Procedure and a device for the sterilization of packaging material

Abstract

Sterilization of a web of packaging material is accomplished by applying a film of sterilizing liquid to the web, passing the web through an atmosphere saturated with steam and sterilizing liquid while the film is maintained at a temperature just below its boiling point and then drying the film by a flow of hot dry sterilized air.

Description

The invention refers to a procedure and a device for the sterilization of packaging material, both the procedure and the device being especially applicable to the sterile packaging and filling of precedently sterilized products, especially liquid products, into containers formed from plastic or plastic coated paper webs.

One of the problems affecting such packaging procedures and equipment is the sterilization of that plastic coated face of the web which will form the internal face of the container, i.e. that face which, remaining in a prolonged contact with the contents, is liable to contaminate them if it is not sterilized to a very high degree. Sterilization by the mere application of heat to this face would require temperatures which would destroy its plastic coating. The choice of suitable chemical sterilizing substances is extremely restricted by the requirement that even their traces must be completely eliminated from said treated face of the web before it is formed into containers and these containers are filled. The most suitable sterilizing agent for this purpose has proved to be hydrogen peroxide, because after its application it can be completely evaporated at temperatures which do not endanger the plastic coating of the paper web. However, the use of hydrogen peroxide results in a number of problems. The sterilizing action of cold peroxide is too slow for today's web processing rates. Warm peroxide exerts a sterilizing action which is quicker and more effective, but it still raises further problems. The proposal of passsing the web through a tank containing heated peroxide resulted in the drawback of heavy losses of peroxide due to its decomposition by heat and its absorption on and uncoated face of the web. Furthermore decolorization of anything printed on the uncoated surface and discomfort and various unpleasant effects, such as irritation of the mucosae and discoloration of the hair, to the personnel are encountered in an atmosphere containing peroxide vapors. It has also been suggested to apply hydrogen peroxide vapors directly upon that coated face of the web, which will form the interior surface of the containers. Its evaporation was obtained by spraying the peroxide solution together with jets of hot air, which caused the evaporation of the sprays before they hit the coated web surface. However, tests have shown that this procedure did not attain the same degree of sterilizing effect as that exerted by a protracted contact with warm hydrogen peroxide. In fact, sterilization tests performed on a dry concentration of 10.sup.6 spores/sq. cm of Bacillus Subtilis spread on a plastic coating, have shown that at a temperature of not over 150.degree.C and at an exposure time of not over 20 seconds, the mortality of the bacilli caused by H.sub.2 O.sub.2 in a vapor phase is practically nil ( 1 log. cycle max.).

Sterilization reaches an insufficient maximum of 2 log. cycles when H.sub.2 O.sub.2 is sprayed and suddenly evaporated by hot air circulation. Sterilization has however proved optimal, with 5 log. cycles, with a liquid film of H.sub.2 O.sub.2 of 15 % concentration when its temperature is raised just below its boiling point by radiation and its evaporation is kept at a minimum for approximately 20 seconds.

The results of such comparative tests, evidencing the efficiency of the sterilization method of the invention are shown in the attached table.

To realize these optimal results, in the procedure and device of the invention, the hydrogen peroxide solution is applied as a cold film of uniform thickness to the interior, plastic coated surface of the web. Subsequently, the web passes through a sterilization chamber filled with practically stationary, sterile, steam saturated atmosphere and the peroxide film on it is subjected, immediately upon its entrance into the chamber, to a sudden heating to a temperature just below its boiling point. Throughout the remaining portion of its travel through this chamber the film is kept at this temperature, while the saturated atmosphere of the chamber keeps its evaporation at a minimum. At the end of its passage through said vapor filled chamber the interior web face has attained the above indicated high degree of sterilization. Immediately thereafter, the web passes into a second chamber, wherein the interior web face is dried by a steam of precedently sterilized hot dry air, and thence moves into the successive processing stations of the packaging machine, in which it is transformed into containers and the containers are filled and sealed.

__________________________________________________________________________ Test conditions Exposure Tempera- H.sub.2 O.sub.2 concen- Minimum time in ture tration survival Test method seconds (.degree.C) (weight %) index .sup.(x) __________________________________________________________________________ Contact of the packaging material with 20-60 120-150 11-18 10.sup.-.sup.1 vapor phase H.sub.2 O.sub.2 to H.sub.2 O.sub.2 of the vapors H.sub.2 O.sub.2 Sudden evaporation, caused by circulated 20 120-150 11-18 10.sup.-.sup.2 hot air, of a H.sub.2 O.sub.2 solution sprayed or to hot of the sprinkled on the packaging material air air Sudden evaporation, caused by hot air 20 120-150 11-18 10.sup.-.sup.3 circulation, of a H.sub.2 O.sub.2 solution applied to hot of the in a continuous and uniform film upon air air the packaging material H.sub.2 O.sub.2 solution applied in an even and 20 80-100 11-18 10.sup.-.sup.5 continuous film to the packaging material to radia- of the and heated by radiation under conditions tions H.sub.2 O.sub.2 minimizing its evaporation __________________________________________________________________________ .sup.(x) between the spores having survived the treatment and the initia spores.

The procedure and the device of the invention will be better understood from the following description, made with reference to the attached drawings, of two of its possible embodiments.

In the drawings:

FIGS. 1A, 1B and 1C are a vertical section through the first embodiment;

FIG. 2 is a schematic drawing, on a larger scale, of the web wetting station of FIG. 1A;

FIG. 3 is a section, taken along the line III--III, of FIG. 1B;

FIGS. 4A-B are a vertical section through the second embodiment;

FIG. 5 is a section taken along line V-V of FIG. 4B; and

FIG. 6 is a schematic drawing of an elevational view perpendicular to the view of FIGS. 1A-C.

The web 1 is drawn by the usual (and therefore not shown) drive rolls from an(also not shown) feed roll, thence, with its coated face 1a downward, under a directing roll 4 and vertically upward through the sterilization and the drying chamber.

In the web wetting station, generally indicated at 2, a wetting cylinder 3 is partially immersed in a 15 % hydrogen peroxide solution contained in tank 5 and kept there at a constant level by any suitable known and therefore not shown system. The rotation imparted by the web 1 to the directing roll 4 is transmitted through any suitable means, such as a gear or belt drive, to cylinder 3, which, in its rotation, transfers a hydrogen peroxide film 5a from the tank 5 and to the plastic coated surface 1a of web 1.

Cylinder 6 presents at each end a raised rim 7 which presses resiliently against the margins of the web 1 on cylinder 4, whereby also roll 6 is entrained in rotation by the web. Rims 7 form a clearance between the surface of cylinder 6 and the web face 1a, which serves to equalize the liquid film on face 1a and determine its thickness at the entrance of the web into the sterilization chamber.

A wiper blade 8 serves to recover any liquid from the surface of cylinder 6.

The sterilization chamber may be of any shape permitting the arrangement of the heaters and the creation of a steam saturated atmosphere according to the following description. However, since in packaging practice, at a certain step, the paper web must anyhow be folded in the middle and its two margins must be sealed together in a successive stage to form the web into a tube, it is convenient to take advantage of this provision to let the web itself form two walls of the sterilization and the subsequent drying chamber. For this purpose, the doubled-up web 1 is passed over a (not shown guide roll 30 or between a pair of guide rolls mounted just over line Z--Z of FIG. 1 or 4 as seen in FIGS. 1C and 6, whose axis or axes respectively are at a right angle with those of the cylinders in the wetting station 2. Consequently, the paper web issues flat from between cylinders 4 and 6, assumes gradually the approximately semicircular curvature shown in FIG. 3 or 5, with its coated face turned inward, while its margins 9 and 10 gradually approach each other, until the web is completely doubled-up, with said margins pressed together when it reaches the guide roll 30 or guide rolls. The space portion delimited by web 1 from a level just above cylinders 4 and 6, where it is still flat, to the level where it is completely doubled-up, is closed by a triangular plate 11, whose sides present two flanges 12 and 13 (FIG. 3), which hug and guide web margins 9 and 10 during their convergence, while its base almost contacts face 1a at a level where it is still flat. Owing to this arrangement, plate 11 and web 1 define together a sufficiently well enclosed space, which forms the sterilization chamber. Plate 11 is backed by a boxlike structure 19.

In the embodiment according to FIGS. 1 to 3, the heating of the peroxide film is effected by infrared radiators, such as infrared lamps, the emitted wavelengths being comveniently selected in the range from 2.5 to 3 microns so that they correspond to their maximum absorption by the liquid film on the web. In this manner it is possible to selectively heat to a desired temperature said liquid film while preventing the excessive heating of the supporting web material.

The radiators 14 and 15 are aligned in a vertical row on plate 11 and separated by horizontal baffles 16 which extend from plate 11 as near to the web surface 1a as it is possible without the danger of damaging it, and thereby they separate the sterilization chamber into compartments, with the purpose of keeping the atmosphere in the chamber as stationary as possible. The baffles are made from materials which absorb as little as possible of the radiations of the heaters 14 and 15.

Each radiator or heater is of a shape approximately following the contours assumed by the web at their level (see especially FIG. 3), and its rays are directed by semicircular reflectors 17 of a parabolic cross section in conical beams upon the web survace 1a. This arrangement permits the heating of this surface uniformly both in a transverse and in a longitudinal sense, because the radiators are spaced from each other so that the edges of their conical beams of radiation overlap.

Upon its entrance into the sterilization chamber, the peroxide film is heated by the lowermost radiators 14 very quickly to a temperature just below its boiling point. For this purpose, radiators 14 are placed either nearer to web 1 or made of a greater power than radiators 15. The task of the successive radiators 15 is to maintain the liquid film at the temperature imparted to them by the radiators 14 for the remaining portion of its travel through the sterilization chamber.

To prevent or at least to minimize the evaporation of the peroxide film during its passage through the sterilizing chamber and to prolong thereby its contact with the web face 1a, in order to obtain the desired optimal sterilization, the atmosphere of the chamber is saturated with steam and hydrogen peroxide vapors of a temperature equal to that of said heated film. The hydrogen peroxide vapors are obtained by spraying H.sub.2 O.sub.2 nozzles 31 into the chamber, while steam is injected into it through a distributor 32 at a pressure slightly above the external preesure. These devices come into operation each time the packaging machine is started and/or the steam and H.sub.2 O.sub.2 vapor concentration drops below the level of saturation.

The sterilization chamber with its highly saturated atmosphere and the arrangement of the heaters permit therefore a prolonged contact of a very hot film of sterilizing liquid with the interior web surface, to attain its best possible sterilization.

Safety systems of any known and suitable type turn the radiators off whenever the movement of the web stops. Such systems are per se known and therefore neither described nor illustrated.

The terminals 18 of the radiators 14 and 15 are located within a box 19, which also contains the conductors for the connection with the electric mains.

The drying chamber 22 forms a continuation of the sterilization chamber since its walls are also formed by the web 1 and the plate 11. This chamber is separated from the sterilization chamber by a diaphragm 20 which extends from plate 11 towards web 1. Slightly above said diaphragm, plate 11 presents an opening 11a and slightly below its upper end a second opening 11b. An upward curved deflector plate 21 extends from the lower edge of opening 11a towards the web and similarly a downward curved deflector plate 23 extends from the upper edge of opening 11b towards said web. In said chamber 22 the H.sub.2 O.sub.2 film, which enters at a temperature near its boiling point, comes into sudden contact with a stream of hot dry pre-sterilized air entering through opening 11a, passing along web face 1a and issuing through opening 11b, or in the contrary direction, as it seems fit. Owing to the high temperature of the liquid film, the change from a vapor saturated into a completely dry atmosphere and to the high temperature of the air, the liquid film is removed, without leaving the smallest residue, in an extremely short time. The temperature of the air stream can be kept as low, for instance as 100.degree.C so, as not to endanger the plastic coating of the web. As illustrated in J. H. Perry, Chemical Engineer's Handbook, 10, 18 (1963) an exposure time of 5 seconds is amply sufficient to totally remove an H.sub.2 O.sub.2 layer of 10 .mu. at a temperature of 90.degree.C of the packaging material by means of a hot air stream of 100.degree.C at a speed of over 2 meters/second.

In the embodiment of FIGS. 4A, 4B and 5, electric resistors, instead of infrared lamps, are used as infrared radiation sources, and the differences in structure in the sterilization chambers between the first and this embodiment are due to the greater thermal inertia of these radiation sources, so that means must be provided to immediately remove them from the vicinity of the web in the case of a break-down of the web transport mechanism or during the starting-up time of the packaging machine, during which web 1 is still stationary.

For this purpose, the high-temperature electrical resistors 14' and 15' are not mounted directly upon plate 11', as in the former embodiment, but on a box-like structure 25, and they project into the sterilization chamber through a generally triangular opening extending from the lower to the upper end of plate 11'. Similarly to the radiators 14, also the lowermost radiators 14' of this embodiment are either more powerful or kept nearer the liquid film on web surface 1a than the successive radiators 15' for the purpose already illustrated in connection with the first embodiment

Structure 25 is connected by piston rods 26 to double acting hydraulic cylinders 28 which it is automatically retracted whenever the web stops for any of the aforementioned causes. A casing 29 is welded or otherwise fastened to plate 11' and forms, together with web 1, a completely enclosed space 27.

It is clear that the invention is not limited to the embodiment shown, and that especially the wetting station for the web, the sterilization and the drying chambers may be given any other shape without departing from the concept of the invention.

Claims

What is claimed is:

1. A process for the sterilization of the surface of a web of packaging material which is to become the internal surface of the container formed from the web, comprising the steps of:

applying to the web surface a film of a sterilizing liquid:

bringing said web surface, after the application of said film, past and in contact with an atmosphere formed within an essentially closed sterilization chamber to prevent the evaporation of said film in said chamber;

spraying said chamber with steam and vapors of said sterilizing liquid unitl said atmosphere is saturated therewith;

heating said liquid film immediately upon its contact with said atmosphere to a temperature just below its boiling point;

keeping said liquid film at this temperature throughout its passage past said atmosphere;

drying said hot liquid film with a flow of hot dry sterilized air thereover at its issue from said saturated atmosphere.

2. A process according to claim 1, wherein the sterilizng liquid is hydrogen peroxide and the atmosphere is saturated with steam and hydrogen peroxide vapors.

3. A process according to claim 1, wherein said liquid film is kept at a temperature just below its boiling point by infrared radiations of a wavelength such as to be selectively absorbed by said liquid film.

4. A process according to claim 3, wherein the wavelength of the infrared radiations is in the range from 2.5 to 3 micron.

5. A device for the sterilization of the surface of a web of packaging material which is to become the internal surface of the container formed from the web, comprising:

means to apply a film of sterilizing liquid to said web surface;

an essentially closed sterilization chamber, said chamber having an inlet and an outlet end for the passage of said liquid filmed surface in thereto and out thereof;

heating means arrayed in said chamber from its inlet towards its outlet, those at its inlet being for heating said liquid film quickly to a temperature just below its boiling point, the successive ones being for keeping said liquid film at said temperature; and

means to completely saturate the interior of said chamber with steam and vapors of said sterilizing liquid, thereby preventing the evaporation of said liquid film within said chamber.

6. A device according to claim 5, additionally comprising:

baffles within said chamber, interposed between said heating means to minimize motion of said atmosphere within said sterilization chamber.

7. A device according to claim 5, wherein the means to apply a film of sterilizing liquid to the interior face of said web comprises:

a directing roll to direct said web towards said sterilization chamber and rotated by the movement of said web;

a wetting cylinder driven by said directing roll to apply a film of said sterilizing liquid to the interior web face;

an equalizing cylinder to evenly distribute and determine the final thickness of said liquid film.

8. A device according to claim 5, additionally comprising a drying chamber forming a continuation of said sterilization chamber, the inlet of said drying chamber coinciding with the outlet of said sterilization chamber; and means in said drying chamber to apply a current of hot sterilized gas to said liquid film.

9. A device according to claim 5, wherein said heating means comprises a plurality of infrared radiators, their emission being of a wavelength such as to be selectively absorbed by said liquid film.

10. A device according to claim 9, wherein said infrared radiators are retractable electric resistors projecting into said chamber of sterilization.

11. A device in accordance with claim 5 further including means for causing the web to bend in the middle and form a substantilly semi-circular cross-sectional contour with said surface on the inside, throughout the passage of said surface past said sterilization chamber and wherein said sterilization chamber comprises a plate having outwardly extending flanges on the sides thereof and said semi-circular web the edges of which pass between said flanges.

12. A device according to claim 11 wherein said heating means present a curvature pararlleling the contours assumed by said web at their level.

13. A device according to claim 11, said heating means compries a succession of heaters and wherein said sterilization chamber is subdivided into compartments by baffles interposed between successive heaters and extending from said plate to the immdediate vicinity of the interior web surface.