CN-115989407-B - Inspection method for optical laminate

CN115989407BCN 115989407 BCN115989407 BCN 115989407BCN-115989407-B

Abstract

Provided is an inspection method for an optical laminate, which can suppress excessive detection of defects existing on the surface of a release film and can detect defects existing between a polarizer and an optical film with high accuracy. The method includes a transmission inspection step (S1) for detecting defect candidates based on a transmission image generated by light transmitted through an optical laminate (S), a cross-nicol prism inspection step (S2) for detecting defect candidates based on cross-nicol prism images generated by light transmitted through polarizing filters (6 a, 6 b) for inspection and the optical laminate, the polarizing filters (6 a, 6 b) for inspection being arranged so as to be cross-nicol prisms with respect to the polarizing axis of a polarizer (10), a reflection inspection step (S3) for detecting defect candidates based on a reflection image generated by light reflected by the optical laminate, and a calculation step (S4) for determining that defect candidates detected in both the transmission inspection step and the cross-nicol prism inspection step but not detected in the reflection inspection step are defects existing between the polarizer and an optical film (20).

Inventors

Kimuta Zhiya
YAMASHITA YUJI

Assignees

日东电工株式会社

Dates

Publication Date: 20260512
Application Date: 20210308
Priority Date: 20200831

Claims (5)

1. An inspection method of 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 thickness directions, the method comprising the steps of: A transmission inspection step of generating a transmission image of the optical laminate using light transmitted through the optical laminate, and detecting a defect candidate existing in the optical laminate based on the transmission image; A crossed nicols inspection step of generating a crossed nicols image of the optical laminate using light transmitted through an inspection polarizing filter arranged so as to be crossed nicols with respect to a polarizing axis of the polarizer, and detecting a defect candidate existing in the optical laminate based on the crossed nicols image; a reflection inspection step of generating a reflection image of the optical laminate using light reflected by the optical laminate, and detecting a defect candidate existing in the optical laminate 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 crossed nicols inspection step, and the defect candidate detected in the reflection inspection step, In the calculation step, a defect candidate detected in both the transmission inspection step and the crossed nicols inspection step and 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, wherein, The release film is a membrane film and, The optical film is located between the diaphragm and the polarizer, In the crossed nicols inspection step, the polarizing filter for inspection is disposed on the separator side.
3. The method for inspecting an optical laminate according to claim 1 or 2, wherein, The orientation direction of the release film is within + -6 DEG relative to a predetermined orientation direction.
4. The method for inspecting an optical laminate according to claim 1 or 2, wherein, The image pickup unit for generating the transmission image in the transmission inspection process is the same as the image pickup unit for generating the crossed nicols image in the crossed nicols inspection process, Switching between a timing of performing image capturing by the image capturing unit in the transmission inspection process and a timing of performing image capturing by the image capturing unit in the crossed nicols inspection process.
5. The method for inspecting an optical laminate according to claim 1 or 2, wherein, The transmission inspection step and/or the crossed nicols inspection step includes a noise removal step in which a defect candidate having a size larger than a predetermined threshold value among the detected defect candidates is excluded from the defect candidates.

Description

Inspection method for optical laminate Technical Field The present invention relates to 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 of at least one of the polarizer and the optical film in the thickness direction. The present invention relates to an inspection method of 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. Background Conventionally, an inspection method for optically inspecting defects of an optical laminate including a polarizer to determine whether the optical laminate is good or bad has been known. Examples of defects of the optical laminate include foreign matter (appropriately referred to as "adhesion foreign matter" in the present specification) existing 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) existing on the surface of the optical laminate. The optical condition under which defects are easily detected varies depending on the type of defects. Thus, various inspection methods combining a plurality of optical conditions have been proposed. For example, patent documents 1 and 2 propose an inspection method for detecting defects of an optical film 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). Further, patent document 3 proposes an inspection method in which defects of an optical laminate are detected based on a reflected image of the optical laminate generated by light reflected by an optical laminate including a polarizer and an orthogonal nicol image of the optical laminate generated by light transmitted through the optical laminate and an inspection polarizing filter arranged so as to become an orthogonal nicol with respect to a polarizing axis of the polarizer (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, a surface protective film) is further laminated on the outermost surface side of at least one of the thickness directions, defects (foreign matter, dirt, damage, etc.) 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 without remaining when the optical laminate is used (for example, the optical laminate is bonded to a liquid crystal cell). The present inventors studied an inspection method for detecting defects based on an orthogonal nicol prism image of an optical laminate including a polarizer, and found that although it is possible to detect adhesion foreign matter existing between layers of the optical laminate, defects existing on the surface of a release film without harm are also detected (overdetection). Therefore, there is a case where an optical laminate having only defects on the surface of the release film (which are not problematic because of no defects between layers) is treated as a defective product, and the yield of the optical laminate is deteriorated. Patent document 3 describes that, in order to suppress the above-described excessive detection, if the position of a defect candidate detected based on the reflected image of the optical laminate is the same as the position of a defect candidate detected based on the crossed nicols image of the optical laminate, the defect candidate is not treated as a defect (claim 1, paragraph 0083, etc. of patent document 3). However, as a result of the studies by the present inventors, it is clear that even in the inspection method in which the reflection image and the cross nicol prism image are combined as described above, excessive detection of a harmless defect may not be sufficiently suppressed. The inspection method described in patent document 1 aims to accurately count the number of defects (paragraph 0007 of patent document 1), and is not a method for suppressing excessive detection of harmless defects. The inspection method described in patent document 2 aims to accurately determine the type of defect (paragraph 0018 of patent document 2), and is not a method for suppressing excessive detection of a harmless defect. Prior art literature Patent literature Patent document 1 Japanese patent laid-open publication No. 2003-329601 Patent document 2 Japanese patent application laid-open No. 2012-167975 Patent document 3 Japanese patent No. 4960161 Disclosure of Invention Problems t