Film measuring device and film measuring method

Abstract

To provide a film measuring device capable of more accurately measuring the film thickness of a coating film. [Solution] The film measurement device 1 comprises an imaging unit 2 that captures an image of a coating film to obtain gradation data for each pixel, a light source 3, an optical unit 4 that irradiates the coating film with light output from the light source 3 and causes reflected light from the coating film to be incident on the imaging unit, a data calculation unit that calculates the retroreflectance for each pixel in the imaging area and the zero point number at which the retroreflectance is less than a set value based on the image captured by the imaging unit 2, and a film thickness calculation unit that calculates an estimated film thickness of the coating film from the zero point number using an approximation formula obtained from the correlation between the zero point number and a specified film thickness of the coating film.

Description

[Technical field]

[0001] The present invention relates to a film measurement device and a film measurement method. [Background technology]

[0002] Conventionally, various methods have been used to measure the film thickness of a battery electrode plate of a lithium ion battery (secondary battery). For example, a method is known in which the surface of the battery electrode plate is scanned with a radiation film thickness meter to measure the amount of radiation absorbed by the battery material coated on the substrate, thereby calculating the film thickness of the battery electrode plate. As a method for measuring the film thickness of the electrodes coated on both sides of the battery electrode plate, a thickness measurement system is known in which the film thickness of the battery electrode plate is calculated by scanning the front and back sides of the battery electrode plate with two radiation film thickness meter (see Non-Patent Document 1).

[0003] In addition, as a method for measuring the film thickness of a battery electrode plate, a film measurement method has been proposed in which, in order to accurately obtain the reflected luminance of the coating film, the image data of a cylindrical blackbody cavity is subtracted from the image data of the film to remove the reflected luminance inside the optical system from the image data of the film (see Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Yokogawa Technical Report Vol.62 No.1 (2019) "WEBFREX3ES Battery Electrode Thickness Measurement System" [Patent documents]

[0005] [Patent Document 1] Patent No. 5318303 Summary of the Invention [Problem to be solved by the invention]

[0006] In the electrode manufacturing process for secondary batteries, the film thickness is controlled in the pressing process after the coating process, so it is necessary to accurately measure the film thickness after the pressing process. The pressing process reduces the film thickness of the battery material, but the total amount of battery material does not change. Therefore, even if the amount of radiation absorbed by the battery material after the pressing process is measured with a radiation film thickness meter, it is not possible to calculate the film thickness of the thinner battery material. In addition, considering the effects of radiation exposure on the human body, a radiation film thickness meter is not suitable as an instrument for measuring the film thickness of battery electrode plates.

[0007] In the pressing process, both ends of the coating film are sometimes measured manually with a micrometer. However, it is difficult to use a micrometer to measure the area near the center of the roll on which the coating film is formed. There are also other methods, such as placing two optical distance meters on the front and back sides of the coating film and calculating the change in distance, or measuring the film thickness variation on the roll with an optical distance meter. However, with either method, it is difficult to accurately measure the film thickness on each side individually.

[0008] On the other hand, if the surface of a metal material is flat and opaque, a laser range finder can be used to measure the distance to the target surface. Attempts have been made to use this principle to measure the distance to a battery electrode plate to measure the film thickness. However, this method is susceptible to the effects of roll eccentricity, fluttering of the electric electrode plate, surface roughness, etc., and has not yet been put to practical use. Even with this method, it is difficult to measure the film thickness on the front and back surfaces of the battery electrode plate separately. Furthermore, the application of capacitance-type range finders, eddy-current-type range finders, etc. has also been considered, but has not yet been put to practical use.

[0009] An object of the present invention is to provide a film measurement device and a film measurement method that can more accurately measure the film thickness of a coating film formed on the front and back surfaces of a battery electrode plate in the electrode manufacturing process for a secondary battery. [Means for solving the problem]

[0010] A film measurement device according to one embodiment of the present invention includes an imaging unit that captures an image of a coating film to obtain gradation data for each pixel, a light source, an optical unit that irradiates the coating film with light output from the light source and causes reflected light from the coating film to be incident on the imaging unit, a data calculation unit that calculates the retroreflectance for each pixel in an imaging area and a zero point number at which the retroreflectance is less than a set value based on the image captured by the imaging unit, and a film thickness calculation unit that calculates an estimated film thickness of the coating film from the zero point number using an approximation formula obtained from the correlation between the zero point number and a specified film thickness of the coating film.

[0011] Furthermore, a film measurement method according to another aspect of the present invention is a film measurement method for measuring the film thickness of a coating film, and includes the steps of irradiating light output from a light source onto the coating film, capturing an image formed by reflected light from the coating film to obtain gradation data for each pixel, calculating the retroreflectivity and zero point number for each pixel in the captured area based on the captured image, and calculating an estimated film thickness of the coating film from the zero point number using an approximation formula obtained from the correlation between the zero point number and a specified film thickness of the coating film. Effect of the Invention

[0012] According to the film measurement device and the film measurement method of the present invention, the film thickness of a coating film can be measured more accurately. [Brief description of the drawings]

[0013] [Figure 1] 1 is a configuration diagram of a film measuring device 1 according to a first embodiment. [Diagram 2] 2 is a block diagram showing an example of a hardware configuration of a data processing device 8. FIG. [Diagram 3] 2 is a block diagram showing an example of a functional configuration of a data processing device 8. FIG. [Figure 4] 10 is a flowchart showing a procedure for a process of calculating the number of zero points included in an imaging area. [Diagram 5] 2 is a side view showing the arrangement of a film measurement unit in the coating system 100. FIG. [Figure 6] FIG. 2 is a perspective view showing the arrangement of a film measurement unit in the coating system 100. [Figure 7] 2 is a side view showing the arrangement of a membrane measurement unit in the press system 200. FIG. [Figure 8] FIG. 13 is a diagram showing a luminance image and a binarized image of a positive electrode one-side coating film after coating. [Figure 9] FIG. 13 is a diagram showing a luminance image and a binarized image of a positive electrode one-side coating film after pressing. [Figure 10] FIG. 13 is a diagram showing a luminance image and a binarized image of a coating film on both sides of a negative electrode after coating. [Figure 11] FIG. 13 is a diagram showing a luminance image and a binarized image of a negative electrode double-sided coating film after pressing. [Figure 12] FIG. 1 is a diagram showing the correlation between the reflectance rφ(R,G,B)% and the zero point number after coating and after pressing of a positive electrode single-side coating film. [Figure 13] FIG. 1 is a diagram showing the correlation between the reflectance rφ(R,G,B)% and the zero point number after coating and after pressing of a coating film on both sides of a negative electrode. [Figure 14] FIG. 13 is a diagram showing an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) of a positive electrode coating film and a specified film thickness T, and an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) and a specified density ρ. [Figure 15] FIG. 13 is a diagram showing an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points of a positive electrode coating film and a specified film thickness T, and an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points and a specified density ρ. [Figure 16] FIG. 13 is a diagram showing an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) of a negative-electrode coating film and a specified film thickness T, and an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) and a specified density ρ. [Figure 17] FIG. 13 is a diagram showing an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points of a negative electrode coating film and a specified film thickness T, and an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points and a specified density ρ. [Figure 18]1 is a diagram showing the distribution of the reflectance and the number of zero points of each sample after coating and pressing of a positive electrode one-side coating film. FIG. 2 is a diagram showing the distribution of the estimated film thickness Te of each sample after coating and pressing of a positive electrode one-side coating film. [Figure 19] FIG. 1 is a diagram showing the distribution of estimated film thickness Te of each sample of a positive electrode single-side coating film after coating and after pressing. [Figure 20] FIG. 13 is a diagram showing the distribution of reflectance and zero points of each sample after coating and pressing of a coating film on both sides of a negative electrode. [Figure 21] FIG. 13 is a diagram showing the distribution of estimated film thickness Te of each sample of a negative-electrode double-sided coating film after coating and after pressing. [Figure 22] FIG. 13 is a diagram showing the distribution of estimated density ρe of each sample of a positive electrode single-sided coating film after coating and after pressing. [Diagram 23] FIG. 13 is a diagram showing the distribution of estimated density ρe of each sample of a negative-electrode double-sided coating film after coating and after pressing. [Figure 24] FIG. 1 is a diagram showing the distribution of reflection color values ​​Lab of each sample of a positive electrode single-sided coating film after coating and after pressing. [Diagram 25] FIG. 13 is a diagram showing the distribution of reflection color values ​​Lab of each sample of a negative-electrode double-sided coating film after coating and after pressing. [Figure 26] FIG. 13 is a diagram showing a luminance image and a binarized image of the center portion of a coating film on one side of a positive electrode. [Figure 27] FIG. 13 is a diagram showing a luminance image and a binarized image of an end portion of a positive electrode single-side coating film. [Figure 28] FIG. 13 is a diagram showing a luminance image and a binarized image of the rear surface of a negative electrode double-sided coating film. [Figure 29] FIG. 13 is a diagram showing a luminance image and a binarized image of the surface of a coating film on both sides of a negative electrode. [Diagram 30] FIG. 13 is a diagram showing the distribution of reflectance and the number of zero points at the center and end portions of each sample of a positive electrode single-side coating film. [Diagram 31] FIG. 1 is a diagram showing the distribution of estimated film thickness Te at the center and end portions of each sample of a positive electrode single-side coating film. [Diagram 32]FIG. 13 is a diagram showing the distribution of reflectance and the number of zero points at the back surface and the center of the front surface of each sample of a negative-electrode double-sided coating film. [Diagram 33] FIG. 13 is a diagram showing the distribution of estimated film thickness Te at the back surface and the center of the front surface for each sample of a negative-electrode double-sided coating film. [Diagram 34] FIG. 13 is a diagram showing the distribution of estimated density ρe at the center and end portions of each sample of a positive electrode single-side coating film. [Diagram 35] FIG. 13 is a diagram showing the distribution of estimated density ρe at the back surface and the center of the front surface of each sample of a negative-electrode double-sided coating film. [Diagram 36] FIG. 1 is a diagram showing the distribution of reflection color values ​​Lab of the center and end portions of each sample of a positive electrode single-side coating film. [Figure 37] FIG. 2 is a diagram showing the distribution of color difference values ​​Δ(L, a, b, E) between the center and end portions of each sample of a positive electrode single-sided coating film. [Figure 38] FIG. 1 is a diagram showing the distribution of reflection color values ​​Lab of the back surface and the center of the front surface of a negative electrode double-sided coating film. [Figure 39] FIG. 1 is a diagram showing the distribution of color difference values ​​Δ(L, a, b, E) between the back surface and the center of the front surface of each sample of a negative-electrode double-sided coating film. [Diagram 40] FIG. 13 is a diagram showing the distribution of calibration calculation luminance values ​​in imaging areas of 500×500 pixels and 2000×50 pixels. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a film measurement device and a film measurement method according to the present invention will be described. Note that all of the drawings attached to this specification are schematic diagrams, and the shape, scale, aspect ratio, and the like of each part are modified or exaggerated from the actual ones in consideration of ease of understanding, etc.

[0015] In the embodiment described below, an example will be described in which the film measurement device and the film measurement method according to the present invention are applied to a film measurement device and a film measurement method for a battery electrode plate used in a lithium ion battery. However, the film measurement device and the film measurement method according to the present invention are not limited to lithium ion batteries, but can be applied to secondary batteries in general that have a porous coating film structure. In the following description, the band-shaped battery electrode plate in the electrode manufacturing process for lithium ion batteries is also referred to as an "electrode sheet."

[0016] FIG. 1 is a configuration diagram of a film measuring device 1 according to the first embodiment. The film measuring device 1 is a device for measuring the film thickness, density, and reflection color value (hereinafter, also referred to as "film thickness, etc.") of a coating film formed on an electrode sheet. As shown in FIG. 1, the film measuring device 1 includes an imaging unit 2, a light source 3, an optical unit 4, a retroreflector 7, and a data processing device 8. In FIG. 1, in order to easily understand the optical paths of the incident light and the reflected light that proceed coaxially with the optical axis OA1 of the imaging unit 2 and the optical axis OA2 of the retroreflector 7, the optical paths of the incident light and the reflected light are drawn along the respective optical axes. In addition, the measurement object S is actually a strip-shaped electrode sheet, but in FIG. 1, it is drawn as a sheet of electrode sheet.

[0017] The imaging unit 2 is a color camera equipped with a CMOS type image sensor. The image sensor of the imaging unit 2 has, for example, 2048 x 1536 pixels (RGB). The imaging unit 2 receives incident light on a light receiving surface, and converts the optical image formed on the light receiving surface into gradation data (RGB luminance signal) for each pixel and outputs it. That is, the imaging unit 2 captures an image of a coating film (described later) to be measured and obtains gradation data for each pixel. The operation of the imaging unit 2 is controlled by an imaging control unit 31 (described later).

[0018] An optical axis OA1 of the imaging unit 2 is inclined at an angle θ1 with respect to a perpendicular line PL of the measurement object S at a point P on the surface (measurement surface) of the measurement object S. When the measurement distance of a telecentric lens 5 (described later) is 110 mm, the angle θ1 is, for example, 10° to 15°. In addition, the exposure time for capturing an image of the coating film in the imaging unit 2 is, for example, 10 μsec.

[0019] The light source 3 is a white LED light source that outputs white LED light. The white LED light source is characterized by having a higher luminance value on the short wavelength side of 400 nm compared to other light sources, and stable temperature characteristics. As shown in FIG. 1, a part of the LED light output from the light source 3 is reflected by a beam splitter 6 (described later) and irradiated onto a measurement target S. The light source 3 is supplied with power from an LED power supply (not shown). The operation of the light source 3 is controlled by a light source control unit 32 (described later).

[0020] In the online manufacturing process, the electrode sheet is transported at a speed of 100 m / min. If the exposure time of the imaging unit 2 is shortened to accommodate this speed, the image will be dark with a normal light source, making it difficult to capture the zero point (described later). If the exposure time of the imaging unit 2 is lengthened, the gradation at each point of the image will be averaged in the direction of transport of the electrode sheet, making it difficult to calculate the number of zero points. To solve this problem, it is desirable to combine a high-power LED light source with an optical fiber light guide or the like (not shown) as the light source 3 to increase the amount of light. According to experiments by the present inventors, it has been confirmed that by combining a high-power LED light source with an optical fiber light guide or the like to increase the amount of light, the zero point of the coating film can be well captured even when an electrode sheet transported at a speed of 100 m / min is captured with an exposure time of 10 μsec (movement amount 1.6 μm / 1 μsec).

[0021] The optical unit 4 is an optical device that irradiates the light output from the light source 3 onto the measurement object S and causes the reflected light from the measurement object S to enter the imaging unit 2. The optical unit 4 includes a telecentric lens 5 and a beam splitter 6. The telecentric lens 5 is a coaxial epi-illumination lens designed so that the chief ray is parallel to the optical axis. The telecentric lens 5 is disposed so that the lens center coincides with the optical axis OA1 of the imaging unit 2.

[0022] The beam splitter 6 is an optical element that splits incident light into transmitted light and reflected light. The beam splitter 6 is provided between the telecentric lens 5 and the imaging unit 2. The beam splitter 6 is disposed so that its transmission / reflection surface is inclined at approximately 45° with respect to the optical axis OA1 of the imaging unit 2.

[0023] The retroreflector 7 is an optical component that reflects incident light along its incident optical path. The optical axis OA2 of the retroreflector 7 is inclined at an angle θ2 with respect to the perpendicular line PL of the measurement object S at a point P on the surface of the measurement object S. The angle θ2 is 10° to 15°, the same as the angle θ1. By using the retroreflector 7 that reflects the light incident from the measurement object S back toward the measurement object S, the influence of the inclination of the measurement object S can be reduced. The inclination of the measurement object S is, for example, about ±3° with respect to the reference plane.

[0024] In the optical system configuration shown in FIG. 1, a part of the LED light output from the light source 3 (incident light L1) is reflected by the beam splitter 6 and then irradiated onto the measurement target S via the telecentric lens 5. The incident light L1 irradiated onto the measurement target S is reflected by the surface of the measurement target S and enters the retroreflector 7 as reflected light L2. The reflected light L2 that enters the retroreflector 7 is reflected by the surface of the retroreflector 7 and then enters the surface of the measurement target S as reflected light L3. The reflected light L3 that enters the surface of the measurement target S is reflected by the surface of the retroreflector 7 and then enters the imaging unit 2 as reflected light L4 via the telecentric lens 5 and the beam splitter 6. In the imaging unit 2, an optical image of the reflected light L4 is formed on the light receiving surface, and the optical image is converted into gradation data and output.

[0025] The data processing device 8 is a device that controls the operation of the film measurement device 1, and also measures the film thickness, density, and reflection color value of the coating film on the measurement object S based on image data obtained by photographing the measurement object S. The data processing device 8 is electrically connected to the imaging unit 2 and the light source 3 via a communication cable.

[0026] Fig. 2 is a block diagram showing an example of a hardware configuration of the data processing device 8. As shown in Fig. 2, the data processing device 8 includes a CPU (Central Processing Unit) 11, a ROM (Read Only Memory) 12, a RAM (Random Access Memory) 13, a bus 14, an input / output interface 15, an output unit 16, an input unit 17, a storage unit 18, a communication unit 19, and a drive 20.

[0027] The CPU 11 executes various processes according to a program recorded in the ROM 12 or a program loaded from the storage unit 18 to the RAM 13. The RAM 13 also stores data and the like required for the CPU 11 to execute various processes. The CPU 11, the ROM 12, and the RAM 13 are interconnected via a bus 14. An input / output interface 15 is also connected to this bus 14.

[0028] The input / output interface 15 is connected to an output unit 16, an input unit 17, a storage unit 18, a communication unit 19, and a drive 20. The output unit 16 is composed of a display, a speaker, etc., and outputs various information as images and sounds. The input unit 17 is composed of a keyboard, a mouse, a touch panel, etc., and accepts input of various information. The storage unit 18 is composed of a hard disk, a DRAM (Dynamic Random Access Memory), etc., and stores various data. The communication unit 19 communicates with other devices via a network N including the Internet.

[0029] Removable media 21, which may be a magnetic disk, an optical disk, a magneto-optical disk, or a semiconductor memory, is appropriately attached to the drive 20. Programs read from the removable media 21 by the drive 20 are installed in the storage unit 18 as necessary. The removable media 21 can also store various data stored in the storage unit 18 in the same manner as the storage unit 18.

[0030] Fig. 3 is a block diagram showing an example of a functional configuration of the data processing device 8. As shown in Fig. 3, the data processing device 8 includes a CPU 11, a storage unit 18, and a communication unit 19. The CPU 11 comprehensively controls the operation of the data processing device 8. In the process of measuring the thickness, density, and reflection color value of a coating film formed on the surface of the measurement target S, the CPU 11 functions as an imaging control unit 31, a light source control unit 32, a data calculation unit 33, a film thickness calculation unit 34, a density calculation unit 35, and a color value calculation unit 36, which will be described later.

[0031] The imaging control unit 31 controls the operation of the imaging unit 2 (opening and closing the shutter, setting of the exposure time, etc.). The light source control unit 32 controls the operation of starting / stopping the output of LED light from the light source 3, the output level, and the like.

[0032] The data calculation unit 33 calculates the retroreflectance (hereinafter also referred to as "reflectance") and the number of zero points for each pixel in each imaging region based on the image (grayscale data) captured by the imaging unit 2. A zero point is a pixel whose reflectance is less than a set value. The number of zero points is the number of zero points in the imaging region. The number of zero points correlates with the number and size of cavities, which will be described later.

[0033] Here, an example of a method for calculating the number of zero points performed by the data calculation unit 33 will be described. FIG. 4 is a flowchart showing the procedure of a process for calculating the number of zero points included in the imaging area. The process of each step shown in FIG. 4 is mainly executed in the data calculation unit 33. Here, an example will be described in which it is determined whether or not the reflectance obtained from the gradation data for each of n pixels (1 to n pixels) included in the imaging area is less than a threshold value. Note that the method for calculating the number of zero points in the data calculation unit 33 is not limited to the example shown in FIG. 4.

[0034] In step S101 shown in FIG. 4, the data calculation unit 33 resets the zero point count z to zero. In step S102, the data calculation unit 33 resets the pixel number i of the target imaging region to zero. In step S103, the data calculation unit 33 increments the pixel number i. In step S104, the data calculation unit 33 acquires the gradation data of pixel number i from the image DB 41 (see FIG. 3) in the storage unit .

[0035] In step S105, the data calculation unit 33 compares the reflectance rφ included in the gradation data of pixel number i with a threshold reflectance rφ(th) and determines whether the reflectance rφ is equal to or less than the threshold reflectance rφ(th). The threshold reflectance rφ(th) is, for example, 0.001%.

[0036] In the judgment of step S105, if the data calculation unit 33 judges that the reflectance rφ is equal to or less than the threshold reflectance rφ(th), the process proceeds to step S106. On the other hand, in the judgment of step S105, if the data calculation unit 33 judges that the reflectance rφ exceeds the threshold reflectance rφ(th), the process proceeds to step S107.

[0037] In step S106 (step S105: YES), the data calculation unit 33 increments the zero point count z stored in the image DB 41 (see FIG. 3). Note that when starting the process of this flowchart, the zero point count z is reset to an initial value (0).

[0038] In step S107, data calculation unit 33 determines whether pixel number i=n. If data calculation unit 33 determines in step S107 that pixel number i=n, ​​the process proceeds to step S108. On the other hand, if data calculation unit 33 determines in step S107 that pixel number i=n does not hold, the process proceeds to step S103. Thereafter, a loop process from steps S103 to S107 is executed until pixel number i=n is determined in step S107.

[0039] In step S108 (step S107: YES), the data calculation unit 33 stores the zero point number z in the image DB 41 of the storage unit 18. In the image DB 41, the zero point number z is stored in association with the identification number of the target imaging area. After the data of the zero point number z is stored in the image DB 41 of the storage unit 18 in step S108, the process of this flowchart ends.

[0040] Returning to Fig. 3, the film thickness calculation unit 34 calculates the estimated film thickness of the coating film from the zero points obtained from the image data using an approximation equation (described later) for the film thickness obtained from the correlation between the zero points and the designated film thickness of the coating film. The "designated film thickness" is the actual measured film thickness. The "estimated film thickness" is the calculated film thickness value calculated from the approximation equation.

[0041] The density calculation unit 35 calculates an estimated density of the coating film from the zero points obtained from the image data using an approximation formula (described later) obtained from the correlation between the zero points and the designated density of the coating film. The "designated density" is the actual measured value of the density. The "estimated density" is the calculated value of the density calculated from the approximation formula.

[0042] The color value calculation unit 36 ​​calculates the reflection color value of the coating film using the reflectance rφ(R,G,B)% obtained from the image data and a conversion formula (described later). The color value calculation unit 36 ​​also calculates a color difference value from the reference reflection color value and the calculated reflection color value.

[0043] The storage unit 18 includes databases for storing various data, such as an image DB 41 and an approximation DB 42. The image DB 41 is a database that stores gradation data captured by the imaging unit 2, a luminance image obtained from the gradation data, a binarized image, and the number of zero points for each imaging region. The approximation DB 42 is a database that stores data related to approximation equations and conversion equations (described later) used in the calculations of the film thickness calculation unit 34, the density calculation unit 35, and the color value calculation unit 36.

[0044] Next, a description will be given of how the film measuring device 1 is used in the electrode manufacturing process of a lithium ion battery. The manufacturing process of an electrode for a lithium ion battery includes a kneading process, a coating process, a pressing process, a slitting process, etc. The film measurement device 1 is used to measure the film thickness, density, and reflection color value of a coating film in the coating process and the pressing process. FIG. 5 is a side view showing the arrangement of a film measurement unit in the coating system 100. FIG. 6 is a perspective view showing the arrangement of a film measurement unit in the coating system 100. In the following description, the width direction of the electrode sheet (sample) is defined as the X direction. The X direction corresponds to the horizontal direction of the image capture screen. Hereinafter, the X direction is also referred to as the "width direction X" or the "horizontal direction X". The moving direction of the electrode sheet is defined as the Y direction. The Y direction corresponds to the vertical direction of the image capture screen. Hereinafter, the Y direction is also referred to as the "vertical direction Y").

[0045] 5, the coating system 100 includes a first roll 103, a conveying device 104, a die coater 105, a drying furnace 106, a winding device 107, and a second roll 108. The coating system 100 also includes film measurement units 110A and 110B.

[0046] The first roll 103 is a strip-shaped substrate 101 wound around a reel. The conveying device 104 is a device that conveys the base material 101 pulled out from the first roll 103 toward a drying furnace 106 .

[0047] The die coater 105 is a device that applies an electrode material to both sides of the substrate 101 (foil) for the positive electrode and the negative electrode. When manufacturing an electrode sheet for the positive electrode, for example, a transition metal oxide is applied to both sides of an aluminum foil in the die coater 105. When manufacturing an electrode sheet for the negative electrode, for example, a graphite-based material is applied to both sides of a copper foil in the die coater 105. The electrode material may be applied to one side of the substrate 101 at a time. In this specification, the substrate 101 with the electrode material applied to both sides is also referred to as an "electrode sheet 102."

[0048] The drying furnace 106 is a device that dries the electrode material coated on both sides of the electrode sheet 102. In FIG. 5, a heating device and the like installed inside the drying furnace 106 are omitted. The winding device 107 is a device that conveys the electrode sheet 102 sent out from the drying furnace 106 toward the second roll 108. The second roll 108 is the electrode sheet 102 wound on a reel. As shown in FIG. 5, the coating system 100 is configured to continuously perform coating of the electrode material by the die coater 105 and drying by the drying furnace 106 online while moving the substrate 101 pulled out from the first roll 103 toward the second roll 108. In the coating process, the electrode sheet 102 wound around the second roll 108 is sent to the next pressing process.

[0049] The coating system 100 includes film measurement units 110A and 110B downstream of the drying furnace 106. The film measurement units 110A and 110B have substantially the same configuration, and therefore are collectively referred to as "film measurement unit 110" in the following description. The film measurement unit 110A measures the thickness and other properties of the coating film formed on the first surface of the electrode sheet 102. The film measurement unit 110B measures the thickness and other properties of the coating film formed on the second surface of the electrode sheet 102, which is opposite to the first surface.

[0050] As shown in Fig. 6, the film measurement unit 110 includes a film measurement device 1, a thermometer 111, and a scanning device 112. In the film measurement device 1, the imaging unit 2, the light source 3, the optical unit 4, and the retroreflector 7 (see Fig. 1) are housed in one case. Although not shown, a data processing device 8 (see Fig. 1) is disposed externally via a communication cable.

[0051] The thermometer 111 is a device that measures the temperature of the coating film formed on the electrode sheet 102. The thermometer 111 is, for example, an infrared radiation thermometer. The thermometer 111 is provided in the film measuring device 1. The scanning device 112 is a device that moves the film measuring device 1 and the thermometer 111 back and forth along the width direction X of the electrode sheet 102. The operation of the scanning device 112 is controlled by the data processing device 8 (imaging control unit 31).

[0052] It is believed that as the temperature of the coating film of the electrode sheet 102 increases, the electrode material expands, increasing the porosity (the ratio of cavities per unit area). The surface temperature of the electrode sheet 102 sent out from the drying furnace 106 may become higher than room temperature. In that case, a difference occurs in the measurement data from the room temperature, making it impossible to perform accurate measurement. Therefore, during online measurement, the temperature of the coating film is measured with a thermometer 111 together with an image of the coating film, and by comparing this with the data from offline measurement, it is possible to determine whether or not there is an effect of temperature.

[0053] 7 is a side view showing the arrangement of the film measurement unit in the press system 200. As shown in FIG. 7, the press system 200 includes a second roll 108, a conveying device 201, a press roll 202, a winding device 203, and a third roll 204.

[0054] The second roll 108 is a strip-shaped electrode sheet 102 that is wound around a reel in the coating process (see FIG. 5). The conveying device 201 is a device that conveys the electrode sheet 102 unwound from the second roll 108 toward the press roll 202.

[0055] The press roll 202 is a device that compresses the electrode sheet 102 to a preset thickness. The winding device 203 is a device that transports the electrode sheet 102 fed from the press roll 202 toward the third roll 204. The third roll 204 is the electrode sheet 102 wound up on a reel. In the pressing process, the electrode sheet 102 wound up on the third roll 204 is sent to the next slitting process (description omitted).

[0056] The press system 200 includes film measurement units 120A and 120B downstream of the press roll 202. Since the configurations of the film measurement units 120A and 120B are substantially the same, they are collectively referred to as the "film measurement unit 120" in the following description. The film measurement unit 120A measures the film thickness and the like of the coating film formed on the first surface of the electrode sheet 102. The film measurement unit 120B measures the film thickness and the like of the coating film formed on the second surface of the electrode sheet 102 opposite to the first surface.

[0057] The film measurement unit 120 includes a film measurement device 1 and a scanning device 112. In the film measurement device 1 shown in FIG. 6, the imaging unit 2, light source 3, optical unit 4, and retroreflector 7 (see FIG. 1) are housed in one case. In addition, the data processing device 8 (see FIG. 1) is disposed externally via a communication cable. The film measurement unit 120 differs from the film measurement unit 110 in that it does not include a thermometer 111 (see FIG. 6). The other configurations are substantially the same as those of the film measurement unit 110, so a description of each part will be omitted. The configuration of the film measurement unit 120 may be the same as that of the film measurement unit 110 of the coating system 100.

[0058] Next, the correlation between the reflectance of the coating film and the number of zero points will be described with reference to Fig. 8 to Fig. 11. In Fig. 8 to Fig. 11, the images on the left side show luminance images of reflectance rφ(R,G,B)% obtained from images (gradation data) of an electrode sheet produced as a sample. The images on the right side show binarized images calculated from the luminance images.

[0059] The imaging area was not the entire camera field of view, but 500 x 500 pixels (250,000 points) in the center of the camera field of view. The measurement area on the sample was 4 mm square (1 pixel = 8 μm square). In the binarized image, pixels where the calculated reflectance was 0.001% or less (including pixels where the reflectance was a negative value) were set as zero points. The number of zero points out of the 250,000 points was also calculated to obtain the number of zero points (see Figure 4).

[0060] Fig. 8 is a diagram showing a luminance image and a binary image of a positive electrode coating film on one side after coating. Fig. 9 is a diagram showing a luminance image and a binary image of a positive electrode coating film on one side after pressing. Fig. 10 is a diagram showing a luminance image and a binary image of a negative electrode coating film on both sides after coating. Fig. 11 is a diagram showing a luminance image and a binary image of a negative electrode coating film on both sides after pressing. All of Figs. 8 to 11 are images in which the brightness of the sample has been multiplied by 15.

[0061] The battery electrode plate of a lithium-ion battery has many holes (cavities) formed so that the ionic liquid can penetrate into the coating film. The cavities have a complex structure and are continuous to the substrate. A part of the light incident on the surface of the coating film is reflected by the coating surface, and the rest enters the cavities. The light that enters the cavities is repeatedly reflected until it reaches the surface of the substrate, where it is reflected and exits the cavities again. Since the coated battery electrode plate has a thick film, the optical path length of the cavities is also long. This reduces the amount of light exiting the cavities, and the reflectance at the cavities is low. In addition, since the coated battery electrode plate has a large surface roughness, the amount of light reflected at the coating film surface is reduced, and the reflectance is low. Therefore, it is thought that the coated battery electrode plate has a high number of zeros.

[0062] In contrast, the pressed battery electrode plate has a thinner film thickness, so the optical path length in the cavity is shorter. This increases the amount of light emitted from the cavity, and the reflectance in the cavity increases. In addition, the pressed battery electrode plate has a smaller surface roughness, so the amount of light reflected by the coating film surface increases, and the reflectance increases. Therefore, it is thought that the pressed battery electrode plate has a smaller number of zeros.

[0063] The zero score in the binarized image of the positive electrode single-sided coating film after coating (before pressing) shown in FIG. 8 was 47,093. The zero score in the binarized image of the positive electrode single-sided coating film after pressing shown in FIG. 9 was 24,766. On the other hand, the zero score in the binarized image of the negative electrode double-sided coating film after coating (before pressing) shown in FIG. 10 was 22,324. The zero score in the binarized image of the negative electrode double-sided coating film after pressing shown in FIG. 11 was 1,397. From the above results, it was revealed that the zero score after pressing was significantly lower than the zero score after coating in both the positive and negative electrode coating films. Thus, the reflectance and the zero score are correlated with the film thickness. That is, if the film thickness is thick, the reflectance is low and the zero score is high. Also, if the film thickness is thin, the reflectance is high and the zero score is low. Next, the correlation between the reflectance and the zero score will be explained in more detail.

[0064] FIG. 12 is a diagram showing the correlation between the reflectance rφ(R,G,B)% and the zero point number after coating and pressing of the positive electrode one-sided coating film. The specified film thickness after coating was 65 μm, and the specified film thickness after pressing was 55 μm (reduction ratio 84.6%). The reflectance ratio after coating and after pressing was 1.2, and the zero point ratio after coating and after pressing was approximately 0.56. As shown in FIG. 12, the correlation R between the reflectance rφ(R,G,B)% and the zero point number after coating and pressing of the positive electrode one-sided coating film was 2 The average was 0.99 or more. Each plot point shown in Fig. 12 was measured offline (the same applies to Fig. 13 described later).

[0065] FIG. 13 is a diagram showing the correlation between the reflectance rφ(R,G,B)% and the zero point number after coating and pressing of the coating film on both sides of the negative electrode. The specified film thickness after coating was 110 μm, and the specified film thickness after pressing was 73 μm (reduction ratio 66.4%). The reflectance ratio after coating and after pressing was 1.7, and the zero point ratio after coating and after pressing was approximately 0.073. As shown in FIG. 13, the correlation R between the reflectance rφ(R,G,B)% and the zero point number after coating and pressing of the coating film on both sides of the negative electrode was 2 The average was 0.97 or higher. Thus, in both the positive electrode single-sided coating film and the negative electrode double-sided coating film, there is a high correlation between the reflectance and the zero point number, and these are important parameters in measuring the film thickness, density, and reflection color value.

[0066] Next, we will explain the approximate formulas obtained from the correlation between the reflectance of the coating film and the specified film thickness and the correlation between the reflectance of the coating film and the specified density, and the approximate formulas obtained from the correlation between the zero points of the coating film and the specified film thickness and the correlation between the zero points of the coating film and the specified density.

[0067] FIG. 14 is a diagram showing an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) of the positive electrode coating film and the designated film thickness T, and an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) and the designated density ρ. In FIG. 14 (and FIG. 15 described later), the designated film thickness T after coating is 65 μm (density 1.47 g / cm 3 ), the specified thickness T after pressing is 55 μm (density 1.73 g / cm3 ) Note that the approximation formula is calculated using the average value of two samples, so in FIG. 14 and FIGS. 15 to 17 described later, the correlation of the calibration curve is R 2 = 1.0. In this embodiment, an example will be described in which rφ(G), which has a high correlation with film thickness, is used as the average reflectance (see FIG. 12). However, depending on the object, rφ(R) or rφ(B) may have a higher correlation. Therefore, rφ(R) or rφ(B) may be used as the average reflectance instead of rφ(G), or the average value of rφ(R), rφ(G) and rφ(B) may be used.

[0068] The horizontal axis in FIG. 14 indicates the average reflectance rφ(G)%. The average reflectance rφ(G)% is the average value of rφ(G)% among the retroreflectances rφ(R,G,B) of all pixels (e.g., 250,000 points) included in the imaging area. On the vertical axis in FIG. 14, the scale on the left side indicates the specified film thickness T (μm), and the scale on the right side indicates the specified density ρ (g / cm 3 ) The designated film thickness T is a value obtained by measuring the thickness of the sample and subtracting the thickness of the substrate from the measured value. The designated density ρ is a value calculated by measuring the weight of the sample, subtracting the weight of the substrate from the measured value, and applying a conversion formula together with the measured value of the designated film thickness T.

[0069] In FIG. 14, an example of an approximation formula for the estimated film thickness Te obtained from the correlation between the average reflectance rφ(G) of the positive electrode coating film and the specified film thickness T is shown below. y=-45.746x+108.53 R 2 =1.0 (1) By using the approximation formula (1), the estimated film thickness Te of the positive electrode coating film can be calculated from the measured average reflectance rφ(G).

[0070] In FIG. 14, an example of an approximation formula for the estimated density ρe obtained from the correlation between the average reflectance rφ(G) of the positive electrode coating film and the specified density ρ is shown below. y=1.1894x+0.3382 R 2 =1.0 (2) By using the approximation formula (2), the estimated density ρe of the positive electrode coating film can be calculated from the measured average reflectance rφ(G).

[0071] FIG. 15 shows an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points and the specified film thickness T of the positive electrode coating film, and an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points and the specified density ρ. The horizontal axis of FIG. 15 is the number of zero points. On the vertical axis of FIG. 15, the scale on the left side indicates the specified film thickness T (μm), and the scale on the right side indicates the specified density ρ (g / cm 3 )

[0072] In FIG. 15, an example of an approximation formula for the estimated film thickness Te obtained from the correlation between the number of zero points of the positive electrode coating film and the specified film thickness T is shown below. y=0.000500x+42.107 R 2 =1.0 (3) By using the approximation formula (3), the estimated film thickness Te of the positive electrode coating film can be calculated from the number of measured zero points.

[0073] In FIG. 15, an example of an approximation formula of the estimated density ρe obtained from the correlation between the number of zero points of the positive electrode coating film and the specified density ρ is shown below. y=-0.0000130x+2.0652219 R 2 =1.0 (4) By using the approximation formula (3), the estimated density ρe of the positive electrode coating film can be calculated from the number of zero points measured.

[0074] FIG. 16 shows an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) of a negative electrode coating film and the specified film thickness T, and an example of a calibration curve of an approximation formula obtained from the correlation between the average reflectance rφ(G) and the specified density ρ. The horizontal axis of FIG. 16 indicates the average reflectance rφ(G) %. On the vertical axis of FIG. 16, the scale on the left side indicates the specified film thickness T (μm), and the scale on the right side indicates the specified density ρ (g / cm 3 In FIG. 16 (and FIG. 17 described later), the specified film thickness T after coating is 110 μm (density 1.45 g / cm 3 ), the specified thickness T after pressing is 73 μm (density 2.18 g / cm3 ).

[0075] In FIG. 16, an example of an approximation formula for the estimated film thickness Te obtained from the correlation between the average reflectance rφ(G) of the negative electrode coating film and the specified film thickness T is shown below. y=-41.605x+173.33 R 2 =1.0 (5) By using the approximation formula (5), the estimated film thickness Te of the negative electrode coating film can be calculated from the measured average reflectance rφ(G).

[0076] In FIG. 16, an example of an approximation formula for the estimated density ρe obtained from the correlation between the average reflectance rφ(G) of the negative electrode coating film and the specified density ρ is shown below. y=0.8208x+0.2004 R 2 =1.0 (6) By using the approximation formula (6), the estimated density ρe of the negative electrode coating film can be calculated from the measured average reflectance rφ(G).

[0077] FIG. 17 shows an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points and the specified film thickness T of a negative electrode coating film, and an example of a calibration curve of an approximation formula obtained from the correlation between the number of zero points and the specified density ρ. The horizontal axis in FIG. 17 is the number of zero points. On the vertical axis in FIG. 17, the scale on the left side indicates the specified film thickness T (μm), and the scale on the right side indicates the density ρ (g / cm 3 ) is shown.

[0078] In FIG. 17, an example of an approximation formula for the estimated film thickness Te obtained from the correlation between the number of zero points of the negative electrode coating film and the specified film thickness T is shown below. y=0.00157x+68.38062 R 2 =1.0 Equation (7) By using the approximation formula (7), the estimated film thickness Te of the negative electrode coating film can be calculated from the number of measured zero points.

[0079] In FIG. 17, an example of an approximation formula of the estimated density ρe obtained from the correlation between the number of zero points of the negative electrode coating film and the specified density ρ is shown below. y=-0.0000309x+2.2711392 R 2 =1.0 Equation (8) By using the approximation formula (8), the estimated density ρe of the negative electrode coating film can be calculated from the measured number of zero points.

[0080] Next, a specific example in which the estimated film thickness Te is calculated using an approximation formula based on reflectance rφ(R,G,B)% and an approximation formula based on the number of zero points will be described. The process of calculating the estimated film thickness Te using the approximation formula based on the number of zero points is executed by the film thickness calculation unit 34 (see FIG. 3). In this embodiment, for comparison with the process of calculating the estimated film thickness Te using the approximation formula based on the number of zero points, the film thickness calculation unit 34 executes a process of calculating the estimated film thickness Te using the approximation formula based on reflectance rφ(R,G,B)%.

[0081] FIG. 18 is a diagram showing the distribution of reflectance and zero points of each sample after coating and pressing of a positive electrode single-sided coating film. FIG. 19 is a diagram showing the distribution of estimated film thickness Te of each sample after coating and pressing of a positive electrode single-sided coating film. In FIG. 18 and FIG. 19, the numbers on the horizontal axis indicate the number of measurements (number of data) of the sample. Numbers 1 to 20 on the horizontal axis indicate the number of measurements after coating (designated film thickness 65 μm). Numbers 21 to 40 on the horizontal axis indicate the number of measurements after pressing (designated film thickness 55 μm).

[0082] On the vertical axis of Fig. 18, the scale on the left indicates the reflectance rφ(R,G,B)%, and the scale on the right indicates the zero points. In Fig. 18, white circles (◯) indicate plot points of zero points. White diamonds (◇) indicate plot points of R (red). White squares (□) indicate plot points of G (green). White triangles (△) indicate plot points of B (blue).

[0083] The vertical axis of Fig. 19 indicates the estimated film thickness Te (μm). In Fig. 19, the diamonds (◇) indicate plot points of the estimated film thickness Te calculated by approximation formula (1) using reflectance rφ(R,G,B)%. The white circles (◯) indicate plot points of the estimated film thickness Te calculated by approximation formula (3) using the number of zero points.

[0084] 19, when the estimated film thickness Te after coating was calculated using approximation formula (1) with reflectance rφ(R,G,B)%, the standard deviation σ for the specified film thickness T was 0.97 μm. On the other hand, when the estimated film thickness Te after coating was calculated using approximation formula (3) with zero points with measurements 1 to 20, the standard deviation σ for the specified film thickness T was 1.00 μm.

[0085] On the other hand, when the estimated film thickness Te after pressing was calculated using the approximation formula (1) with reflectance rφ(R,G,B)% for 21 to 40 measurements, the standard deviation σ for the specified film thickness T was 1.94 μm. Also, when the estimated film thickness Te after pressing was calculated using the approximation formula (3) with the number of zero points for 21 to 40 measurements, the standard deviation σ for the specified film thickness T was 1.42 μm.

[0086] Thus, for the positive electrode one-side coating film after pressing, the standard deviation σ of the estimated film thickness Te calculated using approximation formula (1) with reflectance rφ(R,G,B)% was 1.36 times larger than the standard deviation σ of the estimated film thickness Te calculated using approximation formula (3) with zero points. Therefore, when calculating the estimated film thickness Te of the positive electrode one-side coating film, it is considered more desirable to use approximation formula (3) with zero points rather than approximation formula (1) with reflectance rφ(R,G,B)%.

[0087] FIG. 20 is a diagram showing the distribution of reflectance and zero points of each sample after coating and pressing of a coating film on both sides of a negative electrode. FIG. 21 is a diagram showing the distribution of estimated film thickness Te of each sample after coating and pressing of a coating film on both sides of a negative electrode. In FIG. 20 and FIG. 21, the numbers on the horizontal axis indicate the number of measurements of the sample (number of data). Numbers 1 to 40 on the horizontal axis indicate the number of measurements after coating / before pressing (designated film thickness 110 μm). Numbers 41 to 80 on the horizontal axis indicate the number of measurements after pressing (designated film thickness 73 μm).

[0088] On the vertical axis of Fig. 20, the scale on the left side indicates reflectance rφ(R,G,B)%, and the scale on the right side indicates the number of zero points. The meaning of the plotted points in Fig. 20 is the same as in Fig. 18. The vertical axis of Fig. 21 indicates the estimated film thickness Te (μm), the same as in Fig. 19. The meaning of each plotted point in Fig. 21 is the same as in Fig. 19.

[0089] 21, when the estimated film thickness Te after coating was calculated using approximation formula (5) with reflectance rφ(R,G,B)% for measurements 1 to 40, the standard deviation σ of the estimated film thickness Te relative to the specified film thickness T was 1.23 μm. When the estimated film thickness Te after coating was calculated using approximation formula (7) with the number of zero points for measurements 1 to 40, the standard deviation σ of the estimated film thickness Te relative to the specified film thickness T was 2.59 μm.

[0090] 21, when the estimated film thickness Te after pressing was calculated using approximation formula (5) with reflectance rφ(R,G,B)%, the standard deviation σ of the estimated film thickness Te relative to the specified film thickness T was 4.42 μm. On the other hand, when the estimated film thickness Te after pressing was calculated using approximation formula (7) with the number of zero points with measurements of 41 to 80, the standard deviation σ of the estimated film thickness Te relative to the specified film thickness T was 0.86 μm.

[0091] Thus, for the negative electrode double-sided coating film after pressing, the standard deviation σ of the estimated film thickness Te calculated using approximation formula (5) with reflectance rφ(R,G,B)% was 5.14 times larger than the standard deviation σ of the estimated film thickness Te calculated using approximation formula (7) with zero points. Therefore, when calculating the estimated film thickness Te for the negative electrode double-sided coating film, it is considered more desirable to use approximation formula (7) with zero points rather than approximation formula (5) with reflectance rφ(R,G,B)%.

[0092] As shown in Figs. 20 and 21, for the positive electrode coating film and the negative electrode coating film, by calculating the estimated film thickness Te using the approximation formulas (3) and (7) obtained from the correlation between the zero points and the specified film thickness of the coating film, the film thickness of the coating film after coating and after pressing can be measured more accurately.

[0093] In the manufacture of secondary batteries, the uniformity of the battery material on the front and back surfaces of the battery electrode plate is also important. Therefore, it is necessary to measure not only the thickness of the coating film but also its density and reflection color value more accurately. In addition, in order to improve the yield, it is desirable to be able to measure these physical properties online. However, the conventional film measurement method described above has a problem in that the thickness, density, and reflection color value of the coating film formed on the front and back surfaces of the battery electrode plate cannot be measured more accurately and online. In the film measurement device 1 of the first embodiment, as described below, the density and reflection color value of the coating film formed on the front and back surfaces of the battery electrode plate can be measured more accurately and online.

[0094] Next, a specific example in which the estimated density ρe is calculated using an approximation formula based on the reflectance rφ(R,G,B)% and an approximation formula based on the number of zero points will be described. The process of calculating the estimated density ρe using the approximation formula based on the number of zero points is executed by the density calculation unit 35 (see FIG. 3). In this embodiment, for comparison with the process of calculating the estimated density ρe using the approximation formula based on the number of zero points, the density calculation unit 35 executes a process of calculating the estimated density ρe using the approximation formula based on the reflectance rφ(R,G,B)%.

[0095] FIG. 22 is a diagram showing the distribution of the estimated density ρe of each sample of the positive electrode single-sided coating film after coating and after pressing. In FIG. 22, the values ​​on the horizontal axis indicate the number of measurements (number of data) of the sample. Numbers 1 to 20 on the horizontal axis indicate the number of measurements (number of data) of the sample after coating (specified density 1.47 g / cm 3 ) are shown. The horizontal axis shows the number of measurements after pressing (specified density 1.73 g / cm 3 ) are shown.

[0096] The vertical axis of Fig. 22 is the estimated density ρe (g / cm 3) in Fig. 22. In Fig. 22, diamonds (◇) indicate plot points of estimated density ρe calculated by approximation formula (2) using reflectance rφ(R,G,B)%. White circles (◯) indicate plot points of estimated density ρe calculated by approximation formula (4) using the number of zero points. The same samples as those used to measure the film thickness were used for density measurement. Therefore, the distribution of reflectance and number of zero points of each sample after coating and pressing of the positive electrode single-sided coating film is the same as in Fig. 18 (not shown).

[0097] In the measurements 1 to 20 shown in FIG. 22, when the estimated density ρe after coating is calculated using the approximate formula (2) based on the reflectance rφ(R, G, B), the standard deviation σ for the specified density ρ is 0.025 g / cm 3 On the other hand, when the estimated density ρe after coating was calculated using the approximation formula (4) with the zero point number for the measurement numbers 1 to 20, the standard deviation σ for the specified density ρ was 0.026 g / cm 3 It became.

[0098] In addition, in the measurements of 21 to 40 shown in FIG. 22, when the estimated density ρe after pressing is calculated using the approximate formula (2) based on the reflectance rφ(R, G, B)%, the standard deviation σ for the specified density ρ is 0.050 g / cm 3 In addition, when the estimated density ρe after pressing was calculated using the approximation formula (4) with the zero point number for the measurement numbers 21 to 40, the standard deviation σ for the specified density ρ was 0.037 g / cm 3 It became.

[0099] Thus, in the positive electrode one-side coating film after pressing, the standard deviation σ of the estimated density ρe calculated by approximation formula (2) using the reflectance rφ(R,G,B)% was 1.35 times larger than the standard deviation σ of the estimated density ρe calculated by approximation formula (4) using the zero points. Therefore, when calculating the estimated density ρe of the positive electrode one-side coating film, it is considered more desirable to use approximation formula (4) using the zero points rather than approximation formula (2) using the reflectance rφ(R,G,B)%.

[0100] FIG. 23 is a diagram showing the distribution of the estimated density ρe of each sample after coating and pressing of the negative electrode double-sided coating film. In FIG. 23, the values ​​on the horizontal axis indicate the number of measurements (number of data) of the sample. Numbers 1 to 40 on the horizontal axis indicate the number of measurements (number of data) after coating (specified density 1.45 g / cm 3 The horizontal axis shows the number of measurements of the specimen after pressing (specified density 2.18 g / cm 3 The vertical axis of Fig. 23 shows the estimated density ρe (g / cm 3 ) The meaning of each plot point in Fig. 23 is the same as in Fig. 22. The same samples as those used to measure the film thickness were used for the density measurement. Therefore, the distribution of the reflectance and the number of zero points of each sample after coating and pressing of the negative electrode double-sided coating film is the same as that in Fig. 22 (not shown).

[0101] In the measurements 1 to 40 shown in FIG. 23, when the estimated density ρe after coating is calculated using the approximate formula (6) based on the reflectance rφ(R,G,B)%, the standard deviation σ of the estimated density ρe relative to the specified density ρ is 0.024 g / cm 3 On the other hand, when the estimated density ρe after coating is calculated using the approximation formula (8) with zero points, the standard deviation σ of the estimated density ρe relative to the specified density ρ is 0.051 g / cm 3 It became.

[0102] In addition, in the case of the measurement numbers 41 to 80 shown in FIG. 23, when the estimated density ρe after pressing is calculated by the approximation formula (6) using the reflectance rφ(R, G, B)%, the standard deviation σ of the estimated density ρe with respect to the specified density ρ is 0.088 g / cm 3 On the other hand, when the estimated density ρe after pressing was calculated using the approximation formula (8) with the zero point number for the measurement numbers 41 to 80, the standard deviation σ of the estimated density ρe relative to the specified density ρ was 0.017 g / cm 3 It became.

[0103] Thus, in the positive electrode coating film after coating, there is no significant difference between the standard deviation σ of the estimated density ρe calculated by the approximation formula (6) using the reflectance rφ(R,G,B)% and the standard deviation σ of the estimated density ρe calculated by the approximation formula (8) using the zero point number. However, in the positive electrode one-sided coating film after pressing, the standard deviation σ of the estimated density ρe calculated by the approximation formula (2) using the reflectance rφ(R,G,B)% is 1.35 times larger than the standard deviation σ of the estimated density ρe calculated by the approximation formula (4) using the zero point number. In addition, in the negative electrode coating film after pressing, the standard deviation σ of the estimated density ρe calculated by the approximation formula (6) using the reflectance rφ(R,G,B)% is 5.18 times larger than the standard deviation σ of the estimated density ρe calculated by the approximation formula (8) using the zero point number, resulting in a large difference. Therefore, when calculating the estimated density ρe of the positive electrode coating film and the negative electrode coating film using an approximation formula, it is considered more desirable to use the approximation formula (8) using zero points.

[0104] As shown in Figs. 22 and 23, for the positive electrode coating film and the negative electrode coating film, it is found that the densities of the coating film after coating and after pressing can be measured more accurately by calculating the estimated density ρe using an approximation formula obtained from the correlation between the zero points and the specified density of the coating film.

[0105] Next, a specific example in which the reflected color value Lab is calculated based on the reflectance rφ(R,G,B) % of the coating film in the color value calculation unit 36 ​​will be described. Fig. 24 is a diagram showing the distribution of reflection color values ​​Lab of each sample after coating and pressing of a positive electrode single-sided coating film. In Fig. 24, the values ​​on the horizontal axis indicate the number of measurements (number of data) of the sample. Numbers 1 to 20 on the horizontal axis indicate the number of measurements after coating (designated film thickness 65 µm). Numbers 21 to 40 on the horizontal axis indicate the number of measurements after pressing (designated film thickness 55 µm).

[0106] In the vertical axis of FIG. 24, the scale on the left indicates the lightness value L, and the scale on the right indicates the chromaticity values ​​a and b. The chromaticity value a represents the color intensity between green (-) and red (+). The chromaticity value b represents the color intensity between blue (-) and yellow (+). In FIG. 24, the diamonds (◇) indicate plot points of the lightness value L calculated based on the reflectance rφ(R,G,B)%. The white squares (□) indicate plot points of the chromaticity value a calculated based on the reflectance rφ(R,G,B)%. The white triangles (△) indicate plot points of the chromaticity value b calculated based on the reflectance rφ(R,G,B)%. The same samples as those used in the film thickness and density measurements were used to measure the color values.

[0107] An example of a conversion formula for calculating the reflection color value Lab of a coating film using the reflectance rφ(R,G,B)% is shown below. Note that the XYZ components of the standard light source D65 are X(R) 10 =94.811, Y(G) 10 =100.00, Z(B) 10 =107.333.

[0108] L = 116 × (rφ(G) / 100.00) 1 / 3 -16 Formula (9) a = 500 × [{rφ(R) / R 10} 1 / 3 -(rφ(G) / G 10 ) 1 / 3 ] Formula (10) b = 200 × [{rφ(G) / G 10} 1 / 3 -(rφ(B) / B 10 ) 1 / 3 ] Formula (11)

[0109] The reflection color value Lab of the positive electrode one-side coating film after coating and pressing can be calculated by using the above formulas (9) to (11) and the reflectance rφ(R,G,B)% used in measuring the film thickness, etc. When the reflectance values ​​rφ(R), rφ(G), and rφ(B) are small, for example, when they correspond to any of the following formulas (12) to (14), the calculation is performed using the corresponding formulas (15) to (17) below.

[0110] 0.008856≧(rφ(R)=94.811) rφ(R) * =7.787×rφ(R) / 94.811+16.0 / 116.0 Formula (12) 0.008856≧(rφ(G)=100.0) rφ(G) * =7.787×rφ(G) / 100.0+16.0 / 116.0 Formula (13) 0.008856≧(rφ(B)=107.3) rφ(B) * =7.787×rφ(B) / 107.3+16.0 / 116.0 Formula (14)

[0111] L = 116 × (rφ(G) * )-16 Equation (15) a = 500 × (rφ(R) * -rφ(G) * ) Formula (16) b = 200 × (rφ(G) * -rφ(B) * ) Formula (17)

[0112] As shown in Figure 24, it can be seen that the lightness value L is greater in the 21-40 measurements after pressing than in the 1-20 measurements after coating. It can also be seen that the distribution position of the chromaticity values ​​a and b changes between the 1-20 measurements after coating and the 21-40 measurements after pressing. For the positive electrode single-sided coating film, the reflected color value Lab calculated after coating and after pressing linearly indicates the change in physical properties that occurs in the positive electrode single-sided coating film (coating material) after coating and after pressing.

[0113] FIG. 25 is a diagram showing the distribution of reflection color values ​​Lab of each sample after coating and pressing of the negative electrode double-sided coating film. In FIG. 25, the values ​​on the horizontal axis indicate the number of measurements (number of data) of the sample. Numbers 1 to 40 on the horizontal axis indicate the number of measurements after coating (designated film thickness 110 μm). Numbers 41 to 80 on the horizontal axis indicate the number of measurements after pressing (designated film thickness 73 μm). The vertical axis and the items of each plot point in FIG. 25 are the same as those in FIG. 24.

[0114] As shown in Figure 25, the lightness value L was greater in the measurement numbers 41 to 80 after pressing than in the measurement numbers 1 to 40 after coating. It can also be seen that the distribution positions of the chromaticity values ​​a and b change between the measurement numbers 1 to 40 after coating and the measurement numbers 41 to 80 after pressing. In the case of the double-sided negative electrode coating film as well, the reflected color value Lab calculated after coating and after pressing linearly indicates the change in physical properties that occurred in the double-sided negative electrode coating film (coating material) after coating and after pressing.

[0115] As shown in Figs. 24 and 25, for the positive electrode single-sided coating film and the negative electrode double-sided coating film, the reflection color value Lab can be calculated by using the reflectance rφ(R,G,B)% and the conversion formula. By calculating the reflection color value Lab, one color can be specified. Then, by calculating the color difference value Δ(L,a,b,E), which is the difference between this reflection color value Lab and the reflection color value of the reference film thickness (hereinafter also referred to as the "reference reflection color value"), the change in film thickness and density after coating and after pressing can be detected. In addition, by calculating the color difference value Δ(L,a,b,E), it can be determined, for example, whether the degree of mixing of the coating material is uniform in the width direction of the electrode sheet.

[0116] In online measurement, the color difference value Δ(L, a, b, E) in the width direction of the electrode sheet or the running direction of the line can be calculated by the following formula using the reference reflection color value (L0, a0, b0) and the reflection color value Lab. ΔE in formula (21) is the total color difference calculated from ΔL, Δa, and Δb, and represents the distance between the reference value and the sample value in the color space.

[0117] ΔL=L-L0 formula (18) Δa=a-a0 (19) Δb=b-b0 formula (20) ΔE=√(ΔL 2 +Δa 2 +Δb 2 ) Formula (21)

[0118] As described above, according to the film measuring device 1 of the first embodiment, the reflection color value Lab can be calculated based on the reflectance rφ(R,G,B)% of the positive electrode coating film and the negative electrode coating film. In addition, the color difference value Δ(L,a,b,E) can be calculated using the reference reflection color value (L0,a0,b0) and the reflection color value Lab. Therefore, in online measurement, by calculating the color difference value Δ(L,a,b,E) in the width direction of the electrode sheet or the running direction of the line, it is possible to determine in real time whether the degree of mixing of the coating material is uniform. This is expected to improve the yield in the coating process and the pressing process.

[0119] If the surface of aluminum or copper, which is the base material of the battery electrode plate, oxidizes, its performance as an electrode decreases. Whether the base material has been oxidized or not can be determined by measuring the reflectance of the uncoated part of the electrode plate, which is not coated with the electrode material. Since the uncoated part of the base material has a higher reflectance than the coated part, the shutter for capturing the base material in the imaging unit 2 (see Figure 1) is set to capture the reflectance of the uncoated part. The exposure time for imaging the substrate and the exposure time for imaging the coating film are set, respectively. Then, imaging is performed using a black body calibration plate (described later) corresponding to both exposure times, so that the reflectance of the substrate and the reflectance of the coating film can be measured simultaneously or alternately. In this case, the reflected color value can also be measured at the same time, so that not only the presence or absence of oxidation of the substrate but also abnormalities in the substrate can be detected.

[0120] Next, as a second embodiment, an embodiment in which the imaging unit 2 is used as a line sensor camera will be described. In lithium-ion batteries, the substrate constituting the electrodes is not limited to being strip-shaped, but may also be cylindrical. When a coating film formed on such a cylindrical substrate is imaged with a measurement area of ​​500 x 500 pixels, the image becomes blurred due to the difference in measurement distance between the upper and lower sides in the circumferential direction. In order to image such a cylindrical coating film more accurately, we propose a method of using the imaging unit 2 as a line sensor camera.

[0121] In the film measuring device 1 of the second embodiment, the imaging area of ​​the imaging unit 2 is set to 2000×50 pixels, and the imaging unit 2 is used as a line sensor camera. As in the first embodiment, an image sensor having, for example, 2048×1536 pixels (RGB) can be used as the imaging unit 2. When the imaging area is set to 2000×50 pixels, the measurement area on the sample is 16 mm×0.4 mm (1 pixel=8 μm square). Here, the 2000×50 pixels are divided into 40 segments (50×50 pixels, 0.5 mm pitch) in the horizontal direction X of the sample and measured. The measurement area of ​​the image sensor having 2048×1536 pixels can be used as 2000×50 pixels by, for example, changing the image processing program executed in the imaging control unit 31 (see FIG. 3).

[0122] Next, the luminance image and the binary image of the coating film captured by the film measurement device 1 of the second embodiment will be described with reference to Figs. 26 to 29. In Figs. 26 to 29, the upper images show luminance images of reflectance rφ(R,G,B)% obtained from an image (gradation data) of an electrode sheet produced as a sample. The lower images show binary images calculated from the luminance images.

[0123] Fig. 26 is a diagram showing a luminance image and a binary image of the center of a positive electrode single-sided coating film. Fig. 27 is a diagram showing a luminance image and a binary image of an end of a positive electrode single-sided coating film. Fig. 28 is a diagram showing a luminance image and a binary image of the back surface of a negative electrode double-sided coating film. Fig. 29 is a diagram showing a luminance image and a binary image of the front surface of a negative electrode double-sided coating film.

[0124] As shown in Figures 26 and 27, it can be seen that there is little difference between the brightness image and the binary image at the center and the edge of the positive electrode single-sided coating film after coating. Similarly, as shown in Figures 28 and 29, it can be seen that there is little difference between the brightness image and the binary image at the back and front of the negative electrode double-sided coating film after coating.

[0125] In this way, it can be seen that by reducing the number of scanning pixels in the vertical direction Y from 500 to 50, there is almost no image blurring when capturing images online while scanning one film measuring device 1 in the horizontal direction X. Furthermore, by reducing the number of scanning pixels in the vertical direction Y from 500 to 50, the image capturing cycle can be shortened, making it possible to perform measurements while moving the film measuring device 1 at high speed.

[0126] Next, a specific example will be described in which the estimated film thickness Te is calculated using an approximation formula based on reflectance rφ(R,G,B)% and an approximation formula based on zero points in the film measuring device 1 (2000×50 pixels) of the second embodiment. In the second embodiment, for comparison with the process of calculating the estimated film thickness Te using the approximation formula based on zero points, the film thickness calculation unit 34 also executes a process of calculating the estimated film thickness Te using the approximation formula based on reflectance rφ(R,G,B)%.

[0127] FIG. 30 is a diagram showing the distribution of reflectance and the number of zero points at the center and end of each sample of a positive electrode single-sided coating film. FIG. 31 is a diagram showing the distribution of estimated film thickness Te at the center and end of each sample of a positive electrode single-sided coating film. In FIG. 30 and FIG. 31, the values ​​on the horizontal axis indicate the number of measurements of the sample (number of data). 1 to 50 on the horizontal axis indicate the number of measurements of the sample in which the center was measured. 51 to 100 on the horizontal axis indicate the number of measurements of the sample in which the end was measured. The designated film thickness T is 65 μm. The calibration curve of the approximation formula for calculating the film thickness is the same as that of the first embodiment (500×500 pixels).

[0128] The scale on the left side of Figure 30 indicates the reflectance rφ(R,G,B)%, and the scale on the right side indicates the zero points. In Figure 30, white circles (◯) indicate plot points of zero points. White diamonds (◇) indicate plot points of R (red). White squares (□) indicate plot points of G (green). White triangles (△) indicate plot points of B (blue).

[0129] The vertical axis of Fig. 31 indicates the estimated film thickness Te (μm). In Fig. 31, the diamonds (◇) indicate plot points of the estimated film thickness Te calculated by approximation formula (1) using reflectance rφ(R,G,B)%. The white circles (◯) indicate plot points of the estimated film thickness Te calculated by approximation formula (3) using the number of zero points.

[0130] 31, when the estimated film thickness Te after coating of the positive electrode was calculated using approximate formula (1) with reflectance rφ(R,G,B)% for measurements 1 to 50 (center), the standard deviation σ for the specified film thickness T was 1.50 μm. On the other hand, when the estimated film thickness Te after coating was calculated using approximate formula (3) with the number of zero points for measurements 1 to 50, the standard deviation σ for the specified film thickness T was 0.70 μm.

[0131] In addition, when the estimated film thickness Te after coating the positive electrode was calculated using approximate formula (1) with reflectance rφ(R,G,B)% for 51 to 100 measurements (ends), the standard deviation σ for the specified film thickness T was 1.0 μm. On the other hand, when the estimated film thickness Te after coating the positive electrode was calculated using approximate formula (3) with zero points for 51 to 100 measurements, the standard deviation σ for the specified film thickness T was 0.44 μm.

[0132] As described above, in the second embodiment in which the imaging area is set to 2000 × 50 pixels, the estimated film thickness Te of the positive electrode coating film calculated by the approximation formula (3) using the number of zero points has a smaller difference from the specified film thickness T than the estimated film thickness Te calculated by the approximation formula (1) using the reflectance rφ(R, G, B) %.

[0133] FIG. 32 is a diagram showing the distribution of reflectance and the number of zero points on the back surface and the center of the front surface of each sample of a double-sided negative electrode coating film. FIG. 33 is a diagram showing the distribution of the estimated film thickness Te on the back surface and the center of the front surface of each sample of a double-sided negative electrode coating film. In FIG. 32 and FIG. 33, 1 to 50 on the horizontal axis indicate the number of samples measured on the back surface. 51 to 100 on the horizontal axis indicate the number of samples measured on the center of the front surface. The specified film thickness T is 110 μm. The calibration curve of the approximation formula for calculating the film thickness is the same as that of the first embodiment (500 × 500 pixels).

[0134] 33, when the estimated film thickness Te after coating the negative electrode was calculated using approximation formula (5) with reflectance rφ(R,G,B)% for measurements 1 to 50 (reverse side), the standard deviation σ for the specified film thickness T was 1.50 μm. On the other hand, when the estimated film thickness Te after coating the negative electrode was calculated using approximation formula (7) with the number of zero points for measurements 1 to 50, the standard deviation σ for the specified film thickness T was 1.1 μm.

[0135] In addition, when the estimated film thickness Te after coating the negative electrode was calculated using approximate formula (5) with reflectance rφ(R,G,B)% for 51 to 100 measurements (center of the surface), the standard deviation σ for the specified film thickness T was 2.2 μm. On the other hand, when the estimated film thickness Te after coating the negative electrode was calculated using approximate formula (7) with zero points for 51 to 100 measurements, the standard deviation σ for the specified film thickness T was 1.8 μm.

[0136] As described above, in the second embodiment in which the imaging area is set to 2000 × 50 pixels, the estimated film thickness Te of the negative electrode coating film calculated by the approximation formula (3) using the number of zero points has a smaller difference from the specified film thickness T than the estimated film thickness Te calculated by the approximation formula (1) using the reflectance rφ(R, G, B) %.

[0137] Next, a specific example will be described in which the estimated density ρe is calculated using an approximation formula based on reflectance rφ(R,G,B)% and an approximation formula based on zero points in the film measuring device 1 (2000×50 pixels) of the second embodiment. In the second embodiment, for comparison with the process of calculating the estimated density ρe using an approximation formula based on zero points, the density calculation unit 35 also executes a process of calculating the estimated density ρe using an approximation formula based on reflectance rφ(R,G,B)%.

[0138] Fig. 34 is a diagram showing the distribution of the estimated density ρe at the center and edge of each sample of the positive electrode single-sided coating film. In Fig. 34, the horizontal axis is the number of samples measured, as in Fig. 31. The vertical axis in Fig. 34 is the estimated density ρe (g / cm 3 ) in Fig. 34. In Fig. 34, diamonds (◇) indicate plot points of estimated density ρe calculated by approximation formula (2) using reflectance rφ(R,G,B)%. White circles (◯) indicate plot points of estimated density ρe calculated by approximation formula (4) using the number of zero points. The same samples as those used in measuring the film thickness are used in measuring the density. Therefore, the distribution of reflectance and number of zero points of each sample at the center and end of the positive electrode single-sided coating film is the same as that in Fig. 30 of the second embodiment (not shown). The calibration curve of the approximation formula for calculating density is the same as that of the first embodiment (500 x 500 pixels).

[0139] As shown in FIG. 34, when the estimated density ρe of the central part is calculated by the approximation formula (2) using the reflectance rφ(R, G, B) for the number of measurements 1 to 50, the standard deviation σ for the specified density ρ is 0.045 g / cm 3 On the other hand, when the estimated density ρe of the central part is calculated by the approximation formula (4) using the zero point number for the measurement numbers 1 to 50, the standard deviation σ for the specified density ρ is 0.018 g / cm 3 It became.

[0140] In addition, as shown in FIG. 34, when the estimated density ρe of the end portion is calculated by the approximation formula (2) using the reflectance rφ(R,G,B)% for the number of measurements 51 to 100, the standard deviation σ for the specified density ρ is 0.26 g / cm 3In addition, when the estimated density ρe of the end portion was calculated using the approximation formula (4) with the number of zero points for the measurement numbers 51 to 100, the standard deviation σ for the specified density ρ was 0.013 g / cm 3 It became.

[0141] As described above, in the second embodiment in which the imaging area is set to 2000 × 50 pixels, it can be seen that the estimated density ρe of the positive electrode coating film calculated by the approximation formula (4) using the zero point number has a smaller difference from the specified density ρ than the estimated density ρe calculated by the approximation formula (2) using the reflectance rφ(R, G, B) %.

[0142] Fig. 35 is a diagram showing the distribution of the estimated density ρe at the back surface and the center of the front surface of each sample of the negative electrode double-sided coating film. In Fig. 35, the horizontal axis is the number of samples measured, just like Fig. 34. The vertical axis in Fig. 35 is the estimated density ρe (g / cm 3 ) is shown. The same samples as those used in measuring the film thickness are used in measuring the density. Therefore, the distribution of the reflectance and the number of zero points of each sample on the back surface and the center of the front surface of the negative electrode double-sided coating film is the same as that in FIG. 32 of the second embodiment (not shown). The calibration curve of the approximation formula for calculating the density is the same as that of the first embodiment (500 × 500 pixels).

[0143] In the measurements 1 to 50 shown in FIG. 35, when the estimated density ρe of the back surface is calculated using the approximate formula (6) based on the reflectance rφ(R, G, B), the standard deviation σ for the specified density ρ is 0.021 g / cm 3 On the other hand, when the estimated density ρe of the back surface is calculated using the approximation formula (8) with the zero point number for the measurement numbers 1 to 50, the standard deviation σ for the specified density ρ is 0.029 g / cm 3 It became.

[0144] In addition, when the estimated density ρe at the center of the surface is calculated using the approximate formula (6) based on the reflectance rφ(R, G, B) in the measurement numbers 51 to 100 shown in FIG. 35, the standard deviation σ for the specified density ρ is 0.035 g / cm 3On the other hand, when the estimated density ρe at the center of the surface was calculated using the approximation formula (8) with the zero point number for the measurement numbers 51 to 100, the standard deviation σ for the specified density ρ was 0.042 g / cm 3 It became.

[0145] Next, a specific example will be described in which the reflection color value Lab is calculated based on the reflectance rφ(R,G,B)% of a coating film in the film measurement device 1 (2000×50 pixels) of the second embodiment. Fig. 36 is a diagram showing the distribution of reflection color values ​​Lab of the center and edge of each sample of a positive electrode single-side coating film. In Fig. 36, the numbers on the horizontal axis indicate the number of measurements of the sample (number of data). 1 to 50 on the horizontal axis indicate the number of measurements of the sample where the center was measured. 51 to 100 on the horizontal axis indicate the number of measurements of the sample where the edge was measured.

[0146] On the vertical axis of Fig. 36, the scale on the left indicates lightness value L, and the scale on the right indicates chromaticity values ​​a and b. In Fig. 36, diamonds (◇) indicate plot points of lightness value L calculated based on reflectance rφ(R,G,B)%. White squares (□) indicate plot points of chromaticity value a calculated based on reflectance rφ(R,G,B)%. White triangles (△) indicate plot points of chromaticity value b calculated based on reflectance rφ(R,G,B)%.

[0147] In measuring the color value of the coating film on one side of the positive electrode, the same samples as those used in the measurements of film thickness and density described above are used. Therefore, the distribution of the reflectance and zero points of each sample at the center and end of the coating film on one side of the positive electrode is the same as that in FIG. 30 of the first embodiment (not shown). In addition, the conversion formula for calculating the reflection color value Lab of the coating film using the reflectance rφ(R,G,B)% is the same as that in the first embodiment.

[0148] Fig. 37 is a diagram showing the distribution of color difference values ​​Δ(L, a, b, E) between the center and end portions of each sample of the positive electrode single-sided coating film. As shown in Fig. 37, it can be seen that the color difference value ΔE, which is the total color difference, is small, on average 1 or less, at the center and end portions of each sample of the positive electrode single-sided coating film.

[0149] Fig. 38 is a diagram showing the distribution of the reflection color value Lab of the back surface and the center of the front surface of the negative electrode double-sided coating film. In Fig. 38, the horizontal axis is the number of samples measured, as in Fig. 36. The vertical axis and the plot points in Fig. 38 have the same meaning as in Fig. 36.

[0150] In measuring the color value of the coating film on both sides of the negative electrode, the same samples as those used in the measurements of thickness and density described above are used. Therefore, the distribution of the reflectance and zero points of each sample on the back surface and the center of the front surface of the coating film on both sides of the negative electrode is the same as that shown in Fig. 32 (not shown). In addition, the conversion formula for calculating the reflection color value Lab of the coating film using the reflectance rφ(R,G,B)% is the same as that in the first embodiment.

[0151] Fig. 39 is a diagram showing the distribution of color difference values ​​Δ(L, a, b, E) between the back surface and the center of the front surface of each sample of the negative electrode double-sided coating film. As shown in Fig. 39, it can be seen that the color difference value ΔE, which is the total color difference, is small, on average 1 or less, between the back surface and the center of the front surface of each sample of the negative electrode double-sided coating film.

[0152] In this way, in the second embodiment where the imaging area is set to 2000 x 50 pixels, the reflection color value Lab calculated after coating linearly indicates the change in physical properties that occurs in the coating film on one side of the positive electrode and the coating film on both sides of the negative electrode (coating material) after coating. Therefore, in online measurement, by calculating the color difference value Δ(L, a, b, E) of the coating film, it is possible to judge in real time whether the degree of mixing of the coating material is uniform.

[0153] In an embodiment in which the imaging unit 2 is used as a line sensor camera, a method of performing calibration measurement on an imaging area of ​​2000×50 pixels may be, for example, a method using the following equation (22). Calibration calculation brightness value = CW-CB Equation (22) In formula (22), CW is the luminance value measured with a reflective calibration plate set at the measurement position, and CB is the luminance value measured with a blackbody calibration plate set at the measurement position.

[0154] The distribution of luminance values ​​calculated using the above formula (22) is shown in FIG. 40. FIG. 40 is a diagram showing the distribution of calibration calculation luminance values ​​in imaging areas of 500×500 pixels and 2000×50 pixels. The vertical axis of FIG. 40 indicates a value (hereinafter also referred to as a "count number") expressed as a luminance value in 12 bits (0 to 4095). The horizontal axis indicates 200 pixels (number of pixels) obtained by compressing 2000 pixels in the horizontal direction X to 1 / 10. The luminance value is calculated as the average value for every 10 pixels.

[0155] As shown in FIG. 40, when the imaging area is set to the central 500×500 pixels, it can be seen that the luminance change in the horizontal direction X for all of RGB is small. Also, when the imaging area is set to 2000×50 pixels, it can be seen that the luminance change in the horizontal direction X for all of RGB is small. In this way, by calculating the calibration calculation luminance value using the above formula (22), it is possible to reduce the luminance change in the horizontal direction X. Therefore, it is possible to measure a more accurate luminance value not only when the imaging area is set to 500×500 pixels, but also when it is set to 2000×50 pixels.

[0156] When the film measurement device 1 of this embodiment is applied to a coating system 100 shown in FIG. 5 or a press system 200 shown in FIG. 7 (reference), it is desirable to place a blackbody calibration plate and a reflective calibration plate on one or both sides of the electrode sheet in the width direction X and calibrate the luminance value at regular intervals.

[0157] Although the embodiment of the film measuring device and the film measuring method according to the present invention have been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications and changes are possible, such as the modified forms described below, which are also included in the technical scope of the present invention. Furthermore, the effects described in the embodiment are merely a list of the most preferable effects resulting from the present invention, and are not limited to those described in the embodiment. Note that the above-mentioned embodiment and the modified forms described below can be used in appropriate combination, but detailed description will be omitted.

[0158] (Variations) In the first embodiment, an example has been described in which the imaging area of ​​the imaging unit 2 is 500 (X) x 500 (Y) pixels, but this is not limiting. The imaging area may be, for example, 550 x 550 pixels or 450 x 450 pixels. By reducing the number of pixels in the Y direction, the image capture time is shortened, making it possible to perform measurement in a short cycle.

[0159] In the second embodiment in which the imaging unit 2 is used as a line sensor camera, the imaging area is not limited to 2000 × 50 pixels, and may be set to, for example, 2000 × 25 pixels. Although it is preferable to have a large number of data points for the reflectance rφ and the number of zero points, the number of pixels that allows stable measurement may be set according to the specifications, characteristics, etc. of the camera to be used for imaging.

[0160] In the film measurement apparatus 1 of the first and second embodiments, the imaging unit 2 may be disposed so that the optical axis OA1 (see FIG. 1) is perpendicular to the perpendicular line PL of the measurement object S, and the light reflected from the surface of the measurement object S may be directly incident on the imaging unit 2. In this manner, the film measurement apparatus 1 of the first and second embodiments may be configured without using the retroreflector 7.

[0161] In the film measurement device 1 of the first and second embodiments, the data processing device 8 (see FIG. 1) may be connected to the imaging unit 2 and the light source 3 via a network. Examples of the network include the Internet, a LAN (Local Area Network), and a VPN (Virtual Private Network). In the film measurement device 1, the processing of the data processing device 8 may be performed locally or remotely. [Explanation of symbols]

[0162] 1 Membrane measuring device 2. Imaging unit 3 light source 4 Optics Department 5 Telecentric Lenses 6 Beam splitter 7 Retroreflector 8 Data Processing Device 11 CPU 18 Storage section 31 Imaging control section 32 Light source control unit 33 Data Calculation Section 34 Film thickness calculation section 35 Density calculation section 36 Color value calculation section 41 Image DB 42 Approximate formula DB

Claims

1. an imaging unit that captures an image of the coating film and obtains gradation data for each pixel; A light source; an optical unit that irradiates the coating film with light output from the light source and causes reflected light from the coating film to be incident on the imaging unit; A data calculation unit that calculates a retroreflectance for each pixel in an imaging area and a zero point number at which the retroreflectance is less than a set value based on the image captured by the imaging unit; a thickness calculation unit that calculates an estimated thickness of the coating film from the zero point number by using an approximation formula obtained from the correlation between the zero point number and a specified thickness of the coating film; A film measurement device comprising:

2. a density calculation unit that calculates an estimated density of the coating film from the zero point number by using an approximation formula obtained from a correlation between the zero point number and a specified density of the coating film; The film measuring device according to claim 1 .

3. A color value calculation unit is provided that calculates a reflection color value of the coating film by using the retroreflectance and a conversion formula. The film measuring device according to claim 1 .

4. A retroreflector that retroreflects light reflected by the coating film, The optical unit irradiates the coating film with light output from the light source, causes the reflected light from the coating film to enter the retroreflector, and causes the light reflected by the retroreflector and then reflected again by the coating film to enter the imaging unit as the reflected light. The film measuring device according to claim 1 .

5. A film measurement method for measuring a film thickness of a coating film, comprising the steps of: irradiating the coating film with light output from a light source; capturing an image formed by light reflected from the coating film to obtain gradation data for each pixel; Calculating the retroreflectance and the number of zero points for each pixel in an imaging area based on the captured image; calculating an estimated thickness of the coating film from the zero points using an approximation formula obtained from a correlation between the zero points and a designated thickness of the coating film; A membrane measurement method comprising:

6. Calculating an estimated density of the coating film from the zero points by using an approximation formula obtained from a correlation between the zero points and a specified density of the coating film. The film measuring method according to claim 5 .

7. Calculating a reflection color value of the coating film based on the retroreflectance, The film measuring method according to claim 5 .

Images