FI70184C - ANORDNING FOER FOERPACKNING AV EN PRODUKT I EN VAKUUMKAMMARE - Google Patents

Description

70184

Device for packaging the product in a vacuum chamber -

Anordning förpackning av en product i en vakuumkammare

The present invention relates to a device for packaging a product.

When packaging products in flexible plastic bags, it is known to evacuate the inside of the package both to improve the storage capacity of the packaged product and to give the package a clean appearance. It is also known to improve the appearance of a sealed package by using a heat-shrinkable (i.e. oriented) film as the package wrapper and performing a shrinkage step on the evacuated, sealed package after sealing in a hot water bath or hot air tunnel during which the plastic film is heat-shrinked.

GB 1 561 837 discloses a combined shrinkage and evacuation system in which a filled flexible container is placed in a vacuum chamber which is then evacuated to reduce the residual air pressure both inside and outside the package to an order of magnitude of 4 torr, after which the package is sealed. The chamber is further evacuated, causing the container surrounding the product to bulge out of the product and contact the conductive heating plates, which cause the film to heat to the self-welding temperature.

FI patent application No. 811673 discloses a cycle in which air is removed from the chamber while the neck of a container formed of hot-shrinkable or self-welding material is shrunk in the chamber, so that only limited air can escape from the package. As a result, the substance in the container bulges out of the product. This bulging is then maintained during the heating phase of the tank, whereby the residual air in the chamber is circulated by means of a fan in the chamber and the heaters. The disadvantage of these known methods, especially when applied to fresh meat, is that the reduction in pressure of 2 70184 in the container during the early stages removes moisture from the surface areas of the product as a mist. Thus, when the bag bulges off the surface of the product, the inside of the container acquires a hazy appearance that does not disappear when the container sinks onto the product.

The object of the present invention is to provide a device for packaging a product, by means of which the possibility of gas remaining in the package can be eliminated and the appearance of the finished package can be improved.

The invention thus relates to a device for packaging a product comprising a vacuum chamber, a device for evacuating the chamber, a support for a filled flexible bag in the chamber, means for circulating hot air around the interior of the chamber and means for sealing the bag in the chamber, and a device for closing and opening the bag. closed when the hot air recirculation means is operating and a means for breaking the bag on the side of the closing device closer to the bag support in the chamber, a programming device for activating the hot air recirculation means before evacuating the chamber and controlling the bag closing device to keep the bag closed during air recirculation operation and opening the device for evacuating the chamber operates and for actuating the sealing means of the bag after the operation of the closing and opening device, the sealing means comprising radiant heat sources, which apply radiant heat to the neck area of the flexible bag.

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In order that the invention may be more readily understood, the following description is given by way of example only with reference to the accompanying drawings, in which Figure 1 is a schematic view of an apparatus for forming a shrinkable, vacuum-sealed package comprising a heat shrinkable film wrapper surrounding Figure 2A. a side view of the wrapper holding device of Fig. 2A seen along the arrow B in Fig. 2A, Fig. 3 is a plan view of the lower part of the chamber, and Fig. 4 is a graph showing the reduction of residual air pressure in the shrinkage chamber as a function of time.

The packaging device shown in Figure 1 comprises a vacuum chamber consisting of a lower chamber part 2 and an upper chamber part, i.e. a lid 3.

In this case, the two packages are placed in the chamber as filled but unsealed containers, in this case as heat-shrinkable bags 4. When the chamber lid 3 is raised, each bag can be placed on a support grid 5 on which the package is placed separately from the chamber 1 walls.

The device shown in Figure 1 further comprises a temperature sensing thermocouple 6 which gives an indication of the temperature of the air inside the chamber, since this is of course an important factor in the shrinkage of the package. The temperature sensor may be part of the air temperature control circuit in the chamber 1.

The chamber also includes a pressure sensor 7, which determines the residual gas pressure in the chamber, because this pressure can also be used to control the evacuation cycle, if desired.

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The chamber further comprises a heating device / consisting of two circular sets of electric resistance heaters 16 around the respective concentric fan rotors 9 at the bottom of the chamber 2. The fan rotors circulate hot air inside the chamber 1 and a hollow contact is effectively obtained between the bag 4 and the product. Additional heaters can be used if desired.

Below the bottom of the chamber is a vacuum pump 10, which is needed to reduce the pressure of the gas remaining in the vacuum chamber 1 to an order of magnitude of 5 torr or less for the purposes explained below.

The various electric resistance heaters 16 are located around the fans so that the heaters 16 also heat the air flow leaving the fans, which is just flowing over the package in the chamber. The thermocouple 6 (Figure 3) monitors the temperature of the chamber heater to maintain its temperature at the value required for shrinkage of the bag material.

Although not shown in Figure 1, the filled bags can be conveyed continuously in succession to the vacuum chamber 1 by the feed conveyor. Likewise, they can be removed from the vacuum chamber 1 by an discharge conveyor.

The chamber of Figure 1 is designed to ensure that when the fans 9 are operating, the air flow passes in a recirculation path which directs the air directly over the different heaters 16, then over the surface of the filled bags 4 and then back to the fan inlet.

Figures 2Δ and 2B show a flexible bag holding device 30 and bag neck heating units 13 and 14 used in the embodiment of the invention shown in Figure 1.

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As shown in Fig. 2A, the flexible bag holding device 30 is supported by an over-support member 31 forming a part of the chamber lid 3 and a lower support member 32 of the lower chamber part 2. As the lid closes on the lower chamber 2, the upper support member 31 descends towards the lower support member 32, settling in the position shown in Fig. 2A.

A flexible bag holding blade 33 made of a suitable rubber-like material is supported by an upper support member 31 to which it is secured by a set of screws 34. The resilient blade 33 contacts its lower edge along a counter member 35 supported by the lower support member 32. The counter member may alternatively be a blade 33. placed on the counter member 35 with the chamber cover 3 in the raised position, lowering the chamber cover 3 to bring the upper and lower support members 31 and 32 to the position shown in Figure 2A automatically keeps the bag neck with the counter member 35 so that any differential air pressure above a certain value can be removed by moving the blade 33 . The pulling of the neck of the bag to the left between the blade 33 and the counter member 35 is resisted by spring-loaded pushers, one of which 36 is shown in Figure 2A, which press the neck of the bag tightly over the counter member 35.

The angle of inclination of the flexible blade 33 is such that air under sufficient differential pressure can escape from inside the bag at least in the mouth areas between successive pushers 36.

The closure of the neck of the bag so as to create as little air space around the neck as possible in the bag is provided by upper and lower heat sources 37 and 38, which are strip lamps emitting infrared heat at a wavelength resulting in optimal heat absorption of the plastic mixture of bags 4 in the chamber.

The wavelength of the light emitted by the lamps 37 and 38 is preferably selected to be the same as the wavelength most easily absorbed by the material of the bag. Suitably, said 70184 wavelength is 3-4 microns for a plurality of plastic films, including multilayer films and laminates such as heat shrinkable (i.e., oriented), three-layer ethylene vinyl acetate, polyvinylidene chloride, and irradiated ethylene vinyl acetate acetate.

A brief exposure of the neck area of the bag to radiation from the heat radiators 37 and 38 is sufficient to heat the bag material to its softening point so that when the bag material sheets are compressed together, they close in the mouth and neck areas.

Contact between the bag material and the upper and lower heat sources 37 and 38 is prevented by means of batten nets 39 and 40 supported by respective pairs of upper and lower support plates 41 and 42 pivotally mounted on pins 41a, 42a. Each support plate 41, 42 has a hole 41b, 42b slidably cooperating with respective cam pins 43 and 44 supported on the respective ends of the vertically movable upper and lower compression rods 45 and 46, respectively. The lower compression rod 46 includes a main body with a resiliently flexible jaw member 46a connected thereto by helical compression springs 46b which ensure that the two compression rods 45 and 46 contact each other as the jaw member 46a springs.

The holding device 30 further includes a shape conductor 48 supported by a counter member 35 which, in the form of Figure 2A of the holding device, contacts the bulging neck of the bag. When a current pulse is applied to the conductor, the conductor breaks the neck of the bag so that gas (usually air) can escape from the bulging neck before closing. The conductor 48 may have, for example, a sawtooth shape or a sinusoidal wavy shape.

As the upper compression bar 45 descends, its cam pins 43 slide down in the holes 41b and cause the upper pivotable support members 41 to rotate counterclockwise to pivot the heat source 37 and its batt net 39 to the right of the trajectory of the lowering upper compression bar 45.

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Likewise, as the lower compression bar 46 rises, its cam pins 44 cooperate with the holes 42b of the lower brackets 42 to pivot these brackets to the side and move the lower heat source 38 and its batt net 40 away from the trajectory of the rising compression bar 46. This allows the film material to be pressed between the two press bars 45 and 46.

At the same time, the blade 47 supported by the main body portion of the lower compression rod 46 is positioned above the resilient jaw 46a by the resilience of the compression springs 46b and can cut excess bag material from the neck during closure.

Fig. 2B shows a drive mechanism by which the upper pressing member 45 is operated during its vertical movement.

As shown in Fig. 2B, the upper pressing member 45 rests in two separate parts on a vertical guide pin 50 supported by the central bearing portion 49 so that the two parts of the upper pressing rod 45 can slide vertically.

The two compression rod portions are connected to the lower ends of respective push pushers 51, the upper ends of the joints of which in turn are articulated to respective double angle lever units 52, 52 ', one of which 52 is shown in Figure 2A.

The left half of the angle levers 52 has a fixed pivot pin 53 at the first corner, a pivot pin 54 at the second corner that articulates it to the push joint 51, and an additional pivot pin 55 at the third corner that articulates it to the other end of the second drive bracket 56.

At 57, the other end of the second drive bracket 56 is articulated to the corresponding angle of the right-hand corner lever unit 52 '. The lever unit 52 also has pivot pins 53 'and 54' corresponding to the pins 53 and 54 described above.

The first drive bracket 58 is connected between the piston rod 59 of the piston 60 and the auxiliary joint pin 61 of the right angle lever unit 52 '. The extension and retraction of the piston rod 59 causes the counterclockwise and clockwise movement of the angle lever units 52, 52 'and thus the upward and downward movement of the compression rods 45, respectively.

A similar drive joint and drive piston exist for down-pressing to move the main rod of the rod 46 up and down.

As also shown in Fig. 2B, a protective member 62 is screwed onto the upper compression rod 45 so as to form a gap in which the blade 47 can fall when the upper and lower compression rods 45 and 46 come together.

The holding devices of Figures 2A and 2B operate in several stages throughout the machine cycle, as will be explained later.

The operation of the device shown in Fig. 1 is as follows when bags 4 formed of heat-shrinkable or oriented film material are used.

A filled but unsealed bag 4 made of heat-shrinkable packaging film is placed in the vacuum chamber 1, and the lid 3 of the chamber is moved downwards to close the chamber and seal the chamber at the edge 20.

One form of hot shrinkable (i.e., oriented) film used in the bag 4 may be a three-layer ethylene vinyl acetate, polyvinylidene chloride, and irradiated ethylene vinyl acetate laminate disclosed in U.S. Patent 3,741,253 and sold by W.R. Grace & Co. under the trademark "Barrier Bag".

During this time, the heat sources 37 and 38 are either de-energized or, more preferably, energized to a low heating level that does not allow them to heat the bag neck membrane to a sufficient melting temperature.

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The compression of the mouth of the bag when it is touched by the flexible holding device 30 ensures that as the outside of the bag is subjected to convection, any excess pressure in the bag can be adjusted by removing gas (usually air) from inside the bag 4 to the extent that the bag remains "swollen". "separately from the surface of the product 21 contained therein. Because bulging depends on factors common to a particular batch of products 21 (e.g., surface temperature, amount of air contained in the product, and surface quality of the product, e.g., tack), it may be appropriate to observe when bulging is likely to occur and then schedule the evacuation process. at the same time for all products in the lot. This is timed by a suitable timer. Other control devices can also be used as required.

Since the bag is still held flexibly over its neck during the heat-shrinking phase, air can still escape from inside the bag through the neck if, albeit unlikely, an excessive pressure difference develops over the bag material. The rest of the bag, on the other hand, shrinks back to the surface of the product 21 so as to obtain a substantially wrinkle-free surface covering the product 21. Still, the neck of the bag is able to close when the compression rods 45 and 46 close together in contact with each other.

At the end of the bubbling step and before the evacuation of the bag begins, energy is briefly applied to the shape conductor 46 to break the neck of the bag and release the remaining gas.

Evacuation of the chamber atmosphere (and now the broken bag 4) continues until the desired vacuum level is reached. During or shortly before the evacuation phase, the lamps 37, 38 can be energized to their maximum level so that they radiate radiant heat at the desired wavelength so that the film material optimally absorbs heat and the neck of the perforated bag is thus heated to the melting temperature.

701 84 10 The pistons 60 are then actuated to bring the upper and lower compression rods 45 and 46 together, thereby simultaneously pivoting away from the sources 37 and 38 and the associated tongue nets 39 and 40.

After the upper pressing bar 45 has come into contact with the bent pressing jaw 46a, the continued operation of the pistons 60 results in the blade 47 cutting the neck of the bag to remove excess fluid therefrom. The pressing members 45 and 46 ensure that the neck remains firmly next to the blade 47 to effect closure. Throughout this step, the mouth portion of the bag is further compressed between the resilient blade 33 and the mating member 35 so that the bag is still securely located within the holding device 30.

Retraction of the upper and lower compression bars 45 and 46 returns the heat sources 37 and 38 and their batten nets 39 and 40 to the position of Figure 2A. The evacuation of the chamber takes place after this retraction of the compression rods 45, 46, so that any residual air can escape from the bag without hindrance.

When the vacuum chamber is re-pressurized when opened, the heated neck portions on the left side of the compression members 45 and 46 are pushed together to provide fusion welding and to reduce any excess around the sealing zone so that the final package has a neat appearance.

The excess bag material removed by the blade 47 still remains between the flexible blade 33 and the counter member 35 and can be removed from the chamber opened during or after removal of the package.

The device described above is particularly suitable for use with moist products such as fresh meat in hot shrinkable bags because the increase in pressure on the surface of the meat during the bag bulging step tends to retain moisture in the product and prevent the inner surface of the bag from spraying when the bag is bulged. In addition, due to the rapid removal of air trapped in the bag, after the bag is punctured, the bag material can quickly contact the product before such spraying occurs. The appearance of the finished package is therefore particularly neat in the case of moist products such as fresh meat.

When all products are packaged with this device, the wrinkling of the product is improved by using a pre-shrinkage step followed by evacuation (as opposed to the conventional order of first vacuum sealing and later shrinkage).

In addition, the finished package obtained using the device according to the invention is much better than known shrink-cleaned packages using a water shrink bath to mitigate the "heat sink" effects of a relatively cool and high heat capacity product, as shrinking the film in contact with air allows a higher shrinkage energy recovery. As a result, the sealing properties of the bag (which are important to maintain the hermetic seal and freshness of the product until the time of use) are more effective. In addition, such a bag is more resistant to improper handling due to its greater thickness.

Because the air pocket left in the bag during the preheating shrinkage phase resists bag collapse and delays contact between the bag and the cold product, this thickness-increasing effect is even more pronounced and so does the wrinkle-free appearance of the bag, which in turn depends on the latent shrinkage energy recovery. In addition, because shrinkage is promoted by airflows around the entire product, the bag shrinks evenly around the product, leaving no air pockets behind the product's "equator" (i.e., the area with the largest cross section perpendicular to the longitudinal axis of the bag).

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In addition, the fact that there is little or no water vapor in the air between the product and the shrinkable bag (caused by the onset of shrinkage before the pressure is reduced, which even causes a small pressure rise, as shown in Figure 4) ensures that less shrinking heat is required. the dry air inside absorbs less heat than the air containing moisture.

Since the lower and upper support members 31 and 32 of the flexible holding device 30 are supported in the lower chamber part 2 and the upper chamber part 3, respectively, they close automatically in contact with each other when the chamber is closed. The only thing the operator needs to do is make sure that the neck of each bag 4 is placed on the respective counter members 35 before the chamber closes.

When the filled bags are fed by a conveyor into the chamber 1, the conveyor may, if desired, be one which ensures that when the bag 4 stops, the neck of the bag is correctly positioned for shrinkage without the operator having to adjust it carefully.

If desired, some other bag holding and closing mechanism can be used. For example, with the chamber closed, the neck of the bag can be tightly assembled in the chamber to the extent necessary to inflate the bag away from the product during the very early stages of evacuation of the chamber. The bracket can then be attached to the neck of the bag once the evacuation and shrinking steps have been completed. Such an in-chamber galvanizing device is disclosed, for example, in GB Patent 1,353,157.

The product is supported on rollers which form an air-permeable lattice 5 which supports the product but still allows a stream of hot shrink air to flow directly around the surface of the product.

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In any conventional post-sealing shrinkage process, the degree of film shrinkage recovery (i.e., the amount by which the film is able to return to its original shape prior to orientational stretching) is limited by the decrease in film temperature upon contact with the product. By ensuring in the present invention that the heating step occurs in the hot shrink film and the chamber air pressure is substantially at atmospheric pressure, much more shrinkage of the film can be restored only during a very short heating step.

In a preferred embodiment, it is intended to evacuate air from the chamber and the package. Of course, it is clear that another gas can be used if desired. In any case, some products may release a gas such as carbon dioxide, which is removed during the evacuation phase. Alternatively, the product may be purged with an inert gas, although air is the major gas component in the chamber and / or bag.

The entire description of a preferred embodiment of the invention describes the use of air circulating fans 9 to improve convection heat transfer. However, heat can, of course, be applied to the packaging film by convection without using a fan-assisted circulation or by some other mechanism, for example by thermal radiation, or without using some kind of air circulation such as the circulation promoted by the fans 9. The use of the device according to the present invention is directed to a hitherto unknown step in which the heat of shrinkage is applied before a significant evacuation of the chamber. The exact mechanism by which heat is applied to the packaging film can therefore be varied without departing from the scope of the invention.

If desired, the heating units 13 and 14 and the flexible holding device 30 may be located only at one end of the chamber or along the other side or both sides and at one end and along one side, so that the operator can vary the position of the bag or bags 4 to be closed. The arrangement of the heaters 13, 14 and the flexible holding device along one side of the chamber ensures that several short bags can be placed side by side along the chamber.

The bulging during the heating step ensures that the plastic material of the wrapper quickly comes off the cool product 21 it contains, making it much easier to shrink it because the heat transferred to the bag material from the hot air stream does not immediately transfer to the product 21 by convection.

The heat of shrinkage is applied only for a short time, for example 2-8 seconds, preferably 3-4 seconds. The actual evacuation is then initiated when the bulging area again touches the surface 21 of the product, by means of film shrinkage and / or by pressure equalization in and around the bag.

The evacuation of the chamber then continues using a vacuum pump 10 until the residual pressure of the vacuum chamber 1 has dropped to a final value of e.g. 5% of the residual air mass.

In an embodiment of the device in which the fans circulate the gas in the chamber, the fans 9 can, if desired, operate continuously during continuous emptying of the chamber, so that as the density of air remaining in the chamber 1 gradually decreases, that air can still shrink the bag material 21 to the outer surface.

At the end of the vacuum phase, the neck of the bag is closed, in this case using welding heaters or using some other suitable welding device such as conventional welding rods.

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The valve 14 is then opened so that the chamber 1 can be pressurized again. The lid of the chamber 1 is then raised so that the finished shrunk and sealed package can be removed from the vacuum chamber 1.

The function of the heaters 16 in the chamber is to keep the temperature of the air around the package high enough so that the heat can be transferred to the bulging bag material to the extent necessary to cause shrinkage. However, when fan-assisted air circulation in the chamber is used, the heaters need not operate continuously provided that the air temperature in the chamber 1, by the time the bag 4 has bulged out of the product 21, is sufficient to shrink the package.

In swelling, temperatures of 90-140 ° C may be required to provide shrinkage when using a biaxially oriented shrink film. The exact value of the temperature depends on various factors such as the quality of the film or the degree of orientation.

A fully automatic modification of the device is possible, in which case all the different process parameters are adjusted and the device is timed to operate automatically from the placement of the filled bag chamber until the automatic removal of the sealed package from the chamber.

The exact duration of the heating phase can be varied within certain limits.

For example, Fig. 4 is a graph showing the pressure in the chamber compared to time. At time t ^ the chamber closes, and the time t ^ indicates the time at which the evacuation of the chamber begins after the bag has shrunk. At time t2, conductor 48 is energized to break the neck of the bag before full vacuum is reached by time t1. At time t, energy is applied to the lamps 37, 38, after which the compression rods 45, 46 are brought together to close the neck and cut off excess material. At this time, the chamber is pressurized again.

The dashed line in Figure 4 shows the pressure in the bag. It can be seen from this that the pressure rises above the initial atmospheric pressure of the line indicating the pressure in the chamber. It is this increase in pressure caused by the application of the heat of shrinkage to the outside of the chamber that causes the bag to bulge.

For any batch of product, the compressive effect of the flexible holding device on the neck of the bag should be such that the bag bulges to such an extent that the heat transferred to the bulging bag material by hot air contact does not immediately dissipate due to the relatively cool product inside the bag.

Since the alignment of the air depends on the circulation of hot air above the bulging packaging film, the fact that the outside of the bag is substantially at atmospheric pressure ensures that the heat capacity of the air in chamber 1 at that intermediate pressure is as high as possible for efficient heat transfer.

As stated above, the temperature of the product, the quality of the packaging film (e.g. bag 4) and the amount of gas contained in the product also affect the bulging operation.

The device is usually adjustable so that the shrinkage-heating time can vary to ensure that the bag is always bulged and settled back sufficiently by the time the main evacuation step begins.

If desired, e.g. when packaging particularly soft products such as cream cheeses, a "soft vacuum" package can be produced by limiting the evacuation step very soon after the pressure is again reduced below the "intermediate pressure" value.

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If desired, the supply of hot air to the chamber 1 can be arranged by means not shown, while the lid 3 descends and until the lid 3 closes over the lower chamber part 2, condensing at the edge 20 and also this closing time. In this way, the best possible supply of hot air to the chamber at the beginning of the heat shrinking phase is obtained.

If desired, the package may contain several different products wrapped in one wrapper (e.g. one bag 4).

Modification of the process may be desirable so that it can be used in the so-called in connection with self-welding films referred to in said FI patent application 811673.

Claims (4)

A device for packaging a product comprising a vacuum chamber (2, 3), a device (10) for evacuating the chamber, a support (5) for a filled flexible bag (4) in the chamber, means (9, 16) for circulation of hot air around the chamber interior and means (13, 14, 45, 46) for sealing the bag in the chamber, characterized by a device (30) for closing and opening the bag comprising means (33, 35) for pouring the mouth of the bag closed during the operation of the air circulation means (9, 16) and a means (48) for perforating the bag on the side of the closure device which is located closer to the bed base (5) in the chamber, a programming device for moving the means (9, 16) for circulating hot air in operation before the evacuation of the chamber (2, 3) and for controlling the device (30) for closing the bag to keep the bag closed during the operation of the air circulation means (9, 16) and for opening the bag (4) before the device (10) for evacuation of the chamber work and for setting the means (13, 14, 45, 46) for sealing the bag in operation after the closing and opening device (30) has functioned, the sealing means comprising radiant heat sources which expose the neck portion of the flexible bag (4) to radiant heat . Device according to claim 1, characterized in that the closing and opening device comprises a compliant pouring means (33) and a motor means (35) against which the compliant pouring means (33) presses the neck (4) and the perforating means comprises an electric heating means. (48), which is positioned between the pouring means (33, 35) and the sealing means (13, 14, 45, 46) and which can be measured by electric current for perforating the neck of the pouring means (4) with the aid of the pouring means (33, 35). of heat. Device according to claims 1 and 2, characterized in that the radiant heat sources are infrared gap lamps (13, 14) which are located opposite each other on either side of the intended position for the neck material of the paw, that the sealing means further comprise pressing means which are parallel to each other. , separate press bars from each other