KR101676333B1 - Method and device for detecting defect - Google Patents

Abstract

The film is run between the first and second polarizing plates arranged in Cross Niccolo. The halogen lamp irradiates the film with light through the first polarizing plate. There is only one bright line in the light emitted by the halogen lamp. The light whose luminance is changed by defects on the film or the like passes through the second polarizing plate and the removing optical system and is incident on the light receiving unit. The output signal of the light receiver is subjected to differential processing. The maximum signal and the minimum signal are detected from the differential processing signal subjected to the differential processing. The difference between the luminance value of the reference signal and the luminance value of the minimum signal is determined as the first differential value and the difference between the luminance value of the reference signal and the luminance value of the minimum signal is determined as the second differential value. When the addition value obtained by adding the first difference value and the second difference value is equal to or more than a predetermined value, the maximum signal and the minimum signal are specified as the defect signal.

Defect detection apparatus, defect detection method

Description

TECHNICAL FIELD [0001] The present invention relates to a defect detection method,

The present invention relates to a defect detection method and apparatus for optically detecting defects on a film.

BACKGROUND ART [0002] In recent years, a liquid crystal display, whose demand is expanding, is attached to a screen as a protective film of a polarizing plate or a phase difference film having optical anisotropy as an optical compensation film. The retardation film (hereinafter, simply referred to as "film") is produced by a process of forming an alignment film on a transparent support and a process of forming a liquid crystal layer by applying liquid crystal on a support on which an alignment film is formed Open Publication No. 9-73081). Although strict quality control is carried out in each process, it is difficult to completely eliminate defects such as unevenness of molecular orientation (alignment defect) due to incorporation of foreign substances during manufacturing, alignment unevenness of coating of liquid crystal layer (phase difference defect), and the like.

When a film is defective, scattering of light occurs. Therefore, in the manufacturing process of the film, an optical defect detecting device is provided to detect defects of the film. This defect detection apparatus is composed of a light emitter for emitting light to a film, a light receiver for receiving light emitted from the film, and a processing circuit for analyzing an output signal from the light receiver. As this photoreceptor, a television camera having an image pickup device (line sensor or area sensor) is used, and a scanning signal (image pickup signal) line-scanned in the width direction of the film is output as an output signal.

In addition, a pair of polarizers is arranged between the light emitter and the light receiver so that the polarization directions of the light are perpendicular to each other (crossed nichol). This pair of polarizing plates prevents light from entering the photoreceptor when there is no defect on the film, and when scattered and diffused by the defect is incident on the photoreceptor when there is a defect on the film, defect detection is facilitated (Japanese Unexamined Patent Application Publication No. 6-148095). In addition, the output signal from the photoreceptor is subjected to differential processing to emphasize the signal of the defective part, and to reduce the signal other than the defective part, that is, the so-called noise signal, thereby facilitating the detection of the defect.

In recent years, there has been a demand for a high-quality film, and a defect detection method with high accuracy that can detect even minute defects. The defect detection accuracy is generally expressed by a value (S / N) obtained by dividing a signal (defect signal) of a defect portion in an output signal from a light receiving device by a signal (noise signal) other than a defect portion. The defect detection precision becomes high.

Therefore, in order to obtain a larger S / N ratio, it is necessary to increase the defect signal and minimize the noise signal. As a method of increasing the defect signal, it is considered to increase the intensity of light scattered and diffused by defects on the film by irradiating the film with a high-luminance light.

However, there are cases where a plurality of steep peak values, so-called bright lines, such as a metal halide lamp, may exist in the light emitter which emits light of high luminance. When such a light having a plurality of bright lines is irradiated on a thin transparent body such as a film, an interference signal having a portion where light is strongly combined is generated on the film. Therefore, since strong light strikes even a defect-free portion, the noise signal becomes large, and as a result, the S / N ratio decreases. In addition, when a pair of polarizing plates are arranged in Cross Nicol and light is transmitted through a pair of polarizing plates even when there is no defect when the polarizing plate is inclined with respect to the slow axis of the film, The noise signal becomes larger due to the influence of the arc. Therefore, even in the case of a light projector having a high luminance, in the case of having a plurality of bright lines, the S / N ratio may be lowered due to the influence of the interference signal.

When a pair of polarizers are arranged in Cross Niccolo to detect defects, the output signal from the light receiver has a high luminance at the central portion in the film width direction from the optical characteristics of the film and the sensitivity characteristics of the light receiver, The luminance gradually decreases. When the differential signal is applied to such an output signal, the defect signal affects the noise signal around the output signal.

For example, as shown in Fig. 7 (A), if a plurality of similar defects exist on the film and the output signal is subjected to differentiation processing in the case where the brightness of scattered or confused light is the same for each defect, The defect signal in which the slope of the noise signal with respect to the width direction of the film is in the negative region becomes smaller than the defect signal in the positive region as shown in Fig. 7 (B), when the inverse value for defect detection is set to a constant luminance value Th, the tilt of the noise signal is detected because the defect signal in the positive region is equal to or larger than Th , And the defect signal in the negative area is not detected because it is less than Th. Therefore, even though both defects are similar, the defective signal is not detected due to whether the inclination of the noise signal is in the positive or negative part, despite the fact that the brightness of scattered and confused light is the same.

An object of the present invention is to provide a defect detection method and apparatus capable of performing defect detection with high accuracy without lowering S / N ratio.

It is still another object of the present invention to provide a defect detection method and apparatus capable of preventing a detection error of a defective portion.

In order to achieve the above object and other objects, the present invention provides a defect detecting apparatus for detecting a defect on a film in a state in which a film is disposed between a first polarizer plate and a second polarizer plate arranged by crossed Nicols, Light receiving means for receiving light emitted from the film through the second polarizing plate; and light receiving means for receiving light emitted from the film through the second polarizing plate, And defect detection means for detecting defects of the defect.

It is preferable that the film is a retardation film, and the polarizing direction of the first and second polarizing plates is oriented at 45 degrees with respect to the slow axis of the retardation film. It is preferable that the light emitting means is a halogen lamp. The first and second polarizing plates are preferably an oxo-based polarizing plate.

The defect detection method of the present invention includes the steps of: projecting light having no or only one light line through the first polarizing plate onto the film; and receiving light emitted from the film through the second polarizing plate And a step of detecting a defect of the film based on an output signal from the light receiving means.

The present invention relates to a defect detecting apparatus for detecting a defect in a film, comprising: light receiving means having a plurality of pixels arranged in a line, for outputting a time series output signal by scanning in a width direction of the film; A maximum signal in which a luminance value is maximum within a predetermined pixel range among the differential signal processing signals obtained by the differential processing means and a maximum signal in which a luminance value is minimum within a predetermined pixel range A difference between a luminance value of the reference signal and a luminance value of the maximum signal is obtained as a first difference value and a luminance value of the reference signal and a luminance value of the minimum signal An adder that obtains an addition value obtained by adding the first difference value and the second difference value; And defect signal specifying means for specifying the maximum signal and the minimum signal detected by the extreme value signal detecting means as a defect signal when the addition value is equal to or more than a predetermined value.

It is also preferable to provide first and second polarizing plates arranged so that their polarization directions are orthogonal to each other, and light projecting means for projecting light toward the film positioned between the first polarizing plate and the second polarizing plate. It is preferable that the film is a retardation film, and the polarizing direction of the first and second polarizing plates is oriented at 45 degrees with respect to the slow axis of the retardation film.

The defect detection method of the present invention includes the steps of obtaining a time series output signal by scanning in the width direction of the film by light receiving means having a plurality of pixels arranged in a line, A step of detecting a maximum signal having a maximum luminance value within a predetermined pixel range of the differential signal and a minimum signal having a minimum luminance value within a predetermined pixel range; Obtaining a difference between a luminance value and a luminance value of the maximum signal as a first difference value and a difference between a luminance value of the reference signal and a luminance value of the minimum signal as a second difference value; A step of obtaining an added value obtained by adding a second difference value and a step of specifying the maximum signal and the minimum signal as a defect signal when the added value is equal to or larger than a predetermined value .

According to the present invention, since the film is illuminated using the light projecting means with few bright lines, it is possible to perform defect detection with high accuracy without lowering the S / N ratio. Further, according to the present invention, a defect is detected by using the maximum value and the minimum value of the differential signal.

1, the retardation film production line 10 includes an alignment film forming apparatus 11, a liquid crystal layer forming apparatus 12, a defect detecting apparatus 13, and a winding apparatus 14.

The alignment film forming apparatus 11 applies a coating liquid containing a resin for forming an alignment film to the surface of the transparent resin film 15 fed out from the film roll 18 and then heat-dries. As a result, a resin layer is formed on the surface of the transparent resin film 15. Thereafter, the alignment film forming apparatus 11 forms an alignment film by rubbing treatment of the resin layer.

The liquid crystal layer forming apparatus 12 applies a coating liquid containing a liquid crystal compound on an alignment film, and after coating, it is heated and dried to form a liquid crystal layer. Then, the liquid crystal layer is irradiated with ultraviolet rays to join the alignment film and the liquid crystal layer. Thereby, a retardation film 16 (hereinafter simply referred to as " film ") having an orientation film and a liquid crystal layer formed on the transparent resin film 15 is obtained. The film 16 is wound on the winding device 14 after passing through the defect detecting device 13. [ Here, the transport direction of the film 16 is set to the X direction until the film 16 is taken out from the film roll 18 and wound around the take-up device 14.

The defect detecting device 13 detects a defect occurring on the film 16. [ Defects include, for example, scratches, thickness irregularities, coating irregularities, molecular orientation irregularities, and the like. In addition to the retardation film, an anti-reflection film or the like may be an object to be inspected by the defect detection apparatus.

The defect detecting apparatus 13 includes guide rollers 20 and 21, a light emitter 22, a light amount adjusting unit 23, a light receiver 24, first and second polarizers 25 and 26, a removing optical system 27, And a controller 28 are provided. The guide rollers 20 and 21 are arranged along the conveying path of the film 16 and rotate in accordance with the conveyance of the film 16. An encoder 30 is connected to the guide roller 21 and the encoder 30 generates an encoder pulse signal every time the film 16 is transported a certain length. The encoder pulse signal is transmitted to the controller 28 and is used to specify the position of the defect in the longitudinal direction of the film 16.

The light emitter 22 is provided below the film transport path 16 and illuminates a strip-shaped band extending in the width direction of the film 16. As the light projector 22, a halogen lamp is used. As shown in Fig. 2, this halogen lamp has only one peak, that is, a bright line, of the radiant intensity between wavelengths of 600 nm and 800 nm. Since the light emitted from the halogen lamp has only one bright line, there is almost no interference call on the film 16. Further, even in the case where an interference call occurs, the brightness of the bright portion where the light is combined and strengthened is only slightly larger than the brightness of the light emitted from the halogen lamp. Therefore, the interference call does not affect the accuracy of the defect detection. The light emitter having no light line or only one light emitter may be other than a halogen lamp. Further, a removal optical system for removing light having a wavelength of 600 nm or more may be provided between the halogen lamp and the first polarizer plate to remove the bright line from the light emitted from the halogen lamp.

The light amount adjusting unit 23 controls the light emitter 22 based on the light amount detection signal detected by a sensor (not shown) provided in the vicinity of the light emitter 22. This makes it possible to irradiate the film 16 with light having a uniform amount of light, so that defect detection can always be performed with the same sensitivity.

The first polarizing plate 25 and the second polarizing plate 25 are constituted by an iodine polarizing plate and the first polarizing plate 25 is sandwiched between the light emitter 22 and the film 16 and the second polarizing plate 26 is sandwiched between the film 16, And the light receiver 24. The first and second polarizing plates 25 and 26 are arranged so that their polarization directions 25a and 26a are orthogonal (crossed nichol). Further, although the first and second polarizing plates are made of an oxo-based polarizing plate from the viewpoints of performance and price, a polarizing plate made of other dye-based polarizing plate, metal polarizing plate, calcite or the like may be used.

The light emitted from the light projector 22 is polarized in the polarization direction 25a by the first polarizing plate 25 in the case of the film 16 having no defect by arranging the first and second polarizing plates 25 and 26 in Cross Nicol The rear film 16 is transmitted as it is, and is blocked by one of the second polarizing plates 26 already. Therefore, most of the light transmitted through the normal part is not incident on the light receiver 24. On the other hand, in the case where the film 16 having alignment defects such as foreign matters or scratches is located, the light emitted from the light projector 22 is polarized in the polarization direction 25a by the first polarizer 25, The defects on the spawning or confusion. The scattered and confused light is transmitted through the second polarizing plate 26 and incident on the light receiver 24 because the direction of polarization is changed.

Alignment defects such as scratches on the film and foreign matter contamination generate scattered light, so that only the scattered light can be transmitted by the cross Nicol arrangement of the two first and second polarizing plates 25 and 26 and can be detected by the light receiver 24. However, the defects (phase difference defects) such as coating thickness irregularities do not generate scattered light, and thus can not be detected in a configuration in which the two first and second polarizing plates 25 and 26 are arranged in crossed Nicols. However, this coating thickness non-uniformity defect is detected by crossing the slow axis of the film 16 and the polarization direction 25a of the first polarizing plate in a state in which the two first and second polarizing plates 25 and 26 are disposed in cross- It is possible to do.

4 shows the relationship between the transmitted light amount ratio of light passing through the first and second polarizing plates 25 and 26 when the angle? Of the polarization direction 25a of the first polarizing plate with respect to the slow axis of the film 16 is changed, . When the angle [theta] is 0 [deg.], The mode is the extinction mode, and the transmitted light amount ratio (%) is " 0.00 ". When the angle [theta] is 45 [deg.], It is a blue mode. In this blue mode, the transmitted light amount ratio (%) is about 0.80. When the angle [theta] is 45 [deg.], The amount of transmitted light becomes largest. Here, the transmitted light amount ratio (%) represents the ratio of the outgoing light from the second polarizing plate 26 to the incident light to the first polarizing plate 25.

5, the transmitted light amount ratio (%) is changed by the phase difference of the defective portion with respect to the normal portion of the film 16, even if the angle is the same. In Fig. 5, " o " indicates an angle &thetas; 0 indicates an angle &thetas; ([theta]) is 45 [deg.]. The larger the phase difference is, the larger the amount of transmitted light is.

As described above, when the angle? Of the polarization direction 25a of the first polarizing plate with respect to the slow axis of the film 16 in the cross-Nicol arrangement of the two first and second polarizing plates 25 and 26 is 45 (Unevenness in coating thickness) (phase difference defect) can be detected from the difference between the amount of transmitted light in the steady portion and the amount of transmitted light in the defective portion that has become uneven in coating thickness.

3, the polarization direction 25a of the first polarizing plate is set so that the angle [theta] of the film 16 with respect to the slow axis direction is set to 45 [deg.], The polarization direction 26a has an angle (90 DEG -theta) with respect to the slow axis direction of the film 16 of 45 DEG. Further, the slow axis direction of the film may be the same as the film conveying direction X.

Fig. 6 shows the light transmission characteristics of a pair of polarizing plates arranged in Cross-Nicol arrangement. When there is no defect on the film, light having a wavelength of less than 700 nm is only emitted from the first and second polarizing plates 25 and 26, but from the characteristics of these polarizing plates, light having a wavelength exceeding 700 nm is leaked at a high transmittance do. The removing optical system 27 is constituted by an infrared cut filter and disposed immediately before the light receiver 24. This infrared cut filter cuts the light (infrared ray) in the area 35 indicated by hatching. Therefore, light (infrared rays) having a wavelength of 700 nm or more is removed from the light emitted from the second polarizing plate 26, and only light having a wavelength of less than 700 nm is incident on the light receiver 24.

The light receiver 24 is constituted by a CCD camera and is provided above the film transport path. The CCD camera has an imaging device in which a plurality of light receiving elements are arranged in a line in the width direction of the film 16 and scans in the width direction of the film 16 to generate a scanning signal (imaging signal) as an output signal. This output signal includes a defect signal due to a defect on the film 16 and a noise signal slightly leaked from the first and second polarizing plates 25 and 26 as shown in Fig. It is preferable that not only one photodetector but also a plurality of photodetectors are provided. As the image pickup device, an image area sensor in which light receiving elements are arranged in two dimensions may be used.

The light receiver 24 generally converts light having a wavelength of more than 700 nm and photoelectrons, but light having a wavelength of 700 nm or more is removed by the removing optical system 27. Therefore, since only the light based on the defect on the film 16 is subjected to photoelectric conversion, the noise signal is suppressed to the minimum, and a sufficiently large S / N (defect signal / noise signal) can be obtained. For example, when the coated stripe is detected by the uneven coating thickness and the S / N ratio is 1.5 when light of 700 nm or more is not removed by the removing optical system 27, when light of 700 nm or more is removed S / N is improved to " 2.1 ".

3, the controller 28 includes a defect signal detecting section 32 for detecting a defect signal from an output signal (image pickup signal) from the photoreceiver 24, a defect signal detecting section 32 for detecting a defect signal from the encoder 30, And a defect position specifying unit 33 for specifying the position of the defect in the longitudinal direction of the film 16 based on the pulse signal. The defect signal detecting unit 32 includes a differential processing unit 32a, an extreme value signal detecting unit 32b, a luminance value calculating unit 32c, and a defect signal specifying unit 32d.

The differential processing section 32a performs differential processing on the output signal 40 as shown in Fig. 7 (A). Thereby, as shown in Fig. 7 (B), a signal 42 (hereinafter referred to as " differential signal processing signal ") in which a portion with a large change in luminance value is emphasized is obtained. 8, the extreme value signal detecting unit 32b includes a maximum signal 50a, 51a, 52a having a maximum luminance value within a predetermined pixel range among the differential signal processing signals 42, Detects the minimum signals (50b, 51b, 52b) in which the luminance value is the minimum.

The luminance value calculator 32c calculates differences (LA1, LB1, LC1) (hereafter referred to as " first difference value ") between the luminance value of the preset reference signal 55 and the luminance value of the maximum signals 50a, 51a, And the difference (LA2, LB2, LC2) (hereinafter referred to as "second difference value") between the luminance value of the reference signal 55 and the luminance value of the minimum signal 50b, 51b, 52b. Here, the reference signal 55 is obtained by averaging the noise signals, and is sequentially updated each time defect detection is performed. The luminance value calculator 32c obtains addition values LA, LB and LC obtained by adding the first differential values LA1, LB1 and LC1 and the second differential values LA2, LB2 and LC2.

The defect signal identifying unit 32d determines whether or not the addition values (LA, LB, LC) obtained by the brightness value calculating unit 32c are equal to or larger than a predetermined value. The maximum signals 50a, 51a, 52a and the minimum signals 50b, 51b, 52b are specified as defect signals when the addition values LA, LB, LC are equal to or larger than a predetermined value. In Fig. 8, all of the addition values (LA, LB, LC) are more than a predetermined value, so that all detected signals are specified as defect signals.

Conventionally, as shown in Fig. 7 (B), since a predetermined threshold value Th is set for the differential processing signal 42 and a signal exceeding the threshold value Th is used as a defect signal, (Right signal in Fig. 7 (B)) even though the signal is a large signal, the signal is not detected as a defect signal. On the other hand, in the present invention, since the defect signal is specified by the change amount of the luminance value instead of the threshold value Th, defects on the film 16 can be reliably detected.

Next, the operation of the defect detection apparatus of the present invention will be described. The film 16 having passed the alignment film forming device 11 and the liquid crystal layer forming device 12 is conveyed to the defect detection device 13. The light projector 22 emits light to the film 16 running between the first polarizing plate 25 and the second polarizing plate 26. Since the light projector 22 uses a halogen lamp, there is only one bright line of light, so that no interference is generated on the film 16, which is one of the causes of increasing the noise signal.

The light from the light projector 22 is polarized in the polarization direction 25a by the first polarizing plate 25. [ When alignment defect such as foreign matter is present on the film 16, the light from the first polarizing plate 25 is changed in polarization direction due to scattering or confusion due to defects, so that light is emitted from the second polarizing plate 26 . This also applies to the case where there is a phase difference defect such as coating unevenness. From the characteristics of the first and second polarizing plates 25 and 26, light having a wavelength of 700 nm or more passes through the first and second polarizing plates 25 and 26 as it is.

The light emitted from the second polarizing plate 26 is incident on the light receiver 24 after the light having a wavelength of 700 nm or more is removed by the removal optical system 27. The light receiver 24 converts the incident light into an electric signal, and then sequentially reads the light signal for each pixel. The output signal (40) of the light receiver (24) is transmitted to the controller (28).

The differential processing section 32a in the controller 28 performs the differential processing on the output signal 40 from the receiver 24. The extreme signals 50a, 51a, and 52a and the extreme signals 50b, 51b, and 52b are detected by the extreme value signal detector from the differential processing signal 42 subjected to the differential processing. The difference between the luminance value of the reference signal 55 preset by the luminance value calculator 32c and the maximum signals 50a, 51a and 52a is referred to as first differential values LA1, LB1 and LC1, And the luminance values of the minimum signals 50b, 51b, and 52b as the second differential values LA2, LB2, and LC2. The luminance value calculator 32c obtains addition values LA, LB and LC obtained by adding the first difference values LA1, LB1 and LC1 and the second difference values LA2, LB2 and LC2. When the obtained added values LA, LB and LC are equal to or more than a predetermined value, the defect signal specifying section 32d identifies the maximum signals 50a, 51a and 52a detected by the extremum signal detecting section 32b and the minimum signals 50b, 51b, 52b as defect signals. The defect position specifying unit 33 specifies a defect position on the film 16 based on the defect signal and the encoder pulse signal. The results at the controller 28 are displayed on a display (not shown).

Although an infrared cutoff filter is used as the removal optical system 27 in the above embodiment, a band-pass filter, a monochrome meter, a wavelength cutoff filter, a color glass filter, a diffraction grating or the like using other dielectric multi-layer films may be used. The wavelength region of the light removed by the removing optical system 27 need not be limited to 700 nm or more, and may be appropriately changed depending on the type of the polarizing plate used for defect detection.

Next, the present invention will be described in detail with reference to Example 1 and Comparative Examples 1 and 2.

[Example 1]

The defect detection on the film 16 was performed using the defect detection device 13 shown in Fig. A light emitter 22 of a halogen lamp is provided below the film 16 to be inspected, and a light receiver 24 is provided above the film 16. A first polarizing plate 25 was provided between the light projector 22 and the film 16 and a second polarizing plate 26 was provided between the film 16 and the light receiver 24. The polarizing direction 25a of the first polarizing plate was set at 45 degrees with respect to the slow axis of the film 16 and the polarizing direction 26a of the second polarizing plate was set at 45 with respect to the X direction. The first and second polarizing plates 25 and 26 used an oxo-based polarizing plate and the light receiver 24 used a CCD line camera.

Immediately before the light receiver 24, a removal optical system 27 composed of an infrared cut-off filter is provided. Light having a wavelength of 700 nm or more in the light to the second polarizing plate 26 was removed by the removing optical system 27. The light receiver 24 detects the light emitted from the removal optical system 27, and transmits the detected signal to the controller 28.

The controller 28 obtains the differential processing signal 42 by subjecting the signal obtained by the light receiver 24 to differential processing. The extreme signal 50a, 51a, 52a which becomes the maximum within the predetermined pixel range and the minimum signal 50b, 51b, 52b which becomes the minimum are detected from the differential signal 42 by the extreme signal detector 32b. The difference between the luminance value of the reference signal 55 and the luminance value of the maximum signals 50a, 51a and 52a is set as the first difference values LA1, LB1 and LC1, LB1 and LC1 and the second difference values LA2 and LB2 are obtained as the second difference values LA2 and LB2 and LC2, LB2, and LC2 are added to obtain addition values LA, LB, and LC. The maximum signals 50a, 51a, and 52a detected by the extreme value signal detecting unit 32b and the minimum signals 50b, 51b, and 52b are determined as defect signals when the obtained added values LA, LB, did.

[Comparative Example 1]

A defect was detected in the same manner as in Example 1 except that light was generated from a metal halide lamp instead of a halogen lamp.

[Comparative Example 2]

The defect was detected in the same manner as in Example 1 except that light was generated from a fluorescent lamp instead of a halogen lamp.

[evaluation]

For the defect inspection performed in Example 1 and Comparative Examples 1 and 2, evaluation was made on the degree of occurrence of an interference call on the film and the degree of S / N, and the respective examples and comparative examples were evaluated comprehensively. Further, the spectral radiant intensities of the floodlights of the examples and comparative examples were measured using a well-known spectrophotometer, and the number of bright lines was examined from the measurement results.

FIG. 9 shows the spectral radiant intensities measured in the examples and the comparative examples, the graph 60 shows the spectral radiant intensity of the halogen lamp, the graph 61 shows the spectral radiant intensity of the metal halide lamp, Indicates the spectral radiant intensity of a fluorescent lamp.

Fig. 10 shows evaluation results of the respective examples and comparative examples. 10 shows the type of the light emitter used in each of the embodiments and the comparative example and the bright line shows the number of bright lines of light generated from the light emitter. In the interference call, " o " indicates that no interference call occurred on the film, and " x " indicates that an interference call occurred on the film. "S" in "S / N" indicates that S / N is 2 or more, and "Δ" indicates that S / N is 1.5 or more. In addition, " o " in the evaluation indicates that a defect causing a product problem was detected, and " x " indicates that a defect in the product could not be reliably detected. Further, if the S / N ratio is "2" or more, the defect can be stably detected.

In Example 1, since there was only one bright line of light generated from the halogen lamp, there was no interference call on the film. On the other hand, in Comparative Examples 1 and 2, since there were two or more bright lines, an interference signal in which a bright portion and a dark portion became distinct occurred on the film. This interference call affects the S / N ratio, which makes it impossible to reliably detect defects that are a problem on the product.

1 is a schematic view of a production line of a retardation film.

2 is a graph showing the spectral radiant intensity of a halogen lamp.

3 is a perspective view of the defect detecting apparatus.

4 is a graph showing the relationship between the angle (?) Of the polarization direction of the first polarizing plate and the transmitted light amount ratio with respect to the film slow axis.

5 is a graph showing the relationship between the phase difference of the film and the transmitted light amount ratio.

6 is a graph showing the spectral transmittance of a pair of polarizers arranged by Cross-Nicol.

FIG. 7A is a graph showing an output signal, and FIG. 7B is a graph showing a differential processing signal obtained by subjecting an output signal to differential processing.

8 is an explanatory diagram for explaining a defect detection method of the present invention.

9 is a graph showing the spectral radiant intensities of a halogen lamp, a metal halide lamp, and a fluorescent lamp.

10 is a table showing the results of Example 1 and Comparative Examples 1 and 2. FIG.

Claims (9)

1. A defect detecting apparatus for detecting a defect on a film in a state in which a film is disposed between a first polarizer plate and a second polarizer plate arranged in a cross Nicoll arrangement, Light projecting means for projecting light having no bright line or only one light onto said film through said first polarizing plate; A removing optical system for removing light having a wavelength of 700 nm or more out of the light emitted from the first polarizing plate, the film, and the second polarizing plate; Receiving means for receiving a light emitted from the removing optical system and having a plurality of pixels arranged in a line and outputting a time-series output signal by scanning in a width direction of the film; And And detection means for detecting a defect of the film based on an output signal from the light receiving means, Differential processing means for performing differential processing on the output signal; Extreme value signal detecting means for detecting a maximum signal having a maximum luminance value within a predetermined pixel range and a minimum signal having a minimum luminance value within a predetermined pixel range among the differentiated signal obtained by the differential processing means; A difference value between a luminance value of a reference signal set in advance and a luminance value of the maximum signal as a first difference value and a difference value between a luminance value of the reference signal and a luminance value of the minimum signal as a second difference value Calculating means; Adding means for obtaining an addition value obtained by adding the first difference value and the second difference value; And And a defect signal specifying means for specifying the maximum signal and the minimum signal detected by the extreme value signal detecting means as a defect signal when the addition value is a predetermined value or more. The method according to claim 1, Wherein the film is a retardation film and the polarizing direction of the first and second polarizing plates is oriented at 45 degrees with respect to the slow axis of the retardation film. 3. The method according to claim 1 or 2, Wherein said light emitting means is a halogen lamp. 3. The method according to claim 1 or 2, Wherein the first and second polarizing plates are an oxo-based polarizing plate. A defect detection method for detecting a defect on a film in a state in which a film is disposed between a first polarizer plate and a second polarizer plate arranged in a cross Nicoll arrangement, A step of projecting light having no light line or only one light onto the film through the first polarizing plate; Removing light having a wavelength of 700 nm or more out of the light emitted from the first polarizing plate, the film, and the second polarizing plate by a removing optical system; A step of scanning the light emitted from the removing optical system in the width direction of the film by light receiving means having a plurality of pixels arranged in a line to obtain a time series output signal; And And a step of detecting a defect of the film based on an output signal from the light receiving means, Performing a differential processing on the output signal; Detecting a maximum signal having a maximum luminance value within a predetermined pixel range of the differential signal and a minimum signal having a minimum luminance value within a predetermined pixel range; Obtaining a difference between a luminance value of the reference signal and a luminance value of the maximum signal as a first difference value and obtaining a difference between the luminance value of the reference signal and the luminance value of the minimum signal as a second difference value; A step of obtaining an addition value obtained by adding the first difference value and the second difference value; And And specifying the maximum signal and the minimum signal as a defect signal when the addition value is a predetermined value or more. delete delete delete delete

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