Device for measuring the permeation of a hollow body such as a container

Device for measuring the permeation of a hollow body provided with an opening such as a neck in particular, this device comprising a chamber in which the follow body is placed, on a support; this hollow body, when placed on its support, together with the chamber defining an internal space and an external space, the device being provided with means for providing sealing between the internal space and the external space, the sealing means comprising three seals, namely a first seal, a second seal termed the intermediate seal, and a third seal, these three seals being housed in grooves belonging to the body of the support, these seals projecting from the side edge of the support and being able and configured to bear against the internal face of the opening of the hollow body; the body of the support, the opening of the object and the seals thus define two spaces positioned between the internal space and the external space, a first space being bordered by a first seal and an intermediate seal, the second space being defined by the intermediate seal and a third seal.

CROSS REFERENCE TO RELATED APPLICATION

This application is a National Stage of International Application No. PCT/FR2006/002813 filed on Dec. 20, 2006, claiming priority based on French Patent Application No. 05 13165 filed Dec. 22, 2005, the contents of all of which are incorporated herein by reference in their entirety.

The present invention relates to a device for determining the permeation properties of a hollow body made of a material that is permeable to at least one gaseous element.

The invention especially applies to the field of packaging, such as plastic containers, intended to contain a liquid food product, optionally under pressure.

By way of example, the plastic container is a polypropylene or PET (polyethylene terephthalate or polyethylene glycol terephthalate) bottle.

The term “permeation” is understood here to mean any physical and/or chemical phenomenon resulting in the passage of a gas through the object studied.

The term “permeation” is especially understood here to mean the leakage of a gaseous element through microcracks in the wall of the object studied, or else the diffusion of the gaseous element through the wall of the object studied.

In the tester devices known from the prior art, that are used to test substantially flat objects, a carrier gas, for example nitrogen, is circulated in a first chamber and a tester gas, for example oxygen, is circulated in a second chamber, the first and second chambers being separated by the wall of the object to be studied.

The stream from the chamber fed with carrier gas is sent to a chemical analysis apparatus, known per se, suitable for detecting the presence, or even measuring the amount of tester gas present in this stream.

This chemical analysis apparatus is, for example, a mass spectrometer.

When it is desired to study the permeation properties of a hollow body, such as a three-dimensional packaging made of a flexible material, in its geometry for subsequent use, it is known to place this hollow body in a tester gas atmosphere, and to circulate a carrier gas stream inside the hollow body, the stream that exits being conveyed to a detection and measurement apparatus. Reference may be made, for example, to documents U.S. Pat. No. 6,857,307 or US 2004/0040372.

It is of course impossible to place the hollow body under vacuum without irreversibly deforming it. Thus, in order to desorb the gaseous molecules present in the plastic of the hollow body, it is standard practise to circulate the carrier gas for several days in order to reach a steady state in which the permeation measurements may be carried out.

The time necessary to obtain this steady state is even longer when the wall thickness and/or internal volume of the hollow body is great.

In order to reduce this time for establishing a steady state, it has been proposed to reduce the pressure uniformly on either side of the wall of the hollow body.

The Applicant has observed that significant measurement errors may be linked to an artifact originating from a loss of sealing between the internal volume of the hollow body and the volume surrounding the hollow body.

The Applicant has observed, in particular, that when the hollow body to be studied has an opening especially such as a neck, which is the case, for example, for bottles, the conventional devices do not make it possible to guarantee a satisfactory sealing at the bottle neck.

The Applicant has set out to overcome these problems.

For this purpose, the invention relates, according to a first aspect, to a device for measuring the permeation of a hollow body provided with an opening such as, in particular, a neck, this device comprising a chamber in which the hollow body is placed on a support; this hollow body, when placed on its support delimiting with the chamber an inner space and an outer space, the device being provided with sealing means between the inner space and the outer space, the sealing means comprising three seals, namely a first seal, a second seal known as an intermediate seal, and a third seal, these three seals being housed in grooves of a body of the support, these seals jutting out relative to the side edge of the body of the support and being able and configured to bear against the inner face of the opening of the hollow body; the body of the support, the opening of the hollow body and the seals thus delimiting two spaces positioned between the inner space and the outer space, a first space being bordered by a first seal and an intermediate seal, the second space being delimited by the intermediate seal and a third seal.

The device has, according to several embodiments, the following, where appropriate combined, characters:the device comprises means that make it possible to maintain a given fluid pressure in the second space, said means advantageously comprising a duct inside the body of the support and connected to a source of compressed gas;the device comprises means that make it possible to detect a gas leak in the first space, a leak originating either from the second space, or from the chamber in which the hollow body is placed. One way that can be envisioned for controlling this leak may be to detect a pressure variation in said space, said means then advantageously comprising a duct inside the body of the support and that connects a pressure sensor to the first space; another way may be to detect a change in the composition or concentration of the gas contained in said space, said means then advantageously comprising a duct inside the body of the support and that connects a suitable detector such as a spectrometer to the first space;the body of the support is substantially cylindrical and three tiered annular grooves that house the seals are arranged at the periphery of the body of the support;the three seals are substantially identical and equidistant;the body of the support juts out from a base, this base being placed on a pedestal, a seal being placed between the base and the pedestal, two half shells covering the base and forming a support stand for a bell jar that delimits the chamber, the body of the support passing through a cutout in the half shells; andwhen the hollow body is in place, the pressure in the first space is substantially equal to atmospheric pressure, and the pressure in the second space is greater than the pressure in the inner space.

Reference will be made toFIG. 1.

Represented in thisFIG. 1is a hollow body1placed in a chamber2. This hollow body1thus delimits an inner space3and an outer space4which are separated from one another. More specifically, the inner space3is formed by the inside of the hollow body1and the outer space4is that which surrounds the hollow body1in the chamber2. A support7, which will be explained in detail later on, holds the hollow body1and isolates it from the outside. A tester gas, such as for example helium, is introduced into the inner space3. The pressure in the inner space3is, for example, around 1 bar.

The outer space4is connected to a detection and measurement apparatus, such as a mass spectrometer5.

The outer space4is placed under vacuum relative to the inner space3so that, when the hollow body1to be tested is permeable, a migration of the gas that it contains is promoted in the direction of the outer space4, which causes a change in the composition of the tester gas that can be detected by the mass spectrometer5.

Reference will now be made toFIG. 2.

A hollow body1such as a bottle6is intended to be placed, neck down, onto a support7. This support7comprises a base8, a pedestal9and a support body10that juts out to receive the hollow body1.

The base8is disk-shaped and rests on the pedestal9. An O-ring11is placed on the lower part of the base8. A cowling, formed from two half shells12,13covers the base8. For this purpose, each half shell comprises a skirt14and an upper part15transverse to the skirt14. Each half shell is also equipped with a cutout16through which the support projection10passes.

The outer space4is delimited by a bell jar17which rests on the cowling formed by the two half shells12,13.

The means that make it possible to maintain a satisfactory seal between the inner space3and the outer space4will now be described.

The body10of the support7is of cylindrical shape and is equipped with three tiered outer annular grooves18,19,20.

Each of these three grooves18,19,20houses a seal21,22,23. The seals bear against the inner face24of the neck25of the hollow body1, the neck being constituted here by the throat of the bottle6, when this bottle6is forced over the body10of the support7. This is because the seals21,22,23jut out beyond the side edge of the body10of the support7.

In one implementation, as represented, the seals21,22,23are substantially identical.

Underneath the first lower seal21, in the space26next to the lip27, the pressure of the outer space4prevails.

Between the first lower seal21and the second intermediate seal22an annular space28is delimited in which atmospheric pressure prevails, which is none other than ambient pressure when the neck25is forced over the body10that juts out from the support7.

Between the second intermediate seal22and the third upper seal23an annular space29is delimited in which a controlled pressure prevails. Advantageously, this controlled pressure is greater than the pressure in the inner space3(above the third seal23).

For this purpose, a first duct30keeps a gas, for example air, under pressure in the space29, this duct30comprising a lower axial part inside the body10and an upper radial part that emerges between the second seal22and the third seal23.

Advantageously, a second duct31connects the annular space28, in which a pressure equal to atmospheric pressure prevails, to a leakage sensor such as a pressure sensor (not represented). This duct31comprises a lower axial part inside the body10of the support7and an upper radial part that emerges between the first joint21and the second joint22. The pressure sensor makes it possible to detect a loss of sealing between the first and the second seal and also a loss of sealing between the second and the third seal, and consequently between the inner space3and the outer space4. Instead of the pressure sensor, a gas composition or concentration detector, such as a spectrometer, could be used in order to detect a change in the composition, symptomatic of a modification of the nature of the gas in the space28, linked to a leak, especially between the inner space3and the outer space4.

It is understood that the terms “first”, “second”, “third”, “lower”, “intermediate” and “upper” are not limiting.

These terms are used in order to facilitate the reading of this description for the seals21,22,23with reference to the positioning of the neck25with its opening pointing downward, the body10of the support that juts out being oriented toward the top of the device.

This orientation corresponds to that which is conventional in commercial devices, which in fact facilitates the positioning and holding of the bell jar17.