CN115989407A - Method for inspecting optical laminate - Google Patents

Method for inspecting optical laminate Download PDF

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Publication number
CN115989407A
CN115989407A CN202180053420.4A CN202180053420A CN115989407A CN 115989407 A CN115989407 A CN 115989407A CN 202180053420 A CN202180053420 A CN 202180053420A CN 115989407 A CN115989407 A CN 115989407A
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China
Prior art keywords
inspection
optical
inspection step
image
layered body
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CN202180053420.4A
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Chinese (zh)
Inventor
木樽智也
山下裕司
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Nitto Denko Corp
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Nitto Denko Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8806—Specially adapted optical and illumination features
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
    • G01N21/892—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the flaw, defect or object feature examined
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
    • G01N21/892—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the flaw, defect or object feature examined
    • G01N21/896—Optical defects in or on transparent materials, e.g. distortion, surface flaws in conveyed flat sheet or rod
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8806—Specially adapted optical and illumination features
    • G01N2021/8848—Polarisation of light
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
    • G01N2021/8854—Grading and classifying of flaws
    • G01N2021/8858—Flaw counting
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8851—Scan or image signal processing specially adapted therefor, e.g. for scan signal adjustment, for detecting different kinds of defects, for compensating for structures, markings, edges
    • G01N2021/8854—Grading and classifying of flaws
    • G01N2021/8861—Determining coordinates of flaws

Abstract

Provided is an inspection method for an optical laminate, which can suppress excessive inspection of defects existing on the surface of a release film and can highly accurately inspect defects existing between a polarizer and an optical film. The invention comprises the following steps: a transmission inspection step (S1) for detecting defect candidates based on a transmission image generated by light transmitted through the optical laminate (S); a cross Nicol prism inspection step (S2) for inspecting defect candidates based on cross Nicol prism images generated by light transmitted through inspection polarizing filters (6 a, 6 b) and an optical laminate, wherein the inspection polarizing filters (6 a, 6 b) are arranged so as to form cross Nicol prisms with respect to the polarization axis of a polarizer (10); a reflection inspection step (S3) for detecting a defect candidate on the basis of a reflection image generated by light reflected by the optical layered body; and a calculation step (S4) for determining that the defect candidate detected in both the transmission inspection step and the cross Nicol inspection step but not detected in the reflection inspection step is a defect existing between the polarizer and the optical film (20).

Description

Method for inspecting optical laminate
Technical Field
The present invention relates to an inspection method for an optical laminate in which a polarizer and an optical film are laminated and a release film is further laminated on the outermost surface side of at least one of the polarizing plates and the optical film in the thickness direction. The present invention particularly relates to a method for inspecting an optical laminate capable of suppressing excessive inspection of defects existing on the surface of a release film and accurately inspecting defects existing between a polarizer and an optical film.
Background
Conventionally, an inspection method for optically inspecting an optical laminate including a polarizer for defects to determine whether the optical laminate is good or bad is known.
Examples of the defects of the optical laminate include foreign matter (appropriately referred to as "adhesive foreign matter" in the present specification) present between layers of the optical laminate (specifically, between a polarizer and an optical film constituting the optical laminate), and defects (foreign matter, dirt, damage, and the like) present on the surface of the optical laminate.
The optical conditions under which defects are easily detected differ depending on the type of defect. Thus, various inspection methods combining a plurality of optical conditions have been proposed.
For example, patent documents 1 and 2 propose an inspection method in which: defects of the optical film are detected based on a transmission image of the optical film generated by light transmitted through the optical film and a reflection image of the optical film generated by light reflected by the optical film (paragraphs 0023 to 0026 and the like of patent document 1, claim 2 and the like of patent document 2).
In addition, patent document 3 proposes an inspection method in which: a defect of an optical laminate is detected based on a reflected image of the optical laminate generated by light reflected by the optical laminate including a polarizing plate and a cross nicol image of the optical laminate generated by light transmitted through the optical laminate and an inspection polarizing filter arranged so as to be cross nicol with respect to a polarizing axis of the polarizing plate (claim 1 and the like of patent document 3).
Here, in the case where the inspection object is an optical laminate in which a polarizer and an optical film (for example, a retardation film) are laminated and a release film (for example, a separator or a surface protection film) is further laminated on the outermost surface side in the thickness direction, defects (foreign matters, dirt, damage, and the like) existing on the surface of the release film are harmless and do not pose a problem. This is because the release film is peeled off and does not remain when the optical laminate is used (for example, when the optical laminate is bonded to a liquid crystal cell).
The present inventors studied a defect inspection method based on a cross nicol image of an optical laminate including a polarizer, and found that although a foreign adhesive substance existing between layers of the optical laminate can be detected, even a harmless defect existing on the surface of a release film is detected (overdetection). Therefore, the optical laminate having only defects on the surface of the release film (which are not problematic because there are no defects between layers) may be handled as a defective product, and the product yield of the optical laminate may be degraded.
Patent document 3 describes the following: in order to suppress the over-detection, when the position of the defect candidate detected based on the reflection image of the optical layered body is the same as the position of the defect candidate detected based on the cross nicol image of the optical layered body, the defect candidate is not treated as a defect (claim 1, paragraph 0083, and the like of patent document 3).
However, as a result of the studies by the present inventors, it has been found that even in the inspection method in which the reflection image and the cross nicol image are combined as described above, excessive detection of a defect which is not harmful may not be sufficiently suppressed.
The inspection method described in patent document 1 has a problem of accurately counting the number of defects (paragraph 0007 of patent document 1), and is not a method of suppressing excessive detection of harmless defects.
The inspection method described in patent document 2 has a problem of accurately discriminating the type of defect (paragraph 0018 of patent document 2), and is not a method of suppressing excessive detection of a harmless defect.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open publication No. 2003-329601
Patent document 2: japanese patent laid-open publication No. 2012-167975
Patent document 3: japanese patent No. 4960161
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made to solve the above-described problems of the conventional techniques, and an object thereof is to provide an inspection method for an optical laminate capable of suppressing excessive detection of defects existing on the surface of a release film and detecting defects existing between a polarizer and an optical film with high accuracy.
Means for solving the problems
As a result of intensive studies to solve the above problems, the present inventors have found that a defect candidate which is not detected in a reflected image but detected in both of a transmission image and a cross nicol image among the transmission image, the cross nicol image, and the reflected image is highly likely to be a defect (adhesive foreign matter) existing between a polarizer and an optical film, and have completed the present invention.
That is, in order to solve the above-described problem, the present invention provides a method for inspecting an optical laminate in which a polarizer and an optical film are laminated and a release film is further laminated on the outermost surface side in at least one of the thickness directions, the method comprising the steps of: a transmission inspection step of generating a transmission image of the optical layered body using light transmitted through the optical layered body and detecting a defect candidate existing in the optical layered body based on the transmission image; a cross nicol inspection step of generating a cross nicol image of the optical layered body by light transmitted through an inspection polarizing filter and the optical layered body, the inspection polarizing filter being disposed so as to be cross nicol with respect to a polarization axis of the polarizer, and detecting a defect candidate existing in the optical layered body based on the cross nicol image; a reflection inspection step of generating a reflection image of the optical layered body using light reflected by the optical layered body and detecting a defect candidate existing in the optical layered body based on the reflection image; and a calculation step of determining a defect existing between the polarizer and the optical film based on the defect candidate detected in the transmission inspection step, the defect candidate detected in the cross nicol inspection step, and the defect candidate detected in the reflection inspection step, wherein the calculation step determines that the defect candidate detected in both the transmission inspection step and the cross nicol inspection step but not detected in the reflection inspection step is a defect existing between the polarizer and the optical film.
According to the present invention, in the transmission inspection step, defect candidates existing in the optical layered body are detected based on the transmission image of the optical layered body. The transmission image is generated, for example, by the following method: a light source is disposed on one surface side of the optical layered body, an imaging unit is disposed on the other surface side, and light emitted from the light source and transmitted through the optical layered body is received by the imaging unit to form an image (image capture) and generate a transmission image. The defect candidates in the transmission image are detected by applying known image processing such as extraction of 2-valued pixels having different luminance values (pixel values) from those of other pixel regions to the transmission image.
In addition, according to the present invention, in the cross nicol inspection step, defect candidates existing in the optical layered body are detected based on the cross nicol image of the optical layered body. The cross nicol prism image is generated, for example, by the following method: a light source and a polarizing filter for inspection are disposed on one surface side of an optical layered body, an imaging unit is disposed on the other surface side, and a light emitted from the light source and transmitted through the polarizing filter for inspection and the optical layered body is imaged and received by the imaging unit to form an image (image pickup) to generate a cross Nicole image. In this case, since the state of the cross nicols is broken by a defect existing between the polarizing filter for inspection and the polarizer of the optical laminate, a pixel region corresponding to the defect existing between the polarizing filter for inspection and the polarizer in the cross nicols image becomes bright (brightness value becomes large). Or the cross nicol prism image can also be generated by: a light source is disposed on one surface side of the optical layered body, a polarizing filter for inspection and an imaging unit are disposed on the other surface side, and light emitted from the light source and transmitted through the optical layered body and the polarizing filter for inspection is received by the imaging unit to form an image (image capture) and thereby a cross nicol image is generated. In this case, since the state of the cross nicol is broken by a defect existing between the polarizer and the polarizing filter for inspection of the optical layered body, a pixel region corresponding to the defect existing between the polarizer and the polarizing filter for inspection becomes bright (brightness value becomes large) in the cross nicol image. The defect candidate in the cross nicol image is detected by applying known image processing such as 2-valuing to the cross nicol image, for example, by extracting a pixel region having a luminance value (pixel value) different from the luminance value (pixel value) of another pixel region (specifically, a pixel region having a luminance value larger than the luminance value of the other pixel region).
Further, according to the present invention, in the reflection inspection step, defect candidates existing in the optical layered body are detected based on the reflection image of the optical layered body. The reflection image is generated, for example, by the following method: a light source and an imaging unit are disposed on one surface side of the optical layered body, and light emitted from the light source and reflected by the optical layered body is received by the imaging unit to form an image (image capture) and generate a reflected image. The defect candidates in the reflected image are detected by applying known image processing such as extraction of 2-valued pixels having different luminance values (pixel values) from those of other pixel regions to the reflected image.
In the present invention, the term "optical film" means an optical film that cannot be peeled off from a polarizer.
In the present invention, the phrase "polarizing filter for inspection arranged so as to be crossed nicols with respect to the polarizing axis of the polarizer" is not limited to the case where the angle formed by the polarizing axis of the polarizer and the polarizing axis of the polarizing filter for inspection is completely 90 °, but includes the case where the angle is in the range of 90 ° ± 10 °.
In the present invention, the transmission inspection step, the cross nicol inspection step, and the reflection inspection step are not necessarily performed in this order, and may be performed in an arbitrary order (including a case where a plurality of inspection steps are partially repeated).
Further, according to the present invention, in the calculation step, the defect candidate that is not detected in the reflection inspection step but detected in both the transmission inspection step and the cross nicol inspection step is determined to be a defect (adhesive foreign matter) existing between the polarizer and the optical film.
Whether or not a defect candidate is detected in both the transmission inspection step and the cross-nicol inspection step is determined, for example, by whether or not a defect candidate detected in the cross-nicol inspection step exists at a position equal to (identical to or close to) a position of a certain defect candidate detected in the transmission inspection step. If a defect candidate detected in the cross-nicol inspection process exists at the same position, it is determined that the defect candidate is detected in both the transmission inspection process and the cross-nicol inspection process. On the other hand, if the defect candidate detected in the cross nicol inspection process does not exist at the same position, it is determined that the defect candidate is not detected in both the transmission inspection process and the cross nicol inspection process.
Whether or not the defect candidate detected in both the transmission inspection step and the cross nicol inspection step is detected in the reflection inspection step is determined, for example, by whether or not the defect candidate detected in the reflection inspection step is present at a position equal to (the same as or near) the position of a certain defect candidate detected in both the transmission inspection step and the cross nicol inspection step. If the defect candidate detected in the reflection inspection step is present at the same position, it is determined that the defect candidate is detected in the reflection inspection step. On the other hand, if the defect candidate detected in the reflection inspection step does not exist at the same position, it is determined that the defect candidate has not been detected in the reflection inspection step.
As described above, according to the findings of the present inventors, there is a high possibility that a defect candidate which is detected in both the transmission image and the cross nicol image and is not detected in the reflection image is a defect (adhesive foreign matter) existing between the polarizer and the optical film. According to the present invention, in the calculation step, the defect candidates that are detected in both the transmission inspection step and the cross nicol inspection step (i.e., detected in both the transmission image and the cross nicol image) and not detected in the reflection inspection step (i.e., not detected in the reflection image) are determined to be defects existing between the polarizer and the optical film, and therefore, it is possible to suppress excessive detection of defects existing on the surface of the release film and to detect defects existing between the polarizer and the optical film with high accuracy.
In the present invention, it is preferable that the release film is a separator, and when the optical film is located between the separator and the polarizer, the polarizing filter for inspection is disposed on the side of the separator in the cross nicol inspection step.
When the optical laminate is to be bonded to a liquid crystal cell of an image display device, the separator side is bonded to the liquid crystal cell (the separator side is bonded after being peeled off). When the liquid crystal cell is bonded to the separator side of the optical laminate, a defect existing between the polarizer of the optical laminate and the liquid crystal cell (specifically, a defect existing between the polarizer and an optical film located on the liquid crystal cell side of the polarizer) appears as a bright spot in the image display device when the liquid crystal cell is driven, which is a problem in terms of quality.
According to the above-described preferred method, since the polarizing filter for inspection is disposed on the side of the separator in the cross nicol inspection step in the same manner as the liquid crystal cell, a defect that becomes a problem when the liquid crystal cell is driven (a defect existing between the liquid crystal cell and the optical film) can be detected as a defect candidate.
In the present invention, if there is a portion of the optical layered body where the orientation direction of the release film and the direction of the polarization axis of the polarizer are greatly deviated, or a portion of the optical layered body where the orientation direction of the release film and the direction of the polarization axis of the polarizing filter for inspection are greatly deviated, even if there is no defect between the polarizing filter for inspection and the polarizer of the optical layered body, the state of the cross nicols at the above-mentioned portion is broken, and the detection accuracy of defect candidates in the cross nicols inspection process is lowered.
Therefore, the present invention is applied to a case where the orientation direction of the release film is within ± 6 ° (more preferably within ± 3.5 °) from a predetermined orientation direction. In this manner, if the release film is oriented (within ± 6 ° with respect to the predetermined orientation direction), it is possible to prevent a decrease in the detection accuracy of defect candidates in the cross nicol inspection step in an optical laminate in which the release film and the polarizer are laminated so that the predetermined orientation direction of the release film coincides with the direction of the polarization axis of the polarizer, or the release film and the polarizer are laminated so that the predetermined orientation direction of the release film coincides with the direction of the polarization axis of the polarizing filter for inspection (in other words, the predetermined orientation direction of the release film is orthogonal to the direction of the polarization axis of the polarizer).
Preferably, the imaging means for generating the transmission image in the transmission inspection step is the same as the imaging means for generating the cross nicol image in the cross nicol inspection step, and a timing at which the imaging means performs imaging in the transmission inspection step and a timing at which the imaging means performs imaging in the cross nicol inspection step are switched.
According to the above preferred method, since the imaging means for generating the transmission image is the same as the imaging means for generating the cross nicol image, the coordinates of the transmission image and the coordinates of the cross nicol image can be accurately matched. Therefore, in the calculation step, it is possible to accurately determine whether or not a defect candidate has been detected in both the transmission inspection step and the cross-nicol inspection step (for example, it is possible to accurately determine whether or not a defect candidate detected in the cross-nicol inspection step exists at a position equivalent to the position of a certain defect candidate detected in the transmission inspection step).
Preferably, the transmission inspection step and/or the cross nicol inspection step includes a noise removal step of removing a defect candidate having a size larger than a predetermined threshold value from among the detected defect candidates.
Defects (adhesive foreign matter) existing between the polarizer and the optical film of the optical laminate are often smaller in size than defects existing on the surface of the release film.
According to the above-described preferred method, in the transmission inspection step and/or the cross nicol inspection step, the defect candidates having a size larger than the predetermined threshold value among the detected defect candidates are excluded from the defect candidates, and therefore, in the calculation step, it is possible to reduce the number of defect candidates determined whether or not the defect candidates are detected in both the transmission inspection step and the cross nicol inspection step. Therefore, there is an advantage that the time required for the calculation process can be shortened.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, it is possible to detect a defect existing between a polarizer and an optical film with high accuracy while suppressing excessive detection of a defect existing on the surface of a release film.
Drawings
Fig. 1 is a diagram schematically illustrating a schematic configuration of an inspection apparatus for executing an inspection method for an optical layered body according to an embodiment of the present invention.
Fig. 2 is a flowchart illustrating an outline of the steps of the method for inspecting an optical layered body according to the present embodiment.
Fig. 3 is a diagram schematically illustrating an example of defect candidates detected in the transmission inspection step S1 shown in fig. 2.
Fig. 4 is a diagram schematically illustrating an example of defect candidates detected in the cross nicol inspection process S2 shown in fig. 2.
Fig. 5 is a diagram schematically illustrating the content of the switching control executed by the control arithmetic unit 9 shown in fig. 1.
Fig. 6 is a diagram schematically illustrating an example of defect candidates detected in the reflection inspection step S3 shown in fig. 2.
Fig. 7 is a diagram schematically illustrating the content of the calculation step S4 shown in fig. 2.
Detailed Description
Hereinafter, an inspection method of an optical layered body according to an embodiment of the present invention will be described with reference to the drawings as appropriate.
Fig. 1 is a diagram schematically illustrating the configuration of an inspection apparatus for executing the method of inspecting an optical layered body according to the present embodiment. Fig. 1 (a) is a side view showing a schematic configuration of the inspection apparatus. Fig. 1 (b) is a sectional view showing a schematic structure of the optical laminate. In fig. 1, X denotes a horizontal direction parallel to the transport direction of the optical layered body S, Y denotes a horizontal direction orthogonal to the X direction, and Z denotes a vertical direction.
< optical layered body S >
First, the structure of the optical laminate S as an inspection target in the inspection apparatus 100 according to the present embodiment will be described.
As shown in fig. 1 (b), the optical laminate S of the present embodiment is cut into a chip shape according to the application, the polarizer 10 and the optical films 20 and 30 are laminated, and further, the peeling films 40 and 50 are laminated on the outermost surface side in the thickness direction (Z direction). In the present embodiment, one of the optical films 20 located below the polarizer 10 is a retardation film, and the other of the optical films 30 located above the polarizer 10 is a protective film. In the present embodiment, one of the release films 40 located below the polarizer 10 is a separator, and the other release film 50 located above the polarizer 10 is a surface protection film.
Hereinafter, each constituent element of the optical laminate S will be described.
[ polarizing plate 10]
The polarizer 10 is typically composed of a resin film containing a dichroic substance.
As the resin film, any suitable resin film that can be used as a polarizer can be used. The resin film is typically a polyvinyl alcohol resin (hereinafter referred to as "PVA resin") film.
As the PVA-based resin forming the PVA-based resin film, any suitable resin can be used. Examples thereof include polyvinyl alcohol and ethylene-vinyl alcohol copolymers. Polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an ethylene-vinyl acetate copolymer.
The average polymerization degree of the PVA-based resin can be appropriately selected according to the purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be determined in accordance with JIS K6726-1994.
Examples of the dichroic substance contained in the resin film include iodine and an organic dye. Can be used alone or in combination of two or more. Preferably, iodine is used.
The resin film may be a single-layer resin film or a laminate of two or more layers.
Specific examples of the polarizer formed of a single-layer resin film include resin films obtained by subjecting a PVA-based resin film to stretching treatment (typically uniaxial stretching treatment) and dyeing treatment with iodine. The dyeing treatment with iodine is performed by, for example, immersing the PVA-based film in an aqueous iodine solution. The stretching ratio in the uniaxial stretching is preferably 3 to 7 times. The stretching may be performed after dyeing, or may be performed while dyeing. In addition, dyeing may be performed after stretching. The PVA-based resin film is subjected to swelling treatment, crosslinking treatment, washing treatment, drying treatment, and the like as necessary.
Specific examples of the polarizer comprising a laminate include a laminate of a resin base and a PVA-based resin layer (PVA-based resin film) laminated on the resin base, and a polarizer comprising a laminate of a resin base and a PVA-based resin layer applied and formed on the resin base. A polarizer comprising a laminate of a resin substrate and a PVA-based resin layer formed on the resin substrate by coating can be produced, for example, by the following method: the PVA-based resin solution is applied to a resin substrate and dried to form a PVA-based resin layer on the resin substrate, thereby obtaining a laminate of the resin substrate and the PVA-based resin layer, and then the laminate is stretched and dyed to make the PVA-based resin layer a polarizer. In the present embodiment, the stretching typically includes stretching by immersing the laminate in an aqueous boric acid solution. The stretching may also include, if necessary, in-air stretching of the laminate at a high temperature (for example, 95 ℃ or higher) before stretching in the aqueous boric acid solution. The obtained laminate of the resin base material and the polarizer may be used as it is (that is, the resin base material may be used as a protective layer for the polarizer), or the resin base material may be peeled from the laminate of the resin base material and the polarizer, and an arbitrary suitable protective layer according to the purpose may be laminated on the peeled surface. Details of such a method for producing a polarizer are described in, for example, japanese patent laid-open No. 2012-73580. The entire disclosure of this publication is incorporated herein by reference.
The thickness of the polarizer 10 is preferably 15 μm or less, more preferably 1 μm to 12 μm, still more preferably 3 μm to 10 μm, and particularly preferably 3 μm to 8 μm.
The polarizer 10 preferably exhibits absorption dichroism at any wavelength in the range of 380nm to 780 nm. The monomer transmittance of the polarizer 10 is preferably 40.0% to 45.0%, more preferably 41.5% to 43.5%. The degree of polarization of the polarizer 10 is preferably 97.0% or more, more preferably 99.0% or more, and still more preferably 99.9% or more.
[ retardation film 20]
The retardation film 20 may be, for example, a compensation plate for imparting a wide viewing angle, or a retardation plate (circularly polarizing plate) for generating circularly polarized light when used together with a polarizing film. The thickness of the retardation film 20 is, for example, 1 μm to 200 μm. Instead of the retardation film 20, other films such as a protective film and a reflective polarizer described later may be used.
The retardation film 20 is typically formed of any suitable resin that can achieve the above-described characteristics. Examples of the resin for forming the retardation film 20 include polyarylate, polyamide, polyimide, polyester, polyaryletherketone, polyamideimide, polyesterimide, polyvinyl alcohol, polyfumarate, polyethersulfone, polysulfone, norbornene resin, polycarbonate resin, cellulose resin, and polyurethane. These resins may be used alone or in combination. Preferred is a cycloolefin-based norbornene resin.
[ protective film 30]
As the protective film 30, any suitable resin film can be used. Examples of the material for forming the resin film include cellulose resins such as (meth) acrylic resins, diacetyl cellulose, and triacetyl cellulose, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, ester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Further, "(meth) acrylic resin" means an acrylic resin and/or a methacrylic resin.
The thickness of the protective film 30 is typically 10 μm to 100. Mu.m, and preferably 20 μm to 40 μm.
The surface of the protective film 30 on the side opposite to the polarizer 10 may be subjected to surface treatment such as hard coat treatment, antireflection treatment, anti-sticking treatment, and antiglare treatment as needed. And/or, if necessary, the surface of the protective film 30 on the side opposite to the polarizer 10 may be subjected to a treatment for improving visibility in the case of visual confirmation through a polarizing sunglass (typically, a treatment for imparting a (elliptical) circularly polarized light function, or a treatment for imparting an ultra-high retardation). In the case where the surface treatment layer is formed by performing the surface treatment, the thickness of the protective film 30 is a thickness including the surface treatment layer.
The retardation film 20 and the protective film 30 are laminated by being bonded to the polarizer 10 via any suitable adhesive layer (not shown). As the adhesive constituting the adhesive layer, a PVA-based adhesive or an active energy ray-curable adhesive is typically used.
[ separator 40]
As the separator 40, any suitable separator can be used. Specific examples thereof include plastic films, nonwoven fabrics, and papers obtained by surface coating with a release agent. Specific examples of the release agent include silicone release agents, fluorine release agents, and long-chain alkyl acrylate release agents. Specific examples of the plastic film include a polyethylene terephthalate (PET) film, a polyethylene film, and a polypropylene film. The thickness of the separator can be set to, for example, 10 μm to 100 μm.
The separator 40 is bonded to the retardation film 20 via an arbitrary suitable adhesive layer (not shown) to be laminated. Specific examples of the adhesive constituting the adhesive layer include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, polyurethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the kind, amount, combination and mixing ratio of monomers forming the base resin of the adhesive, the mixing amount of the crosslinking agent, the reaction temperature, the reaction time and the like, an adhesive having desired characteristics according to the purpose can be prepared. The base resin of the binder may be used alone, or 2 or more kinds may be used in combination. From the viewpoint of transparency, processability, durability and the like, an acrylic adhesive is preferable. Details of the adhesive constituting the adhesive layer are described in, for example, japanese patent application laid-open No. 2014-115468, the description of which is incorporated herein by reference. The thickness of the pressure-sensitive adhesive layer can be set to, for example, 10 μm to 100 μm. The storage modulus G' at 25 ℃ of the pressure-sensitive adhesive layer can be set to, for example, 1.0X 10 4 [Pa]～1.0×10 6 [Pa]. The storage modulus can be determined by, for example, dynamic viscoelasticity measurement.
In the present embodiment, a separator having an orientation direction within ± 6 ° with respect to a predetermined orientation direction is used as the separator 40. For example, if the direction of the polarizing axis of the polarizer 10 of the present embodiment is defined as the X direction, the predetermined orientation direction of the separator 40 is defined as the Y direction, and the separator 40 is laminated such that the angle of the orientation direction of any portion of the separator 40 with respect to the Y direction is within ± 6 °.
[ surface protective film 50]
The surface protective film 50 typically has a base material and an adhesive layer. In the present embodiment, the thickness of the surface protection film 50 is, for example, 30 μm or more. The upper limit of the thickness of the surface protective film 50 is, for example, 150 μm. In the present specification, the "thickness of the surface protective film" refers to the total thickness of the base material and the pressure-sensitive adhesive layer.
The substrate can be composed of any suitable resin film. Examples of the material for forming the resin film include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Ester-based resins (particularly, polyethylene terephthalate-based resins) are preferred.
As the adhesive for forming the adhesive layer, any suitable adhesive can be used. Examples of the base resin of the binder include acrylic resins, styrene resins, silicone resins, polyurethane resins, and rubber resins.
< inspection apparatus 100>
Next, the structure of the inspection apparatus 100 according to the present embodiment will be described.
The inspection apparatus 100 of the present embodiment is an apparatus for inspecting the optical layered body S having the above-described configuration.
As shown in fig. 1 (a), the inspection apparatus 100 of the present embodiment includes: a plurality of belt conveyors 1 that convey the optical layered body S in the X direction; and a cleaning roller 2 for adsorbing and removing foreign matter attached to the outermost surface (uppermost and lowermost surfaces) of the optical layered body S. The inspection apparatus 100 of the present embodiment includes a light source 3 and an imaging unit 4 for performing a transmission inspection step S1 described later. The inspection apparatus 100 of the present embodiment includes a pair of light sources 5a and 5b and a pair of polarizing filters 6a and 6b for inspection for performing a cross nicol inspection step S2 described later. The imaging unit 4 is also used as an imaging unit for executing the cross nicol inspection process S2. The inspection apparatus 100 of the present embodiment includes a light source 7 and an imaging unit 8 for performing a reflection inspection step S3 described later. The inspection apparatus 100 of the present embodiment further includes a control arithmetic unit 9, and the control arithmetic unit 9 is electrically connected to the light source 3, the imaging unit 4, the light sources 5a and 5b, the light source 7, and the imaging unit 8, controls their operations, and processes imaging signals output from the imaging unit 4 and the imaging unit 8 to determine a defect.
The components of the inspection apparatus 100 will be described below.
[ Belt conveyor 1]
The belt conveyor 1 is of the following construction: the endless belt of the rollers mounted on both ends moves with the rotation of the rollers, and conveys the optical stack S placed on the belt. The optical layered body S is cut into chip shapes, placed on the belt conveyor 1 shown at the left end of fig. 1 (a), and sequentially conveyed in the X direction toward the right side of fig. 1 (a) by the respective belt conveyors 1. In the present embodiment, as shown in fig. 1 (b), the optical layered body S is placed on a belt conveyor so that the separator 40 side faces downward, and is conveyed. The transport speed V at which the belt conveyor 1 transports the optical layered body S is set to, for example, 50mm/sec to 750mm/sec.
[ cleaning roller 2]
The cleaning roller 2 includes: an upper and a lower pair of rollers through which the optical layered body S passes; and a rolled adhesive tape that rotates in contact with each roller (not shown). By bringing the pair of upper and lower rollers into contact with the optical layered body S, foreign substances adhering to the outermost surfaces (the uppermost and lowermost surfaces, that is, the lower surface of the separator 40 and the upper surface of the surface protection film 50) of the optical layered body S are adsorbed to the rollers, and the foreign substances adsorbed to the rollers are transferred to the adhesive tape and removed.
By removing the foreign matter present on the outermost surface of the optical layered body S to some extent by the cleaning roller 2 before the transmission inspection step S1 described later is performed, excessive detection of the defect present on the surface of the release film (the separator 40, the surface protection film 50) can be further suppressed.
[ light Source 3]
The light source 3 is a light source for performing the transmission inspection step S1 described later, and is disposed on the lower surface side (the diaphragm 40 side) of the optical layered body S in the present embodiment. The optical axis (indicated by a broken line in fig. 1 a) of the light source 3 is oriented in the vertical direction (Z direction) parallel to the thickness direction of the optical layered body S, and the light source 3 emits light upward in the vertical direction toward the optical layered body S in accordance with a control signal output from the control arithmetic unit 9.
The light source 3 is not limited as long as it can emit light of a wavelength that can transmit through the optical layered body S, and for example, an LED or a halogen lamp can be used.
[ image pickup unit 4]
The imaging unit 4 is an imaging unit for performing a transmission inspection step S1 and a cross-nicol inspection step S2, which will be described later, and is disposed on the upper surface side (surface protective film 50 side) of the optical laminate S in the present embodiment. The optical axis (indicated by a broken line in fig. 1 a) of the imaging unit 4 is oriented in the vertical direction (Z direction) parallel to the thickness direction of the optical layered body S, and the imaging unit 4 receives light emitted from the light source 3 and transmitted through the optical layered body S to form an image in accordance with a control signal output from the control arithmetic unit 9, and outputs an electric signal according to the light amount thereof to the control arithmetic unit 9 as an imaging signal. The imaging unit 4 receives and forms an image by light emitted from the light sources 5a and 5b and transmitted through the polarizing filters 6a and 6b for inspection and the optical layered body S according to a control signal output from the control arithmetic unit 9, and outputs an electric signal according to the light amount thereof to the control arithmetic unit 9 as an imaging signal. The focus of the imaging unit 4 is set on the upper surface of the optical layered body S (the upper surface of the surface protective film 50).
In the present embodiment, as the image pickup unit 4, a line sensor in which a plurality of image forming devices (CCD, CMOS) are arranged in a straight line in a direction (Y direction) orthogonal to the transport direction (X direction) of the optical layered body S and which outputs an image pickup signal at a fixed scanning period (for example, 7 μ sec to 14 μ sec) can be used. By using the line sensor as the imaging unit 4, the field of view in the X direction of the imaging unit 4 becomes small, and therefore, the following advantages can be obtained: the range of irradiation necessary in the X direction of the light emitted from the light sources 3, 5a, 5b may be narrow, so that the restriction conditions relating to the arrangement of the light sources 3, 5a, 5b and the like are relaxed. By conveying the optical layered body S in the X direction and scanning the imaging element of the line sensor in the Y direction, a two-dimensional transmission image is generated in a transmission inspection step S1 described later and a two-dimensional cross-nicol image is generated in a cross-nicol inspection step S2 described later.
However, the imaging unit 4 is not necessarily limited to a line sensor, and for example, a two-dimensional camera with a high-speed shutter can be used as the imaging unit 4.
[ light sources 5a, 5b ]
The light sources 5a and 5b are light sources for performing the cross nicol inspection process S2 described later, and are disposed on the lower surface side (the diaphragm 40 side) of the optical layered body S in the present embodiment. The optical axes (indicated by broken lines in fig. 1 a) of the light sources 5a and 5b are inclined with respect to a vertical direction (Z direction) parallel to the thickness direction of the optical layered body S. Specifically, the optical axis of the light source 5a is inclined toward the downstream side in the transport direction of the optical stack S with respect to the vertical direction, and the optical axis of the light source 5b is inclined toward the upstream side in the transport direction of the optical stack S with respect to the vertical direction. The light sources 5a and 5b emit light upward toward the optical layered body S in accordance with the control signal output from the control arithmetic unit 9.
The light sources 5a and 5b are not limited as long as they can emit light of a wavelength that can transmit through the optical layered body S, and for example, LEDs or halogen lamps can be used.
In the present embodiment, the imaging unit 4 is used as an imaging unit (common) for performing both the transmission inspection step S1 and the cross nicol inspection step S2. That is, since the same imaging unit 4 receives the light emitted from the light source 3 and the light sources 5a and 5b, the direction of the optical axes of the light sources 5a and 5b is different from the direction of the optical axis of the light source 3. In addition, a pair of light sources 5a and 5b is disposed in order to ensure a sufficient amount of light emitted from the oblique direction. However, for example, by using a coaxial epi-optical system composed of a half mirror or the like, the directions of the optical axes of the light sources 5a and 5b can be oriented in the vertical direction in the same manner as the direction of the optical axis of the light source 3, and a configuration can be adopted in which a single light source is used instead of the pair of light sources 5a and 5b.
[ polarizing filters 6a and 6b for inspection ]
The polarizing filters 6a and 6b for inspection are arranged so as to form crossed nicols with respect to the polarizing axis of the polarizer 10 of the optical layered body S. For example, if the direction of the polarization axis of the polarizer 10 is set to the X direction, the direction of the polarization axis of the polarizing filters 6a and 6b for inspection is set to the Y direction orthogonal to the X direction. However, the angle formed by the polarizing axis of the polarizer 10 and the polarizing axes of the polarizing filters 6a and 6b for inspection is not limited to 90 °, and may be in the range of 90 ° ± 10 °.
The structure and manufacturing method of the polarizing filters 6a and 6b for inspection are the same as those of the polarizer 10, and therefore, a detailed description thereof is omitted here.
The polarizing filters 6a and 6b for inspection of the present embodiment are disposed on the lower surface side (the separator 40 side) of the optical layered body S. Specifically, the inspection polarizing filter 6a is disposed between the optical layered body S and the light source 5a, the inspection polarizing filter 6b is disposed between the optical layered body S and the light source 5b, and the light emitted from the light source 5a is transmitted through the inspection polarizing filter 6a and irradiated to the optical layered body S, and the light emitted from the light source 5b is transmitted through the inspection polarizing filter 6b and irradiated to the optical layered body S. In the case of the present embodiment, since the cross nicols are broken down by a defect existing between the inspection polarizing filters 6a and 6b and the polarizer 10, in the cross nicols image of the optical layered body S generated in the cross nicols inspection step S2 described later, a pixel region corresponding to the defect existing between the inspection polarizing filters 6a and 6b and the polarizer 10 is brightened (brightness value is increased), and the defect can be detected as a defect candidate.
However, the present invention is not necessarily limited to this, and the polarizing filters 6a and 6b for inspection may be disposed on the upper surface side (surface protection film 50 side) of the optical laminate S. Specifically, the following structure can be adopted: one polarizing filter for inspection is disposed between the optical layered body S and the imaging unit, and light emitted from the light sources 5a and 5b and transmitted through the optical layered body S is transmitted through the polarizing filter for inspection and received by the imaging unit 4. In this case, since the state of the cross nicols is broken by a defect existing between the polarizing filter for inspection and the polarizer 10, a pixel region corresponding to the defect existing between the polarizing filter for inspection and the polarizer 10 becomes bright (luminance value becomes large) in the cross nicols image of the optical laminate S generated in the cross nicols inspection step S2 described later, and the defect can be detected as a defect candidate.
[ light Source 7]
The light source 7 is a light source for performing a reflection inspection step S3 described later, and is disposed on the lower surface side (the diaphragm 40 side) of the optical layered body S in the present embodiment. The optical axis (indicated by a broken line in fig. 1 a) of the light source 7 is inclined with respect to a vertical direction (Z direction) parallel to the thickness direction of the optical layered body S. In the example shown in fig. 1 (a), the optical axis of the light source 7 is directed in a direction inclined toward the upstream side in the transport direction of the optical layered body S with respect to the vertical direction. However, the optical axis of the light source 7 may be inclined toward the downstream side in the transport direction of the optical layered body S with respect to the vertical direction. Further, for example, by using a coaxial epi-optical system composed of a half mirror or the like, the optical axis of the light source 7 can be directed in the vertical direction. The light source 7 emits light upward toward the optical layered body S in accordance with a control signal output from the control arithmetic unit 9.
The light source 7 is not limited as long as it can emit light of a wavelength that can be reflected by the optical layered body S, and for example, an LED or a halogen lamp can be used.
[ image pickup unit 8]
The imaging unit 8 is an imaging unit for performing a reflection inspection step S3 described later, and is disposed on the lower surface side (the diaphragm 40 side) of the optical layered body S in the present embodiment. The optical axis (indicated by a broken line in fig. 1 a) of the imaging unit 8 is oriented in the vertical direction (Z direction) parallel to the thickness direction of the optical layered body S, and the imaging unit 8 receives and forms an image of light emitted from the light source 7 and reflected by the optical layered body S in accordance with a control signal output from the control arithmetic unit 9, and outputs an electric signal corresponding to the light amount thereof to the control arithmetic unit 9 as an imaging signal. The focus of the imaging unit 8 is set on the lower surface of the optical layered body S (the lower surface of the diaphragm 40).
In the present embodiment, as the imaging unit 8, similarly to the imaging unit 4, a line sensor in which a plurality of imaging elements (CCD, CMOS) are linearly arranged in a line in a direction (Y direction) orthogonal to the transport direction (X direction) of the optical layered body S and an imaging signal is output at a fixed scanning cycle (for example, 7 μ sec to 14 μ sec) can be used. By using the line sensor as the imaging unit 8, the field of view in the X direction of the imaging unit 8 becomes small, and therefore, the following advantages can be obtained: the irradiation range necessary in the X direction of the light emitted from the light source 7 may be narrow, thereby alleviating the constraint conditions relating to the arrangement of the light source 7 and the like. The optical laminate S is transported in the X direction, and the imaging element of the line sensor is scanned in the Y direction, whereby a two-dimensional reflection image is generated in a reflection inspection step S3 described later.
However, the imaging unit 8 is not necessarily limited to a line sensor, and for example, a two-dimensional camera with a high-speed shutter can also be used as the imaging unit 8.
[ control arithmetic unit 9]
The control arithmetic unit 9 is configured by, for example, a personal computer, a Programmable Logic Controller (PLC), or the like, in which a program for executing control processing and arithmetic processing described later is installed.
< inspection method according to the present embodiment >
The method for inspecting the optical layered body S according to the present embodiment using the inspection apparatus 100 described above will be described below.
Fig. 2 is a flowchart illustrating an outline of the steps of the inspection method for the optical layered body S according to the present embodiment.
As shown in fig. 2, the inspection method according to the present embodiment includes a transmission inspection step S1, a cross nicol inspection step S2, a reflection inspection step S3, and a calculation step S4.
The respective steps S1 to S4 are explained below.
[ Transmission inspection Process S1]
In the transmission inspection step S1, a transmission image of the optical layered body S is generated using the light transmitted through the optical layered body S, and defect candidates existing in the optical layered body S are detected based on the transmission image (S11 in fig. 2).
Specifically, the light source 3 and the imaging unit 4 are driven based on the control signal output from the control arithmetic unit 9 at a timing immediately before the optical layered body S reaches the position directly below the imaging unit 4. Then, the image pickup unit 4 receives and forms an image by the light emitted from the light source 3 and transmitted through the optical layered body S, and outputs an electric signal corresponding to the light amount thereof to the control arithmetic unit 9 as an image pickup signal. The control arithmetic unit 9 generates a two-dimensional transmission image based on the input image pickup signal. Then, the control arithmetic unit 9 detects the defect candidates by applying known image processing such as extraction of 2-valued pixels having different luminance values (pixel values) from other pixel regions to the generated transmission image.
Fig. 3 is a diagram schematically illustrating an example of defect candidates detected in the transmission inspection step S1. Fig. 3 (a) is a sectional view schematically illustrating an example of a defect existing in the optical layered body S. Fig. 3 (b) is a diagram schematically illustrating an example of defect candidates detected before the noise removal process S12 of the transmission inspection process S1 is performed. Fig. 3 (c) is a diagram schematically illustrating an example of defect candidates remaining after the noise removal process S12 of the transmission inspection process S1 is performed.
In fig. 3 (a), reference numeral F1 denotes a harmless foreign substance adhering to the surface of the separator 40 as a release film. Reference numeral F2 denotes harmless damage existing on the surface of the separator 40. Reference numeral F3 denotes harmful adhesive foreign substances existing between the polarizer 10 and the phase difference film 20. Reference numeral F4 denotes a harmless foreign substance adhering to the surface of the surface protection film 50 as a release film. Fig. 3 (b) and (c) show transmission images after 2-valued detection, and in fig. 3 (b), 3 pieces of foreign matter F1 (F1 a to F1 c), 2 pieces of damage F2 (F2 a, F2 b), 1 piece of adhesive foreign matter F3, and 2 pieces of foreign matter F4 (F4 a, F4 b) are detected as defect candidates, respectively. In fig. 3 (c), 1 foreign substance F1 (F1 c), 1 damage F2 (F2 a), 1 adhering foreign substance F3, and 2 foreign substances F4 (F4 a, F4 b) are detected as defect candidates, respectively.
The transmission inspection step S1 of the present embodiment includes a noise removal process (S12 in fig. 2) for excluding from the defect candidates, among the detected defect candidates, a defect candidate having a size (for example, an area) larger than a predetermined threshold value. Therefore, among the detected defect candidates shown in fig. 3 (b), foreign objects F1a and F1b and damage F2b, which are defect candidates having a large size, are excluded, and the state shown in fig. 3 (c) is obtained.
[ Cross Nicole prism inspection step S2]
In the cross nicol inspection step S2, a cross nicol image of the optical layered body S is generated by the light transmitted through the polarizing filters 6a and 6b for inspection and the optical layered body S, and defect candidates existing in the optical layered body S are detected based on the cross nicol image (S2 in fig. 2).
Specifically, the light sources 5a and 5b and the imaging unit 4 are driven in accordance with the control signal output from the control arithmetic unit 9 at a timing immediately before the optical layered body S reaches the position directly below the imaging unit 4. Then, the imaging unit 4 receives and forms images of the light emitted from the light sources 5a and 5b and transmitted through the polarizing filters 6a and 6b for inspection and the optical layered body S, and outputs an electric signal corresponding to the light amount thereof to the control arithmetic unit 9 as an imaging signal. The control arithmetic unit 9 generates a two-dimensional cross nicol image based on the input image pickup signal. Then, the control arithmetic unit 9 detects defect candidates by applying known image processing such as extraction of 2-valued pixels having luminance values (pixel values) different from those of other pixel regions (pixel values) (luminance values become larger) to the generated cross nicol image.
Fig. 4 is a diagram schematically illustrating an example of defect candidates detected in the cross nicol inspection process S2. Fig. 4 shows a 2-valued cross nicol image, in which 3 pieces of foreign matter F1 (F1 a to F1 c), 3 pieces of damage F2 (F2 b to F2 d), and 1 piece of adhering foreign matter F3 were detected as defect candidates. The foreign matter F4 adhering to the surface of the surface protection film 50 is not located between the polarizer 10 and the polarizing filters 6a and 6b for inspection, and is therefore not detected in the cross nicol image unlike the transmission image.
In the present embodiment, since the imaging unit 4 for generating the transmission image is the same as the imaging unit 4 for generating the cross nicol image, the control arithmetic unit 9 performs the following control: the timing at which the imaging unit 4 performs imaging in the transmission inspection step S1 and the timing at which the imaging unit 4 performs imaging in the cross nicol inspection step S2 are switched.
Specifically, the control arithmetic unit 9 performs the following control: the timing of light emission from the light source 3 for generating a transmission image and the timing of light emission from the light sources 5a, 5b for generating a cross image are switched for each scanning cycle of the imaging unit 4. That is, the control arithmetic unit 9 outputs a control signal for causing the light source 3 to emit light to the light source 3 in one scanning period, and then outputs a control signal for causing the light sources 5a and 5b to emit light to the light sources 5a and 5b in the next scanning period. The control arithmetic unit 9 outputs a control signal for causing the light source 3 to emit light to the light source 3 in the next scanning period. The control arithmetic unit 9 repeats the above operations until one optical layered body S completely passes directly below the imaging unit 4.
Fig. 5 is a diagram schematically illustrating the contents of the switching control executed by the control arithmetic unit 9. As described above, the control arithmetic unit 9 switches the timing of light emission from the light source 3 and the timing of light emission from the light sources 5a and 5b for each scanning cycle of the imaging unit 4, whereby the imaging unit 4 forms images of light emitted from the light source 3 and transmitted through the optical layered body S (the region indicated by the blank in fig. 5 a) and light emitted from the light sources 5a and 5b and transmitted through the polarizing filters for inspection 6a and 6b and the optical layered body S (the region indicated by the dot-shaped hatching in fig. 5 a) alternately in the X direction at intervals corresponding to the scanning cycles, as shown in fig. 5 a.
The control arithmetic unit 9 extracts only the regions indicated by the blank spaces in fig. 5 (a) based on the scanning period of the imaging unit 4 and synthesizes them in the X direction, thereby generating a transmission image as shown in fig. 5 (b). The control arithmetic unit 9 also generates a cross nicol image as shown in fig. 5 (c) by extracting only the regions in fig. 5 (a) to which the dot-like shadows are applied and combining them in the X direction according to the scanning cycle of the imaging unit 4.
As described above, even if the imaging unit 4 for generating the transmission image is the same as the imaging unit 4 for generating the cross nicol image, the control arithmetic unit 9 can generate the transmission image and the cross nicol image separately.
[ reflection inspection step S3]
In the reflection inspection step S3, a reflection image of the optical layered body S is generated using the light reflected by the optical layered body S, and defect candidates existing in the optical layered body S are detected based on the reflection image (S3 in fig. 2).
Specifically, the light source 7 and the imaging unit 8 are driven by the control signal output from the control arithmetic unit 9 at a timing immediately before the optical layered body S reaches directly below the imaging unit 8. Then, the image pickup unit 8 receives the light emitted from the light source 7 and reflected by the optical layered body S to form an image, and outputs an electric signal corresponding to the light amount thereof to the control arithmetic unit 9 as an image pickup signal. The control arithmetic unit 9 generates a two-dimensional reflection image based on the input image pickup signal. Then, the control arithmetic unit 9 detects the defect candidates by applying known image processing such as extraction of 2-valued pixel regions having luminance values (pixel values) different from those of the other pixel regions to the generated reflection image.
Fig. 6 is a diagram schematically illustrating an example of defect candidates detected in the reflection inspection step S3. Fig. 6 shows a 2-valued reflection image, and 3 foreign matters F1 (F1 a to F1 c) are detected as defect candidates. Since the reflected image is generated by the light reflected by the optical layered body S, only the foreign substance F1 adhering to the surface of the diaphragm 40 on the side where the light source 7 is disposed is detected. In the example shown in fig. 6, only the foreign matter F1 is detected, but a damage F2 similarly existing on the surface of the diaphragm 40 may be detected.
[ operation step S4]
In the calculation step S4, a defect existing between the polarizer 10 and the optical film (in the present embodiment, the retardation film 20) is determined based on the defect candidate detected in the transmission inspection step S1, the defect candidate detected in the cross nicol inspection step S2, and the defect candidate detected in the reflection inspection step S3 (S4 in fig. 2).
Specifically, in the arithmetic step S4, the arithmetic control unit 9 first determines whether or not a certain defect candidate is detected in both the transmission inspection step S1 and the cross nicol inspection step S2 (S41 in fig. 2). Whether or not a defect candidate is detected in both the transmission inspection step S1 and the cross nicol inspection step S2 is determined by whether or not a defect candidate detected in the cross nicol inspection step S2 exists at a position equal to (same as or near) the position of a certain defect candidate detected in the transmission inspection step S1. Specifically, for example, the determination is made by whether or not the barycenter of the defect candidate detected in the cross nicol inspection step S2 is present at a position equivalent to the position of the barycenter of the defect candidate detected in the transmission inspection step S1 (for example, a position of the barycenter ± 2 mm). In the determination of whether or not the defect candidate detected in the cross nicol inspection step S2 is present at the same position as the position of the defect candidate detected in the transmission inspection step S1, it is necessary that the coordinates of the transmission image and the coordinates of the cross nicol image match. In the present embodiment, as described above, since the imaging unit 4 for generating the transmission image is the same as the imaging unit 4 for generating the cross nicol image, the coordinates of the transmission image and the coordinates of the cross nicol image substantially coincide with each other, and it is not necessary to strictly match the coordinates of the two images. However, strictly speaking, as will be understood from the description given with reference to fig. 5, the coordinates of the transmission image and the coordinates of the cross nicol image are offset in the X direction by an interval corresponding to the scanning period of the imaging unit 4, and therefore the arithmetic control unit 9 preferably corrects the offset amount to match the coordinates of the two images.
Fig. 7 is a diagram schematically illustrating the content of the calculation step S4.
Fig. 7 (a) is a diagram schematically illustrating an example of the defect candidates determined to be detected in both the transmission inspection step S1 and the cross nicol inspection step S2 in the calculation step S4 (specifically, S41). As shown in fig. 3 (c), in the transmission inspection step S1, the foreign matters F1c, the damages F2a, the adhesive foreign matters F3, and the foreign matters F4a and F4b are detected as defect candidates, and as shown in fig. 4, in the cross nicol inspection step S2, the foreign matters F1a to F1c, the damages F2b to F2d, and the adhesive foreign matters F3 are detected as defect candidates. For example, since the foreign matter F1c detected in the transmission inspection step S1 is also detected in the cross Nicol inspection step S2, the arithmetic and control unit 9 determines that the foreign matter F1c is detected in both of them (S41: "YES" in FIG. 2). On the other hand, for example, since the damage F2a detected in the transmission inspection step S1 is not detected in the cross nicol inspection step S2, the arithmetic and control unit 9 determines that the damage F2a is not detected in both of them (S41: "no" in fig. 2), and determines that the defect candidate (the damage F2 a) is not the adhesive foreign matter F3 existing between the polarizer 10 and the retardation film 20 (S44 in fig. 2). In the present embodiment, the defect candidates (foreign matter F1c, adhering foreign matter F3) shown in fig. 7 (a) are determined to be defect candidates detected in both the transmission inspection step S1 and the cross nicol inspection step S2 by performing the same calculation on all the defect candidates detected in the transmission inspection step S1.
Next, in the arithmetic step S4, the arithmetic control unit 9 determines whether or not the defect candidate detected in both the transmission inspection step S1 and the cross nicol inspection step S2 is detected in the reflection inspection step S3 (S42 in fig. 2). Whether or not the defect candidate detected in both the transmission inspection step S1 and the cross nicol inspection step S2 is detected in the reflection inspection step S3 is determined by whether or not the defect candidate detected in the reflection inspection step S3 exists at a position equal to (the same as or close to) the position of any of the defect candidates detected in both the transmission inspection step S1 and the cross nicol inspection step S2. Specifically, for example, the determination is made by whether or not the barycenter of the defect candidate detected in the reflection inspection step S3 is present at a position equivalent to the barycenter position of the defect candidate detected in both the transmission inspection step S1 and the cross nicol inspection step S2 (for example, a position of the barycenter ± 2 mm). In the determination of whether or not the defect candidate detected in the reflection inspection step S3 is present at the position equivalent to the position of the defect candidate detected in both the transmission inspection step S1 and the cross-nicol inspection step S2, the coordinates of the transmission image and the cross-nicol image need to be matched with the coordinates of the reflection image. The coordinates of the transmission image and the cross nicol image and the coordinates of the reflection image are offset in the X direction by the time obtained by dividing the distance L (see fig. 1 a) between the imaging unit 4 and the imaging unit 8 in the X direction by the transport speed V of the optical layered body S, and therefore the arithmetic control unit 9 needs to correct the offset amount so that the coordinates of the transmission image and the cross nicol image match the coordinates of the reflection image. Further, since there is a possibility that the coordinates of the transmission image and the cross nicol image may be shifted from the coordinates of the reflection image in the Y direction, it is preferable that the arithmetic control unit 9 detects the edge in the Y direction (edge of the optical layered body S) in the transmission image and the cross nicol image and the edge in the Y direction (edge of the optical layered body S) in the reflection image by applying a known image processing, and matches the coordinates of the transmission image and the cross nicol image with the coordinates of the reflection image so that the positions of the edges match.
Fig. 7 (b) is a diagram schematically illustrating an example of the defect candidates determined to be undetected in the reflection inspection step S3 in the calculation step S4 (specifically, S42). As shown in fig. 6, in the foreign matter F1c and the adhering foreign matter F3 detected in both the transmission inspection step S1 and the cross nicol inspection step S2, the arithmetic and control unit 9 determines that the foreign matter F1c was detected in the reflection inspection step S3 (S42: "yes" in fig. 2) and determines that the defect candidate (the foreign matter F1 c) is not the adhering foreign matter F3 existing between the polarizer 10 and the retardation film 20 (S44 in fig. 2), because the foreign matter F1c is also detected in the reflection inspection step S3, as shown in fig. 7. On the other hand, in the foreign substance F1c and the bonding foreign substance F3 detected in both the transmission inspection step S1 and the cross nicol inspection step S2, as shown in fig. 6 described above, since the bonding foreign substance F3 is not detected in the reflection inspection step S3, the arithmetic control unit 9 determines that the bonding foreign substance F3 is not detected in the reflection inspection step S3 (S42 in fig. 2: no), and determines that the defect candidate (bonding foreign substance F3) is the bonding foreign substance F3 existing between the polarizer 10 and the retardation film 20 (S43 in fig. 2).
According to the findings of the present inventors, there is a high possibility that a defect candidate which is not detected in the reflection image but detected in both the transmission image and the cross nicol image is a defect (foreign matter) existing between the polarizer 10 and the phase difference film 20. According to the inspection method of the present embodiment, as described above, in the calculation step S4, the defect candidate that is detected in both the transmission inspection step S1 and the cross nicol inspection step S2 (i.e., detected in both the transmission image and the cross nicol image) and not detected in the reflection inspection step S3 (i.e., not detected in the reflection image) is determined to be a defect existing between the polarizer 10 and the retardation film 20, and therefore, it is possible to suppress excessive detection of a defect existing on the surface of the release film (the separator 40, the surface protection film 50), and to detect a defect existing between the polarizer 10 and the retardation film 20 with high accuracy.
In the present embodiment, the following case is exemplified: the object to be inspected is an optical laminate S in which the optical films 20 and 30 (the retardation film 20 and the protective film 30) are laminated on both sides in the thickness direction of the polarizer 10, and the release films 40 and 50 (the separator 40 and the surface protective film 50) are laminated on the outermost surfaces in both sides in the thickness direction, but the present invention is not limited thereto. The present invention can be applied to various optical laminates as long as the optical laminate is formed by laminating at least one optical film (for example, only the retardation film 20) on the polarizer 10 and laminating a release film (for example, only the separator 40) on at least one outermost surface side.
In the present embodiment, the case where the inspection target is the optical laminate S divided into the chip shape is exemplified, but the present invention is not limited to this. As in the inspection methods described in patent documents 1 to 3, a configuration may be employed in which inspection is performed while a long optical laminate is conveyed in a roll-to-roll (roll) manner.
In the present embodiment, the case where the light sources 3, 5a, 5b, and 7 are disposed on the lower surface side (the side of the diaphragm 40) of the optical layered body S is exemplified, but the present invention is not limited to this, and a configuration may be adopted in which the light sources 3, 5a, 5b, and 7 are disposed on the upper surface side (the side of the surface protection film 50) of the optical layered body S (the polarizing filters 6a and 6b for inspection are also disposed on the upper surface side of the optical layered body S). In this case, the imaging unit 4 is disposed on the lower surface side of the optical layered body S, and the imaging unit 8 is disposed on the upper surface side of the optical layered body S. In this case, in the cross nicol inspection step S2, the adhesive foreign matter existing between the polarizer 10 and the protective film 30 is detected.
In addition, in the present embodiment, the following case is exemplified: the imaging unit 4 for generating the transmission image in the transmission inspection process S1 is the same as the imaging unit 4 for generating the cross-nicol image in the cross-nicol inspection process S2, but the present invention is not limited thereto, and the imaging unit for generating the transmission image and the imaging unit for generating the cross-nicol image may be separately provided.
In the present embodiment, the case where these steps are performed in the order of the transmission inspection step S1, the cross nicol inspection step S2, and the reflection inspection step S3 (where the timing of performing imaging in the transmission inspection step S1 and the cross nicol inspection step S2 is repeated) is exemplified, but the present invention is not limited to this, and can be performed in any order. In addition, the following procedure can also be employed: after the transmission inspection step S1 and the cross nicol inspection step S2 are performed, only S41 of the operation step S4 is performed, and then S42 of the operation step S4 is performed after the reflection inspection step S3 is performed.
Description of the reference numerals
1: a belt conveyor; 2: a cleaning roller; 3.5 a, 5b, 7: a light source; 4. 8: an image pickup unit; 6a, 6b: a polarizing filter for inspection; 10: a polarizer; 20: a phase difference film (optical film); 30: a protective film (optical film); 40: a separator (release film); 50: a surface protective film (release film); 100: an inspection device; s: an optical laminate; s1: a transmission inspection step; s2: an orthogonal Nicole checking procedure; s3: a reflection inspection step; s4: and (5) a calculation procedure.

Claims (5)

1. An inspection method for an optical laminate in which a polarizer and an optical film are laminated and a release film is further laminated on the outermost surface side in at least one of the thickness directions, the inspection method for an optical laminate comprising the steps of:
a transmission inspection step of generating a transmission image of the optical layered body using the light transmitted through the optical layered body, and detecting a defect candidate existing in the optical layered body based on the transmission image;
a cross nicol inspection step of generating a cross nicol image of the optical layered body by light transmitted through an inspection polarizing filter and the optical layered body, the inspection polarizing filter being disposed so as to be cross nicol with respect to a polarization axis of the polarizer, and detecting a defect candidate existing in the optical layered body based on the cross nicol image;
a reflection inspection step of generating a reflection image of the optical layered body using light reflected by the optical layered body and detecting a defect candidate existing in the optical layered body based on the reflection image; and
a calculation step of determining a defect existing between the polarizer and the optical film based on the defect candidate detected in the transmission inspection step, the defect candidate detected in the cross Nicole inspection step, and the defect candidate detected in the reflection inspection step,
wherein, in the calculation step, the defect candidate that is detected in both the transmission inspection step and the cross nicol inspection step and is not detected in the reflection inspection step is determined to be a defect existing between the polarizer and the optical film.
2. The method for inspecting an optical laminate according to claim 1,
the release film is a separator film that is,
the optical film is positioned between the diaphragm and the polarizer,
in the cross nicol inspection step, the polarizing filter for inspection is disposed on the side of the separator.
3. The method for inspecting an optical laminate according to claim 1 or 2,
the orientation direction of the release film is within ± 6 ° with respect to a predetermined orientation direction.
4. The method for inspecting an optical laminate according to any one of claims 1 to 3,
the imaging unit for generating the transmission image in the transmission inspection process is the same as the imaging unit for generating the cross-nicol image in the cross-nicol inspection process,
switching between a timing at which the imaging unit performs imaging in the transmission inspection step and a timing at which the imaging unit performs imaging in the cross Nicol prism inspection step.
5. The method for inspecting an optical laminate according to any one of claims 1 to 4,
the transmission inspection step and/or the cross nicol inspection step includes a noise removal step of removing a defect candidate having a size larger than a predetermined threshold value from the detected defect candidates.
CN202180053420.4A 2020-08-31 2021-03-08 Method for inspecting optical laminate Pending CN115989407A (en)

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