GB2574057A

GB2574057A - Vacuum dome and vacuum skin packaging apparatus

Info

Publication number: GB2574057A
Application number: GB1808622.3A
Authority: GB
Inventors: Barratt Derek; James Windsor Stephen
Original assignee: Proseal UK Ltd
Current assignee: Proseal UK Ltd
Priority date: 2018-05-25
Filing date: 2018-05-25
Publication date: 2019-11-27
Also published as: GB201808622D0

Abstract

A vacuum dome 12 has an aperture 24 for evacuating its interior 20 and mechanism for maintaining the peripheral edge region 16 at a lower temperature than the rest of its internal surface 94. The rim could be formed of a less conductive material 98 than the rest of the body 14. The rim could include elastomeric seal 98 and the rest of the body could be aluminium. The less conductive material could be mounted 100, coated or otherwise affixed to the body. There could be a thermal break between the rim and body of the vacuum dome and there could be a cooling arrangement in the rim. Ideally the dome is heated while the rim is kept cool and it can be used to apply a packing skin to a tray. A vacuum dome has an aperture, a product support tool with a vacuum chamber, a vacuum source connected to the aperture and the chamber and a valve to isolate them from each other. The valve could be a non return valve in pneumatic lines.

Description

VACUUM DOME AND VACUUM SKIN PACKAGING APPARATUS

Technical Field of the Invention

The present invention relates to a vacuum packing apparatus for skin packing. The present application relates in particular, but not exclusively, to a vacuum dome for use in skin packaging apparatus.

Background to the Invention

Skin packing involves sealing a sheet of transparent plastics film over a product placed on a sheet of material such as card or, where a fresh foodstuff is being packaged, typically a plastics material tray having sealing flange or rim extending about its periphery. Vacuum may be used to obtain a close fit of the transparent film over the product and the film is typically heat sealed to the underlying sheet or tray.

An existing skin packing apparatus comprises a vacuum dome. The dome has body with peripheral edge region which forms an opening to a cavity. An array of apertures extend through the body into the cavity. In use, the dome is mounted to a heater which heats the dome.

Transparent plastics film is drawn out just beneath the dome, extending across the opening to the dome’s cavity. The film may be pre-heated by blowing hot air through the apertures in the dome. A vacuum is then applied to the apertures in the dome drawing air out of the dome and drawing the plastics film towards and into contact with the internal surface of the dome. The film is heated both by contact with the dome by radiant heat from the dome.

A product to be wrapped is placed on a plastics material tray having a sealing flange the same shape as the peripheral edge region of the dome. The tray has at least one aperture extending therethrough. The tray is mounted to a product support tool having a vacuum chamber below the tray, which is also connected to the vacuum source. The product support tool has seal which locates about an opening to the vacuum chamber and the flange of the tray sits on the seal. The chamber and dome are brought together so that that the film overlying the peripheral edge region of the dome is clamped to the flange of the tray between the peripheral edge region of the dome and the product support tool. The heat of the dome, and pressure applied, causes the film to be heat sealed to the flange of the tray.

Vacuum is applied to the chamber beneath the tray to draw air from under the tray and from between the film and the tray, through the aperture(s) in the tray. The dome is then disconnected from the vacuum source and air above atmospheric pressure is admitted into the cavity through the apertures in the dome. This pressurised air urges the heated plastic film onto the product and the tray and the film adheres to the tray surrounding the product, tightly encapsulating the product onto the tray.

The dome is made from a material, usually aluminium, which has a good thermal conductivity. This is advantageous in ensuring that the film is adequately heated when in contact with the surface of the dome inside the cavity. However, it has been found that the tray may become distorted by the heat applied to its flange through the peripheral edge region of the dome, adversely affecting the quality of the seal and finish.

A further issue is the possibility of the film falling prematurely onto the tray during the packaging process if the vacuum in the dome cavity is not adequately maintained.

It is an object of embodiments of the present invention to address one or both of these problems.

Summary of the Invention

According to an aspect of the invention, there is provided a vacuum dome for skin packing apparatus, the dome defining a cavity and a peripheral edge region surround the cavity, with least one aperture formed in the dome through which air may be extracted from the cavity, wherein the dome is heated in use and is configured such that a surface of the peripheral edge region is maintained at a lower temperature than the surface the dome within in the cavity.

By maintaining the surface of the peripheral edge region at a temperature lower than the surface of the dome in the cavity, the amount of heat introduced into the flange of the tray is reduced, whilst the film is still adequately heated through contact with the surface of the dome within the cavity.

In an embodiment, the dome comprises a main body made of a first material and wherein the peripheral edge region comprises a second material having a lower thermal conductivity than the first material. The peripheral edge region may comprise a seal made of said second material mounted to the body. Alternatively, the second material may be coated or otherwise affixed to the body.

The first material may be a metallic material such as aluminium. The second material may be an elastomeric material. The elastomeric material may be a rubber or a synthetic rubber, which may be a silicon rubber.

In another embodiment, the dome comprises a body in which a part of the body defining the cavity is made from a first material and a second part of the body defining the peripheral edge region is made from a second material having a lower thermal conductivity than the first material.

In a further embodiment, a thermal break is provided between the peripheral edge region and a part of the dome which defines the cavity.

In a still further embodiment, the dome comprises a means for cooling the peripheral edge region in use. Fluid channels may be provided in the dome in or adjacent the peripheral edge region through which a cooling fluid can be circulated. The fluid may be water.

The surface may be a surface of a sealing face in the peripheral edge region which in use locates opposite a surface of a product support to which a packaging film is to be bonded. The vacuum dome may be configured for use in skin packaging a product in a tray having a sealing flange and the sealing face may be arranged in use to locate opposite the flange.

According to a second aspect of the invention, there is provided a vacuum dome for skin packing apparatus, the dome having a body defining a cavity, a peripheral edge region surround the cavity, and at least one aperture through which air may be extracted from the cavity, wherein the peripheral edge region includes a sealing face which in use locates opposite a surface of a product support to which a packaging film is to be bonded, wherein the body is made of a first material and a seal made of a second material having a lower thermal conductivity than the first material is mounted to the body along the sealing face.

The seal may be arranged such that, in use, it is operative to press a packaging film onto the product support.

The first material may be a metallic material such as aluminium. The seal may be made of an elastomeric material. The elastomeric material may be rubber or a synthetic rubber, which may be a silicon rubber.

According to a third aspect of the invention, there is provided a vacuum dome for skin packing apparatus, the dome defining a cavity and a peripheral edge region surround the cavity, with least one aperture formed in the dome through which air may be extracted from the cavity, wherein:

a) the dome has a body which defines the cavity and the peripheral edge region made of a first material and a seal made of a second material having a thermal conductivity lower than that of the first material is mounted to a sealing face of the peripheral edge region;

b) the dome has a body made of a first material which defines the cavity and the peripheral edge region and a second material having a thermal conductivity lower than that of the first material is located on a sealing face of the peripheral edge region;

c) the dome has a body which defines the cavity and the peripheral edge region, a part of the body which defines the cavity being made of a first material and a part of the body which defines at least a sealing face of the peripheral edge region being made of a second material having a thermal conductivity lower than that of the first material;

d) the dome has a body which defines the cavity and the peripheral edge region, the dome including an arrangement for cooling at least a sealing face of the peripheral edge region.

According to a fourth aspect of the invention, there is provided a skin packaging apparatus comprising a vacuum dome in accordance with any of the first, second, or third aspects of the invention.

According to a fifth aspect of the invention, there is provided a method of operating a skin packaging apparatus comprising a vacuum dome defining a cavity and a peripheral edge region surround the cavity, least one aperture formed in the dome through which air may be extracted from the cavity, wherein the method comprises heating the vacuum dome whilst maintaining a surface of the peripheral edge region at a lower temperature than the surface the dome within in the cavity.

The method may comprise providing said vacuum dome with a body made from a first material which defines the cavity and the peripheral edge region and mounting a second material having a lower thermal conductivity than the first material to the peripheral edge to define said surface. Said second material may be provided in the form of a seal mounted to the peripheral edge region of the dome. In which case, the method may comprise mounting the seal to a face of the peripheral edge region which in use locates opposite a surface of a product support to which a packaging film is to be bonded, the method comprising using the seal to press the packaging film on to the product support.

The method may alternatively comprise cooling the peripheral edge region of the vacuum dome. The method may comprise circulating a cooling fluid, which may be water, through fluid channels in the dome in or adjacent to the peripheral edge region.

According to a sixth aspect of the invention, there is provided a skin packaging apparatus comprising a vacuum dome defining a cavity and a peripheral edge region surround the cavity, least one aperture formed in the dome through which air may be extracted from the cavity, and a product support tool for holding a product support for packaging, the product support tool defining a vacuum chamber through which air in the product support can be extracted in use, wherein the at least one aperture in the vacuum dome and the vacuum chamber in the product support tool are each selectively connectable with a common vacuum source through a pneumatic circuit, and wherein the pneumatic circuit includes a valve arrangement for fluidly isolating the at least one aperture in the vacuum dome from the vacuum chamber in the product support tool when they are both connected to the vacuum source.

By fluidly isolating the vacuum dome from the vacuum chamber in the product support tool in the pneumatic circuit, the vacuum in the dome cavity can be maintained sufficiently to hold the film in contact with the surface of the dome when the product support tool is connected to the same vacuum source during a packaging process.

The valve arrangement may comprise a non-retum valve in a pneumatic line from the vacuum source to the at least one aperture in the vacuum dome, the non-return valve being configured to prevent air flowing through it in the direction of the vacuum dome. Alternatively, the valve arrangement may include an actuated valve which is actuated by a control system, either at appropriate times in the cycle or in dependence on an output from a pressure sensor in the pneumatic circuit. In an embodiment, the at least one aperture in the vacuum dome and the vacuum chamber in the product support tool are each fluidly connected to the vacuum source through respective pneumatic lines which are connected to the vacuum source through a common pneumatic line to which they are joined, wherein the valve arrangement is located in the respective pneumatic line for the vacuum dome.

Detailed Description of the Invention

In order that the invention may be more clearly understood, an embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1	is a plan view from below of a vacuum dome in accordance with an aspect of the invention and which forms part of a skin packing apparatus in accordance with another aspect of the invention;
Figure 2	is a cross-sectional view through the dome of figure 1, taken on line A- A of figure 1;
Figure 3	is a view on an enlarged scale of detail B in figure 2;

Figures 4-12 are a series of schematic drawings of a skin packaging apparatus in

Figure 13

accordance with an aspect of the invention and incorporating the dome of figures 1 to 3, showing the apparatus during different stages of a packing process; and is a perspective view of a tray for use with the apparatus shown in figures

to 12.

Throughout the drawings the terms up, down, top, bottom and like terms are used to describe the apparatus in the orientation shown in the drawings, which in figures 4 to 12 is the orientation in which it is intended to be used, and are not intended to be otherwise limiting.

Referring to the drawings, skin packing apparatus 10 includes a vacuum dome

12. The dome 12 has a body 14, which on a lower surface defines a peripheral edge region 16 surrounding an opening 18 into an internal cavity 20. The opening 18 is substantially rectangular with rounded corners and the interior surface of the cavity 20 is generally concave, that is to say it defines a volume behind the opening. In the illustrated example, the interior surface 21 of the cavity extends inwardly away from the peripheral edge region 16 of the dome and curves to merge with a generally flat, rectangular base region 22 generally parallel to, but spaced from, the plane of the opening into the cavity. An array of apertures 24 extend through the base region 22 of the dome, opening into the internal cavity 20. The apertures 24 are connected to a pneumatic circuit (indicated generally at 26) to allow air to be introduced into and extracted from the cavity 20.

The dome 12 as illustrated is used in the skin packaging apparatus 10 to package product supported on a generally rectangular plastics moulded tray 28 as shown in figure 13. The tray has a central, substantially flat rectangular base 30 and a sidewall 32 extends upwardly about the periphery of the base 30 to define an interior volume within which product 34 to be packaged is placed. A peripheral sealing flange 36 extents outwardly from the upper end of the side wall 32 generally parallel to the base 30. An aperture 38 is formed through the tray towards each comer of the base 30 and an arcuate raised wall 40 is moulded into each comer of the tray to provide a barrier between the aperture 38 and the remainder of the base 30 where the product is located. In use, the barrier walls 40 help prevent material, especially liquids, on the tray being drawn through the apertures 38 during a packing operation.

The dome 12 is shaped and dimensioned so that its peripheral edge region 16 conforms to and locates on the flange 36 of the tray 28 during a packaging process, with the internal cavity 20 of the dome locating above the interior volume of the tray. It will be appreciated that the dome 12 can be provided in a range of other shapes and sizes for use with differently shaped and/or sized product trays and supports. For example, for use with a circular product tray, the dome may have a substantially circular opening and the internal cavity could be substantially hemispherical.

As illustrated in figures 4 to 12, the skin packaging apparatus 10 includes an upper tool assembly 42 in which the vacuum dome 12 is mounted and a lower or product support tool 44 for holding the tray 28.

The upper tool assembly 42 includes an upper film clamping plate 46 and a dome support 48, which together define a downwardly open central recess 50 within which the vacuum dome 12 is located. The vacuum dome 12 is mounted to a heated support 52 to form a dome sub-assembly which is mounted to the dome support 48 within the central recess by means of springs 54. The heated support 52 contains an electrical heating element which heats the dome body 14. The body 14 of the dome is made from metallic material, such as aluminium, which has a high thermal conductivity so that the heat is spread throughout the body.

The upper tool assembly 42 also includes a lower film clamping plate 56 positioned below the upper film clamping plate 46 and which is movably mounted to the upper film clamping plate by means of actuators 58. The actuators 58 are pneumatic cylinders and are configured to move the lower clamping plate 56 between a lowered, non-clamping position as shown in figure 4 in which it is spaced below the upper film clamping plate 46 and a raised, clamping position as shown in figure 5 in which the lower film clamping plate 56 is proximal to the upper film clamping plate 46 such that a film 60 located between the upper and lower film clamping plates 46, 56 is firmly clamped between the two. The lower film clamping plate 56 defines a central opening 62 which corresponds to the central recess 50 in the upper film clamping plate 46 and which receives part of the lower tool 44 and the tray 28 during the packaging process as described below. It will be appreciated that the actuators 58 need not be pneumatic cylinders and that other types of actuator could be used, such as hydraulic cylinders or electronic actuators.

The lower tool 44 has an annular body 64 which supports the tray 28 below the upper tool assembly 42. The annular body defines a cavity 66 in which the base 30 of the tray 28 locates and has a raised shoulder 68 extending upwardly about the cavity. A seal 70 is provided on an upper surface of the shoulder on which the tray flange 36 sits. A further seal 71 is provided on the upper surface of the annular body radially outside the raised shoulder 68. The further seal 71 engages a lower surface of the lower film clamping plate 56 in use, as described below with reference to figure 9. The cavity 66 of the lower tool 44 forms a vacuum chamber which is connected to a vacuum source 72 forming part of the pneumatic circuit 26, to allow air to be drawn out of the tray 28 during the packaging process.

The pneumatic circuit 26 includes the vacuum source 72, which may be a vacuum pump, and a source 74 of pressurised air (that is to say air above atmospheric pressure), which may be an air compressor. The apertures 24 in the vacuum dome 12 are selectively connectable to either the vacuum source 72 or the source of pressurised air 74 by means of a first valve 76. A second, isolation valve 78 is located in the pneumatic circuit between the first valve 76 and the vacuum dome 12, so that the vacuum dome can be selectively isolated from the remainder of the pneumatic circuit, including the vacuum source 72 and the source of pressurised air 74. The source of pressurised air 74 is connected to the first valve via a sub-circuit 80 which includes a pressure regulator 82, a non-retum valve 84 and a third valve 86. The third valve 86 enables the vacuum dome 12 to be selectively connected to the source of pressurised air 74 directly or through the pressure regulator 82. When connected to the source of pressurised air 74 through the pressure regulator 82, the air supplied to the vacuum dome 12 is at a lower pressure than when it is connected directly to the source of the pressurised air 74. For example, the source of pressurised air 74 may supply air at a pressure in the region of 5 to 7 bar (500 to 700 kPa) , or more particularly at 6 bar (600 kPa), and the pressure regulator 82 may be configured to reduce the pressure of the air supplied to the dome to around 1 bar (100 kPa). The pneumatic circuit includes a fourth valve 90 operable to selectively connect the cavity 66 of the lower tool 44 to the source of vacuum 72 or to atmospheric pressure 88. All the valves in the pneumatic circuit 26 are two-position valves which are electronically actuated by means of a control system.

Operation of the apparatus 10 to skin package a product 34 on a tray 28 will now be described with reference to Figures 4 to 12.

Figure 4 illustrates the apparatus 10 in an at-rest position. The lower film clamping plate 56 is spaced below upper film clamping plate 46 with a film 60 stretched between the two. A tray 28 loaded with product 34 ready to be packaged is supported in the lower tool 44 below the upper tool assembly 42. The valves are set in initial, atrest positions with second valve 78 closed so that the vacuum dome 12 is fluidly isolated from the remainder of the pneumatic circuit and the fourth valve 90 is set to connect the lower tool 44 to atmospheric pressure, isolated from the source of vacuum 72. The first valve 76 is set to connect the second valve 78 in the line to the vacuum dome 12 to the pressurised air supply sub-circuit 80 and the third valve 86 is closed to isolate the first and second valves 76, 78 from the direct pressurised air supply 74.

From the rest position, the lower film clamping plate 56 is raised by the actuators 58 to clamp the film 60 between the upper and lower film clamping plates 46, 56 as illustrated in figure 5. The film 60 is then pre-heated by blowing hot air on to the film through the vacuum dome 12 as shown in figure 6. The first, second and third valves 76, 78, 86 are set to connect the apertures 24 in the vacuum dome 28 directly to the source of the pressurised air 74, so that air is directed through the apertures 24 onto the film 60. The air may be heated as it passes through the vacuum dome 12, which has been heated by the heating support 52, or may be heated by a separate heater. In alternative embodiments, this step in the process may be omitted and/or alternative means for pre-heating the film adopted.

Once the film has been pre-heated, the first valve 76 is switched to connect the apertures 24 in the vacuum dome to the vacuum source 72, drawing the film into contact with the surface of the vacuum dome in the cavity 20 as illustrated in figures 7 and 8. This applies heat directly into the film 60 from the surface of the vacuum dome 12 to prepare the film for the skin process. The base tool 44 is then raised and compressed against the spring-loaded vacuum dome 12 as shown in figure 9, with the further seal 71 engaging the lower film clamping plate 56. The flange 36 of the tray 28 is compressed against the peripheral edge region 16 of the vacuum dome with the film inbetween so that heat and pressure from the dome seals the film 60 to the flange 36. In the next stage shown in figure 10, the fourth valve is switched to connect lower tool cavity 66 to the source of vacuum 72, so that air in the tray 28 beneath the film 60 is drawn out through the apertures 38. In this phase, air is evacuated from the tray down to low pressure, typically under 5 mbar (0.5 kPa), whilst the source of vacuum 72 remains connected to the vacuum dome 12 to hold the film in contact with the surface of the dome. The film 60 is then released from the dome to fall onto the product 34 (figure 11) by connecting the apertures 24 in the dome to the source of pressurised air through the regulator 80, so that air at over atmospheric pressure (typically in the region of Ibar (100 kPa)) is introduced into the dome cavity 20 above the film 60. In this configuration, the first valve is switched to connect the vacuum dome 12 to the pressurised air supply sub-circuit 80 and the third valve 86 is closed so that the pressurised air flows through the regulator 82 and non-return valve 84. In a final step shown in figure 12, the apertures 24 in the vacuum dome 12 are connected directly to the source of pressurised air 74 by opening the third valve 86 so that higher pressure air is admitted into the dome cavity above the film 60. This presses the film 60 firmly into contact with the product 34 and the tray 28 to consolidate the film bonding to the tray. At the same time, the cavity 66 in the lower tool 44 is connected to atmospheric pressure by switching the fourth valve 90.

The apparatus 10 is then returned to the at-rest position shown in figure 4 by lowering the lower tool 44 and the lower film clamping plate 56 and configuring the valves in their at-rest positions. The packaged tray 28 is removed from the lower tool 44 and replaced by a new tray 28 to be packaged and a new section of film 60 is positioned between the upper and lower film clamping plates and the procedure is repeated.

In the method as described above, the flange 36 and film 60 are pressed into contact with the peripheral edge region 16 of the heated vacuum dome 12 throughout the steps illustrated in figures 9 to 12, in which the air is drawn out of the tray through the lower tool 44 and the film being subsequently lowered onto the tray and product. This can include a dwell time in the region of 4 seconds. The dome 12 is generally heated to a temperature of around 200 degrees C - typically 170 to 220 C - so that it heats and softens the film when the film is drawn into contact with it. This enables the film to be drawn into the dome and subsequently to drape over food on the tray and bond to the surface of the tray. In prior art apparatus where the flange and film are pressed directly on to the peripheral edge region 16 of the vacuum dome 12, it has been found that the amount of heat transferred from the dome to the tray flange adversely affects the materials and the quality of the seal/finish. To address this issue in accordance with an aspect of the invention, a seal 92 made of a material having a lower thermal conductivity than the body 14 provided on the peripheral edge region 16 which engages with the film 60 and the flange 36 of the tray. The seal 92 acts as a thermal barrier to reduce the amount of heat transferred into the flange 36 of the tray and in use tends to remain about 70-80 C cooler than the dome. This enables a higher dome temperature to be used whilst maintaining a lower peripheral edge temperature.

Details of the peripheral edge region 16 of the dome are shown in Figure 3. The peripheral edge region 16 includes a sealing face 94 which in use opposes the, usually upper, surface of the tray flange 36. The peripheral edge region 16 also includes an outer lip 95 which extends about the outer edge of the tray flange 36 in use. The outer lip 95 is operative to cut the film 60 when the lower tool 44 is raised to press the flange onto the peripheral edge region of the vacuum dome. Alternatively, the apparatus may have a separate cutting means to sever the film about the tray 28. The seal 92 is located in a groove 96 extending about the sealing face 94. The seal has a head region 98 which projects outwardly of the sealing face and a narrower neck region 100 which locates in a correspondingly narrow part of the groove. The seal 92 is arranged so that the head region 98 engages with the film 60 pressing it onto the tray flange 36 such that the film and flange do not directly contact the sealing face 94. The seal 92 can be made of any suitable material which has a suitable thermal conductivity and which is capable of withstanding the temperature of the dome during the packaging process. The seal could, for example, be made from elastomeric materials such as rubber and synthetic rubber (including silicon rubber), and the like.

Use of a seal 92 on the peripheral edge region 16 of the dome provides a very convenient way of controlling the heat transferred to the tray flange 36 and is easily replaceable. However, other arrangements could be adopted to reduce the temperature of the peripheral edge region 16 of the dome and/or to reduce heat transfer between the dome and the film/tray flange in the peripheral edge region. For example, a material having a lower thermal conductivity than the material forming the remainder of the body of the dome could be coated or otherwise applied to the surface of the dome in the peripheral edge region. The second material could, for example, be provided in the form of an insert which is located in the sealing face. In a further alternative, the peripheral edge region could be made from a different material with a lower thermal conductivity than the remainder of the dome body and/or a thermal break may be incorporated in the dome between the peripheral edge region and the remainder of the dome body. In a still further alternative arrangement, the apparatus could be provided with means for cooling the peripheral edge region 16 of the dome so that its temperature remains lower than the remainder of the dome, in particular the surface of the dome within the cavity. This might include providing fluid passages in or adjacent to the peripheral edge region of the dome through which a fluid, such as water, is passed to cool the peripheral edge region.

In the skin packaging apparatus 10, the vacuum dome 12 and the lower tool 44 are both connected with the same vacuum source 72 at different stages in the packaging process. In the step illustrated in figure 10, the cavity in the lower tool 44 is connected to the source of vacuum 72 to which the vacuum dome 12 has been connected for some time. Because the lower tool is at atmospheric pressure when first connected to the vacuum source, this may result in a temporary rise in the system pressure adversely affecting the vacuum in vacuum dome 12 above the film, allowing the film to come away from the dome prematurely. This is a particular problem where the cavity in the dome is deep, which makes it difficult to keep the film 60 in contact with the surface of the dome. To overcome this issue, a further non-return valve 102 is located in the vacuum part of the pneumatic circuit between the vacuum dome 12 and the lower tool 44 and vacuum source. The further non-retum valve 102 is arranged to close and prevent air flowing in the direction toward the vacuum dome. This prevents the vacuum present in the dome 12 being inadvertently dissipated when the lower tool 44 is connected to the vacuum source. The use of a non-return valve 102 is advantageous as it automatically responds to an increase in pressure in the vacuum part of the pneumatic circuit relative to the vacuum in the dome 12. However, this function could be performed by an actuated valve which is operated by the control system at appropriate times in the cycle (e.g. being closed just prior to the lower tool 44 being connected to the vacuum source) or in dependence to a signal from a pressure sensor. The pressure sensor may be located to sense the pressure in the vacuum part of the pneumatic circuit and the valve closed if the detected pressure rises above a predetermined threshold.

Alternatively, separate vacuum sources could be used for the dome 12 and the lower tool 44.

The above embodiment is described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

1. A vacuum dome for skin packing apparatus, the dome defining a cavity and a peripheral edge region surround the cavity, with least one aperture formed in the dome through which air may be extracted from the cavity, wherein the dome is configured such that, in use, a surface of the peripheral edge region is maintained at a lower temperature than the surface the dome within in the cavity.

2. A vacuum dome as claimed in claim 1, wherein the dome comprises a main body made of a first material and wherein the peripheral edge region comprises a second material having a lower thermal conductivity than the first material.

3. A vacuum dome as claimed in claim 2, wherein the peripheral edge region comprises a seal made of said second material mounted to the body.

4. A vacuum dome as claimed in claim 2, wherein the second material is coated or otherwise affixed to the body.

5. A vacuum dome as claimed in claim 1 or claim 2, wherein the dome comprises a body in which a part of the body defining the cavity is made from a first material and a second part of the body defining the peripheral edge region is made from a second material having a lower thermal conductivity than the first material.

6. A vacuum dome as claimed in claim 1, wherein a thermal break is provided between the peripheral edge region and the part of the dome which defines the cavity.

7. A vacuum dome as claimed in claim 1, wherein the dome comprises a means for cooling the peripheral edge region in use.

8. A vacuum dome for skin packing apparatus, the dome having a body defining a cavity, a peripheral edge region surround the cavity and at least one aperture through which air may be extracted from the cavity, wherein the peripheral edge region includes a sealing face which in use locates opposite a surface of a product support to which a packaging film is to be bonded, wherein the body is made of a first material and a seal made of a second material having a lower thermal conductivity than the first material is mounted to the body along the sealing face.

9. A vacuum dome as claimed in claim 8, wherein the seal is arranged such that, in use, it is operative to press a packaging film onto the product support.

10. A vacuum dome as claimed in any one of claims 3, 8, or 9, wherein the first material is a metallic material and the seal is made of an elastomeric material.

11. A skin packaging apparatus comprising a vacuum dome as claimed in any one of claims 1 to 10.

12. A method of operating a skin packaging apparatus comprising a vacuum dome defining a cavity and a peripheral edge region surround the cavity, least one aperture formed in the dome through which air may be extracted from the cavity, wherein the method comprises heating the vacuum dome whilst maintaining a surface of the peripheral edge region at a lower temperature than the surface the dome within in the cavity.

13. A method as claimed in claim 12, the method comprising providing said vacuum dome with a body made from a first material which defines the cavity and the peripheral edge region and mounting a second material having a lower thermal conductivity than the first material to the peripheral edge to define said surface.

14. A method as claimed in claim 13, wherein said second material is provided in the form of a seal mounted to the peripheral edge region of the dome.

15. A method as claimed in claim 14, wherein the method comprises mounting the seal to a face of the peripheral edge region which in use locates opposite a surface of a product support to which a packaging film is to be bonded, the method comprising using the seal to press the packaging film on to the product support.

16. A skin packaging apparatus comprising a vacuum dome defining a cavity and a peripheral edge region surround the cavity, least one aperture formed in the dome through which air may be extracted from the cavity, and a product support tool for holding a product support for packaging, the product support tool defining a vacuum chamber through which air in the product support can be extracted in use, wherein the vacuum dome and the product support tool are each selectively connectable with a common vacuum source through a pneumatic circuit, and wherein the pneumatic circuit includes a valve arrangement for fluidly isolating the vacuum dome from the product support tool when they are both connected to the vacuum source.

17. A skin packaging apparatus as claimed in claim 16, wherein the valve arrangement includes a non-retum valve in a pneumatic line from the vacuum source to the vacuum dome, the non-return valve being configured to prevent air flowing through it in the direction of the vacuum dome.

18. A skin packaging apparatus as claimed in claim 17, wherein the vacuum dome and the product support tool are each fluidly connected to the vacuum source

5 through respective pneumatic lines which are fluidly connected to the vacuum source through a common pneumatic line to which they are joined, wherein the non-return valve is located in the respective pneumatic line for the vacuum dome.