Method for cooling containers produced by stretch blow molding

Abstract

The present invention relates to a method for producing a container by stretch blow molding, comprising the steps of: placing a preheated preform (9) in a blow mold (4) having a molding cavity (7) in a closed position that forms the cavity of the container to be blown; closing the blow mold (4); blowing the preform (9) in the blow mold (4) through a blow nozzle (21) by introducing air at high pressure P into the preform (9), and essentially simultaneously stretching the preform (9) by inserting a stretch rod (5) inside the preform (9) and pressing it against the bottom (14) of the preform (9) so as to promote axial elongation of the preform (9); simultaneously with or subsequent to degassing the container, cooling the interior of the container thus formed by spraying air through the stretch rod (5). the cooling step is carried out by means of a stretch rod (5) having an internal cavity (16) made in its body (15) and at least one orifice (17) communicating with said internal cavity, wherein the high-pressure air introduced into the preform (9) during the blowing step is stored in the internal cavity (16) of the stretch rod (5) and then said high-pressure air escapes through the orifice (17) of the stretch rod (5) until the pressure in the internal cavity (16) of the stretch rod (5) is substantially equal to the atmospheric pressure of the air in the container after evacuation of the container; - raising the stretch rod (5); - removing the blown container by opening the blow mold (4), in particular wherein the orifices (17) are cylindrical, at least five in number and have a diameter of 2 millimeters (mm) or more.

Description

[Technical Field]

[0001] The present invention is in the field of producing containers by blow molding or stretch blow molding from preforms of thermoplastic material, such as polyethylene terephthalate, hereinafter referred to as "PET," or recycled polyethylene terephthalate, hereinafter referred to as "rPET." More particularly, it relates to a cooling method intended to be used in a stretch blow molding process to form containers. [Background technology]

[0002] It is known to form thermoplastic containers by stretch blow molding from preforms which have been preheated to a temperature sufficient to soften the walls thereof.

[0003] For this purpose, a molding device is used, which comprises a mold having a cavity shaped to correspond to the cavity of the container to be produced. A preheated preform is placed in the cavity. Its walls are then subjected to so-called "biaxial" stretching in order to fit the mold cavity. For this purpose, the preform is stretched axially by a stretch rod to induce axial expansion of the preform. Simultaneously with this stretching action, a pressurized fluid is injected into the mold, which induces radial expansion of the walls.

[0004] Such forming processes are well known. It is preferable for the stretch rod to ensure the proper thickness of the container wall so that the finished container has a perfectly formed base. Material maldistribution is a recurring defect found in containers manufactured by molding and stretch / blow molding methods. In some cases, it may be desirable to thicken certain areas, especially those subject to high stress (especially near the base), so ensuring a consistent container wall thickness is not necessarily a challenge. Rather, the challenge is ensuring that the material thickness conforms to the container's specifications, as defined by its configuration and intended use. Furthermore, such variations in thickness, especially at the base, can make it difficult to evacuate the accumulated heat during the blow molding stage. The cooling provided by the heat-transfer fluid circulating within the mold may prove insufficient to adequately cool the container material.

[0005] To meet these constraints, an additional step of internal cooling may prove to be very useful, which consists in producing cooling of the base by means of stretch rods at the end of the blow molding stage, for a very short time and in a very localized area of ​​the base.

[0006] Therefore, methods have been developed to promote proper material distribution to stringent specifications.

[0007] Additionally, the use of recycled PET in the manufacture of molding and stretch / blow molding containers is on the rise for environmental reasons. This material has different stretching and heat absorption properties, further exacerbating the material distribution challenge. Therefore, controlled cooling of containers formed in this way is even more important.

[0008] Furthermore, despite the greater precision applied in the stretch blow molding process, there is still the problem of deformation of the base after the bottle is removed from the mold, especially due to a lack of skill in the cooling stage. These deformation phenomena increase with a certain acceleration of the production speed.

[0009] In this regard, Japanese Patent Application Laid-Open No. 2001-088202 proposes a drawing and cooling rod with orifices specially provided for cooling the base of the preform. These orifices are located on the body of the rod, above an end piece formed at the end of the rod. The end piece is designed to contact the base of the preform during drawing and then be slightly withdrawn during the cooling stage to allow gas to escape through the orifice, thus cooling the base at the end of the blow molding stage. Nevertheless, with this configuration, the cooling gas escapes in an insufficiently controlled manner and is not precisely directed locally toward the base of the resulting container. Furthermore, the cooling gas is obtained from a pressurized air source, so the cooling consumes a large amount of air, adding extra costs to the production of the container.

[0010] It is also known that U.S. Patent No. 8,574,486 describes a method for blow molding a container in which, after being thermally conditioned in a blow mold, the preform is stretched by a stretch rod and converted into a container under the influence of blow molding pressure, whereupon pressurized gas is directed through the stretch rod into the container to cool the container. The pressurized gas is introduced into the container through at least two flow paths, namely, a first flow path extending through the stretch rod with multiple orifices over part of its length, and a second flow path passing through the side of the cooling rod.

[0011] This type of process allows the container to be cooled by sweeping it with the stretch rod, but nevertheless has the drawback of consuming particularly large amounts of pressurized air, which has a negative impact on the manufacturing costs of the container. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-088202 [Patent Document 2] U.S. Patent No. 8,574,486 Summary of the Invention [Problem to be solved by the invention]

[0013] One of the aims of the present invention is therefore to remedy these problems by proposing a simple and low-cost method for cooling containers produced by stretch blow molding, which limits the consumption of pressurized air for cooling the containers. [Means for solving the problem]

[0014] For this purpose, according to the invention, there is provided a method for producing a container by stretch blow molding, comprising the steps of: - placing the preheated preform in a blow mold having a molding cavity that in the closed position forms the cavity of the container to be blown; - closing the blow mold; - blowing the preform in a blow mold through a blow nozzle by introducing high pressure air P into the preform, and substantially simultaneously stretching the preform by inserting a stretch rod inside the preform and abutting it against the base of the preform so as to promote axial elongation of the preform; - simultaneously with or subsequent to the evacuation of the container, cooling the interior of the container thus formed by injecting air through said stretch rod, the cooling step being carried out by means of a stretch rod comprising an internal cavity made in its body and at least one orifice communicating with said internal cavity, the air under pressure introduced into the preform during the blow-molding step being stored in the internal cavity of the stretch rod and then said air under pressure escaping through the orifices of the stretch rod until the pressure in the internal cavity of the stretch rod is substantially equal to the atmospheric pressure of the air in the container after evacuation of the container; - raising the stretch rod; - removing the blown container by opening the blow mold; A method is proposed which includes:

[0015] The method is notable in that the orifices are cylindrical, at least five in number, and have a diameter of 2 millimeters (mm) or greater.

[0016] Such a configuration of the stretch rod makes it possible to obtain a decompression kinetics of said stretching that follows that of the container, resulting in a more effective cooling of the container.

[0017] According to an essential feature of the invention, in the extension of the body of the stretch rod, the stretch rod comprises, at its distal end, a flat surface, an end piece protruding from said flat surface, and an annular skirt in the extension of said body, and orifices communicating with the internal cavity are arranged and distributed on the flat surface around said end piece so as to direct the cooling gas over the entire lower surface towards the base of the container, thus improving the cooling step.

[0018] Preferably, the cylindrical orifice has a diameter of preferably less than 4 millimeters (mm).

[0019] According to a particularly advantageous variant embodiment, the air at high pressure P introduced into the preform during blow molding is stored in a reservoir fluidly connected to the internal cavity of the stretch rod until the pressure in the cavity of the stretch rod and in the reservoir equals the pressure of the air at high pressure P in the container. Said reservoir therefore allows an increase in the cooling duration and ultimately an improvement in the effectiveness of said container cooling.

[0020] Also, the cavity and / or reservoir of the stretch rod is filled with air at high pressure P during blow molding through a plurality of orifices opening into the cavity of the stretch rod, said orifices being positioned over all or part of the height of the stretch rod and over all or part of the circumference of said stretch rod.

[0021] According to a variant embodiment of the method according to the invention, the stretching rod starts to rise from the beginning of the container degassing.

[0022] According to a second variant embodiment of the method according to the invention, the stretching rod starts to rise from the end of the container evacuation, ie when the pressure inside the container is substantially equal to the atmospheric pressure Pa.

[0023] According to another variant embodiment of the method according to the invention, the stretching rod starts to rise after a time delay t1 from the start of the container degassing.

[0024] Said time delay t1 in raising the stretch rod is preferably between 0.01 and 1 second.

[0025] Preferably, the time delay t1 in raising the stretch rod is equal to or greater than the duration of the vessel evacuation.

[0026] The volume of the compressed air stored in the cavity of the extension rod is 10,000 mm 3 to 150,000mm 3 is.

[0027] Furthermore, the volume of compressed air stored in the reservoir is 1,000mm 3 to 2,000,000 mm 3 is.

[0028] The stretch rod preferably comprises a plurality of orifices distributed along the stretch rod and angularly distributed equidistantly or non-equidistantly around the stretch rod.

[0029] Preferably, said stretch rod comprises at least one orifice arranged at the lower free end of said stretch rod for cooling the base of the container.

[0030] Secondly, the introduction of air at high pressure P into the preform and finally into the internal cavity of the stretch rod is carried out at different increasing pressures P1, P2, . . . Pn.

[0031] Further advantages and features will become more apparent from reading the following description of some variant embodiments, given purely by way of example and not by way of limitation, of the method for cooling containers produced by stretch blow molding according to the invention, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0032] [Figure 1] 1 is a schematic plan view of a rotary moulding machine, showing in particular the moulding units, excluding the blow moulding and stretching means, arranged around a carousel, said blow moulding units in an open or closed position depending on their relative position to the inlet or outlet of the machine. [Figure 2] FIG. 2 is a schematic partial perspective view of one of the molding units of the machine shown in FIG. 1, showing in particular the unit in an open position, as well as an exploded view of the mold made up of three parts, namely two mold halves and a mold base. [Figure 3] 1 is a schematic view along a vertical longitudinal central section of a molding unit of a machine during the first step of a container blow molding cycle, showing in particular the insertion of the distal end of a rod into a preform enclosed inside a mold. [Figure 4] 4 is a schematic view similar to FIG. 3 during another subsequent step at the end of the blow molding cycle, showing in particular the distal end of the rod introduced into the blown container and extending to the base of said blown container. [Figure 5] 5 is a schematic view similar to FIGS. 3 and 4 during another subsequent step after the blow molding cycle, particularly showing the filling of the internal cavity of the stretch rod with pressurized air corresponding to the blow molding air. [Figure 6] 6 is a schematic view similar to FIGS. 3 to 5 during another subsequent step of the initiation of degassing. FIG. [Figure 7] 7 is a schematic view similar to FIGS. 3 to 6 during another subsequent step of initiating cooling, particularly showing the distal end of the rod introduced into the blown container and extending to the base of said blown container; FIG. [Figure 8]8 is a schematic view similar to FIGS. 3 to 7 during another subsequent step during cooling, particularly showing the distal end of the lift rod introduced into the blown container. FIG. [Figure 9] 9 is a schematic view similar to FIGS. 3 to 8 during the final step corresponding to the end of cooling, showing in particular the distal end of the fully elevated rod introduced into the blown container. FIG. [Figure 10] 4 is a vertical longitudinal section of a detail of the molding unit during the first step of blow molding shown in FIG. 3, showing more particularly the stretch rods extending inside the preform. [Figure 11] FIG. 1 is a schematic perspective view of one embodiment of the distal end of a stretch rod. [Figure 12] 12 is a longitudinal cross-sectional view of an embodiment of the distal end of the stretch rod shown in FIG. 11. [Figure 13] 1 is a schematic view along a vertical longitudinal central section of a variant embodiment of the molding unit of the machine during the first step of the cycle of blow molding of a container, showing in particular the insertion of the distal end of the rod into the preform enclosed inside the mold. [Figure 14] 14 is a schematic view similar to FIG. 13 during another subsequent step at the end of the blow molding cycle, showing in particular the distal end of the rod introduced into the blown container and extending to the base of said blown container. [Figure 15] 15 is a schematic view similar to FIGS. 13 and 14 during another subsequent step after the blow molding cycle, particularly showing the filling of pressurized air into the internal cavity of the stretch rod and into a reservoir connected to the internal cavity of the stretch rod, the pressurized air corresponding to the blow molding air. [Figure 16] 16 is a schematic view similar to FIGS. 13 to 15 during another subsequent step of the initiation of degassing. FIG. [Figure 17] 17 is a schematic view similar to FIGS. 13 to 16 during another subsequent step of initiating cooling, particularly showing the distal end of the rod introduced into the blown container and extending to the base of said blown container. FIG. [Figure 18]18 is a schematic view similar to FIGS. 13 to 17 during another subsequent step during cooling, particularly showing the distal end of the lift rod introduced into the blown container. FIG. [Figure 19] 13 to 18 during the final step corresponding to the end of cooling, and in particular showing the distal end of the fully raised rod introduced into the blown container. DETAILED DESCRIPTION OF THE INVENTION

[0033] In the remainder of the description of the container according to the invention, the same reference numerals refer to the same elements. The different figures are not necessarily drawn to scale. Also, the invention is more particularly intended for use in installations for the production of PET bottle containers. However, it will be clear that the invention may be adapted to the production of any type of container without departing from the scope of the invention.

[0034] With reference to Figure 1, the container manufacturing facility comprises a molding machine 1 having at least circularly distributed molding units 2, typically in the form of a carousel 3. With reference to Figures 1 and 2, each molding unit 2 comprises at least one mold 4 and blow molding means incorporating a stretch rod 5, said mold 4 comprising at least two mold halves 4a, 4b, each having an internal molding surface, each mounted on a support 6 so as to be movable about axis X between at least an open position and a closed position of the molding unit 2, said internal surfaces of said at least two mold halves 4a, 4b being joined together to define a molding cavity 7 for the container.

[0035] In practice, the blow moulds 4 are distributed in a circular fashion in the form of a carousel 3, as shown in Figure 1, on which the respective blow moulding equipment is mounted. In practice, however, the body of the blow moulding equipment extends substantially vertically above the moulds and substantially coaxially with the moulding cavities 7 of the blow moulds 4, as shown in Figure 2.

[0036] FIG. 2 shows a schematic perspective view of one of the forming units 2 of the machine according to the exemplary embodiment of FIG. 1, in particular showing the unit in an open position, as well as an exploded view of the mold 4 made of three parts, namely two mold halves 4a, 4b and a mold base 8.

[0037] Since all of these elements are well known to those skilled in the art, they will not be described in further detail in order to provide a better understanding of the present invention.

[0038] Referring to Figure 3, this is a schematic view along the vertical longitudinal central part of the molding unit 2 of the machine during the first step of a cycle of blow molding of containers from PET and / or recycled PET preforms 9, and in particular shows the insertion of the distal end of a rod 5 in a preform 9 enclosed inside a mold 4 and intended to be stretched and blow molded in one of the blow molds 4 of the equipment described above to form a container 2, such as a bottle, said stretch rod 5 being in an elevated position and in the process of being inserted into the preform 9.

[0039] The rod 5 is designed to be attached to the body of the blow molding equipment, also as described above. The stretch rod 5 extends longitudinally parallel to the main axis Y. The stretch rod 5 according to the invention is a hollow stretch rod which has a dual function, firstly the function of stretching and secondly the additional function of cooling the container, as will be explained below. To achieve this, it has a first, so-called proximal end (not shown) which can be attached to a displacement device in the production equipment.

[0040] Said preform 9, shown in more detail in Figure 10, conventionally comprises a tubular elongated body 10 having a longitudinal axis of rotation limited by a wall 11 attached at the top to a threaded neck 12 and at the bottom to a substantially hemispherical base 14, the neck 12 being separated from the body 10 by a radial collar 13 projecting towards the outside of the preform. The preform 9 shown in Figure 10 therefore has rotational symmetry about its longitudinal axis which is substantially coaxial with the axis Y of the rod 5 when the preform 9 is placed in the forming unit 2.

[0041] It should be noted that in the following description, the term "vertical" refers to any direction parallel to the axis of rotation Y of the rod 5, and "transverse" refers to any direction perpendicular to the axis of rotation Y of the rod 5.

[0042] 10-12, the stretch rod 5 comprises a cylindrical or tubular body 15. In some embodiments (not shown), the body 15 of the stretch rod 5 may have a shoulder, i.e., two longitudinal cross sections of different diameters, which is particularly advantageous for blow molding small diameter preforms.

[0043] The body 15 also comprises an axially extending central internal cavity 16 which communicates with a plurality of orifices 17, through which a cooling gas, in particular air, is injected into the interior of the manufactured container in order to cool the same. The orifices 17 are therefore in fluid communication with the internal cavity 16. At its distal end, in the elongated portion of the body 15, the stretch rod 5 comprises a flat surface 18 from which an end piece 19 projects. The stretch rod 5 also comprises an annular skirt 20 in the elongated portion of its body 15.

[0044] In this particular embodiment, the diameter of the annular skirt 20 is equal to the diameter of the body 15 of the stretch rod 1. In this advantageous configuration, the cooling gas is directed in a very localized manner. It is clear that the outer body 15 and the annular skirt 20 can be obtained in one piece or in two pieces without in any way departing from the scope of the invention.

[0045] Said stretch rod 5 has the advantage that it directs the cooling gas over its entire underside towards the base of the vessel, thus improving the cooling step.

[0046] In this particular exemplary embodiment, the orifices 17 communicating with the internal cavity 16 are arranged and distributed on a flat surface 18 around said end piece 19. The orifices 17 allow cooling gas to be injected into the base of the blown container. The orifices 17 are arranged on and around the entire periphery of the flat surface 18, thus allowing the injection of cooling gas from the internal cavity 16 into the inside of the blown container. The orifices 17 are, for example, cylindrical in shape and preferably have a diameter of 1 to 4 millimeters (mm). They may also have other shapes, for example, an oval shape.

[0047] According to a preferred embodiment, the injection area is 3 to 6 square millimeters (mm 2 ) and 20 square millimeters (mm 2 ) The injection area corresponds to the sum of the areas of the orifices 17. This represents the amount of cooling gas that can be injected thanks to the configuration of the rod 5 with the orifices 17 acting as limiting orifices. The protruding end pieces 19 may have any shape. In particular, they may be conical, rounded conical, ovoid, hemispherical, etc. Furthermore, the flat surface 18 is preferably perpendicular to the main body 15 of the stretch rod 5. Secondly, the edges of the annular skirt 20 are rounded. This is particularly advantageous, as it makes it possible to avoid the risk of tearing when the edges of the annular skirt 20 come into contact with the wall of the preform 9, for example during the drawing stage. The annular skirt 20 has, for example, the same diameter as the main body 15 of the stretch rod 5. Furthermore, the annular skirt 20 has a height that is smaller than that of the end pieces 19, so that the end pieces 19 protrude beyond the annular skirt 20. In other words, the distal end of stretch rod 5 is formed by end piece 19, and annular skirt 20 is an extension of outer body 15 relative to flat surface 18. This allows the cooling gas to be directed in a controlled manner as it exits internal cavity 16 through orifice 17. For example, the height of annular skirt 20 is less than the height of end piece 19 by a value of 0.5 to 4 millimeters (mm), and even more preferably by a value of 1 mm.

[0048] According to a preferred embodiment, the stretch rod 5 comprises at least five orifices 17 having a diameter at least equal to 2 mm. Such a configuration of the stretch rod 5 makes it possible to obtain a decompression kinetics of said stretch rod 5 that follows that of the vessel, thus achieving a more effective cooling of said vessel.

[0049] Preferably, the stretch rod 5 comprises a plurality of orifices 17 distributed along and angularly distributed around the stretch rod 5, the orifices 17 communicating with the internal cavity 16 of the stretch rod 5 for cooling the entire body of the container, and at least one orifice 17 located at the lower free end of the stretch rod 5 for cooling the base of the container.

[0050] The cooling step is an additional step in the manufacturing process of PET and recycled PET (rPET) containers. This cooling step, in particular, allows for a reduction in the internal temperature of the manufactured container. Its purpose is to limit the transfer of heat from the inside to the outside after the manufactured container is removed from the mold. This also limits the collapse of the base. This collapse generally has a negative effect on distortion and increases the risk of defective products. In fact, a base that is too hot tends to sag during the removal step from the mold. The manufactured container may have "distortion" or other defects. The term "distortion" refers to the appearance of distortion, such as cracks. Note that the presence of the annular skirt 20 on the stretch rod 5 has the advantage of significantly improving the cooling step by amplifying the action of the cooling gas, which is directed locally to the point where its presence is required. This significantly improves the cooling step of the manufactured container's base, thus achieving optimal cooling performance even when the duration of the cooling step must be very short due to production speed reasons.

[0051] With reference to Figures 3 to 9, a process for producing containers by stretch blow moulding according to the invention is described, with the particularly advantageous step of cooling the container by means of the stretch rods described above.

[0052] Referring to Figure 3, the heated preform 9 is first placed in a blow mold 4 in a closed position, having a molding cavity 7 which forms the cavity of the container to be blown, and when the blow mold 4 is closed, a stretch rod 5 is placed within the preform 5 so as to extend coaxially therewith.

[0053] Next, referring to Figure 4, the preform 9 in the blow mold 4 is blow-molded by introducing high-pressure air P into the preform 9 through a blow molding nozzle 21, and essentially simultaneously, a step is performed in which the preform 9 is stretched by displacing the stretch rod 5 vertically downward into the preform 9 to promote axial elongation of the preform 9 and abut against the base 14 of the preform 9.

[0054] 5, the gas introduced into the preform 9, and ultimately into the container formed by the blow molding, permeates into the internal cavity 16 of the stretch rod 5 through one or more orifices 17 until the pressure within the internal cavity 16 of the stretch rod is substantially equal to the pressure P of the air originally introduced into the preform 9 to form the container. Thus, the high pressure P of air introduced into the preform during the blow molding step is stored within the internal cavity 16 of the stretch rod 5.

[0055] Once the container has been blown, referring to FIG. 6, the high pressure P gas contained in the container is degassed through the blow molding nozzle 21, and then, referring to FIG. 7, the high pressure P air stored in the internal cavity 16 of the stretch rod 5 escapes through one or more orifices 17 of the stretch rod 5 to cool the container until the pressure in the internal cavity 16 of the stretch rod 5 is equal to the atmospheric pressure Pa of the air in the container after degassing of said container.

[0056] During this cooling step, i.e. while the air initially stored in the internal cavity 16 of the stretch rod 5 is escaping, the stretch rod 5 gradually rises until said stretch rod 5 reaches its high position (see FIG. 7), which corresponds to the end of the vessel cooling step.

[0057] In a final step (not shown), the container thus formed and cooled is extracted in the conventional manner by the opening of the blow mould 4 .

[0058] It will be appreciated that according to the method of the present invention, the step of cooling the blown-molded container is carried out without the need to consume additional compressed air dedicated to cooling, which, although a small amount of additional compressed air is consumed during the blow-molding step, makes it possible to reduce the amount of compressed air consumed and ultimately reduce the cost of manufacturing the container.

[0059] In this particular exemplary embodiment, the stretch rod 5 starts to rise from the beginning of the evacuation of the container. However, according to a variant of the method according to the invention, the stretch rod 5 may also start to rise from the end of the evacuation of the container, i.e. after the pressure inside the container has become substantially equal to the atmospheric pressure Pa. It should be noted that in this latter variant of the method, the air contained in the internal cavity is integrally injected onto the base of the container, so as to optimally cool said container base.

[0060] According to another variant embodiment of the method according to the invention, the stretch rod 5 starts to rise after a time delay t1 from the start of the container degassing, said time delay t1 in the raising of the stretch rod in this case preferably being between 0.01 and 1 second.

[0061] Also, to ensure sufficient cooling of the vessel, the volume of pressurized air stored in the internal cavity 16 of the stretch rod 5 is 10,000 mm 3 to 150,000mm 3 is.

[0062] According to a particularly advantageous variant embodiment shown in Figures 13 to 19, the air at high pressure P introduced into the preform 9 during blow molding is stored in a reservoir 22 fluidly connected to the internal cavity 16 of the stretch rod 5 until it equalizes the pressure of the air at high pressure P in the cavity of the stretch rod and in said reservoir. Said reservoir 22 therefore allows an increase in the cooling duration and, finally, an improvement in the effectiveness of said container cooling.

[0063] Thus, referring to Figure 13, a heated preform 9 is first placed in a blow mold 4 in a closed position having a molding cavity 7 which forms the cavity of the container to be blown, and when the blow mold 4 is closed, a stretch rod 5 is placed within the preform 5 so as to extend coaxially therewith.

[0064] Next, referring to Figure 14, the preform 9 in the blow mold 4 is blow-molded by introducing high-pressure air P into the preform 9 through a blow molding nozzle 21, and essentially simultaneously, a step is performed in which the preform 9 is stretched by displacing the stretch rod 5 vertically downward into the preform 9 to promote axial elongation of the preform 9 and abut against the base 14 of the preform 9.

[0065] 15, the gas introduced into the preform 9, and ultimately into the container formed by the blow molding, permeates through one or more orifices 17 into the internal cavity 16 of the stretch rod 5 and into reservoir 22 until the pressure within the internal cavity 16 and reservoir of the stretch rod is substantially equal to the pressure P of the air originally introduced into the preform 9 to form the container. Thus, the high pressure P of air introduced into the preform during the blow molding step is stored within the internal cavity 16 of the stretch rod 5 and reservoir 22.

[0066] Once the container has been blown, referring to FIG. 16, the high pressure P gas contained in the container is degassed through the blow molding nozzle 21, and then, referring to FIG. 17, the high pressure P air stored in the internal cavity 16 and reservoir 22 of the stretch rod 5 escapes through one or more orifices 17 of the stretch rod 5 to cool the container until the pressure in the internal cavity 16 and reservoir 22 of the stretch rod 5 is equal to the atmospheric pressure Pa of the air in the container after degassing of said container.

[0067] During this cooling step, i.e. while the air initially stored in the internal cavity 16 and reservoir 22 of the stretch rod 5 is escaping, said stretch rod 5 gradually rises until it reaches its high position (see Figure 18), which corresponds to the end of the vessel cooling step (see Figure 19).

[0068] In a final step (not shown), the container thus formed and cooled is extracted in the conventional manner by the opening of the blow mould 4 .

[0069] As before, the stretching rod 5 preferably starts to rise from the beginning of the evacuation of the container. However, according to a variant embodiment of the method according to the invention, the stretching rod 5 may also start to rise from the end of the evacuation of the container, i.e. after the pressure in the container has become substantially equal to the atmospheric pressure Pa.

[0070] According to another variant of the method according to the invention, the stretch rod 5 starts to rise after a time delay t1 from the start of the container evacuation. In this case, said time delay t1 in the raising of the stretch rod is preferably between 0.01 and 1 second. The time delay t1 in the raising of the stretch rod is preferably equal to or greater than the duration of the container evacuation, which corresponds to the raising of the rod after the end of the container evacuation.

[0071] As before, the volume of pressurized air stored in the reservoir 22 is preferably 1,000 mm 3 to 2,000,000 mm 3, while the volume of the high-pressure air stored in the internal cavity 16 of the stretch rod 5 is 10,000 mm 3 to 150,000mm 3 Please note that

[0072] Also preferably, the cavity 16 and / or reservoir 22 of the stretch rod 5 is filled with air at high pressure P during blow molding through a plurality of orifices 17 opening into the internal cavity 16 of the stretch rod 5, said orifices 17 being arranged over all or part of the height of the stretch rod 5 and over all or part of the circumference of said stretch rod 5.

[0073] In order to make the cooling as uniform as possible, the stretch rod 5 preferably comprises a number of orifices 17 distributed along and angularly around the stretch rod 5. Furthermore, the stretch rod 5 comprises at least one orifice 17 arranged at the lower free end of the stretch rod 5 for cooling the base of the container.

[0074] Finally, and secondly, the introduction of air at high pressure P into said preform and finally into the internal cavity 16 of the stretch rod 5 and / or into the reservoir 22 is carried out at different elevated pressures P1, P2, ... Pn, said elevated pressures P1, P2, ... Pn corresponding to the different blow molding pressures known in prior art processes, in particular those involving air recovery.

[0075] It will be clear to those skilled in the art that in order to optimize the cooling of the container base, the cross section of the orifice(s) 17 of the rod, the volume of the internal cavity 16 and the reservoir 22 will be determined as a function of the degassing rate (which depends on the volume of the blown container, the blow molding pressure and especially the diameter of the neck).

[0076] Finally, it is clear that the examples given here are merely specific examples and are not limiting with regard to the application area of ​​the invention.

Claims

1. 1. A method for producing a container by stretch blow molding, comprising: - placing the preheated preform (9) in a blow mould (4) having a moulding cavity (7) which in the closed position forms the cavity of the container to be blown; - closing the blow mold (4); - blowing said preform (9) in a blow mold (4) through a blow nozzle (21) by introducing air at high pressure P into said preform (9), and essentially simultaneously stretching said preform (9) by inserting a stretch rod (5) inside said preform (9) and abutting it against the base (14) of said preform (9) so as to promote axial elongation of said preform (9); - simultaneously with or subsequent to the evacuation of the container, cooling the interior of the formed container by injecting air through said stretch rod (5), the cooling step being carried out by means of a stretch rod (5) comprising an internal cavity (16) made in its body (15) and at least one orifice (17) communicating with said internal cavity (16), the high-pressure air introduced into the preform (9) during the blow-molding step being stored in the internal cavity (16) of the stretch rod (5), said high-pressure air then escaping through the orifice (17) of the stretch rod (5) until the pressure in the internal cavity (16) of the stretch rod (5) is substantially equal to the atmospheric pressure of the air in the container after evacuation of the container; - raising said stretch rod (5); - removing the blown container by opening the blow mold (4); wherein the orifices (17) are cylindrical, at least five in number, and have a diameter of 2 millimeters (mm) or greater.

2. 2. The method according to claim 1, characterized in that in the extension of the body (15) of the stretch rod (5), the stretch rod (5) comprises, at its distal end, a flat surface (18), an end piece (19) protruding from said flat surface (18), and an annular skirt (20) in the extension of its body (15), and that orifices (17) communicating with the internal cavity (16) are arranged and distributed on the flat surface around said end piece (19) so as to direct the cooling gas over the entire lower surface towards the base of the container, improving the cooling step.

3. 3. A method according to claim 1 or 2, characterized in that the cylindrical orifice (17) has a diameter preferably less than 4 millimeters (mm).

4. 4. The method according to claim 1, wherein the air at high pressure P introduced into the preform (9) during blow molding is stored in a reservoir (22) fluidly connected to the internal cavity (16) of the stretch rod (5) until the pressure in the internal cavity (16) of the stretch rod (5) and in the reservoir (22) is substantially equal to the pressure of the air at high pressure P in the container.

5. 5. The method according to any one of claims 1 to 4, characterized in that the cavity (16) and / or the reservoir (22) of the stretch rod (5) is filled with air at high pressure P during blow molding through a plurality of orifices (17) opening into the internal cavity (16) of the stretch rod (5), said orifices (17) being arranged over all or part of the height of the stretch rod (5) and over all or part of the circumference of said stretch rod (5).

6. 6. A method according to any one of claims 1 to 5, characterized in that the stretching rod (5) starts to rise from the end of the vessel evacuation, i.e. when the pressure inside the vessel is substantially equal to atmospheric pressure Pa.

7. 6. The method according to any one of claims 1 to 5, characterized in that the stretching rod (5) starts to rise from the beginning of the container degassing.

8. The stretching rod (5) is operated for a time delay t １ 6. The method according to claim 1, wherein the temperature rises after the temperature rise.

9. 9. A method according to claim 8, characterized in that the time delay t1 in raising the stretch rod (5) is between 0.01 and 1 second.

10. Time delay t in the raising of the stretch rod (5) １ 10. The method according to claim 8 or 9, characterized in that the time t is equal to or greater than the duration of the vessel degassing.

11. The volume of the high-pressure air stored in the internal cavity (16) of the stretch rod (5) is 10,000 mm ３ to 150,000 mm ３ 11. The method according to claim 1, wherein

12. The volume of the high-pressure air stored in the reservoir (22) is 1,000 mm ３ to 2,000,000 mm ３ 12. The method according to claim 4, wherein

13. 13. The method according to any one of claims 1 to 12, characterized in that the stretch rod (5) comprises a plurality of orifices (17) distributed along and angularly distributed around the stretch rod (5).

14. 14. A method according to any one of claims 1 to 13, characterized in that the stretch rod (5) comprises at least one orifice (17) arranged at the lower free end of the stretch rod (5).

15. 15. A method according to any one of claims 1 to 14, characterized in that the introduction of air at high pressure P into the preform (9) and finally into the internal cavity (16) of the stretch rod (5) is carried out at different elevated pressures P1, P2, ... Pn.

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