WO2005044540A1

WO2005044540A1 - Container made of polyester resin, its manufacturing process and device for its implementation

Info

Publication number: WO2005044540A1
Application number: PCT/EP2004/012135
Authority: WO
Inventors: Gérard Denis; Alain Contal
Original assignee: Nestle Waters Management & Technology
Priority date: 2003-11-06
Filing date: 2004-10-27
Publication date: 2005-05-19
Also published as: EP1529620B1; EP1529620A1; ATE423670T1; CN1894084B; CN1894084A; DE60326353D1

Abstract

The subject of the invention is a container made of polyester resin that can be obtained by a process comprising the heating of a preform (2) taking substantially the form of a cylindrical tube having an opening (3) at the neck to a temperature above the glass transition temperature of the said polyester, the introduction of the said preform into a mould (1), the stretching of the said preform by a stretching rod (15) and the introduction of an incompressible fluid (17) through the opening of the said preform in order to form the said container. The invention also relates to the process and to the device for manufactoring the container.

Description

Container made of polyester resin, its manufacturing process and device for its implementation

The present invention relates to the field for the manufacture of containers made of polymer material, especially made of polyester. More particularly, it relates to the field for the manufacture of bottles made of polyester, preferably made of polyethylene terephthalate (PET) , containing a liquid, preferably water and especially mineral water.

The subject of the present invention is a polyester container, its process of manufacture by injection of liquid under pressure into a preform. The subject of the invention is also a device for implementing this process.

For many years, PET bottles usually found on the market have been manufactured by blow moulding or stretch-blow moulding PET preforms with compressed air.

A preform usually takes the form of a cylindrical tube closed at one of its ends and open at its opposite end. The top of the preform, which is open, corresponds to the neck of the container. During the conventional process for manufacturing the container from a preform, the preforms are slipped, top down, over the cylindrical pins of a continuous conveying chain which thus transports the preforms through an oven, essentially formed by a straight section bordered on each side by radiative heating means, so as to temperature-condition the plastic for the subsequent stretch-blow moulding step. Next, the hot preform is removed and transferred into a mould of a blow moulding machine. The transfer movement, carried out for example by a transfer arm, is coordinated with that of the blow moulding machine, which is generally in the form of a rotary carousel that rotates continuously about its vertical axis and which carries, on its periphery, a series of identical moulds. Thus, the preform is placed in the mould immediately after the latter has opened and the previously formed container has been removed.

The preform is heated beforehand so as to be in the mould at a temperature above the PET glass transition temperature (about 100 °C) so as to allow forming by stretch-blow moulding. The temperature of the preform at the end of the heating step is slightly above that required inside the mould of the blow moulding machine, so as to take account of the cooling that takes place over the length between the point of heating and the point of blowing. Thanks to the rotary movement and the simultaneous presence of several moulds, such a blow moulding machine can produce containers at very high rates, of the order of several tens of thousands of units per hour, i.e. around 1000 to 2000 bottles per hour per mould.

The stretch-blow moulding is carried out by stretching using a metal rod and by injecting air at pressures ranging from 3 to 40 bar (3 x 10⁵ Pa to 4 x 10⁶ Pa) .

The air is injected through a nozzle whose end is introduced through the opening of the top of the preform. The bottles manufactured by injecting pressurized air have a relatively satisfactory lifetime for a given weight and a given type of material. However, the intrinsic properties and characteristics of PET mean that even better results may be anticipated by modifying the container manufacturing process .

One of the objectives of the present invention is consequently to propose an improved process for manufacturing a polyester container from a preform.

Another objective is to be able, optionally, to integrate the container filling step into the container manufacturing process. Developments in the prior art have already been made in which the container is stretch-blow moulded by the liquid that will subsequently fill the said container. Patent JP 63249616 in the name of Komatsu Ltd relates to such a development. The material used is polyethylene, polypropylene or polyvinyl chloride. Patent FR 1 430 316 also relates to such a filling system, but in this case using polytetrafluoroethylene . Neither of the known documents relates to a filling approach using polyester. In the aforementioned materials, there is not the specificity of polyester, which is to crystallize during the stretching operation. All the aforementioned materials are amorphous and/or semicrystalline, and remain so during the stretching operation.

The present invention relates to a container made of polyester resin that can be obtained by a process comprising the heating of a preform taking substantially the form of a cylindrical tube having an opening at the neck to a temperature above the glass transition temperature of the said polyester, the introduction of the said preform into a mould, the stretching of the said preform by a stretching rod and the introduction of an incompressible fluid through the opening of the said preform in order to form the said container.

Of course, the invention also relates to the container- contents assembly, it being possible for the said assembly to be closed by any closure means known in the prior art. The polyester of the container obtained has a crystallinity of between 25 and 50%. The object of the present invention is to obtain the highest possible crystallinity, since high crystallinity means better mechanical strength of the container. Without wishing to be tied down by one scientific theory, it is known that the polyester preform is amorphous and that the stretching induces crystallization and, at the same time, an exothermic reaction. Heat generation is deleterious to the development of crystallinity. According to the present invention, a first stretching operation is therefore carried out with the stretching rod, causing crystallization and heat generation and at this particular moment the incompressible fluid is introduced, which will very rapidly absorb this generated heat and thus allow the equilibrium level of crystallinity obtained in the final container to be shifted upwards, preferably between 30 and 50%.

The crystallinity is measured on a Lloyd-Davenport density column using the following method. The column is filled with a salt (calcium nitrate) solution having a density gradient. The column is calibrated with balls having a known density between 1.335 and 1.455. Next, small pieces of the container according to the invention are immersed in the column and, after a certain time, they stabilize at a certain height in the column corresponding to a certain density. The measurements are carried out at 23 °C. The following look-up table for a p_c of 1.455 gives the crystallinity. In the table, only the right-hand part of the crystallinity should therefore be considered.

The invention also relates to a process for manufacturing a container made of polyester resin from a preform taking substantially the form of a cylindrical tube having an opening, preferably at a neck, the said process comprising a step of heating the said preform to a temperature above the glass transition temperature of the said polyester, a step of introducing the said preform into a mould, a step of stretching the said preform by a stretching rod and an expansion step carried out inside a cavity, characterized in that, during the said expansion step, a pressurized incompressible fluid is injected through the opening of the said preform in order to form the said container. The containers obtained by this process have much better characteristics than those obtained using a conventional stretch-blow moulding process with inflation by a gaseous fluid. In particular, it has been found that they have a longer lifetime for a given weight and a given type of material. The degree of crystallinity, that is to say the ratio of the mass of crystalline phase to the total mass of polymer, of a container obtained by the process according to the invention may especially be much higher.

For example, in the case of PET bottles, the bottles obtained by the process according to the invention may have crystallinity levels of between 30% and 50%, which gives them longer lifetimes than bottles currently obtained for the same weight and the same type of PET, which possess crystallinity levels of between 25% and 30%.

According to another aspect of the present invention, the said incompressible fluid is a liquid injected under pressure (for example around 40 bar) , at a controlled rate and a controlled pressure (controlled quantity) , preferably the liquid intended to be contained in the said final container to be formed. The speed of the stretching rod for stretching the preform is between 1 and 2 m/s. As a consequence, the material of the container has the same speed of displacement in the mould.

Thus, the liquid used to manufacture the containers may be the liquid to be packaged, for example water and especially mineral water, thereby making it possible to dispense with a subsequent filling step. The step of manufacturing containers and the step of filling these containers are thus integrated into one and the same step. This solution of course has substantial economic advantages and limits the risk of contamination, particularly bacterial contamination, of the empty container.

Advantageously, when the said container to be formed is a PET bottle, the said preform is heated to a temperature above the glass transition temperature of the said PET, typically to about 75°C to 85°C, during the said heating step and the temperature of the said incompressible fluid is between 10 °C and 90 °C during the said expansion step.

According to one preferred embodiment of the invention, the said temperature of the incompressible fluid is between 15 °C and 30 °C. This means that the fluid is introduced into the heated preform at room temperature.

The mould into which the preform is introduced has a temperature of at least 60 °C. Preferably, the temperature of the mould is between 15 and 20°C.

According to another aspect, the present invention also provides a device for implementing a process of the type that has just been defined, the said device being characterized in that it essentially comprises: - a dual cylinder system that includes a mouth for the incompressible fluid feed; and a mould in which the preform having an opening is placed, the said dual cylinder system being placed above the said mould so as to connect its mouth to the opening of the preform at the moment of stretching-filling.

According to the present invention, the dual cylinder system comprises: a first piston for connecting the said system to the opening of the preform; a second piston, coaxial with the first piston, for filling the preform with incompressible fluid, the two pistons being driven by air in the respective chambers of the said pistons; and a stretching rod coaxial with the first and second pistons .

The process according to the invention may be implemented using an installation specifically constructed for this purpose and having the various elements indicated above.

Advantageously, the incompressible fluid feed is connected to a feed of a line for supplying liquid, preferably liquid for filling the containers to be formed.

Consequently, as was explained above, the liquid used to manufacture the containers is the liquid to be packaged, which makes it possible to dispense with an additional filling device. The devices for manufacturing containers and for filling these containers are thus integrated into one and the same device.

The invention will be more clearly understood thanks to the following description, which refers to a preferred embodiment, given by way of non-limiting example, and explained with reference to the drawings in which: Figure 1 is a schematic cross section of the device according to the invention before the stretching-expansion- filling; and Figure 2 is a schematic cross section of the same device during the stretching-expansion-filling phase. The embodiment given here by way of example relates to a process for manufacturing PET water bottles from a heated preform. As may be seen in the appended figures, a preform takes the form of a cylindrical tube closed at its lower end. The top of the preform, which is open, corresponds to the neck of the bottle, that is to say, in this case, the neck onto which a cap has to be screwed.

The process is implemented by means of modifications made to an installation for manufacturing PET miheral water bottles, such as that described above in the introductory part of the present document.

According to the present invention, during the expansion step, injected through the opening of the preform is not pressurized air but an incompressible fluid. It will be advantageous to use, as incompressible fluid for forming the bottle, the liquid that this bottle has to contain, so as to eliminate a subsequent filling step.

To implement the invention, modifications are made to a PET bottle manufacturing installation, as may be seen in the appended figures .

The figures show schematically a mould 1 inside which the body of a preform 2 is contained. The neck 3 of the preform projects to the outside of the mould. The dual cylinder system 4 associated with the mould 1 is designed to be placed above the said mould so as to be connected onto the opening 3 of the preform 2 at the moment of stretching- expansion-filling. The dual cylinder system comprises a body 5 with a first piston 6 and a second piston 7. The first piston 6 has a spring 8 placed in the chamber 9 and a chamber 10. The second piston 7 has a chamber 11 and a chamber 12. Throughout the system, seals 13 are provided, these all being assigned the same reference number. The various piston chambers are connected either to a pressurized air system or to atmospheric pressure. The line 14 feeds the incompressible fluid 17, namely the water for filling the preform. The piston 6 allows the dual cylinder to be connected to the neck 3 of the preform and the piston 7 allows the incompressible fluid to enter the said preform. Finally, a stretching rod 15, coaxial with the first and second pistons, is provided.

The operation of the device according to the invention is as follows. Firstly, the preform has to be heated to a temperature high enough to allow it to undergo stretching. The heated preform is then introduced into the mould 1 and the cycle can commence. Initially, the chamber 10 of the piston 6 is pressurized with air at a pressure of the order of 10 bar, so that the spring 8 is compressed. To allow the dual cylinder system 4 to descend, the chamber 10 is placed at atmospheric pressure, which lowers the piston 6 and thus presses the mouth 16 against the opening 3 of the preform 2. Next, the stretching rod 15 is lowered into the preform so as to carry out a vertical stretching operation. There is then time to allow the water to flow into the preform. The chamber 11 of the piston 7 is at a pressure of the order of 10 bar and the chamber 12 is at atmospheric pressure. It then suffices to raise the pressure in the chamber 12 to the order of 10 bar and to exhaust the chamber 11, in order for the piston 7 to lift off the seat of the mouth 16 and for water to flow into the preform, and in this way cause horizontal stretching. As already mentioned above, the stretching generates heat, which is absorbed by the incompressible fluid, thus allowing the final container to have a higher crystallinity than in conventional stretch-blow moulding devices. Next, the cycle starts again on a new preform. Of course, a conventional moulding machine will be used, in which a novel stretching- filling head will be placed.

The entire system is controlled by servocontrol mechanisms, operated from a central servocontrol unit or automatic controller (not shown) of the bottle manufacturing installation so that the operation of the water injection device is coordinated with the operation of the forming (blow moulding) machine and, more generally, with the operation of the entire bottle manufacturing installation.

The operation of the water injection device coordinated with the operation of the forming or blow-moulding machine is performed with an injection cycle of duration shorter than the duration of the rotation cycle for a mould to rotate about the axis of the forming machine.

The process is optimized for a predetermined stretch rate, for a preform temperature above the glass transition temperature of the polyester used, and for a rapid injection rate, greater than the cooling rate of the material used. Thus, another advantage is a very short cycle time, the incompressible fluid injection time being considerably less than one second, preferably between 0.02 s and 0.5 s and more preferably between 0.1 s and 0.2 s. The pressure of the incompressible fluid is greater than 1 bar, preferably between 1 and 10 bar. To eliminate any air bubbles contained in the circuit, a purge cycle is also provided. The initial cycle is defined via the automatic controller.

The temperature of the water may be between 10 °C and 90 °C depending on the technical constraints imposed by the bottle that it is desired to produce. In particular, the pressure must be high enough to deform the preform and low temperatures impose higher pressures. However, when the technical constraints so allow, the temperature of the liquid will advantageously be 15 °C.

Advantageously, in order for there to be no risk of the neck 3 of the perform 2 being deformed during the expansion cycle, the said neck is isolated from the liquid by an impermeable and/or cooled part.

The containers obtained by this process have much better characteristics than those obtained using a conventional expansion process with blowing by gaseous fluid. In particular, they have a longer lifetime for a given weight and given type of material. The degree of crystallinity, that is to say the ratio of the mass of crystalline phase to the total mass of polymer, of a container obtained by a process according to the invention may in particular be much higher. By using rapid expansion speeds it is possible to achieve a quite high stretch ratio and also quite a high induced crystallization.

For example, in the case of tests carried out with water at water temperatures ranging from 85 °C to 95 °C and at pressures ranging from 2 bar to 3 bar (2 x 10⁵ Pa to 3 x 10⁵ Pa) in the case of PET containers, the containers obtained by the process according to the invention had degrees of crystallinity of possibly up to 50%. To obtain these degrees of crystallinity, all the non-amorphous phases, that is to say the crystalline phase and the mesophase, were combined.

Of course, the invention is not limited to the embodiment described and shown in the appended drawings. Modifications remain possible, especially from the standpoint of the construction of the various elements or the substitution of technical equivalents, without thereby departing from the scope of protection of the invention.

Claims

1. Container made of polyester resin that can be obtained by a process comprising the heating of a preform taking substantially the form of a cylindrical tube having an opening at the neck to a temperature above the glass transition temperature of the said polyester, the introduction of the said preform into a mould, the stretching of the said preform by a stretching rod and the introduction of an incompressible fluid through the opening of the said preform in order to form the said container.

2. Container according to Claim 1, characterized in that it has a crystallinity of between 25 and 50%.

3. Process for manufacturing a container made of polyester resin from a preform taking substantially the form of a cylindrical tube having an opening, preferably at a neck, the said process comprising a step of heating the said preform to a temperature above the glass transition temperature of the said polyester, a step of introducing the said preform into a mould, a step of stretching the said preform by a stretching rod and an expansion step carried out inside a cavity, characterized in that, during the said expansion step, an incompressible fluid is injected through the opening of the said preform in order to form the said container.

4. Process according to Claim 3, characterized in that the said incompressible fluid is a liquid injected under pressure at a controlled rate and a controlled pressure.

5. Process according to either of Claims 3 and 4, characterized in that the injected liquid corresponds to the liquid intended to be contained in the container.

6. Process according to one of Claims 3 to 5, characterized in that the speed of the stretching rod for stretching the preform is between 1 and 2 m/s.

7. Process according to any one of Claims 3 to 6, characterized in that, when the said container to be formed is a PET bottle, the said preform is heated to a temperature above the glass transition temperature of the said PET, typically to about 75°C to 85°C, during the said heating step and the temperature of the said incompressible fluid is between 10 °C and 90 °C during the said expansion step.

8. Process according to Claim 7, characterized in that the said temperature of the incompressible fluid is about 15°C.

9. Process according to any one of Claims 3 to 8, characterized in that the incompressible fluid injection time is considerably less than one second, preferably between 0.02 s and 0.5 s and more preferably between 0.1 s and 0.2 s.

10. Device for implementing the process according to any one of Claims 3 to 9, characterized in that it essentially comprises : - a dual cylinder system that includes a mouth for the incompressible fluid feed; and a mould in which the preform having an opening is placed, the said dual cylinder system being placed above the said mould so as to connect its mouth to the opening of the preform at the moment of stretching-filling.

11. Device according to Claim 10, characterized in that the dual cylinder system comprises: a first piston for connecting the said system to the opening of the preform; a second piston, coaxial with the first piston, for filling the preform with incompressible fluid, the two pistons being driven by air in the respective chambers of the said pistons; and a stretching rod coxial with the first and second pistons .

12. Device according to Claim 10 or 11, characterized in that the incompressible fluid feed is connected to a feed of a line for supplying liquid, preferably liquid for filling the containers to be formed.