GB2084467A

GB2084467A - Method for sterilizing packaging material

Info

Publication number: GB2084467A
Application number: GB8129559A
Authority: GB
Original assignee: Linnich Papier & Kunststoff
Current assignee: Linnich Papier & Kunststoff
Priority date: 1980-10-01
Filing date: 1981-09-30
Publication date: 1982-04-15
Also published as: ES8302580A1; SE8105366L; ATA417081A; DK389281A; DE3036972A1; DE3036972C2; AT376127B; FR2491032B1; NL8104398A; FI71909B; CH655071A5; DK152348C; FI71909C; ZA816813B; FR2491032A1; AU7560681A; CA1180872A; IT1138674B; GB2084467B; ES505948A0

Abstract

A method of sterilizing packaging material, for example containers for liquid material e.g. milk preformed from blanks, in which the surface of the packaging material to be sterilized is treated with superheated steam and acid. Acid is first applied to the surface of the packaging material to be sterilized and then the surface moistened with acid is treated with flowing steam at atmospheric pressure. The acid may be formic, acetic, malic, citric, lactic or ascorbic acid.

Description

Method for sterilizing packaging material The invention relates to a method for sterilizing packaging material, in particular containers for liquid material pre-formed from blanks, in which the surface of the packaging material to be sterilized is treated with super-heated steam and acid.

The sterilization of material of the most varied kinds by means of superheated steam has been known for a long time. However, an effective killing of germs by means of superheated steam sterilization can only be achieved within the short sterilizing times of the order of several seconds necessary for automatic filling methods, when using temperatures in the range of approximately 125 to 1 50 C in the case of packaging material, either in the form of webs, for example plastics film or cardboard coated with plastic material, or in the form of finished containers, for example manufactured from cardboard blanks. This means that sterilization must be carried out at high pressure in the order of magnitude of 2.4 to 5 Bars.However, this considerably increases the expenditure necessary for sterilization, since the sterilizing device, through which the packaging material must be guided, must be sealed with respect to the atmosphere and must be designed for the increased pressure. Furthermore, the material is stressed excessively by the high temperatures.

Therefore, in order to lower the temperatures necessary for destroying bacteria, during sterilization by means of water vapour, an apparatus of the aforementioned type has already been proposed, in which the water vapour is acidified (cf GB PS 10 83 700). However, even with this known method, with an action time of approximately 6 seconds, the temperature of the steam necessary for destroying bacteria cannot be brought below 11 80C when using saturated steam, so that in this case also one must work with a water vapour excess pressure of approximately 2 Bars.

It is therefore the object of the invention to provide a method of the aforementioned type, which allows trouble-free sterilization of the packaging material by means of saturated steam without using a high pressure.

This is achieved according to the invention due to the fact that first of all acid is applied to the surface of the packaging material to be sterilized and then the surface moistened with acid is treated with flowing steam at atmospheric pressure.

Thus, in the method according to the invention, the sterilizing effect is achieved both by the acid as well as by heating by means of steam. In this case it has been found surprisingly that due to the previous application of acid, the bacteria are weakened as regard their resistance to the subsequent heat treatment, in steam and acid, acting partly simultaneously, partly one after the other, to such an extent that it is possible to work with saturated steam at normal pressure.

The acid is either sprayed or atomized in a finely divided form onto the surface of the packaging material to be treated, for example onto the inner walls of a container, so that it forms a thin liquid film on this surface. However, it is also possible to trickle or pour the acid onto the surface, so that an acid layer is formed. The joint use of both measures is likewise conceivable, for example in a case where in an upright container, the acid is atomized at the same time, so that the side walls are moistened by this, but also acid is trickled in, so that an acid layer forms on the base with its corners and angles, which is particularly problematic as regards sterilization.

In order that the subsequent superheated steam treatment serves simultaneously for destroying bacteria and removing acid, it is appropriate to use steam volatile acids, which are easily dispersed by the water vapour. It is particularly advantageous to work with acids which are either contained in the substance with which the packaging material is subsequently filled or are akin to such acids. This is true for example for lactic acid and similar foodstuff acids if the substance is milk or fruit juices. Traces of the acid used for destroying bacteria, which under certain circumstances remain on the packaging material, are consequently prevented from impairing the substance to be packed, as a foreign substance.

The effectiveness of the method can be increased further due to the fact that either the acid is heated before being applied to the surface to be sterilized, so that the heat inherent in the steam leads to a very rapid temperature increase both of the acid as well as of the surface to be treated, or the surface itself, is heated, for example by means of hot air, before the acid is applied.

According to a further embodiment of the method according to the invention, heating of the surface with flowing steam may be followed by a treatment with flowing hot air.

The method according to the invention can be used freely both on continuously moving web-like packaging material as well as on finished containers, for example folded containers made from cardboard blanks. In the case of the latter, the afore-described combined treatment is appropriate, in which acid is applied by spraying or atomization by means of jets as a thin film to the walls, but at the same time a thin acid layer is formed by trickling on the bottom of the container, due to which any corners and cut edges located in the inside of the container are treated. Then the superheated steam is blown in, which causes both the acid film on the side walls as well as the acid layer on the bottom of the container to vaporize and as a result of the heat transfer brings about a heat treatment of the walls and of the base.

However, the method can also be carried out in a manner such that the aforementioned acid layer is formed solely by trickling onto the base of the container, whereupon the superheated steam flowing in is enriched by the vaporized acid and brings about adequate sterilization as it sweeps across the side walls. With this method it is appropriate to ensure by means of a suitable device, for example by an immersion tube that the superheated steam is blown directly onto the acid layer located on the bottom of the container, so that it is enriched with acid and as it flows out of the container sweeps in an enforced manner over the side walls.

The acid can be sprayed by means of conventional atomizer nozzles, which operate with compressed air or with superheated steam under pressure and due to which a fine mist and as a result thereof the aforementioned uniform moistening film is produced on the surfaces to be sterilized. When atomizing with steam, the atomizing medium simultaneously takes over part of the function of the sterilizing method. The acid is thus partly vaporized. Included amongst the acids are in particular organic acids from the group formic acid, acetic acid, malic acid, citric acid, lactic acid and ascorbic acid. However, inorganic acids, for example hydrochloric acid are not excluded.

The invention will be described in detail hereafter with reference to one embodiment illustrated purely diagrammatically in the accompanying drawing.

The drawing shows diagrammatically a conveying section for packaging containers within a filling device, for example for milk. The filling device is not shown in detail, since it can be of known type apart from the series of supply devices for acid, superheated steam and hot air described hereafter. This is true also of the conveying device for moving the containers, which is a bucket chain for example and for the arrangement of this conveying section within a sterile air region, as is normal for aseptic filling.

The containers 1, which are for example folded containers consisting of plastic-coated cardboard, are moved by the conveying device 2, for example a bucket chain, according to a cycle from left to right, so that they assume the positions illustrated in the drawing one after the other. The cycle time amounts for example to 1 to 2 seconds. The capacity of the container 1 is 1 litre.

In a pre-heating station I, hot air at a temperature of approximately 2000C is blown into the inside of the container 1 located therein. Due to this, the inner surfaces of the container are pre-heated to a temperature of approximately 50 to 700C. In the following acid-spraying station II, by means of an atomization nozzle 3 operating with compressed air, an acid mist is produced inside the container, which produces a fine and extensively continuous condensate on the inner walls including the bottom of the container, so that the walls and base support an acid film. 90% lactic acid is used as the acid. For the given capacity of the container 1, the quantity sprayed in amounts to 0.5 ml.The subsequent sterilizing station III comprises three fixed-cycle positions, at which saturated steam at atmospheric pressure, ie.e. at a temperature of 1 000C maximum is blown in through corresponding steam pipes 4.

Consequently, the acid film located on the walls of the container and the container surfaces themselves are heated to the corresponding temperature. Any bacteria present are destroyed, partly by the action of the hot acid and partly by the subsequent steam treatment. The action time of the acid and steam can be varied by selecting any number, possibly a variable number of stations II and Ill along the conveying chain.

The sterilizing station Ill is followed by a subsequent treatment station IV, in which hot air at a temperature of 2000C is once more blown in through suitable nozzles 5. The subsequent treatment station IV comprises by way of example two fixed cycle positions, so that the residues of acid and steam are removed from the inside of the container.

The container 1 is filled with the material to be packed, for example milk, in the filling station V.

The upper end of the container is sealed hermetically in the sealing statio VI.

The quantity of steam which is supplied to the sterilizing station lil is measured so that air present in the container is displaced completely. As a result of the residence time of the container 1 in the sterilizing station Ill, the action time of the steam amounts to approximately 6 seconds. Generally, an action time of 3 to 10 seconds is advisable.

In the subsequent treatment station IV, in which hot air is blown into the inside of the container, it is intended to remove any traces of acid and condensed steam from the walls of the container. However, since lactic acid is used when the material to be packed is milk, i.e. an acid akin to part of the material to be packed, it is not harmful if slight traces of lactic acid remain on the inside of the container, after sterilization in station III. These traces are too slight to be able to cause coagulation or a change in the pH of the milk.

As mentioned, the lactic acid is added at a concentration of 90%. It is generally true that an acid having the highest possible percentage is used, in order to make the pre-treatment step in station II effective.

Although this has not been shown in the embodiment, it is conceivable, due to an appropriate construction of the conveying device 2 in stations II, Ill and VI, to guide the containers so that their open side is directed downwards. Due to this, any possible drop-like accumulations of acid and condensate would run downwards under the effect of gravity and drip off the container. In this way, even acids which are not steam volatile can be removed after the treatment, since they are washed away in a downwards direction by the condensed steam.

In order to demonstate the effectiveness of the method according to the invention, the attached table illustrates the results of a series of experiments, in which in an arrangement similar to that of the afore-described example, milk was packed aseptically under various conditions. Each individual run was carried out with approximately 500 packs having a capacity of 1 litre. The sterility was checked by means of the pH value after a storage time of 11 days at room temperature.

In run A, which serves as an untreated sample, the milk was poured into untreated packs with the result that 25% of the packs were non-sterile. If the packs were treated solely with hot air (3000C for 8 seconds) as in run B or only with steam (for 8 seconds) as in run C, then the non-sterility rate was 14% respectively 7%.

In run D, the packs were treated with 0.3 ml acid and with hot air (at a temperature of 3000C for 8 seconds). In this case, a slight effect was observed in the case of formic acid, but not in the case of acetic and lactic acid.

In run E, which corresponds to the method according to the invention, the packs were treated with acid and steam (0.3 respectively 1 ml acid and the steam effect lasted for 8 seconds), in which case 0.3 ml acid was sprayed in (E1, E3, E5) or 1 ml acid was trickled in (E2, E4, E6). Clear sterilizing effects were obtained in this case. In four out of six cases a very good sterilizing rate was obtained. The advantage of the method according to the invention is obvious.

Table of Experiments Action of Sterile Condition Acid Steam Hot Air Run Treatment % non-sterile - - - A Untreated test 25 - - + B Solely with hot air 14 - + - C Solely with steam 7 + - + D With acid + hot air (no steam) Dl 80% formic acid 0.3ml 2 D, 100% acetic acid 0.3 ml 10 D, 90% lactic acid 0.3ml 7 + + E With acid + steam (no hot air) E1 80% formic acid 0.3 ml 0 E2 80% formic acid 1.0my 0 E3 100% acetic acid 0.3ml 2 E4 100% acetic acid 1.0 ml 0 E5 90% lactic acid 0.3 ml 0.2 E6 90% lactic acid 1.0 ml 0

Claims

1. A method of sterilizing packaging material, for example containers for liquid material pre-formed from blanks, in which the surface of the packaging material to be sterilized is treated with superheated steam and acid, wherein acid is first applied to the surface of the packaging material to be sterilized and then the surface moistened with acid is treated with flowing steam at atmospheric pressure.

2. A method as claimed in claim 1 , wherein the acid is sprayed or atomized onto the surface so as to form a thin film thereon.

3. A method as claimed in claim 1 or 2, wherein the acid is trickled or poured onto the surface so as to form a layer thereon.

4. A method as claimed in any one of claims 1 to 3, wherein the acid is steam volatile.

5. A method as claimed in any one of claims 1 to 4, wherein an acid contained in the material to be packed or an acid akin to this is used as the acid.

6. A method as claimed in any one of claims 1 to 5, wherein an acid from the group consisting of formic acid, acetic acid, malic acid, citric acid, lactic acid, and ascorbic acid is used.

7. A method as claimed in any one of claims 1 to 6, wherein the surface is heated before the acid is applied.

8. A method as claimed in any one of claims 1 to 7, wherein the acid is heated before being applied to the surface.

9. A method as claimed in any one of claims 1 to 8, wherein after heating the surface with flowing steam, the surface is treated with flowing hot air.

10. A method as claimed in any one of claims 1 to 9, wherein the acid is sprayed or atomised onto the surface by means of compressed air or by means of superheated steam which is under pressure.

11. A method of sterilizing packaging material, substantially as herein described with reference to and as illustrated in the accompanying drawing.