Film thickness deviation measuring method, film manufacturing method, film thickness deviation measuring device, and film manufacturing device

Abstract

Provided are technology for measuring a film thickness deviation and technology for manufacturing a film, with which information on a film-thickness deviation can be acquired in a non-contact manner through a simple and safe device configuration. In a method for measuring a film-thickness deviation according to the present invention, a film to be measured is set as an object being measured, a preset background image can be imaged by an imaging means, a reference image in which the background image is captured by the imaging means in a state in which the object being measured is not interposed, or a reference image in which calculations are used to derive how the background image in the state in which the object being measured is not interposed is viewed by the imaging means is acquired, a measurement image, in which the background image is captured by the imaging means with the object being measured interposed between the background image and the imaging means, is acquired, and on the basis of the acquired reference image and measurement image, a displacement amount of the background image in the two images is calculated to obtain the film thickness deviation of the object being measured.

Description

[Technical Field]

[0001] The present invention relates to a technique for non-contact measurement of thickness deviation of a film that transmits visible light, and to the production of a film using the technique for measuring thickness deviation.The present invention particularly relates to a technique that is suitable when the visible light transmittance of the target film is equal to or greater than a specific value. The film that transmits visible light is made of, for example, resin or glass. The film of the present disclosure also includes a sheet. [Background technology]

[0002] The following method is widely used as an in-line, non-contact method for measuring the thickness of resin films: This method involves passing light such as X-rays or infrared rays through the film and measuring the thickness in accordance with the Beer-Lambert law based on the attenuation rate of the transmitted light.

[0003] Patent Document 1 describes an optical interference type film thickness measurement method in which a film is irradiated with white parallel light and the film thickness is calculated from the spectral intensity of the reflected light. Patent Document 2 describes a capacitance type film thickness measurement method. These film thickness measurement methods often involve measuring by moving a single sensor back and forth in a direction perpendicular to the transport direction of the object being measured. However, with this method of measuring by moving the sensor back and forth, the faster the film transport speed, the longer the transport direction interval between film thickness data at the same width position. This makes it difficult to detect quality or operational abnormalities such as sudden changes in film thickness distribution. Another issue is that it is difficult to separate film thickness variations in the transport direction from film thickness variations in the width direction from the film thickness data.

[0004] A conventional technique for addressing such a problem is described in Patent Document 3. Patent Document 3 uses a plurality of X-ray detector elements arranged in the width direction to detect the amount of transmitted X-rays, and discloses that the film thickness is measured on a straight line in a direction perpendicular to the conveying direction by tilting the plurality of X-ray detector elements with respect to the width direction in accordance with the conveying speed and measurement time. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 7-280523 [Patent Document 2] Japanese Patent Application Publication No. 2019-2918 [Patent Document 3] Japanese Patent Application Laid-Open No. 2006-275750 [Non-patent literature]

[0006] [Non-Patent Document 1] "Improvement of the visualization method for density gradients based on the background-oriented Schlieren method," Junichi Akatsuka et al., Transactions of the Japan Society of Mechanical Engineers (Part B), Vol. 77, No. 784, p. 2391, published December 25, 2011 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the film thickness measuring device described in Patent Document 3, multiple X-ray detector elements are tilted with respect to the width direction in accordance with the transport speed and measurement time. This makes it possible to measure the thickness of the film on a straight line perpendicular to the running direction. However, the film thickness measuring device described in Patent Document 3 requires multiple X-ray detector elements. As a result, the film thickness measuring device described in Patent Document 3 has issues such as increased equipment costs and the need to calibrate between the X-ray detector elements, which leads to increased maintenance costs.

[0008] The present invention has been made in light of the above-mentioned points, and an object of the present invention is to provide a film thickness deviation measurement technique that can obtain information on film thickness deviation in a non-contact manner using a simple and safe device configuration, and a film manufacturing technique that uses the measurement technique. [Means for solving the problem]

[0009] The inventors have conducted extensive research to solve the above problems. As a result of their extensive research, they have come up with the idea of ​​applying the background-directed Schlieren method, which is used to calculate the density gradient of a fluid, to measuring the film thickness deviation of a solid film. The inventors then came up with the idea of ​​utilizing the amount of background displacement (amount of movement) between two images: a reference image captured in the absence of an object to be measured, and a measurement image captured through the object to be measured. This led the inventors to discover that it is possible to obtain the film thickness deviation of an object to be measured using a simple and safe device configuration. The present invention was completed based on this finding and further investigation.

[0010] To solve the problem, one aspect of the present invention is a method for measuring film thickness deviation, in which the film to be measured is used as the object to be measured, a preset background image can be captured by an imaging means, a reference image is obtained which is an image of the background image captured by the imaging means without the object to be measured in between, or a reference image derived by calculation of how the background image appears to the imaging means in a state where the object to be measured is not in between, a measurement image is obtained which is an image of the background image captured by the imaging means with the object to be measured interposed between the background image and the imaging means, and the film thickness deviation of the object to be measured is determined by calculating the amount of displacement of the background image in these two images based on the acquired reference image and measurement image.

[0011] The film thickness deviation is calculated, for example, using the following formula (1).

[0012]

number

[0013] however, t: Film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target : Refractive index of the object to be measured n air : Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: A two-dimensional vector representing the amount of displacement of the background image of interest in the measurement image from the same background image in the reference image. v: unit tangent vector of path C "∫ c Δh·vdl": Line integration of the inner product of the above Δh and v over the integral path C from the origin to the measurement point is.

[0014] Another aspect of the present invention is a film manufacturing method in which molten resin is discharged from a die having a plurality of lip gap adjustment means to form a film that is transmissive to visible light, the method comprising the steps of: transporting the film discharged from the die along a predetermined pass line; arranging imaging means on either side of the pass line to capture a background image and a background image; and acquiring a measurement image, which is an image of the background image captured by the imaging means through the film; acquiring a reference image, which is an image of the background image captured by the imaging means without the film being interposed between the background image and the imaging means, or acquiring a reference image derived by calculation of how the background image would appear through the imaging means without the film being interposed; comparing the acquired reference image with the acquired measurement image and calculating the amount of displacement of the background image in the film width direction between the two images, thereby calculating a film thickness deviation profile in the width direction of the film; and operating the lip gap adjustment means based on the calculated film thickness deviation profile so that the film thickness deviation at each point becomes a target value. [Effects of the Invention]

[0015] According to an aspect of the present invention, it is possible to obtain information on film thickness deviation in a non-contact manner using a simple and safe device configuration for a film made of resin, glass, etc. Furthermore, according to an aspect of the present invention, it is possible to obtain information on film thickness deviation in a non-contact manner over the entire length and width of the film, for example. As a result, according to this aspect of the present invention, when producing a film, for example, by quickly reflecting the acquired information on film thickness deviation in the control of the lip gap adjustment means, it is possible to produce a film with higher precision. [Brief explanation of the drawings]

[0016] [Figure 1] This is a conceptual diagram of the optical system of the BOS method, which is used for quantitative visualization of fluid density gradients. [Figure 2] 1 is a schematic diagram illustrating the configuration of a film thickness deviation measuring device according to an embodiment of the present invention. [Figure 3] FIG. 2 is a diagram illustrating an example of the configuration of a calculation unit. [Figure 4] 1 is a schematic configuration diagram of a film manufacturing apparatus according to an embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing the amount of background displacement in the MD and TD directions in an example. [Figure 6] FIG. 1 is a diagram showing the film thickness deviation distribution within the film plane in an example. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment based on the present invention will be described with reference to the drawings. The embodiment described below is an example of the present invention, and the invention is not limited to the following content.

[0018] (Regarding the principles of the present disclosure) The inventors considered applying the background-oriented schlieren method, which is used to calculate the density gradient of a fluid, to measuring the film thickness deviation of a solid film. The background-oriented schlieren method is also called the BOS method. After various investigations, they came up with the idea of ​​using the amount of movement (displacement) of the background between two images: a reference image captured without the object being measured, and a measurement image captured with the object being measured in between. The inventors then discovered that by calculating the amount of background displacement between the two images, it is possible to obtain the film thickness deviation of the object being measured using a simple and safe device configuration.

[0019] The BOS method is a quantitative visualization technique for the density gradient of a fluid. The BOS method measures density gradients by utilizing the phenomenon in which, when a background is viewed through a fluid, the background appears shifted due to differences in refractive index caused by the density gradient (see Figure 1). In this disclosure, this measurement principle is applied to a solid film to measure the film thickness deviation. The BOS method has two advantages over the conventional Schlieren method: the optical system for measurement is simple, and the density gradient can be quantified.

[0020] A conceptual diagram of the optical system of the BOS method is shown in Figure 1. As shown in Figure 1, the optical system of the BOS method consists of a fluid object 11, a background image 12, and an imaging means 13. Figure 1 shows an apparent light path 14 from the imaging means 13 and a true light path 15 due to the presence of the object 11. In this BOS method, a background image 12 is captured through the object 11. At this time, the position of the background image on the image captured by the imaging means 13 is shifted in proportion to the density gradient of the object 11.

[0021] In this phenomenon, the total deflection angle ε can be approximated by the ratio of the amount of deviation Δh of the background image in the captured image to the distance d between the object and the background image. In other words, it can be expressed as "ε = Δh / d". The total deflection angle ε is expressed by the following equation (2): That is, the total deflection angle ε can be found by integrating the density gradient ∂n / ∂x in the direction perpendicular to the optical axis of the refractive index n of the object to be measured over the thickness 2Δz of the object to be measured.

[0022]

number

[0023] Furthermore, the refractive index n and density ρ have the relationship n=ρG+1, where G is the constant of the Gladstone-Dale law. Therefore, the density gradient is expressed by the following equation (3).

number

[0024] In this embodiment, an optical system according to the BOS method is used to obtain the gradient of the film thickness t (film thickness deviation) of a solid film. In this embodiment, the Gladstone-Dale law is not used. Instead, in this embodiment, it is approximated that the refractive index has a gradient in the x direction only at the portion of the film thickness that is in contact with air. This makes it possible to obtain the following equation (4). Note that the x direction is an arbitrary direction selected from the surface direction of the film being measured. The surface direction of the film is a two-dimensional direction perpendicular to the z direction.

[0025]

number

[0026] Furthermore, ε=Δh / d. Therefore, the following equation (5) can be obtained from the equation "ε=Δh / d" and equation (4).

[0027]

number

[0028] Then, by integrating equation (5) in the x direction, the film thickness deviation can be measured. The film thickness deviation is the amount of change in film thickness in the x direction from the set reference position x0. By extending this concept, it is also possible to obtain the film thickness deviation in two dimensions, for example, the x and y directions along the film surface.

[0029] A specific method for determining the film thickness deviation is, for example, a method using the following equation (1). In this specification, the term "reference image" refers to an image of a background image captured by an imaging means without an object to be measured, and the term "measurement image" refers to an image of a background image captured by an imaging means through an object to be measured.

[0030]

number

[0031] where: t: Film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target : Refractive index of the object to be measured n air : Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: A two-dimensional vector representing the amount of displacement of the background image of interest in the measurement image from the same background image in the reference image. v: unit tangent vector of path C "∫ c Δh·vdl": Line integration of the inner product of the above Δh and v over the integral path C from the origin to the measurement point is.

[0032] (Configuration of film thickness deviation measuring device) Next, an example of the film thickness deviation measuring device of this embodiment will be described. FIG. 2 shows a schematic configuration of a film thickness deviation measuring device 20 of this embodiment. As shown in the schematic diagram of FIG. 2, the film thickness deviation measuring device 20 of this embodiment includes a background image 22, an imaging means 23 for capturing the background image 22, and a calculation unit 24. The object 21 to be measured is a film to be measured.

[0033] <Object to be measured> When a measurement image is acquired, the object 21 is placed in front of the background image with the film thickness direction facing the imaging direction. The object to be measured in this embodiment is a film that transmits visible light. Therefore, the imaging means is capable of capturing an image of a background image 22 through the object to be measured 21. In principle, the background image 22 is captured through the object to be measured 21, and therefore the visible light transmittance of the object to be measured 21 is preferably 10% or more, although this depends on the film thickness of the object to be measured. Furthermore, the visible light transmittance is more preferably 30% or more, and even more preferably 70% or more.

[0034] Regardless of the visible light transmittance value, the haze value of the object 21 is preferably 20% or less, more preferably 15% or less, and even more preferably 5% or less. In this embodiment, the visible light transmittance is the total light transmittance in the wavelength range of 400 to 700 nm measured using a haze meter, and the haze value is the ratio of the total light transmittance to the diffuse transmittance, also measured using a haze meter.

[0035] <Background image> Background image 22 may be any pattern or design that can detect the amount of displacement when the position on an image captured by the imaging means changes depending on the presence or absence of object to be measured 21. For example, a spangle pattern may be present on top surface 25A of stand 25 at a position corresponding to background image 22, and the pattern may be captured in detail by imaging means 23. In this case, the spangle pattern may be used as background image 22, and there is no need to provide a special image separately as the background image. If there is no suitable pattern for background image 22, a random dot image or a striped image with a periodic brightness distribution is preferable. Random dot images and striped images may be black and white or grayscale, or may be color images painted in three colors, for example, red, green, and blue. Background image 22 can also be provided by drawing random dots directly on top surface 25A of stand 25, or by attaching paper with a background image printed on top surface 25A.

[0036] Furthermore, a display device for displaying a background image may be provided on the top surface of the stand 25, and the background image may be switched depending on the passage of time or the conditions of the object to be measured. In such a configuration in which a background image is displayed on a display, the image may be switched at high speed to vibrate the background image, thereby improving the effective resolution. The setting of the background image is not limited to these, and various known methods may be used.

[0037] <Image capture means> The image capturing means is a device that captures a background image. A CCD camera, a CMOS camera, or other digital camera can be used as the imaging means 23. The imaging means 23 may also be an area camera or a line camera. However, if it is desired to measure the film thickness deviation in only one specific direction, a line camera may also be used as the imaging means 23. In this case, an improvement in processing speed and a reduction in equipment costs can be expected. The imaging means 23 may be configured with a set of multiple cameras. In this case, it is possible to reduce the imaging area of ​​the object to be measured that each camera is responsible for. This allows for improved resolution and the use of a narrow-angle camera. In this case, the reduction in the area of ​​the background image 22 is expected to reduce the scale of the device.

[0038] Furthermore, the camera of the imaging means 23 may be a monochrome camera when the background image 22 is black and white or grayscale. Also, when the background image 22 is a color image, a device configuration in which separate colors are detected by a plurality of cameras may be adopted, for example, by installing color filters between the imaging means 23 and the object to be measured 21. In this case, using a monochrome camera as the camera of the imaging means 23 is preferable from the viewpoints of cost-effectiveness and spatial resolution.

[0039] <Layout and other details> When capturing a measurement image, the object to be measured is located between the image capturing means and the background image. From the viewpoint of analytical calculation, it is preferable that the object to be measured 21 and the background image 22 are arranged in a parallel relationship. However, if parallel arrangement is not possible due to restrictions on the arrangement of the device, appropriate correction can be made during calculation. Furthermore, the greater the separation between the object to be measured 21 and the background image 22, the better the film thickness deviation resolution. Therefore, the opposing distance between the object to be measured 21 and the background image 22 is preferably 30 mm or more, more preferably 50 mm or more, and even more preferably 200 mm or more. On the other hand, the closer the object to be measured 21 and the background image 22 are, the easier it is to focus during imaging. Therefore, the opposing distance between the object to be measured 21 and the background image 22 is preferably 2000 mm or less, more preferably 1000 mm or less, and even more preferably 600 mm or less. The opposing distance between the object to be measured 21 and the background image 22 is preferably between 30 and 2000 mm, more preferably between 50 and 1000 mm, and even more preferably between 200 and 600 mm. The distance between the object to be measured 21 and the background image 22 is preferably determined based on the required film thickness deviation resolution and the lens configuration of the imaging means 23.

[0040] From the viewpoint of analytical calculation and preventing out-of-focus, it is preferable that the optical axis of the imaging means 23 is perpendicular to the object to be measured 21 and the background image 22. The distance between the imaging means 23 and the object to be measured 21 is preferably determined taking into consideration the angle of view and focal length of the imaging means 23. It is preferable that the imaging means 23 and the object to be measured are disposed so that the object to be measured 21 and the background image 22 do not become out of focus and the imaging range is within the imaging range. The axis connecting the object to be measured 21, the background image 22, and the imaging means 23 may be arranged vertically (perpendicular to the background image) as shown in Fig. 2. However, depending on the installation environment and other constraints, the axis may be arranged horizontally or at any other angle depending on the orientation of the object to be measured 21, the background image 22, etc.

[0041] There may be other structures (not shown), such as glass windows, between the object to be measured 21 and the background image 22, or between the object to be measured 21 and the imaging means 23. However, it is preferable that the structure have a visible light transmittance of 10% or more so that the object to be measured 21 and the background image 22 can be recognized through the imaging means 23. Furthermore, the visible light transmittance is more preferably 30% or more, and even more preferably 70% or more. Furthermore, if the structure has a film thickness deviation, it is preferable to correct the amount of displacement of the background image in the captured image or the calculated film thickness deviation of the object to be measured 21. However, if the distance between the background image 22 and the structure is short and has only an acceptable effect on the calculated film thickness deviation of the object to be measured 21, correction may not be necessary. It is more preferable that the structure has no film thickness deviation.

[0042] <Arithmetic section> The calculation unit 24 executes a process of calculating the film thickness deviation of the object to be measured based on the image captured by the imaging means. Specifically, the calculation unit 24 executes a process of calculating the amount of displacement of the background image between two images, the reference image and the measurement image, thereby calculating the film thickness deviation of the object to be measured. The amount of displacement of the background image is determined, for example, by the amount of movement of a region selected from within the background image. As shown in FIG. 3, the calculation unit of this embodiment includes a reference image acquisition unit 24A, a measurement image acquisition unit 24B, and a film thickness deviation calculation unit 24C.

[0043] [Reference image acquisition section] The reference image acquisition unit 24A performs processing to acquire a reference image, which is an image that serves as a reference for comparison with a measurement image. The process for acquiring the reference image can be exemplified by a first processing method and a second processing method.

[0044] [First processing method] In the first processing method, an image of the background image 22 captured by the imaging means 23 is acquired as a reference image. This reference image is acquired when it is determined that the object to be measured 21 does not exist between the imaging means and the background image. The reference image is a standard image for calibration, so when calculating the film thickness deviation online, it can be performed before obtaining information on the film thickness deviation for the target object.

[0045] [Second processing method] In the second processing method, an image obtained by calculating how the background image 22 looks when the object to be measured 21 is not present and is taken as a reference image. One method for calculating a reference image is to perform projective transformation on the printing data of the background image 22 in accordance with the positional relationship between the imaging means 23 and the background image 22. Another method for calculating a reference image is to detect an image of a marker on the background image that is located outside the area of ​​the object to be measured in the measurement image. Then, a projective transformation matrix is ​​calculated from the marker position, and the reference image is calculated by projectively transforming the printing data that constitutes the background image 22. In this type of reference image calculation method, printing data of the background image 22 is used instead of image data obtained by capturing the background image 22. This type of reference image calculation method converts the printing data into the way it appears from the imaging means to obtain a reference image. In this second processing method, a reference image is acquired by calculation, so that a reference image for calibration can be acquired regardless of whether or not the object to be measured 21 is present.

[0046] <Measurement image acquisition unit> The measurement image acquisition unit 24B acquires, as a measurement image, image data of a background image captured by the imaging means when the object to be measured is present between the background image and the imaging means. The measurement image acquisition unit 24B may acquire a measurement image each time the position of the object to be measured changes relatively, and may perform image processing based on the multiple measurement images acquired in this manner to integrate the multiple measurement images and convert them into a single measurement image.

[0047] <Film thickness deviation calculation section> The film thickness deviation calculation unit 24C calculates the amount of displacement between the background images based on the reference image acquired by the reference image acquisition unit 24A and the measurement image acquired by the measurement image acquisition unit 24B. Then, the film thickness deviation of the object to be measured is calculated from the amount of displacement. The film thickness deviation calculation unit 24C may execute the process of calculating the film thickness deviation every time a measurement image is acquired by the measurement image acquisition unit 24B.

[0048] [Calculation of background displacement] The amount of displacement between the background image in the reference image and the background image in the measurement image can be calculated using various known methods, such as template matching and wavelet analysis. Template matching is a technique used in particle image velocimetry (PIV). When using template matching, a reference image is divided into small inspection windows, for example, 64 pixels square. Then, the cross-correlation coefficient between the image within the inspection window and an area of ​​the same size as the measurement image is calculated, and this calculation is repeated for the entire area or a portion of the measurement image. The point with the highest cross-correlation coefficient is then calculated as the coordinate of the inspection window. Note that the above description of template matching is an example. An inspection window may be set on the measurement image side, and the scanned image may be used as the reference image. Furthermore, the inspection windows may overlap, and the size of the inspection window may be rectangular or other shapes other than square. To reduce the amount of calculation, it is preferable to limit the scanning range by setting a safety factor to the maximum value that can reasonably be considered as the gradient of the film thickness deviation.

[0049] There are several known methods for calculating cross-correlation coefficients. Among these, applying normalized cross-correlation coefficients, especially zero-mean normalized cross-correlation coefficients (ZNCC), is preferable from the viewpoint of robustness to brightness fluctuations. However, normalized cross-correlation coefficients require a large amount of calculation. Therefore, when calculation speed is particularly important, applying sum of absolute differences (SAD) or sum of squared differences (SSD) is preferable. Furthermore, template matching is known to result in erroneous vectors. Various well-known methods can be used to deal with erroneous vectors. For example, methods that set a cutoff value for the cross-correlation coefficient, methods that allow erroneous vectors at a small number of calculation points by taking into account that the film thickness deviation is an integral value, or combinations of these methods can be easily applied to deal with erroneous vectors.

[0050] Wavelet analysis is also preferably applied when measuring film thickness deviation in only one specific direction. When calculating the amount of displacement using wavelet analysis, the background image 22 is preferably a stripe image composed of waves with a predetermined spatial frequency and having a periodic brightness distribution. For example, a stripe image composed of a brightness distribution expressed as a sine wave adopted over the entire region, with the amount of displacement calculated using a value with a safety factor set to the maximum value reasonably conceivable as the gradient of film thickness deviation, can be used as the background image. An example of a method using wavelet analysis in the BOS method for fluids is the method described in Non-Patent Document 1. Here, the continuous wavelet transform is expressed by the following equation (6).

[0051]

number

[0052] Here, the number of elements in one column is represented by n, the i-th luminance by x(i), and the mother wavelet by Ψ(i). The complex conjugate of the wavelet function is represented by Ψ with an overline (superscript bar). The inverse of the scale parameter a corresponds to the frequency. The shift parameter b corresponds to the spatial coordinate. Various functions have been proposed for the mother wavelet Ψ(i), including, for example, the Morlet complex wavelet function expressed by the following equation (7).

[0053]

number

[0054] In continuous wavelet transform, one-dimensional luminance distributions along the stripe direction are extracted from the reference image and the measurement image. Then, continuous wavelet transform can be performed to obtain intensity versus frequency and spatial coordinates. The amount of background displacement can be calculated by calculating the phase of the luminance distribution at each spatial coordinate from the spatial distribution of intensity obtained by the wavelet transform, and then calculating the background displacement from the phase difference between the reference image and the measurement image. However, it is preferable to use a complex wavelet function, which directly obtains phase information in addition to intensity during continuous wavelet transform, to calculate the background displacement from the phase difference between the reference image and the measurement image. Multiplying the phase difference by the period of the luminance distribution gives the displacement Δh on the background image 22. Furthermore, if a specific function other than a sinusoidal wave is used to represent the luminance distribution of the background image 22, it is preferable to use a complex mother wavelet similar to that function. Furthermore, especially when the frequency variation of the stripes due to film thickness deviation is not very large, a constant window size relative to the frequency does not have a significant effect. Therefore, using a short-time Fourier transform instead of a continuous wavelet transform simplifies implementation.

[0055] [Calculation of film thickness deviation] The background displacement Δh obtained as described above can be used to calculate the film thickness deviation. For example, the following equation (8) can be used, in which an integral path is set that first proceeds from the origin in the longitudinal direction of the film being measured, and then proceeds in a direction perpendicular to the outward direction.

[0056]

number

[0057] where: t(x,y): Film thickness deviation obtained by subtracting the film thickness of the object at the origin (0,0) from the film thickness of the object at coordinates (x,y) n target : Refractive index of the object to be measured n air : is the refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: A two-dimensional vector representing the amount of displacement of the background image of interest in the measurement image from the same background image in the reference image. Δhx: x-component of background displacement Δx: length in the x direction per pixel is.

[0058] In the above equation (8), the integral path is specifically written out. However, more generally, it can be expressed in the form of the following equation (1), for example.

[0059]

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[0060] where: t: Film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target : Refractive index of the object to be measured n air : Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: A two-dimensional vector representing the amount of displacement of the background image of interest in the measurement image from the same background image in the reference image. v: unit tangent vector of path C "∫ c Δh·vdl": Line integration of the inner product of the above Δh and v over the integral path C from the origin to the measurement point is.

[0061] (Actions and others) The film thickness deviation of the object to be measured obtained by the above method can be displayed by a known visualization method. When the film thickness deviation is determined in only one specific direction, it is preferable to display it as a line graph. When the film thickness deviation is determined in an in-plane direction, it is preferable to display it as an overlaid line graph or a heat map. In this case, the film thickness deviation is, for example, the film thickness of the object to be measured at the measurement point minus the film thickness of the object to be measured at the origin. For this reason, it may be more preferable to display the film thickness as an absolute value by adding the film thickness of the object to the measurement point at the origin, which is determined by an appropriate method. Examples of methods for obtaining the film thickness of the object to be measured at the origin include measuring only one point using a known film thickness meter such as a contact or transmission type, and using a nominal film thickness regardless of the actual film thickness.

[0062] (Film manufacturing equipment (film manufacturing method)) Next, the film manufacturing apparatus (film manufacturing method) of this embodiment will be described. FIG. 4 shows a schematic configuration of a film manufacturing apparatus 30 of this embodiment. The film manufacturing apparatus 30 of this embodiment has an extruder 35, a T-die 36, a cooling roll 37, a stretching machine 38, and a winder 39. The T-die 36 has a plurality of lip gap adjustment means 361. The film manufacturing apparatus 30 of this embodiment also has a film thickness deviation measuring device. The film thickness deviation measuring device includes the background image 32, the imaging means 33, and the calculation unit 34, which are configured as described above. Reference numeral 40 denotes a lip gap adjustment unit.

[0063] <Extruder> The extruder 35 is equipped with one or more feeders or hoppers, and melts and kneads multiple types of resins and fillers as necessary. The extruder 35 can be either a single-screw extruder or a twin-screw extruder, and may be a multi-stage extruder. A plurality of extruders 35 may be provided and connected to a T-die 36. Note that it is preferable to provide a filter, a vent, and a gear pump to improve the quality of the extruded resin and stabilize the extrusion rate. The extruder 35 may have a known configuration.

[0064] <Tダイ> The T-die 36 discharges the molten resin extruded from the extruder 35 through a gap and continuously forms a resin film of the target thickness. If the film to be produced has a multilayer structure, either the feed block method or the multi-manifold method can be applied. The feed block method is a method in which the molten resin flows together before the T-die. The multi-manifold method is a method in which the single layers are spread inside the T-die and then joined together near the lip.

[0065] [Lip gap adjustment means 361] The T-die 36 has a plurality of lip gap adjusting means 361 provided along the lip longitudinal direction of the T-die 36. The lip gap adjusting means 361 adjusts the width of the lip gap in accordance with a command from the lip gap adjusting unit 40 or manual operation, thereby adjusting the film thickness of the molten resin (film). The lip gap adjusting unit 40 generates and outputs a command for feedback control of the film thickness based on information on the film thickness deviation in the width direction from the calculating unit 34. Any known method may be applied as the lip gap adjustment mechanism of the lip gap adjustment means 361. Suitable examples of such mechanisms include a method in which the amount of pressing is changed by rotating a threaded bolt, a heat bolt type in which a cartridge heater is built in and the lip gap is thermally expanded and contracted, and a method in which adjustment is made by applying hydraulic pressure to the bolt or T-die.

[0066] <Cooling roll 37> The cooling roll 37 cools and solidifies the molten resin extruded from the lip gap of the T-die 36, and forms it into a film. The chill roll 37 is preferably equipped with a pinning device such as an electrostatic application type, a suction chamber type, or an air knife type, or a touch roll, for the purposes of suppressing fluctuations in film thickness and improving surface properties. In addition, to increase the cooling rate of the molten resin, part of the chill roll may be immersed in water or sprayed with water.

[0067] <Stretching machine 38> The stretching machine is a device that stretches the film formed by the cooling roll 37. The stretching process may be performed as needed, and the film to be produced does not need to be stretched. The stretching machine 38 constitutes the stretching step. When stretching is performed using the stretching machine 38, stretching in the machine direction (MD direction: longitudinal direction) and stretching in the width direction (TD direction) can be performed alone or in combination. That is, a method of stretching only in the MD direction, a method of stretching only in the TD direction, a method of sequentially stretching in the MD direction and the TD direction, or a method of simultaneously stretching in the MD direction and the TD direction can be used. Furthermore, various stretching methods can be used, such as a method of sequentially stretching in the MD direction and the TD direction and then re-stretching in the MD direction or the TD direction. Regarding the stretching treatment, it is preferable to select and use a stretching method, including no stretching, depending on the type of resin and the application of the film.

[0068] Furthermore, for longitudinal stretching in the MD direction, examples include single-stage stretching using a pair of rolls with a speed difference, and multi-stage stretching using multiple pairs of rolls. Both of these can be suitably used. Furthermore, examples of methods for raising the temperature of the film for stretching include a method using a preheating roll and a method of heating the film non-contactly using an infrared heater or the like. Both of these can be suitably used. Furthermore, near the outlet of the stretching machine 38, surface treatments such as heat setting to relax the film while heating or corona treatment may be performed. The measured value of the film thickness deviation obtained by the film thickness deviation measuring device can also be used to control the stretching machine 38.

[0069] <Rewinder 39> The winding machine 39 is a device that winds up the produced film into a roll. The film wound into a roll becomes the product to be shipped. It is preferable to install quality assurance equipment such as a surface inspection device, a pinhole inspection device, and a film thickness meter just before the winder 39. It is also preferable to trim the product to the desired width using a slitter or trimmer. Oscillation winding may be performed to prevent gauge bands during winding.

[0070] <Film thickness deviation measuring device> The film thickness deviation measuring device may have a configuration similar to that of the film thickness deviation measuring device of the present embodiment described above. The background image and the imaging means (imaging means) are positioned opposite each other across the film pass line. In the example shown in FIG. 4, the background image 32 and imaging means 33 are positioned at the pass line between the chill roll 37 and the stretching machine 38. However, the background image 32 and imaging means 33 may also be positioned before or downstream of the stretching machine 38. That is, the thickness deviation measurement unit consisting of the background image 32 and imaging means 33 can be installed anywhere from downstream of the T-die 36 to upstream of the winder 39. Considering the speed of feedback control and the possibility that the refractive index of the film 31 may change due to processing in the stretching machine 38, it is preferable to install it upstream of the stretching machine 38. Furthermore, if the background image 32 and imaging means 33 increase the distance between the lip of the T-die 36 and the chill roll 37, there is a risk of increased thickness unevenness in the MD and necking in the TD. For this reason, it is preferable to install the thickness deviation measurement unit downstream of the chill roll 37.

[0071] As described above, the background image 32 may be any image that allows detection of the amount of displacement when the position on the measurement image changes depending on the presence or absence of the film 31. In particular, a random dot image or a striped image with a periodic luminance distribution is preferable as the background image 32 from the viewpoint of resolution. As described above, various digital cameras can be used for the imaging means 33. In this example, the use of a line camera in particular is expected to improve processing speed and reduce equipment costs. The imaging means 33 may also be a collection of multiple cameras. Incidentally, by making the imaging means 33 double as a surface inspection device, it becomes possible to find foreign matter, defects, etc. at an early stage. In this case, a surface inspection calculation unit (not shown) is provided that performs a surface inspection based on the image captured by the imaging means 33.

[0072] It is preferable that the background image 32 and the imaging means 33 are installed on the same structure. In this case, it is possible to prevent misalignment between the background image 32 and the imaging means 33 due to vibrations during operation, etc. Furthermore, it is more preferable that the installed structure has a mechanism that allows it to be pulled out offline during operation to capture a reference image in order to calibrate the misalignment. Furthermore, from the viewpoint of analytical calculations and preventing out-of-focus images, it is preferable to set the optical axis of the imaging means 33 so that it is perpendicular to the film 31 and background image 32. The axis connecting the film 31, background image 32, and imaging means 33 may be arranged vertically as shown in Fig. 4. However, the axis may be arranged horizontally or at any other angle depending on the installation environment and other constraints.

[0073] There may be other visible light-transmitting structures, such as glass windows, in the gap between the film 31 and the background image 32, or between the film 31 and the imaging means 33. However, the structures must be such that the film 31 and the background image 32 can be recognized through the imaging means 33. If the structures have film thickness deviations, it is preferable to correct the displacement of the background image 32 or the calculated film thickness deviation of the film 31. However, if the distance between the background image 32 and the structures is short and has only an acceptable effect on the calculation results of the film thickness deviation of the measured object 31, correction may not be necessary. It is also more preferable that the structures have no film thickness deviations.

[0074] As described above, the calculation unit 34 calculates the amount of background displacement between the reference image and the measurement image to calculate the film thickness deviation. Information on the film thickness deviation in the width direction is then supplied to the lip gap adjustment unit 40. The reference image is, as described above, a captured image or a computationally derived image. The measurement image is an image of a background image 32 captured by an imaging means 33 with a film 31 interposed therebetween, as described above. In this example, the object to be measured is transported along a pass line at a predetermined transport speed. The transport speed at the film thickness deviation measurement position may be relatively slowed down by using a looper system or the like.

[0075] As for the method for calculating the amount of displacement of the background image between the reference image and the measurement image, various known methods can be used, as described above. However, in this example, information on the film thickness deviation is fed back to the control of the lip gap adjustment means. From this perspective, it is preferable to calculate the film thickness deviation only in the TD direction. Furthermore, it is particularly preferable to use wavelet analysis or short-time Fourier analysis to calculate the amount of displacement of the background image. The film thickness deviation is calculated using the displacement of the background image calculated by the above method. As with the calculation method described above, various integral paths can be used. However, in this example, it is preferable to calculate only in the TD direction, from the viewpoint of feeding back the film thickness deviation to the control of the lip gap adjustment means. For example, it is more preferable to use the following equation (9).

[0076]

number

[0077] where: t(x): film thickness deviation obtained by subtracting the film thickness of the film 31 at the origin x = 0 from the film thickness of the film 31 at the TD direction coordinate x n target : Refractive index of film 31 n air : is the refractive index of the atmosphere d: Distance between background image 32 and film 31 Δhx: The distance of the background image of interest in the measurement image from the same background image in the reference image in the TD direction Δx: length in the x direction per pixel is.

[0078] The thickness deviation of the film 31 obtained by the above method can be displayed by a known visualization method. In this embodiment, it is preferable to display only the information on the calculated film thickness deviation in the TD direction from the viewpoint of feeding back the information on the calculated film thickness deviation to the control of the lip gap adjusting means. Furthermore, in order to know the fluctuation of the film thickness deviation over time, it is more preferable to display, for example, a line graph with the TD direction coordinate on the horizontal axis and the film thickness deviation on the vertical axis, with the color of the line changing over time.

[0079] The lip gap adjustment unit 40 compares the film thickness deviation profile of the actual film 31 obtained as described above with the ideal film thickness deviation profile of the film 31 input in advance to the calculation unit 34. Then, the lip gap adjustment means 361 is controlled to increase the lip gap corresponding to the TD direction coordinate in order to thicken the portion where the actual film thickness is thinner than the ideal film thickness. The lip gap adjustment means 361 is also controlled to decrease the lip gap corresponding to the TD direction coordinate in order to thin the portion where the actual film thickness is thicker than the ideal film thickness. That is, the measured film thickness deviation profile is compared with the ideal film thickness deviation profile to determine the film thickness difference at the position corresponding to each lip gap adjustment means 361 in the film width direction. Then, each lip gap adjustment means 361 is feedback-controlled so that the difference falls within a predetermined range.

[0080] Here, necking occurs when the film is discharged from the T-die. For this reason, the distance from the TD center to a specific position on the film 31 when imaged by the imaging means 33 is generally different from the distance from the TD center to the specific position on the molten resin when discharged from the T-die lip. Therefore, it is preferable that the lip gap adjustment unit 40 use various known methods to determine which lip gap adjustment means 361 to issue a command to when it detects the difference between the actual film thickness deviation and the ideal film thickness deviation at a specific TD direction coordinate. It is also known that accuracy is improved by simultaneously moving multiple lip gap adjustment means 361 in consideration of influence coefficients rather than moving only one. For this reason, it is preferable to weight the results of calculations using various known methods and operate multiple lip gap adjustment means 361 simultaneously.

[0081] The above describes the embodiments of the present invention. However, the present invention is not limited to these embodiments, and various modifications are possible without departing from the spirit of the invention. Furthermore, the film in the above description includes resin compositions that are generally called sheets because they are relatively thick.

[0082] (others) The present disclosure may also have the following configuration. (1) A method for measuring film thickness deviation, The film to be measured is the object to be measured. A preset background image can be captured by an imaging means; a reference image is acquired which is an image of the background image captured by the imaging means without the object to be measured being present, or a reference image derived by calculation of how the background image appears when captured by the imaging means without the object to be measured being present; The object to be measured is interposed between the background image and the imaging means, and a measurement image is acquired by capturing the background image with the imaging means; Based on the acquired reference image and measurement image, the amount of displacement of the background image in these two images is calculated to determine the film thickness deviation of the object to be measured. Film thickness deviation measurement method. (2) The film thickness deviation is calculated using the above formula (1). (3) The integral path C is a path that proceeds from a preset origin in a first direction that is either the longitudinal direction of the object to be measured or a direction perpendicular to the longitudinal direction of the object to be measured, and then in a second direction that is perpendicular to the first direction. (4) A method for measuring a film thickness deviation of the object to be measured, which is conveyed so as to pass between the background image and the imaging means, When the film thickness deviation of the object to be measured is the film thickness deviation in the width direction of the object, The integral path C is a line segment that proceeds from the origin in a direction perpendicular to the conveyance direction. (5) The background image is a random dot image, The amount of displacement Δh of the background image is calculated by template matching using normalized cross-correlation coefficients. (6) The background image is a striped image having a periodic brightness distribution and composed of waves having a predetermined spatial frequency, The amount of displacement Δh of the background image is calculated by wavelet analysis. (7) The visible light transmittance of the object to be measured is 10% or more. (8) A film manufacturing method in which a molten resin is discharged from a die having a plurality of lip gap adjusting means to form a film that is transmissive to visible light, The film discharged from the die is transported along a preset path line, a background image and an imaging means for capturing the background image are disposed across the pass line; acquiring a measurement image, which is an image obtained by capturing the background image through the film with the imaging means; acquiring a reference image, which is an image of the background image captured by the imaging means without the film being interposed between the background image and the imaging means, or a reference image derived by calculation of how the background image appears when viewed by the imaging means without the film being interposed; a step of comparing the acquired reference image with the acquired measurement image, and calculating the amount of displacement of the background image between the two images in the film width direction, thereby calculating a film thickness deviation profile in the film width direction; a step of operating the lip gap adjusting means so that the film thickness deviation at each point becomes a target value based on the calculated film thickness deviation profile; A film manufacturing method comprising: (9) The visible light transmittance of the film extruded from the die is 10% or more; A stretching step for stretching a film is provided downstream of the position on the pass line where the measurement image is acquired. (10) A device for measuring the thickness deviation of a film that transmits visible light, The film to be measured is the object to be measured. a background image; and imaging means for capturing the background image; a reference image acquisition unit that acquires a reference image, which is an image of the background image captured by the imaging means without the object to be measured being present, or a reference image derived by calculation of how the background image appears when captured by the imaging means without the object to be measured being present; a measurement image acquisition unit that acquires a measurement image, which is an image obtained by capturing the background image with the imaging means, with the object to be measured being interposed between the background image and the imaging means; a film thickness deviation calculation unit that calculates the amount of displacement of the background image in the reference image and the measurement image based on the acquired two images, thereby determining the film thickness deviation of the object to be measured; Equipped with. (11) The background image is a random dot image. (12) The background image is a striped image that is composed of waves having a predetermined spatial frequency and has a periodic brightness distribution. (13) The object to be measured has a visible light transmittance of 10% or more. (14) A film manufacturing apparatus that extrudes molten resin from a die having a plurality of lip gap adjusting means to form a film that can transmit visible light, The film discharged from the die is transported along a preset path line, Imaging means for capturing background images are arranged on either side of the pass line; a measurement image acquisition unit that acquires a measurement image, which is an image obtained by capturing the background image through the film by the imaging means; a reference image acquisition unit that acquires a reference image obtained by capturing the background image with the imaging means without the film being interposed between the background image and the imaging means, or a reference image derived by calculation of how the background image appears when viewed by the imaging means without the film being interposed; a film thickness deviation information acquisition unit that compares the acquired reference image with the acquired measurement image and calculates the amount of displacement of the background image between the two images in the film width direction, thereby calculating a film thickness deviation profile in the film width direction; a lip gap adjusting unit that operates the lip gap adjusting means based on the calculated film thickness deviation profile so that the film thickness deviation at each point becomes a target value; Film manufacturing equipment. (15) The visible light transmittance of the film extruded from the die is 10% or more; A stretching machine for stretching the film is provided downstream of the position on the pass line where the image is captured by the imaging means. [Example]

[0083] Examples based on this embodiment will be described below. However, the following examples are merely intended to explain one example of the present invention in more detail and are not intended to limit the scope of the present invention.

[0084] (Measurement conditions in this example) In this example, a PET film was used as the film for the object to be measured 21. A photograph of a random dot image was used as the background image 22. A single-lens reflex camera was used as the imaging means 23. As shown in FIG. 2, the imaging means 23 consisting of a single-lens reflex camera, the object to be measured 21 consisting of a PET film, and the background image 22 consisting of a random dot image were arranged in the vertical direction. The vertical direction is the direction perpendicular to the surface of the background image 22. The PET film in this example was an unstretched film with an average thickness of 95 μm extruded by a T-die method, with a standard deviation of 1.8 μm in the MD direction and 25 μm in the TD direction. The PET film and the random dot image were placed 50 mm apart, and the PET film and the SLR camera were placed 600 mm apart.

[0085] (Measurement process of film thickness deviation) First, a reference image was obtained by capturing a background image without the PET film. In other words, a photograph of the random dot image was taken with a single-lens reflex camera without the PET film in between. Next, a background image was captured with the PET film in between to obtain a measurement image. That is, a photograph of the random dot image was captured with a single-lens reflex camera through the PET film. The two images obtained above were then imported into a personal computer, and calculation processing was carried out by the calculation unit 24 to determine the film thickness deviation. In this example, we first calculated the displacements in the MD and TD directions of the background image between two images by pattern matching using ZNCC. The distribution of the calculated background displacements is shown in Figure 5. ZNCC is a normalized cross-correlation of the template matching method.

[0086] Next, the film thickness deviation at each point was calculated from the background displacement distribution using the above-mentioned formula (8), and the film thickness deviation distribution shown in FIG. 6 was obtained. 5 and 6, the horizontal direction is the MD direction and the vertical direction is the TD direction. Also, in Figures 5 and 6, both ends in the MD direction are areas where there is no film and the background image is directly visible. The shading indicates the amount of background displacement or film thickness deviation. As can be seen from Fig. 6, the PET film used in this example has almost no thickness fluctuation in the MD direction, but shows periodic thickness fluctuation in the TD direction. It was also confirmed that the film thickness fluctuation period in the TD direction coincided with the spacing between the heat bolts installed in the T-die, reflecting the width of the T-die lip gap caused by the heat bolts.

[0087] As described above, it has been found that by using the present invention, it is possible to measure film thickness deviation data (information on film thickness deviation) in one-dimensional and two-dimensional directions along the film surface in a non-contact manner using a simple and safe device configuration.

[0088] The entire contents of Japanese Patent Application No. 2023-110735 (filed July 5, 2023), from which this application claims priority, are incorporated herein by reference. While the present application has described a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure would be obvious to those skilled in the art. [Explanation of symbols]

[0089] 20 Film Thickness Deviation Measuring Device 21 Object to be measured 22 background images 23 Imaging means 24 Arithmetic section 24A Reference image acquisition unit 24B Measurement image acquisition unit 24C Film Thickness Deviation Calculation Unit 25 Mounting stand 25A Top surface 30 Film manufacturing equipment 31 Film (object to be measured) 32 background images 33 Imaging means 34 Arithmetic section 35 Extruder 36 T-die 37 Cooling Roll 38 Stretching machine 39 Winder 40 Lip gap adjustment part 361 Lip gap adjustment means

Claims

1. A method for measuring film thickness deviation, comprising: The film to be measured is the object to be measured. A preset background image can be captured by an imaging means; a reference image is acquired which is an image of the background image captured by the imaging means without the object to be measured being present, or a reference image derived by calculation of how the background image appears when captured by the imaging means without the object to be measured being present; The object to be measured is interposed between the background image and the imaging means, and a measurement image is acquired by capturing the background image with the imaging means; Based on the acquired reference image and measurement image, the amount of displacement of the background image in these two images is calculated to determine the film thickness deviation of the object to be measured; The film thickness deviation is calculated using the following formula (1): Film thickness deviation measurement method. [Equation 1] where: t: film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target: refractive index of the object to be measured n air: Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: a two-dimensional vector representing the amount of displacement (amount of movement) of the background image of interest on the measurement image from the same background image in the reference image v: unit tangent vector of path C "∫ c Δh vdl": An operation of integrating the inner product of the above Δh and the above v over an integral path C from the origin to the measurement point is.

2. The integral path C is a path that proceeds from a preset origin in a first direction that is either the longitudinal direction of the object to be measured or a direction perpendicular to the longitudinal direction of the object to be measured, and then in a second direction that is a direction perpendicular to the first direction. The film thickness deviation measuring method according to claim 1 .

3. a method for measuring a film thickness deviation of the object to be measured, the object being transported so as to pass between the background image and the imaging means, When the film thickness deviation of the object to be measured is the film thickness deviation in the width direction of the object, The integral path C is a line segment that proceeds from the origin in a direction perpendicular to the conveying direction. The film thickness deviation measuring method according to claim 1 .

4. The background image is a random dot image, The displacement amount Δh of the background image is calculated by template matching using a normalized cross-correlation coefficient. The method for measuring film thickness deviation according to any one of claims 1 to 3.

5. the background image is a striped image that is composed of waves having a predetermined spatial frequency and has a periodic luminance distribution, The displacement amount Δh of the background image is calculated by wavelet analysis. The film thickness deviation measuring method according to claim 1 or 3.

6. The visible light transmittance of the object to be measured is 10% or more. The method for measuring film thickness deviation according to any one of claims 1 to 3.

7. The visible light transmittance of the object to be measured is 10% or more. The film thickness deviation measuring method according to claim 4.

8. The visible light transmittance of the object to be measured is 10% or more. The method for measuring film thickness deviation according to claim 5.

9. A film manufacturing method for forming a film that is transmissive to visible light by discharging molten resin from a die having a plurality of lip gap adjustment means, comprising: The film discharged from the die is transported along a preset path line, a background image and an imaging means for capturing the background image are disposed across the pass line; acquiring a measurement image, which is an image obtained by capturing the background image through the film with the imaging means; acquiring a reference image, which is an image of the background image captured by the imaging means without the film being interposed between the background image and the imaging means, or a reference image derived by calculation of how the background image appears when viewed by the imaging means without the film being interposed; a step of calculating a film thickness deviation profile, which is a profile of film thickness deviation in the width direction of the film, by comparing the acquired reference image with the acquired measurement image and calculating the amount of displacement of the background image between the two images in the width direction of the film; a step of operating the lip gap adjusting means so that the film thickness deviation at each point becomes a target value based on the calculated film thickness deviation profile; Equipped with The film thickness deviation is calculated using the following formula (1): A film manufacturing method. [Equation 2] where: t: film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target: refractive index of the object to be measured n air: Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: a two-dimensional vector representing the amount of displacement (amount of movement) of the background image of interest on the measurement image from the same background image in the reference image v: unit tangent vector of path C "∫ c Δh vdl": An operation of integrating the inner product of the above Δh and the above v over an integral path C from the origin to the measurement point is.

10. The visible light transmittance of the film extruded from the die is 10% or more, a stretching step for stretching the film, located downstream of a position on the pass line where the measurement image is acquired; The film manufacturing method according to claim 9.

11. A device for measuring film thickness deviation of a film that transmits visible light, The film to be measured is the object to be measured. a background image; and imaging means for capturing the background image; a reference image acquisition unit that acquires a reference image, which is an image of the background image captured by the imaging means without the object to be measured being present, or a reference image derived by calculation of how the background image appears when captured by the imaging means without the object to be measured being present; a measurement image acquisition unit that acquires a measurement image, which is an image obtained by capturing the background image with the imaging means, with the object to be measured being interposed between the background image and the imaging means; a film thickness deviation calculation unit that calculates a displacement amount of a background image in the reference image and the measurement image based on the acquired two images, thereby determining a film thickness deviation of the object to be measured; Equipped with The film thickness deviation is calculated using the following formula (1): Film thickness deviation measuring device. [Equation 3] where: t: film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target: refractive index of the object to be measured n air: Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: a two-dimensional vector representing the amount of displacement (amount of movement) of the background image of interest on the measurement image from the same background image in the reference image v: unit tangent vector of path C "∫ c Δh vdl": An operation of integrating the inner product of the above Δh and the above v over an integral path C from the origin to the measurement point is.

12. The background image is a random dot image. The film thickness deviation measuring device according to claim 11.

13. The background image is a striped image that is composed of waves having a predetermined spatial frequency and has a periodic brightness distribution. The film thickness deviation measuring device according to claim 11.

14. The object to be measured has a visible light transmittance of 10% or more. The film thickness deviation measuring device according to any one of claims 11 to 13.

15. A film manufacturing apparatus that extrudes molten resin from a die having a plurality of lip gap adjustment means to form a film that is transmissive to visible light, The film discharged from the die is transported along a preset path line, Imaging means for capturing background images are arranged on either side of the pass line; a measurement image acquisition unit that acquires a measurement image, which is an image obtained by capturing the background image through the film by the imaging means; a reference image acquisition unit that acquires a reference image obtained by capturing the background image with the imaging means without the film being interposed between the background image and the imaging means, or a reference image derived by calculation of how the background image appears when viewed by the imaging means without the film being interposed; a film thickness deviation information acquisition unit that compares the acquired reference image with the acquired measurement image and calculates the amount of displacement of the background image between the two images in the film width direction, thereby calculating a film thickness deviation profile that is a profile of film thickness deviation in the film width direction; a lip gap adjusting unit that operates the lip gap adjusting means based on the calculated film thickness deviation profile so that the film thickness deviation at each point becomes a target value; The film thickness deviation is calculated using the following formula (1): Film manufacturing equipment. [Equation 4] where: t: film thickness deviation obtained by subtracting the film thickness of the object to be measured at the origin from the film thickness of the object to be measured at the measurement point n target: refractive index of the object to be measured n air: Refractive index of the atmosphere d: Distance between the background image and the object being measured Δh: a two-dimensional vector representing the amount of displacement (amount of movement) of the background image of interest on the measurement image from the same background image in the reference image v: unit tangent vector of path C "∫ c Δh vdl": An operation of integrating the inner product of the above Δh and the above v over an integral path C from the origin to the measurement point is.

16. The visible light transmittance of the film extruded from the die is 10% or more, a stretching machine that stretches the film is provided downstream of a position on the pass line where the image is captured by the imaging means; The film manufacturing apparatus according to claim 15.

Images