Method of sterilizing a packaging material by means of a sterilizing agent in liquid form

Abstract: Method of sterilising a packaging material by means of a sterilising agent in liquid form. The packaging material is discharged in order to eliminate electrostatic surface charges on the packaging material, after which the packaging material is wetted with the sterilising agent which is applied in a finely distributed, electrostatically charged form to those areas of the packaging material which are to be sterilised. The packaging material with the sterilising agent, which has coalesced to a thin, homogeneous film, is finally heated to drive away the sterilising agent from the ready sterilised packaging material.

Description: The present invention concerns a method of sterilising a packaging material by means of a sterilising agent in liquid form, according to the preamble of claim 1. Such a method is known from US-A-4 680 163. Aseptic packaging technology has for a long time been used for packaging foodstuffs and the like, especially products sensitive to bacteria and storage, in order to give the product an extended life so that it can be kept with retained fresh qualities for longer periods of time from the day of packaging without risk of it being spoiled or deteriorating. The technology which is well known to the specialist in the area can for example start out from the fact that the product and the packaging material are each subjected to a sterilising treatment for the purpose of neutralising harmful micro-organisms occurring in the product or the packaging material, in particular pathogenic bacteria, and that the treated product is thereafter enclosed in the sterilised packaging material under sterile conditions in order to avoid a bacterial reinfection of the sterilised product. Aseptic packagings for milk, juice and similar liquid foods are now most frequently produced with the aid of modern, rational packaging machines of the type which, from a strip or sheet of plastic coated paper or cardboard material, forms, fills and closes packagings under aseptic conditions. From, for example, a strip a known packaging machine produces aseptic packagings for milk through the strip being taken for the purpose of sterilisation through a bath containing 10-35% by weight of hydrogen peroxide within a chamber essentially completely screened from the environment (what is known as an aseptic house). After the passage through the bath the strip is taken through the pinching between press rollers in order to remove the surplus sterilising agent from the strip and take it back to the bath, after which the strip, without coming into contact with the machine environment is taken into the forming and filling chamber of the machine which is likewise essentially completely screened from the environment. The strip is shaped into a tube through the two longitudinal edges of the strip being joined to each other in a longitudinal overlap joint at the same time as the packaging material in the tube formed is heated by means of sterile hot air in order to vapourise and drive away the residue of accompanying sterilising agent from the packaging material. The tube is filled with the appropriate previously sterilised contents, heat treated milk, which is fed to the tube through a filler pipe opening into the tube, and separated into closed, filled packagings through repeated transverse sealings of the tube across the longitudinal axis of the tube. The packagings are separated from each other through cuts in the transverse seals and are subsequently given the desired geometric final shape, usually of parallelipiped type, before outfeed of the finished aseptic packagings from the machine. During the whole process an overpressure of sterile hot air is maintained in the shaping and filling chamber in order to prevent unsterile environmental air penetrating and reinfecting the sterilised contents and the packaging material. A precondition for achieving good sterilisation of the packaging material in the above described known method is that the whole strip, after passing through the sterilising bath, is covered by a coherent film of sterilising agent in order to ensure thaet all parts of the packaging material are effectively sterilised. The film should in addition preferably be thin and of even thickness in order to facilitate and make more effective the subsequent driving away of the stabilising agent in the shaping and filling chamber. These two conditions have been shown to be difficult to fulfil in practice and it not infrequently happens that the sterilising agent exhibits an irregular film distribution over the strip surface with alternating thicker and thinner film zones, which not only leads to an uneven, unpredictable sterilisation effect but also makes the drying process more difficult during heating. It sometimes also happens that the sterilising agent is completely missing along certain areas, while other areas of the strip show island-like concentrations of the sterilising agent, which thus further worsens the possibility of achieving the intended evenly good sterilisation effect over the whole strip. Another disadvantage with the above described and other known methods which employ a bath of sterilising agent through which the strip is taken is what is called the edge suction phenomenon which entails that the exposed fibrous material in the longitudinal cut edges easily absorb the sterilising agent in liquid form which is sucked into and retained in the fibrous layer of the strip and finally accompanies the packaging material into the finished packaging. Since the inward facing cut edges in the finished packaging are always well protected no risk occurs that the accompanying sterilising agent should come in contact with and affect the contents of the packaging, but on the contrary the risk is great that the liquid absorbed will at least locally cause deterioration in the rigidity and stability of form of the packaging at the same time as it of course entails an unnecessary loss of sterilising agent. The aim of the present invention is therefore to give indications about a new way of sterilising a packaging material by means of a sterilising agent in liquid form without subsequent problems of the type described above. This aim is achieved through the fact that a method of the type known from US-A-4 680 163 is adapted according to the characterizing part of claim 1. Through first eliminating the surface charges on the packaging material and thereafter applying the sterilising agent form in a finely distributed, electrostatically charged form it has been shown that the finely distributed sterilising agent is not only easily received on the packaging material but in addition it easily coalesces without hindrance from inhibiting electrostatic repulsion forces and forms a homogeneous film completely covering the packaging material with the same good predictable sterilising effect. A further advantage which is gained through the process according to the invention is that the film applied can be made very thin, but of even thickness, which considerably facilitates the subsequent heating of the strip to drive away the sterilising agent. Furthermore the problem with edge suction is completely avoided since the cut edges of the strip do not need to come in contact with the sterilising agent. Further advantageous and practical embodiments of the method according to the invention have further been given the characteristics mentioned in the sub-claims. The invention will be described in greater detail below with reference to the enclosed drawing which explains schematically the process in the carrying out of the method according to a preferred form of the invention. In the drawing what is called an aseptic house with the general reference designation 1 is shown, situated before the forming and filling chamber (not shown) in a packaging machine of the type described previously. The aseptic house 1 comprises a discharging station 2, a sterilising chamber 3 and a drying chamber 4 through which a strip 5 of plastic coated paper or cardboard material is intended to be taken for sterilisation of the packaging material before forming into finished aseptic packagings in the subsequent forming and filling chamber. The discharging station 2 contains two or more ioniser electrodes 5 located in pairs on both sides of the strip 5 and centrally placed in an area 8 delimited by a semicircular, earthed screen 7. Screens 7 facing each other in each such pair of screens have their open sides turned towards each other to form a narrow gap or passage through which the strip 5 is intended to be taken in order to eliminate electrostatic surface charges occurring on both sides of the strip. The sterilising chamber 3 is delimited by a casing 9 with inlet 10 and outlet 11 for the strip 5. On opposite sides in the direction of travel of the strip through the chamber 3 there are squirting or spraying devices 12 placed in the middle facing each other, e.g. spray guns, which are arranged to spray a jet of finely distributed sterilising agent towards the two sides of the strip as it passes by, in such a way that the strip is hit over its whole width and wetted by the jets. Between the respective devices 12 there is a high-tension electrode 13 which is arranged to charge the finely distributed sterilising agent electrostatically before contact with the strip. Even though the high-tension electrode 13 is shown as a separate unit in front of the device 12, it is obvious to the specialist that the electrode 13 can be fitted inside or form part of the device 12. The drying chamber 4 is delimited by a casing 14 with inlet and outlet 15 and 16 respectively for the strip 5 and also inlets 17a and 17b for sterile hot air which, after passing through the drying chamber 4, accompanies the strip out of the chamber through the outlet 16. The drying chamber 4 is divided into two part-chambers, a lower one 4a and an upper one 4b, with the aid of two obliquely placed screens or plates 18 placed at the same level opposite each other. The screens or plates 18 form between them a narrow passage 19 for the strip 5 and sterile air, fed through the lower inlet 17a into the part-chamber 4a, which is directed through it and forced to a high speed of flow in effective contact with the strip 5. In sterilisation with the aid of the device 1 shown one proceeds in the following manner according to the invention. The strip 5 is unrolled from a feed roller which is not shown and is taken through the gap between the semicircular screens 7 situated on each side of the strip at the same time as the electrodes 6 are activated for ionisation of the air in the delimited spaces 8 open towards the strip. The thus ionised, electrically conducting air thereby comes to neutralise or discharge electrostatic surface charges occurring on both sides of the strip, whereby the strip, after passing between the ioniser electrodes 6, is practically entirely electrically discharged and exhibits an electric potential corresponding to earth potential (0 potential). The discharged strip is taken into the sterilising chamber 3 through the inlet 10 and passes between the two opposite facing spraying or squirting devices 12 which spray finely distributed sterilising agent electrostatically charged with the aid of the high-tension electrodes 13 against both sides of the strip as it passes by. The charged, finely distributed sterilising agent is absorbed on the discharged strip and coalesces without hindrance from electrostatic repulsion forces to form a homogeneous film, completely covering both sides of the strip. The strip is taken via outlet 11 into the drying chamber 4 through the inlet 15 at the same time as hot air is fed to the lower part-chamber 4a through the inlet 17a in order to drive away the sterilising agent from the strip. Through the gap 19 the strip is taken further into the upper part-chamber 4b at the same time as further sterile hot air is brought in through the inlet 17b for final drying of the strip. After passing through the chamber 4 the sterilised, dried strip 5 is taken together with the air out through the outlet 16 at the upper end of the chamber and further via a break roller 20 into the machine's forming and filling station for forming into finished aseptic packagings. By the method according to the invention it is thus possible to achieve a good, even sterilising effect with the use of a sterilising agent in liquid form, without subsequent problems of the type connected with the previously described known technology. A considerable advantage is that with the method according to the invention it is possible accurately to regulate the amount or thickness of the film of liquid applied to the strip and in particular it has been shown to be possible to apply the sterilising agent in liquid form as a very thin but coherent film of even thickness which considerably improves and makes more effective the subsequent heating which can thereby be regulated and optimised. Even though the invention has been described with special reference to the embodiment shown it should be observed that for the specialist close modifications are of course possible without going away from the concept of the invention as this is defined by the sub-claims below. For example the heating for driving away the film of sterilising agent from the strip can be carried out in a different way from the one which is particularly described, e.g. with the aid of IR, microwaves, HF (high frequency) etc if this for one reason or another should prove to be more advantageous than using hot sterile air. The driving away of the sterilising agent is optimised by regulating the heating, whether it is done with hot air or in another manner, depending on temperature or moisture content found near the packaging material, which further contributes to improving the economy in carrying out the method, without the good sterilising effect being lost or deteriorating.

Claims: Method of sterilizing a packaging material by applying sterilizing agent in a finelly distributed form onto the surface of said packaging material within a sterilizing chamber (3) using electrical charges for charging said sterilizing agent and drying the sterilized packaging material in a drying station (1) in order to volatize said sterilizing agent from the surface of said packaging material by heating the packaging material, characterized in that a web or strip (5) of said packaging material is first neutralized or discharged from any electrostatic surface charges in a discharging station (2) before said strip (5) is entering said sterilizing chamber (3), that said discharging and sterilizing is carried out simultaneously at both sides of said strip (5) forming a homogeneous thin film of said sterilizing agent on both sides thereof, and that said heating in said drying station is regulated depending on the temperature or the moisture content found near said web or strip (5). Method according to claim 1, characterised by the fact that the strip is discharged with the aid of one or more ioniser electrodes (6), past or between which the packaging material is taken. Method according to claim 1 or 2, characterised by the fact that the strip is discharged to an electric potential corresponding to earth potential (0 potential). Method according to any of the foregoing claims, characterised by the fact that the sterilising agent in liquid form is squirted or sprayed on the packaging material with the aid of one or more squirting or spraying devices (12) placed on both sides of the packaging material, e.g. spray guns, which direct a jet of the finely distributed sterilising agent past a high-tension electrode (13) placed between the device (13) and the strip (5) respectively, with the aid of which the sterilising agent is electrically charged. Method according to any of the foregoing claims, characterised by the fact that the strip is heated by means of IR, microwaves, HF or with the aid of hot air which is brought into contact with the strip. Method according to any of the foregoing claims, characterised by the fact that the sterilising agent in liquid form is constituted by a 10-35% solution of hydrogen peroxide.

Inventors: BALLA GYULA, BERLIN BO, BALLA, GYULA, BERLIN, BO
Applicants: TETRA LAVAL HOLDINGS & FINANCE, TETRA LAVAL HOLDINGS & FINANCE S.A.
Application year: 1991
Main classification: B65B55
IPC codes: B65B55