generator to dust or water which may be present in the production environment.

An object of the present invention is to overcome the above problems and enable thin metal foil closures with suitable thermoplastic coatings to be reliably heat sealed to glass containers, such as, jars and drinking tumblers, and also to containers made from other materials which are not softenable at the heat sealing temperature, at speeds acceptable to industry.

The present invention relates to a method of heat sealing a metal foil closure to the mouth of a container, said closure having a coating of thermoplastic material on its side adjacent the container mouth, comprising the steps of applying the closure to the mouth of the container, directing a flow of heated air onto the closure so as to soften the thermoplastic coating, and then pressing the closure into intimate contact with the periphery of the container mouth.

The invention also consists in a sealing head for heat sealing a metal foil closure to the mouth of a container, in which air nozzle means is located about an opening in the head for directing heated air onto a closure applied to the mouth of a container inserted into the opening, and pressing means is mounted in the head, rearwardly of the opening, for pressing the closure into intimate contact with the periphery of the container mouth when the latter is advanced through the opening.

With the present invention, a turbulent stream of heated air is used to heat the closure whilst it is loosely in engagement with the mouth of the container and after a predetermined time the hot closure is resiliently pressed into contact with the rim and, in the case of a cap, outside surface of the container mouth.

Preferably, a ring of heated air is directed radially inwardly against the closure from a position which encircles the closure, when the container mouth is inserted into the head. To this end, the nozzle means conveniently comprises an annular channel disposed in the head about the periphery of the opening therein, which annular channel is connected to a hot air supply, and is connected to the periphery of the opening by an annular slit or slot through which a ring of hot air may be discharged against the closure on the container mouth.

The pressing means may comprise a resilient member mounted in the head coaxially with and behind the opening. This resilient member has its periphery secured to the head and a central portion flexible rearwardly of the opening against the action of spring pressure when a container mouth is inserted through the opening and pressed against the resilient member. The latter has a peripheral flange projecting forwardly thereof which compresses the skirt of a closure cap against the outside of the rim of the container in response to rearward movement of the central portion of the resilient member by the container.

The heat sealing head of this invention may be used singly or, alternatively, a multiplicity of such heads may be mounted in a rotary machine. The heads may be mounted so as to be reciprocable in a vertical direction for sealing closures to container mouths. However, preferably, the or each head is associated with a vertically reciprocable pedestal which is movable to insert the mouth of a container into the opening in the head and subsequently press the heated closure against the pressing means in the head.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Figure 1 illustrates different types of closures which may be heat sealed by the present invention, Figure 2 shows a vertical section through a heat sealing head constructed in accordance with the invention, Figure 3 is a side elevation, partially in section, of the air heating means in the head, Figure 4 is an underneath plan view of the head, Figures 5, 6 and 7 illustrate the cycle of operations for heat sealing a metal foil closure to the mouth of a glass tumbler or jar, Figure 8 is a plan view of a rotary sealing machine embodying a multiplicity of sealing heads according to the invention, Figure 9 shows a development of the cam rail for controlling the pedestals of the machine shown in Figure 8, and Figure 10 shows a modified version of the cam rail.

Referring to Figure 1 of the drawings, the sealing head hereinafter described is adapted to seal a closure cap C having a cylindrical skirt S to the mouth of a glass container G.

However, this sealing head may also be adapted to heat seal other forms of closures to glass containers, such as a recessed disc or diaphragm D1 or a flat disc D2.

Referring to Figures 2, 3 and 4, the sealing head illustrated in these Figures includes an electrical resistance heating element 1 embedded in a cylindrical metal tube 2 having on its outer surface a coarse pitch screw thread 3 which, in conjunction with a plain cylindrical tube 4 in the head, forms a helical channel through which a metered flow of air may be passed from a supply pipe 5 connected to the start of the helix. The other end of the helical channel feeds a passage 6 tangential to an annular or toroidal channel 7 formed between upper 8 and lower 9 members of the head which are bolted together. These two members are provided with a circular opening 10 which is coaxial with the toroidal hot air channel 7 and through which a container mouth and closure may be inserted.

A narrow gap is provided between the adjacent faces of the upper and lower members 8, members 8 ,9 of the head on the inside of the toroidal air channel. This forms an annular slit 7a so that a thin curtain of hot air, moving radially inwards, can impinge on the skirt and top surface of the closure when it is raised with the container to a position in the plane of the slit.

A temperature sensing element (not shown) such as a thermocouple, is embedded in the upper member 8 of the head close to the air passage 6 and is used to control the electrical input to the heating element so that a predetermined temperature may be maintained in this region. The relatively long heating path for the air flowing through the helical channel 3 ensures that the air temperature is reasonably close to the temperature of the senser.

The heating assembly described is mounted by three pillars 11 so as to minimise heat loss by conduction from the frame of the machine 12 which, in the case of a multi head machine, may be a rotating turret.

A further assembly, shown in Figure 2, is provided behind and coaxial with the air heating assembly. The container and heated closure are lifted into this further assembly to press the closure firmly but resiliently into contact with the rim and sides of the container. It consists of a heat resisting rubber member 13 having a circular recess 14 slightly larger than the closure and of the same depth as the skirt. A flange 1 3a on the outer periphery of the rubber member is used to retain it in its housing which consists of the two generally coaxial cylindrical portions 15 and 16. A spring loaded plate 17 causes the rubber member to be dished so that the recess is opened slightly to receive the closure when it is lifted into contact. Further upward movement of the container causes the rubber member to deflect in the reverse direction so squeezing the skirt of the closure into contact with the container and applying pressure to the container rim. On lowering the container, the spring loaded plate restores the rubber member to its original shape and releases the capped container. The whole of this sealing rubber assembly is mounted in a quickly detachable manner so that assemblies for alternative container sizes may be readily interchanged. The same hot air assembly serves for a range of container sizes.

In operation, the container 18 with a closure cap C, such as an aluminium foil cap, already in position is supported on a pedestal 19 coaxial with the heating and sealing head, as shown in Figure 5. The container is then raised, Figure 6, so that the closure is in the plane of the annular air slit 7a and at the same time the air supply to pipe 5 is switched on. Hot air then impinges on the cap for a predetermined time after which the container is raised a further distance, Figure 7, to press the heated closure into position and the air supply is cut-off. The sealed container then descends and is discharged from the machine.

By modifying the shape of the annular slit 7a so that the inwardly directed curtain of air has a downwardly directed component and by modifying the shape of the rubber member 13 it is possible to seal the recessed type of closure D1 shown in Figure 1.

A rotary machine can be constructed using several of these heads, as shown in plan in Figure 8, where a conveyor 22 presents containers to a rotating star wheel 23 which transfers each container onto a lifting pedestal 19 positioned as shown in Figure 5. Figure 8 shows a rotating turret assembly 24housing six lifting pedestals and sealing heads 19, but any number may be employed to achieve the output desired. An electrical supply is fed to the rotating turret through slip rings and a supply of compressed air through a rotating joint feeds a rotating valve which causes the air to be fed to each head whilst it is traversing a predetermined arc of rotation 25.

Each lifting pedestal is provided with a roller 20 engaging a fixed cam rail 21 the profile of which determines the rise and fall of the pedestal and containers as the turret rotates. Figure 9 shows a development of the fixed cam rail 21 between the point where the input star wheel places the container on the pedestal and the point where the exit star wheel 26 removes it for placement back on the conveyor 22. The container's closure is in the heating position during the pedestal's passage through zone a (see Figures 8 and 9) and the air supply to the associated head is turned on. Over zone b, the hot closure is lifted into contact with the rubber member 13 so that it is pressed firmly onto the container.

Glass containers may vary considerably in diameter, although made to the same nominal dimension, and therefore the closure may initially be a very loose fit on some containers. In this case it is desirable to use a cam rail as shown in Figure 10 where a lift into the sealing or pressing position both precedes and follows the heating period.

Whilst particular embodiments have been described, it will be understood that modi fications can be made without departing from the scope of the invention as defined by the appended claims. For example, although the invention has been particularly described with reference to the sealing of metal foil closures to glass containers, it will be appreciated that it is equally applicable to heat sealing closures to containers or receptacles made from other materials which, like glass, are not readily softenable by heat, for example glazed or unglazed ceramic materials.

WHAT WE CLAIM IS 1. A method of heat sealing a metal foil closure to the mouth of a container, said closure having a coating of thermoplastic material on its side adjacent the container mouth, comprising the steps of applying the closure to the mouth of the container, directing a flow of heated air onto the closure so as to soften the thermoplastic coating, and then pressing the closure into intimate contact with the periphery of the container mouth.

2. A method as claimed in claim 1, wherein the heating step comprises directing a ring of heated air radially inwardly against the closure from a position which encircles the closure.

3. A method as claimed in claim 1 or 2, wherein the closure is in the form of a cap and the pressing step includes pressing the cap skirt into contact with the outside of the container rim.

4. A method as claimed in claim 1, 2 or 3, wherein the heating and pressing steps are effected at successive stations substantially coaxial with the mouth of the container.

5. A method as claimed in claim 4, wherein the heating and pressing steps are effected by a sealing head having pressing means disposed above nozzle means for directing the heated air onto the closure, including the steps of moving the head and container, having the closure applied thereto, relative to one another to position the container mouth adjacent the nozzle means, supplying heated air to the nozzle means thereby to direct the heated air onto the closure and soften the thermoplastic coating, and thereafter further moving the head and container relative to one another so as to press the closure into intimate contact with the container mouth.

6. A method as claimed in claim 5, where- in the supply of heated air to the nozzle means is switched-off upon relative movement of the head and container to effect the pressing step.

7. A method as claimed in any one of the preceding claims, including the step of pressing the closure, into contact with the container mouth prior to the heating step.

8. A method of heat sealing a metal foil closure to the mouth of a container, substantially as hereinbefore described with reference to the accompanying drawings.

9. A sealing head for heat sealing a metal foil closure to the mouth of a container, wherein nozzle means is located about an opening in the head for directing heated air onto a closure applied to the mouth of a container inserted into the opening, and pressing means is mounted in the head, rearwardly of the opening, for pressing the closure into intimate contact with the periphery of the container mouth when the latter is advanced through the opening.

10. A sealing head as claimed in claim 9, wherein the nozzle means is constructed to direct a ring of heated air radially inwardly against the closure.

11. A sealing head as claimed in claim 10, wherein the nozzle means comprises an annular channel disposed in the head about the periphery of the opening therein and connected to the periphery of the opening by an annular slit through which the ring of heated air is discharged, and wherein the heated air is supplied to the annular channel via a tangential passageway connected to the channel.

12. A sealing head as claimed in claim 9, 10 or 11, wherein the pressing means comprises a resilient member mounted in the head substantially coaxially with and rearwardly of the opening in the head.

13. A sealing head as claimed in claim 12, wherein the resilient member has its periphery secured to the head and a central portion flexible rearwardly of the opening against the action of spring pressure when a container mouth is inserted through the opening and pressed against the resilient member.

14. A sealing head as claimed in claim 13, wherein the resilient member has a peripheral flange projecting forwardly thereof which compresses the skirt of a closure cap against the outside of the container rim in response to rearward movement of the central portion of the resilient member by the container.

15. A sealing head as claimed in any one of the preceding claims 9 to 14, including heating means for heating the flow of air supplied to the nozzle means.

16. A sealing head as claimed in claim 15, wherein the heating means includes a helical passageway through which air flows from an air supply to the nozzle means and an electrical heating element disposed within the convolutions of the helical passageway.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. lifted into contact with the rubber member 13 so that it is pressed firmly onto the container. Glass containers may vary considerably in diameter, although made to the same nominal dimension, and therefore the closure may initially be a very loose fit on some containers. In this case it is desirable to use a cam rail as shown in Figure 10 where a lift into the sealing or pressing position both precedes and follows the heating period. Whilst particular embodiments have been described, it will be understood that modi fications can be made without departing from the scope of the invention as defined by the appended claims. For example, although the invention has been particularly described with reference to the sealing of metal foil closures to glass containers, it will be appreciated that it is equally applicable to heat sealing closures to containers or receptacles made from other materials which, like glass, are not readily softenable by heat, for example glazed or unglazed ceramic materials. WHAT WE CLAIM IS

1. A method of heat sealing a metal foil closure to the mouth of a container, said closure having a coating of thermoplastic material on its side adjacent the container mouth, comprising the steps of applying the closure to the mouth of the container, directing a flow of heated air onto the closure so as to soften the thermoplastic coating, and then pressing the closure into intimate contact with the periphery of the container mouth.

17. A sealing head for heat sealing a metal

foil closure to the mouth of a container, constructed and adapted to operate substantially as hereinbefore described with reference to Figures 1 to 7 of the accompanying drawings.

18. A heat sealing machine comprising a multiplicity of heads, each of which is constructed as claimed in any one of the preceding claims 9 to 17, mounted in a circular array on a rotating turret.

19. A machine as claimed in claim 18, including a reciprocable pedestal mounted on the turret underneath each head, and control means for subsequently moving each pedestal so as to insert the mouth of a container disposed thereon into the opening in the associated head, with the closure thereon located adjacent the nozzle means, and subsequently press the heated closure against the pressing means in the head.

20. A machine as claimed in claim 19, wherein the control means is arranged firstly to move each pedestal so as to press the closure against the pressing means prior to locating the container mouth and the closure thereon adjacent the nozzle means.

21. A machine as claimed in claim 19 or 20, including valve means for controlling the supply of air to each sealing head, said valve means being arranged to supply air to each sealing head over a predetermined arc of movement of the turret, corresponding to the period during which each pedestal locates the mouth of a container adjacent the nozzle means of its associated head.

22. A rotary heat sealing machine for heat sealing metal foil closures to the mouths of containers, constructed arranged and adapted to operate substantially as hereinbefore described with reference to Figures 8, 9 and 10 of the accompanying drawings.