EP0101391A1 - Process for producing wrappings for consumer goods by thermoforming thin aluminium-based sheets - Google Patents

Abstract

The invention is characterised in that the thermoforming profile is brought to the temperature of deformation by Joule effect heating and a non-heated mould is used, which is maintained at a constant temperature between room temperature and 100 DEG C. This permits the direct thermoforming of materials that are multilayers of aluminium and organic products, and also avoids any trace of lubricant, ensures sterilisation of the wrapping without any subsequent treatment and produces wrappings without creases. The invention is applicable for the packaging, in appropriate conditions of cleanliness and sterilisation, of products intended for consumption such as, for example, foodstuffs and pharmaceutical products. <IMAGE>

Description

The present invention relates to a method of manufacturing packaging for. consumable products by thermoforming thin blanks of aluminum or aluminum-organic multilayer materials.

In what follows, the term aluminum, without further specification, includes both the aluminum itself and the common aluminum alloys known in French standard AO2 104 under the designation 2002, 3003, 4047, 7020, 8011, 5754 and excludes special alloys such as so-called superplastic alloys.

The term multilayer aluminum-organic materials means all the complex products which combine an aluminum foil with at least one organic form in the form of one or more sheets of varnish, paints or films, or a combination of these various materials.

Thermoforming means a technique very similar to that well known and very commonly used in the plastics industry. It consists in carrying a thin-walled blank, most often a simple flat sheet, or even a preformed blank, at a temperature below the melting point of the material considered but sufficient to soften it and ensure it good plasticity. The blank is then given the desired shape by applying it to the surface of a mold by the action of a pressurized fluid combined or not with a mechanical effect. For blanks with a wall that is sufficiently malleable at the forming temperature, it is also possible to use simple atmospheric pressure by creating a vacuum between the blank and the surface of the mold.

Such a technique has been extended to the manufacture of thin-walled parts made of special aluminum alloys called superplastic alloys. These alloys and their shaping by thermoforming have been described in French patents 2,044,410, 2,146,847, 2,245,428.

In the thermoforming manufacturing process, the periphery of the metal blank is held in place by clamping between the edges of a two-part mule, without being deformed. This tightening ensures the seal between the inside and the outside of the mold. Only the portion of the blank located opposite the hollow (or raised) part of the mold undergoes plastic deformation by elongation of the metal wall in all directions, without there being any sliding of the periphery of the blank clamped between the edges of the two-part mold.

Special alloys, called superplastics, admit significant deformations without rupture, i.e. elongations of the order of 1000 to 2000%, this at temperatures between 0.3 Tf and 0.6 Tf, Tf being the absolute melting temperature of the alloy considered, expressed in ° Kelvin. These superplastic alloys make it possible to manufacture objects whose surface S ₁ is 3 to 4 times the surface S _O of the starting blank. The deformation of the blank must however be slow and require 4 to 10 minutes per operation. This technique is not suitable for rapid production of large quantities of consumer products.

As shown in European patent 1 198 of the company SCAL, the thermoforming process can also be used for the production of parts in aluminum (or in common aluminum-based alloys) other than parts in superplastic alloys.

The thermoforming is carried out by bringing the blank to temperatures between 0.7 Tf and 0.9 Tf and, preferably, close to 0.8 Tf, by means of radiant electrical panels and by deforming it in a mold whose temperature is about 100 ° C higher than that of the blank. The deformation rates of the blank under the pressure of the fluid, whether or not combined with a mechanical effect, are relatively rapid, of the order of 1 to 10 seconds. However, since the aluminum used is not superplastic, we must be content with linear elongations of the wall of the blanks of the order of 100% instead of 1000 to 2000% and surface ratios S ₁ / S _O around 1.5 instead of 4 for superplastic alloys. The relationship between depth and width of deformations obtained is of the order of 0.2 to _0, 3 only.

These processing conditions are suitable for obtaining parts in series such as trays intended for the packaging of consumable products, this is also taught in European patent 1,536 belonging to the applicant. In fact, the coefficients of deformation of the blank are more than sufficient to obtain containers with the desired dimensions; the rate of thermoforming operations is relatively high and can therefore be integrated with those of other operations carried out in a continuous packaging chain. The temperature necessary for the deformation leads to the sanitization of the packaging.

However, such a process has drawbacks in terms of cleanliness and sanitization of the packaging obtained. Indeed, thermoforming of aluminum poses significant problems at the time of demolding because the hot molded part adheres to the surface of the mold also heated, this in particular at its periphery in the part which is clamped between the edges of the mold in two. parts. Also, is it necessary, to facilitate demolding, to coat the surface of the blank or that of the mold with suitable lubricants. However, this leads to pollution of the surface of the trays obtained, hence the need for cleaning or pickling before filling. It is also possible, as explained in European patent 1 198, to use aluminum blanks coated with an adherent layer of artificial alumina obtained by prior oxidation by electrolytic or chemical route. However, this oxidation is a relatively expensive and long operation which slows down the rate of thermoforming which requires the handling of chemicals whose presence, next to consumable products, is not particularly recommended, not to mention the special precautions to be taken do not allow toxic substances to remain in the oxide layer which would adversely affect the quality of the packaged products.

In addition, since most consumable materials cannot be left in contact with bare aluminum without causing this material to degrade in the short term, it is therefore necessary to protect aluminum with organic matter. This is done in European patent 1,536 by coating around 120 ° C of the surface of the tray after thermoforming, to avoid an inevitable destruction of this material in contact with the mold, the temperature of which can be higher than 500 ° C.

This coating phase can reduce the rate of the packaging chain and, in any case, requires an additional operating phase and the maintenance of the tray in an aseptic medium during the transfer from the tray to the coating device.

The object of the present invention is to remedy these defects by proposing a process for manufacturing clean and / or aseptic packaging intended for the packaging of consumable products by thermoforming in a mold of thin blanks of aluminum which is neither lubricated nor chemically treated or made of materials. multilayer aluminum-organic products, in which the blank is brought to the deformation temperature and sanitized by the Joule effect.

This process is also characterized by the fact that or uses an unheated mold whose temperature of the internal wall is maintained at a constant value between ambient and 100 ° C.

Thus, unlike the process described in European patent 1536 in which the blank is heated by means of radiant electrical panels, it is here brought to the deformation temperature by Joule effect. This type of heating can be obtained by any suitable means such as, for example, the continuous or alternative electrical powering of the blank, or by subjecting the blank to the action of magnetic fields of suitable frequency.

It allows the aluminum to be brought quickly to a temperature between 150 and 600 ° C., the value chosen being fixed as a function of the thickness and the quality of the aluminum used. It can be applied either before the blank is introduced into the mold, or during the deformation operation, either by a combination of the two possibilities.

In parallel and also unlike the previous process, the mold is no longer heated to a temperature 100 ° C higher than that necessary for the deformation but, on the contrary, its internal wall is maintained by any suitable means at a constant temperature included between ambient and 100 ° C.

It is therefore understandable that by using such means, it is possible to extend thermoforming to materials in which aluminum is associated with organic products. Indeed, with the Joule effect, it is no longer necessary to bring the assembly to a temperature at least equal to that necessary for thermoforming as one would be obliged to with an external heating, but only aluminum. As, moreover, the mold is relatively cold, the temperature reached by the organic matter remains low. This temperature can furthermore be lowered using a cooled thermoforming fluid.

Thus, blanks of multilayer materials can be subjected directly to thermoforming and there is no longer any need to coat the tray with an organic product after its deformation.

The heating by Joule effect also allows asepticization of the assembly so that one can proceed immediately to the filling of the tray without resorting to the various conventional asepticization methods and carried out by passage through baths of hydrogen peroxide or peracetic acid for example, products the content of which must be carefully checked before filling due to their harmful action on living organisms.

Joule heating has other interesting repercussions. Thus, the mold being no longer heated, it is possible to use for its manufacture insulating materials which have little affinity for aluminum and organic products and this eliminates the risks of sticking.

Consequently, there is no longer any need for a lubricant or surface treatment such as anodization, and the trays obtained have a state of cleanliness compatible with the packaging of consumable products.

All these advantages of the Joule effect, combined with the advantages of thermoforming itself, and in particular the obtaining of trays without folds, unlike packaging produced by stamping and folding, make the invention a process particularly suitable for the manufacture of packaging for the packaging of consumable products.

Such a process can be combined with the thermoforming of blanks formed by pre-cut formats or shapes as well as blanks formed by strips which pass through the mold continuously.

In the first case, there is the advantage of simplifying the tool by eliminating the subsequent cutting operation once the tray has been obtained.

• La figure 1 représente une coupe par un plan vertical de symétrie longitudinale d'une installation de thermoformage de barquettes de conditionnement à partir d'une ébauche composite aluminium-produits organiques dans lequel l'effet Joule est créé par mise sous tension électrique de l'ébauche.
• La figure 2 représente une coupe par un plan horizontal de trace X'X suivant la figure 1.
• La figure 3 représente, suivant la même coupe que la figure 1, une barquette fabriquée dans l'installation objet des figures 1 et 2.
• La figure 4 représente schématiquement une chaîne intégrée de conditionnement comportant la fabrication et le remplissage des barquettes.

The invention will be better understood from the description of a particular embodiment, illustrated by the attached figures.

• Figure 1 shows a section through a vertical plane of longitudinal symmetry of a thermoforming installation of packaging trays from an aluminum-organic product composite blank in which the Joule effect is created by electrically energizing the draft.
• FIG. 2 represents a section through a horizontal plane of trace X'X according to FIG. 1.
• FIG. 3 represents, in the same section as in FIG. 1, a tray manufactured in the installation object of FIGS. 1 and 2.
• FIG. 4 schematically represents an integrated packaging chain comprising the manufacture and filling of the trays.

In Figure 1, we can see a thermoforming installation consisting essentially of a mold in two elements made of insulating material, in this case fine silica particles agglomerated by araldite. The mold could also be made of other materials such as refractory concrete, syndanio, etc. The upper planar element (3) is integral with a movable plate (4) capable of moving vertically under the 'action of a jack (5) and come to apply on the lower element (1) and seal the mold hermetically (1-3). The movable plate (4) is guided by four vertical columns (6). The edges (7-8) of the lower (1) and upper (3) elements of the mold are smooth to ensure better sealing and less adhesion with the blank (9) stretched horizontally between the two elements (1-3) of the mold. The rim (7) forms a fillet (10) with the internal vertical wall of the element (1). The upper element (3) comprises a stage (11) of height h = 2 mm which limits the bearing surface on the flange (7) of the lower element.

The lower element (1) has an orifice (12) placing the interior of the mold in communication with the ambient atmosphere; the upper element (3) is traversed by a pipe connected to a source of compressed air (13) and opening into the mold by an axial orifice (14).

On either side of the mold (1-3) and columns (6), electrical contact devices are essentially fixed consisting of transverse copper bars (15-16) arranged symmetrically and connected to the two terminals of a low voltage electrical circuit (4 V for example), not shown. The bars (15-16) are mounted on two insulating bakelite supports (17-18).

Above each of the bars (15-16), there are two similar bars (15'-16 ') also mounted on insulating supports (17'-18') integral with two jacks (19-20) which, at on demand, bring them down to be applied to the lower bars (15-16) by pinching the blank (9) and passing an electric current through it between the bars (15-16).

It is possible to introduce, inside the element (1), a movable bottom (21) which makes it possible to produce in the same installation parts of different height h.

In Figure 2, which shows a horizontal section of the lower part of the installation, there are bars (15) and (16) mounted on their insulating supports (17) and (18), these assemblies being held by columns (22) and (23). We also see the vertical columns (6) for guiding the movable plate (4). The blank (9) having been thermoformed has a rim (24), a periherical rib (25) which has formed at the level of the fillet (10) and a bottom (26).

In Figure 3, has been drawn, in vertical section, the tray obtained with this installation and which has a bottom (26), a vertical wall (27), a rib. (25) which stiffens the edge (24). This tray has a height h which is a function of the thickness of the movable bottom (21) which is introduced inside the lower element of the mold.

In FIG. 4, a continuous blank is seen in the form of a strip (28) which moves in the direction of the arrow F in a discontinuous advance movement from a roller (29). This strip, not preheated, passes directly into the thermoforming installation (30) consisting of at least one cold mold. The train of aseptic trays, which comes out of the mold, is conveyed through an aseptic enclosure (31) to a filling station (32) then of heat-sealing (33). The full and closed trays are cut in (34) and evacuated directly at the outlet by a conveyor (35) to a shipping station.

• Une bande en alliage d'aluminium du type 8011 de largeur 150 mm, d'épaisseur 0,060 mm, recouverte à sa partie supérieure d'un film de polypropylène de 0,050 mm d'épaisseur est entraînée vers une installation de thermoformage composée d'un moule en syndanio équipé, d'amont en aval, d'un dispositif de contact électrique suivant la figure 1. Il faut noter toutefois que, pour faciliter le fonctionnement, il est préférable que l'élément supérieur (3) soit fixe et que l'élément inférieur (1) soit monté sur vérin ; il en est de même pour les barrettes (15) et (16) qui sont mobiles alors que (15') et (16') restent fixes. Lorsque la bande se présente en face du dispositif aval, on l'arrête. Les barrettes (15 ) et (16) sont alors élevées par des vérins et viennent pincer la bande (9). Les barrettes supérieures (15') et (16') sont mises sous une tension de 3 volts et un courant d'une intensité de l'ordre de 1400 A s'établit. Lorsque l'aluminium a atteint la température de 390° C, ce qui demande environ 4 secondes, l'intensité du courant est réduite à la valeur suffisante pour maintenir la température à cette valeur. Le moule est alors fermé par élévation de l'élément inférieur (1). De l'air est admis par l'orifice (14), la bande (9) se déforme en venant s'appliquer en trois secondes sur les parois de l'élément inférieur (1). L'air contenu dans cet élément (1) s'échappe par l'orifice (12).La pression d'air entre l'élément supérieur (3) et la bande (9) peut monter à 2,5 bars effectifs. La barquette obtenue, représentée par les figures 2 et 3, a des dimensions correspondant très sensiblement à celles de la surface concave de l'élément inférieur (1), en l'occurence une hauteur h : 25 mm pour une longueur de 16C mm et une largeur de 110 mm.

With this chain, the manufacturing process according to the invention was implemented as follows:

• A strip of aluminum alloy of the type 8011 with a width of 150 mm, thickness 0.060 mm, covered at its upper part with a polypropylene film with a thickness of 0.050 mm is entrained towards a thermoforming installation composed of a mold in syndanio equipped, from upstream to downstream, with an electrical contact device according to figure 1. It it should be noted however that, to facilitate operation, it is preferable that the upper element (3) is fixed and that the lower element (1) is mounted on a jack; it is the same for the bars (15) and (16) which are mobile while (15 ') and (16') remain fixed. When the strip is opposite the downstream device, it is stopped. The bars (15) and (16) are then raised by jacks and pinch the strip (9). The upper bars (15 ') and (16') are put under a voltage of 3 volts and a current of an intensity of the order of 1400 A is established. When the aluminum has reached the temperature of 390 ° C, which requires approximately 4 seconds, the intensity of the current is reduced to the value sufficient to maintain the temperature at this value. The mold is then closed by raising the lower element (1). Air is admitted through the orifice (14), the strip (9) deforms by coming to be applied in three seconds on the walls of the lower element (1). The air contained in this element (1) escapes through the orifice (12). The air pressure between the upper element (3) and the strip (9) can rise to 2.5 effective bars. The tray obtained, represented by FIGS. 2 and 3, has dimensions corresponding very substantially to those of the concave surface of the lower element (1), in this case a height h: 25 mm for a length of 16C mm and a width of 110 mm.

As soon as the strip (9) has been applied by air pressure against the surface of the lower element (1) and its bottom (21), giving the tray shaped as shown in Figure 3, the power is cut on the bars (15'-16 '). The bars (15-16) are lowered at the same time as the lower element (1). The tray cools almost instantly on contact with the surface of the mold which has remained at a temperature of the order of 25 ° C. and it easily separates from the mold.

The strip can then be moved a length slightly greater than the length of the tray, then a new thermoforming operation is carried out while the trays formed pass successively through the filling, heat sealing, cutting stations before be picked up by a conveyor at the exit of the aseptic enclosure.

This chain allows with a single mold to obtain a production rate of 2000 trays per hour and which can be improved by advanced automation and a multiplication of molds or imprints.

The present invention finds its application in the packaging under suitable conditions of cleanliness and asepticization of products intended for consumption such as, for example, food products and pharmaceutical products.

Claims (8)

1 ° / - Process for obtaining, in a single operation, from thin blanks in aluminum which is neither lubricated nor chemically treated or in multilayer materials aluminum-organic products of clean and / or aseptic packaging which can be immediately filled with consumable product, by thermoforming, characterized in that the shaping and the sanitization are obtained simultaneously by using the heating created by JOULE effect within the metallic part of the blank. 2 ° / - Method according to claim 1, characterized in that the deformation temperature is between 150 and 600 ° C depending on the quality and thickness of the blank used. 3 ° / - Method according to claim 1, characterized in that an unheated mold is used whose temperature of the internal wall is maintained at a constant value between ambient and 100 ° C. 4 ° / - Method according to claim 1, characterized in that the mold is made of insulating material. 5 ° / - Method according to claim 1, characterized in that one creates the JOULE effect by electrically energizing the blank. 6 ° / -Procédé according to claim 1, characterized in that one creates the JOULE effect by subjecting the blank to the action of magnetic fields of suitable frequency. 7 ° / - Method according to claim 1, characterized in that the blank is constituted by a pre-cut format. 8 ° / - Method according to claim 1, characterized in that the blank is constituted by a strip which passes through the mold continuously.

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