MXPA99003348A - A method of sterilizing containers based on fiber - Google Patents

Abstract

When autoclaving a fibre-based container the cycle time of the sterilizing process can be reduced by the heat transfer medium used for heating and/or the cooling, respectively, of the container being exchanged at a critical temperature for the container.

Description

A METHOD FOR STERILIZING FIBER-BASED CONTAINERS Description of the invention The present invention relates to a method for sterilizing fiber-based containers. More specifically, the invention relates to a method in connection with the autoclaving of a fiber-based container, the cycle time of the sterilization process being reduced. A heat treatment to kill and / or inactivate microorganisms can be carried out by means of moist heat as well as dry heat. In the food industry, heat treatment in moist heat is preferred since the mechanisms of death and biological inactivation are much more effective at a high water content than at a low water content, for example dry heat. In addition, heat transfer in the 'Equipment used for heat treatment is much more effective with moist heat. In a packaging material that has a base layer of paper or cardboard, this layer should be EF .: 29893 made relatively thick in order to give the vessel a necessary dimensional rigidity. However, the containers made from these laminates based on paper or cardboard have the drawback of rapidly losing their mechanical strength properties when subjected to liquid or moisture, which results in the container becoming soft and difficult to handle. Thus, such known containers, made from a packaging laminate with a layer of liquid absorbing fiber, can not be subjected to a thermal treatment with moist heat without deteriorating or losing the desired mechanical rigidity of the packaging laminate, and in this way the dimensional stability of the container. In order to avoid these problems, laminates have been developed for packaging which are adapted to withstand drastic conditions in the form of moisture and / or heat. Such Alternative known packaging material has, for example, a base layer of plastic reinforcement and a filler interspersed with the plastic. This material has proven to be less sensitive to moisture than previously used materials based on paper and cardboard. The containers manufactured from these laminates are very suitable for preservation by means of cooling as well as by heat. When a preservation by means of refrigeration is used, these containers with a solid and / or liquid filling material can be cooled by cooling with water. However, paper and cardboard are inexpensive packaging materials, and thus containers having a laminate with a base layer of one of these materials have been developed. Containers made from such laminated type material in the form of a sheet or net can be heat treated in a moist atmosphere at elevated temperatures. These laminates can, by means of folding, be used for the manufacture of dimensionally stable waterproof packaging containers, which are very suitable to be used at the most extreme conditions in a humid environment, including heat treatment with moist heat at a overpressure. Such severe environments include treatment in autoclaves at temperatures and periods that are accepted for food. This means that the laminate is also highly suitable to be used for the manufacture of a container that is routed to be filled with a product under aseptic conditions. In this context, the product is sterilized and filled under near-sterile conditions in a similarly sterilized container which after filling is sealed in such a manner that the product filled during storage is not re-infected with microorganisms before it is consumed. Such heat treatment of the containers is achieved with a thermal transfer medium containing water. In general, a thermal treatment with moist heat is used to overpressure in autoclaves which are filled with water or steam. In this context, an autoclave treatment cycle can be divided into a lifting time, a holding time, and a cooling time. The lifting time is the time from the start of heating until the desired temperature has been reached. At an overpressure of 0.5 bar, the vapor has a temperature of approximately 110 ° C, and at an overpressure of 1.1 bar the temperature becomes approximately 121 ° C. After the retention time, which is the time required to achieve a sterilization at the desired constant temperature, the pressure in the autoclave is lowered to a normal atmospheric pressure, and during the cooling time the temperature is lowered by cooling the autoclave. Since autoclaving is a sterilization method that uses overpressure, this method is mainly performed as a batch process and not continuously. In this way, it is of interest to enable the reduction of cycle time when sterilized in autoclaves. However, it has become apparent that when the aforementioned containers are thermally treated very extensively they are subject to environments whereby the good sealing properties of the containers against moisture and liquid are partially lost. Due to the soaking of the paper or cardboard layers there is thus a risk that the packaging material loses its mechanical strength properties and that the container becomes soft and difficult to handle. It is thus important that this type of containers be exposed to such environments to the lowest possible degree. In order to solve the aforementioned problems, the method according to the invention has been given the characterizing features of claim 1. When containers containing fiber are sterilized, the cooling of the containers has been previously carried out with air with In order to compensate for the problems mentioned above. However, it has been shown in connection with autoclaving that such containers, for example with a soaking layer of paper or cardboard, tolerate very well the heating up to a critical temperature, as well as the cooling with water in liquid phase as a means of heat transfer. Different types of material require different process times and / or different times for heating / killing / cooling. For all the treated, the critical temperature depends on the thickness of the base layer and the fiber content in its composition, but the other components of the packaging laminate are also important. In this way, the critical temperature varies between about 70 ° C and about 95 ° C, preferably between about 80 ° C and about 85 ° C. With a folded container, made from a material of the laminated type in the form of a sheet or web, which material comprises a base layer, an outer coating and an inner coating, the critical temperature can be as high as about 90 ° C. The sterilization of the filled containers by means of autoclaving is carried out in a cyclic course. Such a cycle comprises the aforementioned subsequent phases one to the other: lifting time, holding time, and cooling time. The thermal transfer time can, according to the invention, be exchanged during the lifting time and / or during the holding time. Since, for example, cooling with air is considerably lower than cooling with water, a combined cooling procedure for containers that are fiber-based and which can be subjected to autoclave heating, in which process the air is replaced with cooling with water, results in a shorter cooling time being achieved. In the corresponding way a steam heating is faster than spraying with water, which is a useful preheating method in relation to the thermal treatment processes. In this way, such exchanges of the heat transfer medium improve the efficiency of the sterilization cycle, and this in turn results in improved process economy. In this context, a heat transfer medium means an agent that transfers heat energy from or to the container. Suitable heat transfer means comprise, for example, water (in the liquid phase), steam, and air. During the cooling of a container after sterilization by means of for example heating in an autoclave, the heat transfer medium, according to the present invention, is exchanged at the I critical temperature, preferably air to water. Cooling below the critical temperature can also be achieved by spraying with cold water, if necessary with accompanying cooling with CO2 or NO2 in order to quickly achieve a sufficiently low temperature. With this in view, it is also possible to complete the cooling phase with dry air. In the same way, the heat transfer medium can be exchanged at the critical temperature during the heating of a container before sterilization in an autoclave. In summary, there are packaging materials that are exposed to environments that require good sealing properties of the container against moisture and liquid. Above a certain critical temperature, these materials can not fully resist eJ. negative effect of water on the mechanical properties of the packaging material. Consequently, the containers are exposed to these unfavorable conditions as briefly as possible, while maintaining the required sterilization effect. According to the invention, this is achieved by the heat transfer medium used for the heating and / or cooling of the container, respectively, being exchanged during heating and / or cooling of the container at a critical temperature for the container, when this it is sterilized by means of thermal treatment, preferably autoclaving. Preferably, the sterilization is carried out in an autoclave, the temperature of which is allowed to rise to the autoclave sterilization temperature, suitable for the application, whose temperature is maintained for a sufficient retention time. Then the container is cooled with a medium that does not contain water, whose medium is preferably air, below the critical temperature, temperature at which the medium is exchanged for water. Calculations from experiments in practice have shown that the process time can be considerably reduced by means of this steam-air-water cycle. Depending on the type of container, the cooling time may for example be shortened with approximately 10 minutes from the previous duration times of approximately 30-50 minutes.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following:

Claims (4)

1. A method in relation to autoclaving a fiber-based vessel, characterized in that during heating and / or cooling at a critical temperature for the vessel, the heat transfer medium used for heating and / or cooling is exchanged. , respectively, of the container.

2. The method according to claim 1, characterized in that the medium during cooling is exchanged from air to water.

3. The method according to claim 1, characterized in that the critical temperature is between about 70 ° C and about 95 ° C.

4. The method according to claim 3, characterized in that the critical temperature is between about 80 ° C and about 85 ° C.