FR3091484A1 - "Method for decontamination of the interior of a preform by emission of a UV laser beam from the exterior of the preform" - Google Patents

Abstract

The invention relates to a method for decontaminating an internal face (24) of a hollow preform (10) made of thermoplastic material open by an opening (16), in particular of a PET preform, comprising a step (E1) d 'irradiation with at least one ultraviolet laser beam (28) emitted along an axis (B) determined by a laser emitter (30) of a laser device (29), characterized in that, throughout the duration of step ( E1) of irradiation, the laser beam (28) is emitted along its axis (B) rectilinear from the outside of the preform (10) to the internal face (24) of the preform (10) by penetrating through its opening (16). Figure for the abstract: Figure 2

Description

Description

Title of the invention: Method for decontaminating the interior of a preform by emission of a UV laser beam from the exterior of the preform

Technical field of the invention

The invention relates to a method for decontaminating the interior of a preform comprising a step of irradiation by means of an ultraviolet laser beam.

Technical background

In the field of food packaging, it is known to carry out a decontamination treatment to sanitize or sterilize at least the interior of a container intended to receive foodstuffs.

The decontamination treatments applied are intended to destroy, or at least reduce, the presence of microbiological organisms or microorganisms, such as in particular germs, bacteria, spores, molds, etc. in order to allow the conservation of foodstuffs.

By container means a hollow body such as for example a bottle, a bottle, a pot, etc., which are all containers obtained by transformation of a preform into thermoplastic material which is most often previously manufactured by injection into a mold.

[0005] Thermoplastics, PET (Polyethylene Terephthalate) is the most commonly used for these applications.

In known manner, the preform is successively thermally conditioned in an oven in order to soften the constituent material and then transformed into a container by blowing in a mold by means of at least one fluid under pressure, with or without drawing.

As a variant, the injected preform is directly transformed into a container without therefore requiring prior thermal conditioning.

In the prior art, the decontamination of a preform is in particular carried out chemically using a sterilizing product such as hydrogen peroxide (H ₂ O ₂ ) or other product having bactericidal properties , virucidal, fungicide, etc. analogues.

Although such chemical decontamination methods are satisfactory, we are looking for alternative solutions which, without sterilizing product, are in particular more environmentally friendly, while retaining equivalent levels of decontamination.

A possible alternative solution consists in carrying out decontamination by ir2 radiation of the internal face of the preform by means of a source emitting ultraviolet radiation, called UV.

Indeed, such irradiation decontamination has the advantage of not requiring the use of any chemical applied to the preform to be decontaminated and this in particular for the benefit of a subsequent absence of any residual traces in the container. final obtained from the preform.

The germicidal effect sought is in particular very effective by exposure of the surface to UVc radiation whose wavelength is between 230 and 300 nm. The irradiation of germs with UVc radiation in fact causes a photochemical reaction which degrades the DNA molecules of the germs, thus blocking their reproductive process.

Decontamination by irradiation by means of ultraviolet radiation has, however, hitherto only been implemented to treat the exterior of the preform.

One of the reasons constituting an obstacle to the use of ultraviolet radiation to decontaminate the interior of a preform is that thermoplastic materials such as PET absorb ultraviolet radiation, in particular UVc. This prevents UV radiation emitted from the outside from passing through the wall of the preform to reach its internal face.

In addition, excessive exposure of one side of the preform to UV radiation may cause local heating and degradation of the preform.

It has already been proposed to decontaminate the interior of a preform by means of a source of non-coherent ultraviolet radiation, such as a UV lamp. However, such a method has limited effectiveness because the intensity of the UV radiation emitted loses decreases with the square of the distance traveled due to the diffusion of UV radiation in all directions.

Summary of the invention

The invention provides a method of decontaminating an internal face of a preform made of thermoplastic material opened by an opening, in particular of a PET preform, comprising a step of irradiation with at least one emitted ultraviolet laser beam. along an axis determined by a laser transmitter of a laser device.

The method is characterized in that, throughout the duration of the irradiation step, the laser beam is emitted along its rectilinear axis from the outside of the preform to the internal face of the preform by penetrating by its openness.

According to other characteristics of the process:

- The preform has an axisymmetric shape with a predetermined main axis passing through the center of its opening, the axis of the laser beam being inclined at a determined angle relative to the main axis of the preform;

- The angle determined between the axis of the laser beam and the main axis of the preform is between 0 ° and 25 °, for example about 2 °;

- The preform rotates relative to the laser beam around its main axis to allow the laser beam to scan the entire internal face, for example at a speed of the order of 10 revolutions per second;

- During the irradiation step, the preform is moved axially along its main axis relative to the laser transmitter;

- The laser beam has a section of about 100 mm ² ;

- The laser beam is emitted in the ultraviolet range with a wavelength between 230 and 300 nm, more particularly between 240 nm and 260 nm, for example 248 nm;

- The laser device is an excimer laser, in particular an exciplex laser, for example a krypton fluoride laser;

- The laser beam is emitted by pulses at a determined frequency, for example the frequency is between 50 Hz and 300 Hz, more particularly the frequency is for example between 100 Hz and 200 Hz;

- Each pulse delivers an energy density less than or equal to 20 mJ / cm ² , for example about 15 mJ / cm ² ;

- The number of pulses emitted during the entire step of irradiating the internal face is between 50 and 300 pulses, preferably between 100 and 200 pulses;

- The method comprises in addition to the irradiation step, a step of heating the body of the preform, for example at a temperature greater than or equal to a transition temperature of the material constituting it.

The invention also relates to a decontamination installation for the implementation of the method carried out according to the teachings of the invention, characterized in that it comprises:

- a base;

- a support for carrying a preform, the support being mounted on the base;

- An ultraviolet laser device comprising a laser transmitter which is carried by the base.

According to another characteristic of the installation, the base is movable to allow the transport of the preforms during the irradiation step.

Brief description of the figures

Other characteristics and advantages of the invention will appear during the reading of the detailed description which will follow for the understanding of which reference will be made to the appended drawings in which:

[Fig.l] Figure 1 is an axial sectional view of a preform intended to be de4 contaminated during the process carried out according to the teachings of the invention;

[Fig-2] Figure 2 is an axial sectional view which shows the preform of the figure during the decontamination process carried out according to the teachings of the invention.

[Fig-3] Figure 3 is a block diagram which represents the two stages of the decontamination process carried out according to the teachings of the invention.

Detailed description of the invention

There is shown in Figure 1, without limitation, an example of a preform 10 of thermoplastic material. The preform 10 is here made of polyethylene terephthalate (PET).

Such a preform is generally obtained by injection of plastic material and has characteristics (dimensions, distribution of the material, etc.) which are determined by the final container to be obtained, in particular its shape or its capacity.

The preform 10 has an axisymmetric shape of main axis A shown vertically in Figure 1. The preform includes in particular a tubular body 12 closed at a lower end by a bottom 14 and which opens upward through an opening 16 upper delimited radially by a neck 18. The main axis A of the preform 10 passes through the middle of the neck 18.

The neck 18 of the preform 10 has its final shape after the manufacture by injection of the preform 10 and corresponds to the neck of the final container. An edge 20 of the free upper end of the neck 18, also called the rim, circumferentially delimits the circular opening 16 constituting the only access to the interior of the preform 10.

In the example shown in Figure 1, the neck 18 has a flange 22 which extends radially projecting outwards.

The body 12 is delimited by a tubular wall which has an internal face 24 situated inside the preform 10 and an external face 26 situated outside.

The preform has for example an opening 16 of internal diameter of about 20 mm and a total height of about 90 mm. The thickness of the wall delimiting the body 12 is for example around 3 mm. These values are given by way of nonlimiting example, the preforms being able to have different dimensions while keeping overall identical proportions.

The invention provides a method of decontamination of the internal face 24 of the preform 10 comprising a step El of irradiation of the internal face 24 with at least one beam 28 ultraviolet laser emitted along an axis B determined by a transmitter 30 laser connected to a laser device 29, comprising in particular a laser cavity in which the laser radiation is created. The laser beam 28 is delivered by the laser emitter 30 which has an exit face 31 which allows the laser beam 28 to exit into the open air in a straight line along its rectilinear axis B.

The laser emitter 30 forms a source of monochromatic electromagnetic radiation whose emission spectrum extends essentially in the field of type C ultraviolet (UVc) whose wavelength is between 230 nm and 300 nm. The wavelength is particularly effective for decontamination use when it is between 240 nm and 260 nm, for example 248 nm.

In theory, a monochromatic source is an ideal source emitting a sine wave of single frequency. In other words, its frequency spectrum consists of a single line of zero spectral width (Dirac).

In practice, such a source does not exist, an actual source having a frequency emission spectrum which extends over a band of small but non-zero spectral width, centered on a main frequency where the intensity radiation is maximum. For the purposes of the present application, such a real source is considered to be monochromatic.

The advantage of monochromatic radiation is that, well chosen, it can be concentrated on a wavelength which is particularly effective in exterminating the germs present in the preform 10.

In addition, the laser beam 28 is formed from a coherent and directional light radiation which retains great energy even when moving away from the emitter 30.

This is a laser device 29 belonging to the family of excimer lasers. It is more particularly an exciplex laser, for example a krypton fluoride (KrE) laser which emits a laser beam 28 whose wavelength is 248 nm.

The section of the laser beam 28 must have dimensions adapted to the dimensions of the preform 10. For this purpose, the laser beam 28 is here calibrated by interposing a diaphragm 32 having a hole 34 for passage of the laser beam 28 having the desired dimensions. Thus, the laser beam 28, after passing through the hole 34, has a calibrated section, for example of 100 mm ² . The section may have a circular, square or any other shape suitable for the treatment.

As shown in Figure 2, throughout the duration of the ir irradiation step, the laser beam 28 is emitted along its rectilinear axis B from the outside of the preform 10 to the internal face 24 of the preform 10 by moving in a straight line and entering the preform 10 only through its opening 16.

To this end, the laser transmitter 30 is arranged outside of the preform 10 for the duration of the step E1 of irradiation.

In the embodiment shown in the figures, the laser beam 28 moves in a straight line along its axis B from the exit face 31 to the internal face 24 of the preform 10 without being guided.

In a variant not shown of the invention, the laser transmitter 30 is equipped with means for guiding the direction of emission of the laser beam 28, such as optical elements or mirrors. These guide means are considered to be part of the laser emitter 30 and they are therefore also arranged outside the preform 10.

FIG. 2 shows an example of a decontamination installation in which the preform 10 is intended to be carried by a support 36, generally close to its flange 22. It is for example a clamp which radially tightens the preform 10 near its flange 22 or else a notch in which the body 12 of the preform 10 is received so as to rest by its flange 22 on the periphery of the notch.

The support 36 is mounted on a base 38. The support 36 is intended to maintain the main axis A of the preform 10 in a determined orientation, here vertical, relative to the base 38.

The base 38 is for example a mobile element allowing the transport of the preforms 10 during the step E1 of irradiation. It is for example a transfer wheel.

According to a variant of the invention, the base 38 is for example fixed relative to the ground. The laser emitter 30 is carried by the base 38. It is arranged so that the laser beam 28 is emitted along its axis B in the direction of the internal face 24 of the preform 10 by penetrating inside. of the preform 10 through its opening 16, preferably without touching the neck 18 or the edge 20.

The emitter 30 is arranged so that the axis B of the laser beam 28 is inclined at an angle a relative to the main axis A of the preform 10 to decontaminate the internal face 24 of the preform 10.

The value of this angle a is particularly important because if the value is too low or too high, the internal face of the bottom 14 of the preform is found overexposed to UVc radiation, either directly or by reflection on the internal face 24 of the body 12 of the laser beam 28. However, when the plastic material is overexposed to UVc radiation, its surface is degraded, and the preform 10 is no longer usable.

Furthermore, it is not possible to remedy this problem by reducing the power of the laser beam 28 since the internal face 24 of the preform 10 would then be insufficiently irradiated, and the decontamination would then not be sufficient.

These are the reasons why it was considered that the use of a laser beam emitted from outside the preform 10 was not possible for decontamination use.

However, the inventor has found that, surprisingly, by selecting an angle a between the axis B of the laser beam 28 and the main axis A of the preform between

0 ° and 25 °, for example between 1 ° and 5 °, more particularly around 2 °, it was possible to obtain the desired decontamination effect on the internal face 24 of the body 12 and of the bottom 14 without causing degradation of the internal face 24 of the preform 10.

To obtain a decontamination of the entire internal face 24 of the preform 10, the preform is rotated about its main axis A relative to the laser beam 28 to allow the laser beam 28 to scan the whole of the internal face 24. Thus, the angle a formed between the axis B of the laser beam 28 and the main axis A of the preform 10 remains substantially constant during the whole of the ir irradiation step.

In a variant not shown of the invention, the transmitter is movable relative to the preform so that the angle a varies in a controlled manner during the decontamination process.

For example, the preform 10 rotates with a continuous and constant speed of rotation of the order of 10 revolutions per second. Such a speed of rotation makes it possible to guarantee a level of exposure sufficient to decontaminate the entire internal face 24 of the preform 10 without degrading the thermoplastic material.

The preform 10 is for example rotated by friction of the outer face 26 of the body 12 with at least one drive roller 40. When the preform is held by a clamp, the jaws of the clamp include for example rollers 42 guide which allow to firmly hold the preform 10 while allowing its rotation.

In a variant not shown of the invention, by mechanical inversion, the laser transmitter 30 comprises means for allowing the rotation of the laser beam 28 around the main axis A of the preform 10.

According to a variant of the invention, during the ir step of irradiation, the preform 10 is moved axially along its main axis A relative to the emitter. Thus, the point of application of the laser beam 28 on the internal face 24 is capable of moving by forming a spiral. This is in particular required for preforms whose length is large relative to the cross section of the laser beam 28.

The maximum amplitude of the axial movement is defined between a depressed position in which the laser beam 28 is near a first end with a diameter of the edge 20 of the neck 18 to a withdrawn position in which the beam 28 laser is arranged at the opposite end of said diameter. The displacement is carried out without ever touching the edge 20, and while maintaining its angle determined with the main axis A of the preform 10 during its displacement.

To achieve this axial translational movement, the support 36 is for example movably mounted on a motorized carriage relative to the base 38.

During the ir irradiation step, the laser beam 28 is emitted in pulses. Each pulse lasts for example between 20 ns and 30 ns, for example 22 ns or 25 ns. The pulses are emitted at a determined frequency, for example the frequency is between 50 Hz and 300 Hz, more particularly, the frequency is for example between 100 Hz and 200 Hz.

The laser device 29 is configured so that each pulse delivers an energy density less than or equal to 20 mJ / cm ² , preferably of the order of 15 mJ / cm ² , so as not to damage the thermoplastic material.

For example, the laser transmitter 30 emits between 50 and 300 pulses, preferably between 100 and 200 pulses, during the entire step E1 of irradiation of the internal face 24 of the preform 10.

It has been found that the use of such a laser beam 28 makes it possible to obtain a sufficient decontamination rate regardless of the distance at which the laser emitter 30 is located due to the advantageous properties of the laser beam 28 with respect to to a conventional UV lamp.

Advantageously, the decontamination process has, in addition to the ir irradiation step El, a step E0 of heating the body 12 of the preform 10. We have indeed observed the cumulative effect of the step El d irradiation and step E0 of heating the thermoplastic material, for example beyond its glass transition temperature, made it possible to improve the decontamination rate of the preform 10. The step E0 of heating precedes for example the step El irradiation as shown in Figure 3.

In a variant not shown of the invention, the heating step E0 is carried out after the step E1 of irradiation.

The invention thus makes it possible to decontaminate the interior of the preform 10 without making use of chemicals, and by limiting the amount of energy used.

The invention also makes it possible to preserve the integrity of the material constituting the preform.

Claims (1)

Claims [Claim 1] Method for decontaminating an internal face (24) of a preform (10) of thermoplastic material opened by an opening (16), in particular of a PET preform, comprising a step (El) of irradiation with at least one ultraviolet laser beam (28) emitted along an axis (B) determined by a laser transmitter (30) of a laser device (29), characterized in that, throughout the duration of the irradiation step (E1), the laser beam (28) is emitted along its rectilinear axis (B) from the outside of the preform (10) to the internal face (24) of the preform (10) by entering through its opening (16). [Claim 2] Method according to the preceding claim, characterized in that the preform (10) has an axisymmetric shape with a determined main axis (A) passing through the center of its opening (16), the axis (B) of the laser beam (28) being inclined at an angle (a) determined relative to the main axis (A) of the preform (10). [Claim 3] Method according to the preceding claim, characterized in that the angle (a) determined between the axis (B) of the laser beam (28) and the main axis (A) of the preform (10) is between 0 ° and 25 °, for example about 2 °. [Claim 4] Method according to claim 2 or 3, characterized in that during the irradiation step (E1), the preform (10) is moved axially along its main axis (A) relative to the laser emitter (30). [Claim 5] Method according to any one of the preceding claims, characterized in that the preform (10) rotates relative to the laser beam (28) around its main axis (A) to allow the laser beam (28) to scan the entire face internal (24), for example at a speed of the order of 10 revolutions per second. [Claim 6] Method according to any one of the preceding claims, characterized in that the laser beam (28) has a section of approximately 100 mm ² . [Claim 7] Method according to any one of the preceding claims, characterized in that the laser beam (28) is emitted in the ultraviolet range with a wavelength between 230 and 280 nm, in particular 248 nm. [Claim 8] Method according to the preceding claim, characterized in that the laser device (29) is an excimer laser, in particular an exciplex laser, for example a krypton fluoride laser. [Claim 9] Method according to any one of the preceding claims, characterized in that the laser beam (28) is emitted by pulses at a determined frequency, for example the frequency is between 50 Hz and 300 Hz, more particularly the frequency is for example between 100 Hz and 200 Hz. [Claim 10] Method according to the preceding claim, characterized in that each pulse delivers an energy density less than or equal to 20 mJ / cm ² , for example around 15 mJ / cm ² . [Claim 11] Method according to any one of claims 9 or 10, characterized in that the number of pulses emitted during the entire step (El) of irradiation of the internal face (24) is between 50 and 300 pulses, preferably between 100 and 200 pulses. [Claim 12] Method according to any one of the preceding claims, characterized in that the method comprises, in addition to the irradiation step (E1), a step (E0) of heating the body (12) of the preform (10), by example at a temperature greater than or equal to a transition temperature of the material constituting it. [Claim 13] Decontamination installation for implementing the process carried out according to any one of the preceding claims, characterized in that it comprises: - a base (38); - a support (36) intended to carry a preform (10), the support (36) being mounted on the base (38); - An ultraviolet laser device (29) comprising a laser transmitter (30) which is carried by the base (38). [Claim 14] Installation according to the preceding claim, characterized in that the base (38) is mobile to allow the transport of the preforms (10) during the step (El) of irradiation. 1/2