MXPA99003399A - A method of sterilizing a package material - Google Patents

Abstract

Containers which are ready to be filled or a package material having a plastic surface can be sterilized by hydrogen peroxidein gaseous phase being supplied to the previously heated plastic surface, the entire sterilization procedure being performed with the hydrogen peroxide in gaseous phase.

Description

METHOD FOR STERILIZING PACKAGING MATERIAL DESCRIPTION OF THE INVENTION The present invention relates to a method for sterilizing packaging material. More precisely, the present invention relates to a method for sterilizing packaging material having a plastic surface, by means of gas-phase hydrogen peroxide which is applied to the previously heated plastic surface. Sterile containers ready to be filled can be obtained in several ways. A method of sterilization implies that the plastic containers are sealed directly in connection with the manufacturing process, for example when they are blow molded. Due to the collapse of the container during the subsequent temperature drop, the sealing in this case causes considerable problems. Therefore, the container must be stored at an elevated temperature since the volume of air enclosed in the container will decrease if the temperature decreases. Such storage is both problematic and expensive. In order to avoid this, among other materials at present, hydrogen peroxide is used in liquid or gas phase, the inside of the containers being sterilized. Hydrogen peroxide is a very oxidant ref .: 29755 powerful but not especially stable and one advantage is that only water is formed as a by-product. However, the half-life of hydrogen peroxide is very long and the sterilizing agent, therefore, has to be removed after it has been allowed to exert its effect. It is assumed that hydrogen peroxide exerts its antimicrobial activity through its powerful oxidizing effect by acting on components in the cytoplasmic membrane of microorganisms. In the sterilization process, the hydrogen peroxide is used as an aqueous solution which is sprayed onto a container. When the container is subsequently heated, the hydrogen peroxide is gasified and can be removed by ventilation after having exerted its effect. According to an alternative sterilization process, a container in a first stage is subjected to hydrogen peroxide in the gas phase, which is allowed to condense inside the container. By this process a homogeneous coating of hydrogen peroxide is obtained which completely covers the packing material. In a subsequent step, the condensed gas is again gasified and finally removed by ventilation. By this procedure an acceptable rate of death of microorganisms can be achieved for commercial sterilization purposes.

When, for example, plastic containers are sterilized, these are in practice coated with a commercial standard solution called "Oxonia Aktiv", which among other things contains hydrogen peroxide and peracetic acid. The solution is allowed to act for a few minutes and then the containers are rinsed with clean sterile water. Such a procedure is complicated and laborious. A further problem is that with certain plastics in the packaging material, especially in the polyester, residues of hydrogen peroxide remain which are adsorbed inside the container as a result of spraying, coating or condensation. They can subsequently have a negative influence on the material with which the container is filled, for example by changing the color. The authorities have established a limit value that should not be exceeded for hydrogen peroxide residues. It is very unusual to treat packaging materials such as polyester aseptically, since this type of material is almost always used for non-alcoholic beverages and the like. However, there is great interest in the market for an aseptic bottle of polyethylene terephthalate (TPE). In order to minimize the risk of the formation of residual products, the hydrogen peroxide can be removed by ventilation, for example at elevated temperature or with sterile air blown into the interior of the container. Such a procedure is expensive and, therefore, it would be desirable if shorter ventilation times could be used, which would result in a lower cost per container. The purpose of the present invention is to eliminate or reduce the aforementioned drawbacks, which arise during a sterilization by means of hydrogen peroxide according to the state of the art. In order to achieve this purpose, the method according to the present invention has obtained the features of claim 1. A sterilization process with a condensation of hydrogen peroxide, comprises four phases of different intervals: a heating phase, a Gasification phase, a holding phase and a ventilation phase. During the heating phase, the container is heated to a suitable temperature. The heating phase is not necessary. However, it reduces the amount of condensate that will later have to be removed by ventilation. during the gasification phase, gaseous hydrogen peroxide is injected into the interior of the previously heated container and onto the surface to be exposed to the treatment, on which the gas is condensed and a condensate is formed in the form of droplets. The gas used is a mixture of air and gasified hydrogen peroxide solution. The hydrogen peroxide solution is applied with a commercial grade purity, consisting of about 65% water and about 35% hydrogen peroxide. However, of course other concentrations can be used, depending on other parameters. During the holding phase, the condensate is allowed to exert its effect and during the ventilation phase the container is ventilated, the condensate is again transformed into a gas phase and removed from the container. In this stage hot air is used that has been prefiltered and sterilized by filtration means. Experiments were carried out with the purpose of achieving an equally effective sterilization than that achieved when hydrogen peroxide is allowed to exert its effect in the form of condensed gas. In these experiments, the hydrogen peroxide according to the present invention was allowed to remain in the gas phase during the entire sterilization process. Compared with the sterilization by means of condensation described above, the method according to the present invention involves, shortly, that the containers are sterilized with gasified hydrogen peroxide, where the containers are first heated to a temperature that is greater than the spray point of the gas used. Afterwards, the containers are blown dry with hot sterile air. Thus, during the sterilization process, the containers during a certain period are exposed to gaseous hydrogen peroxide of a specific temperature, spray point and flow velocity. Apart from the concentration of hydrogen peroxide, these parameters are important in order to achieve a killing effect. In this regard, the spray point is the temperature at which the gaseous hydrogen peroxide must be cooled in order to obtain a condensation, with an aqueous solution of hydrogen peroxide being separated. This temperature depends on the content of hydrogen peroxide in the gas. The spray point is adjusted to be used in an existing sterilization equipment. Preliminary experiments have shown that the amount of residual hydrogen peroxide per unit area varies after contact with different types of packaging materials. There were certain problems with the polyester as a packaging material and, therefore, experiments were carried out on such materials using polyethylene terephthalate bottles. However, other types of containers ready to be filled were also studied. EXAMPLE 1. Comparison between sterilizing effects. A comparison was made between the sterilizing effect achieved by means of gasification / condensation and that obtained by gasification only, in accordance with the present invention. The efficiency to kill microorganisms in the form of logarithmic reduction was defined as the number of microorganisms in a reference sample, minus the number of surviving microorganisms. TPE bottles were inoculated with spores of Bacillus subtilis NCA 7252 and, after the respective sterilization treatment, the results were statistically evaluated with a conventional procedure (based on the NMP method, "Most Probable Number"), which is well known for the technicians in the matter. The containers to be subjected to gasification / condensation or to gasification alone in accordance with the present invention, respectively, received the same treatment during the gas phase and the support phase, which by previous experiments showed that it was optimal.

Thus, in the sterilization process a gassing phase of 3 seconds with gaseous hydrogen peroxide was used, the gas having a temperature of 90 ° C, a dew point of 65 ° C and a flow rate of 40 kg / h. The length of the holding phase was 1 second. Those vessels that were subjected to gasification / condensation, in the heating phase were heated to 50-55 ° C and the vessels were ventilated for 10 seconds with sterile air at 70 ° C, with a flow rate of 40 kg / h. During gasification / condensation, the ventilation time was adjusted in such a way that all the visible condensate had evaporated. Those vessels that had been subjected to the gasification alone in accordance with the present invention, during the heating phase were subjected to a temperature of 70-80 ° C and during the ventilation phase, the vessels were subjected to a flow of 2 seconds of sterile air at 80 ° C, at a flow rate of 60 kg / h. The results indicated that an effect of killing of microorganisms was sufficient in the I form a logarithmic reduction of at least one log 5 (105), with both methods of sterilization.

EXAMPLE 2. Comparison between the residual quantities extracted. Experiments were performed in order to -study if residues were obtained in the sterilized TPE containers according to the present invention. At the same time, a comparison was made with polyethylene (PE) bottles. Both the TPE and PE bottles were subjected to the same sterilization treatment as in Example 1. Apart from that, the time after filling of the bottles and the storage time were varied, and the ventilation time after the two Sterilization procedures was 2 seconds. The residual hydrogen peroxide in each container was measured by means of an HP-10 vial (Chemetrics, 90298-31), in accordance with the manufacturer's instructions. The results obtained are shown in Table 1. Table 1. Residual hydrogen peroxide (ppm) after sterilization (ventilation time, 2 sec). MATERIAL PE TPE Storage time in) 5 10 30 90 Gasification 0. 5 3 3 3 Condensation _ 10 > 10 _ The results show that a significant amount of residual hydrogen peroxide was not obtained in the polyethylene. It is also possible to reduce the residual hydrogen peroxide to an acceptable level in the TPE containers that have been subjected to gasification in accordance with the present invention and then ventilated for a ventilation time as short as 2 seconds. Approximately 3 times more waste was obtained in the TPE bottles sterilized by means of condensation. This trend remained even with a ventilation time as short as 15 seconds (Table 2).

Table 2. Residual hydrogen peroxide (ppm) after sterilization (ventilation time, 15 sec). MATERIAL PE TPE Storage time min) 5 30 250 Gasification 0 0. 3 0. 1 Condensation 0. 8 0. 2 Thus, when gasified in accordance with the present invention, low residual amounts of the hydrogen peroxide used as the sterilization medium were obtained, together with an effective killing of microorganisms. This reduction in the number of microorganisms can also be increased by increasing the spray point (the concentration of the gas) or by prolonging the gasification phase. However, if the spray point is increased too much, the residual amount will be increased in the gasification process according to the present invention. The method of sterilization according to the present invention, preferably, is intended to be used to sterilize containers that are already ready to be filled and / or for packaging materials having a plastic surface, which may comprise polyester, for example terephthalate polyethylene. Nevertheless, the method is not limited to containers that are ready to be filled. On the contrary, it is an advantage if a container is sterilized under "preformed" conditions, that is, before, for example by means of a blow molding, it has its final shape, which has a difficult geometry from the point of view of sterilization. In this case, smaller residual amounts per unit area will be obtained in the finished container. Therefore, the packing material in the form of a sheet or a continuous band, like the containers ready to be filled, can be subjected to the four aforementioned phases, heating phase, gasification phase, holding phase and Ventilation phase, the sterilization being carried out by means of the method according to the present invention. In this rd, the packaging material could be treated continuously. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Claims (5)

1. CLAIMS Having described the invention as an antecedent, what is contained in the following is claimed as property. 1. A method for sterilizing a plastic surface by means of hydrogen peroxide in the gas phase which is applied to the previously heated plastic surface, characterized by the complete sterilization process is carried out with hydrogen peroxide in the gas phase and the plastic surface is heated at a temperature higher than the dew point of hydrogen peroxide in the gas phase.
2. 2. The method according to claim 1, characterized in that the plastic surface comprises a polyester.
3. 3. The method according to claim 1, characterized in that the plastic surface comprises polyethylene terephthalate. .
4. The method according to claim 1 for sterilizing a packaging material for a container, characterized in that the packaging material having a plastic surface is sterilized before the container has been given its final shape.
5. 5. The method according to claim 4, characterized in that the packaging material having a plastic surface is continuously sterilized.