Inspection method

Abstract

The present invention provides an inspection method for determining the presence or absence of defects in a film-like object to be inspected (10) including a circularly polarizing plate (1) and a release film (16a) made of a polyethylene terephthalate resin. By arranging a light source (2), a first retardation filter (3A), a first retardation plate (4A), the object to be inspected (10), a second retardation plate (4B), and a second retardation filter (3B) in a specified configuration and observing the light reflected from the object to be inspected (10), the presence or absence of defects in the circularly polarizing plate (1) is determined. Subsequently, the first retardation plate (4A) and the second retardation plate (4B) are respectively replaced with a third retardation plate and a fourth retardation plate having different in-plane retardation values with respect to light having a wavelength of 550 nm, and light is made incident again to determine the presence or absence of defects in the circularly polarizing plate (1). Using this inspection method, it is also possible to easily detect deformation defects that are difficult to detect using a transmission-type inspection method.

Description

Technical Field

[0001] The present invention relates to an inspection method. Background Art

[0002] A polarizing plate used in a liquid crystal display device, an organic EL display device, etc. is usually composed of a polarizer sandwiched between two protective films. In order to attach the polarizing plate to the display device, an adhesive layer is laminated on one of the protective films, and a release film is further laminated on the adhesive layer. In addition, a release film (surface protective film) for protecting the surface is mostly attached to the other protective film. The polarizing plate is circulated and transported in a state where the release film is laminated in this way, and the release film is peeled off when the polarizing plate is attached to the display device in the manufacturing process of the display device.

[0003] However, for a polarizing plate, there are cases where foreign matter is mixed between the polarizer and the protective film, bubbles remain, or there are alignment defects inside when the protective film has the function of a retardation film during its manufacturing stage (hereinafter, these foreign matters, bubbles, and alignment defects are sometimes collectively referred to as "defects"). When a defective polarizing plate is attached to a display device, the defective part is visually recognized as a bright spot, and the image looks distorted at the defective part. In particular, a defect visually recognized as a bright spot is easily visually recognized during the black display of the display device.

[0004] Therefore, before attaching the polarizing plate to the display device (the polarizing plate in a state with a release film), an inspection for detecting defects of the polarizing plate is performed. This inspection of defects usually uses optical inspection of the polarization axis of the polarizing plate. Specifically, as shown in Patent Document 1, a polarization filter is provided between the polarizing plate to be inspected and a light source, and on this basis, the polarizing plate or the polarization filter is rotated in the plane direction, and their respective polarization axis directions are set to a specific relationship. When the polarization axis directions are orthogonal to each other (that is, in a configuration constituting a cross Nicol state), the linearly polarized light that has passed through the polarization filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light will pass through at this part, so this light is detected, and thus the presence of the defect can be known. On the other hand, when the polarization axis directions of the polarizing plate and the polarization filter are parallel to each other, the linearly polarized light that has passed through the polarization filter passes through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light is blocked at this part, so this light is not detected, and thus the presence of the defect can be known. An inspector detects the light passing through the polarizing plate visually, or automatically detects it by an image analysis processing value obtained by combining a CCD camera and an image processing device, thereby enabling inspection of whether the polarizing plate has defects.

[0005] Prior Art Documents

[0006] Patent Document

[0007] Patent Document 1: Japanese Patent Laid-Open No. 9-229817 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] When the polarizing plate is a circular polarizing plate and the release film is made of a polyethylene terephthalate resin (PET resin), a retardation filter (equivalent to the above polarizing filter) that matches the wavelength dispersion of the PET resin to a certain extent is used. Here, when the circular polarizing plate and the retardation filter are arranged so as to form a crossed Nicol state, according to the above principle, defects are visually recognized as bright spots, but bright spot defects in regions with lower phase difference values such as alignment defects or pinholes in the retardation film of the circular polarizing plate are sometimes visually recognized as black spots. In this case, it is more difficult to make a detection judgment than detecting as bright spots. In particular, when the circular polarizing plate includes a retardation film made of a cured product of a polymerizable liquid crystal compound, this tendency is significant.

[0010] In addition, the principle of the inspection method shown in Patent Document 1 is to observe the light transmitted through the object to be inspected. In this principle, when there are deformation defects in the object to be inspected (for example, wrinkles generated during the cutting of the circular polarizing plate), the optical path length hardly changes between the normal part and the deformed defect part, so it is difficult to optically detect the deformation defects.

[0011] In addition, when the polarizing plate has a release film as described above, the polarization characteristics of the circular polarizing plate are hindered by the birefringence of the release film, so it is difficult to detect defects such as bright spots existing in the polarizing plate with high precision using existing inspection devices.

[0012] Therefore, an object of the present invention is to provide an inspection method that is a reflection-type inspection method and can easily determine whether there are defects in a circular polarizing plate.

[0013] Means for Solving the Problems

[0014] The present invention provides an inspection method for judging the presence or absence of defects in a film-like object to be inspected, which includes a circular polarizing plate composed of a laminated polarizing film and a retardation film, and a release film laminated on the retardation film side of the circular polarizing plate and made of polyethylene terephthalate resin (hereinafter sometimes referred to as "PET resin"). In this method, a light source, a first retardation filter, a first retardation plate, and the object to be inspected with the release film side facing the first retardation plate side are arranged in sequence on the optical path of the light emitted by the light source, and a second retardation plate and a second retardation filter forming a crossed Nicol state with the first retardation filter are arranged in sequence on the optical path of the light reflected by the object to be inspected. The in-plane phase difference value of the first retardation plate with respect to light of wavelength 550 nm (hereinafter, this in-plane phase difference value with respect to light of wavelength 550 nm is sometimes referred to as "Re(550)") is substantially the same as the Re(550) of the release film, and the first retardation plate compensates for the birefringence of the release film. The Re(550) of the second retardation plate is substantially the same as the Re(550) of the first retardation plate, and the second retardation plate compensates for the birefringence of the first retardation plate. The light of the light source is incident on the first retardation filter, and the light reflected by the object to be inspected is observed from the second retardation filter side to judge the presence or absence of defects in the circular polarizing plate. The first retardation plate and the second retardation plate are respectively replaced with a third retardation plate and a fourth retardation plate whose Re(550) is 50 to 100 nm larger than the Re(550) of the release film and which compensate for the birefringence of the release film. After this replacement, the light is incident on the first retardation filter, and the light reflected by the object to be inspected is observed from the second retardation filter side to judge the presence or absence of defects in the circular polarizing plate. It should be noted that here, "substantially the same" in Re(550) means that the difference in Re(550) is only about ±5 nm.

[0015] In this inspection method, the first retardation filter and the second retardation filter are arranged in such a way as to form an orthogonal Nicol state. Therefore, the light reflected from the normal part of the object to be inspected (for example, the light reflected from the surface of the release film) is blocked by the second retardation filter, so that the observation field of view can be sufficiently darkened, and thus it is easy to observe the defective part. On the other hand, for the light reflected from the defective part generated inside the object to be inspected, since the retardation deviates from the ideal value due to this defect (becoming an unwanted elliptically polarized light), the amount of this deviation passes through the second retardation filter, and thus the defective part of the object to be inspected can be detected. Here, considering that the light reflected from the defective part passes through the release film again, the retardation of the release film becomes an obstacle to defect detection. However, since the first retardation plate compensates for the birefringence of the release film, the case where the birefringence of the release film becomes an obstacle to defect detection is suppressed. In addition, by replacing the first retardation plate and the second retardation plate with a third retardation plate and a fourth retardation plate respectively and inspecting the part that was observed as a black defect in the inspection using the first retardation plate and the second retardation plate, the retardation can be adjusted so that this black defect can be observed as a bright defect. In addition, such a reflection-type inspection method has a longer optical path in the object to be inspected compared with the transmission-type inspection method, so that it is also possible to easily detect deformation defects that are difficult to detect by the transmission-type inspection method. According to the above content, it is possible to easily determine whether there are defects in the circular polarizing plate using the inspection method of the present invention.

[0016] In this inspection method, the retardation film may also be composed of a cured product of a polymerizable liquid crystal compound. When the retardation film is composed of a cured product of a polymerizable liquid crystal compound, due to its usual thinness, the possibility of observing black dot defects is increased. Therefore, it is suitable as an object to which the present invention is applied.

[0017] In addition, in this inspection method, during the inspection, at least one of the object to be inspected, the first retardation plate, the second retardation plate, the third retardation plate, the fourth retardation plate, the first retardation filter, and the second retardation filter may be tilted at different angles facing each other, or at least one of the object to be inspected, the first retardation plate, the second retardation plate, the third retardation plate, the fourth retardation plate, the first retardation filter, and the second retardation filter may be rotated in a direction perpendicular to the optical path. By tilting the above-mentioned members, the retardation of the release film or the first and second retardation plates, etc. can be finely adjusted, so that a wider range of inspections can be performed. In addition, by rotating the above-mentioned members, the alignment axes of each structure become easier.

[0018] The first retardation plate and the third retardation plate may also be arranged in the same member. In addition, the first retardation plate and the second retardation plate may also be arranged in the same member.

[0019] Advantages of the Invention

[0020] According to the present invention, there can be provided an inspection method which is a reflection-type inspection method and can easily determine whether there are defects in a circularly polarizing plate. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 FIG. is a view showing an inspection apparatus according to a first embodiment.

[0022] Figure 2 FIG. is a cross-sectional view of an object to be inspected.

[0023] Figure 3 FIG. is a top view of a retardation plate. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same reference numerals are given to the same or corresponding parts in the respective drawings, and redundant descriptions are omitted.

[0025] (Inspection Apparatus and Object to be Inspected)

[0026] The inspection apparatus of the present embodiment inspects the presence or absence of defects on the surface of a circularly polarizing plate, between the respective layers constituting the circularly polarizing plate, or inside the circularly polarizing plate. As Figure 1 shown, the inspection apparatus 100 is configured as follows: a light source 2, a first retardation filter 3A, and a first retardation plate 4A are arranged in sequence, and a second retardation filter 3B and a second retardation plate 4B are respectively arranged so as to be arranged beside the first retardation filter 3A and the first retardation plate 4A. The first retardation filter 3A and the second retardation filter 3B are arranged on substantially the same plane with their surfaces parallel to each other, and the first retardation plate 4A and the second retardation plate 4B are arranged on substantially the same plane with their surfaces parallel to each other.

[0027] As Figure 2 shown, the object to be inspected 10 is in a film shape and includes a circularly polarizing plate 1 as a main body to be inspected, and a release film 16a laminated on the circularly polarizing plate 1 via an adhesive layer 15. For the circularly polarizing plate 1, protective films 12a and 12b are adhered to both surfaces of the polarizing film 11, and a retardation film 14 is formed via an adhesive layer 13 on the protective film 12a on the side where the release film 16a is provided. Further, a surface protective film 16b is laminated on the surface layer of the circularly polarizing plate 1 on the side where the release film 16a is not provided. The circularly polarizing plate 1 is generally used for a display device, such as a liquid crystal display device or an organic EL display device, and when in use, the release film 16a is peeled off and adhered to the display device via the adhesive layer 15.

[0028] It should be noted that in this specification, the "circular polarizing plate" includes a circular polarizing plate and an elliptical polarizing plate. In addition, "circularly polarized light" includes circularly polarized light and elliptically polarized light.

[0029] The polarizing film 11 is a film that converts the light incident from the surface protective film 16b side into linearly polarized light. As the polarizing film 11, for example, a film in which iodine or a dichroic pigment is adsorbed and oriented on a polyvinyl alcohol film; or a film in which a dichroic pigment is adsorbed and oriented on a compound obtained by orienting and polymerizing a polymerizable liquid crystal compound can be cited.

[0030] The protective films 12a and 12b are used to protect the polarizing film 11. As the protective films 12a and 12b, for the purpose of obtaining a polarizing plate having appropriate mechanical strength, protective films commonly used in the technical field of polarizing plates are used. Typically, there are cellulose ester-based films such as triacetyl cellulose (TAC) films, cyclic olefin-based films, polyester-based films such as polyethylene terephthalate (PET) films: (meth)acrylic-based films such as polymethyl methacrylate (PMMA) films, etc. In addition, additives commonly used in the technical field of polarizing plates can also be included in the protective films.

[0031] The protective films 12a and 12b are attached to the display device together with the polarizing film 11 as components of the circular polarizing plate 1, so strict management of the phase difference, etc. is required. As the protective film 12a, typically, a film with an extremely small phase difference is preferably used. In addition, as the protective film 12b, for example, considering the easy observability when visually recognizing the display device through polarized sunglasses, a film having a phase difference of λ / 4 or a film with a small phase difference is used. The protective films 12a and 12b are attached to the polarizing film 11 via an adhesive.

[0032] The retardation film 14 is a film that converts the light incident from the surface protective film 16b side and converted into linearly polarized light by the polarizing film 11 into circularly polarized light. When observed from the release film 16a side, the retardation film 14 is a film that converts the circularly polarized light incident from the release film 16a side into linearly polarized light. The retardation film 14 is not particularly limited as long as it is a film having a phase difference, and it can be a film formed by laminating a λ / 2 film and a λ / 4 film. In this case, the λ / 2 film and the λ / 4 film can be arranged in this order starting from the side closer to the polarizing film 11.

[0033] In addition, the retardation film 14 is preferably composed of a cured product of a polymerizable liquid crystal compound. For the retardation film 14 composed of a cured product of a polymerizable liquid crystal compound, the thickness is usually as thin as about 0.2 μm to 10 μm. In the case of containing foreign substances or the like, the retardation value is likely to decrease at this part. In such a part, linearly polarized light cannot be completely converted into ideal circularly polarized light, but becomes undesired elliptically polarized light. In addition, as will be described later, sometimes when the birefringence of the release film 16a is compensated by the retardation plate 4, even a part that should originally be observed as a bright spot defect is observed as a black spot.

[0034] Examples of the polymerizable liquid crystal compound capable of forming the retardation film 14 include the compounds disclosed in JP-A-2009-173893, JP-A-2010-31223, WO2012 / 147904, WO2014 / 10325, and WO2017-43438. The polymerizable liquid crystal compounds described in these publications can form a retardation film having so-called inverse wavelength dispersion that can perform the same polarization conversion in a wide wavelength range. For example, by coating a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution) on a suitable substrate and subjecting it to photopolymerization, an extremely thin retardation film can be formed as described above. Therefore, a circularly polarizing plate having such a retardation film can form a circularly polarizing plate with an extremely thin thickness. Such an extremely thin circularly polarizing plate is used as a circularly polarizing plate for flexible display materials that has attracted attention in recent years.

[0035] Examples of the substrate for coating the polymerizable liquid crystal compound solution include the substrates described in the above publications. An alignment film can also be provided on such a substrate to align the polymerizable liquid crystal compound. The alignment film can be an alignment film that is photo-aligned by polarized light irradiation or an alignment film that is mechanically aligned by rubbing treatment. It should be noted that such an alignment film is also described in the above publications.

[0036] However, when there are foreign substances or the like in the substrate coated with the polymerizable liquid crystal compound solution, or when the substrate itself has damage or the like, defects may sometimes occur in the coating film itself obtained by coating the polymerizable liquid crystal compound solution. In addition, when the alignment film is subjected to rubbing treatment, sometimes debris of the rubbing cloth remains on the alignment film, which also causes defects in the coating film of the polymerizable liquid crystal compound solution (composition for forming a liquid crystal cured film). In this way, although the retardation film formed of the polymerizable liquid crystal compound can form a retardation film with an extremely thin thickness, there are also factors that cause defects. And, as will be described later, for the defects of the retardation film, sometimes defects that are observed as black spots may occur. In the inspection for determining whether there are defects in the inspection object having a circularly polarizing plate and a release film, the inspection method of the present embodiment is particularly useful, wherein the circularly polarizing plate has a retardation film having such defects.

[0037] The retardation film 14 can be produced by the following method: coating a composition for forming an alignment film on a substrate, and further coating a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound above it. The retardation film 14 thus formed is bonded to the adhesive layer 13 formed on the protective film 12a together with the substrate, and then the substrate is peeled off, so that the retardation film 14 can be transferred to the protective film 12a.

[0038] The release film 16a is peeled off from the circularly polarizing plate 1 when being bonded to the display device. Usually, the peeled release film 16a is discarded. Therefore, unlike the protective films 12a and 12b, strict management of the retardation value is not required. Therefore, when using a commercially available film as the release film 16a, if the retardation value is not compensated, it may cause malfunction in the defect inspection. That is, in the defect inspection of the circularly polarizing plate 1 to which the release film 16a with such an unstrictly managed retardation value is bonded, the retardation of the release film 16a becomes a cause for reducing the inspection accuracy of the inspection device 100.

[0039] It should be noted that, as described in the above background art, in the circularly polarizing plate 1, a surface protective film 16b, which is a kind of release film, is mostly provided on the opposite side of the release film 16a. In Figure 2 the shown circularly polarizing plate 1, the surface protective film 16b is bonded to the protective film 12b side. This surface protective film 16b is also usually peeled off from the circularly polarizing plate 1 when being bonded to the display device, so that, unlike the protective films 12a and 12b, strict management of the retardation value is not required. It should be noted that in Figure 2 , the protective film 12b and the surface protective film 16b can also be bonded via an appropriate adhesive layer or adhesive layer (in Figure 2 , the adhesive layer or adhesive layer is not shown).

[0040] In this embodiment, the release film 16a is made of a PET-based resin. In addition, the surface protective film 16b also uses a film made of a PET-based resin. The film made of a PET-based resin (PET-based resin film) is commonly used as a release film and has the advantage of being inexpensive. On the other hand, as described above, strict management of the retardation is not required for an inexpensive PET-based resin film. Therefore, for example, sometimes the retardation deviates for each product lot. In addition, even for the same PET resin-based film, there may be a deviation in the retardation within the plane. Even for a circularly polarized plate in which such an inexpensive PET resin-based film is attached as a release film, the presence or absence of defects can be detected with high precision by the inspection method of this embodiment.

[0041] Here, a method for obtaining Re(550) of the release film 16a will be described first. As described above, these release films are PET-based resin films, and such films can be easily obtained on the market. For example, a piece of about 40 mm × 40 mm in size is cut out from this film (cut out from a long strip film using an appropriate cutting tool, etc.). Re(550) of this piece is measured three times, and the average value of Re(550) is obtained. Re(550) of the piece can be measured using a retardation measuring device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.) at a measurement temperature of room temperature (about 25°C). It should be noted that in the case of obtaining Re(550) of the surface protective film 16b, the same test may be performed.

[0042] The light source 2 can use various commercially available products, but for example, linearly polarized light such as laser light (including light close to linearly polarized light) is advantageous. The light emitted from the light source 2 is unpolarized light and becomes polarized light in a specified direction through the first retardation filter 3A described later.

[0043] Both the first retardation filter 3A and the second retardation filter 3B are broadband circularly polarized plates. The second retardation filter 3B is adjusted so as to always form an orthogonal Nicol state with the first retardation filter 3A when inspecting the object to be inspected 10. At this time, it should be noted that the light incident on the second retardation filter 3B is the reflected light reflected from the object to be inspected 10. And the polarizing plate and the retardation plate (constituting a layer having retardation) constituting the first and second retardation filters 3A and 3B are so-called defect-free polarizing plates and retardation plates.

[0044] The first retardation plate 4A compensates for the birefringence of light caused by the release film 16a included in the object to be inspected 10. The material constituting the first retardation plate 4A is not particularly limited as long as it compensates for the birefringence of light caused by the release film 16a made of a PET-based resin. It is also possible to prepare a commercially available retardation plate having a Re(550) of 100 to 200 nm and form the first retardation plate 4A by laminating a plurality of them to obtain a desired phase difference value. Since Re(550) generally has additivity, the first retardation plate 4A with a desired Re(550) can be obtained based on the Re(550) of the laminated retardation plates. The second retardation plate 4B cancels out the phase difference of the first retardation plate 4A, and a retardation plate having the same structure as the first retardation plate 4A is preferably used. For the release film 16a made of a PET-based resin, generally, the phase difference value in the in-plane direction or the deviation of the slow axis is large. Therefore, it is preferable to prepare a plurality of types of retardation plates in advance so that various phase difference values can be selected during inspection. In the present embodiment, at least two types of retardation plates are used: a combination of two first retardation plates 4A and second retardation plates 4B having a phase difference value substantially the same as the Re(550) of the release film 16a, and a combination of two third retardation plates 4C and fourth retardation plates 4D having a Re(550) 50 to 100 nm larger than the Re(550) of the release film 16a. Here, the paired first retardation plate 4A and second retardation plate 4B have substantially the same Re(550), and the third retardation plate 4C and fourth retardation plate 4D have substantially the same Re(550). It should be noted that, as described above, a phase difference value substantially the same as the Re(550) of the release film 16a means that the absolute value of the difference between the Re(550) of the release film 16a and the Re(550) of the retardation plate is 5 nm or less.

[0045] Furthermore, considering the deviation of the phase difference value of the release film, it is preferable that the above-described first and second retardation plates 4A and 4B respectively exhibit a phase difference in a range of about ±300 nm with respect to the Re(550) of the release film. Within this range of the phase difference, it is further preferable that the phase difference changes every 50 nm to 100 nm in the in-plane direction of the release film. It is preferable to prepare various retardation plates showing the above-described phase difference in advance. That is, as a series of retardation plates in which the phase difference changes, it is preferable to prepare, in addition to the first retardation plate 4A and the third retardation plate 4C prepared in advance, retardation plates having different phase differences. Next, the case of this retardation plate will be described.

[0046] Figure 3 Shows an outline of a series of retardation plates 4 in which retardation plates having different in-plane phase differences are aggregated. As Figure 3As shown, the retardation plate 4 can be configured such that in one holding member 41 forming the frame body, regions having different in-plane retardation values are connected in two columns in one direction. That is, if one column (the vertical direction in the drawing) in the retardation plate 4 is considered, the region at the end is the region a1 corresponding to the first retardation plate 4A, and it is a region where Re(550) is, for example, 1720 nm. The region adjacent to this region a1 is the region a3 corresponding to the third retardation plate 4C, and it is a region where Re(550) is 1790 nm. The region further adjacent to this region a3 is the region a5 corresponding to the fifth retardation plate 4E, and it is a region where Re(550) is 1860 nm. In the retardation plate 4, the number of such regions in each column is arbitrary, and in Figure 3 it shows up to the nth region a 2n-1 . And in the other column in the retardation plate 4, regions (a2, a4, a6,..., a 2n-1 ) having the same Re(550) as the adjacent respective regions (a1, a3, a5,..., a 2n ) are arranged in pairs. That is, the region corresponding to the first retardation plate 4A (a1) is the second retardation plate 4B (a2), the region corresponding to the third retardation plate 4C (a3) is the fourth retardation plate 4D (a4), and the region corresponding to the fifth retardation plate 4E (a5) is the sixth retardation plate 4F (a6). It should be noted that in each region, the retardation value in the thickness direction can be adjusted by the width of the field of view to be observed in one region.

[0047] For this retardation plate 4, since the respective regions are formed in one holding member 41 as described above, regions having the same Re(550) can be used in pairs in the inspection apparatus 100. That is, the retardation plate 4 has a structure suitable for simultaneously providing the first retardation plate 4A and the second retardation plate 4B. The first retardation plate 4A and the second retardation plate 4B can be used in pairs, and then, by sliding the retardation plate 4, the third retardation plate 4C and the fourth retardation plate 4D can be used in pairs, and the fifth retardation plate 4E and the sixth retardation plate 4F can be used in pairs.

[0048] In order to observe the light reflected from the defective part inside the object to be inspected 10, a detection mechanism 5 including a CCD camera or the like can be arranged at a position on the light path of the reflected light and on the side where the light source 2 is located out of the two sides of the second retardation filter 3B. For example, detection can be automatically performed by image processing analysis by combining a CCD camera and an image processing device, whereby inspection of the object to be inspected can be carried out. Or alternatively, the detection mechanism 5 is not a component, but a person visually observes the second retardation filter 3B. In addition, a partition plate can be appropriately provided between the light source 2 and the CCD camera.

[0049] In addition, the inspection device 100 preferably includes a movable device (not shown), which can tilt at least one of the object to be inspected 10, the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, the fourth retardation plate 4D, the first retardation filter 3A, and the second retardation filter 3B at different angles facing each other, or rotate at least one of the object to be inspected 10, the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, the fourth retardation plate 4D, the first retardation filter 3A, and the second retardation filter 3B in a direction perpendicular to the optical path 9 of light. By tilting the above components, the retardation of the release film 16a made of PET resin or the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, and the fourth retardation plate 4D can be finely adjusted, so that a wider range of inspections can be performed. In addition, by rotating the above components, the alignment of the release film 16a made of PET resin with the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, and the fourth retardation plate 4D becomes easier.

[0050] (Inspection method)

[0051] The inspection method using the inspection device 100 is as follows. First, the object to be inspected 10 is arranged on the side opposite to the first retardation plate 4A and the second retardation plate 4B as viewed from the light source 2 inside the inspection device 100. At this time, the surfaces of the above-mentioned films are all parallel, and the side of the object to be inspected 10 having the release film 16a or the retardation film 14 faces the light source 2 side, and the circular polarizing plate 1 and the first retardation filter 3A are arranged in an orthogonal Nicol state. Here, as the first retardation plate 4A and the second retardation plate 4B, the retardation plate 4 shown is used, and the first retardation plate 4A is arranged to transmit the light before entering the object to be inspected 10, and the second retardation plate 4B is arranged to receive the light reflected by the object to be inspected 10. Figure 3 shown retardation plate 4, and the first retardation plate 4A is arranged to transmit the light before entering the object to be inspected 10, and the second retardation plate 4B is arranged to receive the light reflected by the object to be inspected 10.

[0052] Moreover, the first retardation filter 3A and the second retardation filter 3B are adjusted to be in an orthogonal Nicol state. When the inspection device 100 is provided with the above-mentioned movable device, after the object to be inspected 10 is inserted in an arbitrary orientation, the relative positional relationship of the films can be changed by the movable device to be in an orthogonal Nicol state.

[0053] Light is incident from the light source 2 on the first retardation filter 3A. At this time, it is preferable to set the incident angle with respect to the object to be inspected 10 (the angle based on the perpendicular line to the surface of the object to be inspected 10) to 3° to 30°, and more preferably to set the incident angle with respect to the object to be inspected 10 to 5° to 20°. In the case where the light emitted from the light source 2 is light with low directivity, it is preferable that the reflection angle from the object to be inspected 10 (or the observation angle based on the detection mechanism 5) is within the above angle range.

[0054] The light emitted from the light source 2 is incident on the first retardation filter 3A, passes through the first retardation filter 3A to become circularly polarized light, and then passes through the first retardation plate 4A (optical path 9a). The light that has passed through the first retardation plate 4A is then incident on the object to be inspected 10. Then, it passes through the release film 16a in the object to be inspected 10, is converted into linearly polarized light by the retardation film 14 constituting the circular polarizing plate 1, and is finally absorbed by the polarizing film 11 (the end of the optical path 9a). Here, a part of the light that has passed through the first retardation plate 4A is reflected on the surface of the release film 16a in the object to be inspected 10 (optical path 9b). Since the first retardation filter 3A and the second retardation filter 3B are arranged in an orthogonal Nicol state, this reflected light is blocked by the second retardation filter 3B (the end of the optical path 9b). Therefore, the observation field of view of the second retardation filter 3B of the detection mechanism 5 becomes dark.

[0055] On the other hand, a part of the light incident on the object to be inspected 10 is more strongly reflected at the part of the defect existing in the object to be inspected 10 (defect D existing at the interface between the retardation film 14 and the polarizing film 11, or defect D' existing in the retardation film 14) (optical path 9c). For this reflected light, since the retardation deviates from the ideal due to the defects D and D' (becomes unwanted elliptically polarized light), it cannot be absorbed by the polarizing film, and thus reflected light is generated at this interface. This reflected light is not blocked by the second retardation filter and passes through. When observed from the side of the detection mechanism 5, the defect part is observed as a bright spot.

[0056] In addition, although the first retardation plate 4A is designed to be as consistent as possible with the phase difference value and wavelength dispersion characteristics of the release film 16a to effectively compensate for the birefringence of light caused by the release film 16a, due to the in-plane deviation of the phase difference value of the release film 16a, it is difficult to sufficiently block the light and perform inspection over the entire inspection field of view. In such a case, in the circular polarizing plate 1, in the portion where the phase difference value of the retardation film 14 is reduced, in cooperation with the optical compensation, a defect that should originally be observed as a bright spot may be observed as a black spot. Generally, compared with bright spot defects, black spot defects have a smaller impact on visual recognition, so the defect size of black spot defects is mostly allowed to be larger than that of bright spot defects. As a result, it is sometimes judged to be okay. However, in the case where the black spot defect is a defect that should originally be observed as a bright spot defect caused by the portion where the phase difference value of the retardation film 14 is reduced, it has a greater impact on visual recognition and becomes a problem.

[0057] Therefore, in the present embodiment, for the defect portion visually recognized as a black spot, third retardation plates 4C and fourth retardation plates 4D having an in-plane phase difference different from that of the first retardation plate 4A and the second retardation plate 4B are used. Specifically, the holding member 41 constituting the retardation plate 4 is slid in its surface direction, and the third retardation plates 4C and the fourth retardation plates 4D are placed on the optical path 9 instead of the first retardation plate 4A and the second retardation plate 4B. The second inspection is performed using this configuration.

[0058] In this way, by performing multiple inspections using retardation plates with different in-plane phase difference values, the possibility of observing the defect as a bright spot defect increases, making it easier to accurately identify the defect. It should be noted that in the case where the defect is again visually recognized as a black spot during the inspection using the pair of the third retardation plates 4C and the fourth retardation plates 4D, the holding member 41 is further slid toward the pair of the fifth retardation plates 4E and the sixth retardation plates 4F to perform the third inspection.

[0059] During the inspection, at least one of the object to be inspected 10, the first and second retardation plates 4A, 4B, and the first and second retardation filters 3A, 3B can be tilted at different angles facing each other, or at least one of the object to be inspected 10, the first and second retardation plates 4A, 4B, and the first and second retardation filters 3A, 3B can be rotated in a direction perpendicular to the optical path 9 of the light. By tilting, the phase difference of the release film 16a or the first and second retardation plates 4A, 4B can be finely adjusted, so a wider range of inspections can be performed. In addition, by rotating the above members, the axis of symmetry between the release film 16a made of a PET-based resin and the pair of the first and second retardation plates 4A, 4B becomes easier. These operations can be particularly easily performed when the inspection device 100 is equipped with a movable device.

[0060] In addition, in the inspection method of the present invention, light of a single wavelength or light with a narrow wavelength range is used as the light from the light source 2, so that it is also possible to detect defects with a locally deviated phase difference. Specifically, as the light source, light with a wavelength at which the transmitted light amount is minimized when configured such that the transmission axis of the polarization film of the circularly polarizing plate 1 included in the object to be inspected 10 and the transmission axis of the polarization plate that converts to linearly polarized light included in the phase difference filter do not form an orthogonal Nicol configuration is used. At this time, the first phase difference filter 3A is arranged opposite to the phase difference film 14. In the case of multiple wavelengths, a wavelength in the range of 500 to 600 nm is particularly preferred. Moreover, by using a light source with a half-value width of the intensity peak of 30 nm or less, the inspection accuracy is improved.

[0061] According to the inspection method described above, the third phase difference plate 4C and the fourth phase difference plate 4D are used to inspect the part where a black defect is observed in the inspection using the pair of the first phase difference plate 4A and the second phase difference plate 4B, so that the phase difference can be adjusted to observe the black defect as a bright defect. In addition, since this inspection method is a reflection type inspection method, compared with the transmission type inspection method, the optical path in the object to be inspected 10 becomes longer, so that it is also possible to easily detect deformation defects such as wrinkles that are difficult to detect by the transmission type inspection method. Based on the above content, it is possible to easily determine whether there are defects in the circularly polarizing plate using the inspection method of the present invention.

[0062] The preferred embodiments of the present invention have been described above, but the present invention is in no way limited by the above embodiments. For example, in the above embodiments, the first phase difference filter 3A and the first phase difference plate 4A are shown as different items, but they may also be formed as a single film as a laminate formed by laminating them on each other. The second phase difference filter 3B and the second phase difference plate 4B may also be a single laminate.

[0063] Industrial Applicability

[0064] The present invention can be used for the quality inspection of circularly polarizing plates.

[0065] Description of Reference Numerals

[0066] 1... Circularly polarizing plate; 2... Light source; 3A... First retardation filter; 3B... Second retardation filter; 4... Retardation plate; 4A... First retardation plate; 4B... Second retardation plate; 5... Detection mechanism; 9 (9a, 9b, 9c)... Optical path; 10... Object to be inspected; 11... Polarizing film; 12a, 12b... Protective film; 13... Adhesive layer; 14... Retardation film; 15... Adhesive layer; 16a... Release film; 16b... Surface protective film; 41... Holding member; 100... Inspection device; a... Region; D, D’... Defect.

Claims

1. An inspection method for determining whether there are defects in a film-like object to be inspected, which is a circular polarizing plate having a laminated polarizing film and a retardation film, and a release film laminated on the retardation film side of the circular polarizing plate and made of a polyethylene terephthalate resin. Among them, The light source, the first retardation filter, the first retardation plate, and the object to be inspected with the release film side facing the first retardation plate side are arranged in sequence on the optical path of the light emitted by the light source, and the second retardation plate and the second retardation filter that forms an orthogonal Nicol state with the first retardation filter are arranged in sequence on the optical path of the light reflected by the object to be inspected. The in-plane phase difference value of the first retardation plate with respect to light of wavelength 550 nm is substantially the same as the in-plane phase difference value of the release film with respect to light of wavelength 550 nm, and the first retardation plate compensates for the birefringence of the release film. The in-plane phase difference value of the second retardation plate with respect to light of wavelength 550 nm is substantially the same as the in-plane phase difference value of the first retardation plate with respect to light of wavelength 550 nm, and the second retardation plate compensates for the birefringence of the first retardation plate. The "substantially the same" means that the absolute value of the difference between the two is 5 nm or less. The light of the light source is made incident on the first retardation filter, and the light reflected by the object to be inspected is observed from the second retardation filter side to determine whether there is a defect in the circular polarizing plate. The first retardation plate and the second retardation plate are respectively replaced with a third retardation plate and a fourth retardation plate. The in-plane phase difference values of the third retardation plate and the fourth retardation plate with respect to light of wavelength 550 nm are 50 to 100 nm larger than the in-plane phase difference value of the release film with respect to light of wavelength 550 nm, and the third retardation plate and the fourth retardation plate compensate for the birefringence of the release film. After this replacement, light is made incident on the first retardation filter, and the light reflected by the object to be inspected is observed from the second retardation filter side to determine whether there is a defect in the circular polarizing plate.

2. The inspection method according to claim 1, wherein The retardation film is composed of a cured product of a polymerizable liquid crystal compound.

3. The inspection method according to claim 1 or 2, wherein During the inspection, at least one of the object to be inspected, the first retardation plate, the second retardation plate, the third retardation plate, the fourth retardation plate, the first retardation filter, and the second retardation filter is tilted in such a way that the angles facing each other are different, or at least one of the object to be inspected, the first retardation plate, the second retardation plate, the third retardation plate, the fourth retardation plate, the first retardation filter, and the second retardation filter is rotated in a direction perpendicular to the optical path.

4. The inspection method according to claim 1 or 2, wherein The first retardation plate and the third retardation plate are arranged in the same member.

5. The inspection method according to claim 1 or 2, wherein The first retardation plate and the second retardation plate are arranged in the same member.

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