MOULDING DEVICE FOR MOULDING A CONTAINER STARTING WITH A PARISON IN PLASTIC MATERIAL, MOULDING METHOD AND MOULDING MACHINE

Abstract

(1) for moulding a container starting with a parison (3) in plastic material, comprising: two half-moulds (4a, 4b) defining at least one housing cavity (5) for the parson (3); a stretching rod (23), made of metal material and insertable into said parson (3) to stretch it; a hollow body (25), made of metal material, sized so as to envelop at least partially the parison (3) placed in said housing cavity (5), a voltage difference being applied between the stretching rod (23) and the hollow body (25) so as to generate a plasma inside said housing cavity (5), said plasma having a pressure equal to or higher than the atmospheric pressure.

Claims

1. Device for moulding (1) a container from a parison (3) in plastic material, comprising: two half-moulds (4a, 4b) which may be moved close to each other to define at least a housing cavity (5) of the parison (3); a stretching rod (23), manufactured at least partially in metal material, insertable into said parison (3) to stretch it; a blowing nozzle (6) applicable to the neck (3b) of the parison (3) to blow into it a fluid having a pressure equal to or higher than the atmospheric pressure; a hollow body (25), manufactured at least partially in metal material, sized so as to envelop at least partially the parison (3) placed in said housing cavity (5), characterised in that it comprises means for applying a voltage difference between said stretching rod (23) and said hollow body (25) so as to generate a plasma inside said housing cavity (5), said plasma having a pressure equal to or higher than the atmospheric pressure.

2. Moulding device (1) according to claim 1, wherein said hollow body (25) is obtained from the union of said half-moulds (4a, 4b) in the first configuration, said plasma being generated inside said housing cavity (5).

3. Moulding device (1) according to claim 1, wherein said hollow body (25) has a substantially tubular shape and is moveable inside said housing cavity (5) at least between an operating position in which it partially or entirely envelops a tubular body (3a) of the parison (3), and a rest position in which it is moved away from the parison (3).

4. Moulding device (1) according to claim 3, wherein said hollow tubular body (25) is coaxial to said housing cavity (5).

5. Moulding device (1) according to claim 3 or, wherein said hollow tubular body (25) is formed of a substantially continuous metal sheet.

6. Moulding device (1) according to claim 3 or wherein said hollow tubular body (25) consists of a metal cage formed of a mesh or of a plurality of parallel and distanced bars.

7. Machine for moulding containers from parisons (3) in plastic material, comprising a plurality of moulding devices (1) according to any one of the previous claim 1.

8. Method for moulding a container from a parison (3) in plastic material, comprising the steps of: inserting into said parison (3) a stretching rod (23) manufactured in metal material; enveloping the parison (3) with a hollow body (25) manufactured in metal material and formed by two half-moulds (4a, 4b) that are brought close to each other so as to define a housing cavity (5) of the parison (3); blowing a fluid into said parison (3), said step of blowing comprising the sub-steps of: pre-blowing the fluid having a maximum pressure of around 16 bar; blowing the fluid having a maximum pressure of around 40 bar so as to obtain the container, characterized in that it comprises a step of applying a voltage difference between said stretching rod (23) and said hollow body (25) so as to generate a plasma.

9. Moulding method according to claim 8, wherein the step of applying the voltage difference occurs before or during the step of blowing the fluid into the parison (3).

10. Moulding method according to claim 8 , wherein said hollow body (25) is a substantially tubular body, so the step of enveloping the parison (3) occurs by moving said hollow tubular body (25) linearly along the longitudinal axis (A) of said housing cavity (5) until said hollow tubular body (25) partially or entirely envelops a tubular body (3a) of the parison (3).

11. Moulding method according to claim, further comprising a further step of applying a voltage difference between said stretching rod (23) and said half-moulds (4a, 4b), which occurs subsequently to said blowing step.

12. Moulding device (1) according to claim 4, wherein said hollow tubular body (25) is formed of a substantially continuous metal sheet.

13. Moulding device (1) according to claim 4, wherein said hollow tubular body (25) consists of a metal cage formed of a mesh or of a plurality of parallel and distanced bars.

14. Moulding method according to claim 9, wherein said hollow body (25) is a substantially tubular body, so the step of enveloping the parison (3) occurs by moving said hollow tubular body (25) linearly along the longitudinal axis (A) of said housing cavity (5) until said hollow tubular body (25) partially or entirely envelops a tubular body (3a) of the parison (3).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0031] Further characteristics and advantages of the present invention will become more apparent from the approximate and thus non-limiting description of a preferred, but not exclusive, embodiment of a moulding device for moulding a container starting with a parison in plastic material, a moulding method and a moulding machine, as illustrated in the accompanying drawings, of which:

[0032] FIG. 1 is a sectional view of a first embodiment of a moulding device for moulding a container starting with a parison in plastic material, according to the present invention;

[0033] FIG. 2 is a sectional view of a second embodiment of a moulding device for moulding a container starting with a parison in plastic material, according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0034] With reference to the figures, a moulding device for moulding a container starting with a parison 3 in plastic material, for example PET, is indicated by the number 1.

[0035] The parison 3 has a tubular body 3a and a neck 3b that does not undergo the moulding process.

[0036] The moulding device 1 comprises two half-moulds 4a, 4b that can be moved close to each other to define at least one housing cavity 5 for the parison 3.

[0037] The moulding device 1 further comprises a blowing nozzle 6 (or seal) and a stretching rod 23.

[0038] The blowing nozzle 6 is applicable on the neck 3b of the parison 3 to blow a fluid into it. The pressure of the fluid is preferably higher than the atmospheric pressure. Alternatively, the fluid is at atmospheric pressure. For example, the fluid can consist of air.

[0039] In all the embodiments described and illustrated herein, the fluid is provided by supply means of a known type.

[0040] As can be seen in the figures, the blowing nozzle 6 is applied on the neck 3b of the parison 3 in such a manner as to abut and create a tight seal on a transverse protrusion (known in the field by the technical term bague) of the neck 3b of the parison 3.

[0041] The stretching rod 23 is insertable in the parison 3 to stretch it. The stretching rod 23 is partially or entirely made of metal material.

[0042] The moulding device 1 further comprises a hollow body 25 sized so as to envelop at least partially the parison 3 placed in the housing cavity 5. The hollow body 25 is partially or entirely made of metal material.

[0043] Originally, means are provided for applying a voltage difference between the stretching rod 23 and the hollow body 25 so as to generate a plasma inside the housing cavity 5.

[0044] If the plasma is generated by the fluid (air) already present in the housing cavity 5, it is at atmospheric pressure.

[0045] If the plasma is generated by the blown fluid, it has a pressure equal to or higher than the atmospheric pressure (in that it is obtained starting from a fluid having a pressure equal to or higher than the atmospheric pressure).

[0046] The two half-moulds 4a, 4b are relatively mobile with respect to each other, at least between a first and a second configuration. In the first configuration, the two half-moulds 4a, 4b are moved close to each other to define the housing cavity 5 for the parison 3. In the second configuration, the two half-moulds 4a, 4b are moved away from each other to enable insertion of the parison 3 or to disengage the moulded container. In a first embodiment, the hollow body 25 is obtained by moving the two half-moulds 4a, 4b close to each other in the first configuration; the two half-moulds 4a, 4b enveloping the entire tubular body 3a of the parison 3.

[0047] In other words, the hollow body 25 is provided by the union of the two half-moulds 4a, 4b in the first configuration. The two half-moulds 4a, 4b are preferably made entirely of metal material.

[0048] The two half-moulds 4a, 4b are preferably part of a mould 4. In particular, the mould 4 also comprises a bottom plate (not illustrated) positioned on one of the bases of the mould 4.

[0049] Given that the voltage difference is applied between the stretching rod 23 and the half-moulds 4a, 4b in the first configuration, the plasma is generated inside the housing cavity 5 for the parison 3. In other words, the stretching rod 23 and the joined half-moulds 4a, 4b constitute the electrode and counter electrode of a plasma generator, respectively.

[0050] Given that the seal 6 is at the same potential as the two half-moulds 4a, 4b, the plasma is also generated in the external zone of the neck 3b of the parison 3.

[0051] In the first embodiment, the voltage difference required between the stretching rod 23 and the two joined half-moulds 4a, 4b can reach a value of about 30 k V.

[0052] In a second embodiment, the hollow body 25 is a body that is substantially tubular in shape. This hollow tubular body 25 is therefore separate from the two half-moulds 4a, 4b. In this case, the stretching rod 23 and the hollow tubular body 25 constitute the electrode and counter electrode of a plasma generator, respectively.

[0053] The hollow tubular body 25 is preferably movable inside the housing cavity 5 at least between an operating position, in which it partially or entirely envelops the tubular body 3a of the parison 3, and a rest position, in which it is moved away from the parison 3.

[0054] The moulding device 1 preferably comprises movement means (not illustrated) for moving the hollow tubular body 25 and the movement means are operatively active on the latter to bring it from the rest position to the operative position, and vice versa.

[0055] In particular, the movement means are operatively active on the hollow tubular body 25 to move it linearly along the longitudinal axis A of the housing cavity 5.

[0056] The hollow tubular body 25 is preferably coaxial with the housing cavity 5. In particular, when the hollow tubular body 25 is in the operating position, it proves to be coaxial with the tubular body 3a of the parison 3.

[0057] For example, the hollow tubular body 25 is formed from a substantially continuous metal sheet. Alternatively, the hollow tubular body 25 is formed from a metal sheet having a plurality of holes or through openings. An additional variant comprises a hollow tubular body 25 consisting of a metal cage formed from a mesh or a plurality of parallel spaced bars.

[0058] The moulding machine (not illustrated) proposed herein comprises a plurality of moulding devices 1 described hereinabove.

[0059] The moulding machine is preferably of the rotary carousel type. Alternatively, the moulding machine may be of the linear type.

[0060] The method for moulding a container starting with a parison in plastic material is explained below.

[0061] First of all, the parison 3 must be arranged in the housing cavity 5.

[0062] For this purpose, the two half-moulds 4a, 4b are brought into the second configuration, in which they are at a distance from each other to enable insertion of the parison 3.

[0063] Following this, the two half-moulds 4a, 4b are brought into the first configuration, that is to say, they are moved close to each other to define the housing cavity 5 for the parison 3.

[0064] The blowing nozzle 6 is applied on the neck 3b of the parison 3 in such a manner as to create a tight seal on the bague 6c and close the opening of the parison 3 in a tightly sealed manner.

[0065] The stretching rod 23 is inserted in the parison 3. In particular, the stretching rod 23 passes through the blowing nozzle 6 and gradually penetrates the parison 3.

[0066] The method shall now be described in further detail with reference to the first embodiment.

[0067] In this embodiment, the two joined half-moulds 4a, 4b form the hollow body 25 that envelops the parison 3. In particular, the two joined half-moulds 4a, 4b envelop the tubular body 3a of the parison 3.

[0068] At this point, the fluid at a pressure higher than the atmospheric pressure is blown into the parison 3.

[0069] In particular, the blowing step comprises two separate substeps: one for pre-blowing and one for blowing.

[0070] During the pre-blowing step, the fluid blown into the parison 3 has a maximum pressure of about 16 bar.

[0071] During the pre-blowing step, the stretching rod 23 gradually penetrates the parison 3 until reaching the bottom thereof. After touching the bottom, the stretching rod 23 continues its linear course so as to stretch the tubular body 3a of the parison 3 until substantially reaching the desired length of the container to be obtained.

[0072] During the blowing step, the fluid blown into the parison 3 has a maximum pressure of about 40 bar.

[0073] While the fluid is being blown into the parison 3, a voltage difference is applied between the stretching rod 23 and the joined half-moulds 4a, 4b (forming the hollow body 25) and the voltage difference is such as to bring about an electrical discharge that leads to the generation of plasma. For example, the voltage difference applied is in the range of 20-30kV.

[0074] In particular, the generation of plasma can take place only during the pre-blowing step or during the subsequent blowing step as well.

[0075] Preferably, the application of the voltage difference between the stretching rod 23 and the joined half-moulds 4a, 4b (forming the hollow body 25) also takes place after completion of the step of blowing fluid. For this purpose, following the blowing step, the stretching rod 23 is kept inside the moulded container for a length of time in the range of 1 to 2 seconds.

[0076] Envisaging plasma generation also following the blowing step, sterilization is completed by acting directly upon the moulded container.

[0077] For example, following the blowing step, the residual gas is discharged to the exterior of the moulded container and then the voltage difference is applied between the stretching rod 23 and the joined half-moulds 4a, 4b.

[0078] The generation of plasma in this step is decidedly simpler, for the fluid present in the moulded container is at atmospheric pressure.

[0079] Alternatively, it is possible to generate plasma (i.e., apply the voltage difference between the stretching rod 23 and the joined half-moulds 4a, 4b) only during the pre-blowing step or for part of the pre-blowing step.

[0080] As indicated above, it is also possible to generate the plasma as soon as the parison 3 is loaded into the housing cavity 5 and prior to the blowing step, using the air at atmospheric pressure already present in the housing cavity 5.

[0081] The method shall now be described in further detail with reference to the second embodiment.

[0082] In this embodiment, after or during the joining of the two-moulds 4a, 4b, movement of the hollow tubular body 25 takes places, bringing it from the rest position to the operating position.

[0083] In the preferred variant, the hollow tubular body 25 is coaxial with the housing cavity 5 and is inserted in the latter through a slot (not illustrated) obtained in the mould 4. For example, this slot is obtained in one of the two bases of the mould 4.

[0084] In particular, the hollow tubular body 25 is moved linearly along the longitudinal axis A of the housing cavity 5 until it partially or entirely envelops the tubular body 3a of the parison 3.

[0085] A voltage difference is subsequently applied between the stretching rod 23 and the hollow tubular body 25 and the voltage difference is such as to bring about an electrical discharge that leads to the generation of plasma. For example, the voltage difference applied is in the range of 20-30 k V.

[0086] At the same time, the fluid at a pressure higher than the atmospheric pressure, preferably 8 bar, can be blown into the parison 3. The plasma generated makes it possible to sterilize the parison.

[0087] In this context, sterilization is understood as both the total elimination of microorganisms and the reduction of microorganisms (in this latter case, it is also referred to as decontamination).

[0088] Subsequently, the hollow tubular body 25 is brought back to the rest position. Advantageously, the overall duration of the movements of the hollow tubular body 25 (from the rest position to the operating position, and vice versa) is several tenths of a second.

[0089] Moulding of the container proceeds by blowing fluid at a maximum pressure of about 40 bar in the parison 3.

[0090] In particular, during the pre-blowing process, the stretching rod 23 continues its gradual penetration of the parison 3 until reaching the bottom thereof. After touching the bottom, the stretching rod 23 continues its linear course so as to stretch the tubular body 3a of the parison 3 until substantially reaching the desired length of the container to be obtained.

[0091] After the pre-blowing step, there is a blowing step, in which fluid at a maximum pressure about 40 bar is blown into the parison 3.

[0092] There is a step for applying a voltage difference between the stretching rod 23 and the joined half-moulds 4a, 4b preferably following the blowing step. For this purpose, following the blowing step, the stretching rod 23 is kept inside the parison 3 for a length of time in the range of 1 to 2 seconds.

[0093] By activating the plasma also following the blowing step, sterilization is completed, acting directly on the moulded container.

[0094] For example, following the blowing step, the residual gas is discharged to the exterior of the moulded container and then the voltage difference is applied between the stretching rod 23 and the joined half-moulds 4a, 4b.

[0095] The generation of plasma in this step is decidedly simpler, for the fluid present in the moulded container is at atmospheric pressure.

[0096] If the step for generating plasma after the blowing step is not included, the stretching rod 23 will already begin to retract during the blowing step.

[0097] The characteristics and the advantages of the moulding device and method for moulding a container starting with a parison in plastic material according to the present invention prove to be clearly indicated in the description provided.

[0098] In particular, the moulding device proposed herein also makes it possible to sterilize the parison, owing to the generation of plasma directly inside the housing cavity housing the parison. This moulding device is compact and structurally simple in that it only requires the application of a voltage difference between the metal stretching rod and a hollow body placed in the housing cavity.

[0099] The first embodiment is the simplest one, in that it is the two joined half-moulds that function as a counter electrode with respect to the stretching rod and therefore an additional body that acts as a counter electrode is not required.

[0100] Moreover, when plasma is generated during the moulding process (e.g. only during the pre-blowing step or also during the blowing step), the blowing process takes place by means of the plasma. In this manner, the parison is moulded and sterilized simultaneously.

[0101] Given that sterilization and moulding of the parison are inseparable processes, no further measures are required to maintain ambient contamination below the desired level. In fact, the container is moulded under sterile conditions owing to the plasma generated therein. Therefore, the dimensions are limited and the line is simplified in light of the simultaneous execution of two steps, i.e., sterilization and moulding, which until now had always been performed sequentially.

[0102] In the second embodiment, the hollow tubular body that acts as a counter electrode with respect to the stretching rod is instead present in the housing cavity.

[0103] In this embodiment, the distance between the two electrodes (the stretching rod and the hollow tubular body) is shorter compared to the first embodiment, so that the volume of dielectric between the electrodes facilitates plasma ignition.

[0104] In this case, generation of plasma always takes place in the moulding device, prior to moulding or during part of the pre-blowing step and therefore with decidedly low pressures (even at atmospheric pressure). This makes the plasma generation process simpler. In fact, it is a known fact that an increase in the pressure of the incoming fluid makes it more difficult to activate the plasma because it increases the resistance of the fluid (which functions as a dielectric) to the discharge.

[0105] Moreover, the realization of the hollow tubular body as a metal cage offers the advantage of reducing movement time for moving it (given that the cage is lighter than a body having solid walls), thus making it possible to begin sterilization promptly prior to moulding and making it possible to move the cage away quickly even before the beginning of the pre-blowing step. In fact, the total time required for movement of the metal cage consists of several tenths of a second. Furthermore, by generating the plasma at atmospheric pressure after the blowing step (by means of the application of a voltage difference between the stretching rod and the half-moulds), sterilization is also completed on the moulded container.

[0106] This is even more advantageous in the second embodiment, given that sterilization of the parison is carried out prior to moulding or during the first moulding step.

[0107] Given that sterilization of the parison is carried out in the housing cavity just before the moulding process or at the same time as the moulding process (and possibly subsequently to the moulding process, on the moulded container), a conventional blower can be used. This conventional blower thus becomes a blower/sterilizer.

[0108] The structural complexity of the aseptic blower with an isolator can thus be left aside, along with all the members operating at the interface thereof (e.g. sealing systems between the sterile zone and the external environment, confinement of the stretching rod, sterilization system for the blown air circuit, etc.).

[0109] Sterilization cycles for sterilizing the environment and the blown air prior to production are no longer necessary.

[0110] Moreover, the sterilizer for sterilizing the parisons upstream of the blower can thus be eliminated.

[0111] In conclusion, the use of plasma makes it possible to reduce sterilization time, to avoid the use of chemical agents and the accumulation of peroxides in the container, and to sterilize the internal surface and the external neck of the parison and the container in a substantially uniform manner.