Patent Application
20110219731
The invention relates to a method for filling thin-wall containers including lids to be opened for use, wherein the containers due to their thin walls require an internal pressure to provide a necessary stability in a filled, closed state.
Thin-wall tear up containers of this type are known e.g. as beverage cans. Beverage cans of this type are often filled with carbonated beverages and obtain the necessary internal pressure through the carbon dioxide included in the beverage. Furthermore it is known e.g. from EP 0 906 222 to fill thin-wall containers with a non carbonated beverage and additionally with liquid nitrogen in order to provide the necessary internal pressure after the container is closed.
The containers of this type are closed tight with a lid after filling. The lid has to be opened in order to retrieve the useable content. At this moment the positive pressure in the interior of the container is lost rapidly. Thus, the inner pressure is used for stabilization during storage and transportation and differently from aerosol cans does not have to be maintained during use.
It has now become apparent that a desirable inner container pressure cannot always be adjusted precisely enough in the known manner.
A method is known from EP 1 686 062 A1, wherein activated charcoal and carbon dioxide in the form of dry ice pallets are introduced into the container for providing an internal pressure in the container. The gaseous carbon dioxide released by the dry ice pallets is then partially absorbed by the activated charcoal and released again when the internal pressure of the container drops. The method known from EP 1 686 062 A1 apparently has the disadvantage that it is not really suitable for food containers since they should not include any activated charcoal in addition to the food.
Thus, it is an object of the invention to provide a method which facilitates to adjust an inner pressure of a filled closed food container more precisely.
According to the invention the object is achieved through a method in which a thin wall container, e.g. a metal can is initially filled with useable material as a first filling material and subsequently filled with solid carbon dioxide, thus dry ice, as another filling material and the container is eventually closed tight. The dry ice evaporates (sublimates) subsequently already during the filling of the container and continues to evaporate after the container is closed tight. The evaporation of the dry ice after tightly closing the container facilitates building up a desired internal pressure. The advantage of using solid carbon dioxide instead of the known liquid nitrogen is that the evaporation rate of the solid carbon dioxide which substantially depends from the surface of the solid carbon dioxide is independent from the type of filling material. While e.g. a drop of liquid nitrogen distributes over a solid filling material like peanuts or similar and gets a large surface and thus evaporates quickly, the evaporation rate of the dry ice for liquid filling material like e.g. sterilized milk or also solid filling material like e.g. peanuts is approximately always constant. This means that the amount of carbon dioxide which evaporates after filling in the carbon dioxide and before closing the container tight is in any case substantially similar and in any case sufficient carbon dioxide remains in the container after the container is closed tight in order to be able to adjust the inner pressure in the tightly closed container in a reproducible manner. For liquid filling materials which have the capability to absorb carbon dioxide, however, it needs to be considered that the carbon dioxide which is dissolved in the beverage is not available anymore for providing pressure. Thus, the method according to the invention is suitable in particular for solid materials. For liquids particular requirements have to be fulfilled.
Preferably only dry ice is filled into the container as the only filling material besides the actual useable material, thus the content to be packaged which is to be sold or transported in the container, before the container is closed.
Preferably the volume of the dry ice filled into the container is between 1 g/l and 4 g/l with reference to a gas volume which is computed as a difference between a total volume of the container and the portion of the volume which is filled with a liquid or solid filling material. Such a volume of dry ice yields the desired inner container pressure after closing the container which is required for preventing the thin cylinder section shaped container walls from being crushed.
A preferred method includes e.g. the following method steps:
The preferred method is based on the finding that the sublimation of the dry ice at ambient pressure (1013 hPa) occurs in time frames which facilitate performing the gas tight closing of the metal can body within 500 seconds after filling with dry ice timely enough so that the desired high internal pressure is subsequently generated through additional sublimation of the dry ice remaining in the closed can without having to fill too much dry ice into the can. Thus, it is the goal not to have more than 50% of the dry ice originally filled into the can sublimate until the can is closed.
The filling material is preferably a material including particles which can also be a food material like e.g. nuts. Under certain conditions, this means considering a possible solubility of carbon dioxide in the respective liquid, the method can also be used for packaging liquids.
The container to be filled through the method is preferably a container with a thin wall cylindrical can body made from steel sheet material or aluminum sheet material which includes a total volume of 0.15 l or more and has a wall thickness at the cylindrical wall section between 0.05 mm and 0.12 mm. The can lid for closing the can body is preferably an aluminum lid which is connected gas tight through a gas tight double fold with the can body after filling the can body. As an alternative to closing the filled container with a metal cover (e.g. aluminum or tin plate) a closing can also be provided through a pressure tight can lid made from plastic material. Preferably lids, in particular metal lids are provided with a scored portion for tearing the lid up during use, thus a so-called tear up lid. Alternatively, however, it is also possible to use lids without the scored portion.
The invention shall now be described with reference to an embodiment based on the drawing FIGURE.
a illustrates a non-filled can body that is open on the top and made from thin wall steel or aluminum plate material. A cylindrical wall section 12 of the can body 10 has a wall thickness between 0.05 mm and 0.12 mm;
b illustrates the can body 10 of
c illustrates that subsequently to filling the can body 10 with filling material 14 dry ice 20 is filled into the can body 10. At normal ambient pressure the dry ice 20 starts to sublimate immediately, so that the gas cavity 18 fills with gaseous carbon dioxide.
d eventually illustrates that the can body 10 is subsequently closed gas tight through a lid 22, before all solid carbon dioxide is sublimated. The lid 22 is connected gas tight through a double fold 24 with the can body 10. After closing the container gas tight the conversion of the remaining solid carbon dioxide 20 into gaseous carbon dioxide continues and provides that the interior container pressure eventually reaches the desired level which is required for stabilizing its thin cylindrical walls. A suitable amount of solid carbon dioxide with reference to the gas volume is between 1 g/l gas volume and 4 g/l gas volume. The lid 22 is preferably applied within 500 seconds after filling the solid carbon dioxide into the can body 10.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 043 942.8 | Nov 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/065006 | 11/11/2009 | WO | 00 | 5/20/2011 |
