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) having an irregularly shaped circularly polarizing plate. 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) are arranged in sequence on an optical path (9), and light is made incident to determine the presence or absence of defects in the circularly polarizing plate. Then, 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 at a wavelength of 550 nm, and light is made incident again to determine the presence or absence of defects in the circularly polarizing plate. Since the first retardation filter (3A) and the second retardation filter (3B) form a crossed Nicol state, the leakage light from the irregularly shaped portion of the object to be inspected (10) is greatly suppressed, making it easy to inspect the vicinity of the irregularly shaped portion.

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 generally constituted by sandwiching a polarizer with two protective films. In order to paste the polarizing plate to a 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 as well. 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 when the protective film has the function of a retardation film, there are alignment defects inside (hereinafter, these foreign matter, 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 when the display device is in black display.

[0004] Therefore, in the previous stage before attaching the polarizing plate to the display device (polarizing plate in a state with a release film), an inspection for detecting defects of the polarizing plate is performed. This defect inspection generally uses light 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 crossed Nicol state), 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 that 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 that part, so this light is not detected, and thus the presence of the defect can be known. The inspector detects the light passing through the polarizing plate visually, or automatically detects it by the 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 Unexamined Patent Application Publication No. 9-229817 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] However, in the case where the polarizing plate has a release film as described above, the polarization characteristics of the polarizing plate are hindered by the birefringence of the release film. Therefore, it is difficult to detect defects such as bright spots existing in the polarizing plate with high precision using existing inspection devices.

[0010] In the case where the polarizing plate is a circularly polarizing plate and the release film is made of a polyethylene terephthalate resin (PET resin), a retardation filter (equivalent to the above-mentioned polarization filter) that matches the wavelength dispersion of the PET resin to a certain extent is used. Here, when the circularly polarizing plate and the retardation filter are arranged in an orthogonal Nicol state, according to the above principle, defects are visually recognized as bright spots. However, bright spot defects in regions with low retardation values such as orientation defects or pinholes in the retardation film of the circularly polarizing plate may sometimes be visually recognized as black spots. In this case, it is more difficult to make a detection judgment than when detecting as bright spots. In particular, in the case where the circularly polarizing plate includes a retardation film made of a cured product of a polymerizable liquid crystal compound, this tendency is significant.

[0011] In addition, for design reasons of the display device, the circularly polarizing plate is sometimes made into an irregular shape. For example, a recess is provided on the outer periphery of the circularly polarizing plate, the corners of the outer periphery are rounded, or a through hole is provided. When the irregularly shaped circularly polarizing plate is the object of the above inspection, it is necessary to prepare a light shielding plate having the same shape as the irregular shape. When the irregularly shaped polarizing plate is moved during defect inspection, it is sometimes easy to cause an offset between the shielding plate and the irregularly shaped polarizing plate, so that inspection light leaks strongly in the irregular part, and thus the observation field of view becomes too bright, which becomes an obstacle to detecting minute defects.

[0012] Therefore, an object of the present invention is to provide an inspection method capable of easily determining whether an irregularly shaped circularly polarizing plate has defects.

[0013] Means for Solving the Problems

[0014] The present invention provides an inspection method for judging whether there are defects in a film-like object to be inspected having a circularly polarizing plate and a release film made of polyethylene terephthalate resin (hereinafter sometimes referred to as "PET resin"). The object to be inspected has a shape with a recess recessed from the side of a rectangle toward the inside of the rectangle, or a shape in which the corners of the rectangle are curved, or a shape having a through hole at a position far from the side of the rectangle. A light source, a first retardation filter, a first retardation plate, the object to be inspected, a second retardation plate, and a second retardation filter are arranged in sequence on the optical path of the light emitted by the light source. The in-plane retardation value at a wavelength of 550 nm of the second retardation plate is substantially the same as the in-plane retardation value at a wavelength of 550 nm of the release film (hereinafter, this in-plane retardation value at a wavelength of 550 nm is sometimes referred to as "Re(550)"), and the second retardation plate compensates for the birefringence of the release film. The second retardation filter and the first retardation filter and the circularly polarizing plate form a crossed Nicol state. The Re(550) of the first retardation plate is substantially the same as the Re(550) of the second retardation plate, and the first retardation plate compensates for the birefringence of the second retardation plate. Light is made incident on the object to be inspected from the light source, and observation is made from the side opposite to the light source to judge whether there are defects in the circularly 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, light is made incident on the object to be inspected, and observation is made from the side opposite to the light source to judge whether there are defects in the circularly 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, by respectively replacing the first retardation plate and the second retardation plate with the third retardation plate and the fourth retardation plate and inspecting the part where a black defect is observed in the inspection using the first retardation plate and the second retardation plate, the retardation can be adjusted so that the black defect can be observed as a bright defect. In addition, in this inspection method, the first retardation filter and the second retardation filter are arranged in a crossed Nicol state. Therefore, when there is no object to be inspected on the optical path, the light from the light source is blocked by the second retardation filter. Therefore, the light leakage from the irregular part of the object to be inspected is greatly suppressed and does not become an obstacle when inspecting the vicinity of the irregular part. Based on the above content, it is possible to easily judge whether there are defects in an irregular circularly polarizing plate using the inspection method of the present invention.

[0016] Here, it is also possible that the object to be inspected further has a surface protective film made of a PET-based resin on the side opposite to the side where the release film is provided with respect to the circularly polarizing plate, and a high retardation plate with Re(550) of 5000 nm or more is also disposed between the first retardation plate and the object to be inspected. When the object to be inspected has a surface protective film, sometimes a rainbow pattern is generated in the observation field of view of the inspection due to the in-plane retardation of the surface protective film, which becomes an obstacle to defect observation. In this case, by using a high retardation plate with a relatively high in-plane retardation, the rainbow-colored light can be converted into white light, and thus it will not become an obstacle to observation.

[0017] In addition, at this time, it is preferable to arrange the slow axes of the surface protective film and the high retardation plate to be substantially parallel. Since the in-plane retardation is additive, by making these slow axes substantially parallel to each other, the rainbow-colored light can be reliably converted into white light.

[0018] The circularly polarizing plate may also have a retardation film made of a cured product of a polymerizable liquid crystal compound. When the retardation film is made of a cured product of a polymerizable liquid crystal compound, due to its usual thinness, the possibility of being observed as a black dot defect is increased. Therefore, it is suitable as an object to which the present invention is applied.

[0019] 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, the second retardation filter, the first retardation plate, and the second retardation plate 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, the second retardation filter, the first retardation plate, and the second retardation plate may be rotated in a direction perpendicular to the optical path. By tilting the above-mentioned components, the retardation of the release film or the first and second retardation plates can be finely adjusted, so a wider range of inspections can be performed. In addition, by rotating the above-mentioned components, the alignment of each structure becomes easier.

[0020] The first retardation plate and the third retardation plate may also be configured to be disposed in the same component.

[0021] Advantages of the Invention

[0022] According to the present invention, an inspection method capable of easily determining the presence or absence of defects in a special-shaped circularly polarizing plate can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a diagram showing an inspection apparatus according to the first embodiment.

[0024] Figure 2 It is a top view of the object to be inspected.

[0025] Figure 3 It is a sectional view taken along line III-III of the object to be inspected.

[0026] Figure 4 It is a figure showing an example of a retardation plate.

[0027] Figure 5 It is a figure showing the inspection apparatus of the second embodiment. Detailed Description of the Invention

[0028] 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.

[0029] <First Embodiment>

[0030] The inspection method of the first embodiment will be described.

[0031] (Inspection Apparatus and Object to be Inspected)

[0032] The inspection apparatus of the present embodiment inspects whether there are surface defects on a circularly polarizing plate. As Figure 1 shown, the inspection apparatus 100A is configured such that a light source 2, a first retardation filter 3A, a first retardation plate 4A, a second retardation plate 4B, and a second retardation filter 3B are arranged in sequence.

[0033] As Figure 2 shown, the film-shaped object to be inspected 10 is a circularly polarizing plate with a shape different from a rectangle, and has a concave portion R that is recessed from one side of the rectangle toward the inside of the object to be inspected 10. Here, "based on a rectangle" means that the shape of the object to be inspected 10 is rectangular assuming that the concave portion R does not exist. In addition, the corners of the object to be inspected 10 are processed to be curved. In the present specification, "a shape different from a rectangle" means a shape obtained by deforming a part of a polygon, a perfect circle, an ellipse, or the like. Deformation means providing a concave portion on the outer periphery, rounding the corners, making a curve into a straight line, or providing a through hole.

[0034] As Figure 3 shown, the object to be inspected 10 includes a circularly polarizing plate 1 as the main body to be inspected, and a release film 16a laminated on the circularly polarizing plate 1 via an adhesive layer 15.

[0035] For the circularly polarizing plate 1, protective films 12a and 12b are adhered to both sides of the polarizing film 11, and a retardation film 14 is formed on the protective film 12a on the side having the release film 16a via an adhesive layer 13. Further, a surface protective film 16b is laminated on the surface layer on the side of the circularly polarizing plate 1 that does not have the release film 16a. The circularly polarizing plate 1 is generally used in display devices, such as liquid crystal display devices or organic EL display devices, and when in use, the release film 16a is peeled off and adhered to the display device via an adhesive layer 15.

[0036] It should be noted that in this specification, "circularly polarizing plate" includes circularly polarizing plates and elliptically polarizing plates. In addition, "circularly polarized light" includes circularly polarized light and elliptically polarized light.

[0037] The polarizing film 11 is a film that converts light incident from the surface protective film 16b side into linearly polarized light in the inspection device 100A. 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 in which a polymerizable liquid crystal compound is oriented and polymerized can be cited.

[0038] 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 generally 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 generally used in the technical field of polarizing plates can also be included in the protective films.

[0039] The protective films 12a and 12b are adhered to the display device together with the polarizing film 11 as components of the circularly polarizing plate 1, and thus strict management of the retardation value, etc. is required. As the protective film 12a, typically, a film having an extremely small retardation value is preferably used. In addition, as the protective film 12b, for example, in consideration of the ease of observation when visually recognizing the display device through polarized sunglasses, a film having a retardation of λ / 4 or a film having a small retardation value is used. The protective films 12a and 12b are adhered to the polarizing film 11 via an adhesive.

[0040] The retardation film 14 is a film that converts the light converted into linearly polarized light by the polarizing film 11 into circularly polarized light in the inspection device 100A. The retardation film 14 is not particularly limited as long as it is a film having a retardation, 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.

[0041] 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. When foreign substances or the like are contained, the retardation value is likely to decrease at this part. As described later, in such a part, sometimes, when the birefringence of the release film 16a is compensated by the retardation plate 4, a part that should originally be observed as a bright spot defect may be observed as a black spot.

[0042] Examples of the polymerizable liquid crystal compound that can form 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 having 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.

[0043] Examples of the substrate for coating the polymerizable liquid crystal compound solution include the substrates described in the above publications. An alignment film may be provided on such a substrate to align the polymerizable liquid crystal compound. The alignment film may 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.

[0044] However, when foreign substances or the like are present in the substrate for coating the polymerizable liquid crystal compound solution, or when the substrate itself is damaged, etc., sometimes defects may occur in the coating film obtained by coating the polymerizable liquid crystal compound solution. In addition, when the alignment film is rubbed, sometimes debris of the rubbing cloth remains on the alignment film, which may also cause 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 an extremely thin retardation film, there are also factors that cause defects. And, as 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 an inspection object having a circularly polarizing plate and a release film has defects, the inspection apparatus and inspection method of the present embodiment are particularly useful, wherein the circularly polarizing plate has a retardation film having such defects.

[0045] The retardation film 14 can be produced by the following method: applying an alignment film forming composition on a substrate, and further applying a liquid crystal curing film forming composition containing a polymerizable liquid crystal compound thereon. The thus-produced retardation film 14 is bonded to the adhesive layer 13 formed on the protective film 12a together with the substrate, and then the substrate is peeled off, whereby the retardation film 14 can be transferred to the protective film 12a.

[0046] The release film 16a is peeled off from the circularly polarizing plate 1 when being bonded to the display device. Usually, the peeled-off release film 16a is discarded. Therefore, unlike the protective films 12a and 12b, strict management of the retardation value is not required. Thus, when using a commercially available film as the release film 16a, if the retardation value thereof is not compensated, malfunction may occur in the defect inspection. That is, in the defect inspection of the circularly polarizing plate 1 to which the release film 16a with such 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 100A.

[0047] 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 3 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. Therefore, unlike the protective films 12a and 12b, strict management of the retardation value is not required. And the case of suppressing the color of the observation light band caused by the interference of light due to the retardation value of the surface protective film 16b is described in the second embodiment described later. It should be noted that in Figure 3 , the protective film 12b and the surface protective film 16b can also be bonded via an appropriate adhesive layer or adhesive (in Figure 3 , the adhesive layer or adhesive is not shown).

[0048] In the present embodiment, the release film 16a is made of a PET-based resin. In addition, a film made of a PET-based resin is also used as the surface protective film 16b. The film made of a PET-based resin (PET-based resin film) is generally 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, the retardation may vary from product lot to 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 used as a release film, the presence or absence of defects can be detected with high precision by the inspection method of the present embodiment. It should be noted that in the object to be inspected 10, it is preferable to attach the release film 16a and the surface protective film 16b such that the slow axes thereof are substantially parallel.

[0049] 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 having a size of about 40 mm × 40 mm is cut out from the film (cut out from a long film using an appropriate cutting tool, etc.). Re(550) of the piece is measured three times, and the average value of Re(550) is obtained. Re(550) of the piece can be measured at a measurement temperature of room temperature (about 25°C) using a retardation measurement device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.). It should be noted that in the case of obtaining Re(550) of the surface protective film 16b, the same test may be performed.

[0050] 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 a first retardation filter 3A described later.

[0051] Both the first retardation filter 3A and the second retardation filter 3B are circularly polarized plates. When inspecting the object to be inspected 10, the second retardation filter 3B is adjusted so as to always form a crossed Nicol state with the first retardation filter 3A. Moreover, the polarizing plate and the retardation plate (constituting the layer having retardation) constituting the first and second retardation filters 3A and 3B are so-called defect-free polarizing plates and retardation plates.

[0052] The second retardation plate 4B compensates for the birefringence of light caused by the release film 16a included in the object to be inspected 10. The material constituting the second retardation plate 4B 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 second retardation plate 4B by laminating a plurality of them to obtain a desired retardation value. Since Re(550) generally has additivity, the second retardation plate 4B having a desired Re(550) can be obtained based on the Re(550) of the laminated retardation plates. The first retardation plate 4A cancels out the retardation of the second retardation plate 4B, and a retardation plate having the same structure as the second retardation plate 4B is preferably used. For the release film 16a made of a PET-based resin, generally, the retardation 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 retardation 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 retardation value substantially the same as the Re(550) of the release film 16a, and a combination of two third retardation plates and fourth retardation plates 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 and the fourth retardation plate have substantially the same Re(550). Note that the retardation 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 20 nm or less.

[0053] Moreover, considering the deviation of the retardation value of the release film, it is preferable that the above-described first and second retardation plates 4A and 4B each exhibit a retardation in a range of about ±300 nm with respect to the Re(550) of the release film. Within this range of retardation, it is further preferable that the retardation 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 retardation in advance. That is, as a series of retardation plates in which the retardation changes, it is preferable to prepare, in addition to the first retardation plate 4A and the third retardation plate prepared in advance, retardation plates having different retardations. Next, the case of this retardation plate will be described.

[0054] Figure 4 Shows an overview of a series of retardation plates 4 in which retardation plates having different retardations are aggregated. As Figure 4As shown, the retardation plate 4 can be configured such that in one retardation plate member, regions having different in-plane retardation differences are connected in one direction. That is, the region located at the end (the first region a1; corresponding to the first retardation plate) is a region where Re(550) is, for example, 1720 nm, the region adjacent to this region (the second region a2; corresponding to the third retardation plate) is a region where Re(550) is 1790 nm, and the region further adjacent to this region (the third region a3; corresponding to the fifth retardation plate) is a region where Re(550) is 1860 nm. In the retardation plate 4, the number of such regions is arbitrary, and in Figure 4 it shows up to the nth region a n . It should be noted that in each region, the retardation difference in the thickness direction can be adjusted by the width of the field of view to be observed in one region.

[0055] This retardation plate 4 can be used not only as the first retardation plate 4A arranged adjacent to the first retardation filter 3A when observing from the light source 2 side, but also as the second retardation plate 4B arranged in front of the second retardation filter 3B. On the second retardation plate 4B side, the above-mentioned first region a1, second region a2, and third region a3 respectively become the second retardation plate, the fourth retardation plate, and the sixth retardation plate. And when using two retardation plates 4, 4 as the first and second retardation plates 4A, 4B, regions having the same Re(550) are used in pairs (for example, the first regions a1 with each other, the second regions a2 with each other).

[0056] In order to observe the light that has passed through the object to be inspected 10, a detection mechanism 5 including a CCD camera, etc. can also be arranged on the optical path 9 and at a position on the opposite side of the light source 2 side among the two sides of the second retardation filter 3B. For example, by combining a CCD camera and an image processing device for image processing analysis for automatic detection, the inspection of the object to be inspected can thus be carried out. Or it can also be that the detection mechanism 5 is not a component, but a person visually observes the second retardation filter 3B.

[0057] In addition, the inspection device 100A preferably includes a movable device (not shown), which can tilt at least one of the object to be inspected 10, the first and second retardation plates 4A and 4B, and the first and second retardation filters 3A and 3B at different angles facing each other, or rotate at least one of the object to be inspected 10, the first and second retardation plates 4A and 4B, and the first and second retardation filters 3A and 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 and second retardation plates 4A and 4B can be finely adjusted, so 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 and second retardation plates 4A and 4B becomes easier.

[0058] (Inspection method)

[0059] The inspection method using the inspection device 100A is as follows. First, the object to be inspected 10 is inserted between the first retardation plate 4A and the second retardation plate 4B inside the inspection device 100A. At this time, the surfaces of the above-mentioned films are all parallel, and the side of the object to be inspected 10 with the release film 16a faces the side opposite to the light source 2, and the circular polarizer 1 and the second retardation filter 3B are arranged in a crossed Nicol state. Here, as the first retardation plate 4A and the second retardation plate 4B, the retardation plate 4 shown in the figure is used, and they are both arranged with the first region a1 on the optical path 9. Figure 4 shown retardation plate 4, and are both arranged with the first region a1 on the optical path 9.

[0060] And, the first retardation filter 3A and the second retardation filter 3B are adjusted to be in a crossed Nicol state. When the inspection device 100A is equipped with the above-mentioned movable device, after the object to be inspected 10 is inserted in an arbitrary orientation, the relative position relationship of the films can be changed by the movable device to be in a crossed Nicol state.

[0061] The light emitted from the light source 2 is incident on the first retardation filter 3A, becomes circularly polarized light after passing through the first retardation filter 3A, and then passes through the first retardation plate 4A. When the object to be inspected 10 is moved in an arbitrary direction in the in-plane direction for inspection, at the concave portion R of the object to be inspected 10, the light that has passed through the first retardation filter 3A and the first retardation plate 4A is directly incident on the second retardation plate 4B and is blocked by the second retardation filter 3B that is in a crossed Nicol state with the first retardation filter 3A. When observed from the detection mechanism 5 side, the surface of the second retardation filter 3B is darker.

[0062] On the other hand, in the portion of the object 10 other than the concave portion, the light that has passed through the first retardation filter 3A and the first retardation plate 4A is incident on and transmitted through the object 10, then is incident on the second retardation plate 4B, and is blocked by the second retardation filter 3B that forms a crossed Nicol state with the object 10. At this time, if there is a defect in the circular polarizing plate 1 in the object 10, normal blocking cannot be performed in the defective portion, and when observed from the detection mechanism 5 side, the defective portion is observed as a bright spot.

[0063] Here, when the release film 16a has a retardation, the circularly polarized light that has passed through the object 10 is affected, and the amount of light transmitted through the second retardation filter 3B increases (for example, exceeds 5% or 10% of the light amount of the light source), and the detection accuracy of defects such as bright spots present in the circular polarizing plate 1 decreases. Here, by disposing the second retardation plate 4B between the object 10 and the second retardation filter 3B, the retardation value of the release film 16a in the object 10 is canceled, and the birefringence of the light caused by the release film 16a is compensated.

[0064] In addition, although the second retardation plate 4B is designed to be as consistent as possible with the retardation value and wavelength dispersion characteristics of the release film 16a to effectively compensate for the birefringence of the light caused by the release film 16a, due to the in-plane deviation of the retardation 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 retardation value of the retardation film 14 is reduced, in cooperation with 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 most allow the defect size of black spot defects 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 retardation value of the retardation film 14 is reduced, it has a large impact on visual recognition and becomes a problem.

[0065] Therefore, in the present embodiment, a third retardation plate and a fourth retardation plate having an in-plane retardation different from that of the first retardation plate 4A and the second retardation plate 4B are used for the defect portion visually recognized as a black spot. Specifically, both the first and second retardation plates 4A and 4B are slid in the in-plane direction, and their second regions a2 (third retardation plate, fourth retardation plate) are both located on the optical path 9.

[0066] A second inspection is performed using this configuration.

[0067] In this way, by performing multiple inspections using retardation plates with different in-plane phase differences, the possibility of defects being observed as bright defects increases, making it easier to accurately identify the defects. It should be noted that in the case where the defects are visually identified as black dots again during the inspection using the second region a2 (the third retardation plate and the fourth retardation plate), the two retardation plates 4, 4 are further slid toward the third region a3 (the fifth retardation plate and the sixth retardation plate) for the third inspection.

[0068] 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 retardation of the release film 16a or the first and second retardation plates 4A, 4B can be finely adjusted, enabling a wider range of inspections. Additionally, by rotating the above-mentioned components, the alignment axis between the release film 16a made of PET-based resin and the first and second retardation plates 4A, 4B becomes easier. These operations can be particularly easily performed when the inspection device 100A is equipped with a movable device.

[0069] According to the inspection method shown above, the third retardation plate (a2) and the fourth retardation plate (a2) are used to inspect the part where black defects are observed during the inspection using the pair of the first retardation plate 4A and the second retardation plate 4B, so that the retardation can be adjusted to observe the black defects as bright defects. Additionally, in this inspection method, the first retardation filter 3A and the second retardation filter 3B are arranged in an orthogonal Nicol state. Therefore, when there is no object to be inspected 10 on the optical path, the light from the light source is blocked by the second retardation filter. Thus, the light leakage from the abnormal part of the object to be inspected 10 is greatly suppressed and does not become an obstacle when inspecting the vicinity of the abnormal part. Based on the above content, it is possible to easily determine whether there are defects in the abnormal circularly polarizing plate 1 using the inspection method of this embodiment.

[0070] <Second Embodiment>

[0071] The inspection method of the second embodiment will be described. The differences between the inspection method of the second embodiment and the inspection method of the first embodiment are as Figure 5 shown. In the inspection device 100B, a high-retardation plate 20 is arranged between the first retardation plate 4A and the object to be inspected 10.

[0072] The high retardation plate 20 is a film having the same shape as the object 10 to be inspected, and has a similar concave portion R' at a position corresponding to the concave portion R of the object 10 to be inspected. The high retardation plate 20 supplements the phase difference value of the surface protective film 16b, and thus is preferably made of the same material as the surface protective film 16b, and is preferably made of a polyethylene terephthalate resin.

[0073] For the high retardation plate 20, Re(550) is preferably 5000 nm or more, more preferably 7000 nm or more, still more preferably 8000 nm or more, and particularly preferably 10000 nm or more. In addition, the high retardation plate 20 is preferably arranged such that its slow axis is substantially parallel to the slow axis of the surface protective film 16b.

[0074] According to the inspection using the high retardation plate 20, in addition to the effects achieved in the inspection method of the first embodiment, it is also possible to suppress the case where the color of the observation light band is caused by the interference of light due to the phase difference of the surface protective film 16b. That is, although there is a case where a rainbow-colored pattern is generated in the observation field of the inspection due to the in-plane phase difference of the surface protective film 16b, which becomes an obstacle to defect observation, since the in-plane phase difference value of the high retardation plate 20 is high, the rainbow-colored light can be converted into white light so that it does not become an obstacle to observation. In particular, when the slow axis of the high retardation plate 20 is arranged substantially parallel to the slow axis of the surface protective film 16b, due to the additivity of the in-plane phase difference, the rainbow-colored light can be reliably converted into light outside the visible light range.

[0075] 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 retardation filter 3A and the first retardation plate 4A are shown as mutually different articles, but they may also be formed as a laminate formed by laminating them on each other to form a single film. The second retardation filter 3B and the second retardation plate 4B may also be a single laminate.

[0076] In addition, in the above-described embodiment, retardation plates in which different first regions a1, second regions a2, etc. having different Re(550) are arranged in a line are used as the two retardation plates 4 (the first retardation plate 4A and the second retardation plate 4B). However, the retardation plate may also be configured such that regions having different Re(550) are arranged in a ring shape. For example, a disk-shaped film may be divided into a plurality of regions having different retardation values with a hypothetical line extending radially from the center portion as a boundary. One region (the first region; corresponding to the first retardation plate) is a region where Re(550) is, for example, 1720 nm, a region (the second region; corresponding to the second retardation plate) adjacent to this region is a region where Re(550) is 1790 nm, and a region (the third region; corresponding to the third retardation plate) further adjacent to this region is a region where Re(550) is 1860 nm. The number of such regions is arbitrary. For example, it may be four, six, eight, or the like.

[0077] Industrial Applicability

[0078] The present invention can be used for quality inspection of circularly polarizing plates.

[0079] Description of Reference Numerals

[0080] 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... optical path; 10... object to be inspected; 11... polarizing film; 12a, 12b... protective films; 13... adhesive layer; 14... retardation film; 15... adhesive layer; 16a... release film; 16b... surface protective film; 20... high retardation plate; 100A, 100B... inspection devices; a1... first region (first retardation plate, second retardation plate); a2... second region (third retardation plate, fourth retardation plate); a n ... nth region; R, R’... recesses.

Claims

1. An inspection method for determining whether a film-like object to be inspected has defects, wherein the object to be inspected includes a circularly polarizing plate and a release film laminated on the circularly polarizing plate and made of a polyethylene terephthalate resin, and wherein, the object to be inspected has a shape that is based on a rectangle and has a concave portion that recesses from the sides of the rectangle toward the inside of the rectangle, or a shape in which the corners of the rectangle are curved, or a shape that has a through-hole at a position away from the sides of the rectangle, a light source, a first retardation filter, a first retardation plate, the object to be inspected, a second retardation plate, and a second retardation filter are arranged in sequence on the optical path of the light emitted by the light source, the in-plane retardation value of the second retardation plate at a wavelength of 550 nm is substantially the same as the in-plane retardation value of the release film at a wavelength of 550 nm, and the second retardation plate compensates for the birefringence of the release film, the second retardation filter and the first retardation filter and the circularly polarizing plate form a crossed Nicol state, the in-plane retardation value of the first retardation plate at a wavelength of 550 nm is substantially the same as the in-plane retardation value of the second retardation plate at a wavelength of 550 nm, and the first retardation plate compensates for the birefringence of the second retardation plate, the "substantially the same" means that the difference between the two is within ±5 nm, light is made to enter the object to be inspected, and observation is made from the side opposite to the light source to determine whether the circularly polarizing plate has defects, 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 retardation values of the third retardation plate and the fourth retardation plate at a wavelength of 550 nm are 50 to 100 nm greater than the in-plane retardation value of the release film at a wavelength of 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 to enter the object to be inspected, and observation is made from the side opposite to the light source to determine whether the circularly polarizing plate has defects.

2. The inspection method according to claim 1, wherein, the object to be inspected further includes a surface protection film made of a polyethylene terephthalate resin on the side opposite to the side where the release film is provided with respect to the circularly polarizing plate, a high retardation plate having an in-plane retardation value of 5000 nm or more at a wavelength of 550 nm is further arranged between the first retardation plate and the object to be inspected.

3. The inspection method according to claim 2, wherein, the configuration is such that the slow axis of the surface protection film is substantially parallel to the slow axis of the high retardation plate.

4. The inspection method according to any one of claims 1 to 3, wherein, the circularly polarizing plate has a retardation film made of a cured product of a polymerizable liquid crystal compound.

5. The inspection method according to any one of claims 1 to 3, wherein, In 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, the second retardation filter, the first retardation plate, and the second retardation plate is inclined in such a manner 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, the second retardation filter, the first retardation plate, and the second retardation plate is rotated in a direction perpendicular to the optical path.

6. The inspection method according to any one of claims 1 to 3, wherein the first retardation plate and the third retardation plate are configured to be disposed within the same member.

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