JP2008175565A - Device and method for detecting defect of light transmitting member - Google Patents

Abstract

Defect detection using a polarizing plate is performed with high accuracy.
A first polarizing plate is installed between a traveling film and a projector. A second polarizing plate 26 is installed between the film 16 and the light receiver 24 so as to be orthogonal to the polarization direction of the first polarizing plate 25. The first and second polarizing plates 25 and 26 are composed of iodine-based polarizing plates. A band pass filter 27 is installed between the projector 22 and the first polarizing plate 25. The bandpass filter 27 removes light having a wavelength range of 420 nm or less and 700 nm or more from the light from the projector 22. Thereby, except when the film 16 with a defect is located, light other than the light of a specific polarization plane does not come out from the 1st and 2nd polarizing plates 25 and 26, and the detection precision with respect to a defect is improved. be able to.
[Selection] Figure 1

Description

  The present invention relates to a defect detection apparatus and method for a light transmissive member that detects defects using a polarizing plate.

  An optical compensation film (hereinafter referred to as “retardation film”) that can improve 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 phase difference film is manufactured through a step of forming an alignment film on a long transparent film, and a step of applying a liquid crystal thereon and drying to form a liquid crystal layer (see, for example, Patent Document 1). Such manufacturing processes are under strict control, but molecular orientation unevenness due to foreign matter contamination and adhesion due to various factors in the manufacturing process, thickness unevenness of the transparent film as a support, coating of the liquid crystal layer It is difficult to completely eliminate defects such as unevenness.

Until now, in order to detect such defects, the film to be inspected is irradiated with light from the projector, the light from the film is received by the receiver, and the signal of the light received by the receiver is received. By analyzing, the position, size, and strength of the defect were grasped online. Furthermore, in the method for detecting a transparent defect shown in Patent Document 2, the first polarizing plate is disposed on the front surface of the projector, the second polarizing plate is disposed on the front surface of the light receiver, and the polarization directions of the respective polarizing plates are orthogonal to each other. By doing so, light enters the light receiver only when there is a defect on the film. On the other hand, in the pinhole defect detection method disclosed in Patent Document 3, polarizing plates are respectively installed on the light projector side and the light receiver side of the film to be inspected so that the polarizing directions of the polarizing plates are parallel to each other. Therefore, when the light from the polarizing plate on the projector side passes through the normal part of the film, the light is scattered by the film, so that the intensity of the light emitted from the polarizing plate on the light receiver side becomes weak. When there is a pinhole defect on the film, the light from the polarizing plate on the projector side passes through the pinhole defect as it is, so that the intensity of the light emitted from the polarizing plate on the light receiver side does not change. This improves the accuracy of detection for pinhole defects.
JP-A-9-73081 Japanese Patent Laid-Open No. 6-148095 Japanese Patent Laid-Open No. 6-18445

  However, it is difficult to discriminate minute defects by a conventional defect detection method using a polarizing plate, and it has been desired to improve discrimination accuracy of minute defects. For example, it is necessary to detect a weak signal in order to detect a very small defect. The noise component entering the receiver is kept low, and the difference in the amount of light that reaches the receiver is determined depending on whether the film is defective or not. Need to be larger.

  An object of the present invention is to provide a defect detection apparatus and method for a light transmissive member that can accurately detect defects using a polarizing plate.

  The present inventor has been able to obtain the following knowledge by repeating the examination from the level of the projector and the light receiver, and has reached the present invention. First, it was found that the polarizing filter using iodine has a small transmittance peak in the wavelength region of 400 nm, and the peak portion of the transmittance affects the accuracy of defect detection. It was also found that the polarizing filter using iodine hardly polarized in the part exceeding the wavelength range of 700 nm. On the other hand, a solid-state imaging device such as a CCD used as a light receiver has sensitivity in a wavelength region of 400 nm or less or 700 nm or more. For this reason, it was found that light in a wavelength range of 400 nm or less or 700 nm or more remains as a noise component in the light reception signal for defect determination, which affects the accuracy of defect detection.

  The present invention includes a light projector that irradiates light to a light transmissive member, a light receiver that receives light emitted from the light transmissive member illuminated by the light projector, and the light projector and the light transmissive member. A defect of the light transmissive member is determined based on a first polarizing plate provided therebetween, a second polarizing plate provided between the light transmissive member and the light receiver, and a light reception signal of the light receiver. In the defect detection device for a light transmissive member having a defect determination unit that is provided, the light receiver is provided between the projector and the light receiver, and the first and second polarizing plates are arranged in crossed Nicols. And a removal optical system for removing light in a wavelength region having a high spectral transmittance obtained by measuring light from the light.

  The removal optical system preferably removes light having a wavelength range of 400 nm or less. The removal optical system preferably removes light having a wavelength range of 700 nm or more. It is preferable that the first and second polarizing plates are made of iodine, the light receiver is made of a solid-state imaging device, and the removal optical system removes light of 420 nm or less and light of 700 nm or more. The removal optical system is preferably a dielectric multilayer filter or a monochromator. The removal optical system is preferably provided between the projector and the first polarizing plate.

  It is preferable that the projector includes a metal halide lamp and the removal optical system. The light transmissive member is preferably a phase difference film.

  In the defect detection method for a light transmissive member according to the present invention, a removal optical system is disposed between the projector and the light receiver, and the removal optical system includes the first and second polarizing plates arranged in crossed Nicols. In this case, light in a wavelength region having a high spectral transmittance obtained by measuring light from the light receiver is removed.

  According to the present invention, when a defect is detected using a polarizing plate, it is possible to suppress the influence of noise and accurately perform the defect.

  FIG. 1 is a schematic diagram showing a phase difference film production line 10. The retardation film production line 10 includes an alignment film forming device 11, a liquid crystal layer forming device 12, a defect detection device 13, and a winding device 14. The transparent resin film 15 and the phase difference film 16 are traveling in the X direction in FIG.

  The alignment film forming apparatus 11 applies a coating solution containing an alignment film forming resin to the surface of the long 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. Then, the alignment film forming apparatus 11 performs a rubbing process on the alignment film forming resin layer of the transparent resin film 15 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 evaporates the solvent, followed by heating to form a liquid crystal layer. Then, the formed liquid crystal layer is irradiated with ultraviolet rays to crosslink the liquid crystal layer. Thus, the transparent resin film 15 having the liquid crystal layer formed thereon, that is, a transparent retardation film 16 (hereinafter referred to as “film”) is manufactured.

  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 phase difference film, and may be any member that transmits light, such as a transparent body or a translucent body. For example, an antireflection film can be used.

  The defect detection device 13 includes guide rollers 20 and 21, a projector 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 determination unit 28. The guide rollers 20 and 21 are arranged at a predetermined interval in the conveyance path of the film 16. The guide rollers 20 and 21 are rotatable, and rotate following the conveyance of the film 16. Further, the film 16 is held in a planar shape by the guide rollers 20 and 21 being stretched. 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 conveyed for a certain length. This encoder pulse signal is transmitted to the determination unit 28 and is used when specifying the defect position in the X direction.

  The projector 22 is composed of a metal halide lamp, and is installed below the transport path of the film 16. Further, a light amount adjusting unit 23 is connected to the projector 22, and the light amount adjusting unit 23 is configured so that the light amount is constant based on a light amount detection signal of a sensor (not shown) installed in the vicinity of the projector 22. The projector 22 is controlled. As a result, since the film 16 can be irradiated with light having a uniform amount of light, defects can always be detected with the same sensitivity. The projector is not limited to a metal halide lamp, but may be any projector having high brightness. For example, a high frequency fluorescent lamp, a halogen lamp, a mercury lamp, a laser, etc. are mentioned.

  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 is configured by arranging a large number of light receiving elements in a line in the width direction of the film 16. By using such a light receiver 24, a defect can be detected over the entire width of the film 16, and the resolution for the defect can be increased. The drive frequency of the light receiver 24 is set so that sufficient resolution can be ensured even when the traveling speed of the film 16 is the maximum speed. The light receiver 24 captures an image line by line each time the film 16 is conveyed for a certain length and transmits the image signal to the determination unit 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. The first polarizing plate 25 is between the projector 22 and the film 16, and the second polarizing plate 26 is the film 16 and the light receiver 24. It is installed between. The first and second polarizing plates 25 and 26 are installed in crossed Nicols so that their polarization directions are orthogonal to each other. Therefore, when the film 16 having no defect is located, the light polarized in the specific polarization plane by the first polarizing plate 25 is blocked by the other second polarizing plate 26, so that 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 diffused 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. 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 film polarizer, calcite, etc.

  The removal optical system 27 is composed of a band-pass filter using a dielectric multilayer film, and is installed between the projector 22 and the first polarizing plate 25. The removal optical system 27 removes light having a wavelength range of 420 nm or less and 700 nm or more from the light from the projector 22. As a result, light having a wavelength region exceeding 420 nm and less than 700 is incident on the first and second polarizing plates 25 and 26, and the first and second polarizing plates 25 and 26 have specific polarization planes. There is no light other than light. Therefore, the defect detection accuracy can be improved.

  Even when the first and second polarizing plates 25 and 26 using iodine are arranged in crossed Nicols, the first and second polarizing plates 25 and 26 may be transmitted depending on the wavelength range. As shown in FIG. 2, the orthogonal transmittance according to the wavelength range increases in the vicinity of 400 nm and in the vicinity of over 700 nm. In this way, light in the wavelength range that passes through the first and second polarizing plates 25 and 26 is converted into CCD. When detected by a photoreceiver comprising a camera, the CCD has sensitivity to light in the wavelength range of 400 nm or less and 700 nm or more, and therefore, light in these wavelength ranges is included in the received signal as noise. In order to solve this problem, in the present invention, the removal optical system 27 using a bandpass filter cuts the wavelength regions (hatching regions) A1 and A2 of 420 nm or less and 700 nm or more, and the wavelength region of more than 420 nm and less than 700 nm. Is irradiated onto the film 16. Therefore, light in the wavelength range of 420 nm or less and 700 nm or more is not included in the received light signal as noise, and the defect detection accuracy can be increased.

  A bandpass filter using a dielectric multilayer film is used as the removal optical system, but other monochromators, wavelength cut filters, colored glass filters, diffraction gratings, and the like may be used. Further, the removal wavelength range by the removal optical system 27 is not limited to 420 nm or less and 700 nm or more, and may be appropriately determined according to the type of polarizing plate used for defect detection. For example, the spectral transmittance of the projector may be measured in a state where the polarizing plates to be used are arranged in crossed Nicols, and the region having a high spectral transmittance may be removed. Therefore, when the spectral transmittance is high at 400 nm or less and 700 nm or more, the light in these regions is removed by the removal optical system 27 to obtain inspection light having a wavelength region exceeding 400 nm and less than 700 nm.

  In addition to the positions between the projector 22 and the first polarizing plate 25, the following six positions are conceivable as the installation positions of the removal optical system 27. The first position is immediately before the light receiver 24, the second position is between the light receiver 24 and the second polarizing plate 26, the third position is between the second polarizing plate 26 and the film 16, and the fourth position. Is between the film 16 and the first polarizing plate 25, the fifth position is integrated with the projector 22, and the sixth position is integrated with the projector 22.

  Since the durability of the polarizing plate is generally weak against the light and heat of the projector, the first to fourth positions are not preferable. Since the light receiver 24 is focused on the film 16, the removal optical system 27 should be as far away from the film 16 as possible. Therefore, the third and fourth positions are not preferable. In the case of the sixth position, the defect detection accuracy changes every time the projector 22 is replaced, which is not preferable. On the other hand, when the removal optical system 27 is disposed in the projector 22, the removal optical system 27 can be small, and thus is inexpensive. Therefore, the fifth position is preferable.

  The determination unit 28 performs enhancement processing such as differentiation processing on the imaging signal from the light receiver 24. And the determination part 28 determines the presence or absence of a defect based on the imaging signal to which the emphasis process was performed. Further, the determination unit 28 specifies the position of the defect on the film 16 on the XY plane coordinates based on the signal corresponding to the defective portion of the imaging signal for one line and the encoder pulse signal from the encoder 30. .

  Next, the operation of the defect detection device 13 will be described. The film 16 manufactured by the alignment film forming device 11 and the liquid crystal layer forming device 12 is sent to the defect detection device 13. In the defect inspection apparatus 13, the light from the projector 22 is illuminated through the removal optical system 27 and the first polarizing plate 25 with respect to the film 16 running at a constant speed. At that time, the removal optical system 27 removes light having a wavelength range of 420 nm or less and 700 nm or more from the light from the projector 22. Then, the light enters the first polarizing plate 25, and the first polarizing plate 25 polarizes the light on a specific polarization plane. Here, when the film 16 having no defect is positioned, the polarized light is blocked by the second polarizing plate 26. On the other hand, when the film 16 having a defect is located, the polarization plane of the polarized light changes due to the defect, and light is emitted from the second polarizing plate 26. The light receiver 24 receives the light emitted from the second polarizing plate 26.

  The light receiver 24 performs imaging for one line every time the film 16 is fed for a certain length. For each image pickup, the light receiver 24 sends an image pickup signal to the determination unit 28. And the presence or absence of a defect is detected by the determination part 28, and the location of the defect is specified. Information about this defect is displayed on a display (not shown).

It is the schematic which shows the phase difference film manufacturing line which introduce | transduced the defect detection apparatus of the light transmissive member of this invention. It is a graph which shows the orthogonal transmittance | permeability of a polarizing plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 Defect detection apparatus 16 Film 22 Light projector 24 Light receiver 25 1st polarizing plate 26 2nd polarizing plate 27 Removal optical system 28 Determination part

Claims (9)

Provided between a light projector that irradiates light to the light transmissive member, a light receiver that receives light emitted from the light transmissive member illuminated by the light projector, and the light projector and the light transmissive member. A first polarizing plate, a second polarizing plate provided between the light transmissive member and the light receiver, and a defect determination unit for determining a defect of the light transmissive member based on a light reception signal of the light receiver. In the defect detection device of the light transmissive member having
Provided between the light projector and the light receiver, when the first and second polarizing plates are arranged in crossed Nicols, the spectral transmittance obtained by measuring the light from the light receiver is a high wavelength region A defect detection apparatus for a light transmissive member, comprising a removal optical system for removing light.   The defect detection apparatus for a light transmissive member according to claim 1, wherein the removal optical system removes light having a wavelength range of 400 nm or less.   The defect detection apparatus for a light transmissive member according to claim 1, wherein the removal optical system removes light having a wavelength range of 700 nm or more.   The first and second polarizing plates are made of iodine, the light receiver is made of a solid-state imaging device, and the removal optical system removes light of 420 nm or less and light of 700 nm or more. The defect detection apparatus for a light transmissive member according to claim 1.   5. The defect detecting device for a light transmissive member according to claim 1, wherein the removal optical system is a dielectric multilayer film filter or a monochromator.   6. The defect detecting device for a light transmissive member according to claim 1, wherein the removal optical system is provided between the projector and the first polarizing plate.   6. The defect detecting device for a light transmissive member according to claim 1, wherein the projector includes a metal halide lamp and the removal optical system.   8. The defect detecting device for a light transmissive member according to claim 1, wherein the light transmissive member is a phase difference film. A light projector that irradiates light to the light transmissive member, a light receiver that receives light emitted from the light transmissive member illuminated by the light projector, and a light receiver disposed between the light projector and the light transmissive member. A first polarizing plate, a first polarizing plate disposed between the light transmissive member and the light receiver, and a second polarizing plate disposed between the light transmissive member and the light receiver. In a defect detection method for a light transmissive member using a polarizing plate and a defect determination unit for determining a defect of the light transmissive member based on a light reception signal of the light receiver,
A removal optical system is disposed between the projector and the light receiver,
The removal optical system removes light in a wavelength region having a high spectral transmittance obtained by measuring light from the light receiver when the first and second polarizing plates are arranged in crossed Nicols. A defect detection method for a light-transmitting member.

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