Method for filling plastic containers

Abstract

The invention relates to a method for filling a plastic container (11), wherein an overpressure is accumulated in the filled and closed container (11). The method comprises the method steps of filling the plastic container with a liquid and closing the filled plastic container. In the deformation step, the container is deformed by a mechanical force prior to closing, such that the cross-sectional shape of the container is changed and the volume thereof is thereby increased. In a release step, once the container has been closed, the mechanical force is removed, as a result of which a volume shrinkage in the container results in an accumulation of overpressure and an increase in the filling height of the liquid.

Description

Technical Field

[0001] The invention relates to a method for filling plastic containers according to the preamble of claim 1 . Prior art

[0002] PET bottles are considered rigid and stable because of the increased wall thickness or because they have internal pressure when filled and closed.

[0003] PET has poor barrier properties to water and water vapor. Therefore, even thick-walled containers quickly lose part of their content. The missing water is noticeable by the vacuum in the bottle. The vacuum makes the bottles sensitive to external forces and they deform immediately. Consumers consider such bottles to be unstable. As the water loss progresses, the bottles collapse and eventually become deformed and are usually unsalable on supermarket shelves.

[0004] Therefore, PET bottles are usually provided with an artificial internal pressure. Nitrogen is preferably used for this purpose, since it can be easily added to the filling material in the form of droplets, where the temperature is -195°C and there is enough time to close the container before the nitrogen droplets are converted into gaseous nitrogen. When the nitrogen gasifies, an internal pressure is generated in the bottle. This makes it possible to continuously reduce the weight and wall thickness of the bottle, in particular for still mineral water, ice tea, fruit juice, edible oil, etc.

[0005] Nitrogen is used because it migrates through PET more slowly than water. Water is polar, and PET, being a polar material, is not a good barrier. Nitrogen is non-polar, and therefore PET can maintain internal pressure for a long time despite the simultaneous loss of water.

[0006] However, not all bottles are suitable for this technology. In particular, flat or oval bottles have the problem that they become rounded due to the internal nitrogen pressure and lose their initial flat or oval shape.

[0007] Another problem arises when filling PET bottles: Due to the fast-running filling machines, the bottles cannot often be filled to the very top, as they would overflow. In some filling processes, the displacement of the filling gun must be taken into account, in others, the foaming of the filling material must be taken into account. This is an argument in favor of bottles with increased headspace. The loss of water further enhances the effect of the empty headspace. However, bottles with a large unfilled headspace appear underfilled and are instinctively rated worse by the end consumer than bottles with a well-filled headspace.

[0008] Purpose of the invention

[0009] The disadvantages of the prior art described led to the object of creating an alternative possibility for accumulating pressure in filled, closed bottles, which is cost-effective and additionally provides a well-filled head space.

[0010] describe

[0011] In the case of a method for filling plastic containers, this object is achieved by the features listed in the characterizing part of claim 1. The dependent claims relate to developments and / or advantageous alternative embodiments.

[0012] Preferably, the invention is characterized in that, in the deformation step, before closing, the container is deformed by mechanical force so that the cross-sectional shape of the container changes and its volume is thereby increased, and in the pressure release step, once the container has been closed, the mechanical force is removed, so that the volume contraction causes an overpressure to accumulate in the closed container, and the liquid filling height rises. The container is placed in a prestressed state by the increase in the volume of the bottle caused by the deformation step. Since the plastic container is elastic, the container rebounds to its initial shape as much as possible after the pressure has been released. However, in this case, the liquid and air filled in the sealed head space represent resistance. This causes the container to be pressurized. By elastic volume contraction, the desired internal pressure can be accumulated in a targeted manner. Overpressure makes the bottle grip tighter and more stable for transportation. As with nitrogen-based technologies, the weight of the bottle or its wall thickness can be reduced here. The material saving potential is 10% to 20% by weight. In addition, due to the increase in volume, the container also has an increased head space. During the filling of the deformed container with liquid, the enlarged head space can accommodate the foaming liquid, the volume of the filling gun and the overflowing liquid. By releasing the pressure on the container, the head volume also decreases and the fill level increases. This means that when the container is on the shelf it is well filled and does not appear underfilled to the consumer.

[0013] In a preferred embodiment of the invention, the cross section of the container has a minimum diameter and during the deformation step, the minimum diameter increases. If necessary, the deformation step allows the volume to be more than doubled.

[0014] In a further preferred embodiment, the mechanical force is a compressive force and acts on the container in such a way that the minimum diameter increases. This allows the container to be deformed quickly and precisely before filling using slides on the conveyor belt. The slides compress the container in a horizontal direction, preferably at a point opposite to the minimum diameter.

[0015] In a further preferred embodiment, the mechanical force is a tensile force and acts on the container in a manner that increases the smallest diameter. A suction cup can be used to generate the tensile force, which attaches itself to the outer wall of the container in the region of the smallest diameter and pulls the container apart in the horizontal direction.

[0016] In a particularly preferred embodiment, the container has an oval cross section with a major axis of the largest diameter and a minor axis of the smallest diameter, and the mechanical force acts as a compressive force on the major axis or as a tensile force on the minor axis. The oval cross section can also have an elliptical shape. This shape can be particularly well expanded to a circular cross section. Elastic volume contraction is very suitable for oval containers because after the pressure release step, they return to the desired oval shape and do not remain circular.

[0017] It is particularly preferred that, during the deformation step, the cross section of the container is given a substantially circular shape. This gives the container the greatest possible volume increase.

[0018] It has proven to be advantageous to carry out the deformation step before filling the container. This means that a maximum filling volume can be achieved during filling, which makes filling easier and reliably prevents contamination of the container or the production equipment due to spillage of liquid.

[0019] In another embodiment of the invention, the pressure release step is achieved by expansion of a decorative element attached to the container surface. This means that the pressure release can not only occur in the filling system after the mechanical forces have been removed, but also slowly, so that the internal pressure does not suddenly accumulate. In this case, the corresponding label or "sleeve" (such as a "stretch sleeve") is stretched by the restoring force of the elastic container, which leads to a slower accumulation of internal pressure.

[0020] Further advantages and features will become apparent from the following description of embodiments of the invention with reference to the schematic drawings, in which:

[0021] Figure 1 : shows a cross section of an oval bottle before the deformation step;

[0022] Figure 2 : shows a cross section of the bottle during the deformation step;

[0023] Figure 3 : shows a cross section of the bottle after the pressure release step;

[0024] Figure 4 : is a side view of the bottle before the deformation step;

[0025] Figure 5 : is a side view of the bottle during the deformation step;

[0026] Figure 6 : is a side view of the bottle after the pressure release step; and

[0027] Figures 7a to 7c: are three views used to calculate the surface area or volume of a bottle filled according to the method of the present invention.

[0028] Figures 1 to 4 The container and in particular the bottle are shown in cross section and in side view. The container or bottle is indicated as a whole by the reference numeral 11. The bottle preferably has an oval or elliptical cross section, since this shape is ideal for deforming the bottle. Before the bottle is filled, it is mechanically deformed so that the bottle is brought into an approximately round shape. If the bottle 11 is filled and closed and then mechanically decompressed again, the filling height increases due to the reduced volume 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 then internal pressure can build up in the bottle.

[0029] The oval cross section has a major axis 13 of the largest diameter and a minor axis 15 of the smallest diameter. By mechanical force, the bottle 11 is compressed on the major axis 13 or stretched on the minor axis 15. This gives the bottle 11 Figure 2 The force can be applied as a compressive force via two opposing slides and act on the major axis 13, for example. The force can also act as a tensile force, for example via two opposing suction cups acting on the minor axis 15.

[0030] After the deformation step, the cross section has a shape that is as round as possible, wherein the volume of the bottle has increased significantly. Liquid 12 is filled into the deformed bottle 11 with an increased volume. After the bottle is closed, the force is removed in a pressure release step. The bottle tries to return to its initial cross-sectional shape. While doing so, it compresses the liquid 12 and the air 14 in the closed head space, whereby an internal pressure is built up and the filling level 16 of the liquid 12 rises. This makes the bottle 11 mechanically more stable. The decompressed cross-sectional shape of the filled bottle is as follows: Figure 3 As shown. Due to this effect, the bottle can be made lighter, since the mechanical stability is no longer determined solely by the material or wall thickness of the bottle. The material saving potential is between 10% and 20%. In addition, the increased volume also creates an increased head space. This increased head space can be used during filling to absorb foam generated during filling, to compensate for the volume of a filling gun immersed in the container, or to prevent liquid from overflowing. Due to the pressure relief or the internal pressure generated, the liquid 12 is pushed upwards and partially fills the head space. This allows the fill level of the bottle to be perceived as positive by the consumer. The overpressure makes the bottle grip tighter and more stable for transportation. As in the case of nitrogen-based technologies, the weight of the bottle can be reduced.

[0031] Figures 7a to 7c is part of an illustrative example: Figure 7a , Figure 7b and Figure 7cThree cross sections are shown with the same perimeter (U = 31.4 cm) but different surface areas. The surface area is calculated using the formula for calculating the surface area of ​​an ellipse. To calculate the volume, the bottle height is assumed to be 10 cm. Figure 7a corresponds to the initial cross section of the 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 surface area is 33.9 cm 2 , and the volume is 339ml.

[0032] If the cross section is deformed into a circle with a radius of 5 cm, the surface area becomes 78.5 cm 2 , and the volume is 785ml. Due to deformation, the volume increases by 446ml. After the pressure is released, the cross section is 53.7cm 2 , and the volume is reduced to 537ml. This reduces the volume by 248ml, which can be used to create overpressure and increase the fill level.

[0033] This illustrative example shows the possibility of generating a large volume difference and thus an overpressure by elastic volume contraction.Usually, even a small deformation is sufficient to achieve the desired overpressure.

[0034] List of reference numerals:

[0035] 11 Containers, bottles

[0036] 12 Liquid

[0037] 13 Major axis, maximum diameter

[0038] 14 Air

[0039] 15 Minor axis, minimum diameter of the vessel

[0040] 16 Filling height

Claims

1. A 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), It is characterized in that - in a deformation step, before closing, the container (11) is deformed by mechanical force so that the cross-sectional shape of the container (11) is changed and its volume is thereby increased, and - in a pressure release step, once the container (11) has been closed, The mechanical force is removed, whereby the volume contraction causes an overpressure to build up in the container (11) and the filling level (16) of the liquid (12) to rise.

2. The method according to claim 1, characterized in that The cross section of the container (11) has a minimum diameter (15), and during the deformation step, the minimum diameter (15) increases.

3. The 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 minimum diameter (15) increases.

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

5. The method according to any one of the preceding claims, characterized in that The container has an oval cross-section with a major axis (13) of maximum diameter and a minor axis (15) of minimum diameter, and the mechanical force acts as a compressive force on the major axis (13) or as a tensile force on the minor axis (15).

6. The method according to any one of the preceding claims, characterized in that During the deformation step, the cross section of the container (11) is given a substantially circular shape.

7. The method according to any one of the preceding claims, characterized in that The deformation step is performed before filling the container (11).

8. The method according to any one of the preceding claims, characterized in that The pressure release step is achieved by expansion of a decorative element attached to the container surface.

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