Method and installation for determining a value representative of the absorption coefficient of a preform

Abstract

The present invention relates to a method for determining a value representative of the absorption coefficient (a) of a thermoplastic material constituting a preform (12) as the preform (12) is transported within an installation (10) for producing containers by molding the preform (12), characterized in that it comprises: a step (E1) of measuring a value representative of the transmittance (T) of infrared light through at least one wall (16) of the preform (12) while the preform (12) is moving; a step (E2) of measuring the thickness (s) of the wall (16) of the preform (12) while the preform (12) is moving; and a step (E3) of calculating a value representative of the absorption coefficient (a) of the plastic material, independent of the thickness (s) of the preform (12), based on the measurement of the value representative of the transmittance (T) and on the measurement of the thickness (s).

Description

[Technical Field]

[0001] The invention proposes a method for determining, in an installation for manufacturing containers by molding preforms and in an installation capable of implementing this method, a value representative of the absorption coefficient of the thermoplastic material forming the preform as the preform is conveyed along a predetermined path. [Background technology]

[0002] It is known to manufacture containers by molding, in particular by stretch-blowing, preforms made of thermoplastic material. The material from which the preform is made is generally in an amorphous state that does not allow its cold molding. Therefore, prior to the molding operation, the preform is heated to a temperature above its glass transition temperature, which allows it to be shaped into the final container.

[0003] More specifically, the preform generally has a substantially cylindrical body of revolution with a thick tubular wall, one of its axial ends closed by a thick-walled base and the other end extended by a neck, also tubular, which is formed into its final shape and dimensions, while the body of the preform is intended to undergo a relatively large deformation during the forming step in order to be formed into a container.

[0004] For this reason, to prevent deformation of the preform while the container is being manufactured, it is preferred that only the body of the preform is heated above the glass transition temperature, with the neck being maintained at a temperature below said glass transition temperature.

[0005] Furthermore, the temperature of the body must not exceed its crystallization temperature, which is higher than the glass transition temperature. Above this temperature, the thermoplastic material crystallizes and no longer has the mechanical properties to be molded to the required quality. It is important that the crystallization of the material is induced in a controlled manner during the molding operation so that the polymer chains are oriented in the required direction.

[0006] The mass production of containers is carried out in a production facility in which the preforms travel along a predetermined production path, each preform being supported by a conveying means, which can be formed by a rail conveyor in which the preforms are free to come into contact with one another, or by a conveyor having components for individually gripping each preform.

[0007] The production facility has a heating station that makes it possible to make the body of the preform malleable by heating above the glass transition temperature during a heating step, during which each preform is exposed to heating radiation while it is moving.

[0008] The production facility also includes a molding station located downstream of the heating station in the direction of flow of the preforms through the production facility. During the molding step, the hot preform is placed in a molding unit, e.g., a mold of the molding station, which has a molding imprint corresponding to the resulting container. A pressurized fluid, such as air, is then injected into the malleable body of the preform to press its walls against the mold imprint. Typically, the injection of the pressurized fluid is preceded and / or carried out simultaneously by axial stretching of the preform, in particular by a stretch rod inserted into the preform. Thus, in a known manner, the body undergoes biaxial stretching.

[0009] As it passes through the heating station, each preform is generally exposed to infrared radiation that allows the thermoplastic material to heat up. The temperature to which the preform is heated depends on the absorption factor (A) of the preform relative to the wavelength of the infrared radiation. The absorption factor (A) is sometimes referred to as the "absorbency."

[0010] The absorption factor (A) is defined as the ratio of the flux of absorbed heating radiation to the flux of incident heating radiation. The flux of absorbed heating radiation increases the temperature of the thermoplastic material forming the preform. The absorption factor (A) of a preform therefore makes it possible to know the temperature increase of the preform as a function of the intensity of infrared radiation and the duration of exposure to said radiation. A preform with a high absorption factor (A) requires less energy to heat compared to a preform with a low absorption factor (A).

[0011] The absorption factor (A) can be derived from two other parameters called the transmittance (T) of the preform and its reflectance (R).

[0012] The transmittance (T) is defined as the ratio of the flux of heating radiation transmitted through at least one wall of the preform to the flux of incident heating radiation.

[0013] The reflectivity (R) is defined as the ratio of the flux of heating radiation reflected by the preform to the flux of incident heating radiation. The reflectivity (R) is calculated as a function of the refractive index (n) of the thermoplastic material, for example, according to the following formula:

[0014] R=[(n-1) / (n+1)] 2 where a value of "1" corresponds to the refractive index of air.

[0015] These three factors depend on the wavelength of the radiation considered, which is in the near-infrared range since the preform is heated by heating radiation in this range.

[0016] These three factors are related to each other by the following formula: A=1-RT

[0017] However, the absorption factor obtained depends mainly on two parameters. First, it depends on the absorption coefficient, sometimes called absorbency, of the thermoplastic material. The absorption coefficient is an intrinsic characteristic of the thermoplastic material that does not depend on the shape of the preform. Furthermore, the absorption factor depends strongly on the shape of the preform considered, especially its thickness.

[0018] Preforms belonging to the same batch are intended to be made of thermoplastic material with the same characteristics, and they are intended to have walls with the same thickness. However, when the absorption factor value is determined for two preforms from the same batch, it is not possible to know the percentage of defects that are due to the shape of the preform or the composition of the thermoplastic material.

[0019] Production installations are already known that are equipped with transmittance measuring devices that make it possible to measure the transmittance of a preform by measuring the attenuation of an infrared signal having a given wavelength that passes through the two walls of the preform. Summary of the Invention [Problem to be solved by the invention]

[0020] In these equipment, only the transmittance is measured; no information is provided about the measurement of the preform thickness. Therefore, some documents misuse the terms "absorbance" or "absorption coefficient", but none of these documents include the preform thickness in consideration, so in fact they only provide the absorption factor of the analyzed preform.

[0021] In existing solutions, this measurement makes it possible to modify the operating parameters of the furnace in order to adapt it to the absorption factor of the preform.

[0022] However, known equipment does not allow for analyzing the preforms with sufficient accuracy to determine whether production defects are due to the operation of the heating station, the shape of the preform or the composition of the thermoplastic material.

[0023] This challenge becomes even more important when the preform is made from recycled plastic materials such as recycled polyethylene terephthalate (rPET), which are inherently less homogeneous than virgin plastic materials.

[0024] Additionally, it may be valuable to compare different batches or different formats of the thermoplastic material forming the preforms to quickly identify any quality issues that may be associated with a particular provider. [Means for solving the problem]

[0025] The present invention relates to a method for determining a value representative of the absorption coefficient of a thermoplastic material forming a preform when the preform is conveyed along a predetermined path in an installation for producing containers by molding the preform, the method comprising the steps of: - measuring a value representative of the transmittance of infrared radiation through at least one wall of the preform as it moves along the path; - measuring the wall thickness of the preform as it moves along a path; - calculating a value representative of the absorption coefficient of the plastic material, independent of the thickness of the preform, based on said measurement of the value representative of the transmittance and on said measurement of the thickness; The present invention is characterized by comprising:

[0026] According to another feature of the method carried out in accordance with the teachings of the present invention, the measurement of the value representative of the transmittance and the measurement of the thickness are carried out at the same height of the wall of the preform.

[0027] According to another feature of the method carried out in accordance with the teachings of the present invention, the measurement of the value representative of the transmittance and the measurement of the thickness are carried out at the same point on the wall of the preform.

[0028] According to another feature of the method carried out in accordance with the teachings of the present invention, the measurement of the value representative of the transmittance and the measurement of the thickness are carried out sequentially in two separate measurement zones of the production path.

[0029] According to another feature of the method carried out in accordance with the teachings of the present invention, the measurement of the value representative of the transmittance and the measurement of the thickness are carried out simultaneously in the same measurement zone of the production path.

[0030] According to another feature of the method carried out in accordance with the teachings of the present invention, measuring the value representing the transmittance is carried out by measuring the attenuation of the intensity of a first monochromatic light beam after it passes through at least one wall of the preform, the first light beam having a first predetermined wavelength and emitted perpendicular to the wall of the preform.

[0031] According to another feature of the method carried out in accordance with the teachings of the present invention, the first predetermined wavelength is in the near infrared band, for example between 800 and 1,600 nm.

[0032] According to another aspect of a method performed in accordance with the teachings of the present invention, measuring the wall thickness is performed by a confocal measurement device that emits a second continuous spectrum light beam in a predetermined wavelength range.

[0033] According to another aspect of a method performed in accordance with the teachings of the present invention, measuring the wall thickness is performed by an interferometric measurement device that emits a second continuous spectrum light beam in a predetermined wavelength range.

[0034] According to another feature of a method performed in accordance with the teachings of the present invention, the first wavelength of the first light beam is outside the wavelength range of the second light beam.

[0035] According to another feature of a method carried out in accordance with the teachings of the present invention, the method is repeated for each preform passing through one or more measurement zones.

[0036] The present invention also provides an apparatus for carrying out the method carried out in accordance with the teachings of the present invention, comprising: The installation comprises means for conveying the preforms in a line along a predetermined production path, passing sequentially through zones for heating the bodies of the preforms and through stations for shaping the preforms into containers, in particular by stretch blowing, and the installation comprises: - a device for measuring a value representative of the transmittance of at least one wall of the preform as it passes through an associated measurement zone; - a device for measuring the wall thickness of the preform as it passes through an associated measuring zone; Equipped with.

[0037] According to another feature of the equipment according to the teachings of the present invention, the device for measuring the value representing the transmittance comprises a first light source that emits a first monochromatic light beam having a first wavelength, and the device for measuring the thickness comprises a second light source different from the first light source that emits a second light beam as a continuous spectrum within a predetermined wavelength range.

[0038] According to another feature of the installation according to the teachings of the present invention, the first and second light beams pass through the wall of the preform at the same height.

[0039] According to another feature of the installation according to the teachings of the present invention, the first light beam and the second light beam pass through the wall of the preform at the same point.

[0040] According to another feature of the installation according to the teachings of the present invention, the measurement of the value representative of the transmittance and the measurement of the thickness are carried out sequentially in two separate measurement zones of the production path.

[0041] According to another feature of the installation according to the teachings of the present invention, the measurement of the value representative of the transmittance and the measurement of the thickness are carried out simultaneously in the same measurement zone of the production path.

[0042] According to another feature of the installation according to the teachings of the present invention, the first light source and the second light source are arranged on either side of the production path so as to emit the first light beam and the second light beam coaxially with each other.

[0043] According to another feature of the installation according to the teachings of the present invention, the thickness measurement device comprises a spectrometer that measures the intensity and wavelength of two portions of the second light beam reflected by the outer and inner surfaces, respectively, of the wall of the preform.

[0044] According to another feature of the installation according to the teachings of the present invention, the device for measuring the value representing the transmittance comprises a component for measuring the intensity of the first light beam after the first light beam has passed through at least one wall of the preform.

[0045] According to another feature of the installation according to the teachings of the present invention, the measuring component of the device for measuring values ​​representative of transmittance and the spectrometer of the thickness measuring device are formed by a single spectrometer common to both devices.

[0046] According to another feature of the arrangement according to the teachings of the present invention, the first wavelength of the first light beam is outside the wavelength range of the second light beam.

[0047] According to another feature of the installation according to the teachings of the present invention, the device for measuring the value representative of the transmittance and the device for measuring the thickness are arranged along the production path upstream of the heating zone.

[0048] Further features and advantages of the present invention will become apparent from a reading of the following detailed description, which should be read in conjunction with the accompanying drawings, which are briefly described below. [Brief explanation of the drawings]

[0049] [Figure 1] 1 is a plan view showing a schematic diagram of an installation for manufacturing containers produced in accordance with a first embodiment of the present invention; [Figure 2] FIG. 2 is a side view of a preform intended to be processed by the installation of FIG. 1; [Figure 3] FIG. 2 is a block diagram illustrating a method of implementing the apparatus of FIG. 1 to determine a value representing the absorption coefficient of a preform. [Figure 4]FIG. 2 is a block diagram illustrating an alternative embodiment of the first embodiment of the method. [Figure 5] 5 is a vertical cross-sectional view at section 5-5 of FIG. 1 showing an apparatus for measuring the transmittance of a preform. [Figure 6] FIG. 6 shows the intensity of a monochromatic light beam after passing through two wall thicknesses of the preform of FIG. 5. [Figure 7] 7 is a vertical cross-sectional view at section 7-7 in FIG. 1 showing a confocal measurement device for measuring the wall thickness of a preform. [Figure 8] 8 is a detail of FIG. 7, showing a schematic representation of the reflected portion of the light beam emitted by the confocal measurement device of FIG. 7. [Figure 9] 8 is a diagram showing the intensity of the reflected portions of the light beams emitted by the confocal measurement device of FIG. 7 according to their wavelength. [Figure 10] 8 is a view similar to FIG. 7 showing an alternative embodiment in which the confocal measurement device is replaced by an interferometric measurement device. [Figure 11] 8 shows the intensity of interference of the reflected portions of the light beam emitted by the interferometric measuring device of FIG. 7 according to their wavelength. [Figure 12] FIG. 12 shows the Fourier transform of the curves in FIG. [Figure 13] FIG. 10 is a block diagram illustrating a method for determining a value representing the absorption coefficient of a preform manufactured according to a second embodiment of the present invention. [Figure 14] 14 is a plan view similar to FIG. 1, showing schematically an installation for manufacturing containers produced in accordance with a second embodiment of the invention, in which the method of FIG. 13 can be carried out. [Figure 15] 15 is a vertical cross-sectional view at section 15-15 of FIG. 14 showing the apparatus for measuring the wall thickness of the preform shown in FIG. 7 or FIG. 10 in combination with the transmittance measurement apparatus shown in FIG. [Figure 16] 16 shows the light intensity of the beams transmitted and reflected by the thickness measurement device of FIG. 15 according to their wavelengths when the device is a confocal measurement device. [Figure 17]16 shows the light intensity of the beams transmitted and reflected by the thickness measurement device of FIG. 15 according to their wavelength when the device is an interferometric measurement device. DETAILED DESCRIPTION OF THE INVENTION

[0050] Throughout the remainder of the description, the terms "top", "bottom" and derivative terms "high" and "low" are used for clarity with reference to the orientation of the drawings, but not to a limiting extent.

[0051] Throughout the remainder of the description, wavelengths of optical radiation are expressed in nanometers and are indicated by the abbreviation "nm".

[0052] In theory, a monochromatic light source is an ideal light source that emits a sinusoidal wave of a single frequency, in other words, its frequency spectrum consists of a single line with zero spectral width (Dirac).

[0053] In reality, such sources do not exist, and real sources have frequency emission spectra that extend over a band with a low but non-zero spectral width, e.g., a few tens of nanometers, centered around a dominant frequency at which the intensity of the radiation is greatest.

[0054] Throughout the remainder of the description, such actual light sources are considered to be monochromatic.

[0055] 1 shows diagrammatically an installation 10 for producing a thermoplastic preform 12, more particularly a container 11 made of PET (polyethylene terephthalate) or rPET (recycled polyethylene terephthalate). The thermoplastic material can optionally, but does not necessarily, contain additives that artificially increase the absorption factor of the preform.

[0056] As shown in FIG. 2, each preform 12 comprises a cylindrical body 14 having an "X" axis. The body 14 comprises a transparent sidewall 16 that defines an interior volume. The wall 16 has a shape of revolution about the "X" axis such that at a given height, the wall 16 has a constant thickness. However, the thickness of the wall 16 may vary as a function of height. The wall 16 is defined by an outer surface 18 facing outward from the preform 12 and an inner surface 20 that faces the interior volume.

[0057] The upper end of the body 14 emerges through a neck 22, which assumes the final shape of the neck 22 of the resulting container 11. As a result, the neck 22 is not deformed while the container 11 is being manufactured. The body 14 closes its lower end and comprises a base 24 that is generally hemispherical. The neck 22 comprises a collar 26 disposed at its junction with the body 14. The underside of the collar 26 is intended to form a support surface 28 for supporting the preform 12 while it is being molded and / or transported.

[0058] After being injection molded, the preform 12 is quenched to impart an amorphous state to the thermoplastic material, which can then be made malleable again by heating above the glass transition temperature.

[0059] 1, the manufacturing facility 10 includes a heating station 30 and a forming station 32. The preforms 12 move in a single file along a production path 34 that passes through the heating station 30 and the forming station 32. The direction of movement of the preforms 12 is indicated by arrow "F1" in FIG. 1. During normal operation of the manufacturing facility 10, the preforms 12 constantly move along the production path 34.

[0060] The manufacturing facility 10 generally includes an apparatus (not shown) for supplying preforms 12 in an aligned, row-like arrangement.

[0061] The production path 34 begins from the moment the preforms 12 are aligned and arranged in a row. The preforms 12 can be supported individually, in particular by a conveyor, or housed opposite each other in a line between guide rails, as is the case for the preforms 12 before they reach the heating station 30.

[0062] The purpose of heating station 30 is to heat body 14 of preform 12 to a temperature above the glass transition temperature of the constituent material, e.g., above 70°C if this material is PET. Heating station 30 includes a conveyor 36 (shown diagrammatically) for transporting preform 12 by rotating it on itself.

[0063] The conveyor 36 generally includes mandrels (not shown) that mate with the necks 22 to transport the preforms 12. The mandrels travel along a closed circuit, supported, for example, by links of a chain or even by independent shuttles that travel along rails.

[0064] In this case, the circuit comprises two straight parallel sections connected by a section with a 180° turn. The conveyor 36 further comprises two wheels 38A, 38B for guiding the mandrels in the turning section of the closed circuit.

[0065] The heating station 30 also comprises heating means 40 for heating the preform 12. This may comprise, for example, a lamp facing a reflector or a laser source emitting heating electromagnetic radiation in the near infrared range within a wavelength range of 780 nm to 3,000 nm, the intensity of which is significantly higher in the high-intensity wavelength range of 800 nm to 1,600 nm.

[0066] The heating means 40 are arranged along a heating zone 42 of the path 34 for producing a preform. In the example shown in Figure 1, the heating station 30 comprises a heating area 42 divided into two parts, located upstream and downstream of the turning portion guided by the guide wheel 38B.

[0067] The preforms 12 entering the heating station 30 are individually supported by a conveyor 36 that follows a U-shaped portion of the production path 34, where the preforms 12 pass through a heating zone 42. The preforms 12 are heated during the production run by heating means 40, which are positioned on one or both sides of the preforms 12 with respect to the direction of movement of the preforms 12, as required. The hot preforms 12 are extracted from the heating station 30 after passing through the heating zone 42 and transferred to a mold on the forming station 32 by a first transfer device 44, such as a transfer wheel, interposed between the heating station 30 and the forming station 32.

[0068] The transfer wheel comprises arms (not shown, as this is known per se) which sequentially grip the preforms 12 near their necks as they leave the heating station 30, so that they are each introduced into a mould 46 of the moulding station 32. The moulding station 32 comprises a rotating carousel 48, around which a number of blowing stations 50 are arranged.

[0069] Each blowing station 50 comprises at least one mold 46 defining a cavity having the shape of the container 11. Each blowing station 50 comprises means (not shown) for forming / deforming the body 14 of the preform 12 and forcing it against the imprint of the mold 46, for example by stretch blowing.

[0070] Each hot preform 12 exiting the heating station 30 is introduced into a mold 46 at a blowing station 50, blown therein, and transformed into a container 11. Upon completion, the container 11 is removed from the blowing station 50 by a second transfer device 52 similar to the first transfer device 44.

[0071] In order to automatically and quickly analyze the quality of the preform 12, the present invention proposes a method for determining a value representing the absorption coefficient "a" of the thermoplastic material forming the preform 12, which is independent of the thickness "s" of the wall 16. The method is carried out as the preform 12 moves along the production path 34 in the installation 10 for manufacturing the container 11. Preferably, the preform 12 is constantly moving while the method is being carried out.

[0072] In the illustrated example, the method is carried out as the preforms 12 are transported by a conveyor 36 of the heating station 30. The conveyor 36 transports the preforms 12 through a heating zone 42.

[0073] The method is preferably performed on the preform 12 before it is heated, and thus upstream of the heating zone 42. However, it can also be performed downstream of the heating zone 42 on an already hot preform 12.

[0074] As shown in FIG. 3, the method includes a first step “E1” of measuring a value representing the transmittance “T” of infrared light through at least one wall 16 of the preform 12 during movement of the preform along the production path 34.

[0075] The method further comprises a second step “E2” of measuring the thickness “s” of said wall 16 of said preform 12 while moving along the production path 34 .

[0076] The method then includes a third step "E3" of calculating, based on the measurements of the transmittance "T" and the thickness "s" carried out during the first two steps "E1, E2", a value representative of the absorption coefficient "α" of the thermoplastic material, independent of the thickness "s" of the preform 12. This third step "E3" of calculation therefore obviously takes place after the first two steps "E1, E2".

[0077] During this third calculation step "E3", a value representing the absorption coefficient "α" is calculated based on the Beer-Lambert formula:

[0078] T=e^(-α.2.s) where "T" represents the transmittance, "α" represents the absorption coefficient of the thermoplastic material, and "s" represents the thickness of the wall 16. As will be explained below, it is assumed that the transmittance "T" is measured by a light beam passing twice through the wall 16, in which case the thickness "s" is multiplied by two.

[0079] Alternatively, if the permeability is measured through a single thickness of wall 16, the factor of "2" in front of the thickness "s" is removed from all equations.

[0080] In this case, the present invention proposes to use a normalized transmittance "Tn" as a value representing the absorption coefficient "α." Such a normalized transmittance "Tn" represents the transmittance measured for a wall having a predetermined thickness "sn" made from the same material as the preform 12. The predetermined thickness "sn" is, for example, equal to 4 mm. Therefore, by calculating this normalized transmittance "Tn," it is possible to compare the absorption characteristics of materials forming several preforms with different actual thicknesses. This normalized transmittance "Tn" is calculated using the following formula, which is derived from the Beer-Lambert equation:

[0081]

number

[0082] where "Tn" is the normalized transmittance, "T" is the transmittance measured in the first step "E1", "sn" is the predetermined thickness, and "s" is the thickness measured in the second step "E2".

[0083] Alternatively, the value representative of the absorption coefficient "α" is formed directly by the absorption coefficient "α", which is then calculated by applying the following formula, which is derived from the Beer-Lambert formula:

[0084]

number

[0085] Calculation step "E3" in this case is carried out automatically by the electronic control unit 54 shown in particular in FIGS.

[0086] The first step "E1" of measuring a value representative of the permeability "T" and the second step "E2" of measuring the thickness are carried out at the same height "h" of the wall 16 of the preform 12, the height "h" being determined from a reference point such as, as in the present case, the free end of the neck 22 or the support surface 28 of the collar 26. The shape of revolution of the wall 16 about the "X" axis ensures that the permeability "T" is measured at the portion of the wall 16 that corresponds to the thickness "s" measured during the second step "E2" of measuring the thickness.

[0087] Preferably, the thickness "s" and the transmittance "T" are measured at the same point on the wall 16 so that the value representing the absorption coefficient "α" is as accurate as possible.

[0088] According to a first embodiment of the invention shown in FIG. 1, the measurement of the value representative of the transmittance "T" and the measurement of the thickness "s" are carried out sequentially in a first measurement zone "Z1" and a second measurement zone "Z2" separated from the production path 34.

[0089] This results in a first step "E1" of measuring a value representing the transmittance "T" and a second step "E2" of measuring the thickness "s", performed sequentially. For example, the first step "E1" is performed before the second step "E2", as shown in Figure 3.

[0090] As a variant, the second step "E2" is carried out before the first step "E1", as shown in FIG.

[0091] The first step E1 of measuring the transmittance "T" in this case is carried out by measuring the attenuation of the intensity "I" of a first monochromatic light beam 55 having a predetermined first wavelength "λ1". The first predetermined wavelength "λ1" is in the near-infrared band. It preferably belongs to the range of wavelengths of higher intensity of heating electromagnetic radiation, in this case the range from 800 nm to 1,600 nm.

[0092] To this end, the installation 10 comprises a device 56 for measuring the transmittance "T". As shown in Figure 5, this device 56 is arranged to measure the transmittance "T" of the preform 12 passing through a first measurement zone "Z1".

[0093] The apparatus 56 for measuring transmittance "T" comprises a first light source 58 that emits a first monochromatic light beam 55 having a first wavelength "λ1".

[0094] The first light source 58 may be, for example, a light emitting diode (LED), a superluminescent diode (SLED), or a lamp. A first monochromatic light beam 55 is emitted perpendicular to the wall 16 of the preform 12. The first light beam 55 is emitted to pass through the preform 12 by passing through its major "X" axis.

[0095] The first light beam 55 is more specifically emitted along an axis perpendicular to the tangent of the production path 34 of the preform 12 in the first measurement zone "Z1".

[0096] The first light beam 55 passes through the wall 16 at said height "h".

[0097] The first light beam 55 may be directed by a light directing means such as an optical fiber 60 .

[0098] The apparatus 56 for measuring the transmittance "T" further comprises a component 62 for measuring the intensity "I" of the first light beam 55 after passing through the wall 16 of the body 14 of the preform 12 at least once.

[0099] The component 62 for measuring the intensity "I" in this case is positioned to measure the intensity "I" of the first light beam 55 on the other side of the preform 12 relative to the "X" axis of the preform 12 after passing through the wall 16 twice at two diametrically opposite points at the same height "h" above the preform 12.

[0100] In this configuration, the first predetermined wavelength "λ1" is preferably selected in a wavelength range in which the thermoplastic material is sufficiently transparent for the intensity "I" of the first light beam 55 after the second passage through the wall 16 to be measured with sufficient precision and reliability by the measurement component. Indeed, there is a risk that the intensity "I" of the first light beam 55 will be too attenuated after the second passage through the wall 16 if it is emitted at a wavelength that is easily absorbed by the thermoplastic material.

[0101] For example, in the case of a plastic material made of PET or rPET, the first wavelength "λ1" is in the range between 800 nm and 1,100 nm, or between 1,250 nm and 1,300 nm. The first wavelength "λ1" is, for example, selected from the following values: 850 nm, 860 nm, 880 nm, 940 nm, 950 nm, 960 nm, 980 nm, 1,050 nm, or 1,300 nm.

[0102] In a variant of the invention not shown, the intensity measuring component is arranged to measure the intensity of the first light beam after it has passed once through the wall of the preform, in which case the measuring component comprises a component for blocking the light beam introduced into the preform during the first step, the blocking component directing the blocked light beam to the intensity measuring component.

[0103] The intensity measuring component 62 is, for example, a spectrometer that makes it possible to also measure the wavelength of the first monochromatic light beam 55 in order to reduce the risk of measurement errors due to spurious radiation.

[0104] The measurement component 62 therefore makes it possible to obtain the measurements shown in FIG.

[0105] The radiant light intensity "I0" emitted by the first light beam 55 is known data. The radiant light intensity "I0" emitted by the first light beam 55 can also be measured directly by the measurement component 62 when the preform 12 does not pass through the first measurement zone "Z1".

[0106] After passing through the wall 16 of the preform 12 twice, the light intensity of the first light beam 55 is attenuated. The first light beam 55 has a light intensity referred to as "transmitted light intensity 'I1'."

[0107] It is therefore easy to derive therefrom the transmittance "T" as a function of the ratio of the emitted light intensity "I0" to the transmitted light intensity "I1".

[0108] To more accurately calculate the transmittance "T," it is possible, although not necessary, to weight this ratio by taking into account the amount of first light beam 55 that is reflected each time it enters wall 16. This amount of reflection is calculated as a function of the reflectance coefficient "R," a quantity that is previously known.

[0109] The weighting factor of the first light beam 55 passing through the wall thickness 16 is calculated according to the following formula:

[0110]

number

[0111] The weighting factor for the first light beam 55 passing through the two wall thicknesses 16 is calculated according to the following formula:

[0112]

number

[0113] Therefore, the permeability "T" through two wall thicknesses 16 is calculated by applying the following formula:

[0114]

number

[0115] The transmittance “T” is calculated by the electronic control unit 54 which receives the measurements performed by the measurement component 62 .

[0116] The second step "E2" of measuring the thickness "s" in this case is performed non-contact using an optical thickness measurement device 64. As shown in Figure 1, this thickness measurement device 64 is positioned to measure the thickness "s" of the wall 16 of the preform 12 passing through the second measurement zone "Z2".

[0117] The thickness measurement device 64 includes a second light source 66, separate from the first light source 58, that emits a second light beam 68 as a continuous spectrum within a predetermined wavelength range "λ2," which is bounded by a lower limit "λ2-min" and an upper limit "λ2-max."

[0118] The thickness “s” is then determined by analyzing a first portion of the second light beam 68 reflected by the outer surface 18 and a second portion of the second light beam 68 reflected by the inner surface 20 of the wall 16.

[0119] As shown in FIG. 7, the measurement of the wall thickness “s” is performed, for example, by a confocal thickness measuring device 64 comprising a second light source 66 emitting a second continuous spectrum light beam 68 .

[0120] The second light source 66 may be, for example, a light emitting diode (LED), a superluminescent diode (SLED), or a lamp. A second continuous spectrum light beam 68 is emitted perpendicular to the wall 16 of the preform 12. The second light beam 68 is emitted to pass through the wall 16 by passing through its major X-axis.

[0121] The second light beam 68 is more specifically emitted along an axis perpendicular to the tangent to the path of the preform 12 within the second measurement zone "Z2."

[0122] A second light beam 68 passes through the wall 16 at said height "h".

[0123] The wavelength range "λ2" of the spectrum of the second light beam 68 extends, for example, into the visible band, ie, the lower limit "λ2-min" is about 380 nm and the upper limit "λ2-max" is about 780 nm.

[0124] The second light source 66 comprises continuous spectrum resolving elements 70, each of which is focused in a plane orthogonal to the primary "X" axis of the preform 12 and at a predetermined distance from the resolving element 70 as a function of its wavelength. Thus, each wavelength is focused at a determined axial distance from the resolving element 70. The second light beam 68 thus resolved passes through the wall 16 of the container 68.

[0125] As shown in FIG. 8, in a known manner, the outer surface 18 and the inner surface 20 of the wall 16 of the preform 12 reflect a first portion 68e and a second portion 68i, respectively, of the second light beam 68 thus decomposed.

[0126] Each of the portions 68e, 68i can be identified by an intensity peak "I2-i, I2-e" at a determined wavelength "λ2-i, λ2-e," as shown in Figure 9. Each determined wavelength "λ2-i, λ2-e" corresponds to the wavelength of a component of the second light beam 68 that is focused onto the outer surface 18 and inner surface 20 of the wall 16, respectively.

[0127] The thickness measurement device 64 further includes a light beam splitting component 72 interposed in the path of the second light beam 68. The splitting component 72 allows the second light beam to pass undeflected toward the preform 12 while redirecting reflected portions 68e, 68i of the reflected second light beam 68 to a spectrometer 74 that measures the intensity "I" and wavelength "λ" of the reflected portions 68e, 68i of the second light beam 68.

[0128] The splitting component 72 can be formed by an optical coupler, as is the case here, or by a semi-reflective mirror.

[0129] The second light beam 68 and / or the reflected portions 68e, 68i may be guided by a guidance means such as an optical fiber 76.

[0130] Each reflected portion 68e, 68i of the second light beam 68 is substantially monochromatic. Thus, the first wavelength "λ2-e" shown in FIG. 9 corresponds to the portion 68e of the second light beam 68 reflected by the outer surface 18 of the wall 16, while the second wavelength "λ2-i" shown in FIG. 8 corresponds to the portion 68i of the second light beam 68 reflected by the inner surface 20 of the wall 16. This can be easily identified by the light intensity of each peak. In fact, the portion 68e reflected by the outer surface 18 does not pass through the wall and is therefore not attenuated, while the portion 68i reflected by the inner surface 20 is attenuated by its round trip within the wall 16.

[0131] Depending on the reflected wavelengths "λ2-i, λ2-e" and the refractive index "n" of the material forming the wall 16, the electronic control unit 54 calculates the thickness "s" of the wall 16.

[0132] In a variation of the invention shown in FIG. 10, the thickness "s" of the wall 16 is measured by an interferometric thickness measuring device 64.

[0133] Such a thickness measurement device 64 comprises a second light source 66 that emits a second continuous spectrum light beam 68 in a predetermined wavelength range "λ2" perpendicular to the wall 16 of the preform 12. The second continuous spectrum light beam 68 is emitted perpendicular to the wall 16 of the preform 12. The second light beam 68 is emitted to pass through the wall 16 by passing through its major "X" axis.

[0134] The second light beam 68 is more specifically emitted along an axis perpendicular to the tangent to the path of the preform 12 within the second measurement zone "Z2."

[0135] A second light beam 68 passes through the wall 16 at said height "h".

[0136] The second light source 66 may be, for example, a light emitting diode (LED), a superluminescent diode (SLED) or a lamp.

[0137] The spectrum of the second light beam 68 is selected to allow it to pass through the wall 16 of the container 12 .

[0138] The wavelength range "λ2" of the spectrum of the second light beam 68 extends, for example, to the near-infrared band, with a lower limit "λ2-min" of about 1,530 nm and an upper limit "λ2-max" of about 1,570 nm, for example.

[0139] Unlike confocal measurement devices, in this case the radiation is not resolved.

[0140] When the second light beam 68 passes through the outer surface 18 of the wall 16 of the container 12, a first portion 68e of the second light beam 68 is reflected by the outer surface 18. The first reflected portion 68e has a continuous spectrum and therefore propagates in the opposite direction within the axis of the second light beam 68.

[0141] As a result, second light beam 68 loses intensity "I" as it continues to pass through wall 16. The spectrum of first reflected portion 68e is the same as the spectrum of second light beam 68, only the intensity "I" of first reflected portion 68e is lower than the intensity of second light beam 68.

[0142] The second continuous light beam 68 propagates inside the wall 16 of the container 12 until it reaches the inner surface 20 of the wall 16. A second portion 68i of the second light beam 68 is reflected from the inner surface 20. This second reflected portion 68i has a continuous spectrum and therefore propagates in the opposite direction within the axis of the second light beam 68. The spectrum of the second reflected portion 68i is identical to the spectrum of the second light beam 68.

[0143] The thickness measurement device 64 further includes a light beam splitting component 72 interposed in the path of the second light beam 68. The splitting component 72 passes the second light beam 68 toward the preform 12 without deflection, while redirecting reflected portions 68e, 68i of the second light beam 68 to a spectrometer 74 that measures the intensity "I" and wavelength "λ" of the reflected portions 68e, 68i of the second light beam 68.

[0144] The splitting component 72 can be formed by an optical coupler, as is the case here, or by a semi-reflective mirror.

[0145] The second light beam 68 and / or the reflected portions 68e, 68i may be guided by a guidance means such as an optical fiber 76.

[0146] The spectrometer 74 is in communication with the electronic control unit 54 .

[0147] The first reflected portion 68e and the second reflected portion 68i of the second light beam 68 returning from the wall 16 interfere in a generally known manner, resulting in constructive or destructive interference depending on the difference in path length of each of the reflected portions 68e, 68i caused by the thickness "s" of the wall 16, as shown in Figure 11.

[0148] The interference caused by the overlap of the first and second reflected portions 68e, 68i is analyzed by the spectrometer 74 and / or the electronic control unit 54.

[0149] The first reflected portion 68e and the second reflected portion 68i have the same wave spectrum but are axially offset by a distance equal to the thickness "s" of the wall 16 of the vessel 12.

[0150] In a known manner, depending on the thickness traversed, the intensity "I" of some wavelengths of the superposition of the reflective portions 68e, 68i decreases, and the intensity "I" of other wavelengths of said superposition increases.

[0151] Therefore, the wavelength "λa" that verifies the following equation has a particular maximum intensity "I".

[0152]

number

[0153] where "s" represents the thickness of the wall 16, "n" represents the refractive index of the material forming the wall 16, and "x" is any integer.

[0154] In fact, the intensities "I" of the first reflected portion 68e and the second reflected portion 68i add up to an increase in the intensity "I" in the area of ​​said wavelength "λa".

[0155] However, the wavelength "λb" that verifies the following equation has the minimum intensity "I".

[0156]

number

[0157] where "s" represents the thickness of the wall 16, "n" represents the refractive index of the material forming the wall 16, and "x" is any integer.

[0158] In effect, the intensities "I" of the first reflected portion 68e and the second reflected portion 68i are subtracted to reduce the intensity "I" in the region of wavelength "λb".

[0159] Thus, the interference results in a beat phenomenon, which is a periodic variation of the optical intensity "I" of the superposition of the two reflected portions 68e, 68i as a function of the frequency "1 / λ" of the light wave, as shown in Figure 10.

[0160] By using a Fourier transform, an operation well known to those skilled in the art, it is easy to find the period "P" of this periodic variation, as shown in Figure 12. This period "P" is proportional to the optical thickness, which is equal to the product of the thickness "s" of the wall 16 of the container 12 and the refractive index "n" of the material forming said wall 16. Therefore, by knowing the refractive index "n" of the material, or by calibrating the measurements of a test wall whose thickness has been measured by other known means, it is possible to find the thickness "s" of the wall 16 of the container 12.

[0161] According to a second embodiment of the invention shown in Figure 13, the step "E1" of measuring a value representative of the transmittance "T" and the step "E2" of measuring the thickness "s" are carried out simultaneously. In this case, the measurement of the transmittance "T" and the measurement of the thickness "s" are carried out simultaneously in a common measurement zone "Z" of the production path 34, as shown in Figure 14.

[0162] For this purpose, the transmittance measuring device 56 and the thickness measuring device 64 in this case are arranged in a common measuring zone "Z", as shown in FIG.

[0163] The transmittance measuring device 56 operates in the same manner as described in the first embodiment and has substantially the same structure, and only the structural and operational differences will be described below.

[0164] Similarly, the thickness measurement device 64 operates in the same manner as described in the first embodiment and has substantially the same structure. As in the first embodiment, it can be a confocal or interferometric measurement device. Only the structural and operational differences will be described below.

[0165] FIG. 15 shows an embodiment in which the thickness measurement device 64 is a confocal measurement device comprising a component 70 for decomposing the second light beam 68 .

[0166] In a variation not shown, the thickness measurement device is an interferometric measurement device having a structure identical to that shown in FIG. 15, except for removable disassembly components.

[0167] The first light source 58 and the second light source 66 respectively emit a first light beam 55 and a second light beam 68 into a common measurement zone "Z" of the production path 34 for simultaneously contacting the preforms 12 passing through said measurement zone "Z".

[0168] The first light beam 55 and the second light beam 68 are emitted coaxially and are arranged on either side of the production path 34 such that the first light beam 55 enters the preform body 14 through one side and the second light beam 68 enters the preform 12 through the diametrically opposite side.

[0169] The first light beam 55 and the second light beam 68 are emitted perpendicular to the wall 16 of the preform 12 so as to pass through the wall 16 by passing through its major "X" axis.

[0170] The first light beam 55 and the second light beam 68 are more specifically emitted along an axis perpendicular to the tangent to the path of the preform 12 in a common measurement zone "Z".

[0171] The first light beam 55 and the second light beam 68 pass through the wall 16 at said height "h".

[0172] In this case, the component 62 for measuring the intensity of the first light beam 55 after passing through at least one thickness of the wall 16 is formed by a spectrometer 74 of the thickness measuring device 64. The transmittance measuring device 56 and the thickness measuring device 64 therefore comprise a single common spectrometer 74. This advantageously allows reducing the manufacturing costs of the installation 10.

[0173] This configuration is possible due to the fact that the first light beam 55 and the second light beam 68 are coaxial and in opposite directions. Indeed, the first beam 55, after passing through the two wall thicknesses 16, exits the preform 12 at the axis of the splitting element 72, thus collecting this transmitted first light beam 55 towards the spectrometer 74.

[0174] Also, to enable this configuration, the first wavelength “λ 1 ” of the first monochromatic light beam 55 is preferably outside the wavelength range “λ 2 ” of the second light beam 68 .

[0175] In order to avoid any measurement errors, it is preferable to stay within a free interval 80 between the first wavelength "λ1" of the first monochromatic light beam 55 and the closest limit "λ2-min" or "λ2-max" of the wavelength range "λ2" of the second light beam 68.

[0176] This is because the first wavelength "λ1" is in the range between 800 nm and 1,100 nm or between 1,250 nm and 1,300 nm, while the continuous spectrum wavelength range "λ2" of the second light beam 68 ranges between 380 nm and 780 nm in the case of a confocal measurement device, or between 1,530 nm and 1,570 nm in the case of an interferometric measurement device.

[0177] Therefore, the spectrometer 74 and / or electronic control unit 54 can clearly distinguish between measurements corresponding to the first light beam 55 and measurements corresponding to the reflected portions 68e, 68i of the second light beam 68 based on the measured wavelength values, as shown in Figure 16 in the case of a confocal measurement device or in Figure 17 in the case of an interferometric measurement device.

[0178] Thus, the isolated peak corresponding to the first wavelength "λ1" corresponds to the value used to measure the transmittance "T", and the intensity measured in the wavelength range "λ2" of the spectrum of the second light beam 68 corresponds to the value used to measure the thickness "s" of the wall 16.

[0179] Regardless of the embodiment of the method for determining the value representing the absorption coefficient "α" implemented, in this case the method is repeated for each preform passing through one or more measurement zones "Z, Z1, Z2".

[0180] It is therefore possible to compare a value representing the absorption coefficient "α" for all preforms 12 of the same batch. This value is independent of the actual thickness of each preform 12, making it possible to quickly determine whether production defects in some containers 11 are due to the quality of the material from which the preforms 12 are made, or to other defects.

[0181] Additionally, the values ​​obtained for each of the preforms 12 may be stored for comparison with values ​​obtained for other batches of preforms 12 .

[0182] Alternatively, the method may be performed only on a sample of preforms 12 from the same batch, for example, the method may be repeated on preforms 12 over a determined number of preforms 12, for example, one in two preforms, or one in three preforms.

Claims

1. 1. A method for determining a value representing the absorption coefficient (α) of a thermoplastic material forming a preform (12) in an apparatus (10) for producing a container by molding the preform (12) as the preform (12) is conveyed along a predetermined path (34), comprising: a step (E1) of measuring a value representative of the transmittance (T) of infrared radiation through at least one wall (16) of the preform (12) as it moves along the path (34); a step (E2) of measuring the thickness (s) of said wall (16) of said preform (12) as it moves along a path (34); a step (E3) of calculating a value representative of the absorption coefficient (α) of the plastic material, independently of the thickness (s) of the preform (1), based on said measurement of the value representative of the transmittance (T) and on said measurement of the thickness (s); A method comprising:

2. 2. The method according to claim 1, characterized in that the measurement of the value representative of the transmittance (T) and the measurement of the thickness (s) are carried out at the same height (h) on the wall (16) of the preform (12).

3. 3. A method according to claim 2, characterized in that the measurement of the value representative of the transmittance (T) and the measurement of the thickness (s) are carried out at the same point on the wall (16) of the preform (12).

4. 4. The method according to claim 1, wherein the measurement of the value representative of the transmittance (T) and the measurement of the thickness (s) are carried out sequentially in two separate measurement zones (Z1, Z2) of the production path (34).

5. 4. The method according to claim 1, wherein the measurement of the value representative of the transmittance (T) and the measurement of the thickness (s) are carried out simultaneously in the same measurement zone (Z) of the production path (34).

6. 6. The method according to claim 1, wherein the measurement of the value representative of the transmittance (T) is carried out by measuring the attenuation of the intensity of a first monochromatic light beam (55) after passing through at least one wall of the preform, the first light beam (55) having a first predetermined wavelength (λ1) and emitted perpendicular to the wall (16) of the preform.

7. 7. The method according to claim 6, characterized in that the first predetermined wavelength (λ1) is in the near infrared band, for example between 800 nm and 1,600 nm.

8. 8. The method according to claim 1, wherein the measurement of the wall thickness (s) is performed by a confocal measurement device (64) emitting a second continuous spectrum light beam (68) in a predetermined wavelength range (λ2).

9. 9. The method according to claim 1, wherein the measurement of the thickness (s) of the wall (16) is performed by an interferometric measuring device (64) emitting a second continuous spectrum light beam (68) in a predetermined wavelength range (λ2).

10. 10. The method according to claim 8, wherein the first wavelength (λ1) of the first light beam (55) is outside the wavelength range (λ2) of the second light beam (68).

11. Method according to any one of the preceding claims, characterized in that the method is repeated for each preform (12) passing through one or more measurement zones (Z, Z1, Z2).

12. 12. An installation (10) for carrying out the method according to any one of claims 1 to 11, comprising means for conveying the preforms (12) in a file along a predetermined production path (34) passing through a zone (42) for heating the bodies (14) of the preforms (12) and successively through stations (32) for shaping the preforms (12) into a container (1), in particular by stretch-blowing, and wherein the installation (1) a device (56) for measuring a value representative of the transmittance (T) of at least one wall (16) of the preform (12) as it passes through the associated measurement zone (Z, Z1); a device (64) for measuring the thickness (s) of the wall (16) of the preform (12) as it passes through the associated measurement zone (Z, Z2); The facility (10) comprises:

13. 13. The installation (10) according to claim 12, characterized in that the device (56) for measuring the value representative of the transmittance (T) comprises a first light source (58) emitting a first monochromatic light beam (55) having a first wavelength (λ1), and the device (64) for measuring the thickness (s) comprises a second light source (66) different from the first light source (58) emitting a second light beam (68) as a continuous spectrum within a predetermined wavelength range (λ2).

14. 14. The installation (10) according to claim 13, characterized in that the first light beam (55) and the second light beam (68) pass through the wall (1) of the preform (12) at the same height (h).

15. 15. The installation (10) according to claim 14, characterized in that the first light beam (55) and the second light beam (68) pass through the wall (1) of the preform at the same point.

16. 16. Installation (10) according to claim 14 or 15, characterized in that the measurement of the value representative of the transmittance (T) and the measurement of the thickness (s) are carried out sequentially in two separate measurement zones (Z1, Z2) of the production path (34).

17. 16. Installation (10) according to claim 14 or 15, characterized in that the measurement of the value representative of the transmittance (T) and the measurement of the thickness (s) are carried out simultaneously in the same measurement zone (Z) of the production path (34).

18. 18. The installation (10) according to claim 17, characterized in that the first light source (58) and the second light source (66) are arranged on either side of the production path (34) so ​​as to emit the first light beam (55) and the second light beam (68) coaxially with each other.

19. 19. Installation (10) according to any one of claims 14 to 18, characterized in that the thickness measuring device (64) comprises a spectrometer (74) for measuring the intensity (I) and the wavelength (λ2) of two portions (68e, 68i) of the second light beam (68) reflected by the outer surface (18) and the inner surface (20) of the wall (16) of the preform (1).

20. 20. Installation (10) according to any one of claims 14 to 19, characterized in that the device (56) for measuring a value representative of the transmittance (T) comprises a component (62) for measuring the intensity (I) of the first light beam (55) after it has passed through at least one wall (1) of the preform (12).

21. 19. The installation (10) according to the combined claims 17, 19 and 18, characterized in that the measuring element (62) of the device (56) for measuring the value representative of the transmittance and the spectrometer (74) of the thickness measuring device are formed by a single spectrometer (74) common to both devices (56, 64).

22. 22. The installation (10) according to any one of claims 14 to 21, characterized in that the first wavelength (λ1) of the first light beam (55) is outside the wavelength range (λ2) of the second light beam (68).

23. 23. The installation (10) according to any one of claims 12 to 22, characterized in that a device (56) for measuring a value representative of the transmittance (T) and a device (64) for measuring the thickness (s) are arranged along the production path (34) upstream of the heating zone (42).

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