A METHOD AND AN ARRANGEMENT FOR THE PRETREATMENT OF A MOVING MATERIAL WEB

Abstract: A method and an arrangement for the pretreatment of a moving material web (2) which for the purpose of sterilization is passed through a heated bath containing a sterilizing agent arranged in a container (4). Before the container (4) a heating arrangement is provided having an inlet (9) and an outlet facing towards the container (4) through which the web is conducted for heating of the web so that its temperature corresponds to, or preferably slightly exceeds, the actual bath temperature when the web enters into the bath. The heating is done advantageously with the help of a stream of hot air which is directed with the help of nozzles (10) towards both sides of the web. The inlet (9) is designed appropriately as a narrow gap opening which is in communication with a source of vacuum with the help of which the hot air is brought into intensive countercurrent contact with the web within the region of the said gap opening.

Description: The present invention relates to a method for the pretreatment of a material web, especially a weblike packing laminate comprising layers of paper and plastics and possibly also a metal foil, this web for the purpose of sterilization being brought into contact with a sterilizing agent by passing the web through a heated bath containing the said agent. The invention also relates to an arrangement for the realization of the method. A method and an apparatus according to the preambles of claims 1 and 6 respectively are described in, e.g. DE-A-1 492 482. It is known that so-called aseptic packages can be produced by packing sterilized contents into sterilized packing containers under controlled aseptic conditions. A known aseptic package of non-returnable character is manufactured with the help of a packing machine which from a web of a laminated packing material produces packages in that the longitudinal edges of the web are combined with one another so as to form a tube which is filled with the intended, sterilized contents and is divided into sealed container units through repeated flattening and sealing of the tube along narrow zones located transversely to the tube. After separation by means of cuts in the sealing zones and possible fold-forming and sealing, the container units leave the machine in the form of finished packages of usually parallelepipedic shape. To ensure that the sterilized contents introduced preserve their sterility in the package, the web, or at least the side of the web which is intended to be facing towards the inside of the tube, has to be sterilized before it comes into contact with the contents. The sterilization of the web usually is done in that the web first is brought into contact with a chemical sterilizing agent by passing the web through a heated bath containing the sterilizing agent, whereafter accompanying excess of sterilizing liquid is squeezed out of the web with the help of co-operating pressure rollers between which the web is conducted. Remaining residual amounts of sterilizing liquid are driven off the web with the help of hot air which is blown towards one or both sides of the web, whereafter the web is converted to a tube with the sterilized inside ready to receive the particular sterilized contents. With, for example, hydrogen peroxide, which is an example of a frequently used sterilizing agent on an aseptic packing machine of the type described, it has been found that bacteriological killing effects, which fully comply with prescribed health conditions, are achieved if the sterilizing agent is used in the form of a solution containg approx. 35% hydrogen peroxide (H₂O₂) at a temperature of approx. 65-75°C, preferably approx. 70°C, if it is ensured at the same time that the contact between the material web and the sterilizing solution lasts at least for a certain specified time. For the moving material web, at normal production rhythm of a conventional packing machine, this contact time corresponds to a certain contact distance, which implies that the bath containing the sterilizing solution has to possess a correspondingly long, accessible pass-through distance for the moving material web. For practical reasons, not least for reasons of space, the bath frequently is arranged in the form of a so-called deep bath, that is to say, it is accomodated in a vertical container arranged before the forming and filling zone of the tube, whose height appreciably exceeds its width. The material web which is to be sterilized is then conducted in a vertical loop through the bath around a roller arranged in the lower part of the container with the help of which the moving material web is controlled so that at any time each part of the web is below the liquid level in contact with the sterilizing solution during a period, reckoned from the entry into the bath of the web to its exit from it, corresponding at least to the required contact time. A further advantage gained by using this deep bath is that good contact between the material passing through and the sterilizing solution is ensured at least in the lower part of the container where the contact is intensified owing to the prevailing higher hydrostatic pressure which presses the sterilizing solution towards the passing web. The intensified contact between the hydrogen peroxide solution and the material web is, of course, an advantage from a point of view of bacteriological killing but at the same time entails an increased risk of the hydrogen peroxide solution penetrating into, and degrading, the liquid-absorbent fibrous layer of the material web through cut edges of the web. This risk, which is thus connected with the hydrostatic pressure in the bath and consequently increases at the rate as the hydrostatic pressure increases, is aggravated somewhat also by the fact that the material web in the known sterilization system before it enters into the bath has a temperature corresponding to ambient temperature or in any case being appreciably lower than the temperature of the heated sterilization bath (approx. 65-75°C), which means that the relatively colder material web after entry into the bath is liable to pass through a certain stretch during which the web absorbs heat from the surrounding hydrogen peroxide solution which as a result is cooled down before a condition of equilibrium of temperature between the hydrogen peroxide solution and the web has been reached. As mentioned previously, the bacteriological killing effect is dependent, among other things, on the temperature of the hydrogen peroxide solution, and in order to compensate for the said shorter distance of active bacteria-killing contact, through which the material web is liable to pass before the required equilibrium of temperature between the hydrogen peroxide solution and the material web has been able to establish itself, it has been necessary therefore to "overdimension" the bath somewhat, that is to say design the bath to a corresponding extent deeper than would be the case if this temperature equilibrium had established itself instantaneously already at the entry of the web into the bath. The overdimensioning of the bath means in practice a further increase in hydrostatic pressure and a risk connected therewith of a penetration of liquid into the web in the deeper parts of the bath, or else that the bath is made wider whilst maintaining its depth and thus requires more space. The method described above of sterilizing a packing material web by using a heated bath containing a chemical sterilizing agent, in particular hydrogen peroxide, can be improved, however, if the web prior to passage through the bath is subjected to a heat treatment, and, more particularly, it has been found in accordance with the present invention that substantial advantages are gained if the web during such a preceding heat treatment is heated to such an extent that the temperature of the web on entry into the bath reaches, or slightly exceeds, the actual bath temperature. If, as proposed in accordance with the present invention, the material web is preheated so that its temperature at least corresponds to, or slightly exceeds, the actual bath temperature when the web enters the bath, the zones of the bath less active from a point of view of bacteriological killing described earlier are reduced or even wholly eliminated, and safe preconditions are established to ensure that no negative temperature balance between the material web and the hydrogen peroxide solution is created in any part of the heated bath which consequently does not have to be overdimensioned by being made either deeper and/or wider, but in practice can be given exactly the minimum dimensions which are required so as to achieve, under the given preconditions concerning temperature and concentration of the hydrogen peroxide solution, the desired bacteriological killing effect after a given minimum sojourn time in the bath. By preheating the material web so that its temperature on entry into the bath is even a few degrees higher than the actual bath temperature it has been found that the bath can be made even smaller, in particular made shallower, than what would be required, for example, theoretically if the temperature were to correspond exactly to the bath temperature, without an attendant impaired bacteriological killing effect. This is due to the fact that such an exaggerated preheating in itself brings about an improved killing effect owing to the fact that bacteria on the material web at these high temperatures (70-90°C) to a certain extent are dried out and consequently become more sensitive to the effect of the hydrogen peroxide solution. The proposed preheating of the material web, especially if this is constituted of a packing material consisting of plastic-coated paper, entails the further advantage that readily volatile, nonpolarized or incompletely polymerized monomers which can be found in, and which accompany, the plastic coatings of the material web, and which may impart an unpleasant taste to, or in some other manner affect, the contents of the subsequently produced packing containers, are evaporated and removed from the material web. This expulsion of readily volatile, taste-impairing plastic components can be made more effective still by subjecting the material web during the preheating to a simultaneous evacuation, as a result of which also plastic and paper dust and dust of any other kind which may occur is sucked off the material web and is thus prevented from accompanying the web down into the hydrogen peroxide solution and contaminating it. The invention will be described in more detail in the following with special reference to the attached drawing, wherein Figure 1 illustrates schematically the method in accordance with the invention in the manufacture of so-called aseptic packing containers in accordance with a principle of manufacture well known in itself, and Figure 2 shows an arrangement for the realization of the method in accordance with the invention shown in Figure 1. In accordance with the principle of manufacture illustrated summarily in Figure 1, aseptic packing containers 1 are manufactured, as described earlier, with the help of a conventional packing machine which from a web 2 produces packages in that the two longitudinal edges of the web are joined to one another to form a downwardly growing tube 3 which via a product filling pipe (not shown) inserted through the upper open end of the tube is filled with the particular, sterile-treated contents. The tube 3 is divided by means of repeated flattenings and transverse seals at right angles to the longitudinal axis of the tube into closed, cushionlike container units 1' which, thereafter, are separated from one another by cuts in the sealing zones and after appropriate fold-forming and sealing leave the machine in the form of finished, aseptic packages 1 of usually parallelepipedic shape. As mentioned earlier it is a prerequisite for the finished packages 1 to be aseptic that the contents as well as the web must be sterilized prior to contact with one another, and that the tube-forming and filling operations themselves must be carried out under conditions which prevent infection of the sterilized packing material and contents. The sterilization of the contents usually is done by means of a heat treatment during which the contents are heated according to a given temperature/time scheme and the reinfection-preventing or aseptic environment is assured in that the tube forming and filling operation of the machine is carried out in a casing excluding the environment within which through the introduction of hot air a certain pressure is maintained which effectively prevents the penetration of nonsterile ambient air. The sterilization of the material web 2 is done in that the web, as closely adjoining to the tube-foming and filling zone of the machine as possible, is brought into contact with a liquid, chemical sterilizing agent which in the embodiment shown in Figure 1 is arranged in the form of a so-called deep bath in a vertical container 4 shown by broken lines through which the web 2 is conducted in a vertical loop around a roller 5 provided in the lower part of the bath 4. The container 4, as is clearly evident from Figure 1, has a height dimension which appreciably exceeds the corresponding width dimension of the container in the horizontal plane across the direction of movement of the material web 2. In the example chosen here it is assumed that the material web 2 consists of a laminated material comprising a base layer of paper or cardboard with outer layers of thermoplastics, preferably polythene, and one or more layers of other material, e.g. metal foil or plastics of a type different to that mentioned here, arranged between the plastic and base layer. For example the packing material may have the following conventional composition, reckoned from the outside of the web to its inside: LDPE/paper or cardboard/LDPE/Al-foil/LDPE, this material having good tightness properties against liquid, gases and light and, moreover, it is easy to seal by means of conventional so-called heat sealing. In the example chosen it is assumed, moreover, that the chemical sterilizing agent consists of an approx. 30-50 w/v% hydrogen peroxide solution heated to approx. 65-75°C, e.g. 70°C, and that the container 4 containing the peroxide is dimensioned so that each part of the material web 2 passing through at the actual speed of the machine is in contact sufficiently long with the hydrogen peroxide solution in the bath to achieve an acceptable bacteriological killing effect. From the container 4 the web mixed with hydrogen peroxide is passed through the nip between two mangle rollers 6, by means of which accompanying excess of hydrogen peroxide solution is mechanically squeezed out of the web and is returned down into the container 4, and further up into the tube forming and filling zone of the machine. The web on entering passes a number of nozzles directed towards the inside of the web through which hot air is blown for the driving off of remaining amounts of hydrogen peroxide before conversion of the material web to tubular shape. In accordance with the present invention a heating region 7 indicated by broken lines is provided before the deep bath, seen in the direction of movement of the material web is indicated by arrows, through which the web 2 is conducted for combined conditioning and heating prior to entry into the bath. Within the region 7, as is shown in more detail in Figure 2, there is a substantially rectangular box 8, whose upper end has a narrow inlet gap 9 adapted to the web and whose lower end is open and connects tightly to the subsequent container 4 in the region before entry of the web into the bath. Along the sides 8a of the box there are a number of nozzles 10, evenly distributed in transverse as well as in longitudinal, direction and directed towards both sides of the web passing through which, via a common duct 16, are in communication with a source of hot air and which direct the hot air emanating directly towards both sides of the web, as indicated with the help of the solidly drawn arrows in Figure 2. In the immediate vicinity of the gaplike inlet opening 9 of the box 8 the latter is provided with an expanded portion 11 serving as an evacuation chamber with a constricted, gaplike inlet opening 12 and connection means 14 joined to the evacuation chamber 13, and located preferably on either side of the web 2, which via a duct 15 are in communication with a source of vacuum, not shown. During the passage through the box 8 within the conditioning and heating region 7 shown in Figure 2 the web 2 thus will pass a stream of hot air emanating from the nozzles 10, which owing to the partial vacuum, maintained in the evacuation chamber 13, is directed in counterflow to the web and is brought into intensive contact with both sides of the web within the region of the narrowly designed gap opening 9, as a result of which an effective heating of the web, or at least of the outer plastic coatings of the web, is obtained. Thanks to the heating, any readily volatile components which may impart an unpleasant taste are liberated from the plastic coatings, entrained by the counterflowing air stream and evacuated through the connection means 14. This air stream furthermore contrives to remove to a certain extent fibre and plastic dust which is also extracted through the evacuating connection means 14 and is thus prevented from accompanying the web 2 down into the sterilizing bath and contaminating it. A heating arrangement of the type just described, with the help of which it is thus possible to preheat as well as clean the web prior to its entry into the subsequent sterilizing bath, has been found to be particularly advantageous in the sterilization of packing material webs comprising layers of paper or cardboard and plastics, but it is likewise possible, of course, within the framework of the general basic concept underlying the invention, to use other types of heating arrangements in order to provide the desired preheating of the material web which, for the purpose of sterilization, is intended to be passed through a liquid sterilizing agent.

Claims: A method for the pretreatment of a moving material web (2) which for the purpose of sterilization is passed through a heated bath containing a sterilizing agent, characterized in that the web is heated so that its temperature corresponds to, or slightly exceeds, the actual bath temperature when the web enters into the bath. A method in accordance with claim 1, characterized in that the web is subjected to partial vacuum during the heating. A method for the pretreatment of a laminated packing material web comprising layers of paper and plastics and possibly a metal foil arranged between the paper and plastic layers, in accordance with claim 1 or 2, the web for the said purpose of sterilization being passed through a bath heated to 65-75, preferably 70°C, containing 35% hydrogen peroxide solution, characterized in that the web is heated so that its temperature reaches 70-90, preferably 80°C when it enters into the bath. A method in accordance with anyone of the preceding claims, characterized in that the web is heated by means of hot air which is blown towards both sides of the web, preferably in counterflow to the direction of movement of the web. A method in accordance with claim 4, characterized in that the web is passed through a narrow gap (9) through which the hot air is evacuated for intensive counterflow contact with the web moving through it. An arrangement for the pretreatment of a moving material web (2) which for the purpose of sterilization is passed in a vertical loop down through a container (4) containing a heated bath of a sterilizing agent, characterized in that it comprises heating means installed before the container (4) with the help of which the web is adapted to be heated so that its temperature corresponds, or preferably slightly exceeds, the actual bath temperature when the web enters into the bath. An arrangement in accordance with claim 6, characterized in that the heating means comprises a rectangular box (8) provided with inlet (9) and outlet and having nozzles (10) directed towards both sides of the web moving through, and which are in communication with source of hot air. An arrangement in accordance with claim 7, characterized in that the inlet (9) is designed as a narrow gap opening which via an evacuation chamber (13) provided with connection means (14) is in communication with a source of vacuum.

Inventors: JOHANSSON, GOERAN, OLANDERS, PAER, Johansson, Göran, Olanders, Pär
Applicants: ROBY TEKNIK AB
Application year: 1989
Main classification: B65B55
IPC codes: B65B55