Apparatus and method for injection molding opening devices on sheet packaging material for packaging pourable food products

An apparatus for injection molding an opening device on a sheet packaging material having a hole possessing an axis, formed through a first layer and sealed by a cover portion of a second layer; comprises a mold cavity coaxially housing the cover portion and comprising a first chamber adapted to be filled with molten plastic material on a first side of the cover portion, and a second tubular chamber projecting along the axis from the first chamber and adapted to be filled with the molten plastic material coming from the first chamber through an annular peripheral portion of the cover portion to form, on a second side of the cover portion, a spout; an annular rib delimiting a passage connecting the first and second chamber and defining, when filled with the plastic material, an annular tearable membrane connection portion between the spout and the plastic material covering the cover portion.

TECHNICAL FIELD

The present invention relates to an apparatus and a method for injection molding opening devices on sheet packaging material for packaging pourable food products.

BACKGROUND ART

As is known, many pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.

A typical example of this type of package is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by folding and sealing laminated strip packaging material.

The packaging material has a multilayer structure substantially comprising a base layer for stiffness and strength, which may comprise a layer of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a number of lamination layers of heat-seal plastic material, e.g. polyethylene films, covering both sides of the base layer.

In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.

Packages of this sort are normally produced on fully automatic packaging machines, on which a continuous tube is formed from the web-fed packaging material; the web of packaging material is sterilized on the packaging machine, e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution, which, once sterilization is completed, is removed from the surfaces of the packaging material, e.g. evaporated by heating; the web of packaging material so sterilized is then maintained in a closed, sterile environment, and is folded and sealed longitudinally to form a vertical tube.

The tube is filled with the sterilized or sterile-processed food product, and is sealed and subsequently cut along equally spaced cross sections to form pillow packs, which are then folded mechanically to form respective finished, e.g. substantially parallelepiped-shaped, packages.

Alternatively, the packaging material may be cut into blanks, which are formed into packages on forming spindles, and the packages are filled with the food product and sealed. One example of this type of package is the so-called “gable-top” package known by the trade name Tetra Rex (registered trademark).

To open the packages described above, various solutions have been proposed, including reclosable opening devices made of plastic material and substantially comprising a spout, e.g. tubular, defining a through opening and fitted to a hole in a wall of the package, and a removable, e.g. screw or hinged, cap fitted to and outwardly closing the spout.

When producing the opening device, the opening of the spout is sealed by a plastic confetti portion connected integrally to the spout and detachable from it along a smaller-section annular tearable membrane; on the side facing the cap, the confetti portion has an integral projecting pull ring, the free end of which is pulled by the user to detach the confetti portion from the spout along the tearable membrane and so open the product pour opening. More specifically, the pull ring extends inside, and at a predetermined distance from, the spout.

Using the opening devices described, the package is easy to open, with a reasonable amount of effort required of the user, and the confetti portion is detached neatly from the spout.

The same does not apply, however, in the case of packages requiring not only liquid but also gas sealing where the opening device is fitted to the packaging material.

In such cases, solutions are known in which the confetti portion of the opening device is fixed directly over a prelaminated hole in the packaging material, i.e. a hole formed in the base layer only and covered by the other lamination layers, including the layer of gas-barrier material.

Using this solution, opening the package calls not only for detaching the confetti portion from the spout, but also for tearing the layer of barrier material against the edge of the hole through the base layer. With commonly used barrier materials, such as aluminium, this invariably results in an increased effort by the user to unseal the package and in a jagged, frayed edge of the hole, thus impairing smooth pour-out of the food product.

In order to solve this problem, the Applicant devised a method and apparatus, disclosed in EP-A-2008787, for injection molding the opening device directly on the prelaminated hole of the packaging material.

In practice, the molten plastic material is injected onto one side of the prelaminated hole to cover it up to an annular peripheral portion thereof and to form, in this way, a plastic confetti portion directly attached to the prelaminated hole; the molten plastic material is then forced to pierce the prelaminated hole at such annular peripheral portion to form a pouring spout of the opening device projecting from an opposite side of the prelaminated hole and attached to the confetti portion through a smaller-section annular membrane connection portion adapted to be torn by the user to open the package.

In this way, the material forming the prelaminated hole is first pierced through and then resealed by the plastic material forming the spout. Therefore, the resulting package has the necessary gas-sealing properties, while at the same time is easier to open than known packages with gas barrier.

The Applicant however observed that, during the injection operations, the prelaminated hole was not always regularly pierced on the confetti portion side, but tended to break on the spout side. This caused portions of the material of the prelaminated hole to be entrapped into the plastic material forming the tearable membrane, so making this solution not completely satisfactory as to the effort required to the user to unseal the package and the pouring quality.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide an apparatus and a method for injection molding opening devices on sheet packaging material for packaging pourable food products, which allow to eliminate the aforementioned drawbacks typically associated with known apparatus and methods.

According to the present invention, there are provided an injection molding apparatus as claimed in claim1and an injection molding method as claimed in claim7.

BEST MODE FOR CARRYING OUT THE INVENTION

Number1inFIG. 1indicates as a whole a sealed package for pourable food products, made of a multilayer sheet material2which is folded and sealed in known manner as described in detail above, and to which an opening device3of plastic material is applied using an injection molding apparatus10(shown inFIGS. 3 to 7) according to the present invention.

In the example shown, package1is parallelepiped-shaped and of the type known by the trade name Tetra Brik Aseptic (registered trademark). Apparatus10according to the present invention, however, also applies to advantage to other types of packages, such as the gable-top packages known by the trade name Tetra Rex (registered trademark).

With particular reference toFIG. 2, material2comprises a base layer4for stiffness and strength, which may be made of fibrous material, e.g. paper, or mineral-filled polypropylene material, and a plurality of layers5of heat-seal plastic material, e.g. polyethylene films, covering both sides of base layer4.

In the case of an aseptic package1for long-storage products, such as UHT milk, packaging material2also comprises a layer6of gas-barrier material, e.g. aluminium foil or ethyl vinyl alcohol (EVOH) film, which is superimposed on a layer5of heat-seal plastic material, and is in turn covered with another layer5of heat-seal plastic material forming the inner face of package1eventually contacting the food product.

In other words, layers5and6define respective lamination layers applied to base layer4when producing material2in the form of a continuous strip.

Strip material2also comprises a number of removable portions8(only one shown in the drawings) equally spaced in a lengthwise direction A of the material, and to which opening devices3are subsequently injection molded.

In the following description, reference is made to one removable portion8and one opening device3for the sake of simplicity.

In the example shown, removable portion8is defined by a so-called prelaminated hole, i.e. a hole9formed through base layer4of material2and covered by lamination layers5,6, so that hole9is sealed by a respective sheet cover portion11.

In an alternative embodiment not shown, cover portion11may even be defined by only one or some of layers5,6. For example, cover portion11may be made solely of gas-barrier material.

In another alternative embodiment not shown, cover portion11may be defined by a patch fixed to the rest of material2to seal a hole formed, in this case, through the full thickness of material2.

As shown in particular inFIG. 1, opening device3has an axis B, which is substantially perpendicular to cover portion11and to the lengthwise direction A of strip material2. Opening device3substantially comprises a confetti portion12adhering to one side11aof cover portion11—in the example shown, the side eventually facing inwards of package1—, and a cylindrical tubular pouring spout13, which is fixed to material2about hole9, defines an opening16by which to pour the food product from package1, and extends through cover portion11as a follow-on from the piercing thereof so as to be arranged on both sides11a,11bof the cover portion11. Opening device3also comprises a cap14(FIG. 1) which fits removably to spout13to outwardly close opening16.

More specifically, confetti portion12and spout13are injection molded in one piece, and cap14is formed separately from the whole comprising confetti portion12and spout13.

As shown particularly inFIG. 1, spout13comprises an annular flange portion17, fixed to material2about hole9, and a cylindrical tubular neck portion18projecting axially from an inner lateral edge of flange portion17, and extending through a peripheral annular portion of cover portion11. In other words, neck portion18projects from material2on side11bopposite the side (11a) to which confetti portion12is fixed.

As shown inFIG. 1, confetti portion12and flange portion17are joined by an annular membrane connection portion19, which is smaller in section than portions12and17, so as to tear easily to detach sealing portion15from spout13. In other words, annular membrane connection portion19defines a tear line along which to detach confetti portion12from spout13.

On the side facing cap14, confetti portion12has an integral projecting pull ring21, by which to detach sealing portion15from spout13along annular membrane connection portion19and so free opening16to pour out the product.

More specifically, pull ring21extends inside, and at a predetermined distance from, neck portion18, and is joined to confetti portion12by a tab22.

As shown inFIG. 1, cap14is a screw type, and has a cylindrical lateral wall23with an inner thread24, which engages a corresponding outer thread25on neck portion18of spout13.

In order to injection mold opening device3on strip material2, the latter is step-fed in direction A to position a removable portion8thereof inside molding unit10(FIGS. 3 to 7).

With reference toFIGS. 3 to 7, molding unit10comprises a number of molds30a,30b,30c,30d, which are coaxial with axis B of the opening device3being formed, are located on both sides of material2, and are movable between an open configuration (not shown) allowing feed of material2in direction A, and a closed configuration (FIGS. 3 to 7), in which they define a closed mold cavity31housing cover portion11and adapted to be filled with molten plastic material to define, when the material sets, the whole comprising confetti portion12and spout13.

In the example shown, molds30b,30c,30dare located on the opposite side of material2to mold30a; more specifically, molds30b,30c,30dface side11bof cover portion11, whilst mold30afaces side11aof the same.

As shown inFIGS. 3 to 7, mold30bis radially outer than mold30dwith respect to axis B, whilst mold30cis interposed radially between molds30band30d.

Mold cavity31basically comprises:a first confetti-shaped chamber32of axis B, which houses cover portion11;a second tubular chamber33extending, coaxially with axis B, from one side of a flat annular peripheral portion34of chamber32; anda third chamber35which defines pull ring21of confetti portion12, and extends from the same side as chamber33, and from a radially inner point of chamber32with respect to annular peripheral portion34.

Chamber32comprises a convex central portion36, curving towards chambers33and35, connected to annular peripheral portion34, and having, at axis B, an inlet37connected to a molten plastic injection conduit38extending through mold30a.

Chamber33comprises a first cylindrical portion39projecting along axis B from a side, opposite to inlet36, of chamber32, and a substantially flat annular portion40extending radially outwards from annular peripheral portion34of chamber32and housing a peripheral edge of cover portion11and the portion of whole packaging material2extending around cover portion11.

As shown inFIGS. 3 to 7, chamber35also projects along axis B from the same side of chamber32as cylindrical portion39of chamber33.

In theFIG. 3-7example, chamber32is defined by mold30aon one side, and by molds30cand30don the opposite side, chamber33is defined by molds30a,30cand30b, and chamber35is defined by molds30cand30d.

With particular reference toFIG. 3, mold30ccomprises an annular rib41extending around axis B and delimiting, with mold30a, a narrow-section annular passage42connecting chamber32to chamber33and defining, when filled with the plastic material, the tearable annular membrane connection portion19between spout13and confetti portion12.

As shown in the larger-scale detail ofFIG. 3, annular rib41is bounded by a first annular surface43facing chamber32, by a second annular surface44, transversal to surface43and facing mold30a, and by a third annular surface45, opposite surface43, facing chamber33and having a conical shape around axis B, tapering towards mold30a. Moreover, in the zone of chamber32adjacent to surface43, mold30cis bounded by a surface47, facing mold30aand side11bof cover portion11and forming a corner with the surface43.

Surface43forms, with surface44, a sharp edge46cooperating in use with cover portion11to stretch it and ease its piercing under the pressure of the molten plastic material in order to allow the latter to flow into chamber33.

Advantageously, surfaces43and47form, in the corner zone, an angle α, comprised between 80° and 110° so as to maximise the area along which cover portion11is pressed by the molten plastic material and to obtain that the cut cover portion is moved away from passage42.

In particular, as clearly shown inFIG. 6, after the molten plastic material has fully filled chamber32and passage42so producing the piercing action on cover portion11, the cut edge of the cover portion11is lastly arranged at a distance from edge46on the side of chamber32.

The applicant has observed that the above result can be better achieved in the case in which angle α ranges between 80° and 100°.

According to a preferred embodiment of the present invention, surface43is substantially parallel to axis B, that is surface43may be strictly parallel to the axis B or may form a small angle of at most 5° with the parallel to said axis.

In the specific solution depicted inFIGS. 3 to 7, surface43is strictly parallel to axis B, in the sense that they do not meet at any point, even considering their prolongations.

In particular, surface43has a cylindrical configuration around axis B.

Furthermore, as disclosed in theFIG. 3, surfaces43,44and45have the following geometric relationships:surface43forms an angle, preferably of 90°, with surface44; andsurface45forms an angle β, preferably of 120°, with surface44.

Besides, according to a preferred solution, surfaces44and47are substantially parallel to one another.

At this point, from side11aof cover portion11, molten plastic material is injected along conduit38into chamber32, which is gradually filled from central portion36towards annular peripheral portion34.

The pressure of the molten plastic material injected into chamber32of mold cavity31pushes cover portion11of material2against mold30d, so that side11bof cover portion11contacts mold30d.

At this stage, layer5of heat-seal plastic material of cover portion11, facing mold30a, melts completely with the plastic material injected into mold cavity31.

The molten plastic material spreads radially inside chamber32until it eventually reaches the intersection of chambers32and35, where cover portion11, having no solid support by molds30cand30d, is pierced neatly by the pressure of the molten plastic material, which therefore fills the whole of chamber35to form pull ring21.

In exactly the same way, when the molten plastic material reaches the annular portion at the intersection of chambers32and33, cover portion11is pierced by the pressure of the molten plastic material, which therefore flows into cylindrical portion39of chamber33to form neck portion18of spout13and thread25.

In other words, the molten plastic material pierces through cover portion11at the intersections between chamber32and chambers33and35of mold cavity31to form through openings, which are subsequently sealed off by the plastic material to fully restore the integrity of material2.

Before reaching chamber33, the molten plastic material is forced to pass through narrow-section passage42. During this stage, the molten plastic material advances towards the surface43delimiting the entry into passage42and forming sharp edge46with surface44; cover portion11is therefore pushed by the pressure of the molten plastic material against the sharp edge46, which produces a stretching action on the cover portion11. This stretching action allows to obtain breaking of cover portion11near sharp edge46.

Thanks to the particular geometry of mold30cin the corner region between surfaces43and47, which permits to maximise the contact area between the mold30cand the cover portion11, the cut edge of the latter is therefore moved away from passage42towards said corner region under the thrust of the molten plastic material; in this way, in its final position, the cut edge of cover portion11is arranged at a distance from edge46on the side of chamber32.

Moreover, as specifically shown inFIGS. 6 and 7, because of the particular angle between surfaces43and47and the high speed of the molten plastic material at the entry into passage42, cover portion11is removed completely from annular membrane connection portion19and forms no connecting bridge with spout13.

Once the plastic material filling the whole of mold cavity31sets, molds30a,30b,30c,30dare moved into the open configuration to feed material2once more in direction A, to extract the removable portion8, with respective opening device3formed on it, from molding unit10, and to insert another removable portion8, on which to perform another molding operation, inside cavity31.

The advantages of the injection molding apparatus and method according to the present invention will be clear from the foregoing description.

In particular, at the end of the injection molding operation carried out on the molding apparatus10, it is possible to obtain an opening device3firmly connected to cover portion11of packaging material2, but in which the cover portion is first pierced through and then resealed by the plastic material forming spout13and pull ring21. As a result, package1has the necessary gas-sealing properties, while at the same time being as easy to open as packages with no gas barrier. That is, to unseal the package produced using molding apparatus10, the user simply has to tear the annular membrane connection portion19connecting the plastic parts, as opposed to the gas-barrier material, which has already been pierced through when injection molding opening device3.

As a matter of fact (please see in particularFIGS. 6 and 7), cover portion11is pierced neatly, with no fraying, on the side of confetti portion12by the combined action of the high pressure of the plastic material at the entry into passage42and the particular geometry of the angle α between surfaces43and47, thus greatly improving opening of package1and smooth pour-out of the food product, which is not impaired by the possible presence of fragments of the material of the cover portion in the pouring hole9.

Clearly, changes may be made to molding apparatus10and the molding method as described herein without, however, departing from the scope as defined in the accompanying Claims.

In particular, the molding operations described may be also applied on cover portions of any outer profile, i.e. even not circular, to produce opening devices having tubular pouring spouts with non-circular cross-sections, e.g. oval, elliptical or simply defined by closed-loop profiles.

Moreover, the molding operations described may also be performed directly on blanks of packaging material, after they are formed into open containers on spindles, and before they are filled with the pourable food product and sealed.

Last but not least, molds30a,30b,30c,30dmay even be not coaxial to one another.