Method for filling a plastic container

Abstract

The invention relates to a method for filling a plastic container (11), wherein an excess pressure is built up in the filled and closed container (11). The method comprises the following method steps: Filling the plastic container with a liquid and closing the filled plastic container. In a deformation step, the container, prior to being closed, is deformed by a mechanical force such that the cross-sectional shape of the container is changed and its volume is thereby increased. In a relief step, the mechanical force is removed once the container has been closed, as a result of which the volume contraction in the container causes an excess pressure to build up, and the liquid-filling height to rise.

Description

[0001] Method for filling a plastic container

[0002] Field of the invention

[0003] The invention relates to a method for filling a plastic container according to the preamble of claim 1.

[0004] State of the art

[0005] PET bottles are perceived as stiff and stable either because the wall thickness is increased or because they have internal pressure when filled and sealed.

[0006] PET has a poor barrier to water and water vapor. As a result, even thick-walled containers quickly lose some of their contents. The lack of water becomes noticeable through a vacuum within the bottle. Due to the vacuum, the bottles are sensitive to external forces and immediately deform. Consumers perceive such bottles as unstable. As the water loss progresses, the bottle collapses and ends up deformed and usually unsellable on the supermarket shelf.

[0007] PET bottles are therefore often artificially pressurized. Nitrogen is preferred for this purpose because nitrogen, as a liquid drop at a temperature of -195°C, can be easily added to the contents, allowing enough time for the container to be sealed before the drop converts to gaseous nitrogen. When the nitrogen evaporates, internal pressure is created within the bottle. This has allowed the weight and wall thickness of the bottles to be continually reduced, especially for still mineral water, iced tea, juice, cooking oil, etc.

[0008] Nitrogen is used because nitrogen migrates through PET more slowly than water. Water is polar, and PET, as a polar material, is not a good barrier. Nitrogen is nonpolar, and therefore PET can maintain internal pressure for a long time, despite simultaneous water loss.

[0009] However, not all bottles are suitable for this technology. Flat or oval bottles in particular have the problem that they become round due to the internal nitrogen pressure and lose their originally flat or oval shape. Another problem arises when filling PET bottles: Due to the fast-running filling machines, bottles often cannot be filled to the top because they would overflow. In some filling processes, the displaced volume of a filling lance must be taken into account, in others the foaming of the filling product. This argues for bottles with a larger headspace. The effect of the empty headspace is further amplified by the loss of water. However, bottles with a large empty headspace appear underfilled and are instinctively rated worse by the end consumer than bottles with a well-filled headspace.

[0010] Object of the invention

[0011] The disadvantages of the described prior art give rise to the task of creating an alternative possibility for pressure build-up in a filled, closed bottle, which is cost-effective and additionally provides a well-filled headspace.

[0012] Description

[0013] The stated problem is solved in a method for filling a plastic container by the features stated in the characterizing portion of patent claim 1. Further developments and / or advantageous embodiments are the subject of the dependent patent claims.

[0014] The invention is preferably characterized in that in a deformation step the container is deformed by a mechanical force before closing such that the shape of the cross-section of the container is changed and thereby its volume is increased. In a relaxation step the mechanical force is removed after closing the container, whereby as a result of the volume contraction an excess pressure builds up in the closed container and the fill level of the liquid increases. By increasing the bottle volume, caused by the deformation step, the container is placed in a pre-stressed state. Since the plastic container is elastic, the container springs back to its original shape as best as possible after relaxation. However, the filled liquid and the air in the enclosed headspace represent resistance. This leads to the container being pressurized.Through elastic volume contraction, the desired internal pressure can be built up in a targeted manner. The overpressure makes the bottle firmer to the touch and more stable for transport. Just as with nitrogen-based technology, the weight of the bottle and its wall thickness can be reduced. The material savings potential is 10-20% by weight. In addition, the increased volume of the container also gives it a larger headspace. As the deformed container is filled with liquid, the enlarged headspace can absorb foaming liquid, the volume of the filling lance, and any overflow. By relaxing the container, the head volume is also reduced and the fill level rises. As a result, the container is well filled when placed on the shelf and does not appear underfilled to the consumer.

[0015] In a preferred embodiment of the invention, the cross-section of the container has a smallest diameter, and the smallest diameter increases during the deformation step. The deformation step can more than double the volume as needed.

[0016] In a further preferred embodiment, the mechanical force is a compressive force and acts on the container in such a way that the smallest diameter increases. This allows the container to be quickly and precisely deformed using slides on the conveyor belt before filling. The slides compress the container horizontally, preferably at the points opposite the smallest diameter.

[0017] In a further preferred embodiment, the mechanical force is a tensile force and acts on the container in such a way that the smallest diameter increases. Suction cups can be used to generate the tensile force, which adhere to the outer wall of the container in the area of ​​the smallest diameter and pull the container apart horizontally.

[0018] In a particularly preferred embodiment, the container has an oval cross-section with a major axis with a largest diameter and a minor axis with a smallest diameter. The mechanical force acts as a compressive force along the major axis or as a tensile force along the minor axis. The oval cross-section can also have the shape of an ellipse. This shape can be expanded particularly well to a circular cross-section. Elastic volume contraction is very suitable for oval containers, as they return to the desired oval shape after the relaxation step and do not remain round.

[0019] It is particularly preferred if the cross-section of the container is given a substantially circular shape during the deformation step. This provides the container with the maximum possible increase in volume. It has proven expedient to perform the deformation step before filling the container. This ensures that the maximum filling volume is available during filling, which significantly simplifies filling and reliably prevents contamination of the container or production equipment due to liquid overflow.

[0020] In a further embodiment of the invention, the relaxation step is realized by expanding decorative elements attached to the container surface. This allows the relaxation to occur not only in the filling system after the mechanical force has been removed, but also slowly to prevent a sudden buildup of internal pressure. Appropriate labels or "sleeves," such as "stretch sleeves," are expanded by the restoring force of the elastic container, which leads to a slower buildup of internal pressure.

[0021] Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to the schematic representations. These are not to scale:

[0022] Figure 1 : the cross-section of an oval bottle before a deformation step;

[0023] Figure 2: the cross-section of the bottle during the deformation step;

[0024] Figure 3: the cross-section of the bottle after a relaxation step;

[0025] Figure 4: the side view of the bottle before the forming step;

[0026] Figure 5: the side view of the bottle during the deformation step;

[0027] Figure 6: the side view of the bottle after the relaxation step and

[0028] Figures 7a to 7c: three views for calculating the area and volume of a bottle filled according to the method according to the invention.

[0029] Figures 1 and 4 show a container, and in particular a bottle, in a cross-section and a side view. The container and bottle, respectively, are designated overall by the reference numeral 11. The bottle preferably has an oval or elliptical cross-section, as this shape is ideal for deforming the bottle. Before filling the bottle, it is mechanically deformed so that the bottle is approximately circular. If the bottle 11 is filled and closed and then mechanically released again, the fill level rises as a result of the volume reduction, and an increased internal pressure builds up. The principle of elastic deformation is used here so that the bottle 11 acquires a larger volume during the filling process, and internal pressure can subsequently build up in the bottle.

[0030] The oval cross-section has a major axis 13 with a largest diameter and a minor axis 15 with a smallest diameter. A mechanical force compresses the bottle 11 along the major axis 13 or expands it along the minor axis 15. This gives the bottle 11 the cross-section shown in Figure 2. The force can be applied as a compressive force, for example, via two opposing sliders acting on the major axis 13. The force can also act as a tensile force, for example, via two opposing suction cups acting on the minor axis 15.

[0031] After the deformation step, the cross-section has a shape that is as circular as possible, in which the volume of the bottle is significantly increased. A liquid 12 is poured into the deformed bottle 11 with the increased volume. After the bottle is sealed, the force is removed in a relaxation step. The bottle attempts to return to its original cross-sectional shape. In doing so, it compresses the liquid 12 and the air 14 located in the sealed headspace, building up internal pressure and increasing the fill level 16 of the liquid 12. This makes the bottle 11 mechanically more stable. The relaxed cross-sectional shape of the filled bottle is shown in Figure 3. This effect makes it possible to make bottles lighter because the mechanical stability is no longer determined solely by the material or the wall thickness of the bottle. The material savings potential is between 10-20%.In addition, the increased volume also creates an increased headspace. This increased headspace can be used during filling to absorb foam generated during filling, to compensate for the volume of the filling lance immersed in the container, or to prevent liquid from spilling over. The relaxation or the resulting internal pressure pushes the liquid 12 upwards and partially fills the headspace. This gives the bottle a level of fill that consumers perceive as positive. The overpressure makes the bottle firmer to the touch and more stable for transport. As with nitrogen-based technology, the weight of the bottle can be reduced.

[0032] Figures 7a to 7c are part of an illustrative example: Figures 7a, 7b, and 7c show three cross-sections with identical circumferences (U = 31.4 cm) but different areas. The areas were calculated using the formula for calculating the area of ​​an ellipse. For the volume calculation, a bottle height of 10 cm was assumed. Figure 7a corresponds to the initial cross-section of bottle 11 before the deformation step. The major axis a has a length of 15 cm, and the minor axis b has a length of 2.9 cm. The area is 33.9 cm. 2 and the volume is 339 ml.

[0033] If the cross section is deformed to a circle with a radius of 5 cm, the area changes to 78.5 cm 2 and the volume is 785 ml. The volume increases by 446 ml due to the deformation. After relaxation, the cross-sectional area is 53.7 cm 2and the volume is reduced to 537 ml. This reduces the volume by 248 ml, which can be used to create overpressure and to raise the fill level.

[0034] This illustrative example demonstrates the potential for generating large volume differences and thus excess pressure through elastic volume contraction. Typically, even a small deformation is sufficient to achieve the desired excess pressure.

[0035] Legend:

[0036] 11 containers, bottles

[0037] 12 Liquid

[0038] 13 Main axis, largest diameter

[0039] 14 Air

[0040] 15 Minor axis, smallest diameter of the container

[0041] 16 Filling height

Claims

1 . Method for filling a plastic container (11), comprising the following method steps: Filling the plastic container (11) with a liquid (12) and closing the filled plastic container (11), characterized in that - that in a deformation step, the container (11) is deformed by a mechanical force before closing in such a way that the shape of the cross-section of the container (11) is changed and thereby its volume is increased and - that in a relaxation step the mechanical force is removed after the container (11) has been closed, whereby an overpressure builds up in the container (11) as a result of the volume contraction and the filling level (16) of the liquid (12) increases.

2. Method according to claim 1, characterized in that the cross section of the container (11) has a smallest diameter (15) and in the deformation step the smallest diameter (15) is enlarged.

3. Method according to claim 1 or 2, characterized in that the mechanical force is a compressive force and acts on the container (11) in such a way that the smallest diameter (15) increases.

4. Method according to claim 1 or 2, characterized in that the mechanical force is a tensile force and acts on the container (11) in such a way that the smallest diameter (15) increases.

5. Method according to one of the preceding claims, characterized in that the container has an oval cross-section with a main axis (13) with a largest diameter and a secondary axis (15) with a smallest diameter and the mechanical force acts on the main axis (13) as a compressive force or as a tensile force on the secondary axis (15). Method according to one of the preceding claims, characterized in that the cross-section of the container (11) is given a substantially circular shape in the deformation step. Method according to one of the preceding claims, characterized in that the deformation step is carried out before filling the container (11). Method according to one of the preceding claims, characterized in that the relaxation step is realized by expanding decorative elements attached to the container surface.

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