METHOD FOR MOULDING HOLLOW CONTAINERS IN MOLECULARLY ORIENTATABLE PLASTICS MATERIAL

Abstract: Apparatus for moulding hollow containers in molecularly orientatable plastics material, which comprises a plurality of operating units, composed of at least one injection moulding group (2) for hollow preforms (19) having walls of great thickness, one or more axial elongation groups (3) for the preforms, at least one blowmoulding group (4) and at least one discharge unit (5), disposed in sequence at equal intervals along the closed path of a conveyor (6) having trollies (7) which can be advanced by steps, which trollies (7) possess jaws (15) adapted for gripping the neck of the preform and for supporting same throughout the entire travel through the conveyor. The method of moulding the containers comprises the successive phases of injection moulding an internally hollow preform, closed at one end, having walls of great thickness and a collar open at the top, of bringing the preform to a temperature at which a molecular orientation takes place as a consequence of a mechanical deformation in the plastics material, and at this temperature, of carrying out one or more axial elongations of the preform and of carrying out the blowmoulding of the elongated preform.

Description: APPARATUS AND METHOD FOR MOULDING HOLLOW CONTAINERS IN MOLECULARLY ORIENTATABLE PLASTICS MATERIAL This invention relates to an apparatus and a method for the moulding of hollow containers in molecularly orientatable plastics material. For many purposes containers of plastics material are used, suitable for containing liquids such as, for example, drinks and the like. Such drinks frequently have added carbon dioxide, or indeed contain gases which can become released when the temperature varies or the drink is agitated, causing the container to'become pressurised. Containers suitable for this purpose must, therefore, be resistant to the internal pressure applied to them and, moreover, must also be impermeable over long periods to the gases dissolved in the contained liquids. A plastics material suitable for this purpose is polyethylene terephthalate, which can be subjected to mechanical stretching deformations at an appropriate temperature, which impart to it a molecularly orientated structure suitable for providing characteristics of mechanical strength and impermeability to gases substantially higher than those of the non-orientated polymer and suitable for use in the aforementioned containers. Polyethylene terephthalate in fact, known by the abbreviation PET, has undergone in the years following its discovery a continual improvement of the technology of production, permitting the use of said material for a vast range of applications with rather successful results, in particular for the production of hollow objects such as containers, bottles and the like. Compared with other materials, in fact, polyethylene terephthalate lends itself especially to the production of hollow objects, suitable for containing foods also saturated with gases (of the orangeade type and so on). For this purpose, it is particularly advantageous to achieve a molecular orientation in two orthogonal directions in the material, thereby obtaining the best results in regard to mechanical strength and impermeability to gases, of fundamental importance for such containers. The problem therefore presents itself of realising an apparatus for the moulding of containers which shall enable a molecularly orientated structure to be obtained in the greater part of the container, with a rapid production cycle and high versatility in use, which shall be adaptable, for example, to seasonal variations in production or to other requirements. In particular, it is extremely important to carry out a thermal conditioning of the workpiece during moulding, at the moment of its mechanical deformation in order to achieve the internal molecular orientation, which shall provide the maximum uniformity of temperature throughout the thickness of the workpiece, so as to achieve the orientation throughout the entire section subjected to deformation. According to one aspect of the present invention, there is provided an apparatus for moulding hollow containers in molecularly orientatable plastics material, characterised by a plurality of operating units, composed of at least one injection moulding group for hollow preforms having walls of great thickness, one or more axial elongation groups for the preforms, at least one blowmoulding group and at least one discharge unit, disposed successively at equal intervals along the closed cycle path of a conveyor having trollies capable of advancing by steps, which trollies possess jaws adapted for gripping the neck of the preform and for supporting same throughout the travel along the conveyor. The jaws of the trollies may possess shaped opposite surfaces having the negative form of the neck of the receptacle being moulded, which constitute the moulding shape of the corresponding portion of the preform, and the members for supporting the preforms along their travel through the conveyor. With advantage, in one particular form of embodiment, the apparatus may comprise two operating units, each composed of an injection group, one or more axial elongation groups, a blowmoulding group and a discharge unit, disposed in sequence along the closed cycle path of the trolley conveyor, these units being capable of operating independently, served by the single trolley conveyor. According to a different form of embodiment, the apparatus may comprise a discharge unit disposed ahead of the blowmoulding group and adapted for discharging the preforms after their axial elongation and before they are blowmoulded, for storage or for sale, or it may comprise a preforms loading unit disposed in front of a blowmoulding group, for the moulding of containers starting from elongated preforms previously stored. For the purpose of enabling the apparatus to be of dimensions corresponding to the production requirements, the conveyor can have a preselectable length as a function of the number of operating stations provided on it. Preferably, the injection moulding group includes a press, comprising a lifting cylinder for a mould block of a mould comprising one or more mould cavities-, the lifting cylinder being adapted for bringing the mould block into coupling engagement with the jaws of the trolley and for bringing the injection point of the mould into register with the nozzle of the injection moulding machine, and a cylinder for introducing corresponding mandrels inside the mould cavities of the mould block, determining in co-operation with same and with the internal form of the jaws of the nozzle the volume of the preform to be injection moulded. The axial elongation group can comprise one or more thermal stabilisation moulds, equipped with heat exchange devices and carrying cavities adapted for receiving the prefroms carried by a trolley of the conveyor, which moulds can be raised by an actuator for coupling to the jaws of the trolley, a further actuator being provided, carrying mandrels, appropriately equipped with heat exchange means, such as for example a circulation of heat exchange fluid, the mandrels being adapted for entering into the preforms and causing their elongation. Preferably, the blowmoulding group comprises two half-moulds which can be clamped by means of a closure device, around the preforms carried by the jaws of the conveyor trolley, these jaws being equipped with mould cavities surrounding the preforms and each corresponding to the shape of the container, and comprises a blowing device, having nozzles which can be introduced into the trolley as far as the mouth of the preform or preforms, the nozzles being connected to a pneumatic apparatus and equipped with internal arms, which can be introduced into the preforms as far as their closed end. In one particular form of embodiment, the clamping device for the blowmoulding group is composed of lever means operated by an actuator member, coupled together for the simultaneous closing of the two half-moulds around the preforms. According to a second aspect of the present invention, there is provided a method of moulding hollow containers in molecularly orientatable plastics material, characterised by the steps of injection moulding an internally hollow preform, closed at one end, having walls of great thickness and an open-topped collar, bringing the preform to a temperature at which a molecular orientation takes place as a consequence of a mechanical deformation in the plastics material and, at this temperature, carrying out one of more axial elongations of the preform and blowmoulding the elongated preform. According to a third aspect of the present invention, there is provided a method of moulding hollow containers in molecularly orientatable plastics material, characterised in that it comprises the steps of injection moulding of an internally hollow preform, closed at one end, of bringing the preform to a temperature at which a molecular orientation takes. place as a consequence of a mechanical deformation in the plastics material, of carrying out one or more axial elongations of the preform itself and of discharging the elongated preform, having walls of reduced thickness, for the purpose of its storage, said preform being able to be taken up again later, raised to the temperature adapted for carrying out molecular orientation by drawing and shaped by blowmoulding to the form of the final receptacle. The phase of injection moulding the preform, in one particular form of embodiment of the method, comprises the partial introduction of a mandrel into the mould block of an injection moulding press, the injection of a predetermined quantity of the plastics material in the plasticised state, this quantity corresponding to the volume of the preform, into the space existing between the mould and the mandrel, the cooling of the material down to a temperature at which a molecular orientation takes place as a consequence of a mechanical deformation of the material itself, and the full introduction of the mandrel into the mould block for moulding the preforms For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: : Figure 1 is a schematic plan view of one form of embodiment of an apparatus for moulding hollow containers in molecularly orientatable plastics material; Figure 2 is a side view, partly in section, of the machine shown in Figure 1, in section along the line II-II; Figure 3 is a section taken along the line III-III of Figure 1; Figure 4 shows an injection moulding group in an open position; Figure 5 shows the injection moulding group in a partly closed position; Figure 6 shows the injection moulding group in the closed position; Figure 7 shows a thermal conditioning and axial elongation group; Figure 8 shows a blowmoulding group for the container; Figure 9 shows a preform as produced by the injection moulding group; Figure 10 shows the preform after a first elongation; Figure 11 shows the preform after a second elongation; Figure 12 shows the preform after blowmoulding; ; Figure 13 shows a sectional detail of a trolley and of its runway; Figure 14 shows a plan view of the trolley; Figure 15 is a side view of the trolley; Figure 16 is a section taken along the line XVI-XVI of Figure 14 and shows a device for opening the jaws; Figure 17 is a schematic plan view of the apparatus in one particular arrangement; and Figure 18 is a schematic plan view of the apparatus in a different arrangement. As Figure 1 shows, an apparatus for the production of hollow blowmoulded containers comprises substantially an extruder 1, capable of being connected to an injection moulding group 2, ¯ a plurality of thermal conditioning and axial elongation groups 3, a blowmoulding group 4 and a discharge station 5. These groups are connected to one another by a conveyor 6, equipped with trollies 7 carrying the workpieces during the moulding procedure. The spacings between the trollies 7, which are connected to one another by rigid bars 8, is equal to or a sub-multiple of the distance existing between the aforementioned groups, in such a way that each forward step of the conveyor 6 corresponds to the locating of a trolley 7 beneath one of the.working groups. The conveyor 6 is carried on floors 9, which support the groups present and are secured to a base frame 10 by columns 11. The injection moulding group 2, illustrated in greater detail in Figure 4, is composed of a press, which comprises a mould block 12 and the mandrels 13; the mould block 12 is carried by a cylinder 14, by which it can be caused to approach the floor 9 and brought into the injection moulding position, becoming engaged onto conical projections 15a of the jaws 15 of the trolley 7, inside which jaws there are formed the mould cavities corresponding to the external surfaces of the neck of the receptacle. Pins or mandrels 13 are carried by a movable frame 16, operated by a cylinder 17 for introduction into mould cavities 18 of the mould block. In correspondence with the mandrels 13, holes 9a are present in the floor 9 adapted for permitting the mandrels to enter the mould block 12, by passing through the trolley 7 locked in position beneath them; similar holes are also present in correspondence with the other groups of the apparatus. The injection moulding group produces by moulding or pressing the hollow objects 19, known as "preforms", which are adapted to be subjected to the successive moulding operations. These preforms remain, after moulding, suspended from the support jaws 15 of the trollies 7, which jaws contain the mould cavity adapted for permitting the shaping, during injection, of the neck of the container, bearing the threaded coupling 20. The preforms 19 are then transferred by the conveyor 6 to the first thermal conditioning and axial elongation group 3a, where they are brought to the temperature necessary for performing on them a first elongation with molecular orientation in the axial direction, usually. between 900C and 1100C for polyethylene terephthalate. Each group 3, illustrated in detail in Figure 7, comprises thermal stabilisation moulds 21, adapted for bringing the preforms to the drawing temperature, these moulds being supported by a plate 22 which can be raised by a cylinder 23 until they close against the jaws 15, thus closing the preforms 19. Above the floor 9 there is a frame 24, on which is mounted a cylinder 25, carrying mandrels 26, suitably equipped with internal circulation of heat exchange fluid and adapted to be introduced into the preforms 19 for the purpose of causing the desired elongation. The blowmoulding group 4, illustrated in Figures 2, 3 and 8, comprises two half-moulds 26, capable of being clamped around the preforms 19 by means of a closure device, sliding on guide bars 26a. The closure device may comprise, for example, as illustrated in Figure 2, a pair of levers 27, operated by a cylinder 28 and acting via rods 29 on the two half-moulds 26. The ends of the cylinder 28 are articulated to the lower ends of the levers 27; for the purpose of permitting simultaneous closure of the two half-moulds 26 symmetrically about the centre line position of the blowmoulding group, that is in correrspondence with the axis of the container to be moulded, a rocker lever 30 is provided, pivotal about a pin 31 and connected by connecting rods 32 to the ends of the cylinder 28. Above this cylinder is located a blower device having nozzles 33, capable of being introduced by a cylinder 34 through the floor 9 and trollies 7 to fit into the preforms 19 and carrying bars 35 for centering the ends of the preforms during blowing, the bars being introduced into the preforms themselves by the cylinder 36, guided by columns 37. In this group, blown containers 38 are moulded, remaining suspended from the jaws 15. Blowing for moulding the containers 38 produces tension in the walls of the containers in a direction perpendicular to the tension produced by the elongation, thus producing containers having walls drawn in two orthogonal directions, thereby producing an optimum molecular orientation. In fact, as indicated in Figures 9, 10, 11 and 12, the preform 19, which is shown in Figure 9 with the dimensions it possesses immediately after injection moulding, undergoes one or more axial elongations, shown in Figures 10 and 11, at the temperature at which the molecular orientation takes place, these axial elongations producing a first orientation in the direction indicated by the arrows A. The blowing operation then leads to a container having the form shown in Figure 12, and causes a drawing and molecular orientation in the circumferential direction, as indicated in the Figure by the arrow C, this orientation being added to the axial orientation A. The trolley of the conveyor 7 is described, by way of example, with reference to Figures 13 to 16. It is composed of a body 39, equipped with guide rollers 40 and carried by the guides 41 beneath the floors 9, on which the jaws 15 are mounted, divided into two parts to enable them to open. The successive trollies are connected to one another by bars 42 and are spaced apart in such a way as to transfer a trolley from one station to the next at each advancement step As illustrated in the Figures, near to the end of each trolley a hole 43 is located in the body 39, and corresponding inclined planes 44, formed on the two jaws 15, into which a wedge 45 carried by an actuator of the discharge station 5 can enter, as shown in Figure 16 in two phases, at the right shown partially introduced and with the jaws 15 still closed, but at the left shown fully introduced, thereby determining the relative movement apart of the jaws, in opposition to elastic closure means, such as for example the spring 46, and thereby causing-the-workpiece carried by the jaws to be dropped and discharged, the jaws 15 being slidably guided on the guide and support profiles 47 of the body 39. The structure of the apparatus enables the productive cycle to be carried out in an optimum manner, with reduction of the times required for the execution of the operations, and permits the maximum flexibility in operation, it being possible to vary the length of the conveyor and the number of groups mounted on it. For example, it is possible to decide upon an axial elongation of the preforms in one or more phases, by providing one or more elongation groups 3; to provide a discharge station for the injection moulded preforms, for example after they have been elongated, for the storage or sale of semifinished products having a smaller bulk than the finished containers; to provide an automatic loading station 48 for the preforms, which previously have been stored, for the purpose of carrying out their blowing, as illustrated in Figure 17, associated with a preheating furnace 49 for the preforms adapted for raising them to the temperature at which the deformation with molecular orientation takes place; to provide further working stations, for various finishing operations and possibly for production-line filling of the containers produced, or again to provide two oppositely situated injection moulding groups, followed by associated axial elongation and blowing groups along the same conveyor, as illustrated in Figure 18. The use of. the apparatus permits, in particular, the subsidiary operations which can be carried out on the containers to be executed, such as labelling, checks and inspection of various types, surface coating, fitting of a support base, in-line filling and the like, all directly, by providing an appropriate extension of the conveyor so as to enable the further operating stations required to be arranged upon it, without the need to have recourse to one or more further machines, thereby achieving a considerable saving, both from the economic point of view and from the point of view of functioning and overall size of the various members necessary for the production of the finished container, which is thus completed in a single complex. The presence of the elongation phases enables the thickness of the preform to be brought to a lower value, suitable for enabling a high uniformity in the temperature of the walls of the workpiece to be obtained in a short time, in the successive working phases, which require an appropriate temperature for the workpieces and provide, for this purpose, thermal conditioning times, thus enabling a complete molecular orientation to be achieved throughout the thickness. As shown in Figures 5 and 6, injection is arranged, in a convenient form of embodiment, in two successive phases. The first phase consists of injecting the material in the plastic condition by the mandrels 13, only partly inserted into the mould cavities 18 of the mould block 12, with partial filling of the volume available; the second phase provides for the complete introduction of the mandrels into the respective mould cavities, causing the injected material to flow until it entirely fills the space available, thereby forming the neck and mouth of the receptacle. This procedure enables injection to be carried out at a low pressure into the mould cavity, avoiding or considerably reducing the deterioration of the material and consequent formation of acetaldehyde. The second phase of moulding is formed with the material at a lower temperature than the injection temperature and makes it possible to impart to the material, which in this phase undergoes a mechanical deformation leading to a reduction in its thickness, an initial molecular orientation, which therefore leads to an improvement in its characteristics, in particular the permeability to gases, including in the zone of the neck, which is not further drawn later. The drawing of the preform, carried out in two or more times, with the present apparatus and method, gives to the container an increased capacity for gas retention and a perfect distribution of the material, enabling a high uniformity of thickness to be achieved, with limited operating pressures and with reduction in the times required for the production cycle. After the moulding of the preform by injection, in fact, the preform is stabilised in temperature in two or more periods, using one or more predrawing stations, so as to decrease the total cycle time and to provide the possibility to the molecules of the material to start the first orientation gradually, preconditioning them in the first phase and completing the orientation in the second phase. In ¯ this manner, the preform is well stabilised throughout its length and the reheating times for same are reduced when it is desired to carry out blowing of the .preform after a certain period of conservation time in the store, an operation which is possible only with this system. The apparatus also provides the possibility of doubling the production at the desired instants, by diversification of production in the same cycle. The apparatus can be connected to a station for monitoring the strength of the bottles under load, for monitoring the presence of microscopic holes, of the mouth adjustment of the bottle, and so on, for which operations the known installations, due to their structure and design, require additional operating machines. With this apparatus there is also the possibility of carrying out the fitting of the lower base directly in the machine, without the use of supplementary machines. From that which has been stated and described above, said installation may be described as single-stage and double-stage simultaneously. These applications cannot be made on conventional plants at present in existence without the use of additional equipment.

Claims: CLAIMS 1. An apparatus for moulding hollow containers in molecularly orientatable plastics material, characterised by a plurality of operating units, composed of at least one injection moulding group (2) for hollow preforms (19) having walls of great thickness, one or more axial elongation groups (3) for the preforms, at least one blowmoulding group (4) and at least one discharge unit (5), disposed successively at equal intervals along the closed cycle path of a conveyor (6) having trollies (7) capable of advancing by steps, which trollies (7) possess jaws (15) adapted for gripping the neck of the preform (19) and for supporting same throughout the travel along the conveyor (6). 2. An apparatus according to claim 1, characterised in that the jaws (15) of the trollies (7) possess shaped opposite surfaces having the negative form of the neck of the receptacle being moulded, which surfaces constitute the moulding shape for the corresponding portion of the preforms and the support members for the preforms along the path of the conveyor. 3. An apparatus according to claim 1 or 2, characterised in that it comprises two operating units, each composed of an injection moulding group (2), one or more axial elongation groups (3), a blowmoulding group (4) and a discharge unit (5), disposed in succession along the closed cycle path of the trolley conveyor (6), said units being capable of operating independently and being served by the single trolley conveyor (6). 4. An apparatus according to claim 1, 2 or 3, characterised in that it comprises a discharge unit (5) disposed before the or each blowmoulding group (4), the discharge unit being adapted for discharging the preforms after their axial elongation and before they are blowmoulded, for the purpose of storage or sale. 5. An apparatus according to any one of the preceding claims, characterised in that it comprises a loading unit for preforms disposed in front of a blowing group. 6. An apparatus according to any one of the preceding claims, characterised in that the conveyor has a length which can be preselected according to the number of operating stations provided thereon. 7. An apparatus according to any one of the preceding claims, characterised in that the or each injection moulding group (2) is composed of a press comprising. a lifting cylinder (14) for a mould block (12) of a mould having one or more mould cavities (18), adapted for bringing the mould block (12) to be coupled to the jaws (15) of the trolley (7) and for bringing the injection point of the mould into register with the nozzle of the injection extruder, and a cylinder (25) for introducing the corrresponding mandrels or pins (26) into the mould cavities of the. mould block, determining in co-operation with same and with the internal form of the jaws of the nozzle, the volume of the preform to be injection moulded. 8. An apparatus according to any one of the preceding claims, characterised in that the or each axial elongation group (3) comprises one or more thermal stabilisation moulds (21), equipped with heat exchange devices and carrying mould cavities adapted for receiving the preforms (19) carried by a said trolley of the conveyor, which moulds can be raised by means of an actuator (23) to be coupled with the jaws (15) of the trolley, a further actuator (25) being provided carrying mandrels (26) appropriately equipped with internal heat exchange fluid circulation and adapted to be introduced into the preforms (19) and for causing their elongation. 9. An apparatus according to any one of the preceding claims, characterised in that the blowmoulding group (4) comprises two half-moulds (26) capable of being clamped by means of a closure device (27, 28, 29) around the preforms (19) carried by the jaws (15) of the conveyor trolley (7), equipped with mould cavities surrounding the preforms, each corresponding to the shape of the container, and a blower device having nozzles (33) capable of being introduced into the trolley (7) as far as the mouth of the preform or preforms and connected to a pneumatic apparatus and equipped with internal bars, which can be introduced into the preforms as far as their closed end. 10. An apparatus according to claim 9, characterised in that the clamping device of the blowmoulding group is composed of lever means (2) operated by an actuator member (28), coupled together for the simultaneous closing of the two half-moulds (26) around the preforms. 11. A method of moulding hollow containers in molecularly orientatable plastics material, characterised by the steps of injection moulding an internally hollow preform, closed at one end, having walls of great thickness and an open-topped collar, bringing the preform to a temperature at which a molecular orientation takes place as a consequence of a mechanical deformation in the plastics material and, at this temperature, carrying out one or more axial elongations of the preform and blowmoulding the elongated preform. 12. A method according to claim 11, characterised by the fact that the step of injection-moulding of the preform comprises the partial introduction of a mandrel into a mould block of an injection mould, the injection of a predetermined quantity of the plastics material in the plasticised state, this quantity corresponding to the volume of the preform, into a space existing between mould block and mandrel, cooling of the material down to a temperature at which a molecular orientation takes place as a consequence of a mechanical deformation in the material itself, and the complete introduction of the mandrel into the mould block for forming the preform. 13, A method of moulding hollow containers in molecularly orientatable plastics material, characterised in that it comprises the steps of injection moulding of an internally hollow preform, closed at one end, of bringing the preform to a temperature at which a molecular orientation takes place as a consequence of a mechanical deformation in the plastics material, of carrying out one or more axial elongations of the preform itself and of discharging the elongated preform, having walls of reduced thickness, for the purpose of its storage, said preform being able to be taken up again later, raised to the temperature adapted for carrying out molecular orientation by drawing and shaped by blowmoulding to the form of the final receptacle.

Inventors: GIACOBBE, FERRUCCIO
Applicants: GIACOBBE, FERRUCCIO
Application year: 1986
Main classification: B29C49
IPC codes: B29C49, B29L22