NL8502528A - Package gas leak testing system - subjects to varying external gas pressure and measures wall distortion - Google Patents

Abstract

The system tests a package partly filled with a product and sealed for gas leakage, the package having a distorting wall section. It is subjected on all sides to a varying gas pressure different from atmospheric to a predetermined pattern and ending with atmospheric pressure. Distortion of the wall section is measured at two or more pressure levels, the difference between them being used as a yardstick for the degree of gastightness.

Description

855O93 / vdV / Ba / kd

Short indication: Method and device for determining the gastightness of a package.

The invention relates to a method for determining the gastightness of a partially filled and closed product package of which at least one wall part is deformable.

In particular for relatively rigid plastic containers sealed with a thin film, which is an adhesive or heat treatment has bonded to the rim of the container, but also for flexible plastic bags, where the edges of the opening are joined together in the same manner, it is desirable if not required to have a method which is conclusive can give information about the gas- and in particular airtightness of the packaging, since in some countries the use of such packaging is only accepted if every delivered, filled packaging has been checked for airtightness and has been approved.

The packaging may leak due to a number of causes, namely: - imperfections in the sealing seam, as a result of which it is locally interrupted; 20 - not sealed from the lid film or flexible bag material due to manufacturing defects or damage; - not being closed from the rigid plastic container due to manufacturing defects or damage.

The object of the invention is to provide a method for the presence of a leak in a package not being completely filled with product in a very simple and rapid manner, wherein the gas pressure in the head space of the package is atmospheric or slightly under-atmospheric .

The method according to the present invention provides this possibility and is therefore characterized in that a package is subjected on all sides to a changing gas pressure deviating from the atmospheric pressure according to a predetermined pattern. and ending with atmospheric pressure, wherein the deformation of the deformable wall part is measured at at least two pressure levels of the run through pressure range and the difference between the measured values is determined as a measure of the grass density.

By measuring the deformations of the deformable wall part at at least two pressure levels and determining the difference between those deformations, it is possible to distinguish quickly and easily between gas-tight and non-gas-tight or leaky packages.

The manner of measuring the deformation of the deformable wall part of the packages is known in the art.

Mention can be made of measuring the deformation by mechanical scanning of the deforming surface; optical measurement by distance measurement from a fixed point 20 or determination of deformation by changing the reflection against the deforming surface. These and other methods can be applied; this will not be further discussed in the present description since these skilled persons are generally known.

In particular, in the method according to the invention, the pressure range passed through will be an underpressure range.

As will be apparent from the examples, however, the method is not limited to the use of an underpressure range; Also when using an overpressure range and when using both an underpressure part and an overpressure part of the range, the method according to the invention will be made possible to make a good distinction between gastight and leaky packages.

According to a particular embodiment of the working method, the return to atmospheric pressure takes place quickly; in another embodiment, the return to atmospheric pressure takes place in at least two steps. ,

The invention is also embodied in a device for determining the gastightness of partially product-filled and closed packages consisting of means for supplying and discharging the packages and means for determining the airtightness, which method is characterized in that the means for determining the gas density are formed by: a closable chamber in which at least one package can be accommodated; means connected to the chamber for changing the gas pressure in the chamber according to a predetermined pattern and means for determining the deformation of a deformable wall part of the packaging present in the chamber.

The method according to the invention will now be elucidated on the basis of a number of examples, in which, as packaging, one can think of a tub-shaped packaging made of relatively rigid plastic, which is filled with a product and leaving a small head space, and sealed. is fitted with a thin-walled deep-drawn cover made of foil material which is sealed on the rim of the tub. One can also think of a bag-shaped packaging made entirely of deformable plastic (also called 25 pouch).

The headspace pressure of a tightly closed package may be atmospheric or slightly sub-atmospheric.

For further consideration, the following three cases are distinguished: 1. The packaging is well gastight; 2. The packaging has a small leak, such that when the ambient pressure changes, equalization of the pressure in the head space with the ambient pressure is delayed; 3. The package has a greater leak, such that when the ambient pressure changes, the pressure equalization in the 8502528 one head space with the ambient pressure proceeds almost immediately.

The invention will now be explained with the aid of the drawing, in which:

Fig. 1a - represents a tub-shaped package made of plastic which is closed with a thin-walled deep-drawn foil cover, which is sealed on the rim of the tub;

Fig. lb - represents a bag made entirely of thin-walled plastic, a so-called "pouch"; FIG. 2 - shows an ambient pressure / time graph for a package with underpressure in the head space and an underpressure range.

Fig. 3 - represents a graph as in fig. 2 for a packaging with underpressure in the head space and an overpressure range 15;

Fig. 4 - shows a graph as in fig. 2 for a package with atmospheric pressure in the head space and a negative pressure range;

Fig. 5 - shows a graph as in fig. 2 for a package with 20 atmospheric pressure in the head space and an overpressure range.

The following tables show the deformation behavior of containers as in Figures 1a and b when the printing paths according to Figures 2 to 5 are run through.

25

TABLE I

Packaging with negative pressure in headspace Negative pressure range; Fig. 2 Measuring points 1, 2, 3 and 4 (2) - (1) (3) - (2) (4) - (3) 30 Packaging closed 0 ++ 0

Small leak + + +

Large leak 0 0 0 85 0 2 oZq -5- 01 '

Key ï 0 = no deformation + = deformation sphere ++ = strong deformation sphere = deformation hollow 5 - = strong deformation hollow

TABLE II

Packaging with negative pressure in headspace Overpressure range? Pig. 3 Measuring points 5 and 6 10 (6) - (5)

Packaging closed 0

Small leak +

Large leak 0

TABLE III

15 Packaging with atmospheric pressure in headspace Negative pressure range: Fig. 4 Measuring points 7, 8, 9 and 10 Pressure range a (trailed) (8) - (7) (10) - (8) 20 Packaging closed ++ 0

Small leak +

Large leak 0 0

Pressure range a to 8, then dotted pressure range b via 9.

(8) - (7) (9) - (8) 25 Packaging closed ++ +

Small leak + 0

Big leak 00

TABLE IV

Packaging with atmospheric pressure in headspace 30 Overpressure range; Fig. 5

Measuring points 11 and 12 3502 Ολο -6- (12) - (11)

Packaging closed O

Small leak +

Major leak 0 5 Discussion of the results:

Tables I and II show that it is especially possible with the measurements from Table I to distinguish dense from leaky containers. Measurement (2) - (1) makes it possible to remove the packages with a small leak? measurement 10 (3) - (2) makes it possible to distinguish from the remaining containers between dense, thus good, packaging and packaging with a large leak.

Measurements according to Table II are suitable if no large leaks can occur in the packaging by, for example, the choice of material or another check for large leaks beforehand.

In table III, measurement (8) - (7) - gives the possibility to immediately separate the packages with a large leak? measurement (10) - (8) then makes a distinction between the packages 20 which are completely gastight and packages with a small leak.

According to pressure range a to 8 and then part b through 9, it would be possible by measurement (9) - (8) to identify the complete dense packages in one go. In that case, however, the behavior of a package with a small leak is questionable, so that measurement according to pressure range a is nevertheless preferred.

In Table IV, the measurements (12) - (11) immediately give the possibility of removing packages with a small leak.

Such a measurement would be suitable for use if large leak packages could otherwise be identified, as indicated in Table II.

In figures 2 and 3 it holds that for a good, gastight packaging the gas pressure in the head space P ^ is smaller than the normal air pressure P atm? if a leak is present, P 2 = P atm. In figures 4 and 5 it holds that for a good, gastight packaging approximately equals Patm- or Pk 2a: Patm.

A 5 Ö 9 * "ft

W v V i. W w V

Claims (6)

Method for determining the gastightness of a partly product-filled and closed packaging of which at least one wall part is deformable, characterized in that a packaging is subjected on all sides to a changing gas pressure which deviates from the atmospheric pressure a predetermined pattern and ending with atmospheric pressure, wherein the deformation of the deformable wall part is measured at at least two pressure levels of the run through pressure range and the difference between the measured values is determined as a measure of the gas density. 2. A method according to claim 1, characterized in that the pressure path traversed is an underpressure path. IS Method according to claims 1 and 2, characterized in that return to atmospheric pressure takes place quickly. 4. Method according to claims 1 and 2, characterized in that return to atmospheric pressure takes place in at least two steps. 5. A method according to claim 1, characterized in that the printing range comprises both an underpressure section and an overpressure section. 6. Device for determining the gastightness of partially-filled and closed packages consisting of means for supplying and discharging the packages and means for determining the airtightness, characterized in that the means for determining the gas densities are formed by: a closable chamber in which at least one package can be accommodated; means connected to the chamber for changing the gas pressure in the chamber according to a predetermined pattern and means for determining the deformation of a deformable wall part of the packaging present in the chamber. 8502 52 8