STERILIZATION PROCESS

Abstract: A sterilization arrangement which is adaptable to pumpable fluid-carrying packages on a conventional forming, filling and sealing machines as they are conveyed intermediate the turret for forming and sealing one end of the cartons and the section for filling and sealing the other end thereof. The process involved includes the following steps: spraying an up to 35% solution of hydrogen peroxide at room temperature into the open ends of paperboard packages having one sealed end resulting in a 300-400 parts per million concentration in the package; conveying the packages through an outside heating section very nearly in contact with a stationary cover member, while blowing hot air at a temperature in the range of 340-400°F upwardly past the packages; conveying the cartons beneath and very nearly in contact with the stationary cover member extending along the length of a sterilization section and subjecting the packages to surrounding air at a temperature of 200-230°F; drying the packages in a drying section by directing sterile air at a temperature of 200-­ 240°F into the open tops of the cartons, with the hydrogen peroxide concentration being reduced to a maximum of 0.05 parts per million; and unloading the respective sterilized cartons into the filling and final end sealing section.

Description: TECHNICAL FIELD This invention relates generally to sterilization processes and, more particularly, to a sterilization process for packages using hydrogen peroxide sterilant. BACKGROUND ART The previous method of blowing hot air into a carton into which hydrogen peroxide has been sprayed causes the liquid hydrogen peroxide to be immediately vaporized and expelled from the carton. The necessary time duration factor is uncontrollable and is too short for effective sterilizing. Other means have been attempted other than generating a hydrogen peroxide and water vapor atmosphere within the carton. Such other process involves generating a hydrogen peroxide vapor in a circulating loop and applying this vapor to an open carton relying on condensation to distribute the hydrogen peroxide within the carton. It has not been effective with minimal kill rate resulting. Various methods of dipping and/or spraying of hydrogen peroxide sterilant, in combination with heating, are described in US-A-4,169,123; US-A-4,225,556; US-A-3,566,575; US-A-4,566,251; and US-A-4,631,173. US-A-3899862 discloses a process and apparatus for continuously cold sterilising, aseptically filling and dosing containers, in which each successive container is dosed by a dosing device with a quantity of a sterilising agent which is retained within the container for a sufficient time for sterilisation to take place, is conveyed through a tunnel within which a gaseous environment under slight overpressure is maintained, and is filled and has a sterile lid applied under sterile conditions within the tunnel. The dosing device doses either a jet of undiluted sterilizing gas, for example hydrogen chloride, or a micro-droplet of a gas-generating liquid. After dosing, the containers are kept closed by a temporary sealing means for a certain time. This may be effected in various ways. A foil can be caused to extend over the container openings. To enable renewal of this foil following possible wear thereof by the containers passing under it, it is led from a supply roller to an uptake roller. The foil can be kept pressed over the container openings by a sterile air blowing device, or by an elastic block. Alternatively, an endless belt of, for example, impermeable PVC-foam closing the container openings can advance with the containers. The sterilizing agent is flushed from the sterilized containers by jets of dry sterile air supplied by a plurality of nozzles. DISCLOSURE OF THE INVENTION An object of the present invention is to provide an improved high-speed sterilization method which is efficient and effective for open ended thermoplastic coated paperboard packages. Another object of the invention is to provide an improved sterilization method which may be used in conjunction with a conventional indexing type forming, filling and sealing machine, intermediate one end forming and sealing operation, and the filling and other end forming and sealing operation on the machine, such as the intermediate sterilization section of US-A-4,556,251. A further object of the invention is to provide a high-speed sterilization process which achieves a consistent index spore reduction of at least 8D with hydrogen peroxide residuals under 0.1 ppm in conventional paperboard packages. According to the present invention, there is provided a sterilization method comprising introducing a sterilizing agent at room temperature into open ends of containers having their opposite ends closed, conveying the containers along a stationary cover member with the open ends substantially obturated thereby while sterilizatlon occurs, flushing the containers with sterile air, and conveying the sterilized and flushed containers through filling and open end sealing stations, characterized In that the introducing of the sterilizing agent comprises the spraying-In of a solution of hydrogen peroxide, that the containers are comprised of paperboard, that, while the cover member substantially obturates the containers, the outside surfaces of the containers are subjected to hot sterile air at a first temperature and then the outside surfaces of the containers are subjected to sterile air at a second temperature higher than room temperature but lower than said first temperature, that the flushing comprises drying the containers with sterile air at a third temperature intermediate said first temperature and said second temperature and directed into the open ends thereof, resulting in a final desired maximum in parts per million of hydrogen peroxide, and that the sterilized and dried containers are unloaded onto a conveyor adapted to carry the containers through said filling and open end sealing stations. Preferably, the sterilization method includes the steps of (a) spraying air up to 35% hydrogen peroxide solution, resulting in a 300-400 parts per million concentration, at room temperature, or approximately 21°C (70°F), into open ended paperboard cartons after the cartons leave the typical turret on which one end closure thereof will have been formed and sealed; (b) moving each carton through an outside heating section just beneath a stationary cover member, while blowing hot air at a temperature in the range of 171-204°C (340-400°F) upwardly and sidewardly past the packages, raising the inside temperature of the hydrogen peroxide film to approximately 71°C (160°F); (c) conveying the cartons beneath the stationary cover member extending through a sterilization section, very nearly in contact therewith, and subjecting the outside surfaces of the cartons to air at a temperature in the range of 93-110°C (200-230°F), raising the inside temperature of the hydrogen peroxide film to approximately 88°C (190°F); (d) conveying the cartons away from the cover member into a drying section and drying the cartons with sterile air at a temperature in the range of 93-116°C (200-240°F) directed into the open ends of the cartons, raising the Inside temperature of the hydrogen peroxide film to approximately 99°C (210°F) and resulting in a maximum hydrogen peroxide concentration of 0.05 parts per million; and unloading the sterilized and dried cartons from the drying section onto a conveyor adapted to carrying the cartons through the filling and final end sealing stations. BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, In which:- Figure 1 is a block diagram illustration of the steps involved in a sterilization method, including an optional intermediate step; FIGURE 2 is a schematic illustration of the structure utilized to carry out the method embodied in Figure 1; FIGURE 3 is an enlarged cross-sectional view taken along the plane of the line 3-3 of Figure 2, and loocking in the direction of the arrows; and FIGURE 4 is an enlarged view of a portion of the Figure 2 structure. BEST MODE OF CARRYING OUT THE INVENTION Referring now to Figure 1, there is illustrated a block diagram depicting the following progressive steps: A. Spraying an approximately 35% solution of hydrogen peroxide, resulting in a concentration of 300-400 parts per million, at room temperature, say 21°C (70° F), into the open tops of paperboard cartons after they have been stripped from respective mandrels of a forming, filling and sealing turret whereupon one of the end closures of the cartons were formed and sealed; B. Conveying each carton through an outside heating section beneath a stationary cover member nearly in contact therewith, while bowing hot air at a temperature in the range of 171-204°C (340-400°F) upwardly past the cartons, raising the inside temperature of the hydrogen peroxide film to approximately 71°C (160°F); C. Conveying the cartons through a sterilization section beneath a stationary cover member very nearly in contact therewith and subjecting the outside surfaces of the cartons to sterile air at a temperature in the range of 99-110°C (210-230°F), raising the inside temperature of the hydrogen peroxide film to approximately 88°C (190°F); D. Conveying the cartons away from the cover member and drying the cartons with sterile air at a temperature in the range of 93-116°C (200-240°F) directed into the open ends of the cartons, raising the inside temperature of the hydrogen peroxide film to approximately 99°C (210°F) and reducing the hydrogen peroxide to a range of 0.01-0.05 parts per million; and E. Unloading the sterilized and dried cartons from the drying section onto a conveyor adapted to carrying the cartons through the filling and final end sealing stations. As further illustrated in Figure 1, the above step D may be changed to two station with inside-directed air at 149-160°C (300-320°F), raising the inside temperature of the hydrogen peroxide film to approximately, 93°C (200°F); followed by two stations, rather than six, with the inside-directed air at 105-116°C (220-240°F), resulting in a hydrogen peroxide reduction to a minimum concentration of 0.05 parts per million. Referring now to the apparatus 10 utilized for the above described method, as represented in Figure 2, there is illustrated a loading section 12, a spraying section 14, an outside heating section 16, a sterilization section 18, a drying section 20, and an unloading section 22, with conveyor means therethrough represented at 23 and having an index time of 3.2 seconds. A pair of spray nozzles 24 and 26 are offset from the center of the packages on alternate opposite sides of the center as each package progresses, for spraying the hydrogen peroxide in step A twice into each package in the spraying section 14 for optimum interior surface coverage. A heat plenum 28 and exhaust units 30 are operatively connected respectively below the closed ends and above the open ends of the packages, with hot air being directed past the packages from the heat plenum to the exhaust units for the outside heating operation in the section 16, as described in step B above. This air is alternately directed at angles of 5° below horizontal and 5° above horizontal at alternate stations, as represented at outlets 32 and 34 of the heat plenum 28 in Figure 2, and shown in Figure 3. A stationary cover member 36 is mounted along the lengths of each of the outside heating section 16 and the sterilization section 18, with the cartons moving therepast very nearly in contact therewith, with sterile air, as described in step C above, provided from a heat plenum 38 to exhaust units 40, through the plenum outlets 32 and 34. As shown in Figure 3, in addition to hot air flowing past the lengths of the packages, from the closed ends to the open ends thereof, hot air may be directed laterally past the sides of the packages from outlets 42, particularly during index dwell periods, for each of the seven stations of section 16 and the eight stations of section 18. A heat plenum 44 in the drying section 20 serves to provide sterile air through a plurality of outlets 46a, 46b, 46c, 46d, 46e and 46f into the open tops of the packages. Specifically, the outlets are variously offset from the centers of the respective packages as they dwell beneath the outlets, as shown in Figure 4, providing an effective sweeping pattern of the sterile air in the Packages. INDUSTRIAL APPLICABILITY It should be apparent that the invention provides an efficient and effective sterilization arrangement which is adapted to being mounted on a forming, filling and sealing machine, intermediate the ends forming and sealing turret and the filling and other end sealing stations thereof. More specifically, in this arrangement, the packages are sprayed with up to 35% solution of hydrogen peroxide and indexed into heating stations where the carton is covered to retain a generated vapor atmosphere of hydrogen peroxide and water. Hot air is directed in a precise manner to the outside surfaces of the package to evenly increase the package's inside surface temperatures. The liquid hydrogen peroxide and water mixture is vaporized as the inside surface temperature rises. The water is more easily vaporized at lower temperatures and as the package inside surface temperature rises during heating the liquid mixture remaining on the package surfaces becomes increasingly more concentrated with hydrogen peroxide. This increase in concentration of hydrogen peroxide contributes to a higher microbiological kill rate. Simultaneously, as the peroxide vapor increases inside the carton, its partial pressure increases. This causes the liquid peroxide remaining on the package surfaces to vaporize at even higher temperatures. The higher temperature peroxide liquid, in intimate contact with the package's inside surfaces, resultes in an even higher kill-rate. The circulating vapor inside the package will condense out on the cooler surfaces of package. This results in heating of these cooler surfaces and an improvement in their respective kill-rate contribution. The circulating hydrogen peroxide vapor inside the carton volume has an additive sterilizing effect on these hot surfaces where the peroxide liquid has been completely vaporized. The sterilizing factors of (1) the concentration of the liquid peroxide sterilant (2) the temperature at which sterilization occurs, (3) the intimate contact of the sterilant with the surface to be sterilized, and (4) the time elasped of the sterilization process are all controlled by this outside heating process. While but one embodiment of the invention has been shown and described, other modifications thereof are possible within the scope of the following claims.

Claims: A sterilization method comprising introducing a sterilizing agent at room temperature into open ends of containers having their opposite ends closed, conveying the containers along a stationary cover member with the open ends substantially obturated thereby while sterilization occurs, flushing the containers with sterile air, and conveying the sterilized and flushed containers through filling and open end sealing stations, characterized in that the introducing of the sterilizing agent comprises the spraying-in of a solution of hydrogen peroxide, that the containers are comprised of paperboard, that, while the cover member substantially obturates the containers, the outside surfaces of the containers are subjected to hot sterile air at a first temperature and then the outside surfaces of the containers are subjected to sterile air at a second temperature higher than room temperature but lower than said first temperature, that the flushing comprises drying the containers with sterile air at a third temperature intermediate said first temperature and said second temperature and directed into the open ends thereof, resulting in a final desired maximum in parts per million of hydrogen peroxide, and that the sterilized and dried containers are unloaded onto a conveyor adapted to carry the containers through said filling and open end sealing stations. A method according to claim 1, wherein the spraying-in occurs on a forming, filling and sealing machine just after the open-ended containers are stripped from respective mandrels thereof whereon the said opposite ends thereof were formed and sealed. A method according to claim 1 or 2, wherein the solution of hydrogen peroxide is approximately up to 35% solution, giving a concentration in the range of 300-400 parts per million. A method according to any preceding claim, wherein said first temperature is in the range of 171-204°C (340-400°F). A method according to claim 4, wherein the containers attain an inside hydrogen peroxide film temperature of approximately 71°C (160°F). A method according to any preceding claim, wherein said second temperature is in the range of 93-110°C (200-230 °F). A method according to claim 6, wherein the containers attain an inside hydrogen peroxide film temperature of approximately 88°C (190°F). A method according to any preceding claim, wherein said third temperature is in the range of 93-116°C (200-240°F). A method according to claim 8, wherein the containers attain an inside hydrogen peroxide film temperature of approximately 99°C (210°F). A method according to any preceding claim, wherein said final desired maximum is 0.05 parts per million. A method according to any preceding claim, wherein the spraying-in occurs over two indexing stations. A method according to any preceding claim, wherein the subjection to the hot sterile air at the first temperature occurs over seven indexing stations. A method according to any preceding claim, wherein the subjection to the sterile air at the second temperature occurs over eight indexing stations. A method according to any preceding claim, wherein the drying with sterile air at a third temperature occurs over six indexing stations. A method according to any one of claims 11 to 14, wherein the time for each index is approximately 3.2 seconds. A method according to any one of claims 1 to 13, and further comprising, between the subjection to sterile air at the second temperature and the drying with sterile air at the third temperature, drying the containers with sterile air at a temperature in the range of 149-160°C (300-320°F) directed into the open tops of the containers. A method according to claim 16, wherein the drying with sterile air at a temperature in the range 149-160°C (300-320°F) occurs over two indexing stations. A method according to claim 16 or 17, wherein the drying with sterile air at the third temperature occurs over two indexing stations. A method according to claim 16, 17, or 18, wherein the containers attain an inside hydrogen peroxide film temperature of approximately 93°C (200°F). A method according to any preceding claim, wherein the sterile air at the first temperature and the sterile air at the second temperature is provided by a continuous flow of hot air from adjacent said opposite ends of the containers past the outside surfaces thereof. A method according to claim 20, wherein said hot air is directed at 5° off vertical at alternate indexing stations throughout the subjection to sterile air at the second temperature and the drying with sterile air at the third temperature. A method according to claim 20, and further comprising blowing hot air laterally past the outside surfaces of the containers between indexes. A method according to any one of claims 1 to 20, wherein, in the drying with sterile air at the third temperature, the sterile air is directed into the open ends of the containers in a manner alternating between leading and lagging the container centre, so as to sweep the container interiors uniformly.

Inventors: RANGWALA, BADRUDDIN KALIMUDDIN, REDDING, ROBERT M., STEFANOVIC, SAVA
Applicants: ELOPAK SYSTEMS AG
Application year: 1989
Main classification: B65B55
IPC codes: A61L2, B65B55