Chemical apparatus and process disinfecting – deodorizing – preser – Process disinfecting – preserving – deodorizing – or sterilizing – Using microwave energy
Reexamination Certificate
1998-08-07
2003-03-25
McKane, Elizabeth (Department: 1744)
Chemical apparatus and process disinfecting, deodorizing, preser
Process disinfecting, preserving, deodorizing, or sterilizing
Using microwave energy
C422S020000, C422S307000
Reexamination Certificate
active
06537492
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for surface sterilising items and a plant suitable for sterilising bottles.
From DE patent publication No. 40 18 142 a method is known for filling containers such as bottles, where microwaves are applies to the containers before filling for sterilising the containers. Humidity present on the surfaces of the containers evaporates, and the heat developed by the vapour kills undesired microorganisms on the surfaces. Before or during the treatment with microwaves, water may additionally be applied to or injected into the containers; thereby vapour is created due to the treatment with microwaves, said vapour killing the microorganisms. The development of steam is stated to take place in the course of a few seconds.
From the correspondence relating to the prosecution of Danish Patent Application No. 2354/89 a microwave packaging sterilising system for washing and sterilising plastic packagings is known, in particular for returnable bottles of polymeric plastic. In this system a washing of the packaging takes place at a temperature not exceeding 35-40° C. to prevent shrinking of the packaging. To obtain, with certainty, a visual cleanness of the packagings at this low temperature, ultrasound is used, making it possible to avoid addition of lye to the washing water.
The washed packaging is not sterile after washing at such a low temperature, and therefore a sterilising using microwaves is carried out after the washing.
It is stated in the correspondence as a fact that the packaging would be heated to a temperature above deformation temperature if it was subjected to microwaves in a wet condition. This is explained by the fact that high amounts of energy would be transferred to the remaining moisture in and on the packaging. To prevent the application of microwave from heating the plastic material above the deformation temperature, it is therefore stated in the correspondence that during the sterilising treatment with microwaves an exact control of the microwave energy should be exerted as well as a removal of moisture from the packaging by means of a drying and cooling flow of sterile air.
It is, however, not described in the correspondence how this control of the microwave energy is to be carried out. It is only stated that the packaging can endure big amounts of microwave energy when it is dried, as it has a crystalline crystal lattice structure and consequently is not influenced by the microwave energy which exclusively kills bacteria and spores because they are “organic”.
There is no detailed description in the correspondence of how the system is to be operated or worked in order not to heat the packaging in an inappropriate way and to in fact kill the microorganisms effectively, and it seems doubtful if a full sterilisation would be obtainable at all by following the instructions given in the correspondence.
Further, Swedish patent publication No. 462.281 discloses a method and an apparatus for sterilising empty packaging containers by application of steam under pressure, preferably at a temperature of 120-140° C., and preferably by additional use of hydrogen peroxide. Then microwaves are applied to the containers, which makes the temperature rise to around 145° C.
From Swedish patent publication No. 465.512 a method is known for sterilising a width of packaging material by spraying on a sterilising liquid such as hydrogen peroxide solution, which is then removed from the width of material by applying infrared light, microwaves, high-frequency energy or hot air.
Finally, German patent publication No. 34 14 268 discloses a method and an apparatus for killing germs in food containers, like for instance cups for dairy products, by applying hydrogen peroxide to the containers, the peroxide being atomized by means of ultrasound at a frequency above 1 MHz. At the end of the process the containers are subjected to a thermal treatment by means of hot air or microwave.
None of the methods described in these three publications may be used for sterilising heat sensitive items.
DESCRIPTION OF THE INVENTION
The object of the invention is to provide an effective surface sterilising of items which are penetrable by high-frequency electric energy, in particular items which do not withstand heat exceeding a certain limit. It is part of the object that a definite part of the surface of the item is to be sterilised. This part will often be the whole surface of the item, but if the item for instance is a container, the surface in question may be the whole interior surface of the item.
Important examples of said items are plastic containers which have been shaped by blow moulding or vacuum moulding in hot condition, for instance the commonly used returnable bottles for soft drinks made from PET (polyethylene terephthalate) or the likewise commonly used flat trays of vacuum-shaped PE (polyethylene) film, PS (polystyrene) film or the like for packing for instance meat products in self-service stores. Such containers often possess a so-called elastic memory or “residual activity”, by which is to be understood the phenomenon that the item may “remember” a shape and a size, which it had at an earlier stage of manufacture, and that it often is liable to return to this shape when heated.
Moreover, the items may for instance comprise containers for packing preserves or semipreserves (for instance translucent containers with screw lids for marmalade, herrings, etc.) or for packing non-preserved technical products like unpreserved plastic paint.
Said soft drink bottles are case as a so-called preform, i.e. a bottle in which the mouth area with thread etc. has its final size and shape, but in which the container part is quite small and thick-walled. These preforms take up very little room and may therefore at a low cost be transported from a central place of manufacture to various finishing places, often in other countries, where they are blown up in a hot condition for the container part to take up the desired shape and size. The container part may then be given a desired, individual shape according to the wish of the soft drink producer without the need for using different preforms.
It has turned out that these soft drink bottles tend to shrink on account of said elastic memory, already at temperatures slightly above 40° C. Therefore, known washing and sterilising processes are not suitable for cleaning such bottles, as the bottles are liable to shrink at the temperatures used in these known processes, typically around 60° C. or above. Such shrinking is obviously undesirable, and a major part of the bottles have to be discarded after having been cleaned a few times using the known processes.
At the same time there is a considerable need for an effective cleaning and sterilising of such bottles, as partly the owners (the soft drink producing factories) want them to be refilled with differing products without any preceding sorting, which, as evidenced by experience, may give a distaste from the previously contained product, and partly the users after emptying the bottles notoriously use them for the most differing purposes, like for instance storing of petrol or diesel oil, or refilling with different strongly tasting beverages, like a Danish fashion drink “sm{dot over (a)} gr{dot over (a)}” (“Small Gray Ones”; liquorice-and-ammonium-chloride-drops dissolved in vodka).
To meet the above object the present invention discloses a method, an apparatus and a plant.
The desired sterilising is obtained by heating a liquid film, and the heating is carried out by subjecting the item to high-frequency electric energy.
Experiments have shown that it is extremely important that the liquid to be heated by the high-frequency electric energy is actually present on the item in the form of a liquid film. Only in this way is the generation of a sterilising amount of heat ensured over the entire desired surface, without the heat development becoming so intense that an undesirable heating of the item itself takes place.
By providing the liquid
Diffclean A/S
McKane Elizabeth
Ostrolenk Faber Gerb & Soffen, LLP
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