Forming containers

A method comprises forming a preform of plastic material, expanding said preform to obtain a container, said forming comprising compression-forming said preform in that mould arrangement wherein said expanding occurs; a method comprises expanding a preform in a mould arrangement to obtain a container, before said expanding it being provided to form a dose of plastic material in a paste state in said mould arrangement to obtain said preform; an apparatus comprises a forming mould arrangement, a punch device for expanding a preform in said mould arrangement, an abutting device cooperating with said punch device, said punch device and said abutting device identifying a configuration in which said punch device and said abutting device cooperate to define a forming unit for compression-forming a semifinished product of plastic material to obtain said preform and a further configuration in which said punch device and said abutting device cooperate to define an expansion unit of said preform to obtain a container.

The invention relates to forming containers from a semifinished product, for example in plastic material such as a pad formed by injection, or a disc or a dose of plastic material in a paste state.

The state of the art comprises systems for thermoforming containers from flat film in single-layered or multilayered plastic material.

Systems are furthermore known for forming containers that provide for expanding, by means of pressurised air, in a forming mould, a preform of a container obtained by injection. JP-2001 000362600, publication JP-2003 159743, is furthermore known that discloses a system for forming containers comprising in sequence:positioning a semifinished disc-shaped product in plastic material near an opening of a forming mould for forming containers;expanding said semifinished product in said forming mould by means of a punch inserted into said mould through said opening.

Before being positioned near the opening, the semifinished product is formed in a suitable forming mould for forming the semifinished product, in which a dose of thermoformable plastic material is placed between a punch and a die that can be moved up to and be removed from one another to give the dose the desired shape.

JP-2001 000362600 therefore has the drawback of using two types of mould, i.e. a mould for forming the semifinished product and a mould for forming containers.

Furthermore, JP-2001 000362600 involves subjecting the plastic material to a complete heating and cooling cycle to form the semifinished product and to a further heating and cooling cycle to form the container.

U.S. Pat. No. 6,264,050 discloses a forming system in which starting from a sheet material, precursors of containers are formed that are then separated from the sheet material and expanded in a forming mould by compressed air to obtain formed containers.

U.S. Pat. No. 6,264,050 has the drawback of using different apparatuses to form the precursors and to expand the latter to obtain containers.

An object of the invention is to improve the known systems to obtain containers.

A further object is to make the manufacturing systems for blown containers more compact.

A further object is to improve the forming conditions of a semifinished element positioned near the opening of a forming mould for forming containers.

In a first aspect of the invention, there is provided a method comprising:forming a preform of plastic material,expanding said preform to obtain a container;
wherein said forming comprises compression-forming said preform in that mould arrangement in which said expanding occurs.

In a second aspect of the invention, there is provided a method comprising:expanding a preform into a mould arrangement to obtain a container,wherein before said expanding, there is provided forming a dose of plastic material in a paste state in said mould arrangement to obtain said preform.

In a third aspect of the invention, there is provided an apparatus comprising:a forming mould arrangement,a punch device for expanding a preform in said forming mould arrangement,an abutting device cooperating with said punch device,wherein said punch device and said abutting device identify a configuration in which said punch device and said abutting device cooperate to define a compression-forming unit for compression-forming a semifinished product in plastic material to obtain said preform, and a further configuration in which said punch device and said abutting device cooperate to define an expansion unit of said preform to obtain a container.

Owing to these aspects of the invention, it is possible to form containers from semifinished products located in a single forming mould. In fact, the semifinished product to be formed is placed at the opening of the mould arrangement, is then shaped to obtain a preform and this preform is then expanded without the preform having to be extracted from the mould arrangement, as on the other hand occurs in known forming systems.

Furthermore, it is possible to obtain better control of forming through the effect of the shaping of said semifinished product and the presence of abutting device that acts on the semifinished product together with the punch device on an opposite side of the latter.

Furthermore, a particularly compact forming system it is obtained.

Furthermore, the plastic material is subjected to a single heating cycle that comprises a progressive heating and cooling in several phases.

In particular, the invention enables containers to be obtained starting from a semifinished product in plastic material that may comprise an element with a thin thickness, for example a disc obtained by shearing from a film, or an injected body, or a dose of plastic material in a paste state.

In all the aforementioned cases, obtaining a preform by compression-forming from the semifinished product, enables the subsequent obtaining the container by blow-forming to be improved.

The preliminary step of obtaining a preform having a prefixed geometry, for example walls having different thickness in various points of the preforms, enables in fact a different heating phase of the preform prior to the expansion phase of the latter to be avoided.

The advantage of being able to create a preform and subsequently expand it appears particularly clear in the case of the element with a thin thickness and of the dose of plastic material in a paste state, that both could not be subjected to an expansion phase without previously be conformed as a preform.

In the case of the injected body, it is a question of an element that is structurally more similar to a preform. Nevertheless, also in this case the compression-forming of a preform from the injected body brings significant advantages.

Obtaining a preform in two phases (i.e. injection and subsequent compression-moulding) in fact enables plastic material to be used having a high molecular weight, which is very appreciated in order to facilitate operations of stretch-blow-forming.

Any defects in the injected body due, for example, to the low viscosity that is typical of plastic material with high molecular weight, can be subsequently eliminated in the compression-moulding phase, enabling containers that are free of defects to be obtained.

In particular, it is possible to use injection moulds provided with an injection opening (gate) of considerable dimensions, in order to facilitate the flow of the plastic material.

The discontinuity created in the injected body by the orientation of the injection opening is subsequently eliminated during the subsequent phase of compression-forming.

The possibility of using plastic material with a high molecular weight and of obtaining preforms substantially free of defects and having walls with a controlled thickness, enables the preforms to be subjected to blowing that acts both axially and radially, in the same mould.

With reference toFIG. 1, a mould2is shown for forming a container4(seeFIG. 6), comprising a base plate6on which there is fixed an external casing10of a die8that is internally provided with a cavity. Within the casing10there is fixed a liner12that defines an intermediate part14of the cavity9and carries at its opposite ends a first member16and a second member18, which respectively define a first end zone20and a second end zone22of the cavity9.

The first member16has an opening24and defines a seat26in which can be received a semifinished product50from which the container4is formed.

The second member18receives within itself a base part30in an axially sliding manner as will be explained in greater detail below.

The base plate6has a pair of bushes32in which respective guide rods34are slidingly fitted, the respective ends of which are connected by a first crosspiece36and by a second crosspiece38.

The second crosspiece38and the first crosspiece36are on opposite sides of the die8, the second crosspiece38supporting a punch40turned towards the die8.

The punch40and the base part30are movable inside the die8independently of one another, in such a way as to identify a first configuration, in which the punch40and the base part30cooperate to define a forming unit for compression-forming the semifinished product50to obtain a preform51, and a second configuration, in which the punch40and the base part30cooperate to define an expansion unit for the expansion of the preform51to obtain the container4.

In particular, in the first configuration, the punch40and the base part30are arranged near the opening24.

In the first configuration the base part30cooperates with the die8to define a chamber inside which the punch40can penetrate to press the plastic material against wall elements delimiting said chamber.

Subsequently, after the preform51has been formed, the base part30and the punch40are removed from the opening24to identify the second configuration, in which the base part30cooperates with the die8to define a further chamber inside which the punch40expands the preform51to obtain the container4.

The punch40comprises a punch body42inside which is axially slideable a stem44passing through a hole45of the second crosspiece38and having a shaped head46turned towards the die8.

The head46is housed in a chamber48provided in the punch body42into which an operating fluid, for example air at controlled pressure, can be introduced and from which it can be extracted.

In the position inFIG. 1, a disc shaped semifinished product50is positioned in the seat26at the opening24. The semifinished product50is obtained by shearing from a single-layer or multilayered film.

The first crosspiece36is kept fixed and the base plate6is made to slide on the pair of rods34in the direction indicated by the arrow F to bring the first crosspiece36up to the punch40, as shown inFIG. 2.

In this way, the top surface52of the die8approaches an annular front surface56of the punch40in such a way that an axial and central projection54of the latter penetrates inside the seat26and interacts with the surface of the semifinished product50turned towards it.

Once the projection54is in the interaction position disclosed above, the base part30is taken by an actuator60in the direction indicated by the arrow F1through the cavity9to the opening24in such a way as to interact with a further surface of the semifinished product50opposite the surface that is in contact with the shaped head46.

In this interaction position, a temperature control device (not shown) intervenes on the semifinished product50in such a way as to take it to the thermoforming temperature whereas the semifinished product50is shaped by the combined action of the shaped head46and the base part30.

Alternatively, the semifinished product50can be positioned in seat26when it is already at the temperature at which compression-forming occurs.

Subsequently, now with reference toFIG. 3, whilst the base plate6is kept in the position disclosed inFIG. 2, the base part30is returned by the actuator60to its initial position in a direction F2opposite direction F1.

Furthermore, the stem44shifts the shaped head46to the base part30, stopping before reaching it. In this way, the semifinished product50has a peripheral part tightened between the projection54and the seat26and a central part that is drawn by the shaped head46to form a precursor58of a container.

With reference toFIG. 4, compressed air is introduced into the chamber48that occupies the precursor58of a container and expands the precursor58until it reaches the walls that define the cavity9.

This is made possible by the fact that the stem44has a transverse dimension that is smaller than that of the shaped head46and therefore when the shaped head46is outside the chamber48, the air that is introduced into the chamber48tcan exit by the side of the head46.

With reference toFIG. 5, it is shown how, in order to extract the shaped container4, it is necessary to open the die8by separating the casing and liner parts and the inserts that make it up.

As shown inFIG. 6, the container4has a flange62radially protruding from a neck64that leads away from a converging wall part66that is joined to a central wall part68.

A base70has a peripheral support edge72that converge into a divergent wall74connected to the central wall part68.

InFIG. 7the temperature levels are shown in a forming cycle of the container4in the apparatus1ofFIGS. 1 to 5.

During a first phase, the semifinished product50is heated to temperature T1, advantageously coinciding with the plasticization temperature of the plastic material, i.e. the temperature at which compression-forming of the preform occurs. After a set period of time in which the semifinished product50is maintained at the temperature T1, the semifinished product is cooled to the temperature T2, advantageously coinciding with the forming temperature, i.e. the temperature at which stretch-blow-forming of the container occurs.

At temperature T2the preform is expanded to create a container. The container is kept at temperature T2for a certain period of time and is then progressively cooled to temperature T3, coinciding for example with ambient temperature.

In the diagram inFIG. 8, in which the typical temperature levels of a system for forming containers according to the state of the art are shown, for example JP-2001 000362600, it is noted how after bringing the material to temperature T1i.e. to plasticization temperature, to obtain a preform in a first mould for forming preforms, the preform has to be cooled to temperature T3, for example to ambient temperature, and be subsequently heated in a second mould for forming the containers.

As shown with reference toFIG. 9, in the seat26there is inserted, instead of the disc50, a semifinished product53injection-formed before it is inserted into the seat26in a suitable mould that is not shown. The semifinished product53has a substantially circular shape with a central depression, but more in general, it may have any suitable shape, according to necessity, to obtain a preform51shown inFIG. 2, and it acts as a preliminary preform to obtain the preform51.

FIG. 10shows a variation in which instead of a disc50, or of a preliminary preform53, the semifinished product to be positioned near the opening24comprises a dose55of extruded plastic material in a paste state. In this embodiment, unlike what has been described with reference toFIGS. 1 to 9, the base part30is in a position near the opening24in such a way as to substantially occupy it, preventing the dose from falling into the cavity9in an uncontrolled manner. The dose55is thus released on the base part30, when the latter is in the position shown inFIG. 10waiting to cooperate with the punch40to give rise to the preform51.

In this embodiment, the dose of plastic material, when it is positioned on the base part30, is already at the temperature at which compression-forming of the preform51occurs.

For this purpose, the dose of plastic material can be extruded and subsequently cooled inside the extruder to the temperature at which compression-forming occurs.

Alternatively, two serially arranged extruders can be provided.

The apparatus embodiments inFIGS. 9 and 10operate, in terms of forming of the preform51, and the subsequent forming of the container4, as already disclosed with reference toFIGS. 2 to 5.

With reference toFIG. 17, the temperature levels in a forming cycle of the container4are shown, the latters being different from the ones of the forming cycle inFIG. 7.

Initially, a semifinished product, such as a flat element, or an injected body, or a dose of plastic material in a paste state, is introduced into the mould2, this semifinished product having been previously heated to a temperature T1, at which temperature the semifinished product is compression-formed to create a preform51.

Subsequently, the semifinished product is kept at a temperature T1′, at least during the compression-forming phase.

Thereafter, the perform51thereby obtained is expanded to create a container4.

Expansion of the preform occurs at a temperature T2′ that is lower than the temperature T1′, the difference between the temperature T1′ and T2′ being rather limited. In other words, the temperature T1′ and T2′ are near to each other.

In a further heating cycle, which is not shown, the temperature at which expansion of the preform occurs substantially coincides with the temperature at which the preform was compression-formed.

A small or possibly non-existent difference between the temperature at which expansion of the preform occurs and the temperature at which the preform was compression-formed enables a more uniform distribution of the temperature to be obtained in the thickness of the preform, and therefore enables stretch-blow-forming to be optimised.

The container obtained is subsequently cooled to a temperature T3′.

As shown inFIG. 11, a forming apparatus similar to the one disclosed with reference toFIGS. 1 to 10can also be fitted onto a rotating machine.

In the particular case in which forming of the container occurs starting from a dose55of plastic material in a paste state, it is provided for that the dose is conveyed above the opening24occupied by the base part30by a turntable100that is made to rotate around an axis B parallel to the longitudinal axis A. In a peripheral zone of the turntable100spoons101are supported by a side of the table, which spoons101pick up a dose55from an outlet102of an extruder103and deposit it on the base part30in a raised position.

The base part30is a component of the cavity8fitted to a bottom part104of a carousel105that is rotatable around a main axis C of the machine. The bottom part104can thus be provided with a plurality of cavities distributed along its periphery. The carousel105is provided with a top part106fitted with a corresponding plurality of punches superimposed on the cavities8.

On the turntable100a star107is fitted that is provided with arms108between which gaps109are defined between which the formed containers4are received singly that are released by the respective punches40.

The containers4are picked up by the punches40by means of the star107and are transferred by the arms108to an unloading zone S whilst they rest on the turntable100.

In one version, that is not shown, a plurality of apparatuses1can be provided that are fitted to form a set of pressing units arranged in line.

From the comparison betweenFIGS. 12 and 13, it is possible to provide that the base part30can be positioned at variable distances from the top of the cavity8. In this way, it is possible to use the same cavity8to obtain different formats of containers4,4′ by simply arranging the base part30at different distances from the top of the cavity8. In particular, it is shown how the different arrangement of the base part can provide containers that differ from one another by a preset height H.

In such cases, the intermediate part14could have a cylindrical form with constant cross-section that extends at least for a portion that occupies the possible different positions that the base part30can take up.

The head46and/or the base part30may be made of several parts arranged concentrically in relation to one another, in such a way as to make possible to form preforms51, or containers4, having the most widely varying geometries. For this purpose, the parts that form the head46and/or the base part30are slideable in relation to one another and can be independently powered.

With reference toFIG. 14, it is shown how the base part30may comprise a central portion80surrounded by a peripheral portion82that may slide axially along a longitudinal axis A of the mould2in relation to the central portion80. In this way, the central portion80can for example be positioned either in such a way that its internal surface84is substantially coplanar with an internal peripheral surface86of the peripheral portion82to form a substantially flat container base.

Alternatively, as shown by the broken line, the internal surface84can be shifted further to the inside of the cavity9in such a way as to form a container base that has a central zone70athat is raised in relation to the peripheral edge72.

With reference toFIG. 15, it is shown how the shaped head46comprises an external annular part200and an internal annular part202, both of which are driven independently in a direction W parallel to the axis A. In this way it is possible to move the internal part202and the external part200, as well as the central portion80and the peripheral portion82, in such a way as to enable a preform51to be obtained as shown inFIG. 2. In particular, the central portion80faces the internal part202and substantially has a transverse dimension that is larger than that of the latter. In this way it is possible, as shown inFIG. 16, for the internal part202to penetrate inside the peripheral portion82in such a way as to give rise to a central projection206in a preform204.