Film measurement device and film measurement method

Abstract

The present invention addresses the problem of providing a film measurement device capable of more accurately measuring the film thickness of a coating film.　A film measurement device 1 comprises: an imaging unit 2 that captures an image of a coating film and acquires gradation data for each pixel; a light source 3; an optical unit 4 that shines light output from the light source 3 onto the coating film and causes reflected light from the coating film to enter the imaging unit; a data calculating unit that, on the basis of the image captured by the imaging unit 2, calculates the coefficient of retroreflection of each pixel in the imaging region and the number of zero points at which the coefficient of retroreflection is less than a set value; and a film thickness calculating unit that calculates an estimated film thickness of the coating film from the number of zero points, using an approximation formula obtained from a correlation between the number of zero points and a specified film thickness of the coating film. The abovementioned problem is thus resolved.

Description

Film measurement device and film measurement method

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

[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 a battery material coated on a substrate, thereby calculating the film thickness of the battery electrode plate. As a method for measuring the film thickness of electrodes coated on both sides of a battery electrode plate, a thickness measurement system is known in which two radiation film thickness meters are used to scan the front and back surfaces of the battery electrode plate, thereby calculating the film thickness of the battery electrode plate (see Non-Patent Document 1).

[0003] Furthermore, 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, thereby removing the reflected luminance inside the optical system from the image data of the film (see Patent Document 1).

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

[0005] Patent No. 5318303

[0006] In the electrode manufacturing process for secondary batteries, 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. Furthermore, 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] During the pressing process, both ends of the coating film are sometimes measured manually with a micrometer. However, it is difficult to measure the center of the roll on which the coating film is formed using a micrometer. Other methods include placing two optical distance meters on the front and back sides of the coating film and calculating the change in distance, or measuring film thickness fluctuations on the roll using 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 or other material is flat and opaque, a laser rangefinder 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 and measure the film thickness. However, this method is susceptible to the effects of roll eccentricity, fluttering of the electrode plate, and surface roughness, and has not yet been put to practical use. Even with this method, it is difficult to separately measure the film thickness on the front and back surfaces of a battery electrode plate. Furthermore, the application of capacitance-type rangefinders and eddy-current-type rangefinders has also been considered, but these have not yet been put to practical use.

[0009] The present invention aims 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.

[0010] A film measurement device according to one embodiment of the present invention comprises an imaging unit that captures an image of a coating film and acquires 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 enter the imaging unit; a data calculation unit that calculates, based on the image captured by the imaging unit, the retroreflectivity for each pixel in the imaging area and a zero point number at which the retroreflectivity is less than a set value; 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 the coating film with light output from a light source, capturing an image formed by the light reflected from the coating film to obtain gradation data for each pixel, calculating the retroreflectivity and zero point number for each pixel in the captured image 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.

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

[0013] 1 is a configuration diagram of a film measurement device 1 according to a first embodiment. FIG. 2 is a block diagram showing an example of the hardware configuration of a data processing device 8. FIG. 3 is a block diagram showing an example of the functional configuration of the data processing device 8. FIG. 4 is a flowchart showing the processing steps for calculating the number of zero points included in an imaging area. FIG. 5 is a side view showing the arrangement of a film measurement unit in a coating system 100. FIG. 6 is a perspective view showing the arrangement of a film measurement unit in a coating system 100. FIG. 7 is a side view showing the arrangement of a film measurement unit in a press system 200. FIG. 8 is a diagram showing a luminance image and a binarized image of a positive electrode single-side coating film after coating. FIG. 9 is a diagram showing a luminance image and a binarized image of a positive electrode single-side coating film after pressing. FIG. 10 is a diagram showing a luminance image and a binarized image of a negative electrode double-side coating film after coating. FIG. 11 is a diagram showing a luminance image and a binarized image of a negative electrode double-side coating film after pressing. FIG. 12 is a diagram showing the correlation between the reflectance rφ(R, G, B)% and the number of zero points of a positive electrode single-side coating film after coating and after pressing. FIG. 13 is a diagram showing the correlation between the reflectance rφ(R, G, B)% and the number of zero points of a negative electrode double-side coating film after coating and after pressing. 1 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 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. FIG. 2 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 the 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 the specified density ρ. FIG. 3 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 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. FIG. 4 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 the 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 the specified density ρ. FIG. 5 is a diagram showing the distribution of reflectance and the number of zero points of each sample of a positive electrode single-side coating film after coating and after pressing. 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. FIG. 2 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. FIG. 3 is a diagram showing the distribution of reflectance and zero points of each sample of a negative electrode double-side coating film after coating and after pressing. FIG. 4 is a diagram showing the distribution of estimated film thickness Te of each sample of a negative electrode double-side coating film after coating and after pressing.1 is a diagram showing the distribution of estimated density ρe of each sample of a positive electrode single-side coating film after coating and after pressing. FIG. 2 is a diagram showing the distribution of estimated density ρe of each sample of a negative electrode double-side coating film after coating and after pressing. FIG. 3 is a diagram showing the distribution of reflected color values ​​Lab of each sample of a positive electrode single-side coating film after coating and after pressing. FIG. 4 is a diagram showing the distribution of reflected color values ​​Lab of each sample of a negative electrode double-side coating film after coating and after pressing. FIG. 5 is a diagram showing a luminance image and a binarized image of the center of a positive electrode single-side coating film. FIG. 6 is a diagram showing a luminance image and a binarized image of the edge of a positive electrode single-side coating film. FIG. 7 is a diagram showing a luminance image and a binarized image of the back surface of a negative electrode double-side coating film. FIG. 8 is a diagram showing the distribution of reflectance and the number of zero points at the center and edge of each sample of a positive electrode single-side coating film. FIG. 9 is a diagram showing the distribution of estimated film thickness Te at the center and edge of each sample of a positive electrode single-side coating film. 1 is a diagram showing the distribution of reflectance and the number of zero points at the back surface and the central portion of the surface of each sample of a negative electrode double-sided coating film. FIG. 2 is a diagram showing the distribution of estimated film thickness Te at the back surface and the central portion of the surface of each sample of a negative electrode double-sided coating film. FIG. 3 is a diagram showing the distribution of estimated density ρe at the central portion and edge portion of each sample of a positive electrode single-sided coating film. FIG. 4 is a diagram showing the distribution of estimated density ρe at the back surface and the central portion of the surface of each sample of a negative electrode double-sided coating film. FIG. 5 is a diagram showing the distribution of reflected color values ​​Lab at the central portion and edge portion of each sample of a positive electrode single-sided coating film. FIG. 6 is a diagram showing the distribution of color difference values ​​Δ(L, a, b, E) at the central portion and edge portion of each sample of a positive electrode single-sided coating film. FIG. 7 is a diagram showing the distribution of reflected color values ​​Lab at the back surface and the central portion of the surface of a negative electrode double-sided coating film. FIG. 8 is a diagram showing the distribution of color difference values ​​Δ(L, a, b, E) at the back surface and the central portion of the surface of each sample of a negative electrode double-sided coating film. FIG. 9 is a diagram showing the distribution of calibration calculation luminance values ​​in imaging areas of 500 × 500 pixels and 2000 × 50 pixels.

[0014] Hereinafter, an embodiment of a film measurement device and a film measurement method according to the present invention will be described. Note that the drawings attached to this specification are all schematic diagrams, and the shape, scale, aspect ratio, etc. of each part have been modified or exaggerated from the actual product 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 film measurement method according to the present invention are applied to a battery electrode plate used in a lithium-ion battery. However, the film measurement device and film measurement method according to the present invention are not limited to lithium-ion batteries, and can be applied to secondary batteries in general that have a porous coated film structure. In the following description, the strip-shaped battery electrode plate used 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 measurement device 1 according to a first embodiment. The film measurement 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 measurement 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, which travel 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 depicted along their respective optical axes. Furthermore, the measurement object S is actually a strip-shaped electrode sheet, but in FIG. 1 it is depicted as a single electrode sheet.

[0017] The imaging unit 2 is a color camera equipped with a CMOS 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 its light-receiving surface and converts the optical image formed on the light-receiving surface into gradation data (RGB luminance signals) for each pixel, and outputs the converted data. That is, the imaging unit 2 captures an image of the coating film (described below) 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 below).

[0018] The 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 the telecentric lens 5 (described below) is 110 mm, the angle θ1 is, for example, 10° to 15°. 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. A white LED light source is characterized by 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 portion of the LED light output from the light source 3 is reflected by a beam splitter 6 (described below) and irradiated onto the measurement target S. Power is supplied to the light source 3 from an LED power supply (not shown). The operation of the light source 3 is controlled by a light source control unit 32 (described below).

[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 would 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 in the image would be averaged in the direction of transport of the electrode sheet, again 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 light intensity. Experiments by the inventors have confirmed that by combining a high-power LED light source with an optical fiber light guide or the like to increase the light intensity, 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 imaged 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 measurement target S with light output from the light source 3 and causes reflected light from the measurement target 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 positioned 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 normal 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, which reflects the light incident from the measurement object S back toward the measurement object S, the influence of the tilt of the measurement object S can be reduced. The tilt of the measurement object S is, for example, approximately ±3° with respect to the reference plane.

[0024] In the optical system configuration shown in FIG. 1 , a portion of the LED light output from the light source 3 (incident light L1) is reflected by the beam splitter 6 and then passes through the telecentric lens 5 to be irradiated onto the measurement object S. The incident light L1 irradiated onto the measurement object S is reflected from the surface of the measurement object S and enters the retroreflector 7 as reflected light L2. The reflected light L2 that enters the retroreflector 7 is reflected from the surface of the retroreflector 7 and then enters the surface of the measurement object S as reflected light L3. The reflected light L3 that enters the surface of the measurement object S is reflected from the surface of the retroreflector 7 and then passes through the telecentric lens 5 and the beam splitter 6 to enter the imaging unit 2 as reflected light L4. In the imaging unit 2, an optical image of the reflected light L4 is formed on a 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 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 the 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 in accordance with programs recorded in the ROM 12 or programs loaded from the storage unit 18 into the RAM 13. The RAM 13 also stores data and the like required for the CPU 11 to execute various processes. The CPU 11, ROM 12, and 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 types of 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 types of information. The storage unit 18 is composed of a hard disk, a DRAM (Dynamic Random Access Memory), etc., and stores various types of data. The communication unit 19 communicates with other devices via a network N including the Internet.

[0029] Removable media 21, such as a magnetic disk, optical disk, magneto-optical disk, or 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 needed. The removable media 21 can also store various data stored in the storage unit 18 in the same way as the storage unit 18.

[0030] Fig. 3 is a block diagram showing an example of the 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 film 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 (opening / closing of the shutter, setting of exposure time, etc.) of the imaging unit 2. The light source control unit 32 controls the start / stop of output of LED light from the light source 3, the output level, etc.

[0032] The data calculation unit 33 calculates the retroreflectivity (hereinafter also referred to as "reflectivity") and the number of zero points for each pixel in each imaging area based on the image (gradation data) captured by the imaging unit 2. A zero point is a pixel whose reflectivity is less than a set value. The number of zero points is the number of zero points in the imaging area. 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 for processing to calculate the number of zero points included in the imaging area. The processing of each step shown in FIG. 4 is mainly executed by 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] 4, the data calculation unit 33 resets the zero point number z to zero. In step S102, the data calculation unit 33 resets the pixel number i of the target imaging area 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 the pixel number i from the image DB 41 (see FIG. 3) of the storage unit 18.

[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) to determine 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 determination of step S105, if the data calculation unit 33 determines 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 determination of step S105, if the data calculation unit 33 determines 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 number of zero points z stored in the image DB 41 (see FIG. 3). Note that when the process of this flowchart starts, the number of zero points z is reset to the initial value (0).

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

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

[0040] Returning to Figure 3, the film thickness calculation unit 34 calculates the estimated film thickness of the coating film from the number of zeros obtained from the image data using an approximate formula (described later) for film thickness determined from the correlation between the number of zeros and the specified film thickness of the coating film. The "specified film thickness" is the actual measured film thickness. The "estimated film thickness" is the calculated film thickness value calculated from the approximate formula.

[0041] The density calculation unit 35 calculates the estimated density of the coating film from the number of zeros obtained from the image data using an approximation formula (described later) derived from the correlation between the number of zeros 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 types of data, such as an image DB 41 and an approximation formula DB 42. The image DB 41 is a database that stores gradation data captured by the imaging unit 2, luminance images obtained from the gradation data, binarized images, the number of zero points for each imaging region, etc. The approximation formula DB 42 is a database that stores data related to approximation formulas and conversion formulas (described later) used in the calculations of the film thickness calculation unit 34, density calculation unit 35, and color value calculation unit 36.

[0044] Next, the use of the film measurement device 1 in the electrode manufacturing process for lithium ion batteries will be described. The electrode manufacturing process for lithium ion batteries 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 the coating film in the coating and pressing processes. FIG. 5 is a side view showing the arrangement of the film measurement unit in the coating system 100. FIG. 6 is a perspective view showing the arrangement of the 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 will also be referred to as the "width direction X" or the "horizontal direction X." The movement 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 will also be 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 oven 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 on a reel. The transport device 104 is a device that transports the substrate 101 unwound 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 each of the positive and negative electrodes. When manufacturing an electrode sheet for a 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 a 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 coated with the electrode material on 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 not shown. The winding device 107 is a device that transports the electrode sheet 102 delivered 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 online coating of the electrode material by the die coater 105 and drying by the drying furnace 106 while moving the substrate 101 drawn from the first roll 103 toward the second roll 108. In the coating process, the electrode sheet 102 wound on the second roll 108 is sent to the subsequent 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 the "film measurement unit 110" in the following description. The film measurement unit 110A 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 110B measures the film thickness and the like 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 a single 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 thought that as the temperature of the coating film of the electrode sheet 102 increases, the electrode material expands, increasing the porosity (the ratio of voids 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 this case, a difference will occur in the measurement data compared to that at room temperature, making accurate measurement impossible. Therefore, during online measurement, the temperature of the coating film is measured with a thermometer 111 along 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 the 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 pulled out 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 around a reel. In the pressing process, the electrode sheet 102 wound around 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. Because 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, which is 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 a single case. The data processing device 8 (see FIG. 1) is located 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 a coating film and the number of zero points will be explained with reference to Figures 8 to 11. In Figures 8 to 11, the images on the left 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 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) at 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 with a calculated reflectance of 0.001% or less (including pixels with a negative reflectance value) were set as zero points. The number of zero points in the 250,000 points was calculated to obtain the number of zero points (see Figure 4).

[0060] Fig. 8 shows a luminance image and a binarized image of a positive electrode single-sided coating film after coating. Fig. 9 shows a luminance image and a binarized image of a positive electrode single-sided coating film after pressing. Fig. 10 shows a luminance image and a binarized image of a negative electrode double-sided coating film after coating. Fig. 11 shows a luminance image and a binarized image of a negative electrode double-sided coating film after pressing. All of Figs. 8 to 11 are images where the brightness of the sample has been multiplied by 15.

[0061] Lithium-ion battery electrode plates have many holes (cavities) formed in them to allow ionic liquid to penetrate the coating film. These cavities have a complex structure and are continuous all the way to the substrate. Some of the light incident on the surface of the coating film is reflected by the coating, while 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. Because the coated battery electrode plate has a thick film, the optical path length in the cavities is also long. This reduces the amount of light that exits the cavities, resulting in low reflectivity in the cavities. Furthermore, because the coated battery electrode plate has high surface roughness, the amount of light reflected from the coating film surface is reduced, resulting in low reflectivity. This is thought to be why the coated battery electrode plate has a high number of zeros.

[0062] In contrast, the pressed battery electrode plate has a thinner film thickness, which shortens the optical path length in the cavity. This increases the amount of light emitted from the cavity, resulting in a higher reflectance in the cavity. In addition, the pressed battery electrode plate has a smaller surface roughness, which increases the amount of light reflected from the coating film surface, resulting in a higher reflectance. Therefore, it is thought that the pressed battery electrode plate will have a lower number of zeros.

[0063] The number of zeros in the binarized image of the positive electrode single-sided coating film after coating (before pressing) shown in FIG. 8 was 47,093. The number of zeros 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 number of zeros in the binarized image of the negative electrode double-sided coating film after coating (before pressing) shown in FIG. 10 was 22,324. The number of zeros 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 number of zeros after pressing was significantly lower than the number of zeros after coating for both the positive electrode and negative electrode coating films. As such, reflectivity and zeros are correlated with film thickness. That is, the thicker the film thickness, the lower the reflectivity and the higher the number of zeros. Furthermore, the thinner the film thickness, the higher the reflectivity and the lower the number of zeros. Next, the correlation between reflectivity and zeros will be explained in more detail.

[0064] FIG. 12 is a diagram showing the correlation between the reflectance rφ(R, G, B)% and the number of zero points for the positive electrode single-sided coating film after coating and after pressing. 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 number of zero points for the positive electrode single-sided coating film after coating and after pressing was ２ The plotted points shown in FIG. 12 were 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 number of zero points for the negative electrode double-sided coating film after coating and after pressing. 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 number of zero points for the negative electrode double-sided coating film after coating and after pressing was ２ As described above, in both the positive electrode single-side coated film and the negative electrode double-side coated film, there is a high correlation between the reflectance and the zero score, 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 number of zero points of the coating film and the specified film thickness and the correlation between the number of zero points of the coating film and the specified density.

[0067] FIG. 14 shows 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 / cm ３ ) 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 instead of rφ(G) as the average reflectance, 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) %, which is the average value of rφ(G) % among the retroreflectances rφ(R, G, B) of all pixels (e.g., 250,000 pixels) included in the imaging area. On the vertical axis in Fig. 14, the scale on the left indicates the specified film thickness T (μm), and the scale on the right 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 using a conversion formula together with the measured value of the designated film thickness T.

[0069] In FIG. 14, an example of an approximate 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 approximate 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 represents the number of zero points. On the vertical axis of FIG. 15, the scale on the left side represents the specified film thickness T (μm), and the scale on the right side represents the specified density ρ (g / cm ３ ) is shown.

[0072] In FIG. 15, an example of an approximate 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 approximate formula for 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 measured zero points.

[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 the 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 represents the average reflectance rφ(G) %. On the vertical axis of FIG. 16, the scale on the left side represents the specified film thickness T (μm), and the scale on the right side represents 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 / cm ３ )

[0075] In FIG. 16, an example of an approximate 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 approximate 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+0.2004R 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 the 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 represents the number of zero points. On the vertical axis in FIG. 17, the scale on the left side represents the specified film thickness T (μm), and the scale on the right side represents the density ρ (g / cm ３ ) is shown.

[0078] In FIG. 17, an example of an approximate 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 approximate equation (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 approximate formula for 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 approximate equation (8), the estimated density ρe of the negative electrode coating film can be calculated from the number of measured zero points.

[0080] Next, a specific example will be described in which the estimated film thickness Te 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. 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 the reflectance rφ(R, G, B)%.

[0081] FIG. 18 shows the distribution of reflectance and zero points for each sample after coating and pressing of the positive electrode single-sided coating film. FIG. 19 shows the distribution of estimated film thickness Te for each sample after coating and pressing of the positive electrode single-sided coating film. In FIGS. 18 and 19 , the numbers on the horizontal axis indicate the number of measurements (number of data points) for 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 reflectance rφ(R, G, B)%, and the scale on the right indicates the number of zero points. In Fig. 18, white circles (◯) indicate plot points of zero points. 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 represents the estimated film thickness Te (μm). In Fig. 19, diamonds (◇) represent plot points of the estimated film thickness Te calculated using approximation formula (1) with reflectance rφ(R, G, B) %. Open circles (◯) represent plot points of the estimated film thickness Te calculated using approximation formula (3) with zero points.

[0084] 19, when the estimated film thickness Te after coating was calculated using approximate 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 approximate formula (3) with the number of zero points, 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 approximate 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 approximate 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 single-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 single-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 shows the distribution of reflectance and zero points for each sample after coating and pressing of the double-sided negative electrode coating film. FIG. 21 shows the distribution of estimated film thickness Te for each sample after coating and pressing of the double-sided negative electrode coating film. In FIGS. 20 and 21 , the numbers on the horizontal axis indicate the number of measurements (number of data points) for the sample. 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 estimated film thickness Te (μm), 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 approximate 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. Furthermore, when the estimated film thickness Te after coating was calculated using approximate formula (7) with the number of zeros 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 approximate 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 approximate 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 approximate formulas (3) and (7) obtained from the correlation between the number of zero points and the specified film thickness of the coating film, it is possible to measure the film thickness of the coating film after coating and after pressing 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. Furthermore, to improve 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 it is not possible to measure the thickness, density, and reflection color value of the coating film formed on the front and back surfaces of the battery electrode plate more accurately and online. As described below, the film measurement device 1 of the first embodiment can measure the density and reflection color value of the coating film formed on the front and back surfaces of the battery electrode plate more accurately and online.

[0094] Next, a specific example will be described 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. 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-side coating film after coating and after pressing. In FIG. 22, 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 represent the density after coating (specified density 1.47 g / cm ３ 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 represents the estimated density ρe (g / cm ３ ) are shown. In Figure 22, diamonds (◇) indicate plot points of the estimated density ρe calculated using approximation formula (2) based on the reflectance rφ(R, G, B)%. Open circles (◯) indicate plot points of the estimated density ρe calculated using approximation formula (4) based on the number of zero points. The same samples as those used to measure the film thickness were used for measuring the density. Therefore, the distribution of the 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 Figure 18 (not shown).

[0097] In the measurement numbers 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) using the zero point number for measurements 1 to 20, the standard deviation σ for the specified density ρ was 0.026 g / cm ３ This is what happened.

[0098] In addition, when the estimated density ρe after pressing is calculated using the approximate formula (2) based on the reflectance rφ(R, G, B)% for the measurement numbers 21 to 40 shown in FIG. 22, 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) using 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 This is what happened.

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

[0100] FIG. 23 is a diagram showing the distribution of the estimated density ρe of each sample of the negative electrode double-sided coating film after coating and after pressing. 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 represent the density after coating (specified density 1.45 g / cm ３ The horizontal axis shows the number of measurements after pressing (specified density 2.18 g / cm ３ The vertical axis of FIG. 23 shows the estimated density ρe (g / cm ３ ) are shown. The meaning of each plotted 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 measuring the density. Therefore, the distribution of the reflectance and the number of zero points of each sample after coating and pressing of the double-sided negative electrode coating film is the same as in Fig. 22 (not shown).

[0101] In the measurement numbers 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 ３On the other hand, when the estimated density ρe after coating is calculated using the approximation formula (8) using the zero point number, the standard deviation σ of the estimated density ρe relative to the specified density ρ is 0.051 g / cm ３ This is what happened.

[0102] In addition, in the measurement numbers 41 to 80 shown in FIG. 23, when the estimated density ρe after pressing 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 0.088 g / cm ３ On the other hand, when the estimated density ρe after pressing was calculated using the approximation formula (8) using 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 This is what happened.

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

[0104] As shown in FIGS. 22 and 23 , it can be seen that for the positive electrode coating film and the negative electrode coating film, 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 number of zero points and the specified density of the coating film.

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

[0106] On the vertical axis of Figure 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 ranging from green (-) to red (+). The chromaticity value b represents the color intensity ranging from blue (-) to yellow (+). In Figure 24, diamonds (◇) represent plot points of the lightness value L calculated based on the reflectance rφ(R,G,B)%. The open squares (□) represent plot points of the chromaticity value a calculated based on the reflectance rφ(R,G,B)%. The open triangles (△) represent plot points of the chromaticity value b calculated based on the reflectance rφ(R,G,B)%. The same samples used to measure the color values ​​were used to measure the film thickness and density.

[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. 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 Equation (9) a=500×[{rφ(R) / R １０} １／３ −(rφ(G) / G １０ ) １／３ ] Equation (10) b=200×[{rφ(G) / G １０} １／３ −(rφ(B) / B １０ ) １／３ ] Formula (11)

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

[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 larger in the 21 to 40 measurements after pressing than in the 1 to 20 measurements after coating. It can also be seen that the chromaticity values ​​a and b change in distribution position in the 21 to 40 measurements after pressing compared to the 1 to 20 measurements after coating. 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] Figure 25 shows the distribution of reflected color values ​​Lab for each sample after coating and pressing of the double-sided negative electrode coating film. In Figure 25, the numbers on the horizontal axis indicate the number of measurements (number of data points) for 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 plotted point in Figure 25 are the same as those in Figure 24.

[0114] As shown in Figure 25, the lightness value L was greater for measurements 41 to 80 after pressing than for measurements 1 to 40 after coating. It was also found that the chromaticity values ​​a and b changed in their distribution positions for measurements 41 to 80 after pressing compared to measurements 1 to 40 after coating. In the case of the double-sided negative electrode coating film as well, the reflected color values ​​Lab calculated after coating and after pressing linearly indicate the changes in physical properties that occurred in the double-sided negative electrode coating film (coating material) after coating and after pressing.

[0115] As shown in Figures 24 and 25, the reflection color value Lab can be calculated for the positive electrode single-side coating film and the negative electrode double-side coating film by using the reflectance rφ(R, G, B)% and the conversion formula. By calculating the reflection color value Lab, a single color can be identified. 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 a reference film thickness (hereinafter also referred to as the "reference reflection color value"), changes in film thickness and density after coating and after pressing can be detected. Furthermore, by calculating the color difference value Δ(L, a, b, E), it is possible to determine, for example, whether the degree of mixing of the coating material is uniform across the width 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 is calculated by the reference reflection color value (L ０ , a ０ , b ０ ) and the reflected color value Lab, it can be calculated using the following formula: 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−a ０ Formula (19) Δb=bb ０ Equation (20) ΔE=√(ΔL ２ +Δa ２ +Δb ２ ) Formula (21)

[0118] As described above, according to the film measurement 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. ０ , a ０ , b ０ ) and the reflected color value Lab, the color difference value Δ(L, a, b, E) can be calculated. Therefore, in online measurement, by calculating the color difference value Δ(L, a, b, E) in the width direction of the electrode sheet or in 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 yields in the coating process and pressing process.

[0119] If the surface of aluminum or copper, which serves as the base material for a battery electrode plate, oxidizes, its performance as an electrode deteriorates. Whether the base material has oxidized can be determined by measuring the reflectance of the uncoated portion of the electrode plate, which is not coated with the electrode material. Because the uncoated portion of the base material has a higher reflectance than the coated portion, the imaging unit 2 (see Figure 1) sets a shutter time for imaging the base material and an exposure time for imaging the coating film. Then, by performing imaging using a blackbody calibration plate (described below) corresponding to each exposure time, the reflectance of the base material and the reflectance of the coating film can be measured simultaneously or alternately. Since the reflection color value can also be measured simultaneously, it is possible to detect not only the presence or absence of oxidation of the base material but also abnormalities in the base material.

[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 a strip shape, but may also be cylindrical. When a coating film formed on such a cylindrical substrate is imaged using a measurement area of ​​500 x 500 pixels, image blur occurs between the upper and lower sides in the circumferential direction due to the difference in measurement distance. In order to more accurately image such a cylindrical coating film, a method of using the imaging unit 2 as a line sensor camera is proposed.

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

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

[0123] Fig. 26 is a diagram showing a luminance image and a binarized image of the center of a positive electrode single-sided coating film. Fig. 27 is a diagram showing a luminance image and a binarized image of an end portion of a positive electrode single-sided coating film. Fig. 28 is a diagram showing a luminance image and a binarized image of the back surface of a negative electrode double-sided coating film. Fig. 29 is a diagram showing a luminance image and a binarized 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 binarized image at the center and edge of the coated positive electrode single-sided film. Similarly, as shown in Figures 28 and 29, it can be seen that there is little difference between the brightness image and the binarized image at the back and front of the coated negative electrode double-sided film.

[0125] As described above, it can be seen that reducing the number of scanning pixels in the vertical direction Y from 500 to 50 results in almost no image blurring when capturing images online while scanning one film measurement 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 measurement 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 the number of zeros in the film measurement 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 the number of zeros, the film thickness calculation unit 34 also performs a process of calculating the estimated film thickness Te using the approximation formula based on reflectance rφ(R, G, B)%.

[0127] FIG. 30 shows the distribution of reflectance and the number of zero points at the center and edge of each sample of a positive electrode single-sided coating film. FIG. 31 shows the distribution of estimated film thickness Te at the center and edge of each sample of a positive electrode single-sided coating film. In FIGS. 30 and 31 , the numbers on the horizontal axis indicate the number of measurements (number of data points) for each sample. Numbers 1 to 50 on the horizontal axis indicate the number of measurements for samples in which the center was measured. Numbers 51 to 100 on the horizontal axis indicate the number of measurements for samples in which the edge was measured. The specified 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 Fig. 30 indicates the reflectance rφ(R, G, B) %, and the scale on the right side indicates the number of zero points. In Fig. 30, white circles (◯) indicate plot points of zero points. 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 represents the estimated film thickness Te (μm). In Fig. 31, diamonds (◇) represent plot points of the estimated film thickness Te calculated using approximation formula (1) with reflectance rφ(R, G, B) %. Open circles (◯) represent plot points of the estimated film thickness Te calculated using approximation formula (3) with 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 zeros for measurements 1 to 50, the standard deviation σ for the specified film thickness T was 0.70 μm.

[0131] Furthermore, 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 (end portion), 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 the number of 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, it can be seen that 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 shows the distribution of reflectance and the number of zero points for the back surface and the central portion of the front surface of each sample of a double-sided negative electrode coating film. FIG. 33 shows the distribution of estimated film thickness Te for the back surface and the central portion of the front surface of each sample of a double-sided negative electrode coating film. In FIGS. 32 and 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 central portion 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 negative electrode coating was calculated using approximate formula (5) with reflectance rφ(R, G, B)% for measurements 1 to 50 (rear surface), 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 negative electrode coating was calculated using approximate formula (7) with the number of zeros for measurements 1 to 50, the standard deviation σ for the specified film thickness T was 1.1 μm.

[0135] Furthermore, 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 the number of zeros 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, it can be seen that 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 the reflectance rφ(R, G, B)% and an approximation formula based on the number of zeros in the film measurement 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 the approximation formula based on the number of zeros, the density calculation unit 35 also performs a process of calculating the estimated density ρe using the approximation formula based on the reflectance rφ(R, G, B)%.

[0138] Fig. 34 is a diagram showing the distribution of estimated density ρe at the center and edge of each sample of the positive electrode single-side coating film. In Fig. 34, the horizontal axis represents the number of samples measured, as in Fig. 31. The vertical axis in Fig. 34 represents estimated density ρe (g / cm ３ ) is shown. In Figure 34, diamonds (◇) indicate plot points of the estimated density ρe calculated using approximation formula (2) based on the reflectance rφ(R, G, B)%. White circles (◯) indicate plot points of the estimated density ρe calculated using approximation formula (4) based on the number of zero points. The same samples as those used in measuring the film thickness are used for measuring the density. Therefore, the distribution of the 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 Figure 30 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 x 500 pixels).

[0139] As shown in FIG. 34, when the estimated density ρe of the central portion is calculated using the approximate formula (2) based on 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 using the approximation formula (4) based on the number of zero points in the measurement numbers 1 to 50, the standard deviation σ for the specified density ρ is 0.018 g / cm ３ This is what happened.

[0140] Furthermore, as shown in FIG. 34, when the estimated density ρe of the edge portion is calculated using the approximate formula (2) based on the reflectance rφ(R, G, B)% for the measurement numbers 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) based on 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 This is what happened.

[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 number of zero points 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, as in Fig. 34, represents the number of samples measured. The vertical axis in Fig. 35, as in Fig. 34, represents the estimated density ρe (g / cm ３ ) are shown. The same samples as those used to measure 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 in the first embodiment (500 × 500 pixels).

[0143] In the measurement numbers 1 to 50 shown in FIG. 35, when the estimated density ρe of the rear 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) based on the number of zero points in the measurement numbers 1 to 50, the standard deviation σ for the specified density ρ is 0.029 g / cm ３ This is what happened.

[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 ３ On the other hand, when the estimated density ρe at the center of the surface was calculated using the approximation formula (8) based on the number of zero points for the measurement numbers 51 to 100, the standard deviation σ for the specified density ρ was 0.042 g / cm ３ This is what happened.

[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 the coating film using the film measuring device 1 (2000 × 50 pixels) of the second embodiment. FIG. 36 is a diagram showing the distribution of the reflection color values ​​Lab of the center and edge portions of each sample of a positive electrode single-sided coating film. In FIG. 36, the numbers on the horizontal axis indicate the number of measurements of the sample (number of data). The numbers 1 to 50 on the horizontal axis indicate the number of measurements of the sample in which the center portion was measured. The numbers 51 to 100 on the horizontal axis indicate the number of measurements of the sample in which the edge portion was measured.

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

[0147] The same samples were used to measure the color values ​​of the positive electrode single-side coating film as those used to measure the film thickness and density. Therefore, the distribution of the reflectance and zero points of each sample at the center and edge of the positive electrode single-side coating film is the same as that shown in Figure 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 of the first embodiment.

[0148] 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 a positive electrode single-sided coating film. As shown in Fig. 37, the color difference value ΔE, which is the total color difference, is small, averaging 1 or less, at the center and end portions of each sample of a positive electrode single-sided coating film.

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

[0150] The same samples were used to measure the color values ​​of the negative electrode double-sided coating film as those used in the measurements of film thickness and density described above. Therefore, the distribution of reflectance and zero points for each sample on the back surface and the central portion of the front surface of the negative electrode double-sided coating film is the same as that shown in Figure 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] 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 a 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, at 1 or less, between the back surface and the center of the front surface of each sample of a 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 reflected color values ​​Lab calculated after coating linearly represent the changes in the physical properties of the positive electrode single-side coating film and the negative electrode double-side coating film (coating material) after coating. Therefore, by calculating the color difference value Δ(L, a, b, E) of the coating film in online measurement, it is possible to determine 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 for an imaging area of ​​2000 x 50 pixels may use, for example, the following formula (22): Calibration calculation luminance value=CW-CB Formula (22) In formula (22), CW is the luminance value measured with a reflective calibration plate set at the measurement position. 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 Figure 40. Figure 40 is a diagram showing the distribution of calibration calculation luminance values ​​in imaging areas of 500 x 500 pixels and 2000 x 50 pixels. The vertical axis of Figure 40 indicates a value (hereinafter also referred to as "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 Figure 40, when the imaging area is set to the central 500 x 500 pixels, it can be seen that the luminance change in the horizontal direction X for all RGB is small. Also, when the imaging area is set to 2000 x 50 pixels, it can be seen that the luminance change in the horizontal direction X for all 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 x 500 pixels, but also when it is set to 2000 x 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 install a blackbody calibration plate and a reflective calibration plate on one or both sides of the electrode sheet in the width direction X, and to calibrate the brightness value at regular intervals.

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

[0158] (Modifications) In the first embodiment, an example was described in which the imaging area of ​​the imaging unit 2 was 500 (X) × 500 (Y) pixels, but this is not limiting. The imaging area may be, for example, 550 × 550 pixels or 450 × 450 pixels. Reducing the number of pixels in the Y direction shortens the image capture time, making it possible to perform measurements 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 desirable to have a large number of data points for the reflectance rφ and the number of zero points, it is sufficient to set the number of pixels that allows stable measurement depending on the specifications, characteristics, etc. of the camera used for imaging.

[0160] In the film measurement device 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 way, the film measurement device 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.

[0162] REFERENCE SIGNS LIST 1 Film measurement device 2 Imaging unit 3 Light source 4 Optical unit 5 Telecentric lens 6 Beam splitter 7 Retroreflector 8 Data processing device 11 CPU 18 Storage unit 31 Imaging control unit 32 Light source control unit 33 Data calculation unit 34 Film thickness calculation unit 35 Density calculation unit 36 ​​Color value calculation unit 41 Image DB 42 Approximation formula DB

Claims

1. A film measurement device comprising: an imaging unit that captures an image of a coating film and acquires 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 enter the imaging unit; a data calculation unit that calculates the retroreflectivity for each pixel in the imaging area and the zero point number at which the retroreflectivity 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.

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

3. The film measurement device according to claim 1, further comprising a color value calculation unit that calculates the reflection color value of the coating film using the retroreflectance and a conversion formula.

4. The film measurement device according to claim 1, further comprising a retroreflector that retroreflects light reflected by the coating film, wherein the optical unit irradiates the light output from the light source onto the coating film, 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.

5. A film measurement method for measuring the 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 the light reflected 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.

6. The film measurement method according to claim 5, further comprising a step of calculating an estimated density of the coating film from the zero point number using an approximation formula obtained from the correlation between the zero point number and the specified density of the coating film.

7. The film measurement method according to claim 5, further comprising a step of calculating a reflection color value of the coating film based on the retroreflectance.

Images