Method and apparatus for directly characterizing a membrane having porosity and method for manufacturing such a membrane

Abstract

A method for characterizing a membrane, the method comprising the steps of: characterizing the membrane to obtain the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement; determining at least one property of the membrane, the determination being based on the grammage of the membrane obtained by ultrasonic measurement, the grammage of the membrane obtained by X-ray measurement, and at least one corresponding calibration curve establishing a correspondence between the at least one property and the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement or a combination thereof.

Description

Technical Field

[0001] The background of the present invention is the background of membrane manufacturing, and more specifically the background of manufacturing membranes with porosity, which requires controlling the characteristics of the membrane during its formation. Background Art

[0002] The membrane being formed can present a width of up to ten meters or more and continuously travel along the processing direction, which requires continuous monitoring by a non-contact measurement system. Monitoring the characteristics of such a membrane is performed by in-situ measurement equipment including sensors mounted on a mechanical frame, which is capable of moving these sensors across the width of the traveling membrane being formed.

[0003] Some sensors perform absorption measurements of a certain radiation sent through the product: the emission head of the sensor sends radiation towards the product, while the detection head performs measurements of the radiation transmitted through the product. These two heads are moved together across the product so as to always face each other.

[0004] The radiation can be of various types, each type corresponding to a given sensor type: ultrasonic waves as described in US 5,621,173 or US4,446,735; β-radiation; X-rays as described in GB 1271438 or EP 1950527; or infrared radiation. The sensor type is selected according to the material to be characterized and the specific needs of the practitioner.

[0005] Characterizing a membrane that is homogeneous (i.e., made of a single solid phase) during its formation and adjusting the manufacturing parameters in response to continuous characterization is a task routinely performed. Reference can be made, for example, to the patent document US 7,813 829B2. However, characterizing a membrane with cavities is more problematic because the cavities make it difficult to interpret the acquired data. Thus, so far, only relatively complex and indirect characterization methods are known, such as the method described in WO 2021 / 063641 A1.

[0006] The non-destructive evaluation of bonded aviation components is described in the article "Non-destructive Evaluation of the Quality of Adhesive Using Ultrasound, X-ray, and Feature-based Delta Fusion" by Jasiuniene Elena et al., Applied Science, Vol. 12, No. 24, 2022 / 12 / 01, p. 12930, which involves the fusion of images obtained by ultrasonic pulse-echo and radiography techniques.

[0007] Object of the Invention

[0008] In view of the above problems, the applicant has considered a method of combining measurement data of two types of sensors to characterize a membrane, thereby allowing the porosity or density of a membrane including a cavity to be directly determined and thus the thickness of the membrane to be determined. This method can be implemented by a measuring device for the membrane, by a method of manufacturing the membrane, and by a production line for the membrane. Summary of the Invention

[0009] To this end, a first aspect of the present invention relates to a method of characterizing a membrane, the method comprising the steps of: characterizing the membrane to obtain the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement; determining at least one property of the membrane selected from density, porosity, and thickness, the determination being based on the grammage of the membrane obtained by ultrasonic measurement, the grammage of the membrane obtained by X-ray measurement, and at least one corresponding calibration curve or a combination thereof establishing a correspondence between the at least one property and the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement, wherein the at least one corresponding calibration curve establishes a correspondence between the at least one property and the ratio of the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement.

[0010] The advantage of this method lies in the possibility of directly measuring properties of the membrane such as its porosity or its density (which cannot be directly measured by known conventional means). Such methods can be implemented in the membrane manufacturing process, in a measuring device for the membrane, or in a production line, especially when the membrane has a porosity that generally makes it difficult to characterize.

[0011] Additional non-limiting features according to the first aspect of the present invention, taken alone or in any technically feasible combination:

[0012] - The at least one calibration curve can represent the correlation between, on the one hand, the ratio of the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement and, on the other hand, the at least one property of the membrane;

[0013] - The step of characterizing the membrane may further include the step of measuring the basis weight of an additive contained in the membrane, and the step of determining at least one property of the membrane is also based on the measured basis weight of the additive;

[0014] - The additive may be a pore-forming agent.

[0015] A second aspect of the present invention relates to a measuring device, the measuring device including a sensor, the sensor including a transmitter head and a detector head, the transmitter head including (i) an X-ray source (S XR)(i) and (ii) an ultrasonic source, the detector head comprising (i) an X-ray sensor and (ii) an ultrasonic sensor, the measuring device being configured to perform an X-ray characterization and an ultrasonic characterization of a film positioned between the emitter head and the detector head of the sensor, the measuring device being configured to perform the method of characterizing a film according to the first aspect of the present invention. The measuring device may comprise a selective sensor system configured to measure the basis weight of an additive comprised in the film, the measuring device being further configured to perform the method of characterizing a film according to the first aspect of the present invention using the basis weight.

[0016] A third aspect of the present invention relates to a method of manufacturing a film, the method comprising the steps of: introducing a chemical compound into a preparation device; outputting a film from an outlet of the preparation device through a shaping device; characterizing the film according to the first aspect of the present invention to determine the at least one property of the film; comparing the at least one property of the film with a target value for this property; and based on the comparison, generating and sending a feedback signal to at least one of the shaping device and the preparation device to adjust at least one manufacturing parameter. The step of characterizing the film may further comprise measuring the basis weight of an additive comprised in the film, and the step of determining the at least one property of the film may also be based on the measured basis weight of the additive.

[0017] A fourth aspect of the present invention relates to a production line for manufacturing a film, the production line comprising: a preparation device configured to prepare a mixture to form a film and having an outlet equipped with a shaping device configured to impart a shape to the film; and a measuring device according to the second aspect of the present invention configured to characterize the film shaped by the shaping device, the production line being configured to perform the method of manufacturing a film according to the third aspect of the present invention. In the production line, the measuring device according to the second aspect of the present invention may further comprise a selective sensor system configured to measure the basis weight of an additive comprised in the film, the measuring device may further be configured to perform the method of characterizing a film according to the first aspect of the present invention using the basis weight, and the production line may be configured to perform the method of manufacturing a film according to the third aspect of the present invention using the measured basis weight of the additive. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Many other features and advantages of the present invention will become apparent upon reading the following detailed description when considered in conjunction with the accompanying drawings, in which:

[0019] - Figure 1 shows a combined X-ray / ultrasonic measurement system;

[0020] - Figure 2 shows the sensors of the Figure 1 system;

[0021] - Figure 3 shows a film production line of an X-ray / ultrasonic measurement system including Figure 1 ;

[0022] - Figure 4 shows a measurement method according to the present invention;

[0023] - Figure 5 shows a first calibration curve that can be used in the Figure 4 shown method;

[0024] - Figure 6 shows a second calibration curve that can be used in the Figure 4 shown method;

[0025] - Figure 7 shows a film manufacturing method according to the present invention; and

[0026] - Figure 8 shows a film having porosity. DETAILED DESCRIPTION

[0027] The reason for not using direct measurement in characterizing a film having porosity is that the cavities present in the film render conventional characterization methods inoperative.

[0028] In terms of X-ray characterization by absorption, X-rays are attenuated according to the amount of material they pass through, but are independent of the distribution of that material. For a film without cavities, the thickness profile (e.g., in m) can be directly derived from the basis weight profile, which is obtained by dividing the basis weight value (e.g., in g / m 2 ) by the density of the film (e.g., in g / m 3 ), which is a known constant when the film is homogeneous and made of a known material. However, when cavities are present, even though the material constituting the film may be known, the density of the film is unknown. As a result, X-ray characterization of a porous film will give information about the amount of material (i.e., the basis weight or grammage) that constitutes the film and through which the X-rays pass, rather than information about its thickness, density, or porosity, which are the parameters typically sought by practitioners.

[0029] In terms of ultrasonic characterization, the film to be characterized emits ultrasonic waves in response to being excited by incoming exciting ultrasonic waves. The presence of the interfaces of the cavities within the film will randomly scatter the ultrasonic waves, and the cavities have the spurious effect of reducing the amplitude of the ultrasonic waves emitted by the film. The actual result is that the basis weight derived from the attenuation of the ultrasonic waves passing through the film will appear higher than its actual basis weight and in an uncontrolled manner according to the characteristics of the cavities.

[0030] In this embodiment, we consider that in the grammage measurement by an ultrasonic measurement system, the contribution of the cavity to the apparent grammage of the film is proportional to the grammage of the material forming the film. Although the present invention is not limited to this specific model, it will be used to explain the approach leading to the method. The above consideration is explained by the following equations Eq.1 and Eq.2:

[0031]

[0032] where g RX (film) represents the result of X-ray absorption measurement of the true grammage g of the film, which is equivalent to the grammage g of the material constituting the film Mat . The X-ray absorption measurement result g RX (film) is considered accurate, and thus the equation of formula 1 is considered accurate. In formula Eq.2, g US (film) represents the measurement result of the true grammage g of the film obtained by the ultrasonic measurement system, but is not accurate and thus is different from g, where g Mat represents the grammage of the material of the substance constituting the film (excluding the cavity), and α is (multiplied by g Mat ) a factor representing the contribution of the cavity to the grammage of the film as perceived by the ultrasonic measurement system. When there is no cavity in the film, formula Eq.3 will be true:

[0033] g US (film) = g Mat = g Eq.3

[0034] Inserting Eq.1 into Eq.2 gives formula Eq.4:

[0035] g US (film) = g RX (film) + α × g RX (film) Eq.4

[0036] and gives formula Eq.5: 0

[0037]

[0038] We see that α (which represents the contribution of the cavity to the ultrasonic measurement result of the film) can be expressed as a function of the ratio between the ultrasonic measurement result and the X-ray absorption measurement result. Therefore, upon proper calibration, it seems possible to directly express the porosity φ of the material or the density ρ of the material via a combination of X-ray characterization and ultrasonic characterization of the film grammage.

[0039] The specific implementation of this principle is described in detail below, as Figures 1 to 8As shown. Such specific embodiments allow for the direct characterization of the porosity and density of membranes with cavities. Based on these results, and since the basis weight or grammage g of the material is known from X-ray measurements, the thickness t of the membrane can also be derived based on the following formula Eq.6.

[0040]

[0041] The specific embodiments described in detail below include a measuring device 100 configured to implement in a practical manner the principles outlined above, and a production line 300 including the device to control the production of membranes (including membranes with porosity). Figure 8 Such a membrane F with a thickness t and including a cavity Cav is shown.

[0042] Measuring device

[0043] Figure 1 A measuring device 100 in operation is shown, which includes: a frame 10 defining an aperture 12, the frame and the aperture extending in the width direction W; a sensor 20 that can move within the aperture 12 in the width direction W; and a drive system 30 configured to move the sensor 20 in the width direction W. The sensor 20 includes a transmitter head 22 and a detector head 24 facing the transmitter head 22. In (a), the measuring device 100 is represented in a front view, as seen in the processing direction M, which is in the direction of the cycle of the membrane F being manufactured. When traversing the aperture, the membrane is held in a horizontal plane perpendicular to the vertical direction indicated by Z in the figure. In (b), the measuring device 100 is represented in a top view, as seen from above, showing only a small portion of the membrane F. The measuring device 100 is configured to characterize the membrane F being formed that travels horizontally through the aperture 12 and between the transmitter head 22 and the detector head 24 of the sensor 20 in the processing direction M perpendicular to the width direction W. dir extends; a sensor 20 that can move within the aperture 12 in the width direction W dir ; and a drive system 30 configured to move the sensor 20 in the width direction W dir The sensor 20 includes a transmitter head 22 and a detector head 24 facing the transmitter head 22. In (a), the measuring device 100 is represented in a front view, as seen in the processing direction M dir which is in the direction of the cycle of the membrane F being manufactured. When traversing the aperture, the membrane is held in a horizontal plane perpendicular to the vertical direction indicated by Z in the figure. In (b), the measuring device 100 is represented in a top view, as seen from above, showing only a small portion of the membrane F. The measuring device 100 is configured to characterize the membrane F being formed that travels horizontally through the aperture 12 and between the transmitter head 22 and the detector head 24 of the sensor 20 in the processing direction M perpendicular to the width direction W dir in the processing direction M dir perpendicular to the width direction W.

[0044] A control system 40 is functionally connected to the sensor 20 and the drive system 30 and is configured to operate the sensor 20 and the drive system 30. The control system is equipped with a computer memory and an electronic computer configured to utilize the numerical data obtained from the sensor. The control system is configured to scan the membrane F being formed across its width by moving the sensor 20 in the width direction W. dir The control system is configured to scan the membrane F being formed across its width by moving the sensor 20 in the width direction W.

[0045] Figure 2 The sensor 20 is shown in more detail. The transmitter head 22 includes (i) an X-ray source S XRand (ii) an ultrasonic source S US ; conversely, the detector head 24 includes (i) an X-ray sensor Sens XR and (ii) an ultrasonic sensor Sens US .

[0046] The sensor 20 is configured such that, in operation, the X-ray source S XR emits X-rays XR towards the X-ray sensor Sens XR such that the X-ray sensor Sens XR detects the X-rays XR that have passed through the film F to be characterized, and the ultrasonic source S US emits ultrasonic waves US towards the ultrasonic sensor Sens US such that the US sensor Sens US detects the ultrasonic waves that have passed through the film F. These two characterizations (X-ray and ultrasonic) are preferably performed simultaneously, but may also be performed successively.

[0047] The control system 40 connected to the sensor 20 forms both an X-ray characterization system and an ultrasonic characterization system, or in other words, forms a combined X-ray and ultrasonic characterization system.

[0048] Production line

[0049] Figure 3 An embodiment of a production line 300 for implementing a manufacturing method 700 according to the present invention for a film F formed of a polymer in this embodiment is shown.

[0050] The production line 300 includes a preparation device 330, which includes: an inlet 320 through which chemical compounds forming a mixture 310 are introduced into the preparation device 330; and an outlet 340. The outlet 340 is equipped with a shaping device 345 configured to adjust the distance between two lips through which the film F is extruded. The mixture may include a polymer and additives intended to form the polymer film.

[0051] The preparation device 330 is intended to prepare the polymer 310 for shaping into a film, for example by using a heater and a thermometer to bring it to a suitable temperature.

[0052] In this embodiment, according to a conventional manufacturing process, the inlet 320 may include a screw for feeding the polymer in a molten state into the preparation device 330, and the outlet 340 may include a die through which the molten polymer is pushed and shaped into a film.

[0053] At the die outlet, the resulting film moves linearly in the processing direction Mdir and is then wound around the rotating roller 360 according to the rotation R of the rotating roller.

[0054] Between the outlet 340 of the manufacturing apparatus and the roller 360, the film can undergo any conventional manufacturing steps, including, for example, calendering, heating, stretching, cutting, or drying steps.

[0055] Furthermore, the measuring device 100 is configured to characterize the film F after it exits the outlet 340 and on its way to the rotating roller 360.

[0056] The film F formed of a polymer includes cavities because it has porosity, and its porosity, density, or thickness cannot be directly measured by conventional measuring devices.

[0057] Direct measurement of porosity or density

[0058] Figure 4 A measuring method 400 for implementing the above principle is shown.

[0059] In step S10, a set of calibration samples is provided to obtain a calibration curve.

[0060] These samples are made of materials with known compositions (such as known polymers), each sample having a specific known porosity and density and having the shape of a film. The porosity is selected to at least cover the range of interest regarding the porosity of the film to be characterized. The number of samples can be determined by the practitioner based on the desired resolution or accuracy of the calibration curve.

[0061] For the sake of simplicity, we will consider in this embodiment the case where the calibration samples are made of the same material as the film to be characterized.

[0062] For example, to characterize a film made of polypropylene, a set of samples consists of 20 polypropylene films having cavities (expressed as 100% to n%, where n is a multiple of 5 included between 1 and 20). Thus, this set of samples covers a porosity range of 0% to 95%.

[0063] In step S20, each of the samples is characterized by the sensor 20 to obtain, for each sample in the sample, the grammage g US (sample) obtained by ultrasonic measurement and the grammage g RX (sample).

[0064] In step S30, a correlation is established between the ratio g US (sample) / g RX (sample) for each sample and the porosity or density of the corresponding sample. For example, the data related to the same sample is stored in the same row of a table recorded in the computer memory of the control system 40, as shown in Table 1 below, where the nth sample is represented by Sn and the associated porosity, density, grammage gUS (sample), grammage g RX (sample) and ratio g US (sample) / g RX (sample) (Pn, Dn, g respectively US (n), g RX (n) and g US (n) / g RX (n)) for identification.

[0065] Sample Porosity Density <![CDATA[g US (sample)]]> <![CDATA[g RX (sample)]]> Ratio S1 P1 D1 <![CDATA[g US (1)]]> <![CDATA[g RX (1)]]> <![CDATA[g US (1) / g RX (1)]]> S2 P2 D2 <![CDATA[g US (2)]]> <![CDATA[g RX (2)]]> <![CDATA[g US (2) / g RX (2)]]> S3 P3 D3 <![CDATA[g US (3)]]> <![CDATA[g RX (3)]]> <![CDATA[g US (3) / g RX (3)]]> S4 P4 D4 <![CDATA[g US (4)]]> <![CDATA[g RX (4)]]> <![CDATA[g US (4) / g RX (4)]]>

[0066] Table 1

[0067] At step S40, the calibration curve is defined based on the data collected in Table 1 and stored in the computer memory in a conventional manner to establish the ratio g US (film) / g RX (film) between the given range of values and the densification characteristics (either porosity or density) of the film. This is done, for example, by defining a curve that fits the experimental points plotted on such a graph, which has the ratio on the x-axis and the selected densification characteristic on the y-axis.

[0068] In this document, the calibration curve is a general term for designing the correlation between experimental data and known characteristics. Here, it represents the correlation between, on the one hand, the ratio of the grammage of the film obtained by ultrasonic measurement and the grammage of the film obtained by X-ray measurement and, on the other hand, the densification characteristics (porosity φ or density ρ) of the film.

[0069] Figure 5 The calibration curve CC(ρ) is shown in the form of a graph, allowing the density ρ of the film to be characterized to be derived from the ratio g US (film) and g RX (film) of g US (film) / g RX (film) of the film to be characterized.

[0070] Similarly, Figure 6 The calibration curve CC(φ) is shown in the form of a graph, allowing the porosity φ of the film to be characterized to be derived from the ratio g US (film) and g RX (film) of g US (film) / g RX (film) of the film to be characterized.

[0071] At step S50, the film to be characterized is characterized by sensor 20 in order to obtain the grammage g US (film) and g RX (film) of the film obtained by ultrasonic measurement and X-ray measurement respectively, and these measurement data of the film are stored in a computer memory. US (film) and g RX (film), and these measurement data of the film are stored in a computer memory.

[0072] At step S60, the control system 40 determines at least one intensive property (i.e., the density, porosity or both) of the film based on the measurement data (grammage g US (film) and g RX (film)) of the film and the corresponding calibration curve stored in the computer memory, and stores the density or the porosity in the computer memory. In addition, the thickness t of the film as an extensive property can be derived from the grammage g RX (film) of the film obtained by X-ray measurement and the density ρ of the film obtained by applying formula Eq.6. US (film) and g RX (film)) and the corresponding calibration curve stored in the computer memory, and stores the density or the porosity in the computer memory. In addition, the thickness t of the film as an extensive property can be derived from the grammage g RX (film) of the film obtained by X-ray measurement and the density ρ of the film obtained by applying formula Eq.6. RX (film) and the density ρ of the film obtained by applying formula Eq.6.

[0073] Steps S10 to S40 together constitute a preparation step PS for the characterization steps S50 and S60 of the film to be characterized. Once this preparation step has been executed once, the calibration curve is stored in the computer memory of the control system 40. Therefore, the preparation step SP does not have to be executed again, and the characterization step CS (with sub-steps using the calibration curve stored in the computer memory) including steps S50 and S60 can be repeated independently of the preparation step SP.

[0074] In this embodiment, a set of polypropylene samples is used to define the calibration curve for characterizing polypropylene films. By introducing a correction factor defined by the ratio of the density of other materials divided by the density of polypropylene, it is naturally possible to characterize films made of other materials than polypropylene from the same calibration curve. More generally, any material can be used to form the set of calibration samples, and films formed of any material can be characterized as long as the density ratio between the two materials is known.

[0075] In addition, the presence of additives added to the matrix material of the film can be measured and taken into account, because it affects the basis weight of the film itself and thus affects the determination of density, porosity and thickness. For example, in the case where the film includes a known cavitating agent (i.e., a chemical compound of known density) for forming cavities, the proportion of the cavitating agent in the film can be measured by a specific sensor and introduced into the calculation of the density and porosity of the film by calculating the corrected density of the material (matrix material + cavitating agent) forming the film. The cavitating agent can be of inorganic type (e.g., calcium carbonate particles) or organic type (e.g., polybutylene terephthalate (PBT), which is immiscible in the film matrix polymer (e.g., polypropylene)).

[0076] Thus, step S50 may include using a selective sensor system 370 (such as a scanner configured to characterize Figure 3 membrane F) to measure the distribution of additives in the membrane, the selective sensor system including sensors capable of specifically measuring the basis weight of the additives contained in the membrane. Such sensors may be based, for example, on the absorption of infrared radiation by the additives. Additionally, in step S60, the determination of the density, porosity, and thickness of the membrane is based on the measured basis weight of the additives and the corresponding calibration curves in addition to the measurement data of the membrane (gram weight g US (film) and g RX (film)).

[0077] Figure 3 Illustrates a case where the selective sensor system is integrated in the measuring device 100 and controlled by the control system 40. Alternatively, the selective sensor system 370 may be independent of the measuring device 100.

[0078] The above description specifically applies to a model in which, in the gram weight measurement by the ultrasonic measurement system, the contribution of the cavity to the apparent gram weight of the membrane is proportional to the gram weight of the material forming the membrane, and the physical quantity of interest is expressed as a function of the ratio g US (film) / g RX (film). A more general method would consider gUS(film) and gRX(film) as independent variables and establish the correlation between the intensive properties (porosity φ or density ρ) of the membrane and both the gram weight of the membrane obtained by ultrasonic measurement and the gram weight of the membrane obtained by X-ray measurement by determining a two-dimensional calibration curve through conventional interpolation or regression.

[0079] Manufacturing method

[0080] The manufacturing method according to the present invention is as Figure 7 shown and includes: step S710 of introducing a chemical compound into the preparation device 330 via the inlet 320; step S720 of outputting the chemical compound from the outlet 340 and forming it into a membrane F by the forming device 345; and step S730 of winding the sheet or membrane around the rotating roller 360.

[0081] Steps S50 and S60 of the characterization step CS are interposed between steps S720 and S760, the characterization step allowing the membrane to be characterized between the forming device 345 and the roller 360. Starting from step S60, at step S740, at least one measured property (porosity, density, thickness) of the membrane is compared with the target value of this property using the control system 40.

[0082] At step S750, based on the comparison of step S740, a feedback signal FB is generated and sent to the forming device 345 and / or to the preparation device (330) to adjust at least one manufacturing parameter, such as the distance between the two lips through which the polymer film F is extruded, the temperature or the proportion of additives added to the polymer forming the film. More generally, when the practitioner sees that the feedback signal is adapted, the feedback signal can be used to adjust any parameter that affects the porosity, density or thickness of the film. By proceeding in this way, step S720 is adjusted in response to the characterization step CS that forms a feedback loop.

[0083] By studying the drawings, the disclosure and the appended claims, those skilled in the art can understand and realize other variations of the disclosed embodiments when practicing the claimed invention.

Claims

1. A method (400) for characterizing a membrane (F), the method comprising the following steps: - Characterizing the membrane (F) in order to obtain the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement; - Determining at least one property (ρ, φ, t) of the membrane selected among density (ρ), porosity (φ) and thickness (t), the determination being based on the grammage of the membrane obtained by ultrasonic measurement, the grammage of the membrane obtained by X-ray measurement, and at least one corresponding calibration curve (CC(ρ), CC(φ)) establishing a correspondence between the at least one property (ρ, φ, t) and the ratio of the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement, or a combination thereof, wherein the at least one corresponding calibration curve (CC(ρ), CC(φ)) establishes a correspondence between the at least one property (ρ, φ, t) and the ratio of the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement.

2. The method according to claim 1, wherein the at least one calibration curve represents the correlation between, on the one hand, the ratio of the grammage of the membrane obtained by ultrasonic measurement and the grammage of the membrane obtained by X-ray measurement and, on the other hand, the at least one property of the membrane.

3. The method according to claim 1 or 2, wherein the step of characterizing the membrane further comprises measuring the basis weight of an additive comprised in the membrane (F), and wherein the step of determining at least one property (ρ, φ, t) of the membrane is also based on the measured basis weight of the additive.

4. The method according to claim 3, wherein the additive is a nucleating agent.

5. A measuring device (100), the measuring device comprising a sensor (20), the sensor (20) comprising a transmitter head (22) and a detector head (24), the transmitter head comprising (i) an X-ray source (S XR ) and (ii) an ultrasonic source (S US ), the detector head comprising (i) an X-ray sensor (Sens XR ) and (ii) an ultrasonic sensor (Sens US ), the measuring device being configured to perform X-ray characterization and ultrasonic characterization of a film (F) positioned between the transmitter head (22) and the detector head (24) of the sensor (20), The measuring device is configured to perform the method (400) for characterizing a membrane (F) according to claim 1 or 2.

6. The measuring device according to claim 5, the measuring device further comprising a selective sensor system (370) configured to measure the basis weight of an additive comprised in the membrane, the measuring device being further configured to perform the method (400) for characterizing a membrane (F) according to claim 3 or 4.

7. A method (700) for manufacturing a membrane (F), the method comprising the following steps: - Introducing a chemical compound into a preparation device (330); - Outputting the membrane (F) from an outlet (340) of the preparation device (330) through a forming device (345); - Characterizing the membrane (F) according to any one of the methods according to claim 1 or 2 in order to determine the at least one property of the membrane; - Comparing the at least one property of the membrane with a target value for the property; and - Based on the comparison, generating and sending a feedback signal (FB) to at least one of the forming device (345) and the preparation device (330) to adjust at least one manufacturing parameter.

8. The method according to claim 7, The step of characterizing the membrane further includes measuring the basis weight of the additive contained in the membrane, and the step of determining at least one property (ρ, φ, t) of the membrane is also based on the measured basis weight of the additive.

9. A production line (300) for manufacturing a membrane (F), the production line comprising: - a preparation device (330) configured to prepare a mixture (310) to form a membrane (F) and having an outlet (340) equipped with a shaping device (345), the shaping device being configured to impart a shape to the membrane (F); and - a measuring device (100) according to claim 5, the measuring device being configured to characterize the membrane shaped by the shaping device (345), the production line being configured to carry out the method (700) for manufacturing a membrane (F) according to claim 7.

10. The production line according to claim 9, wherein the measuring device (100) according to claim 5 further includes a selective sensor system (370) configured to measure the basis weight of the additive contained in the membrane, the measuring device being further configured to carry out the method (400) for characterizing the membrane (F) according to claim 3 or 4, the production line being configured to carry out the method (700) for manufacturing a membrane (F) according to claim 8.

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