JP7647551B2 - Radiation transmission inspection device for film product reels, method for manufacturing film product reels using the same, and method for transmitting radiation through film product reels - Google Patents

Description

The present invention relates to a radiographic inspection device that inspects for foreign objects that may be mixed into a film product reel on which film has been wound, a method for manufacturing a film product reel using the same, and a radiographic inspection method for a film product reel.

Films such as various polymer films are generally supplied to manufacturers who use the film in a rolled state as a raw film. In particular, when a film narrower than the raw film is used, the film is unwound from a wide raw film roll, slit to a desired film width, and the slit film is wound around a core to form a film product reel. When the slit film is used, the film is unwound again from the film product reel and used. When a film that has been subjected to various surface treatments is used, the film is unwound from an untreated raw film roll, surface-treated, and the treated film is wound around a film product reel. When a surface-treated and slit film is required, the surface-treated film is generally wound around a core, and then the film is unwound from the film product reel, slit, and wound around a core again.

When the film product reel obtained through such a process is unwound and used, minute foreign objects mixed in the film product reel may cause a problem. Therefore, it is required to detect foreign objects mixed in the film product reel. For example, when the film unwound from the film product reel is used as a battery separator film to be inserted between the positive and negative electrodes of a lithium ion secondary battery, the foreign objects mixed in the film product reel become foreign objects on the battery separator film. If the foreign objects are, for example, minute metal pieces, they may cause a short circuit between the positive and negative electrodes of the lithium ion secondary battery or dissolve in the electrolyte and deteriorate the battery characteristics. Therefore, an inspection method and device for detecting minute foreign objects mixed in the film product reel is required. For battery separator films, it is necessary to detect metal foreign objects with a size of 100 μm or less, for example, about several tens of μm. However, in the case of non-metallic foreign objects that do not have electrical conductivity, even larger foreign objects may not be a problem, so it is preferable to be able to determine the size and material or type of the foreign objects when detecting foreign objects in a film product reel for a battery separator film.

Furthermore, if it were possible to know where in a film product reel foreign matter exists, it would be possible to use the film from sections where no foreign matter exists, thereby enabling more efficient use of the film.

Various types of radiographic inspection devices are known as methods for inspecting defects and foreign bodies on battery separator films (see Patent Documents 1 and 2). However, for example, in the defect inspection device disclosed in Fig. 3 of Patent Document 1, a difference in detection sensitivity occurs between the left side (radiation source unit 2 side) of the separator winding 10 and the right side (sensor unit 3 side) of the separator winding 10, and a significant difference in detection sensitivity occurs particularly in a wide separator winding reel. In addition, physical interference between the radiation source unit 2 and the separator winding 10 may prevent the right side (sensor unit 3 side) from maintaining sufficient detection sensitivity (e.g., 100 μm), making it difficult to apply the device to inspect wide reels.

JP 2018-91825 A International Publication WO2020/004435

Therefore, an object of the present invention is to provide an inspection device capable of detecting minute foreign bodies contained in a film product reel on which film is wound and transported at high speed, including whether or not the foreign bodies are metal foreign bodies, a method for manufacturing a film product reel using the same, and a method for transmitting radiation through a film product reel.

In order to solve the above problems, the radiographic inspection device for film product reels according to the present invention is a radiographic inspection device for inspecting foreign bodies contained in a film product reel formed by winding a long film around the outer peripheral surface of a core for multiple revolutions, and includes a mounting table on which the film product reel is placed, a pair of a radiation source and a detector that transmit and receive radiation in a radial direction relative to the circumferential surface of the film product reel, and an image processing unit that generates a foreign body detection image from the radiation detection result obtained by the detector. Here, the radiation refers to electromagnetic waves including X-rays, β-rays, γ-rays, infrared rays, etc. As the detector, an area camera in which image pickup elements are arranged two-dimensionally, a line camera in which image pickup elements are arranged one-dimensionally, or a TDI (Time Delay Integration) camera in which multiple line cameras are arranged perpendicular to the arrangement direction can be used. When using a line camera or a TDI camera, it is preferable to arrange the arrangement of the image pickup elements parallel to the reel rotation axis.

According to the radiographic inspection device for film product reels of the present invention, radiation is transmitted in the radial direction relative to the circumferential surface of the film product reel, making it possible to detect foreign objects with high sensitivity even if the reel width increases.

In the radiographic inspection device for film product reels according to the present invention, it is preferable that the focal point of the radiation is disposed in the inner hollow portion of the core, and the detector is disposed radially outward of the core. By disposing the detector on the outer side, it is not necessary to impose restrictions on the size of the detector, and the field of view of one image can be increased.

In the radiographic inspection device for a film product reel according to the present invention, it is preferable that the device has a function of rotating the film product reel in a circumferential direction. Also, the pair of the radiation source and the detector may be rotated in the circumferential direction of the film product reel.

In the radiographic inspection device for film product reels according to the present invention, it is preferable that the device has a function of moving the film product reel in the width direction. Also, the pair of the radiation source and the detector may be moved in the width direction of the film product reel. With such a configuration, it is possible to inspect the entire width of a film product reel having a width equal to or larger than the field of view of one imaging. Also, by making the amount of movement in one time of moving in the width direction less than half the minimum field of view width (the field of view width of the film product reel at the position closest to the radiation source), it is possible to image the same foreign object in two or more fields of view. In this case, the depth of foreign object contamination can be estimated based on foreign object detection images before and after moving in the width direction, so it is possible to determine whether or not a foreign object is included in the film portion of the film product reel.

In the radiographic inspection device for film product reels according to the present invention, it is preferable that the image processing unit determines whether or not the foreign object is contained in the film portion of the film product reel based on the foreign object detection image obtained in advance for the core before the film is wound. In this way, by comparing the foreign object detection image of the film product reel with the foreign object detection image obtained in advance for the core before the film is wound, foreign objects contained in the core that do not directly affect the performance of the film product can be subtracted and only foreign objects contained in the film portion can be detected, thereby preventing a film product reel in which foreign objects are contained only in the core from being erroneously determined to be defective, thereby avoiding a decrease in yield in radiographic inspection.

In order to solve the above problems, the method for producing a film product reel according to the present invention includes a step of winding a long film around a core to obtain a film product reel, and a foreign matter inspection step of inspecting the film product reel for foreign matter using the above-mentioned radiographic inspection device. According to the method for producing a film product reel according to the present invention, it is possible to efficiently produce a film product reel with little foreign matter mixed in. In particular, when the film is made of a polyolefin microporous membrane, the film product reel is often used as a battery separator film inserted between the positive and negative electrodes of a lithium ion secondary battery, and it is necessary to detect minute metallic foreign matter of about several tens of μm, so it is effective to include a foreign matter inspection step using the above-mentioned radiographic inspection device in the film product reel production process.

In order to solve the above problems, a radiographic inspection method for a film product reel according to the present invention is a method for generating a foreign object detection image from a radiation detection result obtained by transmitting radiation in a radial direction relative to the circumferential surface of a film product reel formed by winding a long film multiple times around the outer peripheral surface of a core. According to such a radiographic inspection method for a film product reel according to the present invention, because radiation is transmitted in a radial direction relative to the circumferential surface of the film product reel, it is possible to detect foreign objects with high sensitivity even if the reel width increases.

According to the present invention, radiographic inspection of film product reels is possible, which is capable of detecting foreign objects with high sensitivity even when the reel width increases.

1A and 1B are schematic diagrams for explaining a radiographic inspection method for a film product reel according to one embodiment of the present invention, in which (A) is a front view of the end of the reel, (B) is a front view of the circumferential surface of the reel, and (C) is a perspective view of the reel. 1A and 1B are schematic diagrams for explaining a radiographic inspection method for a film product reel according to another embodiment of the present invention, in which (A) is a perspective view of a reel when a detector of a different type from that in FIG. 1 is used, and (B) is a schematic diagram showing that a difference in projection magnification occurs between the center and the ends of the detector. 2A and 2B are schematic diagrams for explaining a method of detecting foreign bodies using the radiographic inspection method of FIG. 1, in which (A) shows a case where the reel rotation axis and the X-ray focal point position are aligned, and (B) shows a case where the reel rotation axis and the X-ray focal point position are misaligned. 2 is a schematic diagram for explaining a method for estimating a contamination depth by the radiographic inspection method of FIG. 1. 1A and 1B show a radiographic inspection device according to an embodiment of the present invention, in which FIG. 10 is a schematic diagram for explaining a radiographic inspection method for a film product reel according to another embodiment of the present invention. FIG.

Preferred embodiments of the present invention will now be described with reference to the drawings.

First Embodiment
Fig. 1 is a schematic diagram for explaining a radiographic inspection method for a film product reel according to one embodiment of the present invention, where (A) is a front view of the reel end, (B) is a front view of the reel circumferential surface, and (C) is a perspective view of the reel. In Fig. 1(A), when X-rays are irradiated onto a film 3 wound around a core 2 for multiple turns, an X-ray source 4 is disposed on the central axis of rotation of the cylindrical core 2. The irradiated X-rays 5 are transmitted through the film 3 and received by a detector 6 consisting of a TDI camera provided outside the core 2, and foreign objects are detected by detecting differences in the brightness of the received X-rays and performing image processing.

Fig. 1(B) is a front view of the circumferential surface of the reel, and Fig. 1(C) is a perspective view of the reel. By irradiating the product reel 1 with X-rays while moving the product reel 1 in the reel width direction and receiving the irradiated X-rays 5 with a detector 6, it is possible to detect foreign objects across the entire width of the product reel 1. Also, instead of moving the product reel 1, the same effect can be obtained by moving the pair of detector 6 and X-ray source (not shown) in the reel width direction.

Here, the advantage of using a TDI camera as the detector 6 in this embodiment will be described with reference to FIG. 2. FIG. 2 is a schematic diagram for explaining a radiographic inspection method for a film product reel according to another embodiment of the present invention, in which a detector 26 (area camera) of a different type from the detector 6 (TDI camera) in FIG. 1 is used. As shown in FIG. 2(A) , the side surface of the product reel is curved, so that as shown in FIG. 2(B) , a difference in projection magnification (D/d=FID/FOD) occurs between the center of the reel circumferential direction and the end of the reel circumferential direction of the detector 26 (area camera). The larger the projection magnification, the smaller the foreign object can be detected, and the difference in projection magnification results in variation in detection sensitivity. Therefore, by using a line camera rather than an area camera as a detector, or a TDI camera in which multiple line cameras are arranged in the flow direction and integrated to increase sensitivity, inspection can be performed with a constant detection sensitivity over the entire circumference of the product reel. Here, d is the actual dimension of the foreign particle, D is the dimension of the foreign particle projected on the detector, FID (Focus to Image Distance) refers to the distance from the focus to the detector, and FOD (Focus to Object Distance) refers to the distance from the focus to the object.

Fig. 3 is a schematic diagram for explaining a method for detecting foreign bodies by the radiographic inspection method of Fig. 1. In Fig. 3(A), the X-ray focal point 16 is arranged on the rotation axis of the core 2, so that the irradiated X-rays 5 are received by the detector 6 while rotating the product reel 1, which is an inspection sample having a curved surface shape, in the circumferential direction of the reel, and the luminance in the TDI camera can be properly integrated. In contrast, in Fig. 3(B), the rotation axis of the core 2 and the X-ray focal point 16 are arranged out of alignment, so that the foreign body B is not properly projected, and the luminance in the TDI camera cannot be properly integrated. However, this does not apply when an integration error is allowed even when a TDI camera is used, or when a detector that does not require luminance integration, such as a line camera or an area camera, is used, and the position of the X-ray focal point 16 may be changed as appropriate, taking into account the following advantages.

(Advantages of moving the X-ray focal point 16 closer to the detector side from the central axis of rotation)
As described above, the projection magnification (detection sensitivity) can be increased by increasing the FID or decreasing the FOD. That is, by moving the X-ray focal point 16 closer to the detector side from the central axis of rotation, the projection magnification can be increased while maintaining the FID.

(Advantages of moving the X-ray focal point 16 away from the central axis of rotation)
If the thickness of the core is t, the FOD to the inner surface of the core is FOD(inner), and the FOD to the outer peripheral surface of the reel is FOD(outer), the projection magnification for a foreign object present on the inner surface of the core is FID/FOD(inner), and the projection magnification for a foreign object present on the outer peripheral surface of the reel is FID/FOD(outer) = FID/(FOD(inner) + t). The ratio of the two is (FID/FOD(inner))/{FID/(FOD(inner) + t)} = 1 + t/FOD(inner), and the closer this is to 1, the smaller the variation in detection sensitivity is, which is preferable. In other words, by increasing FOD(inner) (moving the X-ray focal point 16 away from the central axis of rotation), the variation in detection sensitivity can be reduced.

Fig. 4 is a schematic diagram for explaining a method for estimating the foreign object intrusion depth by the radiographic inspection method of Fig. 1. As shown in Figs. 3(B) and (C), when X-rays are irradiated while moving the product reel 1 (or a pair of detector 6 and X-ray source 4) in the reel width direction and the irradiated X-rays 5 are received by the detector 6, one foreign object moves and traces a trajectory on the foreign object detection image as shown in Fig. 4. By reading the relationship between the displacement (Δx) of the product reel and the displacement (x ₁ -x ₂ ) of the foreign object on the foreign object detection image and performing a geometric calculation using Equation 1, the foreign object intrusion depth (z) can be calculated using FID and FOD.

(Formula 1) z=Δx×FID/(x ₁ −x ₂ )−FOD

5A and 5B show a radiographic inspection apparatus according to an embodiment of the present invention, in which (A) is a front view and (B) is a left side view. The radiographic inspection apparatus 11 is provided with a mounting table 13 on which a product reel 1, which is formed by winding a film 3 around a core 2, is mounted via a core receiver 12.

To start the inspection, the mounting table 13 is first moved in the width direction of the product reel 1 using the width direction movement mechanism 14, thereby inserting the radiation source fixing frame 15 fixing the X-ray source 4 into the inner hollow portion of the core 2. The moving destination can be a predetermined inspection start position, or it may be moved to an end (edge) of the film 3 detected by the irradiated X-ray 5 and the detector 6, or to an end of the film 3 detected by a separately installed sensor, and then the inspection may be started. Also, instead of moving the mounting table 13, the pair of the X-ray source 4 and the detector 6 may be moved in the width direction relative to the fixed mounting table 13.

Next, the core receiver 12 is rotated while irradiating the X-rays so that the X-ray focal point 16 of the irradiated X-rays 5 is positioned on the central axis of rotation of the core 2, thereby rotating the product reel 1, and the data continuously detected by the detector 6 is image-processed to generate a foreign object detection image. In order to rotate the core at a constant speed, the core receiver is preferably made of a material that has a large friction with the core, such as rubber. As a measure other than the material, the core receiver and the core surface may be processed to have unevenness and may be rotated by engaging them. Since the core 2 is provided with a rotation position marker 17, a foreign object detection image for one revolution can be obtained by using the rotation position marker 17 detected by the rotation position sensor 18 for each revolution. In addition, image noise can be suppressed by averaging the foreign object detection images for multiple revolutions. In addition, when a line camera or a TDI camera is used as the detector 6, it is preferable to match the scanning speed of the camera with the rotation speed of the core receiver 12 in order to obtain an image without distortion. At this time, the rotation speed of the core receiver 12 or the core 2 may be measured by a speedometer such as an encoder in case the rotation speed fluctuates, and may be synchronized with the scanning speed of the camera. The irradiation width of the irradiated X-rays 5 may be wider than the detector.

Next, the mounting table 13 is moved in the width direction by a predetermined amount using the width direction movement mechanism 14, and a foreign object detection image is generated again. By repeating this process across the entire width of the product reel 1, a foreign object detection image of the entire product reel 1 can be obtained. When performing a so-called stereoscopic imaging inspection in which it is determined whether or not a foreign object is contained in the film 3 portion of the product reel 1 based on foreign object detection images before and after moving the product reel 1 or the pair of the X-ray source 4 and the detector 6 in the width direction, it is preferable to set the amount of movement of the mounting table 13 per time to less than half the width of the foreign object detection image for one revolution. Furthermore, the rotation of the product reel 1 may be stopped when the mounting table 13 is moved, or the mounting table 13 may be moved while the product reel 1 is rotating.

Once a foreign object detection image of the entire product reel 1 has been obtained, the X-ray irradiation is stopped, the rotation of the product reel 1 is stopped, and the mounting table 13 is moved widthwise to a position where the radiation source fixing frame 15 is exposed from the core 2, and the product reel 1 is removed from the core receiver 12.

Second Embodiment
In FIG. 1, an area camera is used as the detector 6, and the rest are the same. Unlike a TDI camera or a line camera, an area camera does not need to measure or control the rotation speed of the product reel 1 because it captures images in a stationary state. The flow of full-circumference inspection at a specific width position of the product reel 1 is as follows: rotate the product reel 1 θ → standstill → capture image → rotate the product reel 1 θ → .... Here, θ is the rotation angle of the product reel 1 when capturing images of the next field of view. In addition, when an area camera is used, it is preferable to shift the position of the X-ray focal point 16 from the central axis of rotation of the core 2. This makes it possible to estimate the position of the foreign object when the same foreign object is detected in multiple fields of view during full-circumference inspection. The principle of this will be explained with reference to FIG. 6.

6 is a schematic diagram showing a case where the same foreign object is detected in two fields of view before and after the product reel 1 is rotated in the circumferential direction around the origin O. First, on the line segment _s1 , the three points of the X-ray focal point, the foreign object, and the foreign object projection position on the detector are on the same line, so Equation 2 is established.
(Formula 2) (FID-b)/(A ₁ -a)=(y ₁ -b)/(x ₁ -a)

Similarly, for the line segment _s2 , Equation 3 holds.
(Formula 3) (FID-b)/(A ₂ -a)=(y ₂ -b)/(x ₂ -a)

Next, since the position of foreign matter contamination after rotation is a position obtained by rotating the position of foreign matter contamination before rotation by θ, Equation 4 and Equation 5 are established.
(Formula 4) x ₂ = x ₁ × cos θ - y ₁ × sin θ
(Formula 5) _y2 = _x1 ×sinθ+ _y1 ×cosθ

By solving the simultaneous equations of Equations 2 to 5, _x1 , _y1 , _x2 , and _y2 can be obtained. From these coordinates, ^the polar coordinates (r, φ) of ^the foreign matter mixing position ( _x1 , _y1 ) can be obtained as r = ( _x12 + _y12 ) ^1/2 , φ = arctan ( _y1 / _x1 ). In this case, depending on whether r is smaller or larger than the outer diameter of core 2, it can be determined whether ^the foreign matter is inside the core or in the film.

Here, if the X-ray focal point 16 is on the central axis of rotation of the core 2 (when a = b = 0), the projection position on the detector will be the same regardless of the radius of the foreign object contamination position, and the position cannot be found using formulas 2 to 5. Therefore, in this embodiment, it is preferable to shift the X-ray focal point 16 from the central axis of rotation of the core 2. However, in either case, the foreign object contamination position can be found using formula 1 based on images before and after movement in the width direction, as in the first embodiment.

Once the foreign matter contamination position is determined, the actual dimension can be calculated from the definition equation of the projection magnification, d = D x (r/FID), and the sensitivity variation in the circumferential direction when using the area camera shown in Figure ₂ can be corrected. At this time, calculation errors can be suppressed by calculating d1 and _d2 using the dimensions _D1 and D2 on the detector at each foreign matter contamination position ( _x1 , _y1 ), ( _x2 , _y2 ) and the X-ray focus-to-detector distances FID1 and _FID2 to calculate _d1 and _d2 and then calculating the average value. Here, _FID1 and _FID2 are the lengths of the line segments _s1 and _s2 , respectively.

In this embodiment, θ is appropriately set so that the same foreign object is detected in multiple fields of view in the circumferential direction without lengthening the inspection time. If θ is large, it may be possible to detect it in only one field of view, and if θ is small, it will take a long inspection time. However, θ does not need to be constant over the entire circumference, and it is possible to set θ to minimize the overlap with the next field of view during normal operation, and to temporarily reduce θ to detect in multiple fields of view only when a foreign object is detected. In addition, although the above description is given of a case where detection is performed in two fields of view, the same calculation can be performed even when detection is performed in three or more fields of view, and errors can be further suppressed by averaging the calculated values, etc.

The manufacturing process to which the inspection method of the present invention is applied is not limited to polyolefin battery separator films, but is also suitable for manufacturing processes of coating separators, nonwoven battery separators, capacitor films, MLCC release films, polyolefin microporous films used for high-precision filtration, etc.

REFERENCE SIGNS LIST 1 product reel 2 core 3 film 4 X-ray source 5 irradiated X-rays 6, 26 detector 11 radiographic inspection device 12 core receiver 13 placement table 14 width direction movement mechanism 15 radiation source fixing frame 16 X-ray focus 17 rotation position marker 18 rotation position sensor FID focus-detector distance FOD focus-object distance

Claims (7)

A radiographic inspection device for inspecting a film product reel having a long film wound around an outer circumferential surface of a core for foreign objects, comprising:
a mounting table on which the film product reel is placed;
a radiation source and detector pair disposed between an inside of the core and an outer peripheral surface of the film product reel for transmitting and receiving radiation in a radial direction of the film product reel;
an image processing unit that generates a foreign object detection image from the radiation detection result obtained by the detector;
having
Further, the pair of the radiation source and the detector has a function of rotating in the circumferential direction or moving in the width direction,
a radiation transmission inspection device for a film product reel, the image processing unit determining whether or not the foreign object is contained in a film portion of the film product reel based on the foreign object detection images before and after moving the pair of the radiation source and the detector in the circumferential direction or width direction of the film product reel. A radiographic inspection device for inspecting a film product reel having a long film wound around an outer circumferential surface of a core for foreign objects, comprising:
a mounting table on which the film product reel is placed;
a radiation source and detector pair disposed between an inside of the core and an outer peripheral surface of the film product reel for transmitting and receiving radiation in a radial direction of the film product reel;
an image processing unit that generates a foreign object detection image from the radiation detection result obtained by the detector;
having
the mounting table has a function of rotating the film product reel in the circumferential direction or moving the film product reel in the width direction,
A radiographic inspection device for film product reels, wherein the image processing unit determines whether or not the foreign object is contained in a film portion of the film product reel based on the foreign object detection images before and after moving the film product reel in a circumferential direction or a width direction of the film product reel. 3. The radiographic inspection apparatus according to claim 1 , wherein the focal point of the radiation is disposed in an inner cavity of the core. 4. The radiographic inspection device according to claim 1, wherein the image processing unit determines whether or not the foreign object is contained in the film portion of the film product reel based on the foreign object detection image previously obtained for the core before the film is wound. 13. A method for manufacturing a film product reel, comprising: a step of winding a long film around a core for a number of revolutions to obtain a film product reel; and a foreign body inspection step of inspecting the film product reel for foreign bodies using a radiation transmission inspection device according to any one of claims 1 to 4 . The method for producing a film product reel according to claim 5 , wherein the film comprises a microporous polyolefin membrane. For a film product reel having a long film wound around an outer peripheral surface of a core for multiple revolutions, a foreign object detection image is generated from a radiation detection result obtained by transmitting radiation from a radiation source in a radial direction of the film product reel between the inside of the core and the outer peripheral surface of the film product reel and receiving the radiation with a detector ;
moving the film product reel or the pair of the radiation source and the detector in a circumferential direction or a width direction of the film product reel, and then generating the foreign object detection image again;
A radiographic inspection method for a film product reel, comprising: determining whether or not a foreign object is contained in a film portion of the film product reel based on the foreign object detection images before and after the movement in the circumferential direction or width direction.

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