JP2006047143A - Film inspection method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method of a film for easily detecting even extremely small defects. <P>SOLUTION: In the film inspection method, first and second polarizing plates 3, 4 are arranged in a crossed Nicol state at both the sides of the film 1, linear light is applied from the outside of the first polarizing plate 3 by a linear light source 2, light is received by a CCD line sensor 5 arranged outside the second polarizing plate 4, a signal obtained from the CCD line sensor 5 is converted to a digital signal by an A/D converter 6, the obtained digital signal is binarized by an image processing unit 7, a first direction in which a plurality of CCD cameras 5a are aligned in the CCD line sensor 5 is made parallel to the line direction of the linear light emitted from the linear light source 2 when detecting the presence or absence of defects, and the light reception surface of the CCD line sensor 5 for reducing the quantity of received light in the CCD line sensor 5 is inclined to the upper surface of the film 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film inspection method capable of detecting a defect due to foreign matter or the like generated in a transparent or translucent film, and more specifically, first and first arranged in a crossed Nicols state on both sides of a film. The present invention relates to a film inspection method using the polarizing plate 2.

  Conventionally, various synthetic resin films that are transparent or translucent have been used in the optical field. When this type of transparent or translucent film is mass-produced, defects may occur due to foreign matters mixed in or gel-like foreign matters. When such a defect occurs, not only the appearance of the film is impaired, but also the optical performance and the like may be greatly impaired.

  Therefore, conventionally, it has been necessary to inspect whether or not the above-mentioned defect exists in a manufactured transparent or translucent film with high accuracy. Patent Document 1 below discloses an example of a transparent defect detection method for such a film. In the method described in Patent Document 1, the first polarizing plate is arranged on one side of the film to be inspected, and the second polarizing plate is arranged on the other side. A projector for irradiating the film with light is disposed outside the first polarizing plate, and the outside of the second polarizing plate is covered by light transmitted through the second polarizing plate. An imaging device for imaging the inspection area of the inspection film is disposed.

  The film to be inspected is irradiated with light from the projector through the first polarizing plate. The light transmitted through the film to be inspected is guided to the imaging device via the second polarizing plate. In the inspection method described in Patent Document 1, the video signal obtained from the imaging device is processed in the image processing unit of the image processing device, the processed video signal is output to the monitor, and the image is displayed on the monitor. It is configured.

In the above inspection method, the first polarizing plate and the second polarizing plate are arranged in a state where the polarization planes of the first polarizing plate and the second polarizing plate are shifted from each other by about 20 degrees, and there is a defect in the film to be inspected. In this case, since the defect rotates the plane of polarization of the irradiated light, the luminance changes remarkably. And the presence or absence of a defect is detected by the change of the said brightness | luminance.
Japanese Patent Laid-Open No. 6-148095

  In the transparent defect detection method described in Patent Document 1, as described above, when a defect due to a foreign matter or the like occurs, the polarization plane of light incident on the film rotates, and the brightness changes based on the rotation of the polarization plane. The presence or absence of defects was detected. However, in this inspection method, the imaging apparatus is configured to receive as much light as possible, so that the defect cannot be detected when the change in the amount of light due to the defect is small. In other words, in the case of a defect that causes only a small light amount change, a defect that causes a large light amount change is detected because the ratio of the light amount change incident on the imaging device is small relative to the absolute value of the light amount. I couldn't.

  The object of the present invention is to detect the presence or absence of defects as accurately as possible in the case where defects due to the presence of, for example, gel-like foreign substances exist in a transparent or translucent film in view of the above-described state of the art. It is in providing the film inspection method which enables this.

  1st invention of this application is a film inspection method which detects the defect of the transparent or translucent film which has a length direction and a width direction, Comprising: In the area | region inspected of the said film, it is on the one surface side of a film The first polarizing plate is disposed on the other surface side in such a relationship that the first and second polarizing plates are in a crossed Nicols state, and a linear light source is used from the outside of the first polarizing plate. The film is irradiated with linear light extending in the film width direction on one surface of the film through the first polarizing plate, and the light passing through the second polarizing plate on the other surface side of the film Receiving a light by a CCD line sensor having a plurality of CCD cameras arranged along the direction of, and capturing an image of a detection area of the film, converting the output signal of the CCD line sensor into a digital signal, and Digital Binarizing the signal and detecting the presence or absence of a film defect based on the binarized signal, wherein the transmission axis direction of the first or second polarizing plate is parallel to the first direction. The line direction of the light emitted from the linear light source is parallel to the first direction, and the light receiving surface of the CCD line sensor is inclined with respect to the film surface.

  In the film inspection method according to the first aspect of the present invention, preferably, the first direction in which a plurality of CCD cameras are arranged in the CCD line sensor is at an inclination angle of 25 degrees or less with respect to the width direction of the film. Tilt.

  2nd invention of this application is a film inspection method which detects the defect of the transparent or translucent film which has a length direction and a width direction, Comprising: In the area | region inspected of the said film, it is on the one surface side of a film The first polarizing plate is disposed on the other surface side in such a relationship that the first and second polarizing plates are in a crossed Nicols state, and a linear light source is used from the outside of the first polarizing plate. The film is irradiated with linear light extending in the film width direction on one surface of the film through the first polarizing plate, and the light passing through the second polarizing plate on the other surface side of the film Receiving a light from a CCD line sensor having a plurality of CCD cameras arranged along the direction of the image and capturing an image of a detection area of the film, and converting the output signal of the CCD line sensor corresponding to each pixel into a digital signal Process Binarizing the digital signal and detecting the presence or absence of a film defect based on the binarized signal, the transmission axis direction of the first or second polarizing plate being the first direction The first direction in which a plurality of CCD cameras are arranged in the CCD line sensor is inclined at an inclination angle of 25 degrees or less with respect to the width direction of the film and emitted from the linear light source. The line direction of light is parallel to the first direction.

  In the film inspection method according to the first aspect of the present invention, the first and second polarizing plates are arranged in a relationship of being in a crossed Nicols state, and the transmission axis direction of the first or second polarizing plate is the first direction. The film is disposed between the first and second polarizing plates. Then, linear light is irradiated from the outside of the first polarizing plate using a linear light source, the light passing through the second polarizing plate is received by the CCD line sensor, and an image of the inspection area of the film is captured. Is done. In this case, in the first invention, the light receiving surface of the CCD line sensor is inclined with respect to the film surface. Therefore, since the light receiving surface of the CCD line sensor is not arranged so that the light emitted from the line light source is incident at the maximum light amount, even if the light amount change due to the defect is small, such a light amount change is not caused. The presence of few defects can be reliably detected. In addition, since the light is refracted in the portion where the defect is generated, not only the light traveling straight toward the CCD line sensor but also the light traveling toward the CCD line sensor due to refraction is received by the CCD line sensor. be able to. Therefore, even when the film does not have birefringence, the difference between the amount of light indicating the presence of a defect portion and the amount of light received at the surrounding normal portion is enlarged, thereby reliably detecting minute defects. It becomes possible.

In the first invention, in the CCD line sensor, when the first direction in which a plurality of CCD cameras are arranged is inclined at an inclination angle of 25 degrees or less with respect to the width direction of the film, birefringence When inspecting a film having the property, a minute defect can be detected more reliably. That is, when inspecting a film having birefringence, when linearly polarized light that has passed through the first polarizing plate passes through the film, the traveling speed of the slow axis component and the film fast axis component of the film is high. Because it is different, it passes through the film as elliptically polarized light. Since this elliptically polarized light includes the transmission axis direction component of the second polarizing plate, the light of the transmission axis direction component of the second polarizing plate passes through the second polarizing plate and is received by the CCD line sensor. Is done. In this case, if the slow axis or the fast axis of the film is completely perpendicular or parallel to the transmission axis or the absorption axis of the first polarizing plate, the film slow axis component or the film fast axis component It becomes the linearly polarized light which consists only of either. That is, since the light emitted from the film becomes the same linearly polarized light as before entering the film, the amount of light passing through the second polarizing plate is reduced. On the other hand, as described above, when the first direction is inclined at an angle of 25 degrees or less with respect to the width direction of the film, the light is transmitted through the film including the light transmitted through the defect portion. Since the total amount of light that has been transmitted increases, the amount of light transmitted through the film can be increased even when a defect that does not rotate the plane of polarization so much occurs. Therefore, such a defect can be detected more reliably.

  In the film inspection method according to the second aspect of the present invention, the first and second polarizing plates are arranged in a crossed Nicols state, and the transmission axis direction of the first or second polarizing plate is the first direction. The inspection region of the film is disposed between the first and second polarizing plates. Then, line-shaped light is irradiated from the outside of the first polarizing plate using a line-shaped light source, the light passing through the second polarizing plate is received by the CCD line sensor, and an image of the inspection region of the film is obtained. Imaged. In this case, in the CCD line sensor, the first direction in which a plurality of CCD cameras are arranged is inclined at an inclination angle of 25 degrees or less with respect to the width direction of the film.

  Therefore, when inspecting a film having birefringence, when the linearly polarized light transmitted through the first polarizing plate passes through the film, the traveling speed depends on the film slow axis component and the film fast axis component. Are different from each other and pass through the film as elliptically polarized light. Since this elliptically polarized light includes the transmission axis direction component of the second polarizing plate, the light of the transmission axis direction component of the second polarizing plate is transmitted through the second polarizing plate and received by the CCD line sensor. Will be.

  At this time, if the slow axis or fast axis of the film is completely perpendicular or parallel to the transmission axis or absorption axis of the first polarizing plate, the film slow axis component or the film fast axis component It becomes linearly polarized light consisting of only one of them. That is, since the light emitted from the film becomes the same linearly polarized light as before entering the film, the amount of light passing through the second polarizing plate is minimized.

  On the other hand, in the second invention, in the CCD line sensor, the first direction in which a plurality of CCD cameras are arranged is inclined at an angle of 25 degrees or less with respect to the width direction of the film. The total amount of light transmitted through the film, including the light transmitted through the defective portion, is increased. Therefore, even when a defect that does not rotate the polarization plane so much occurs, the amount of light transmitted through the film can be increased, so that such a defect can be detected.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a schematic perspective view for explaining a film inspection method according to an embodiment of the present invention, and FIG. 2 is a schematic front view thereof.

  In the film inspection method of the present embodiment, a long film 1 is prepared as an inspection object. As the film 1, an appropriate synthetic resin film that is transparent or translucent can be used. In the present embodiment, a defect in the film 1 having the length direction and the width direction is detected.

  A linear light source 2 is disposed below the film 1. As the line-shaped light source 2, an appropriate light source that transmits line-shaped, that is, linear light, can be used. The line-shaped light is configured to be irradiated toward the lower surface 1 a of the film 1. As is clear from FIG. 1, the direction of the line irradiated from the line light source 2 is arranged so as to form an inclination angle α with respect to the width direction W of the film 1. This inclination angle α is set to 25 degrees or less.

  A first polarizing plate 3 through which the light passes is disposed in front of the line light source 2. The first polarizing plate 3 passes only the component in the light transmission axis direction of the first polarizing plate 3 out of the light emitted from the line-shaped light source 2 to be linearly polarized light. Accordingly, the linearly polarized light is irradiated onto the film 1.

  On the other hand, a second polarizing plate 4 is disposed above the upper surface 1 b of the film 1. The second polarizing plate 4 is configured such that its polarization plane forms an angle of 90 degrees with the polarization plane of the first polarizing plate 3. Therefore, the 1st, 2nd polarizing plates 3 and 4 are arrange | positioned so that it may become a crossed Nicols state. Further, the second polarizing plate 4 is disposed at a position facing the first polarizing plate 3 with the film 1 interposed therebetween. In the present embodiment, the plurality of second polarizing plates 4 are attached to the lower surfaces of the plurality of CCD cameras 5a. The plurality of CCD cameras 5a are arranged in a straight line as shown in FIG. 1, and a CCD line sensor 5 is constituted by the plurality of CCD cameras 5a. Each CCD camera 5a has a plurality of CCD elements corresponding to a plurality of pixels, and each CCD element is configured to output a signal corresponding to each pixel.

  The direction in which the plurality of CCD cameras 5a are arranged is the first direction in the present invention, and this first direction is parallel to the line-shaped light emitted from the line-shaped light source 2 described above. . Accordingly, the first direction is inclined so as to form an inclination angle α with respect to the width direction W of the film 1. And the inclination | tilt angle (alpha) is 25 degrees or less.

  In the inspection method of this embodiment, as shown in FIG. 2, the light receiving surface of the CCD line sensor 5 is not parallel to the upper surface of the film 1 but is inclined with respect to the upper surface of the film 1. That is, the CCD line sensor 5 is not arranged so that the light emitted from the line light source 2 has the maximum light amount. Therefore, even if the change in the amount of light due to the presence of a defect is slight, the ratio of the change in the amount of light to the absolute value of the amount of light becomes high, so that the presence of such a defect can be reliably detected. In FIG. 2, only the positions where the first and second polarizing plates 3 and 4 are arranged are schematically shown by broken lines.

  An A / D converter 6 as A / D conversion means is electrically connected to the CCD line sensor 5. The A / D converter 6 converts a video signal corresponding to each pixel output from each CCD element of the CCD line sensor 5 into a digital signal. An image processing device 7 is connected to the A / D converter 6. The image processing device 7 binarizes the digital signal obtained from the A / D converter 6 and detects the presence or absence of a defect based on the binarized signal. More specifically, the digital signal corresponding to the luminance obtained from the A / D converter is set to “1” when the digital signal is larger than the threshold, and “0” when the digital signal is lower than the threshold. And binarized. When a defect exists, the luminance increases, so that a “0” signal is output as a binarized signal, thereby determining that a defect exists.

  The threshold for binarization can be determined by various methods. For example, the output signal corresponding to each pixel is averaged, an average value is obtained, and “1” is obtained when the value obtained by subtracting the average value from the value of the output signal corresponding to each pixel is a positive value. As described above, the threshold value may be the average value. In addition, the threshold value may be determined so that the value obtained by subtracting the average value from the value of the output signal of each pixel instead of the average value is binarized according to a preset threshold value.

  More specifically, the image processing device 7 displays an image based on the binarized signal. This point will be described in detail when a specific process of the inspection method is described later.

  As described above, the image processing device 7 binarizes the digital signal obtained from the A / D converter 6 and determines whether or not there is a defect and an image on a monitor or the like based on the binarized signal. Has a function of outputting a signal for displaying. The image processing apparatus 7 may be provided with the monitor.

  Next, specific steps of the film 1 inspection method will be described.

  First, a transparent or translucent long film is positioned between the first and second polarizing plates 3 and 4 as shown in FIGS. The film 1 is irradiated with light from the line light source 2 through the first polarizing plate 3. In the first polarizing plate 3, only the component parallel to the transmission axis of the first polarizing plate 3 passes and such linearly polarized light is incident on the film 1.

  When the film 1 has no defect, the linearly polarized light passes through the film 1 and reaches the second polarizing plate 4. The second polarizing plate 4 is arranged in a crossed Nicols state with respect to the first polarizing plate 3. Accordingly, the linearly polarized light that has passed through the first polarizing plate 3 does not pass through the second polarizing plate 4. Accordingly, a sufficient amount of light cannot be given to each CCD camera 5a of the CCD line sensor 5. Therefore, when the signal output from the CCD line sensor 5 is converted into a digital signal by the A / D converter 6, the digital signal becomes a digital signal corresponding to such a low-brightness signal. Therefore, in the image processing apparatus 7, the digital signal obtained from the A / D converter 6 has a value equal to or less than the above-described threshold value, and therefore outputs a signal “0”. That is, it indicates that there is no defect.

  When the image processing apparatus 7 is provided with a monitor, the pixel is in a dark state according to the signal “0” as described above.

  On the other hand, as shown in FIG. 3, when a defect 1A exists due to a foreign substance such as a gel-like substance in a part of the film 1, as shown in FIG. The light X that has passed through the first polarizing plate 3 is refracted. That is, in the case where the defect 1A exists in each CCD camera unit 5a of the CCD line sensor 5, not only the light traveling straight toward the CCD camera 5a but also the light X caused by refraction due to the existence of the defect 1A. It will be incident. And the light X by such refraction also enters. Therefore, when the defect 1A is present as compared with the normal part around the defect 1A, a larger amount of light is incident on the CCD camera 5a.

On the other hand, in this embodiment, as shown in FIG. 2, the light receiving surface of the CCD line sensor 5 is inclined with respect to the upper surface of the film 1. As described above, the CCD line sensor 5 is not disposed so as to receive the light emitted from the line light source 2 with the maximum amount of light, but is inclined with respect to the film surface as described above. . Therefore, even if there is a defect in the film 1 that slightly changes the amount of light, the ratio of the slight change in light amount due to the presence of the defect to the amount of light received by the CCD line sensor 5 becomes relatively large. for that reason,
It is possible to detect a defect that causes only a slight change in the amount of light with high accuracy.

  That is, as shown in FIG. 2, the light receiving surface of the CCD camera 5 a is not orthogonal to the alternate long and short dash line Q orthogonal to the film 1, in other words, is inclined with respect to the upper surface of the film 1. An alternate long and short dash line P in FIG. 2 indicates a direction orthogonal to the light receiving surface of the CCD camera 5a.

  The graph of incident light intensity in the lower part of FIG. 2 means that the incident light intensity is highest when light in the direction indicated by the alternate long and short dash line Q is incident on the CCD camera 5a from the front. That is, when the light receiving surface of the CCD camera 5a is tilted as described above and light in the direction indicated by P enters from the front, the incident light intensity decreases according to the deviation from the center of the light source.

  As described above, when the defect 1A exists, the signal output from the CCD element corresponding to the pixel in the portion where the defect 1A exists becomes a video signal corresponding to high luminance. A video signal corresponding to the high luminance is output to the A / D converter. Since the digital signal output from the A / D converter 6 is a DC voltage signal having a magnitude corresponding to the high luminance, the image processing apparatus 7 recognizes that such a digital signal is larger than a threshold value. The signal “1” is output. That is, it is determined that there is a defect. Further, when the image processing apparatus 7 is provided with a monitor, a portion corresponding to the portion where the defect exists is displayed brightly on the monitor screen.

  FIG. 5A is a diagram schematically showing an inspection image after A / D conversion. Here, when there is a defect in the center, a portion surrounded by a broken line L is compared with a surrounding normal portion. Appears bright. Further, when the digital signal is binarized and discriminated into a signal “1” and a signal “0” and displayed by the image processing apparatus, the circle indicated by the solid line M in FIG. The display is brighter than in the broken line M shown in FIG. That is, the brightness of the surrounding normal part and the part where the defect exists is further increased by the binarization process, and the presence or absence of the defect can be easily determined.

  The first and second polarizing plates 3 and 4 are arranged in a crossed Nicols state, but the transmission axis direction of one polarizing plate 3 and 4 is aligned with the first direction in the CCD line sensor 5. If not, the polarizing plates 3 and 4 are in a completely crossed Nicol state at the center of the CCD line sensor 5, but deviate from the crossed Nicol state at the edge of the field of view. For this reason, the optical conditions in the field of view are not uniform, and the detection of defects becomes inaccurate. Therefore, the direction of the transmission axis of the polarizing plates 3 and 4 is preferably parallel to the first direction described above.

  When the direction of the transmission axis or absorption axis of the first and second polarizing plates 3 and 4 is deviated from 90 degrees, the sensitivity is different between the center and the end of the field of view in the CCD line sensor 5 in the same manner. Optical conditions in the field of view tend to be non-uniform. Therefore, it is desirable that the polarizing plates 3 and 4 are arranged in a crossed Nicols state as described above.

  In the above-described embodiment, as described above, the first direction of the CCD line sensor 5, that is, the direction in which the plurality of CCD cameras 5 a are arranged forms an angle α with respect to the width direction W of the film 1. It is inclined. Therefore, when the film 1 is a film having birefringence, defects can be detected with higher accuracy.

That is, in the case of the film 1 having birefringence, the linearly polarized light transmitted through the first polarizing plate 3 when the first and second polarizing plates 3 and 4 are arranged in the crossed Nicols state. When the light passes through the film 1, the traveling speed is different between the slow axis component and the fast axis component of the film 1, so that the light passes through the film 1 as elliptically polarized light. This elliptically polarized light includes a transmission axis direction component of the second polarizing plate 4. Accordingly, the light in the transmission axis direction component passes through the second polarizing plate 4 and is received by the CCD line sensor 5.

At this time, when the slow axis or fast axis of the film 1 is completely orthogonal or parallel to the transmission axis or absorption axis of the second polarizing plate 4, the light incident on the CCD line sensor 5 is The linearly polarized light has only the slow axis component or the fast axis component. In other words, the linearly polarized light incident on the CCD line sensor 5 is the same polarized light as before incident on the film 1. Therefore, the amount of light received by the CCD line sensor 5 becomes small, which is not preferable.
In contrast, in the above-described embodiment, the first direction of the CCD line sensor 5, that is, the direction in which the plurality of CCD cameras 5 a are arranged is inclined with respect to the width direction W of the film 1 and an angle α of 25 degrees or less. Has been. Therefore, the slow axis or fast axis of the film 1 forms an angle α with the transmission axis or absorption axis of the second polarizing plate 4, and the amount of light given to the CCD line sensor 5 is as described above. It is not the minimum. That is, as shown in FIG. 6, when the defect 1A exists, light R having a sufficient intensity to indicate the presence of the defect is given to the CCD line sensor 5, thereby causing the defect in the film having birefringence. Detection can be performed with high accuracy.

  However, in the above-described embodiment, the first direction in which the plurality of CCD cameras 5a in the CCD line sensor 5 are arranged is inclined so as to form the inclination angle α with the width direction W of the film 1, but the film 1 is If the film does not have refractive properties, the first direction may be parallel to the width direction W of the film 1.

  Next, specific experimental examples will be described.

Example 1
A film 1 having a width of 1000 mm was prepared. The film 1 has a plurality of defects, but defects A to C were selected in advance. The defect A is a gel-like translucent defect and has a size of 146 μm × 181 μm. The defect B is a transparent defect due to the shape transfer of the foreign matter, and the size is 100 μm × 50 μm. The defect C is a transparent defect due to the shape transfer of the foreign matter, and the size is 90 μm × 51 μm.

  Using the inspection apparatus schematically shown in FIGS. 1 and 2, the film 1 having a width of 1000 mm was conveyed in the length direction at a speed of 25 m / min. As the CCD line sensor 5, a plurality of conventional CCD cameras arranged in a straight line was used. Each CCD camera 5a has a 2048-bit CCD element. Each CCD camera 5a has a field of view of about 112 mm along the width direction of the film 1. The camera resolution in the width direction of the film to be inspected is 0.055 mm, and the camera resolution in the length direction is 0.055 mm.

  As the line-shaped light source 2, a light source that emits line-shaped light and having a light amount of 60000 lux was used. The line direction of the light from the linear light source is parallel to the first direction in which the CCD cameras 5a in the CCD line sensor 5 are arranged, and is inclined by 17.5 degrees with respect to the width direction W of the film 1. It was. The direction of the transmission axis of the first polarizing plate 3 was inclined by 17.5 degrees with respect to the width direction of the film 1.

  The light receiving surface of the CCD line sensor 5 was inclined with respect to the upper surface of the film 1. The inclination angle was adjusted so that the amount of light received by the CCD line sensor 5 was ¼ of the maximum amount of light received when directly facing each other.

  About the 2nd polarizing plate 4, it has arrange | positioned so that it may become a 1st polarizing plate 3 and a crossed Nicols state.

Using the above manufacturing apparatus, light was irradiated from below the film 1 and inspected according to the inspection method described above. At this time, an average value of output signals of all pixels was obtained on the program of the image processing device 7. A value obtained by subtracting the average value from the output signal value of each pixel was binarized according to a preset threshold value. The state of the pixel that exceeds the threshold is set to “1”, and the pixel that generates an output that does not exceed the threshold is set to “0”. In this way, a binarized signal of “1” or “0” was obtained, and the presence / absence of a defect was determined based on the binarized signal. That is, it was determined that a pixel having a value of “1” is defective. Further, the S / N ratio, which is the ratio between the amount of light received at the defective portion and the amount of received light at the normal portion around the defect, was obtained based on the image on the monitor as shown in FIG. As a result, the defect A was 11.8, the defect B was 3.0, the defect C was 4.8, and the defects A to C were reliably detected.

(Example 2)
The film, target defects, line speed and apparatus were the same as in Example 1. However, the line direction of the linear light source 2 was inclined so as to form an angle of 20 degrees with respect to the film width direction W. The direction of the transmission axis of the first polarizing plate 3 arranged in front of the line light source 2 was inclined so as to form an angle of 20 degrees with respect to the width direction W of the film. Further, the light receiving surface of the CCD line sensor 5 is installed so that the visual field is aligned with a position shifted in the length direction from the center of the line light source 2, and is formed on the upper surface of the film 1 so as to be 1/4 of the maximum light receiving amount. It was inclined to.

  As a result of performing the same processing as in Example 1, the S / N ratio was 11.6 for defect A, 3.2 for defect B, 4.7 for defect C, and defects A to C. It was detected reliably.

(Comparative Example 1)
The film, target defects, line speed and apparatus were the same as in Example 1. However, the inclination angle α of the line light source 2 with respect to the film width direction W was set to 10 degrees. In addition, the first polarizing plate 3 was configured such that the direction of the transmission axis of the first polarizing plate 3 disposed in front of the line-shaped light source 2 forms an angle of 10 degrees with respect to the film width direction W. Further, the CCD line sensor 5 was installed so that the visual field was aligned with the center of the line light source 2, and the light receiving surface was parallel to the upper surface of the film 1 so that the maximum amount of received light was obtained.

  As a result of performing the same processing as in Example 1, the S / N ratio is 1.8 for the defect A, 2.2 for the defect B, 4.7 for the defect C, and the defect A is not detected. In some cases, defect C was not detected.

(Comparative Example 2)
The film, target defects, line speed, and apparatus were substantially the same as in Example 1. However, the direction of the line of the linear light source 2 was arranged so as to form an inclination angle of 12.5 degrees with respect to the film width direction W. In addition, the first polarizing plate 3 was configured so that the direction of the transmission axis of the first polarizing plate 3 was at an angle of 12.5 degrees with respect to the film width direction W. Further, the CCD line sensor 5 was installed so that the visual field was aligned with the center of the line light source 2, and the light receiving surface was parallel to the upper surface of the film 1 so that the maximum amount of received light was obtained.

  As a result of performing the same processing as in Example 1, the S / N ratio is 1.2 for defect A, 1.4 for defect B, 1.0 for defect C, and detection for defect B. In some cases, defect A and defect C were not detected.

(Comparative Example 3)
The film, target defects, line speed, and apparatus were substantially the same as in Example 1. However, the direction of the line of the linear light source 2 was arranged so as to form an inclination angle of 20 degrees with respect to the film width direction W. In addition, the first polarizing plate 3 was configured so that the direction of the transmission axis of the first polarizing plate 3 was 20 degrees with respect to the film width direction W. Further, the CCD line sensor 5 is installed so that the visual field is aligned with the center of the line light source 2, and a neutral density filter having a maximum light receiving amount of ¼ is installed on the front surface of the line light source 2.

  As a result of performing the same processing as in Example 1, the S / N ratio is 1.0 for the defect A, 1.0 for the defect B, and 1.0 for the defect C, and all defects are detected. Was not.

(Comparative Example 4)
The film, target defects, line speed and apparatus were substantially the same as in Example 1. However, the line direction of the linear light source 2 was set to be parallel to the film width direction W. The direction of the transmission axis of the first polarizing plate 3 was also parallel to the width direction W of the film. Further, the light receiving surface of the CCD line sensor 5 was installed without being tilted, and was installed so that the visual field was along the center of the line-shaped light source 2 and adjusted so that the maximum amount of received light was obtained.

  The first and second polarizing plates 3 are arranged such that the direction of the transmission axis or absorption axis of the first polarizing plate 3 forms an angle of 70 degrees with the direction of the transmission axis or absorption axis of the second polarizing plate 4. , 4 are arranged.

  As a result of performing the same processing as in Example 1, the S / N ratio is 1.0 for the defect A, 1.0 for the defect B, and 1.0 for the defect C, and all defects are detected. Was not. It was also confirmed that the average amount of light in the normal part varies within the camera field of view.

  The results of Examples 1 and 2 and Comparative Examples 1 to 4 are summarized in Table 1 below.

The schematic perspective view for demonstrating the film inspection method which concerns on one Embodiment of this invention. The schematic front view for demonstrating the film inspection method which concerns on one Embodiment of this invention. The partial notch front sectional drawing which shows the state which has produced the defect in the film. The schematic front sectional drawing which shows the state through which the light passes through the part with a normal film, and the part which the defect has produced. (A) and (b) show an image obtained based on the digital signal output from the A / D converter and an image obtained by binarizing the digital signal obtained from the A / D converter. Each schematic diagram shown. The partially notched cross-sectional view for explaining the traveling state of light when the film has birefringence. The figure for demonstrating the magnitude | size of the signal which is the light-receiving amount of a defective part, and the magnitude | size of the noise equivalent to the light-receiving amount of a normal part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Film 1A ... Defect 1a ... Lower surface 1b ... Upper surface 2 ... Line-shaped light source 3 ... 1st polarizing plate 4 ... 2nd polarizing plate 5 ... CCD line sensor 5a ... CCD camera 6 ... A / D converter 7 ... Image processing apparatus

Claims (3)

A film inspection method for detecting defects in a transparent or translucent film having a length direction and a width direction,
In the region to be inspected of the film, the first polarizing plate is arranged on one side of the film, the second polarizing plate is arranged on the other side, and the first and second polarizing plates are arranged in a crossed Nicols state. ,
Using a linear light source from the outside of the first polarizing plate, irradiating linear light extending in the film width direction on one surface of the film through the first polarizing plate,
The light passing through the second polarizing plate on the other side of the film is received by a CCD line sensor having a plurality of CCD cameras arranged along the first direction, and an image of the detection area of the film is taken. And a process of
Converting the output signal of the CCD line sensor into a digital signal;
Binarizing the digital signal and detecting the presence or absence of film defects based on the binarized signal,
The transmission axis direction of the first or second polarizing plate is parallel to the first direction, the line direction of light emitted from the linear light source is parallel to the first direction, and the CCD A film inspection method, wherein a light receiving surface of a line sensor is inclined with respect to a film surface.   The film inspection according to claim 1, wherein a first direction in which a plurality of CCD cameras are arranged in the CCD line sensor is inclined at an inclination angle of 25 degrees or less with respect to a width direction of the film. Method. A film inspection method for detecting defects in a transparent or translucent film having a length direction and a width direction,
In the region to be inspected of the film, the first polarizing plate is arranged on one side of the film, the second polarizing plate is arranged on the other side, and the first and second polarizing plates are arranged in a crossed Nicols state. ,
Using a linear light source from the outside of the first polarizing plate, irradiating linear light extending in the film width direction on one surface of the film through the first polarizing plate,
The light passing through the second polarizing plate on the other side of the film is received by a CCD line sensor having a plurality of CCD cameras arranged along the first direction, and an image of the detection area of the film is taken. And a process of
Converting the output signal of the CCD line sensor into a digital signal;
Binarizing the digital signal and detecting the presence or absence of film defects based on the binarized signal,
The transmission axis direction of the first or second polarizing plate is parallel to the first direction, and the first direction in which a plurality of CCD cameras are arranged in the CCD line sensor is the width direction of the film. And inclining at an inclination angle of 25 degrees or less, and making the line direction of the light emitted from the linear light source parallel to the first direction.

Images