WO2009103927A2

WO2009103927A2 - Process and device for manufacturing a plastic container by blow moulding

Info

Publication number: WO2009103927A2
Application number: PCT/FR2009/050249
Authority: WO
Inventors: Jean-François CARER
Original assignee: Hts
Priority date: 2008-02-21
Filing date: 2009-02-17
Publication date: 2009-08-27
Also published as: TW201000298A; FR2927835A1; WO2009103927A3

Abstract

Process for manufacturing a plastic container (13) by blow moulding, in which a preheated preform (5) is placed in a mould (1, 2), while leaving part of the preform (5) intended to form the neck (6) of the container (13), outside the mould (1, 2), and a pressurized gas is blown into the preform (5), the deformation of said preform being assisted by stretch means, so as to make it conform to the internal walls of the mould (1, 2), characterized in that said stretch means apply a stretch force of at least 4 N to said preform (5) after a time of at most 1/30 s following the start of stretching, so as to make the material of the preform (5) undergo a displacement of at least 1/100 mm during this period. Device for implementing this method.

Description

Method and device for manufacturing a plastic container by blowing.

The invention relates to the blow molding of plastic containers. Usually, plastic containers such as bottles made of

PET (polyethylene terephthalate) can be manufactured as follows. A preform is produced by injection on which, during the injection, a portion intended to constitute the neck of the container is conformed. The preform is then heated (at about 110 ° C for the PET), and it is introduced between the two parts of a mold placed in spaced apart position. Then the mold is closed by putting said parts in contact, while leaving the neck of the preform emerge from the closed mold. Then a sealing nozzle is applied to the neck through which a pressurized gas such as air is blown. The latter inflates the hot preform so as to apply against the walls of the mold by creating in the plastic an empty interior space to transform the preform into a container. When the material has been cooled, with the aid of a cooling device of the mold, the sealing nozzle is removed, a gripping device grasps the neck emerging from the mold, and the walls of the mold are spread apart to release the recipient. This one is then evacuated to undergo the following stages of its manufacture.

Conventionally, the shaping of the preform during blowing is assisted by a mechanical stretching system. This is conventionally constituted by a stretching rod, that is to say a rod which exerts pressure on the preform, along its longitudinal axis, so as to contribute to its elongation, in combination with the blowing. The use of this stretching rod helps to obtain a good centering and a good positioning of the preform in the mold during blowing, so a satisfactory conformation of the final container.

Conventionally, the forming operation begins with a so-called "pre-blowing" operation during which the air is injected onto the preform at a pressure (10 to 20 bar) lower than during the actual blowing phase (25). at 40 bars). The duration of the pre-blowing phase is generally about twice that of the blowing phase. The stretch rod is operated at the beginning of pre-blowing. Different types of devices are usually used for moving the stretch rod.

Pneumatic control can be used. But it has the disadvantage of not allowing a fine control of the position of the cane and its power of use.

Hydraulic control can be used. Compared to a pneumatic control, more is limited in terms of speed of movement, but a higher power of use can be applied. Its disadvantages on the accuracy of the operating parameters are similar to those of the pneumatic control.

A mechanical control can be used, but such a system is heavy to put in place.

Finally, it is possible to use an electrical system comprising a ball screw. This system has the advantage over pneumatic and hydraulic systems to provide better control of the control speed of the drawing rod, which however remains limited to about 2m / s. It has the disadvantage of having a fairly large wear of parts that limits its life without maintenance.

In general, existing systems provide facilities with productivities and operational details that would be desirable to improve.

The object of the invention is to provide a method and a device for manufacturing plastic containers by blowing a hot preform inside a mold, assisted by a simultaneous stretching of the preform, providing better productivity and better control accuracy and results than existing processes and devices.

To this end, the subject of the invention is a method for manufacturing a plastic container by blowing, according to which a pre-heated preform is placed in a mold by allowing some of the preform to form the neck of the mold to emerge from the mold. container, and pressurized gas is blown on the preform by assisting its deformation by stretching means, so as to make it fit the inner walls of the mold, characterized in that said drawing means apply to said preform a force at least 4 N after not more than 1/30 s after the start of drawing, so that cause the material of the preform to move at least 1/100 mm during this time.

Said drawing force of at least 4 N is preferably obtained after a period of at most 1/100 s after the beginning of the drawing. Said blowing can be carried out in a single step.

Said blowing can be performed at pressures between 15 and 25 bar.

The preform can be in PET.

The invention also relates to a device for manufacturing at least one blown plastic container, comprising at least one mold in which a preheated preform made of said plastic material can be placed, means for drawing the preform and their control means, and means for blowing a gas onto the preform comprising an injection nozzle that can be applied to the preform, characterized in that said drawing means make it possible to apply to said preform a force of stretching of at least 4 N after a period of not more than 1/30 s after the start of stretching, so as to cause movement of the preform material of at least 1/100 mm during this period when said preform is made of PET and is preheated to 110 ^<C ,. Said blowing means may allow to inject on the preform a pressurized gas of 15 to 25 bars.

Said drawing means may comprise a drawing rod applicable to said preform.

Said stretching rod can be controlled by electromagnetic means.

Said electromagnetic means may comprise a linear motor integral with the drawing rod and a magnetic rail serving as a force transmitter to the linear motor.

Said device may comprise a plurality of molds and drawing rods, said drawing rods being fixed to a bracket itself controlled by a single set of control means. As will have been understood, according to the method of the invention, a relatively high drawing force is applied to the preform, namely at least 4N, as soon as a very short period of time (at most 1 1/100, preferably at most 1 / 10Os) after the beginning of the stretching operation, and so as to cause the material of the preform to move at least 1 / 100mm during this period of time.

The inventors have found that if this condition is respected, a quality of the blown product could be reached very satisfactorily by applying during blowing a pressure which can be relatively moderate (typically 15 to 25 bar), and especially by giving the possibility of removing the pre-blowing stage. In this case, the blowing takes place during a single phase (during which it is possible however to vary the air pressure, and also the force and the thrust speed of the stretching rod, in a progressive manner. and controlled), and significantly shortens the duration of the vessel manufacturing process, so we increase the productivity of the facility, and we can simplify the design of the blower and its annexes.

These conditions can be obtained thanks to the device according to the invention, in which the drawing means, for example a drawing rod, are controlled by electromagnetic means including a linear motor, integral with the drawing means, and a rail magnetic, which are not in contact with each other. There is no problem of wear of moving parts. In addition, such a system allows to obtain almost instantaneously a high thrust force, as is necessary for the implementation of the method according to the invention. Finally, it is easy to control in a fine way, in particular, by computer means, so as to impose precise support forces and speeds of movement of the drawing means, by keeping them constant or by varying them a predetermined manner according to curves whose user experience would show that they lead to optimal product quality. Similarly, it allows the implantation of precise measuring means of the various operating parameters and displacements of the drawing means. This makes it possible to make fine corrections to the operating parameters in response, for example, to a planned or unexpected modification of the viscosity of the preform due, for example, to a temperature change that may not be exactly what was theoretically expected.

The invention will be better understood on reading the description which follows, with reference to the following appended figures: FIGS. 1 and 2 which show schematically, front view (FIG. 1) and profile view (FIG. installation according to the invention before the implementation of the method according to the invention;

- Figures 3 and 4 show the same installation at the beginning of the implementation of the method according to the invention; - Figures 5 and 6 show the same installation at the end of the implementation of the method according to the invention.

FIGS. 1 and 2 show diagrammatically seen from the front (FIG. 1) and from the profile (FIG. 2) the essential elements of an exemplary blowing device according to the invention, the following elements of which are visible: - the two parts 1, 2 of the mold, in spaced apart position, and the contours 3, 4 of the interior spaces are shaped, conventionally, to define the shape of the blow molding container; these mold parts 1, 2 have construction details and ancillary equipment for their movement and heating / cooling which are conventional designs and are not shown;

a preform 5, constituted conventionally by a piece of material intended to form the container to be manufactured, for example PET for bottles for food use; as is known, this preform is preheated to a temperature allowing it to be shaped by blowing (of the order of 110O for PET), and is held in place by a device not shown; its upper part 6 is conventionally already shaped so as to constitute the neck of the container to be formed;

an air injection nozzle 7, made of a gas-permeable material and connected to conventional means (not shown) for injecting pressurized air which can emerge from it by its lower face 8; it goes without saying that other gases than air can be used, the air having the advantage of being inexpensive and readily available in compressed form; a stretching rod 9 which can slide to the control inside a longitudinal orifice passing through the nozzle 7;

according to the invention, means for controlling the stretching rod 9 which have the following properties: they allow the stretching rod 9 to apply to the preform 5 a deformation force of 4N or more, obtained after a maximum duration of 3/1 Os, preferably at most 1 / 10Os, and so as to obtain after these 3/1 Os, preferably after these 1 / 100s, simultaneously with the blowing, a displacement of the rod 9 in the preform 6 of at least 1/100 mm (thus a corresponding displacement of the material of the preform 5); these conditions are representative of what is necessary to obtain in order to be able to do without a pre-blowing operation at relatively low pressure (10-20 bars), to be followed by a blowing operation at a substantially higher nominal pressure. high (25-40 bar), replacing this process by a single blowing phase that can be performed in a range of relatively average pressures, typically of the order of 15 to 25 bar, while obtaining a product of satisfactory quality.

Of course this does not exclude the use of higher blowing pressures, for example up to 40 bars in the case where one would have a preform 5 large or difficult to form a material. Said control means are, in the preferred but not necessarily exclusive example, envisaged by the inventors, electromagnetic means comprising:

a magnetic motor (linear motor) and its guide means (not shown) moved without contact by a magnetic rail 11; a path analyzer 12 fixed to the linear motor 11 and making it possible to determine and regulate its position and his displacement.

These organs are conventional in devices of all types using a linear motor and need not be described more precisely here.

Figures 3 and 4 show the same elements as Figures 1 and 2, seen in the same way, while the device is at the very beginning of its operation. To know :

the mold walls 1, 2 have been closed again on the preform 5, leaving only the neck 6 outside the mold; - The drawing rod 9 is lowered, with the linear motor 10 which supports it, until coming into contact with the bottom of the inside of the preform 5, to anticipate the descent of the rod 9 relative to the start of the blowing;

the injection nozzle 7 has been placed in contact with the neck 6 of the preform 5; optionally, a housing (not shown) may be provided on the lower face 8 of the nozzle 7 to receive at least the upper end of the neck 6; it is thus possible to improve the sealing of the contact between the nozzle 7 and the preform 5 to ensure better control of the process.

Then we proceed to the injection of air under pressure in the nozzle 7, and the descent of the stretch rod 9 in the preform 5 to the bottom of the mold 1, 2 to assist its shaping. According to the invention, as permitted by the use of the electromagnetic control device of the rod 9, the rod 9 is moved immediately with a relatively large force, namely at least 4N, obtained after at most 1 / 30s, of preferably, even at most 1 / 100s, and so as to cause a displacement of the material of the preform 5 (in other words a depression of the rod 9 in the preform 5) of at least 1 / 100mm. It is on this condition that, contrary to the usual practice, it is possible to avoid having to divide the blowing in two stages, the first of which is conducted at a relatively moderate pressure and the second at a relatively high pressure. The use of the method according to the invention, allowed in a privileged manner by the adoption of an electromagnetic system 10, 11 for controlling the movement of the rod 9, makes it possible to achieve the shaping of the container 13 with a single blowing step, which can be carried out in a range of average pressures, for example 15 to 25 bar. Figures 5 and 6 show the installation in its final state with the container

13 and the stretching rod 9 arrives near the bottom of the container 13. After that, the mold is opened by spacing the parts 1, 2, the rod 9 and the motor 10 are raised and the container 13 is seized by the collar 6 to be evacuated for the next steps of its treatment. FIGS. 1 to 6 show an installation in which a motor 10 controls a single drawing rod 9. However, it goes without saying that the motor 10 could command a stem bearing itself a multiplicity of rods 9 helping to form an equal number of containers 13 using an equal number of mussels 1, 2 that would be associated with them. It is thus possible to form several containers 13 simultaneously, which increases the productivity of the installation.

The use of a rod 9 controlled by electromagnetic means 10, 11 to obtain the stretching of the preform 5 is a preferred example of a drawing device, but it could be envisaged to use, for the implementation of the method of the invention, other types of stretching devices functionally equivalent in terms of the forces applied to the preform

5 and displacements that they would impose on the material constituting the preform 5.

One of the advantages of the process according to the invention is also that it can allow a lower preform preheating temperature than in conventional processes, typically between 1 and 200 less depending on the materials treated.

It would remain in the spirit of the invention to perform the blowing in two stages, as is conventionally the case, while applying the drawing force in the conditions that have been said. This would deprive oneself of some of the advantages of the invention, namely the simplification of the blowing process and the increase in productivity. But one could use lower blow pressures than in the conventional method, and / or reduce the preheating temperature of the preform 5, and / or use different materials from those used in conventional methods that would not allow their deformation in adequate conditions, unlike the method according to the invention.

Claims

A method of manufacturing a blow-molded plastic container (13) in which a pre-heated preform (5) is placed in a mold (1, 2) by allowing some of the mold (1, 2) to emerge from the mold (1, 2). preform (5) intended to form the neck (6) of the container (13), and a pressurized gas is blown on the preform (5) by assisting its deformation by drawing means, so as to make it conform to the walls internal mold (1, 2), characterized in that said drawing means apply to said preform (5) a drawing force of at least 4 N after a period of at most 1/30 s after the start stretching, so as to cause movement of the material of the preform (5) by at least 1/100 mm during this time.

2. Method according to claim 1, characterized in that said drawing force of at least 4 N is obtained after a period of at most 1/100 s after the start of stretching.

3. Method according to claim 1 or 2, characterized in that said blowing is performed in a single step.

4. Method according to claim 3, characterized in that said blowing is performed at a pressure between 15 and 25 bar.

5. Method according to one of claims 1 to 4, characterized in that the preform (5) is PET.

6. Device for manufacturing at least one plastic container (13) by blowing, comprising at least one mold (1, 2) in which can be placed a preform (5) preheated made of said plastic material, means of stretching of the preform (5) and their control means, and means for blowing a gas on the preform (5) comprising an injection nozzle (7) which can be applied to the preform (5), characterized in that said drawing means is capable of applying to said preform (5) a drawing force of at least 4 N after a duration of at most 1 / 30s after the beginning of the drawing, so as to causing the material of the preform (5) to be displaced by at least 1/100 mm during this time, when said preform (5) is made of PET and is preheated to 110 °.

7. Device according to claim 6, characterized in that said blowing means are used to inject on the preform (5) a pressurized gas of 15 to 25 bar.

8. Device according to claim 6 or 7, characterized in that said drawing means comprise a drawing rod (9) applicable to said preform (5).

9. Device according to claim 8, characterized in that said drawing rod (9) is controlled by electromagnetic means.

10. Device according to claim 9, characterized in that said electromagnetic means comprise a linear motor (10) integral with the drawing rod (9) and a magnetic rail (11) serving as a force transmitter to the linear motor (10). ).

11. Device according to one of claims 8 to 10, characterized in that it comprises a plurality of molds (1, 2) and stretching rods (9), said drawing rods (9) being fixed to a stem itself controlled by a single set of control means.