EP0000801B1 - Method for producing oriented hollow bodies - Google Patents

Description

The present invention relates to a process for the production of oriented hollow bodies of thermoplastic material, such as bottles and similar articles, the neck of which has an orifice ring at its upper part allowing the application of a tight closure.

It is well known to produce hollow bodies made of thermoplastic material which have substantially improved mechanical properties by using production techniques leading to an orientation, preferably biaxial, of the macromolecules constituting their wall. According to a common technique for producing such hollow bodies, which is described in particular in French patent applications 2261 117 of February 12, 1974, 2,263,874 of March 15, 1974, 2,297,127 of October 30, 1975 and 2,345,280 of March 22 1976 registered in the name of SOLVAY & Cie, we first blow out preforms, of generally cylindrical shape, generally comprising a closed bottom and a molded neck in its final form. These preforms are then thermally conditioned so as to bring them to an optimum temperature for orientation by stretching. Then, these conditioned preforms are blown in order to give them the shape of the desired hollow bodies. The diameter of the preforms and their length are chosen so that they are strongly stretched, preferably biaxially, during the final blowing.

As it is generally essential that the hollow bodies produced according to this technique can be provided with a perfectly sealed closure, their necks are usually molded, not during the final blowing, but during the blowing of the preforms. Indeed, as the thermoplastic material is at a relatively high temperature during the blowing of the preforms, the neck can be molded while ensuring perfect fidelity of the details and precise calibration of the orifice.

Unfortunately, the final molding of the neck, during the blowing of the preforms has serious drawbacks. Thus, when the neck area does not have symmetry of revolution, for example because it is threaded, special precautions must be taken to transfer the preforms without damaging the neck and to position them correctly in the final blow mold. In addition, the thermoplastic material is misused at the neck since the wall necessarily has a thickness almost equal to that of the starting tubular parison and has unattractive properties since it is not oriented.

To overcome these drawbacks, it has been proposed, as described in French patent application 2 293 297 filed on December 4, 1974 in the name of CARNAUD TOTAL INTERPLASTIC, to carry out the molding of the neck of the hollow body completely during molding by final blow. However, it has been found that the molding of the neck during this last step is difficult because it is carried out at a relatively low temperature and the plastic material is no longer at an optimal molding temperature. We are therefore often led to have to resort to complex techniques such as those described in French patent application 2 005 138 filed March 28, 1969 in the name of HERCULES INC. or in French patent application 2 062 304 filed on September 17, 1970 in the name of R. BOSCH GmbH to obtain a more correct molding of the neck.

In patent US 3,833,332 filed on November 17, 1972 in the names of R. and S. AMBERG, there is also described a device for molding stackable preforms into non-molecularly oriented containers having a threaded neck in which the preforms are warmed to molding temperature and are then shaped by blowing in a suitable mold. The preforms used have a peripheral external rim which is used to maintain the preform during heating and the final forming and can be eliminated after the latter forming. In this technique, the edge of the preform may be deformed during heating and during the final forming.

The Applicant has now found a process which, while allowing the tight sealing of the hollow bodies produced, overcomes the aforementioned drawbacks of the usual technique in a remarkably simple manner.

The present invention therefore relates to a process for the production of oriented hollow bodies of thermoplastic material, the neck of which has an orifice ring at its upper part and a molded lower part, in which preforms are blow molded from a hot tubular parison of thermoplastic material, the preforms are thermally conditioned at a temperature capable of inducing the orientation of the thermoplastic material during its stretching, and the preforms are blown into final blow molds and in which the ring is molded. orifice in its final form during the blow molding of the preforms and the lower part of the neck is molded during the final blowing.

The shape and dimensions of the orifice ring are not critical and are chosen, in general, according to the closure which it is desired to use on the hollow bodies produced. Thus, the ring can have a rounded profile at its upper part and at right angles to its lower part when it is desired to close the hollow bodies with metal capsules. For other types of closures, such as screw caps, the ring may have a circular or rectangular section for example. In general, the height of the ring is between 1 and 10 mm and its thickness between 0.5 and 5 mm.

In the method according to the invention, the orifice ring can be molded with very great precision since the thermoplastic material can be brought to its ideal temperature to ensure the fidelity of the details and the precision of the calibration during the production of the preforms. Furthermore, the transfer of the preforms no longer poses a problem and their positioning in the final blow mold is greatly simplified since the orifice ring can have a symmetry of revolution without disadvantage. Therefore, the problem of angular positioning of the preforms is eliminated and it suffices to ensure the positioning in height which can be very simple since it can even be done by gravity. Finally, the method according to the present invention gives the possibility of stretching the lower part of the neck during its molding during the final blowing.

The preforms which can be used to carry out the process according to the invention can be in any form, provided that they comprise, in the upper part of their neck, in the region adjacent to the opening of the hollow body, a ring of molded orifice in its final form.

According to a preferred embodiment, the preforms are provided with a false neck located above the orifice ring. This false neck is eliminated either before or after the final blowing. Generally, the thermoplastic material which constitutes it is recycled by grinding. This false neck can be advantageously used for blowing the preform by means of a needle, or the transfer and positioning of the preforms. The false neck can be closed or opened, according to the blowing technique used for molding the preforms, and it can be provided with ribs, grooves and lugs depending on the operation that one wishes to make of it.

According to an also preferred embodiment, the preforms used have a closed hemispherical bottom and a body of generally cylindrical shape. The maximum diameter of the preforms is preferably between 20 and 80% of the maximum diameter of the oriented hollow bodies produced from these preforms. Their height can be equal to that of the desired hollow bodies but, in general, it is preferred that the height of the preforms is between 20 and 80% of the height of the oriented hollow bodies produced from these preforms.

The preforms are molded from a hot tubular parison of thermoplastic material, the production of which presents no particular difficulty and can be ensured by a conventional extruder.

The technique used for the blow molding of the preforms can be arbitrary as long as it allows the production of an orifice ring molded with precision in its final form. Thus, one can advantageously use the process described in Belgian patent 826 676 filed March 14, 1975 by the Applicant, which relates specifically to the production of preforms equipped with a closed hemispherical bottom. We can refer to it for the production of the preforms usable according to the invention obviously taking into account that the neck of the preforms must not be molded in its entirety but must only comprise an orifice ring at its upper part.

According to a preferred variant of the method according to the invention, the false neck, which is preferably housed on the preforms, is kept during the final blowing operation and extends, at least in its upper part, from the final blowing mold . In this way the false neck can be exploited to ensure the introduction of the preform into the final blow mold as well as the positive extraction of the oriented hollow body produced by means of a gripping member acting at the false neck. The false neck can, in this case, be removed later by a bar turning operation. To this end, it is advantageous to use bar turning devices such as those described in Belgian patents 673913 of December 17, 1975, 774525 of October 27, 1971 and 809448 of July 7.14, filed in the name of the Applicant. For this purpose, it is useful to provide a groove making an angle on the preform between the orifice ring and the false neck so as to facilitate the action of the turning tool. For bar turning, the positioning can advantageously be ensured by the false neck itself.

When the final blowing of the conditioned preforms is carried out by means of a blowing nozzle which is inserted into the preforms and the preforms are of the type with false closed neck, it is obviously advisable to provide, before the final blowing, a cutting of the false necks in order to provide an opening allowing the insertion of the blowing nozzles into the preforms.

It is advantageous that the molding of the preforms is used to condition the preforms produced by cooling them or, at least, to initiate the thermal conditioning. This result can in particular be achieved by equipping the preform molds with suitable means such as refrigerant pipes.

The thermal conditioning can be carried out or continued by the usual means, and for example in one or more thermostatted enclosures in which the preforms remain after they are removed from the mold and before their introduction into the blow molds.

Thermal conditioning can consist of cooling the preforms so as to bring them in the desired temperature range, or to cool them more strongly and then reheat them to bring them into this same range. The temperature is obviously chosen according to the nature of the thermoplastic material.

By thermal conditioning, the preforms can be brought to a uniform temperature over their entire useful height or over their entire thickness. It is also possible to carry out thermal programming along preforms. Thus, it may be advantageous to bring the region of the preforms located just below the orifice ring to a temperature slightly higher than the rest of the preforms so as to promote the stretching and, consequently, the thinning of this region. during the final blowing.

During the thermal conditioning of the preforms, it is obviously not necessary to treat the false necks as well as the orifice rings since the first are removed later and the second are molded into their final shape.

After having been thermally conditioned, the preforms are introduced into the final blow molds where they are given the final shape of the desired oriented hollow bodies and where one proceeds in particular to the molding of the lower part of the neck, below the orifice ring .

According to a preferred embodiment of the method according to the invention, the final blowing is carried out by means of a blowing nozzle which is inserted into the preforms and which is designed so as to participate in the axial stretching of the preforms before or during their blowing. It is particularly advantageous to use, for this purpose, the blowing technique which is described in Belgian patent 838 910 of 25.2.1976 in the name of the Applicant.

During the final blowing, it is advisable to correctly position the orifice ring of the preforms in a housing provided in the mold cavity, avoiding any deterioration of this ring.

The seal between the blowing nozzles and the preforms during the final blowing can be ensured by pressing the nozzle directly on the orifice ring. The nozzle can also rest on the false neck of the preforms and more particularly on its lower part. The blowing nozzles can, in these two cases, be used simultaneously to ensure the internal calibration of the necks.

The shape imparted to the lower part of the neck of the final blowing may be any. The molding may in particular consist of a thread. However, since the material making up the preforms is, at the time of final blowing, at temperatures which are relatively different from the ideal temperature for molding details, it is preferable, as far as possible, to avoid forming moldings having radii very small curvatures, for example less than 1 mm.

The method according to the invention can be used to produce oriented hollow bodies from any thermoplastic material which can be molecularly oriented by drawing. Examples of the latter include resins with a predominant vinyl chloride content, polyolefins, acrylic copolymers with a high content of acrylic nitrile, thermoplastic polyesters such as polyethylene glycol terephthalate, and polycarbonates.

The process according to the invention can be easily carried out by means of a simple apparatus comprising molds for molding the preforms, the imprint of which ensures the molding of the orifice ring in its final form, and final blow molds. whose imprint ensures the precise housing of the orifice ring and the molding of the lower part of the neck.

One can very advantageously use a device derived, mutatis mutandis, from that described in Belgian patent 837 324 filed on 6.1.1976 by the Applicant. In this case, the apparatus comprises a machine for blowing preforms which is fed by a continuous tubular parison of thermoplastic material and whose molds aligned end to end in a contiguous manner on a first rotary support have suitable imprints allowing the production of a false neck, a thermal conditioning device bringing the preforms to the orientation temperature, a final blowing machine comprising a plurality of molds mounted on a second rotary support and also having suitable imprints and a transfer device, consisting of a endless chain equipped with supports, ensuring the transfer of the preforms from the preform blowing machine to the final blowing machine by passing them through the thermal conditioning device.

In such a device, contrary to what is specifically described in the aforementioned Belgian patent 837 324, it is not necessary to provide a device for deburring the necks of the preforms upstream of the final blowing machine since the false necks can be kept during the final blowing operation. However, when the molds equipping the preform blowing machine are designed so as to produce preforms in which the false necks are closed, as is the case, for example, when the molding of the preforms is carried out by blowing using a hollow needle which laterally pierces the successive portions of parison enclosed in the preform molds, it is useful to provide a device, for example similar to that described in Belgian patent 837 324, to open these false necks upstream of the machine final blowing, for example by removing their upper part. However, this device can be mounted directly in the blow molds. movable blades which are actuated after blowing the preforms and cutting transversely the molded false necks at a certain distance from the orifice rings provided on the preforms.

The supports equipping the preform transfer chain are preferably adapted to grip these preforms at their false neck during transfers. It is however possible to provide supports adapted to support the preforms below their orifice ring as described in the aforementioned Belgian patent 837 324.

The final blowing machine can be similar to that described in Belgian patent 837 324. It is preferable that the blowing nozzles fitted to this machine are of the same type as that described in Belgian patent 838 910 already mentioned above.

This final blowing machine can very advantageously be equipped with extendable radial arms provided at their end with a clamp adapted so as to grip the false neck of the preforms, the upper part of which at least projects beyond the final blowing mold. After opening the final blow mold, the radial arm can be used to positively remove the hollow body from the mold, move it away from the final blow machine and transfer it, for example, to a conveyor which evacuates the hollow bodies to a free-cutting installation where their fake bottleneck is eliminated.

The invention is illustrated by the figures of the appended drawings which relate to molds which are particularly suitable for carrying out the process according to the invention by means of an apparatus such as that described in Belgian patent 837 324. It is however understood that these figures are given by way of illustration and that therefore they in no way limit the scope of the present invention.

• - la figure 1 est une vue en coupe et en élévation d'un moule convenant particulièrement pour le moulage des préformes;
• - la figure 2 est une vue en coupe partielle et en élévation d'un ensemble de moulage convenant pour le soufflage final des préformes obtenues à l'aide du moule de la fig. 1;
• -la figure 3 est une vue en coupe partielle et en élévation analogue à celle de la fig. 2 montrant l'extraction du corps creux orienté finalement moulé.

In these drawings,

• - Figure 1 is a sectional and elevational view of a mold particularly suitable for molding preforms;
• - Figure 2 is a partial sectional view in elevation of a molding assembly suitable for the final blowing of the preforms obtained using the mold of FIG. 1;
• FIG. 3 is a view in partial section and in elevation similar to that of FIG. 2 showing the extraction of the finally molded oriented hollow body.

As it appears in fig. 1, the preform mold 1, which can be mounted with other identical on a rotary blow molding device not shown, has an imprint 2 whose relief allows the blow molding from a portion of hot tubular parison of thermoplastic material, of a preform comprising a closed hemispherical bottom 3, a generally cylindrical body 4, an orifice ring 5 molded in its final shape and a closed false neck 6 surmounting this ring. The preform is molded by blowing using a retractable hollow needle 7 which pierces the parison in the region intended to form the false neck and which is connected, in a manner known per se, to a source of non-pressurized fluid represented. The walls of the mold 1 are equipped with refrigeration channels, not shown, the function of which is to cool the molded preform in order to allow it to be removed from the mold and possibly to ensure total or partial thermal conditioning of the preform. The length of the molded preform is substantially less than the height of the hollow body oriented to produce and its diameter is significantly less than the maximum diameter of the same hollow body.

After molding and refrigeration, the preform is extracted from the mold 1 and is transferred by passing through a conditioning device. thermally, to the final blow mold. During this transfer, the upper part of its false neck 6 is cut in order to open the upper part of the preform. The means used for the transfer grip the preform at its false neck 6 and cooperate with the groove which is formed therein so that the upper part of the false neck 6 is released in order to allow the cutting of this part.

The thermally conditioned preform is introduced into a final blow mold 8 which is shown in FIG. 2 and is mounted on a rotary support, not shown.

The mold 8 comprises an imprint 9, the relief of which has a recess 10 allowing the precise housing of the orifice ring 5 molded in its final shape on the preform. The introduction of the preform into the mold 8 is carried out in such a way that, when the mold is closed, the orifice ring 5 comes to be housed precisely in the recess. This introduction can in particular be ensured, for example by means of the device for transferring the preforms, via the false neck 6.

The imprint 9 of the mold 8 reproduces in hollow the shape of the desired oriented hollow body 11 and in particular comprises a relief 12 allowing information during the final blowing of the lower part of the neck 13 of the hollow body.

The open false neck 6 of the preform overflows from the mold 8 during the final blowing operation. It is used to ensure airtightness during blowing. To this end, the blowing nozzle 14 has a shoulder 17 which comes to bear on the internal lower part of the false neck 6 and firmly applies the latter against the edge of the opening 18 of the mold 8.

The blowing nozzle 14 comprises a calibration sleeve 19 which precisely controls the opening diameter of the neck of the hollow body 11, and ensures the sealing and the retention of the preform during the final blowing.

The rotary final blowing device is setting of the preforms and being constituted by provided with a series of extendable radial arms 20 which each collaborate with a final blow mold 8. The ends of these arms 20 are equipped with removable clamps 21 adapted so as to come to close on the false necks 6 of the preforms, the upper part of which extends beyond the final blow molds 8.

As shown in FIG. 3, after opening the final blow mold 8 and removing the blow nozzle 14, the molded oriented hollow body 11 is held by a clamp 21 which thus ensures that it is removed from the mold cavity 9. Next, the arm 20 can be extended to radially take out the molded oriented hollow body 11 from the final blowing machine and bring it onto an evacuation conveyor 22 where it is abandoned by opening the clamp 21. The control of the radial arms can be ensured by mechanical means such as cams or by electrical, pneumatic or hydraulic means. The radial extension movement of the arms 20 can be amplified by known devices such as rack and pinion devices. The radial arms 20 fitted with clamps 22 can also be exploited by a reverse movement to ensure the introduction of the conditioned preforms into the final blow molds 8.

Thanks to the invention, it is easy to produce, with a remarkably high yield, oriented hollow bodies of thermoplastic material to which it is easy to apply closures, such as capsules, very tightly and which, therefore, particularly suitable for the packaging of carbonated drinks such as beer and lemonades.

Claims (10)

1. Process for the production of oriented hollow bodies which are made from a thermoplastic and whose neck possesses an orifice ring (5) at its upper part and a moulded lower part (13), in which process preforms (4) are moulded from a hot tubular parison of thermoplastic, the preforms (4) are heat-conditioned at a temperature which is capable of causing the orientation of the thermoplastic when the latter is drawn, and the preforms (4) are blown in final blowing moulds (8), characterised in that preforms (4) are blow moulded which possess the orifice ring (5) in its final shape and which at the top possess a false throat (6), located above the orifice ring (5), and the lower part (13) of the neck of the hollow bodies is moulded during the final blowing.

2. Process according to Claim 1, character- sed in that the lower part of the neck is drawn during the final blowing.

3. Process according to Claim 2, characterised in that the lower part of the neck is heated, during the heat conditioning, to a higher temperature than is the remainder of the preforms.

4. Process according to any one of Claims 1 to 3, characterised in that a nozzle ( 14), which rests directly against the orifice ring (5) so as to ensure that there is no leak is used for the final blowing.

5. Process according to any one of Claims 1 to 4, characterised in that at least the upper part of the false throat (6) is made to protrude from the final blowing mould (8).

6. Process according to any one of Claims 1 to 5, characterised in that the preforms (4) and the hollow bodies (11) are gripped at their false throat (6) for transfer purposes.

7. Process according to any one of Claims 1 to 6, characterised in that the preforms (4) and the hollow bodies (11) are positioned by means of their false throat (6).

8. Process according to any one of Claims 1 to 7, characterised in that the preforms (4) are blow-moulded by means of a retractable hollow needle (7) which comes into action at the level of the false throat (6).

9. Process according to any one of Claims 1 to 8, characterised in that the preforms (4) have a hemispherical base (3) and a body of cylindrical general shape.

10. Process according to any one of Claims 1 to 9, characterised in that a nozzle (14) which rests against the false throat (6) to ensure that there is no leak is used for the final blowing.

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