JP2009236826A - Defect detector and defect detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a defect with high precision without lowering an S/N ratio. <P>SOLUTION: First and second polarization plates 25 and 26 are provided between a halogen lamp 22 and a light receiver 24. The first and second polarization plates 25 and 26 are arranged so that polarization directions 25a and 26a may cross each other at a right angle. A film 16 travels between the first and second polarization plates 25 and 26 and a removing optical system 27 is provided immediately in front of the light receiver 24. Only one bright line is present in a wavelength region of 600-800 nm of light emitted from the halogen lamp 22. Accordingly, an interference fringe does not almost occur on the film 16. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a defect detection apparatus and method for detecting a defect using a pair of polarizing plates having polarization directions orthogonal to each other.

  An optical compensation film (hereinafter referred to as “retardation film”) capable of improving the viewing angle of a liquid crystal display device by forming a liquid crystal layer having optical anisotropy on a transparent film is known. This retardation film is manufactured through a step of forming an alignment film on a long transparent film and a step of forming a liquid crystal layer by applying a liquid crystal thereon and drying (see, for example, Patent Document 1). Each manufacturing process is under strict quality control, but it completely eliminates defects such as molecular orientation unevenness due to foreign substance contamination and adhesion, transparent film thickness unevenness, and liquid crystal layer coating unevenness. It is not easy.

Until now, in order to detect such defects, light from a projector is irradiated to an inspection object such as a retardation film, and the light from the inspection object is received by the light receiver. By analyzing the signal, the position, size, and strength of the defect were grasped online. Furthermore, the first polarizing plate is disposed between the projector and the inspection target, and the second polarizing plate is disposed between the inspection target and the light receiver so that the polarization directions of the respective polarizing plates are orthogonal (crossed Nicols). Thus, an inspection method is known in which only light scattered and diffused by a defect on the inspection object enters the light receiver (see Patent Document 2).
JP-A-9-73081 Japanese Patent Laid-Open No. 6-148095

  In recent years, since a further high-quality retardation film is required, there is a demand for a highly accurate defect detection method capable of detecting even minute defects. Defect detection accuracy is generally expressed by an S / N ratio, and it is essential to improve the S / N ratio in order to increase the accuracy of defect detection. Here, the S / N ratio is represented by a value obtained by dividing a signal of a defective portion (hereinafter referred to as “defect signal”) by a signal of a portion other than the defect (hereinafter referred to as “noise signal”).

  As described above, in defect inspection with a pair of polarizing plates arranged in crossed Nicols, a light signal scattered or confused by a defect is used as a defect signal, and a light signal slightly transmitted from a pair of polarizing plates as a noise signal. It is included. Therefore, in order to improve the S / N ratio, it is necessary to minimize the noise signal and increase the defect signal. As one method of increasing the defect signal, there is a method of intensifying the light scattered and diffused by the defect by using a projector that emits light with high luminance for irradiation of the inspection object.

  However, some projectors that emit light with high luminance have a plurality of emission lines such as a metal halide lamp. When such a projector is used for defect inspection of a thin transparent body such as a retardation film, clear interference fringes are formed on the film. Since bright portions where light is intensified due to interference fringes are formed on the film, the light signal slightly transmitted from the pair of polarizing plates is increased. Therefore, the noise signal becomes large, and as a result, the S / N ratio decreases. Therefore, even if the projector has a high luminance, when a projector having a plurality of bright lines is used, the S / N ratio may be reduced due to the influence of interference fringes.

  An object of this invention is to provide the detection apparatus and method which can perform a defect detection with sufficient precision, without reducing S / N ratio.

  In order to achieve the above object, the present invention uses the first polarizing plate provided on one surface side of the film and the second polarizing plate provided on the other surface side of the film. In the defect detection device for detecting a defect of the film by disposing the polarizing plate and the second polarizing plate in crossed Nicols, the light having no bright line or only one is transmitted through the first polarizing plate, Based on a light projector that projects light onto the film, a light receiver that receives light emitted from the film via the second polarizing plate, and a light reception signal obtained by the light receiver, a defect of the film is detected. And a defect detection unit.

  The film is a retardation film, and the polarization direction of the first and second polarizing plates is preferably oriented in a direction of 45 ° with respect to the slow axis of the retardation film. The projector is preferably a halogen lamp. The first and second polarizing plates are preferably iodine-based polarizing plates.

  In the defect detection method of the present invention, light having no bright line or only one light is projected onto the film via the first polarizing plate, and the light emitted from the film is passed through the second polarizing plate. And detecting defects in the film based on a light reception signal obtained by the light receiver.

  According to the present invention, by projecting light having no bright line or having only one bright line onto the film, interference fringes are hardly generated on the film. Thereby, accurate defect detection can be performed without reducing the S / N ratio.

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

  The alignment film forming apparatus 11 applies a coating solution containing an alignment film forming resin to the surface of the transparent resin film 15 fed from the film roll 18 and heat-drys it. Thereby, an alignment film forming resin layer is formed on the surface of the transparent resin film 15. The alignment film forming apparatus 11 performs a rubbing process on the alignment film forming resin layer to form an alignment film.

  The liquid crystal layer forming apparatus 12 applies a coating liquid containing a liquid crystal compound on the alignment film of the transparent resin film 15, and heat-drys after application to form a liquid crystal layer. Then, the liquid crystal layer is irradiated with ultraviolet rays to crosslink the liquid crystal layer. Thereby, a retardation film 16 (hereinafter referred to as “film”) in which an alignment film and a liquid crystal layer are formed on the transparent resin film 15 is manufactured. The film 16 is wound up by the winding device 14 after passing through the defect detection device 13 described in detail below. Here, let the conveyance direction of the film 16 until it leaves the film roll 18 and is wound up by the winding device 14 be an X direction. The X direction coincides with the slow axis direction of the film 16.

  The defect detection device 13 detects defects generated on the film 16. Examples of defects include scratches, thickness unevenness, coating unevenness, and molecular orientation unevenness. The film to be inspected is not limited to the retardation film, and may be any member that transmits light, such as a transparent body or a translucent body, such as an antireflection film.

  The defect detection device 13 includes guide rollers 20 and 21, a halogen lamp 22, a light amount adjustment unit 23, a light receiver 24, first and second polarizing plates 25 and 26, a removal optical system 27, and a controller 28. The guide rollers 20 and 21 are arranged in the conveyance path of the film 16 so as to be spaced apart at a constant interval. These guide rollers 20 and 21 are rotatable, and rotate following the conveyance of the film 16. Further, the film 16 is held in a flat shape by the guide rollers 20 and 21 being stretched. An encoder 30 is connected to the guide roller 21. The encoder 30 generates an encoder pulse signal every time the film 16 is conveyed for a certain length. The encoder pulse signal is transmitted to the controller 28 and used when specifying the defect position.

  The halogen lamp 22 is installed below the conveyance path of the film 16. As shown in FIG. 2, the halogen lamp 22 has only one bright line between wavelengths of 600 nm and 800 nm. Therefore, interference fringes hardly occur on the film 16. Even if an interference fringe is generated, the brightness of the bright part of the interference fringe where the light is intense is only slightly larger than the brightness of the light emitted from the halogen lamp 22. Therefore, interference fringes do not affect the accuracy of defect detection. Note that the projector need not be limited to the halogen lamp as long as the projector has no bright line or only one projector.

  The light amount adjusting unit 23 controls the halogen lamp 22 so that the light amount becomes constant based on a light amount detection signal detected by a sensor (not shown) installed in the vicinity of the halogen lamp 22. Thereby, since the film 16 can be irradiated with light having a uniform amount of light, defect detection can always be performed with the same sensitivity.

  The light receiver 24 is composed of a CCD camera, and is installed above the transport path of the film 16. The light receiver 24 includes a large number of light receiving elements arranged in a line in the width direction of the film 16, and images the film one line in the width direction each time the film 16 is conveyed for a certain length. Signals obtained by imaging include light signals scattered and confused by defects (hereinafter referred to as “defect signals”) and signals such as light slightly transmitted from the first and second polarizing plates 25 and 26 (hereinafter referred to as “noise”). Signal "). These signals are transmitted to the controller 28. The number of light receivers is not limited to one and may be two or more.

  The first and second polarizing plates 25 and 26 are composed of iodine-based polarizing plates, and the first polarizing plate 25 is disposed between the halogen lamp 22 and the film 16 as shown in FIG. Is installed 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 Nicols). In addition, although the iodine type polarizing plate is used from the surface of performance and a price, you may use not only this but the polarizing plate which consists of a dye type polarizing plate, a metal polarizer, calcite.

  By disposing the first and second polarizing plates 25 and 26 in crossed Nicols, when the film 16 having no defect is positioned, the light polarized by the first polarizing plate 25 to the specific polarization plane is the other second polarized light. Since the light is blocked by the plate 26, the light hardly enters the light receiver 24. That is, the light receiver 24 is in a dark field state. On the other hand, when the film 16 having a defect is located, the light polarized on the specific polarization plane by the first polarizing plate 25 is scattered and confused by the defect, and the polarization plane changes. When the polarization plane changes in this way, light comes out from the other second polarizing plate 26. That is, the light receiver 24 is in a light receiving state.

  The polarization direction 25a of the first polarizing plate is set so that the angle θ with respect to the X direction (the slow axis direction of the film 16) is 45 °, and the polarization direction 26a of the second polarizing plate is an angle with respect to the X direction. (90 ° −θ) is set to be 45 °.

  FIG. 4 shows the ratio of the amount of incident light incident on the first polarizing plate 25 and the amount of transmitted light transmitted through the second polarizing plate 26 with respect to the angle θ (transmitted light amount ratio (%)). It is a graph which shows whether it changes. FIG. 5 is a graph showing how the transmitted light amount ratio changes with respect to the phase difference of the film 16, and “◯” indicates the transmitted light amount ratio when the angle θ is 0 °, and “□”. Indicates the transmitted light amount ratio when the angle θ is 15 °, “Δ” indicates the transmitted light amount ratio when the angle θ is 30 °, and “◇” indicates the transmitted light amount ratio when the angle θ is 45 °. .

  As shown in FIG. 4, when the angle θ is 45 °, the transmitted light amount ratio is the highest. Therefore, by setting the angle θ to 45 °, the amount of light scattered and confused by defects such as scratches increases, so that the S / N ratio can be improved. Further, as shown in FIG. 5, the phase difference dependency of the transmitted light amount ratio gradually increases as the angle θ increases from 0 ° to 45 °, and the phase difference dependency increases most when the angle θ is 45 °. Phase difference defects such as coating unevenness may not be detected because the amount of light scattered and confused by the phase difference defect is small, but by setting the angle θ to 45 °, the transmitted light amount ratio of the phase difference defect part Therefore, not only defects such as scratches but also phase difference defects can be reliably detected.

  The removal optical system 27 is composed of an infrared cut filter and is installed immediately before the light receiver 24. The removal optical system 27 removes light having a wavelength of 700 nm or more from the light from the second polarizing plate 26. As a result, only light having a wavelength of less than 700 nm is incident on the light receiver 24, so that the defect can be detected with high accuracy at a high S / N ratio for the following reason.

  FIG. 6 shows the state of the light of the first and second polarizing plates 25 and 26 when the angle θ of the polarization direction 25a of the first polarizing plate is 45 ° with the removal optical system 27 removed from the defect detection device 13. The first and second polarizing plates 25 and 26 substantially block light with a wavelength up to 700 nm, but transmit light with a high transmittance with respect to light with a wavelength exceeding 700 nm. On the other hand, the light receiver 24 is sensitive to light having a wavelength exceeding 700 nm. For this reason, light having a wavelength exceeding 700 nm is included in the noise signal of the light receiver 24.

  Therefore, light having a wavelength of 700 nm or more (light in the hatching area 35) is removed by the removal optical system 27 so that only light having a wavelength of less than 700 nm enters the light receiver 24. For this reason, light having a wavelength of 700 nm or more is not included in the noise signal of the light receiver 24. Thereby, since a noise signal can be suppressed to the minimum, a sufficiently large S / N ratio can be obtained. Note that the S / N ratio when a coating stripe that is a defect is detected is 1.5 when light having a wavelength of 700 nm or more is not removed, whereas it is 1.5 when light having a wavelength of 700 nm or more is removed. Will improve to 2.1.

  Although an infrared cut filter is used as the removal optical system 27, a band pass filter using a dielectric multilayer film, a monochromator, a wavelength cut filter, a colored glass filter, a diffraction grating, or the like may be used. Further, the wavelength range of the light removed by the removal optical system 27 is not necessarily limited to 700 nm or more, and may be appropriately changed according to the type of polarizing plate used for defect detection. Further, a removal optical system that removes light having a wavelength of 600 nm or more may be installed between the halogen lamp 22 and the first polarizing plate 25 to remove bright lines from the light from the halogen lamp 22.

  In addition to the position immediately before the light receiver 24 (hereinafter referred to as “installation position of the present invention”), the following six installation positions are conceivable for the removal optical system 27. The first installation position is between the halogen lamp 22 and the first polarizing plate 25, the second installation position is between the light receiver 24 and the second polarizing plate 26, and the third installation position is the second polarizing plate 26. Between the film 16, the fourth installation position is between the film 16 and the first polarizing plate 25, the fifth installation position is inside the halogen lamp 22, and the sixth installation position is integrated with the halogen lamp 22. is there.

  Which of the first to sixth installation positions is optimal will be examined below. Generally, since the polarizing plate is weak against the light and heat of the halogen lamp 22, the second to fourth installation positions are not preferable. In contrast, at the first installation position, the light from the halogen lamp 22 indirectly strikes the polarizing plate via the removal optical system 27, so that the performance of the polarizing plate is not deteriorated by light or heat. Therefore, the first installation position is preferable.

  Since the focus of the light receiver 24 is adjusted to the film, the distance between the removal optical system 27 and the film 16 should be as far as possible. Therefore, the third and fourth installation positions are not preferable. Further, the sixth installation position is not preferable because the defect detection accuracy changes every time the halogen lamp 22 is replaced. On the other hand, if the removal optical system 27 is disposed in the halogen lamp 22, the removal optical system 27 can be small, and hence the cost is low. Therefore, the fifth installation position is preferable.

  From the above, it is preferable to install the removal optical system 27 at any of the installation position, the first installation position, and the fifth installation position of the present invention, but the removal optical system 27 is installed at the installation position of the present invention. Sometimes the S / N ratio is highest. Therefore, it is most preferable to install the removal optical system 27 at the installation position of the present invention.

  The controller 28 detects a defect signal based on the imaging signal from the light receiver 24, and detects a defect position on the film 16 based on the defect signal and the encoder pulse signal from the encoder 30. Specific part 28b.

  Next, the operation of the defect detection apparatus of the present invention will be described. A film 16 manufactured by the alignment film forming device 11 and the liquid crystal layer forming device 12 is fed into the defect detection device 13. The film 16 travels between the first polarizing plate 25 and the second polarizing plate 26. Light is emitted from the halogen lamp 22 to the first and second polarizing plates 25 and 26.

  Light from the halogen lamp 22 is polarized to a specific polarization plane by the first polarizing plate 25. Here, when there is no defect on the film 16, the polarized light is blocked by the second polarizing plate 26. On the other hand, when there is a defect on the film 16, the polarized light is scattered and confused by the defect, The scattered / confused light comes out of the second polarizing plate 26. The light emitted from the second polarizing plate 26 is removed by the removal optical system 27 with a wavelength of 700 nm or more. The light that has passed through the removal optical system 27 is received by the light receiver 24.

  The light receiver 24 performs imaging for one line every time the film 16 is fed for a certain length. The defect signal detection unit 28a detects a defect signal based on the imaging signal from the light receiver 24. The defect position specifying unit 28 b specifies the position of the defect on the film 16 based on the defect signal and the encoder pulse signal from the encoder 30. The result of the controller 28 is displayed on a display (not shown).

  The present invention will be specifically described by the following examples and comparative examples. The present invention is not limited to the following examples and comparative examples.

[Example 1]
The defect detection on the film 16 was performed using the defect detection apparatus shown in FIG. A halogen lamp 22 was installed below the film 16 to be inspected, and a light receiver 24 was installed above it. A first polarizing plate 25 was installed between the halogen lamp 22 and the film 16, and a second polarizing plate 26 was installed between the film 16 and the light receiver 24. At that time, the polarization direction 25a of the first polarizing plate 25 and the polarization direction 26a of the second polarizing plate 26 are set to cross Nicols so that the light receiver 24 is in a dark field state when there is no defect. Further, the polarization direction 25a of the first polarizing plate 25 is set to 45 ° with respect to the slow axis (X direction (film transport direction) of the film 16, and the polarization direction 26a of the second polarizing plate 26 is set to 45 with respect to the X direction. The iodine polarizer was used for the first and second polarizers, and a CCD line camera was used for the light receiver.

  Further, a removal optical system 27 composed of an infrared cut filter is installed immediately before the light receiver 24. The removal optical system 27 removed light having a wavelength of 700 nm or more from the light from the second polarizing plate 26. The light receiver 24 detected the light emitted from the removal optical system 27 and transmitted the detected signal to the controller 28.

[Comparative Example 1]
Defect detection was performed in the same manner as in Example 1 except that light was emitted from a metal halide lamp instead of the halogen lamp.

[Comparative Example 2]
Defect detection was performed in the same manner as in Example 1 except that light was emitted from a fluorescent lamp instead of the halogen lamp.

[Evaluation]
About the defect inspection performed in Example 1 and Comparative Examples 1 and 2, after evaluating how much interference fringes were generated on the film and how much the S / N ratio was, each Example and Comparative Example Was comprehensively evaluated. In addition, the spectral radiant intensity of the projectors of the examples and comparative examples was measured using a known spectrometer, and the number of bright lines in the projectors of the examples and comparative examples was examined from the measurement results.

表１の「投光器」は各実施例及び比較例で使用する投光器の種類を、「輝線」は投光器の輝線の数を示している。また、「干渉縞」の「○」はフィルム上に干渉縞が発生しなかったことを、「×」はフィルム上に鮮明な干渉縞が発生したことを示している。また、「Ｓ／Ｎ」の「○」は２以上であることを、「△」は１．５以上であることを示している。また、「評価」の「○」は製品上問題となる欠陥を検出したことを、「×」は製品上問題となる欠陥を確実に検出できなかったことを示している。なお、Ｓ／Ｎ比については、「２」以上あれば安定的に欠陥検出を行うことができる。 Table 1 below shows the evaluation results of the examples and comparative examples. FIG. 7 shows the spectral radiant intensity measured in each example and comparative example. Graph 60 shows the spectral radiant intensity of the halogen lamp, graph 61 shows the spectral radiant intensity of the metal halide lamp, and graph 62 shows the spectral radiant intensity of the fluorescent lamp. Indicates strength.

The “projector” in Table 1 indicates the type of projector used in each example and comparative example, and the “bright line” indicates the number of bright lines of the projector. In addition, “◯” of “interference fringes” indicates that no interference fringes are generated on the film, and “x” indicates that clear interference fringes are generated on the film. In addition, “O” in “S / N” indicates that it is 2 or more, and “Δ” indicates that it is 1.5 or more. Further, “◯” in “Evaluation” indicates that a defect causing a product problem has been detected, and “X” indicates that a defect causing a product problem has not been reliably detected. If the S / N ratio is “2” or more, defect detection can be performed stably.

  In Example 1, since the halogen lamp had only one bright line, no interference fringes were generated on the film. On the other hand, in Comparative Examples 1 and 2, since there are two or more bright lines, a bright fringe and a dark fringe are clearly formed. Due to the influence of the interference fringes, the S / N ratio was lowered, and it was not possible to reliably detect defects that would cause problems in products.

It is the schematic of a phase difference film manufacturing line. It is a graph which shows the spectral radiant intensity of a halogen lamp. It is a perspective view of a defect detection apparatus. It is a graph which shows the relationship between angle (theta) and transmitted light amount ratio. It is a graph which shows the relationship between the phase difference of a film, and transmitted light amount ratio. It is a graph which shows the spectral transmission factor of a pair of polarizing plate arrange | positioned at cross Nicol. It is a graph which shows the spectral radiant intensity of a halogen lamp, a metal halide lamp, and a fluorescent lamp.

Explanation of symbols

13 Defect Detection Device 16 Film 22 Halogen Lamp 24 Light Receiver 25 First Polarizing Plate 26 Second Polarizing Plate 27 Removal Optical System

Claims (5)

Using a first polarizing plate provided on one side of the film and a second polarizing plate provided on the other side of the film, the first polarizing plate and the second polarizing plate are crossed Nicols. In the defect detection device that arranges and detects defects in the film,
A projector that projects light having no bright line or only one light onto the film through the first polarizing plate;
A light receiver for receiving the light emitted from the film through the second polarizing plate;
A defect detection apparatus comprising: a defect detection unit that detects a defect of the film based on a light reception signal obtained by the light receiver.   The said film is a phase difference film, The polarization direction of the said 1st and 2nd polarizing plate is orient | assigned to the direction of 45 degrees with respect to the slow axis of the said phase difference film. Defect detection device.   3. The defect detection apparatus according to claim 1, wherein the projector is a halogen lamp.   The defect detection apparatus according to claim 1, wherein the first and second polarizing plates are iodine-based polarizing plates. Using a first polarizing plate provided on one side of the film and a second polarizing plate provided on the other side of the film, the first polarizing plate and the second polarizing plate are crossed Nicols. In the defect detection method of arranging and detecting defects in the film,
Light having no bright line or only one is projected onto the film through the first polarizing plate,
The light emitted from the film is received by a light receiver through the second polarizing plate,
A defect detection method, comprising: detecting a defect of the film based on a light reception signal obtained by the light receiver.

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