Cooling method for a container manufactured by stretch blow molding

Abstract

Method for cooling a container manufactured by stretch blow molding. The present invention relates to a method for manufacturing a container by stretch blow molding, comprising at least the following steps: - placing a pre-heated preform (9) in a blow mold (4) having, in the closed position, a molding cavity (7) forming the impression of the container to be blown; - closing said blow mold (4); - blowing said preform (9) into the blow mold (4) by means of a blow nozzle (21) by introducing air under high pressure P into said preform (9) and, substantially simultaneously, a stretching step of said preform (9) by inserting a stretching rod (5) inside said preform (9) bearing against the bottom (14) of said preform (9) so as to facilitate the axial elongation of the latter;- cooling of the inside of said container thus formed by projecting air through said drawing rod (5) simultaneously or after degassing of the container; - raising of said drawing rod (5); - extraction of said blown container by opening said blow mold (4);The said process is remarkable in that the cooling step is carried out by means of a drawing rod (5) having an inner cavity (16) and at least one orifice (17) communicating with the inner cavity (16), the high-pressure air P introduced into the preform (9) during the blowing step being stored in the inner cavity (16) of the drawing rod (5) then said high-pressure air P escaping from the orifice (17) of the drawing rod (5) to cool the container until the pressure in the inner cavity (16) of the drawing rod (5) is substantially equal to the atmospheric pressure Pa of the air in the container after degassing of the container. Fig. 3;

Description

Description Title of the invention: Method for cooling a container manufactured by stretch blow molding technical field

[0001] — The present invention relates to the field of manufacturing containers by blow molding or stretch blow molding from preforms made of thermoplastic material, such as by for example polyethylene terephthalate, hereinafter "PET" or polyethylene terephthalate recycled, hereinafter “rPET”. Its main purpose is a cooling process- dissement intended to be implemented in a stretch blow molding technique for the container formation. State of the art

[0002] — It is known to form containers from thermoplastic material by stretching blowing of preforms previously heated to a temperature sufficient for soften the walls.

[0003] — For this purpose, a forming device is used which includes a mold having a cavity shaped to the imprint of the desired container. The preform previously The heated material is received in the cavity. Then, its walls are subjected to a stretching process called "Biaxial" to fit the mold's imprint. To do this, the preform is stretched axially by means of a stretching rod to cause axial expansion of the preform. Simultaneously with this stretching operation, a pressurized fluid is injected. in the preform so as to cause radial expansion of the wall.

[0004] Such a forming process is well known. In order for the final container to have a With a perfectly molded base, it is best if the drawing rod is suitable for To ensure a satisfactory thickness of the container wall. Poor distribution material is a recurring defect observed on containers produced by a process molding and stretching / blowing. This does not necessarily mean ensuring that the thickness of the container wall should be constant, because in some cases it may be sub- hateful to thicken certain areas, especially those intended to withstand stress important (especially near the bottom). It's more about ensuring that the material thickness corresponds to the container specifications, as defined in depending on its shape and use. Furthermore, such variations in thickness, particularly in the background, can make it difficult during the blowing phase, the removal of the accumulated calories. The cooling thus provided by the The heat transfer fluid circulating in the mold may then prove insufficient for cool the container material properly.

[0005] — To meet these constraints, an additional internal cooling step can prove very useful. This step consists of generating cooling of the bottom by the drawing rod, at the end of the blowing phase, over a very short time, in very localized areas of the bottom. Processes have thus been developed to promote a distribution of material adapted to demanding specifications. Furthermore, in the field of container manufacturing by molding and stretch / blow molding, recycled PET is increasingly used for environmental reasons. This material further exacerbates the problem of material distribution because it exhibits different stretching and heat absorption properties: controlling the cooling of the resulting container is therefore even more crucial. Furthermore, despite the refinements made to the stretch blow molding processes, there are still problems of deformation of the base after demolding of the bottle, in particular due to a lack of control of the cooling phase, a deformation phenomenon that is growing due to the constant acceleration of production rates. In this regard, we are familiar with document JP2001088202, which proposes a stretching and cooling rod with orifices specifically designed to cool the bottom of a preform. These orifices are located on the rod body, above the nozzle formed at its end. The nozzle is designed to be in contact with the bottom of the preform during stretching, then slightly retracted during the cooling phase to allow gas to escape from the orifices and thereby cool the bottom at the end of the blowing phase. However, in this configuration, the cooling gas escapes in a poorly controlled manner and is not precisely directed to a localized area at the bottom of the resulting container. Furthermore, the said cooling gas is supplied by a source of pressurized air, so that said cooling consumes a large quantity of air, which generates an additional cost in the manufacture of the containers. We also know of US patent 8574486B2, which describes a blow molding process for containers, in which a preform, after heat conditioning inside a blow mold, is drawn by a drawing rod and transformed into a container under the effect of blow pressure, and in which pressurized gas is carried into the container through the drawing rod to cool it. This pressurized gas is introduced into the container through at least two flow paths: a first flow path extending through the drawing rod, which has a plurality of orifices along part of its length, and a second flow path passing alongside the drawing rod. This type of process, although allowing the container to be cooled by sweeping with the drawing rod, nevertheless has the disadvantage of being partial- particularly a consumer of pressurized air, increasing the manufacturing cost of the containers. Disclosure of the invention One of the aims of the invention is therefore to remedy these drawbacks by proposing a simple and inexpensive method of cooling a container manufactured by stretch-blowing by limiting the consumption of pressurized air to cool the containers. To this end, and in accordance with the invention, a method for manufacturing a container by stretch blow molding is proposed, comprising at least the following steps: - placement of a pre-heated preform in a blow mold which, in the closed position, has a molding cavity forming the imprint of the container to be blown; - closing of said blow mold; - blowing of said preform into the blow mold by means of a blow nozzle by the introduction of air under high pressure P into said preform and, substantially simultaneously, a stretching step of said preform by insertion of a stretching rod inside said preform, bearing against the bottom of said preform so as to facilitate the axial elongation of the latter: - cooling of the inside of said container thus formed by projecting air through said drawing rod simultaneously or after degassing of the container; - raising of said drawing rod; - extraction of said blown container by opening of said blow mold; The said process is remarkable in that the cooling step is carried out by means of a drawing rod having an inner cavity and at least one orifice communicating with the inner cavity, the high-pressure air P introduced into the preform during the blowing step being stored in the inner cavity of the drawing rod and then said high-pressure air P escaping from the orifice of the drawing rod to cool the container until the pressure in the cavity of the drawing rod is equal to the atmospheric pressure Pa of the air in the container after degassing of the container. According to a particularly advantageous embodiment, the high-pressure air P introduced into the preform during blow molding is stored in a reservoir fluidly connected to the cavity of the drawing rod until the pressure in the cavity of the drawing rod and in said reservoir equals the pressure of the high-pressure air P in the container. This reservoir thus increases the cooling time and, ultimately, the efficiency of said cooling of the containers. Furthermore, the cavity of the drawing rod and / or the reservoir are filled, during blowing, with air under high pressure P through a plurality of orifices opening into the cavity of the drawing rod, said orifices being positioned on all or part of the height of the drawing rod and on all or part of the circumference of said drawing rod. According to one embodiment of the method according to the invention, the drawing rod begins to rise from the start of the degassing of the container. According to a second embodiment of the process according to the invention, the drawing rod begins to rise from the end of the degassing of the container, that is to say when the pressure in the container is substantially equal to atmospheric pressure Pa. According to another embodiment of the method according to the invention, the drawing rod begins to rise after a time delay t, from the start of the degassing of the container. Said time delay t, of the raising of the drawing rod is preferably between 0.01 and 1 second. Preferably, the time delay t, of the raising of the drawing rod is greater than or equal to the duration of the degassing of the container. Furthermore, the volume of high-pressure air stored in the cavity of the drawing rod is between 10,000 and 150,000 mm3. Furthermore, the volume of air under high pressure stored in the tank is between 1000 and 2000000 mm°. The said drawing rod preferably comprises a plurality of orifices distributed along the said drawing rod and angularly distributed around the said drawing rod, equidistant or not. Preferably, said drawing rod has at least one orifice positioned at the lower free end of said drawing rod in order to cool the bottom of the containers. Incidentally, the introduction of air under high pressure P into said preform and, finally, into the inner cavity of the drawing rod, is carried out at different increasing pressures P1, P2,..Pn. Brief description of the drawings Other advantages and features will become clearer from the following description of several embodiments, given by way of non-limiting examples, of the cooling process for a blow-molded container according to the invention, with reference to the attached drawings in which: [Fig.1] is a schematic top-view representation of a molding machine of the rotary type, illustrating in particular the molding units, with the exception of the blowing and stretching means, distributed around a carousel, said blowing units being, depending on their relative position with respect to the inlet or outlet of the machine, in an open or closed position, [Fig.2] is a partial schematic perspective representation of one of the molding units of the machine shown in [Fig.1], illustrating in particular, outside the unit in the open position, an exploded view of a mold made in three parts, namely two half-molds and a mold bottom, [Fig.3] is a schematic representation according to a vertical longitudinal median section of a molding unit of the machine, during a first stage of a container blowing cycle, showing in particular the insertion of the distal end of the stem into a preform enclosed within a mold, [Fig.4] is a schematic representation similar to [Fig.3], during another subsequent step at the end of the blowing cycle, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container, [Fig. 5] is a schematic representation similar to figures 3 and 4, during another subsequent step after the blowing cycle, showing in particular the filling of the inner cavity of the drawing rod with pressurized air, corresponding to the blowing air, [Fig. 6] is a schematic representation similar to figures 3 to 5, during another subsequent stage of initial degassing, [Fig.7] is a schematic representation similar to figures 3 to 6, during another subsequent stage of initial cooling, notably showing the distal end of the rod introduced into the blown container and extending to the bottom of said blown container, [Fig.8] is a schematic representation similar to figures 3 to 7, during another subsequent cooling medium stage, notably showing the distal end of the rod introduced into the rising blown container, [Fig.9] is a schematic representation similar to figures 3 to 8, during a final stage corresponding to the end of cooling, showing in particular the distal end of the rod introduced into the blown container, fully raised, [Fig.10] is a vertical longitudinal cross-sectional view of a detail of the molding unit during the first blowing stage shown in [Fig.3], showing more particularly the drawing rod extending inside the preform, [Fig.11] is a schematic perspective view of one embodiment of the distal end of the drawing rod, [Fig.12] is a longitudinal cross-sectional view of the embodiment of the distal end of the drawing rod shown in [Fig.11], [Fig.13] is a schematic representation according to a vertical longitudinal median section of an embodiment variant of the molding unit of the machine, during a first stage of a container blowing cycle, showing in particular the insertion of the distal end of the stem into a preform enclosed within a mold, [Fig.14] is a schematic representation similar to [Fig.13], during another subsequent step at the end of the blowing cycle, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container, [Fig.15] is a schematic representation similar to figures 13 and 14, during another subsequent step after the blowing cycle, showing in particular the filling of the inner cavity of the drawing rod and a reservoir connected to the inner cavity of the drawing rod with pressurized air, the pressurized air corresponding to the blowing air, [Fig.16] is a schematic representation similar to figures 13 to 15, during another subsequent stage of initial degassing, [Fig.17] is a schematic representation similar to figures 13 to 16, during another subsequent stage of initial cooling, showing in particular the distal end of the rod introduced into the blown container and extending to the bottom of said blown container, [Fig.18] is a schematic representation similar to figures 13 to 17, during another subsequent cooling medium stage, notably showing the distal end of the rod introduced into the rising blown container, [Fig.19] is a schematic representation similar to figures 13 to 18, during a final stage corresponding to the end of cooling, showing in particular the distal end of the rod introduced into the blown container fully raised. Method of carrying out the invention In the following description of the container according to the invention, the same numerical references designate the same elements. The different views are not necessarily drawn to scale. Furthermore, the present invention is more particularly intended for implementation in a PET bottle manufacturing plant; however, it is quite clear that the invention can be adapted for the manufacture of any type of container without departing from the scope of the invention. With reference to [Fig. 1], said container manufacturing facility comprises, typically, a molding machine l comprising at least molding units 2 distributed circularly, in the form of a carousel 3. Each molding unit 2, with reference to Figures 1 and 2, comprises at least one mold 4 and blowing means incorporating a stretching rod 5, said mold 4 comprising at least two half-molds 4a, 4b which each have an internal molding face and which are respectively mounted on supports 6 movable around an axis X, between at least one open position and one closed position of the molding unit 2, in which said internal faces of said at least two joined half-molds 4a, 4b together delimit a molding cavity 7 of the container. In practice, the blow molds 4 are arranged in a circular pattern, in the form of a carousel 3 as seen in [Fig. 1], and surmounted by their respective blow molding units. Also in practice, and as seen in [Fig. 2], the body of the blow molding unit extends substantially vertically above the mold and substantially coaxially with the molding cavity 7 of the blow mold 4. Fig. 2 schematically represents a perspective view of one of the molding units 2 of the machine according to the embodiment example of Fig. 1, illustrating in particular, outside the unit in the open position, an exploded view of a mold 4 made in three parts, namely two half-molds 4a, 4b and a mold bottom 8. Since all these elements are well known to a person skilled in the art, they will not be described in more detail for a better understanding of the invention. With reference to [Fig.3], which is a schematic representation according to a vertical longitudinal median section of a molding unit 2 of the machine, during a first step of a blow-molding cycle of a container from a PET and / or recycled PET preform 9, showing in particular the insertion of the distal end of the rod 5 into a preform 9 enclosed within a mold 4 and intended to be stretched and blown into one of the blow molds 4 of an installation described briefly above, so as to form a container 2, such as a bottle, said stretching rod 5 is in the raised position and being inserted into the preform 9. The rod 5 is designed to be mounted within the body of the blow molding system mentioned above. The drawing rod 5 extends longitudinally, parallel to the main axis Y. The drawing rod 5 according to the invention is a hollow drawing rod, which thus performs a dual function: a drawing function on the one hand, and a cooling function for the container on the other, as will be detailed later. To this end, it has a first end, referred to as the proximal end (not shown), which is adapted to be attached to a displacement device internal to the manufacturing system. The said preform 9, shown in more detail in [Fig.10], conventionally comprises an elongated, tubular body 10 with a longitudinal axis of revolution, limited by a wall 11 integral at the upper part with a threaded neck 12, the neck 12 being separated from the body 10 by a radial collar 13 projecting outwards from the preform, and at the lower part by a substantially hemispherical base 14. Thus, said preform 9 illustrated in [Fig. 10] exhibits rotational symmetry about its longitudinal axis which is substantially coaxial with the Y-axis of the rod 5 when the preform 9 is placed in the molding unit 2. It will be noted that, in the following description, any direction parallel to the axis of revolution Y of the rod S will be called "vertical" and any direction perpendicular to the axis of revolution Y of the rod 5 will be called "transverse". Referring to Figures 10 to 12, the drawing rod 5 comprises a cylindrical or tubular body 15. In embodiments not shown in the figures, the body 15 of the drawing rod 5 may have a shoulder, i.e., have two longitudinal sections with two different diameters. This is particularly advantageous for blowing small-diameter preforms. The body 15 also includes a central internal cavity 16 extending axially and communicating with a plurality of orifices 17 through which a cooling gas, in particular air, is injected into the manufactured container in order to cool it. The orifices 17 are thus in fluidic communication with the internal cavity 16. Extending from the body 5, at its distal end, the drawing rod 5 includes a flat 18. A tip 19 projects from this flat 18. The drawing rod 5 further includes an annular skirt 20 extending from its body 4. In this particular embodiment, the diameter of the annular skirt 20 is equal to the diameter of the body 5 of the drawing rod. In this advantageous configuration, the cooling gas is directed in a highly localized manner. It is clear that the outer body 5 and the annular skirt 20 can be made in one piece or in two parts without departing from the scope of the invention. The said drawing rod 5 has the advantage of directing the cooling gas towards the bottom of the container, over its entire lower surface, and thus improving the cooling stage. In this particular embodiment, the orifices 17, communicating with the inner cavity 16, are arranged and distributed on the flat surface 18, around the nozzle 19. The orifices 17 allow the cooling gas to be projected onto the bottom of the blow-molded container. The orifices 17 are positioned on the flat surface 18 and around its entire circumference, thus allowing the cooling gas to be projected from the inner cavity 16 into the interior of the blow-molded container. The orifices 17 are, for example, cylindrical and preferably have a diameter between 0.3 and 3 millimeters (mm). They can also be of another shape, for example, a circular shape. oblong. Furthermore, according to a preferred embodiment, the projection surface is between 3 and 6 square millimeters (mm²) and does not exceed 20 square millimeters (mm²). The projection surface corresponds to the sum of the areas of the orifices 17. It represents the quantity of cooling gas that can be projected thanks to the configuration of the rod 5, which includes orifices 17 acting as restriction orifices. The protruding tip 19 can be of any shape. In particular, said tip 19 can be conical, rounded conical, ovoid, hemispherical, etc. In addition, the flat 18 is preferably perpendicular to the body 15 of the drawing rod 5. Optionally, the edges of the annular skirt 20 are rounded. This is particularly advantageous because it avoids any risk of tearing when the said edges of the annular skirt 20 come into contact with the wall of the preform 9, for example during the stretching phase.The annular skirt 20 has, for example, the same diameter as the diameter of the body 15 of the draw rod 5. In addition, the annular skirt 20 has a height less than the height of the tip 19 so that said tip 19 protrudes from the annular skirt 20. In other words, the distal end of the draw rod 5 is formed by the tip 19 and the annular skirt 20 is an extension of the outer body 15 relative to the flat 18. This allows the cooling gas to be directed in a controlled manner as it leaves the inner cavity 16 through the orifices 17. For example, the height of the annular skirt 20 is less than the height of the tip 19 by a value between 0.5 and 4 millimeters (mm), or even more preferably by a value of 1 mm. Preferably, said drawing rod 5 has a plurality of orifices 17 distributed along said drawing rod 5 and angularly distributed around said drawing rod 5, said orifices 17 being in communication with the internal cavity 16 of said drawing rod 5, to cool the whole body of the container and at least one orifice 17 positioned at the lower free end of said drawing rod 5 in order to cool the bottom of the containers. The cooling stage is an additional step in the manufacturing process of PET and recycled PET ("rPET") containers. This cooling stage reduces the internal temperature of the resulting container and aims to limit heat transfer from the inside to the outside after the container is removed from the mold. It also helps to limit bottom collapse, which generally has a negative impact on stress, increasing the risk of rejects. Indeed, a bottom with an excessively high temperature will tend to collapse during the mold removal stage. The resulting container may then potentially exhibit stress or other defects. Stress refers to marks of stress such as cracks. It should be noted that the The presence of the annular skirt 20 of the drawing rod 5 has the advantage of significantly improving the cooling stage by amplifying the action of the cooling gas, the gas being directed locally to where it is needed. This then makes it possible to considerably improve the cooling stage of the bottom of the resulting container, and therefore to achieve optimal cooling, even when, for reasons of throughput, the duration of the cooling stage must be very short. With reference to figures 3 to 9, the manufacturing process of a container by stretch blow molding with a particularly advantageous cooling step according to the invention of a container from the stretch rod previously described will be described below. With reference to [Fig.3], a preform 9 heated being previously placed in a blow mold 4 having, in closed position, a molding cavity 7 forming the impression of the container to be blown, the blow mold 4 being closed, the stretching rod 5 is positioned in the preform 5 in such a way that the latter extends coaxially with the preform 5. Next, with reference to [Fig.4], said preform 9 in the blow mold 4 is blown through a blow nozzle 21 by the introduction of air under high pressure P into said preform 9 and, substantially simultaneously, a stretching step of said preform 9 by vertical downward movement of said stretching rod 5 in said preform 9 bearing against the bottom 14 of said preform 9 so as to facilitate the axial elongation of the latter. With reference to [Fig. 5], the gas introduced into the preform 9, and ultimately the container formed by the blowing process, enters the inner cavity 16 of the drawing rod 5 through the orifice(s) 17, until the pressure inside the inner cavity 16 of the drawing rod is substantially equal to the pressure P of the air initially introduced into the preform 9 to form the container. Thus, high-pressure air P introduced into the preform during the blowing step is stored in the inner cavity 16 of the drawing rod 5. Once the container has been blown, with reference to [Fig.6], the high-pressure gas P contained in the container is degassed through the blow nozzle 21 and then, with reference to [Fig.7], the high-pressure air P stored in the inner cavity 16 of the drawing rod 5 escapes from the orifice(s) 17 of the drawing rod 5 to cool the container until the pressure in the inner cavity 16 of the drawing rod 5 is equal to the atmospheric pressure Pa of the air in the container after the degassing of said container. During this cooling stage, i.e. the escape of the air initially stored in the internal cavity 16 of the drawing rod 5, the latter is progressively raised, with reference to [Fig. 7], until said drawing rod 5 reaches its high position, the high position of the stretching rod corresponding to the end of the container cooling stage. In a final step, not shown in the figures, the container thus formed and cooled is extracted in a conventional manner through the opening of the blow mold 4. It is clear that, according to the process of the invention, the cooling step of the blown container is carried out without having to consume additional compressed air solely dedicated to cooling, which reduces the consumption of compressed air, although a little more compressed air is consumed during the blowing step, and ultimately reduces the manufacturing costs of the containers. In this particular embodiment, the drawing rod 5 begins to rise from the start of the degassing of the container; however, according to a variant of the process according to the invention, the drawing rod 5 may begin to rise from the end of the degassing of the container, that is to say after the pressure in the container is substantially equal to atmospheric pressure Pa. It will be noted that, in this latter variant of the process, the air contained in the internal cavity is entirely projected onto the bottom of the container so that the cooling of said bottom of the container is optimal. According to another embodiment of the method according to the invention, the drawing rod 5 begins to rise after a time delay t, starting from the beginning of the degassing of the container. In this case, said time delay t, for the rising of the drawing rod is preferably between 0.01 and 1 second. Furthermore, the volume of air under high pressure stored in the internal cavity 16 of the drawing rod 5 is between 10000 and 150000 mm³: in order to ensure sufficient cooling of the container. According to a particularly advantageous embodiment shown in Figures 13 to 19, the high-pressure air P introduced into the preform 9 during blowing is stored in a reservoir 22 fluidly connected to the inner cavity 16 of the drawing rod 5 until the pressure in the cavity of the drawing rod and in said reservoir equals the pressure of the high-pressure air P in the container. This reservoir 22 thus increases the cooling time and, ultimately, the efficiency of said cooling of the containers. Thus, with reference to [Fig.13], a preform 9 heated being previously placed in a blow mold 4 having, in closed position, a molding cavity 7 forming the impression of the container to be blown, the blow mold 4 being closed, the stretching rod 5 is positioned in the preform 5 in such a way that the latter extends coaxially with the preform 5. Next, with reference to [Fig. 14], said preform 9 in the blow mold 4 is blown through a blow nozzle 21 by the introduction of air under high pressure P in said preform 9 and, substantially simultaneously, a stretching step of said preform 9 by vertical downward movement of said stretching rod 5 in said preform 9 bearing against the bottom 14 of said preform 9 so as to facilitate the axial elongation of the latter. With reference to [Fig. 15], the gas introduced into the preform 9, and ultimately the container formed by the blowing process, enters the inner cavity 16 of the drawing rod S through the orifice(s) 17, as well as the reservoir 22, until the pressure inside the inner cavity 16 of the drawing rod and the reservoir is substantially equal to the pressure P of the air initially introduced into the preform 9 to form the container. Thus, high-pressure air P introduced into the preform during the blowing step is stored in the inner cavity 16 of the drawing rod 5 and in the reservoir 22. Once the container has been blown, with reference to [Fig.16], the high-pressure gas P contained in the container is degassed through the blow nozzle 21 and then, with reference to [Fig.17], the high-pressure air P stored in the inner cavity 16 of the drawing rod 5 and in the reservoir escapes from the orifice(s) 17 of the drawing rod 5 to cool the container until the pressure in the inner cavity 16 of the drawing rod 5 and in the reservoir 22 is equal to the atmospheric pressure Pa of the air in the container after the degassing of said container. During this cooling stage, i.e. the escape of the air initially stored in the inner cavity 16 of the drawing rod 5 and in the reservoir 22, the latter is raised progressively, with reference to [Fig.18], until said drawing rod 5 reaches its high position, the high position of the drawing rod corresponding to the end of the cooling stage of the container, with reference to [Fig.19]. In a final step, not shown in the figures, the container thus formed and cooled is extracted in a conventional manner through the opening of the blow mold 4. In the same way as before, the drawing rod 5 preferably starts to rise from the beginning of the degassing of the container; however, according to an alternative embodiment of the method according to the invention, the drawing rod 5 may start to rise from the end of the degassing of the container, that is to say after the pressure in the container is substantially equal to atmospheric pressure Pa. According to another embodiment of the method according to the invention, the drawing rod 5 begins to rise after a time delay t; from the start of the degassing of the container. In this case, said time delay t; for the rise of the drawing rod is preferably between 0.01 and 1 second. The time delay t; for the rise of the drawing rod is preferably greater than or equal to the duration of the degassing of the container, which corresponds to a rise of the stem after the end of the degassing of the container. It will be observed that the volume of air under high pressure stored in the reservoir 22 is preferably between 1000 and 2000000 mm, the volume of air under high pressure stored in the inner cavity 16 of the drawing rod 5 being between 10000 and 150000 mm* in the same way as before. Furthermore, preferably the inner cavity 16 of the drawing rod 5 and / or the reservoir 22 are filled, during blowing, with air under high pressure P through a plurality of orifices 17 opening into the inner cavity 16 of the drawing rod 5, said orifices 17 being positioned over all or part of the height of the drawing rod 5 and over all or part of the circumference of said drawing rod 5. In order to ensure that the cooling is as homogeneous as possible, said drawing rod 5 preferably has a plurality of orifices 17 distributed along said drawing rod 5 and angularly distributed around said drawing rod 5. In addition, said drawing rod 5 has at least one orifice 17 positioned at the lower free end of said drawing rod 5 in order to cool the bottom of the containers. Finally, and incidentally, the introduction of air under high pressure P into said preform and, ultimately, into the internal cavity 16 of the drawing rod 5 and / or into the reservoir 22, is carried out at different increasing pressures P1, P2, Pn. Said increasing pressures P1, P2, Pn correspond to the different blowing pressures well known in prior art processes including air recovery in particular. It goes without saying that a person skilled in the art will size the cross-section of the orifice(s) 17 of the rod, the volume of the internal cavity 16 and of the reservoir 22, according to the degassing rate (said degassing rate depending on the volume of the blown container, the blowing pressure and the diameter of the neck in particular) in order to optimize the cooling of the bottom of the container. Finally, it is clear that the examples just given are only specific illustrations and are in no way limiting as to the fields of application of the invention.

Claims

Claims

1. A method of manufacturing a container by stretch blow molding, comprising at least the following steps: - placing a preform (9) previously heated in a mold blowing (4) having, in the closed position, a cavity of molding (7) forming the imprint of the container to be blown; - closing said blow mold (4); - blowing said preform (9) into the blowing mold (4) by through a blowing nozzle (21) by the introduction of air under high pressure P in said preform (9) and, in a significant manner- possibly simultaneously, a step of stretching said preform (9) by inserting a stretching rod (5) inside said preform (9) in bearing against the bottom (14) of said preform (9) so as to facilitate the axial elongation of the latter; - cooling the interior of said container thus formed by projection of air through said stretching rod (5) simultaneously or after degassing of the container; - raising of said drawing rod (5); - extraction of said blown container by opening said mold of blowing (4); characterized in that the cooling step is carried out by by means of a drawing rod (5) comprising an internal cavity (16) and at least one orifice (17) communicating with the interior cavity (16), the high pressure air P introduced into the preform (9) during the blowing step being stored in the inner cavity (16) of the rod stretching (5) then said high pressure air P escaping from the orifice (17) of the drawing rod (5) to cool the container until the pressure in the inner cavity (16) of the drawing rod (5) is sens- possibly equal to atmospheric pressure Pa of the air in the container after degassing the container.

2. Method according to claim 1 characterized in that the air under high pressure P introduced into the preform (9) during blowing is stored in a reservoir (22) fluidly connected to the interior cavity (16) of the drawing rod (5) until the pressure in the cavity in- inner (16) of the drawing rod (5) and said reservoir (22) is sen- possibly equal to the pressure of the air under high pressure P in the container.

3. A method according to any one of claims 1 or 2 characterized in that the inner cavity (16) of the drawing rod (5) and / or the tank (22) are filled, during blowing, with high pressure air P through a plurality of orifices (17) opening into the cavity in- inner (16) of the drawing rod (5), said orifices (17) being po- located over all or part of the height of the drawing rod (5) and on all or part of the circumference of said drawing rod (5).

4. Method according to any one of claims 1 to 3 characterized in that the drawing rod (5) begins to rise from the end of the degassing of the container, i.e. when the pressure in the container is approximately equal to atmospheric pressure Pa.

5. Method according to any one of claims 1 to 3 characterized in that the drawing rod (5) begins to rise from the beginning of the degassing of the container.

6. Method according to any one of claims 1 to 3 characterized in that the drawing rod (5) begins to rise after a time- risation t, from the start of degassing of the container.

7. Method according to claim 6 characterized in that the tempo- t, of the rise of the drawing rod (5) is between 0.01 and ] second.

8. A method according to any one of claims 6 or 7 characterized in that the time delay t, of the rise of the drawing rod (5) is greater than or equal to the duration of degassing of the container.

9. A method according to any one of claims | to 8 characterized in that the volume of high pressure air stored in the cavity in- inner (16) of the drawing rod (5) is between 10000 and 150000 mm.

10. | Method according to any one of claims 2 to 9 characterized in that the volume of high pressure air stored in the tank (22) is between 1000 and 2000000 mm°*.

11. | Method according to any one of claims 1 to 10 characterized in that said stretching rod (5) comprises a plurality of orifices (17) distributed along said drawing rod (5) and angularly distributed around said drawing rod (5).

12. | Method according to any one of claims 1 to 11 characterized in that said stretching rod (5) comprises at least one orifice (17) po- located at the lower free end of said drawing rod (5).

13. | Method according to any one of claims 1 to 12 characterized in that the introduction of high pressure air P into said preform (9) and, ultimately, into the internal cavity (16) of the drawing rod (5), is carried out at different increasing pressures P1, P2, ..Pn.