EP0299821A1 - Device for filling trays with a neutral gas - Google Patents

Abstract

A device for filling trays, containing foodstuffs, with a neutral gas, installed in a mould above which is placed a bell-shaped element which applies and seals a closure and protection film on the trays. The device comprises a pipe (8b) for creating a vacuum and filling the volume of the tray with a neutral gas, a reserve 12 of neutral gas at atmospheric pressure connected to the pipe (8b). The reserve comprises a chamber and a wall (27) which can be deformed, the reserve supplies a tray with gas at atmospheric pressure and is supplied by a reservoir (14) of compressed gas. <IMAGE>

Description

The present invention relates to a device for filling neutral gas with plastic trays containing fresh products, in particular food products.

It is known to produce plastic trays by the thermoforming technique: above a metal bench comprising cells or molds, a sheet of plastic material is brought in to cover the cells. The sheet is then stamped and takes the form of trays by matching shapes. Stamping takes place hot, the sheet being either produced by extrusion immediately upstream of the stamping bench, its temperature being still high, or warmed before stamping.

The sheets thus have a large quantity of trays which are then filled with product and then closed and protected by a flexible plastic film.

At the time of closing it is essential to expel the air which is in contact with the product in order to avoid any fermentation.

When the product to be preserved is dry (grains for example) it is possible to make only the vacuum without replacing the air sucked by another gas, but when the product to be preserved is a fresh product (for example meat, cooked dish ,. ..) the container cannot be closed under vacuum, for reasons of presentation, and the air is replaced by a neutral gas. The closure film must be flat on the tray because a more or less domed appearance of the surface suggests fermentation and the tray cannot be sold. It is therefore important that the quantity of neutral gas is equal to the quantity of air withdrawn.

This substitution of air by neutral gas is usually carried out in an apparatus which comprises a bench surmounted by a bell for welding the closure film. The bench comprises molds, of shapes identical to those of stamping, in which the trays are housed. At the bottom of the molds a pipe is connected to a vacuum pump. This vacuum called "lower vacuum" keeps the tray against the walls of the mold. The bell includes:
- a cold plate against which a flexible plastic film is extended,
- around the plate, a heating iron to weld the film to the tray,
- and above a pipe connected to the vacuum pump to achieve the "upper vacuum" above the film.

Air suction pipes from the tray connected to the same vacuum pump are housed in the sides of the bench and open into the top of the tray through perforations made on the horizontal upper edges of said trays (the vacuum thus produced is called "empty package").

An apparatus of this kind is described in US Pat. No. 3,659,393. However, this apparatus creates the lower vacuum and the pack vacuum through orifices which communicate in a common pipe, and which serves as a filling pipe for neutral gas. Therefore, the injection is defective because the vacuum is not maintained under the tray during filling. This is why we generally provide separate pipes for the three voids, and even secondary pipes. parallel to the previous ones for the injection of neutral gas.

When the lower and upper voids are produced, the air is extracted from the interior of the tray until the voids are balanced; then pressurized neutral gas is injected.

In fact, for practical reasons of production rate which must be as fast as possible and cost of installation, we use a common vacuum pump, and we simultaneously vacuum in the three parts of the volume (lower, upper , package) using a single control valve. However, the trays obtained frequently have a major defect: the surface of the upper film is concave. It is assumed that this is due to the fact that the tray is not pressed against the bottom wall by a lower vacuum produced in priority.

An attempt has been made to solve this problem by playing on the sections of the suction lines and on the pressure drops, so as to achieve the package emptiness last. But this solution is to the detriment either of the duration of creation of the vacuum and therefore of the production rate, or of the quality of the vacuum: the air still present in the tray, even in small quantities, remains a very significant drawback.

The quantity of neutral gas to be injected is controlled by a very sensitive pressure gauge or vacuum gauge generally located in the suction line of the "empty package". This quantity injected under pressure must be very rigorously controlled because when the tray is subjected to atmospheric pressure, it is essential that the protective film is flat and not convex or concave.

And precisely, the quantities of gas are difficult to control because the pressure gauge partly measures the dynamic pressure of the incoming gas and not only the static pressure. In addition, the measurements are variable since the volume to be injected depends on that occupied by the product, and it is not possible to determine correction coefficients for manometric measurements. As a result, the injection is often stopped when there is already too much gas, or not enough.

To the preceding difficulties is added the fact that when the product is hot, for example at a temperature of the order of 25 to 30 ° in addition, the injected gas gradually expands, considerably increasing the measurement difficulties.

The objective of the present invention is to remedy these drawbacks and to propose a device which ensures automatic filling of the exact quantity of gas necessary for obtaining a flat surface of the closure sheet.

A second objective of the invention is to propose an air evacuation process which improves the quality of filling of the trays with neutral gas, while not slowing down the production rate.

The subject of the invention is a device for filling food trays with neutral gas, of the type comprising a lower mold intended to receive the tray, an upper bell intended to apply and seal a sealing and protective film on the tray, the bell comprising a volume evacuation pipe located above the film, the mold comprising a volume evacuation pipe located between the tray and the mold, characterized in that it comprises:
- At least one line for evacuating the interior volume of the container, and at least one gas filling line for said volume of the container;
a reserve of neutral gas at atmospheric pressure connected to the filling pipe, the reserve supplying the tray with gas at substantially atmospheric pressure according to the request of said tray, and
- a compressed gas tank intended to supply the reserve automatically according to its needs.

• 1°- lorsque le gaz neutre est aspiré vers la barquette, une dépression s'en suit dans la réserve, déforme la membrane et éloigne la cible du capteur ;
• 2°- selon la distance séparant la cible et le capteur, soit le capteur détecte la présence et l'alimentation en gaz est coupée, soit il ne détecte pas la présence et l'électrovanne alimente la réserve en gaz neutre.

- les conduites de mise sous vide du volume intérieur de la barquette et de remplissage sont confondues;
- la (ou les) conduite de mise sous vide et de remplissage du volume intérieur de la barquette est logée dans les flancs du moule;
- la conduite de mise sous vide et de remplissage du volume intérieur de la barquette est placée dans une buse pincée entre le moule et la cloche supérieure, disposée sur la face arrière du dispositif;
- le film d'obturation est à bande étroite, la conduite de mise sous vide du volume intérieur de la barquette est confondu avec la conduite de mise sous vide supérieur, et la conduite de remplissage dudit volume de la barquette est placée dans une buse pincée entre le moule et la cloche supérieure disposée sur la face arrière du dispositif;The device according to the invention is also remarkable for the following characteristics:
- The neutral gas reserve comprises at least one chamber and an at least partially deformable wall so that the volume of the reserve is variable;
- It includes means for measuring the deformation of the deformable wall, these means being connected to a supply solenoid valve disposed between the reserve and the reservoir.
- It includes at least one member for controlling the deformation at rest of the deformable wall, preferably of the type with adjustable elastic resistance, in order to control the shape of the film when the tray is closed;
- It comprises a first chamber with rigid walls, a second chamber communicating with the first comprising a deformable membrane subjected on one side to atmospheric pressure, on the other to the pressure of the gas in the reserve, and in that the means of deformation measurement are of the proximity detector type comprising a target arranged on the membrane to move as a function of its deformations, and a sensor aligned with the target and connected to a signal amplifier itself connected to the solenoid valve, the sensor being intended to detect the presence of the target, so that:

• 1 ° - when the neutral gas is sucked towards the tray, a vacuum follows in the reserve, deforms the membrane and moves the target away from the sensor;
• 2 ° - depending on the distance between the target and the sensor, either the sensor detects the presence and the gas supply is cut, or it does not detect the presence and the solenoid valve supplies the reserve with neutral gas.

- the lines for evacuating the interior volume of the tray and for filling are combined;
- The line (s) for evacuating and filling the interior volume of the tray is housed in the sides of the mold;
- The vacuum and filling line for the interior volume of the tray is placed in a nozzle pinched between the mold and the upper bell, disposed on the rear face of the device;
- the sealing film is a narrow strip, the line for evacuating the interior volume of the tray coincides with the upper vacuum line, and the line for filling said volume of the tray is placed in a pinched nozzle between the mold and the upper bell disposed on the rear face of the device;

• 1) inférieur,
• 2) supérieur,
• 3) paquet,

les conduites d'aspiration étant d'une section la plus grande possible, afin d'éviter les résistances à l'aspiration, les opérations d'aspiration étant séparées les unes des autres par des fermetures des vannes, des conduites respectives de telle sorte que les vides inférieurs et supérieurs appliquent étroitement respectivement la paroi de la barquette sur les parois du moule et le film contre la cloche, ce qui élimine toute fuite de gaz neutre dans les volumes inférieurs et supérieurs lors du remplissage.The subject of the invention is also a method of prior vacuuming of a device for filling food trays with neutral gas, characterized in that successively and in order we make the voids:

• 1) lower,
• 2) superior,
• 3) package,

the suction lines being of as large a cross-section as possible, in order to avoid resistance to suction, the suction operations being separated from one another by closings of the valves, respective lines so that the lower and upper voids tightly apply the wall of the container respectively to the walls of the mold and the film against the bell, which eliminates any leakage of neutral gas in the lower and upper volumes during filling.

The device according to the invention provides the following advantages:
- the state of the membrane represents the final state of the top sheet of the tray and can thus be fully controlled: it is possible to predict geographic or climatic situations different from those of the location of the operation: low pressure (altitude ), high temperature (countries or hot seasons);
- certain products absorb part of the injected gas (pastry doughs absorb CO2, vegetables absorb nitrogen, etc.): the invention, by its organs for controlling the deformation of the deformable wall, makes it possible to predict and correct this absorption by injecting an additional quantity of gas;
- It is also possible to voluntarily create a deformation of the protective sheet, this deformation then having the function of immobilizing the food product by concordance of shape.
the gas supply to the trays can be automated, the volume of the gas reserve at atmospheric pressure being automatically supplied as a function of the gas consumption of the trays.
- it is possible to condition hot products by first calibrating the presence detector as a function of the temperature of the product.

• - figure 1 : une vue schématique en perspective de l'installation de remplissage de barquette par du gaz neutre selon l'invention,
• - figure 2 : une vue schématique du dispositif de remplissage selon l'invention dans sa forme préférentielle.
• - figure 3 : une vue schématique en coupe transversale du banc de la figure 1,
• - figure 4 : une vue schématique en coupe longitudinale du banc dans une variante de réalisation,
• - figure 5 : une vue schématique en coupe transversale du banc dans une seconde variante de réalisation.

In order to better understand the invention, the following drawing shows:

• FIG. 1: a schematic perspective view of the installation for filling the container with neutral gas according to the invention,
• - Figure 2: a schematic view of the filling device according to the invention in its preferred form.
• FIG. 3: a schematic cross-sectional view of the bench in FIG. 1,
• FIG. 4: a schematic view in longitudinal section of the bench in an alternative embodiment,
• - Figure 5: a schematic cross-sectional view of the bench in a second embodiment.

FIG. 1 represents a metal bench 1 comprising molds 22. A plastic sheet 2 previously formed in trays 3 is placed on the bench; the trays being inserted into the molds, and garnished of food products 4. The sheet 2 has perforations 5 along its lateral edges.

On the bench 1 we see a bell 6 covering the plastic sheet 2 transversely over its entire width, and longitudinally along the length of a tray; this provision is not limiting, the bell can cover several trays.

A flexible plastic film 7 is inserted between the bell 6 and the sheet 2. It is intended to form the upper sheet of the tray and the bell is provided for sealing the film 7 along the edges of the tray.

The bench 1 and the bell 6 have pipes 8, 9, 10 connected to a common vacuum unit 11, controlled by valves 33, 34, 35 and necessary to produce the "upper", "lower" and "pack" voids ". The pipe sections are as large as possible in order to avoid resistance to suction.

Figure 1 also shows next to the bench 1 a neutral gas reserve box 12 connected on the one hand to the bench by a pipe 8b controlled by a valve 13 and on the other hand to a cylinder of compressed neutral gas 14 by a pipe 15 controlled by a solenoid valve 16.

3 shows a cross section of the bench 1 of Figure 1 at a mold 22 surmounted by the bell 6. The edges 17 of the bell 6 rest on the edges 18 of the mold by pinching the ends of the plastic sheet 2 and film 7 so that the volume between the bell and the mold is closed.

The bell is of the same constitution as in the existing devices described above: a cold plate 19, surrounded by a heating iron 20, and above a pipe 10 controlled by a valve to achieve the upper vacuum.

The mold 22 has a pipe 9 connected to the vacuum unit 11 below, and controlled by a valve 33, to produce the lower vacuum. The side walls 21 of the mold project inwardly to present a bearing surface for the iron 20 and to accommodate a pipe 8 for suction and filling. This pipe opens into the volume 30 of the tray located above the product through the orifices 5 and makes it possible to empty the package and fill the volume with gas 30. In this embodiment, the same pipe is used for the vacuum and filling but of course the existing molds, with separate pipes, can be used.

Line 8 is divided into two: line 8a is connected to the vacuum unit 11 and controlled by a valve 35 while line 8b is connected to the reserve 12 and is controlled by valve 13.

The neutral filling gas reserve box 12 shown in FIG. 2 has internally:
- A first chamber 23 with rigid walls, of volume much greater than that of volume 30, supplied by an inlet of neutral gas 25 coming from a bottle 14 or any other pressurized source, and provided with an outlet opening 26 connected to the filling valve 13.
a second chamber 24, communicating with the first 23, of variable volume, closed by a flexible deformable membrane 27 subjected on the outside side to atmospheric pressure so that any variation in the quantity of gas in the reserve 12 is accompanied by a deformation of the membrane 27, so now atmospheric pressure inside chambers 23 and 24.

Thus, the gas contained in the two chambers 23, 24 is, at rest, constantly at atmospheric pressure and when the valve 13 is opened, the volume 30 is supplied substantially at atmospheric pressure.

The deformation of the membrane is also used to determine the volume of neutral gas present in the reserve 12 and to trigger the opening and closing of the solenoid valve 16 supplying the reserve. To this end, measurement means are arranged in the vicinity of the membrane 27.

In the embodiment shown in FIG. 2, these means consist of a proximity detector. They include a target 28 disposed on the membrane 27 and a sensor 29 aligned with the target and connected to a signal amplifier 31. The sensor detects the presence of the target and sends an all-or-nothing signal to the solenoid valve:
. or it detects the presence of the target 28 on the membrane 27 and the signal it sends commands the closing of the solenoid valve 16: the supply to the reserve 12 is interrupted.
. either it no longer detects the presence of the target 28 (maximum target-sensor distance) and the signal it sends controls the opening of the solenoid valve 16 which then supplies the reserve 12. This maximum detection distance is the limit threshold deformation.

This means of detecting the variation in volume is not limiting and any other type of equivalent detector can be used.

The operation of the device is as follows:

1) a tray 3 containing a food product is installed in the mold 22 and covered with the protective film 7.

The bell 6 is positioned on this mold; the valve 13 being closed, the lower vacuum, the upper vacuum and the package vacuum are created.

In order to avoid any gas leakage in the lower volume between the mold and the tray during filling, it is necessary to operate as follows:
. the tray and the sealing film being in place, the three valves 33,34,35 are closed;
. the vacuum pump is started;
. then successively and in order, the valve 33 is opened for a duration t1, and it is closed (lower vacuum), the valve 34 is opened for a duration t2 and it is closed (upper vacuum), the valve 35 is opened for a duration t3 and we close it (empty package). Each duration t1, t2, t3 corresponds to the time necessary to obtain a predetermined maximum depression (of the order of a few millibars). These durations can overlap or juxtapose.
- The reserve 12 being previously filled with gas at atmospheric pressure, the valve 13 is then opened for a predetermined duration t4. The depression of the volume 30 then sucks the gas from the reserve 12. A certain amount of gas then flows from the reserve and the membrane deforms to maintain the internal pressure in the chambers 23, 24 at atmospheric pressure.

When the deformation reaches the limit threshold, the sensor no longer detects the presence of the target, the solenoid valve opens and the gas flows from the reservoir 14 into the chamber 23.

The gas flows from the chamber 23 to the tray 3 until the sensor again detects the presence of the target. The calibration of the detector can be carried out in such a way that the sensor detects the presence of the target when the atmospheric pressure is reached in the volume 30. When the volume 30 is filled, that is to say when the membrane is stationary , either at the end of the predetermined time t4, or by measuring the sensor, the valve 13 is closed and the film 7 can be sealed on the tray. The atmospheric pressure is then restored on each side of the tray and it is passed to the next tray.

This process of producing voids in successive staggered stages also brings the surprising advantage not only of not lengthening the total duration of the operation, but in certain cases of shortening it which makes it possible to increase the rate of the order 10%. This is all the more sensitive as the cross section of the pipes 8, 9, 10 is large.

Thus, with this device, the gas supply to the tray is carried out according to the needs of the tray and not by pressure injection as above.

It is possible to modify the gas demand of the tray by modifying the properties of the membrane and the values of the limit threshold of detection of the sensor. We can then provide a slight depression in the tray or conversely a slight overpressure; this makes it possible to predict significant geographic or climatic changes: hot seasons, high altitudes, for example.

For example, it is possible to modify the detection threshold either by modifying the position of the sensor at rest, or by modifying the sensitivity threshold; by modifying the detection threshold it is possible to close the solenoid valve 16:
- Either in a position of the membrane 27 where the chamber 24 is and remains in depression relative to atmospheric pressure as well as the volume 30, which allows to keep an upper film 7 curved inward.
- Either in a position of the membrane 27 where the chamber 24 is and remains in overpressure relative to the atomospheric pressure as well as the volume 30 which allows to keep an upper film 7 curved outward.

The device also makes it possible, by prior calibration of the detector as a function of temperature, to provide for the expansion of the neutral gas when hot products are packaged.

In addition, there is between the sensor 29 and the target 28 or between the target and the bottom wall of the chamber 24 an elastic member 32 of resistance, controllable, for example a tarable spring; this member is intended to control, that is to say to control, the shape of the membrane at rest. It is then possible to provide at rest a convex (or concave) shape of the membrane, in order to inject a quantity of gas into the tray, greater (or less) than the quantity corresponding to atmospheric pressure. For example in the case where the food contained in the tray is a pastry dough, the gas used being CO2, it must be injected in excess because it is partly absorbed by the dough. Such an organ makes it possible to control exactly this excess quantity to be injected.

The shape and dimensions of the chamber 24 are determined so that in the event of a detector or solenoid valve failure preventing the supply 12 of neutral gas, the deformation of the membrane 27 under the effect of significant depression, or limited to the interior contours of the chamber without rupture of the membrane. The hemispherical shape and the dimensions of the chamber thus determine a maximum safety deformation volume which prevents the membrane from tearing.

In addition, the dimensions of the chamber are used with the characteristics of flexibility and elasticity of the membrane when it is desired to obtain a significant depression in the tray, relative to atmospheric pressure. This is the case when the protective film 7 must surround and maintain the product in the tray (for example for pizzas, or other similar products).

Depending on the elasticity of the membrane and its fidelity, when the depression must be significant, provision is made for either a chamber 24 of large volume, or a membrane of great resistance (thickness and rigidity). The calibration of the device is then carried out for a volume of the chamber 24 and a membrane surface determined according to the resistance of the membrane.

Figures 4 and 5 illustrate two variants of the device according to the invention.

In FIG. 4, the device comprises a mold 22 devoid of conduits 8 for package vacuum 8a and filling 8b. These are replaced by a nozzle 36 connected to said lines 8a and 8b. The nozzle is arranged on the rear face of the device where the shutter film roll 7 is located, between the film 7 and the plastic sheet 2, and it is pinched between the bell 6 and the mold 22. The edges of the mold and of the bell which pinches the nozzle 36 have a flexible seal 37, intended to seal the volume located between the bell and the mold.

In FIG. 5, the device comprises a mold 22 devoid of conduits 8 for packet vacuum and filling, and the sealing film is "narrow band", that is to say of width reduced to that of the heating iron 20 The volume 38 between the bell 6 and the iron 20 communicates with the volume 30 of the tray. In this variant, a nozzle 36, partially shown, is used, intended only for filling the gas tray, and the package vacuum is produced at the same time as the upper vacuum via line 10 due to the communication of volumes 30 and 38.

Claims (10)

1. Device for filling food trays with neutral gas, of the type comprising a lower mold intended to receive the tray, an upper bell intended to apply and seal on the tray a sealing and protective film, the bell comprising a pipe for evacuating the volume located above the film, the mold comprising a line for evacuating the volume located between the tray and the mold, characterized in that it comprises:
- At least one vacuum (8a) and filling (8b) gas pipe for the interior volume (30) of the tray, at least one volume vacuum pipe (30) and at least one filling pipe .
- a reserve (12) of neutral gas at atmospheric pressure connected to the filling pipe (8b), the reserve comprising at least one chamber (23) and an at least partially deformable wall (27) so that the volume of the reserve is variable, the reserve (12) supplying the tray (3) with gas at substantially atmospheric pressure according to the request of said tray (3).
- a reservoir (14) of compressed gas intended to supply the reserve (12) automatically according to its needs. 2. Device for filling food trays with neutral gas according to claim 1 characterized in that the reserve of neutral gas comprises at least one chamber (23) and a wall (27) at least partially deformable so that the volume of the reserve (12) is variable. 3. Device for filling food trays with neutral gas according to claim 2 characterized in that it comprises means (28,29) for measuring the deformation of the deformable wall (27), these means being connected to a solenoid valve ( 16) supply disposed between the reserve (12) and the reservoir (14). 4. Device for filling food trays with neutral gas according to claim 2 characterized in that it comprises at least one member (32) for controlling the deformation of the deformable membrane (27). 5. Device for filling food trays with neutral gas according to claim 2 characterized in that it comprises a first chamber (23) with rigid walls, a second chamber (24) communicating with the first comprising a deformable membrane (27) subjected on one side to atmospheric pressure, on the other to the pressure of the gas in the reserve (12), and in that the means (28, 29) for measuring the deformation are of the proximity detector type comprising a target (28) arranged on the membrane to move according to its deformations, and a sensor (29) aligned on the target and connected to a signal amplifier (31) itself connected to the solenoid valve (16), the sensor intended to detect the presence of the target, so that: 1 ° - when the neutral gas is sucked towards the tray (3), a vacuum ensues in the reserve (12), deforms the membrane (27) and moves the target away from the sensor; 2 ° - depending on the distance between the target and the sensor, either the sensor detects the presence and the gas supply is cut, or it does not detect the presence and the solenoid valve supplies the reserve with neutral gas. 6. Device for filling food trays with neutral gas according to claim 1 characterized in that the vacuum lines (8a) of the interior volume (30) of the tray and filling (8b) are combined (8). 7. Device for filling food trays with neutral gas according to claim 6 characterized in that the (or) line (s) (8) for evacuating and filling the interior volume of the tray is housed in the sides of the mold. 8. Device for filling food trays with neutral gas according to claim 1 characterized in that the line (8) for evacuating and filling the interior volume of the tray is placed in a nozzle (36) pinched between the mold (22) and the upper bell (6), disposed on the rear face of the device. 9. Device for filling food trays with neutral gas according to claim 1 characterized in that the sealing film (7) is a narrow band, the pipe for evacuating the interior volume of the tray coincides with the pipe (10) of upper vacuum, and the pipe (8b) for filling said volume of the tray is placed in a nozzle (36) pinched between the mold (22) and the bell (6) upper disposed on the rear face of the device. 10. Method for placing under vacuum a device for filling food trays with neutral gas, characterized in that successively and in order, the voids are made:
1) lower,
2) superior,
3) package,
the suction lines (8a, 9,10) being of as large a section as possible, in order to avoid resistance to suction, the suction operations being separated from each other by valve closings ( 33, 34, 35), respective pipes so that the lower and upper voids closely apply the wall of the container respectively to the walls of the mold (22) and the film against the bell (6), which eliminates any leakage. of neutral gas in the lower and upper volumes during filling.

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