GB1564399A - Methods of forming evacuated sealed packs particularly of foods - Google Patents

Description

(54) METHODS OF FORMING EVACUATED SEALED PACKS, PARTICULARLY OF FOODS.

(71) We, UNILEVER LIMITED, a company organised under the laws of Great Britain, of Unilever House, Blackfriars, London, E.C.4, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a method of forming evacuated sealed packs, particularly packs containing preserved foodstuffs.

Many vacuum packing methods are known, and in general these require relatively expensive equipment. The present invention is concerned with providing a method which can be used in conjunction with existing formfill seal or other bag filling machinery, without extensive modification. Thus, the present invention aims to be able to convert for example a normal, existing fill seal machine into a vacuum packing machine at low cost.

Accordingly the invention provides a method of forming an evacuated sealed pack comprising the steps of providing an open mouth bag containing the product to be packed, inserting a steam injection nozzle into the mouth zone of said bag, injecting steam via said nozzle into the bag so as to purge air from the interior of said bag, applying tensile forces across a lateral zone of the bag mouth so as to laterally stretch the bag and flatten said bag mouth onto the nozzle, withdrawing the nozzle from the bag while retaining lateral tensile forces in said lateral zone and thereby allowing the flattened bag to progressively close behind the nozzle, and sealing the closed evacuated bag.

The steam nozzle should preferably have a flattened shape so that the bag mouth can adequately flatten on to it and minimise gas leakage.

It will be recognised that the steam both purges the bag of air and by virtue of condensation causes a vacuum to be produced in the bag. Also, the method involving stretching in conjunction with use of a flattened nozzle enables the nozzle to be removed from the bag without breaking the vacuum. Use of steam is known for vacuum packing, but hitherto a satisfactory economical method of retaining the vacuum and sealing has not been achieved.

Use of steam implies the introduction of a degree of moisture, and therefore it will be understood that the invention is not applicable to the packing of products which would be affected by moisture, for example dried powdered materials. Also, the use of steam to flush and purge out air from the bag can only be used where the product to be packed is suitable for such air purging. Thus, where the product includes small air pockets which would resist the steam flushing the invention would not be suitable, for example particulate materials like peas. On the other hand, the invention is particularly applicable for packing pieces of meat, or of other integral products which form a composite whole for example by the presence of a sauce or gravy.

The nozzle should be sufficiently flattened in shape so that when the bag mouth is flattened on to the nozzle the bag mouth is virtually closed by this operation. In practice while steam is being injected into the bag it isnotnecessary that tensile forces be applied to give full closing of the bag at this stage, since the steam and purged air will be escaping under slight over pressure and an effective one way valve is achieved. However at the next stage in the process as the nozzle is taken out of the bag, a perfect closing is achieved by the lateral stretching, and the vacuum is retained.

Following formation of the vacuum it is preferable to retain the lateral stetching until a permanent seal has been made on to the bag. This seal, usually a heat seal, is preferably effected over a fairly wide band (e.g.

about 12 mm) in the mouth zone of the bag so as to ensure that any steam bubbles or product particles in the region of the seal zone are trapped.

An embodiment of the invention will now be described by way of example with reference to the diagrammatic drawings.

Figure 1 is a side elevation of a bag with an injection nozzle located above it prior to commencement of the process; Figure 2 is a plan view of the bag and nozzle in the Figure 1 position; Figure 3 is a side elevation of the bag after an injection nozzle has been inserted therein; Figure 4 is a plan view of the Figure 3 arrangement; and Figure 5 is a graphical representation of the timing sequence.

Referring to Figure 1 a bag 1, filled with a product to be packed for example two pieces of preserved meat, is held between side grippers 2. Referring to Figure 2 it can be seen that in this condition the bag mouth is open.

Located above the open mouth of the bag is a flattened steam injection nozzle 3 divergent in the direction of flow of steam from the nonle. This nozzle has a flattened depth which is less than the width of the open mouth bag and its width is about a third the length of the bag mouth opening, so that it can readily enter into said bag.

The next stage of the process is that the nozzle is inserted into the bag and steam is injected into the bag. Due to the divergent shape of the injection nozzle, the steam, injected at a pressure of between 0.5 and 0 9 atm above atmospheric, is able to be forced into the lower corners of the bag and is thereby able to purge air out of the bag.

Referring to Figure 3, the grippers 2, spring loaded, are then moved apart so as to provide tensile forces across a lateral zone 4 of the bag mouth, through which zone of the bag mouth the nozzle passes, so as to flatten the bag onto the nozzle and almost close the bag (see Figure 4).

The spring loaded stretching across the zone 4 causes the bag to form a one way valve which enables the purged air and steam to continue to pass out of the bag without further air being able to enter the bag. There are, in practice, slight gaps 5 at the corners of the nozzle as can be seen from Figure 4 but the over pressure from the steam ensures that air and steam can only flow outwards so that air cannot enter the bag.

The next stage in the process is that steam pressure is shut off and the steam injection nozzle is drawn out of the bag while retaining the lateral stretching across the zone 4. As the nozzle moves out of the bag the bag walls in the laterally stretched zone 4 come together and completely close the bag without loss of vacuum.

Thereafter while retaining the lateral tension in the zone 4, the bag is moved to a heat sealing station and there a heat seal is placed just above the zone 4 so as to provide an evacuated sealed pack.

practice bags were used, measuring 170 mm x 200 mm, made of a heat sealable foil laminate (12 micron polyester laiminated with 9 micron aluminium and 70 micron modified high density polyethylene). Tension of 3 to 4 kg laterally across the bag served to adequately seal the bag, and the nozzle of divergent shape had a wdith which was about a third that of the open mouth of the bag i.e.

60 mm. Its depth externally was 3 to 3.5 mm giving an internal depth of 1 to 1-5 mm.

Figure 5 shows the time sequence of the various operations schematically. In this Figure, on a linear time scale, the function A represents the time of the nozzle within the bag (the sloping parts at each end being representative of entry and withdrawal); the function B represents thetime of steam flushing (about 1 to 15 seconds in practice); and the function C represents the timing of the stretching of the bag mouth, this commencing about 0 3 seconds after the commencement of steam flushing.

WHAT WE CLAIM IS: 1. A method of forming an evacuated sealed pack comprising the steps of (a) providing an open mouth bag containing a product to be packed; (b) inserting a steam injection nozzle into the mouth zone of said bag; (c) injecting steam via said nozzle into the bag so as to purge air from the interior of said bag; (d) applying tensile forces across a lateral zone of the bag mouth so as to laterally stretch the bag and flatten the bag mouth onto the nozzle; (e) withdrawing the nozzle from the bag while retaining lateral tensile forces in said lateral zone so that the bag progressively closes behind the nozzle; and (f) sealing the closed evacuated bag.

2. A method according to Claim 1 in which the sealing of the closed evaucated bag is by heat sealing.

3. A method according to any one of the preceding claims in which the nozzle is of flattened shape and is divergent in the direction of flow of the steam from the nozzle.

4. A method according to any one of the preceding claims in which the nozzle points downwards.

5. A method according to any one of the preceding claims in which the product comprises pieces of meat.

6. A method of forming an evacuated sealed pack substantially as herein described.

7. An evacuated sealed pack formed by a method according to any one of the preceding

Claims (1)

1. claims.