FR2818186A1 - Thermofusible polymer preform treatment procedure uses ultrasonic vibrations applied along at least one axis to reduce gas/vapour permeability - Google Patents

Abstract

Treatment procedure comprises subjecting preforms to ultrasonic vibrations along one or more predetermined axes, e.g. in line with and perpendicular to their lengthwise axes, at above 60 deg C. Vibrations are applied at or after injection, but before pre-heating phase prior to blow-moulding, using a sonotrode associated with the preform mould. The treatment procedure for thermofusible polymer preforms consists subjecting them to ultrasonic vibrations along one or more predetermined axes, e.g. in line with and perpendicular to their lengthwise axes, after heating to and maintaining at a temperature of above about 60 deg C. The vibrations are applied at or after the moment of injection, but before the pre-heating phase prior to blow-moulding, using a sonotrode associated with the preform mould, and after vibrating the preforms are cooled to below 60 deg C before pre-heating.

Description

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The present invention relates to a process for the treatment of preforms made of a hot-melt polymer such as, in particular, polyethylene terephthalate (PET). , this treatment process being essentially physical and making it possible to reduce the permeability to gases and vapors of the walls of the containers produced by blowing from these preforms.

The invention also relates to a device for the implementation of this preform processing method.

Finally, it relates to a preform obtained after treatment according to this process.

The international patent application published under NO WO 00/12290 having for title Process for processing a preform for the production of a container by blowing describes a technique which consists in exposing the preform to ultrasonic vibrations during or after a heating phase of the preform, this phase being preliminary to the actual blowing, and this exposure to ultrasound having in particular the aim of increasing the barrier layer of the container produced from this preform.

This process is very advantageous in that it is purely physical and relatively simple to implement, unlike the known processes which usually involve techniques for coating the container with a different material and which, therefore, are complex and expensive, or those which consist in producing the preforms using multilayer materials.

The process of blowing the containers from a preform generates a bi-stretching of the material in two perpendicular directions. This bi-stretching combined with partial or total crystallization makes it possible to increase in a way

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 known, about 20 to 30% impermeability compared to amorphous PET and to increase the mechanical resistance to shocks.

The method described in the international application mentioned above makes it possible to considerably increase this impermeability. Research first showed that it was advantageous to apply ultrasonic vibrations during the preheating phase of preforms, oriented mechanical agitation due to vibrations adding to molecular agitation due to heating to accelerate the rise in temperature of the material, maintained at a temperature of the order of 80 C or more. It was thought that the application of ultrasonic vibrations in a given direction could temporarily generate a preferred molecular orientation, and that the immediate implementation of the blowing process could preserve this preferred orientation, by generating in the blown container a molecular structure. able to reinforce the barrier layer, that is to say impermeability to gases and vapors.

This process has a major drawback. The conventional container blowing lines cannot be used since a device suitable for applying ultrasound must be mounted on the path of the preforms between the preheating furnace and the zone of introduction into the molds. These lines being very complex, it seems difficult to envisage transforming them and adding additional devices to them without carrying out a new expensive study and delicate adjustments of these machines.

The object of the present invention is to overcome these drawbacks by providing a process for processing preforms which is not linked to the type of container blowing machine.

This object is achieved by a process as described in the preamble, characterized in that one applies to these preforms, brought or maintained at a temperature

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supérieure à environ 60oC, des vibrations ultrasoniques selon au moins un axe prédéterminé, l'application desdites vibrations ultrasoniques étant faite au moment de l'injection desdites préformes ou postérieurement à cette injection, mais antérieurement à une phase de préchauffage des préformes en vue de la fabrication de récipients par soufflage à partir de ces préformes.

higher than about 60oC, ultrasonic vibrations along at least one predetermined axis, the application of said ultrasonic vibrations being made at the time of the injection of said preforms or after this injection, but prior to a preheating phase of the preforms for the purpose of manufacture of containers by blowing from these preforms.

According to a variant of the method, these preforms are cooled to a temperature below 60 ° C. after the application of ultrasonic vibrations and before the preheating phase with a view to their use for the manufacture of containers by blowing.

According to a first embodiment, said ultrasonic vibrations are applied along at least one axis substantially parallel to the longitudinal axis of the preforms.

According to a second embodiment, said ultrasonic vibrations are applied along at least one axis substantially perpendicular to the longitudinal axis of the preforms.

According to a third embodiment, said ultrasonic vibrations are applied along at least one axis making an angle between 0 and 90 degrees relative to the longitudinal axis of the preforms.

According to a preferred embodiment, said ultrasonic vibrations are applied by means of a sonotrode associated with at least part of the mold for injecting said preforms.

According to a variant, said ultrasonic vibrations are applied by means of a sonotrode associated with a support carrying said preforms during a cooling phase at the outlet of the injection mold.

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The device for implementing the treatment method according to the invention is characterized in that it comprises means for applying to these preforms brought or maintained at a temperature above 600C ultrasonic vibrations along an axis substantially parallel to their axis longitudinal, the application of said ultrasonic vibrations being made at the time of the injection of said preforms or after this injection, but prior to a preheating phase of the preforms for the purpose of manufacturing containers by blowing from these preforms.

In a particularly advantageous manner, the device comprises means for cooling these preforms to a temperature below 60oC, after the application of the ultrasonic vibrations and before the preheating phase with a view to their subsequent use for the manufacture of containers by blowing.

According to a first variant, the device comprises means for applying said ultrasonic vibrations by means of a sonotrode associated with at least part of the mold for injecting said preforms.

According to a second variant, the device comprises means for applying said ultrasonic vibrations by means of a sonotrode associated with a support carrying said preforms, during a cooling phase at the outlet of the injection mold.

The preform obtained with the treatment of the process according to the invention is characterized in that it comprises at least one anisotropic zone produced by the application to this preform, hot or maintained at a temperature above 60oC, of ultrasonic vibrations according to at least a predetermined axis, the application of said ultrasonic vibrations being made at the time of the injection of said preform or after this injection.

Advantageously, said preform comprises an anisotropic zone obtained in addition by cooling it to a temperature below 60 C during

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d'une phase antérieure à son préchauffage en vue de son utilisation pour la fabrication d'un récipient par soufflage.

a phase prior to its preheating for use in the manufacture of a container by blowing.

In a particularly advantageous manner, said anisotropic zone generates in the walls of the container obtained by blowing a value of the permeability to gases and to vapors of less than 0.03 cm 3 / container / per day under a pressure of 0.2 atmosphere.

The present invention and its advantages will appear better in the following description of different embodiments of the invention, with reference to the appended drawings, in which: FIG. 1 is a graph illustrating the reflectivity curves of two bottles blown respectively from an untreated preform and a preform treated according to the method of the invention, and FIG. 2 schematically represents a particular embodiment of the device for implementing the method according to the invention.

The method according to the invention consists in treating the preforms by exposing them to ultrasonic vibrations during or after their manufacture by injection, but prior to their use as a basic product for the production of containers by a blowing process. The temperature of the preforms is preferably equal to or greater than about 60 C at the time of the application of the ultrasound. Therefore, it may be advantageous to carry out this treatment during injection, directly at the outlet of the preform injection mold, or during their cooling. However, this step is not compulsory and it is possible, although less economical, to allow the preforms to cool, to store them if necessary and to reheat them to around 60 C to make them undergo the ultrasound treatment thereafter.

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procédé a une perméabilité inférieure à 0, 03 cm3/bouteille/jour et, de préférence, inférieure à ou de l'ordre de 0, 01 cm3/bouteille/jour pour une valeur de la pression intérieure du récipient de l'ordre de 0,2 atmosphère. This ultrasonic treatment has the effect of a molecular reorganization in the thickness of the walls of the preforms. The ultrasonic vibrations put the molecules in motion. These movements are oriented mainly along the axis or axes of application of ultrasound. Since there are temperature gradients in the thickness of the walls, the different layers which have different temperatures, have different elastic moduli and do not offer the same reaction to ultrasound. This results in shearing between the layers, which creates gas, vapor and ultraviolet radiation barriers. These barriers are due to the formation of complex molecular networks which slow down the diffusion of gases, increase reflectivity and consequently reduce transparency to ultraviolet rays. In addition, it has been found that the application of ultrasonic vibrations has the effect of promoting crystallization. and the mesh of the molecular chains in two substantially perpendicular directions, which is commonly called the bi-orientation of the polymer chains. Resonance phenomena of ultrasonic vibrations result in the creation of anisotropy zones in the thickness of the walls of the preforms. The increase in the barrier effect is also due to the presence of these anisotropic zones whose impermeability to oxygen and carbon dioxide molecules is increased. For a standard PET bottle, that is to say one whose preform has not been subjected to treatment according to the method of the invention, the gas permeability is of the order of 0.07 cm 3 / bottle / day. A bottle made with a preform treated according to the

process has a permeability less than 0.03 cm 3 / bottle / day and, preferably, less than or of the order of 0.01 cm 3 / bottle / day for a value of the internal pressure of the container of the order of 0 , 2 atmosphere.

The penetration of ultraviolet rays is reduced by approximately 30%. This value is derived from a measure of reflectivity. The greater the barrier layer, the more the walls reflect the radiation and consequently prevent its penetration into the interior of the container. These results are highlighted by FIG. 1 which illustrates the reflectivity curves R as a function of the

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 wavelength λ of two bottles, one of which (curve A) is produced with a preform treated according to the method of the invention and the other (curve B) is a standard bottle. The increase in reflectivity is very noticeable in the range of wavelengths between 340 and 660 nanometers.

According to an advantageous embodiment, illustrated by FIG. 2, the preforms are subjected to ultrasonic vibrations via a central core 10, which constitutes the interior part of the injection mold 11, separated from the exterior part 12 of this mold by a space 13 corresponding to the thickness of the walls of the preforms. Ultrasound is applied by means of a sonotrode mounted on the core 10. The plastic material is injected into the space 13 which separates the core from the external part by an inlet channel 14. As mentioned above, it is possible to carry out this treatment during the cooling phase of the preforms, the latter being placed in supports during this phase, or subsequently, even after complete cooling. In this case, preheating prior to at least 60 C is required before the ultrasound treatment.

Ultrasonic vibrations can be applied along preferred axes. One of these axes is the longitudinal axis of the preform. However, to increase the barrier effect, it is advantageous to apply the vibrations along at least two crossed axes, for example the longitudinal axis and an oblique or transverse axis, which can be substantially perpendicular to the longitudinal axis. The sonotrodes must be constructed accordingly and brought into contact with the preform, directly or through an intermediate piece, or through an intermediate fluid in contact with the preform.

The preforms obtained after treatment according to the method of the invention are distinguished by the fact that they comprise at least one anisotropic zone produced by the application to these preforms maintained or brought to a temperature above 60oC, of ultrasonic vibrations according to at at least one predetermined axis, the application of said ultrasonic vibrations being made to the

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 at the time of injection of said preforms or after this injection. In some cases, these preforms can be lowered to a temperature below 60 C or more or less equal to room temperature for their subsequent use for the manufacture of containers by blowing.

soufflage, une valeur de la perméabilité aux gaz et aux vapeurs inférieure à 0, 03 cm3/récipientlpar jour sous une pression de 0, 2 atmosphère. This anisotropic zone generates in the walls of the container, after the

blowing, a gas and vapor permeability value of less than 0.03 cm 3 / container per day under a pressure of 0.2 atmospheres.

The advantages are very significant, because the increase in the barrier to gases and vapors makes it possible to use the containers obtained from the preforms treated for new applications, in particular for liquids sensitive to oxidation.

The present invention is not limited to the preferred embodiments described, but may undergo various modifications or variants obvious to a person skilled in the art.

Claims (14)

 1. Process for the treatment of preforms made of an injected hot-melt polymer, such as in particular polyethylene terephthalate (PET), this treatment process being essentially physical and making it possible to reduce the permeability to gases and vapors of the walls of the containers produced by blowing at starting from these preforms, characterized in that one applies to these preforms, brought or maintained at a temperature above about 60oC, ultrasonic vibrations along at least one predetermined axis, the application of said ultrasonic vibrations being made at the time of injection of said preforms or after this injection, but prior to a preheating phase of the preforms for the manufacture of containers by blowing from these preforms. 2. Method according to claim 1, characterized in that these preforms are cooled to a temperature below 60oC, after the application of ultrasonic vibrations and before the preheating phase for their subsequent use for the manufacture of containers by blowing. 3. Method according to claim 1, characterized in that said ultrasonic vibrations are applied along at least one axis substantially parallel to the longitudinal axis of the preforms. 4. Method according to claim 1, characterized in that said ultrasonic vibrations are applied along at least one axis substantially perpendicular to the longitudinal axis of the preforms. 5. Method according to claim 1, characterized in that said ultrasonic vibrations are applied along at least one axis forming an angle between 0 and 90 degrees relative to the longitudinal axis of the preforms. <Desc / Clms Page number 10>  6. Method according to claim 1, characterized in that said ultrasonic vibrations are applied by means of a sonotrode associated with at least part of the injection mold of said preforms. 7. Method according to claim 1, characterized in that said ultrasonic vibrations are applied, by means of a sonotrode associated with a support carrying said preforms, during a cooling phase at the outlet of the injection mold. . 8. Device for implementing the preform processing method according to claim 1, characterized in that it comprises means for applying to these preforms brought or maintained at a temperature above 60 C ultrasonic vibrations along a substantially axis parallel to their longitudinal axis, the application of said ultrasonic vibrations being made at the time of the injection of said preforms or after this injection, but prior to a preheating phase of the preforms with a view to the manufacture of containers by blowing from these preforms. 9. Device according to claim 8, characterized in that it comprises means for cooling these preforms to a temperature below 60oC, after the application of ultrasonic vibrations and before the preheating phase for their subsequent use for manufacturing of containers by blowing. 10. Device according to claim 8, characterized in that it comprises means for applying said ultrasonic vibrations by means of a sonotrode associated with at least one part (10) of the injection mold (11) of said preforms. 11. Device according to claim 9, characterized in that it comprises means for applying said ultrasonic vibrations by means of a <Desc / Clms Page number 11>  sonotrode associated with a support carrying said preforms during a cooling phase at the outlet of the injection mold. 12. Preform obtained with the treatment according to the method of claim 1, characterized in that it comprises at least one anisotropic zone produced by the application to this preform, brought or maintained at a temperature above 60oC, of ultrasonic vibrations according to at least one predetermined axis, the application of said ultrasonic vibrations being made at the time of the injection of said preform or after this injection. 13. Preform according to claim 12, characterized in that it comprises a

 anisotropic zone obtained in addition by cooling it to a temperature below 60oC during a phase prior to its preheating for use in the manufacture of a container by blowing. 14. Preform according to claim 12, characterized in that said anisotropic zone generates, in the walls of the container after blowing, a value of the permeability to gases and vapors of less than 0.03 cm3 / container / per day under pressure 0.2 atmosphere.