GB2145686A - A method and apparatus for packaging in flexible heat-shrinkable containers - Google Patents

Description

1 GB 2 145 686 A 1

SPECIFICATION

A method and apparatus for packaging in flexible heat-shrinkable packages This invention relates to a method and an apparatus for packaging articles and products of various description in flexible heat-shrinkable packaging material. This method is specially useful for packaging food products, especially perishable ones.

Known and currently employed are methods and machines for vacuum packaging various products in flexible, heat-shrinkable, bags or containers, the respective machines being provided with suction nozzles for the evacuation of the bags. With some known methods of this type, which require no vacuum chamber for their operation, an operator manually inserts the vacuum suction nozzle into the mouth of a bag or heat-shrinkable container contain- ing a product to be packaged. After complete evacuation of the air in the container, the mouth is sealed tight with a clamp or clip. Then, the sealed bags are temporarily placed in hot water to cause the container material to heat-shrink all around the product.

With alternative prior methods, heat-shrinking is effected in a vacuum chamber rather than by immersion in hot water. In UK Patent No. 1,561,837 filed March 29,1976 and in Canadian Patent No.

934,718 filed July 22,1971, both assigned to W.R. Grace & Co., the container whereinto the productto be packaged has been previously placed, is positioned inside a chamber, the chamber, and hence the container, are evacuated, the mouth of the container is sealed while the chamber is under vacuum, the chamber vacuum level is increased (chamber is evacuated to a greater extent) to cause the container to bulge out, the walls of the bulging container are heated from a heat source within the vacuum chamber, and atmospheric pressure is restored, at a controlled rate, inside the chamber to accomplish heat-shrinking of the wrapper around the product.

The above-mentioned prior methods have several limitations and disadvantages. Thus, the former of the prior methods outlined above involves a complex, laborious, and uneconomical step of immersion in boiling water.

The vacuum chamber method is often complicated to implement because all of the main opera- tions are carried out within the chamber, access to which can cause pneumatic seal problems.

Other prior packaging methods provide for the products to be packaged under a protective gas atmoshpere (C02, N2 etc.) as disclosed by US Patents Nos. 3,968,692 filed December 30,1974 and assigned to Elektrowatt AG and 3,939,624 filed March 4,1975 and assigned to CVP Systems, Inc. Such methods involve no heat-shrinking operations, and hence make no use of heat-shrinkable packaging films.

It is a primary object of this invention to obviate such prior method drawbacks by providing a method of vacuum packaging with heat-shrinking, which can be readily and effectively implemented.

Another object of the invention is to provide a method whereby the preservation of the packaged product can be improved, with special reference to the instance of perishable products.

A further object of the invention is to provide a method which is highly reliable and simple and enables heat-shrunk packages to be produced under vacuum which are free of wrinkles and of the utmost value as regards their aesthetic presentation.

Also an object of this invention is to provide an apparatus adapted to implement the inventive method.

A not unimportant object of the invention is that of providing an apparatus for vacuum packaging in flexible heat-shrinkable packages which has simple design and construction.

These and other objects, such as will be apparent hereinafter, are achieved by a method according to this invention for vacuum packaging in flexible packaging materials, which comprises the steps of:

a) placing a product to be packaged into a container of a heat-shrinkable thermoplastic material; b) injecting an insulating gas into the container until it is caused to bulge out such that the container walls are detached from the contained product; c) heating the container by application of the heat from an external heat source to induce heatshrinking of the container; d) removing said insulating gas from the container under continued heat application; and e) sealing the container.

According to a further aspect of the invention, the objects set forth are achieved by an apparatus for vacuum packaging products in containers formed of flexible heat-shrinkable packaging materials, characterized in that it comprises:

0 nozzle means in communication with a suction means and gas injection means; ii) a means of arranging filled containers with their openings in communication with said nozzle means; iii) at least one cut-off valve in communication with said nozzle means; iv) at least one vent valve in communication with said cut-off valve; v) a means of heating said container; and vi) a means of sealing said container tight.

Further features and advantages of the invention will be more clearly understood from the following description of preferred, though not exclusive, embodiments thereof, with reference to the accompanying drawings, where:

Figure 1 is a diagrammatic view of an apparatus according to the invention; Figure 2 is a diagrammatic illustration of the step sequence which characterizes the inventive method; and Figure 3 is a diagrammatic illustration of a modified embodiment of the inventive apparatus.

Making reference to Figures 1 and 2, the packaging apparatus according to the invention comprises a heat source 1, which can supply heat, for example, either by convection or radiation. Preferably, for a heat source, an electric resistance heater combined with a blower will be used.

A product 2 to be packaged is introduced into a 2 GB 2 145 686 A 2 container 3 formed of a flexible thermoplastic mate rial of a heat-shrinkable nature either manually or through conventional loading means for such appli cations, not shown. The container, with the product to be packaged inside it, is positioned at a nozzle 4, it being, for example, fed by a specially provided conveyor, e.g. a belt conveyor. A suitable clamp 5 provides a tight fit of the mouth of the container 3 onto the nozzle 4. The nozzle 4 is in communication with a suction means through valve 8, e.g. a vacuum pump (not shown), and with a means 7 of injecting a pressurized gas, for example, through a three-way connector, generally indicated at 6. Specially pro vided valves 8 and 9 control the opening and/or closing of said suction means and intake means. The nozzle 4 also communicates with the outside atmos phere through a third cut-off valve 10 and additional vent valve 12 connected thereto.

A sealing means 11 is arranged either to heat seal the neck or mouth of the container 3 on completion of the packaging operation, or to apply a strap or clip thereon. The sealing means may comprise heated pressure sealing bars, or as an alternative, where the material of the container 3 is of the self-sealing type, a means of sealing by just heat application. Alterna tively, a conventional clipping means may be used.

The packaging method of this invention will be next described with reference to Figure 2. With the sequence indicated at A, the container enclosing the product to be packaged is inserted with its mouth into the nozzle 4, and the clamp 5 is tightened around the container mouth to provide a perfect sea] between the container and nozzle. Where the insulat ing gas of the following step is other than air, e.g.

nitrogen or C02, a pre-evacuation step is carried out at this time. For this purpose, the valve 8 is opened to put into communication the interior of the con tainer 3 with the vacuum pump, with the valves 9 and 10 being held closed. As air is removed from the space between the product 2 and container 3, the latter will collapse to contact the surface of the product 2. On completion of the air removal step, the insulating gas injection sequence, indicated at B, takes place. Where the insulating gas is air, the pre-evacuation step would be omitted, and the cycle 110 would be resumed by directly going to the gas injection step. During this step, with the valves 8 and closed, the valve 9 is opened to admit pressurized gas from a specially provided pressure bottle 7 (Figure 1) through a pressure reducer 11 into the space between the container 3 and product 2. The gas injection step is continued until the walls of the container 3 bulge out and separate completely from the surface of the product 2, to be insulated there from by the gas layer.

The gas pressure at this stage will be the least required to fully detach the container walls from the product, and such as to avoid rupture of the walls.

Depending on the material used for the container, the pressure level may range, for example, from 20 to 1,000 mm H20.

Thereafter, the operative sequence indicated at C in the drawing takes place, wherein heat begins to be applied by means of the heat source 1 and by closing the valves 8 and 9 while opening the cut-off valve 10.130 Under the action of the applied heat, the container 3 undergoes a heat shrinking effect which causes the previously introduced insulating gas to be discharged through the cut-off valve 10 and vent valve 12 whereby the walls of the container 3 collapse down to contact the surface of the product 2. In suchh conditions, quick heating heating of the bag walls can be achieved without the heating rate being hindered by the thermal inertia of the product 2 placed inside the container, owing to the provision of the insulating gas between the product and container, i.e., if the product 2 is a chilled or frozen product separation of the bag walls from the product by the gas provide insulation so the wall can be heated through its thickness. Otherwise the chilled product in contact with the bag wall acts as a heat sink.

The exit of gas from the container is appropriately controlled through the vent valve 12, which is calibrated for a preset pressure level dependent on the container size, material of the wrapper, and heat shrinking temperature. Said vent valve 12 can prevent, during the heat shrinking process, both rupture of the container as caused by excess pressure, and a too high rate of gas removal. In fact, if the container is emptied quickly before the wrapperwalls have reached their heat shrinking temperature, the result will be an inadequate heat shrinking.

The heat shrinking step may be completed, as illustrated by the sequence indicated at D, by continued application of heat and by opening the valve 8 connected to the vacuum suction system, while closing at the same time the cut-off valve 10. Thus, complete removal of the insulating gas is assured along with the desired level of vacuum in the container 3. The sequence D is specially useful where the product being packaged is of a perishable nature.

Finally, the package sealing step, as illustrated by the sequence E, takes place, for example, by heat sealing with the sealing bars 11 in operation. During this step, the excess portion of the container walls is cut off and removed from the nozzle after releasing the clamp 5. Heating is continued to completion of the heat shrinking process also at the mouth area after sealing.

The material useful for the container in the inventive method is any thermoplastic material exhibiting heat-shrinking properties, and possibly heat welding properties. Single layer films may be used such as biaxially oriented, radiation crosslinked, polyethylene films like the films sold by W. R. Grace & Co. as "D-FILM" or as "CRYOVAC D-FILM" (Trademarks of W. R. Grace & Co.) or bi-oriented plastified polyvinylidene chloride, like the one sold by W. R. Grace &Co. "S-FILM" (Trademark of W. R. Grace & Co.). Alternatively, multilayered films are used which have at least one heat-shrinkable layer and additional layers performing the function of a heat welding layer, of a gas barrier, etc., depending on the final use contemplated. For the heatshrinkable layer, bi-oriented polyvinylidene chloride and copolymers thereof with ethylenically unsaturated monomers, fluorocarbon polymers, and fluorohydrocarbon polymers, may be used.

3 GB 2 145 686 A 3 For the sealing layer, for example, a polyvinyl acetate or EVA (ethylene-vinyl acetate) copolymer may be used. The packaging material may comprise, moreover, additional intermediate layers, e.g. of polyvinylidene chloride, nylon, etc.

An example of a multilayer film useful with this invention is an oriented film having layers of irradi ated ethylene-vinyl acetate copolymer/vinylidene chloride copolymer/ethylene-vinyl acetate, or a bia xially oriented film having layers of nylon/nylon/ irradiated polyethylene.

The container used with this invention may be in sheet form, to be folded up in the process, or seamless tubing closed at one end, or a preformed bag.

With reference to Figure 3 of the drawings, an alternative embodiment is shown of an apparatus according to this invention, which allows the inven tive process to be carried out in a semi-continuous or continuous fashion.

The apparatus comprises a plurality of nozzles, e.g. four, which are mounted pivotally about a vertical center axis, each of them being communi cated to a vacuum pump, an insulating gas blowing means, a cut-off valve, and a vent valve, as described hereinabove. Timers control appropriately the open ing and closing sequence of the various control valves to enable each nozzle to complete its proces sing cycle, as described with reference to Figure 2, in an independent and non-synchronous manner with respect to the other nozzles. Each nozzle performs a complete processing cycle during its full revolution about the vertical axis, so that upon returning to its starting point, or station A, a nozzle is ready to receive afresh container with a product to be 100 packaged therein and again complete one revolution to go through all of the processing sequences B-C-D-E, the finished package being discharged at the point illustrated as station E. The heating and heat shrinking step is expediently effected by pas sing the rotating nozzles through a heat tunnel preferably a convective hot airtunnel but radiation may also be employed, as indicated at 13. To ensure a uniform heat application and rapid transfer of heat, for example, electric resistors and blowers may be provided inside the tunnel, which would be arranged evenly across the side and top walls of the tunnel.

As an example, to implement this embodiment of the method and apparatus according to the inven tion, an existing multistation apparatus may be used, such as the "Girovac (Trademark of W. R.

Grace & Co.)" machine from W. R. Grace & Co. or "Roto-Matic" machine from Tipper-Tie Division Divi sion of Rheem Manufacturing Company, equipping it with all the necessary facilities mentioned above, i.e., a hot airtunnel, heat welding bars, and for each nozle, a cut-off valve and vent valve.

The invention will be now illustrated by the following example, given herein byway of illustra tion and not of limitation thereof.

Example 1

For a container, a bag is used of a biaxiaily oriented heat-shrinkable material, of the type avail able commercially under the trademark "Barrier 130 Bag" and being distributed by W. R. Grace & Co. Said material comprises an outer surface layer of irradiated ethylene-vinyl acetate, copolymer, an intermediate, gas impervious layer of plastified vinylidene chloride copolymer, and an inner surface layer of heat sealable ethylene-vinyl acetate copolymer. A product is introduced into the container. In this specific case, a cut of cooked ham is packaged. Next, by means of a sealing clamp, the bag mouth is inserted over a nozzle of a multistation machine, as shown in Figure 3. During the step A, the container with the product therein is secured and sealed to a nozzle. The product being packaged is conveyed over a surface provided with rotating rollers, while through the nozzle, during the step B, air at a pressure of 200 mm H20 is introduced. This pressure can be controlled accurately, for example, with a manostat which automatically closes the gas intake valve upon reaching a preset level. During the step, the cut-off vent valve is closed. The ham cut being packaged is then started along a hot air heating tunnel 13 which has sufficient length to provide perfect heat shrinkage. Heating is accomplished by means of an electric resistance device incorporating a fan, such as "Leister Forte S" unit or similar unit of 10,000 watts. The tunnel interior temperature is about 1700C. A residence time in the tunnel of 4-5 seconds is adequate to provide full heat shrinkage. During this step, the cut-off valve 10 is opened.

The outflow of the gas contained in the container is appropriately controlled by the vent valve 12, which includes a calibration spring arrangement effective to prevent rupture of the container as well as too fast a removal of the air. At the tunnel end, the vent valve opens fully to allow all of the contained air out. For application in many practical cases, and with special reference to delicate materials, the cycle may be terminated at this point by closing the container with a clip or by heat sealing. Where, on the contrary, heat shrinking is less may be provided through the vacuum forced suction system. This additional step is particularly suitable for stronger products where the shrink forces in the wrapping material will not distort the product.

It may be appreciated from the foregoing that the method and apparatus according to the invention achieve their objects. Thus, the method affords the achievement of a quick and effective heat shrinkage owing to the absence of contact during the heating and shrinking step between the container material and the product, and, therefore, the absence of heat dissipation to the product. Further, this method is more promising from the standpoint of preservation of the packaged product, owing to the insulating gas introduction step ensuring complete removal of the air from the container. Moreover, the presence of the insulating gas layer during the first heating step allows just slight heating of the product and contributes, in turn, to an improved preservation of the product. A highly improved heat shrinkage of the bag material is achieved with the method according to the invention, having no wrinkles, and being aesthetically appealing, similar to that obtained by employing a complex vacuum chamber as with conventional methods. The method and apparatus 4 GB 2 145 686 A 4 described hereinabove are susceptible of many modifications and variations, as the skilled person in the art will readily recognize, without departing from the scope of the invention as herein described and 5 claimed.

The '1nsulating gas" used in the method of the present invention is a gas, preferably an inert gas, which thermally insulates by expanding the bag and placing the bag out-of-contact with the product, i.e., the gas separates the bag and product so that the product will not chill the bag and keep it from being heated to its shrinkable temperature.

Claims (29)

1. A method of vacuum packaging in flexible packaging materials wherein a product to be pack aged is inserted in container formed from a heat shrinkable thermoplastic material 1eaving an open ing for communication to the outside characterized by the steps of:

a) injecting an insulating inert gas into the contain er until the latter is caused to bulge out such that the container walls are detached from the contained product; b) heating the container by heat application from an external heat source to induce heat shrinking of the container; and, c) removing said insulating gas from the container while still applying heat; and thereafter sealing the container.

2. A method according to Claim 1, wherein in said step a) the insulating gas is air.

3. A method according to Claim 1, wherein in said step a) the insulating gas is selected from either 100 nitrogen or C02.

4. A method according to Claim 3, characterized by an additional step wherein the air is evacuated from said container prior to said step a) by injecting an insulating gas.

5. A method according to any of the preceding claims, wherein said heating step b) is effected by either convection or radiation.

6. A method according to any of the preceding claims, wherein the gas removal step c) is effected by the heat-shrinking action of said container.

7. A method according to anyof Claims 1 to 5, wherein said gas removal step c) is effected by the heat shrinking of said container and subsequent application of a vacuum suction means.

8. A method according to anyof Claims 1 to 7, wherein sealing during step c) is effected by heat sealing through application of heat and pressure on the walls of said container around said opening.

9. A method according to any of Claims 1 to 7, wherein said sealing during step c) is effected by application of a tight clip.

10. A method according to any of the preceding claims, wherein said container is characterized by a single layer film selected from irradiation cross linked polyethylene and plastified vinylidene chlor ide copolymer said single layerfilm being biaxially oriented.

11. Amethod according to anyof Claims 1 to 9, wherein said container comprises a multilayer 130 laminated film having at least one heat-shrinkable outer surface layer and a heat-sealable inner surface layer.

12. A method according to Claim 11, wherein said multi-layer film includes a layer selected from the group consisting of polyvinylidene chloride and vinylidene chloride copolymer.

13. A method according to Claim 11, wherein said heat-sealable layer is selected from copolymers of ethylene-vinyl acetate.

14. A method according to any of the preceding claims, wherein said container comprises a preformed bag.

15. A method according to any of the preceding claims, wherein the insulating gas admitted during step a) is at a maximum pressure in the 20 to 1,000 mm H20 range.

16. A method according to any of the preceding claims, wherein the heating during said step b) is carried out up to a temperature in the 60'C to 3000C range.

17. A method according to the preceding claims, characterized in that it is carried out as a continuous process.

18. An apparatus for vacuum packaging products in containers formed from flexible, heatshrinkable packaging materials, characterized in that it comprises in combination:

a) nozzle means in communication with vacuum means and gas injection means; b) a means of clamping said filled containerwith an opening in said container in communication with said nozzle means; c) at least one cut-off valve in communication with said nozzle means; d) at least one ventvalve in communication with said cut-off valve; e) a means of dry heating said container; and f) a means of sealing said container tight.

19. An apparatus according to Claim 18, com prising at least one nozzle connected, by means of a three-way connection, respectively to said suction means, said injection means, and said cut-off and ventvalves.

20. An apparatus according to Claim 18, com prising control valves arranged to cut-off the connec tion between said nozzle and said suction and injection means.

21. An apparatus according to any of Claims 18 to 20, wherein said vent valve is caused to open upon reaching a pre-determined pressure threshold inside said container whic, h is adjustable.

22. An apparatus according to Claim 21, wherein adjustment of the opening pressure for the vent valve is performed through either a spring means or pneumatic means.

23. An apparatus according to any of Claims 18 to 22, wherein said means of heating said container comprises electric resistance heaters and blowers operative to directthe heatflow.

24. An apparatus according to any of Claims 18 to 23, wherein said sealing means (f) comprises heat sealing pressure bars.

25. An apparatus according to any of Claims 18 to 24, wherein said sealing means (f) comprises a GB 2 145 686 A 5 clip-applying means.

26. An apparatus according to Claim 18, cornprising a plurality of said nozzles adapted for rotation about a vertical center axis, each said nozzle being arranged to perform said vacuum packaging in accordance with independent and nonsynchronous cycles with respect to the other of said nozzles, each cycle being performed during a complete revolution of each said nozzle.

27. An apparatus according to Claim 26, wherein said means of heating said container comprises a heating tunnel.

28. A method of vacuum packaging in flexible packaging materials, such method being substantial- ly as hereinbefore described with reference to the accompanying drawings.

29. Apparatus for vacuum packaging in containers formed from flexible packaging materials, such apparatus being constructed and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Printed in the UK for HMSO, D8818935, 2185,7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.