Inspection method

Abstract

The present invention is an inspection method for judging the presence or absence of defects in a circularly polarizing plate (1) having a stacked polarizing film (11) and a phase difference film (14), and a film-like object to be inspected (10) which is stacked on the phase difference film (14) side of the circularly polarizing plate (1) and is composed of a polyethylene terephthalate resin. A light source (4), a band pass filter (2) which transmits light of a predetermined wavelength, a first polarizing section (3A), the object to be inspected (10), and a second polarizing section (3B) are arranged so that the angle of incidence θ of light to the object to be inspected (10) is changed in such a manner that the influence of the phase difference possessed by the release film (16a) is reduced. The light reflected by the object to be inspected (10) is observed from the second polarizing section (3B) side, whereby the presence or absence of defects in the circularly polarizing plate (1) is judged.

Description

Technical Field

[0001] This invention relates to inspection methods. Background Technology

[0002] Polarizing plates used in liquid crystal display devices or organic EL display devices are typically constructed by sandwiching a polarizing film between two protective films. To attach the polarizing plate to the display device, an adhesive layer is laminated onto one of the protective films, and a release film is further laminated onto the adhesive layer. Additionally, a release film (surface protection film) is usually also laminated onto the other protective film to protect its surface. The polarizing plate is transported in this laminated state, and the release film is peeled off during the bonding process with the display device in the manufacturing process.

[0003] However, during the manufacturing process of polarizing plates, there are instances where foreign matter gets mixed between the polarizer and the protective film, air bubbles remain, or the protective film has internal alignment defects when it functions as a phase retardation film (hereinafter, these foreign matter, air bubbles, and alignment defects are sometimes collectively referred to as "defects"). When a polarizing plate with defects is bonded to a display device, the area with the defect is visually perceived as a bright spot, and the image appears distorted at the defective area. In particular, defects that are visually perceived as bright spots are easily visually identifiable when the display device is in black.

[0004] Therefore, in the initial stage of attaching the polarizing plate to the display device (the polarizing plate in the state with the release film), an inspection is performed to detect defects in the polarizing plate. This defect inspection typically utilizes light inspection of the polarization axis of the polarizing plate. Specifically, as shown in Patent Document 1, a polarizing filter is placed between the polarizing plate (the object to be inspected) and the light source. Furthermore, the polarizing plate or the polarizing filter is rotated in a planar direction, setting their respective polarization axis directions in a specific relationship. When the polarization axis directions are mutually orthogonal (i.e., in a configuration forming an orthogonal Nicol configuration), linearly polarized light passing through the polarizing filter does not pass through the polarizing plate. However, if the polarizing plate has a defect, linearly polarized light will pass through that location, and thus the light is detected, indicating the presence of a defect. On the other hand, when the polarization axis directions of the polarizing plate and the polarizing filter are parallel to each other, linearly polarized light passing through the polarizing filter passes through the polarizing plate. However, if the polarizing plate has a defect, linearly polarized light is blocked at that location, and thus the light is not detected, indicating the presence of a defect. The polarizer can be inspected for defects by visually detecting the light passing through it or by automatically detecting the image resolution values ​​generated by combining a CCD camera and an image processing device.

[0005] Existing technical documents

[0006] Patent documents

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

[0008] The problem that the invention aims to solve

[0009] When the polarizer is a circular polarizer and the release film is made of polyethylene terephthalate (PET) resin, a phase retardation filter (equivalent to the aforementioned polarizing filter) that matches the wavelength dispersion of the PET resin to a certain extent is used in the inspection of the polarizer. Here, when the circular polarizer and the phase retardation filter are arranged in an orthogonal Nicol configuration, according to the above principle, defects are visually identified as bright spots. However, bright spot defects such as orientation defects or pinholes in the phase retardation film of the circular polarizer are sometimes visually identified as black spots. In this case, detection and judgment are more difficult than detecting them as bright spots. This tendency is particularly pronounced when the circular polarizer contains a phase retardation film made of a cured polymeric liquid crystal compound.

[0010] Furthermore, the inspection method shown in Patent Document 1 is based on observing light that has passed through the object being inspected. In this principle, when the object being inspected has deformation defects (e.g., wrinkles produced during the cutting of a circular polarizing plate), the optical path length hardly changes between the normal portion and the defective portion, making it difficult to optically detect the deformation defects.

[0011] Furthermore, 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, making it difficult to use existing inspection equipment to detect defects such as bright spots in the polarizing plate with high precision.

[0012] Therefore, the purpose of this invention is to provide an inspection method, which is a reflective inspection method, that can easily determine whether a circular polarizing plate has defects.

[0013] Solution for solving the problem

[0014] This invention provides an inspection method for determining whether a film-like object to be inspected, comprising a circular polarizing plate having a stacked polarizing film and a phase difference film, and a release film made of polyethylene terephthalate resin stacked on the phase difference film side of the circular polarizing plate, has defects. In this method, a light source, a bandpass filter transmitting light of a predetermined wavelength, a first polarizing section, and the object to be inspected with the release film side facing the first polarizing section are arranged sequentially in the optical path of the light emitted by the light source. A second polarizing section, forming an orthogonal Nicol configuration with the first polarizing section, is positioned in the optical path of the light reflected from the object to be inspected. The light from the light source is incident on the bandpass filter, causing the angle of incidence of the light onto the object to change in a manner that reduces the influence of the phase difference of the release film. The light reflected from the object to be inspected is observed from the second polarizing section side to determine whether the circular polarizing plate has defects.

[0015] In this inspection method, the first polarizing section and the second polarizing section are configured in an orthogonal Nicol configuration. Therefore, light reflected from a normal portion of the object under inspection (e.g., light reflected from the surface of the release film) is blocked by the second polarizing section, thus sufficiently darkening the viewing field. In the case of a defective portion, this defective portion can be easily observed as a bright spot. For light reflected from a defective portion generated inside the object under inspection, or light reflected after passing through a defective portion, the phase difference deviates from the ideal due to the defect (becoming undesirable elliptically polarized light). This deviation is transmitted through the second polarizing section, thus enabling detection of the defective portion of the object under inspection. It is anticipated that the overall brightness of the viewing field would increase due to the phase difference of the release film, thus hindering defect detection. However, in this inspection method, the angle of incidence of light towards the object is changed in a way that minimizes the influence of the phase difference of the release film. Specifically, the angle of incidence is changed so that the phase difference manifested by the release film is close to an integer multiple of the wavelength of the incident light. Therefore, even when the release film has a phase difference, the viewing field can be sufficiently darkened. Furthermore, compared to transmission-type inspection methods, this reflective inspection method results in a longer optical path in the inspected object, thus making it easier to detect deformation defects that are difficult to detect using transmission-type inspection methods. Based on the above, the inspection method of the present invention can easily determine whether a circular polarizing plate has defects.

[0016] In this inspection method, it is preferable to perform inspection using a bandpass filter after inspection using a bandpass filter, using a bandpass filter whose wavelength of light that is most easily transmitted differs from the wavelength of light that the bandpass filter most easily transmits. Thus, for example, it is possible to inspect for the presence or absence of two types of defects: those with a phase difference value greater than a predetermined value (which are mostly observed as blue when visually identified as defects, hence hereinafter referred to as blue spots) and those with a phase difference value smaller than a predetermined value (which are mostly observed as red when visually identified as defects, hence hereinafter referred to as red spots).

[0017] In the inspection method of the present invention, it is preferable to prepare a light source and two test pieces with circularly polarized plates having the same structure as the circularly polarized plates of the object being inspected before inspection. The two test pieces are arranged such that the phase retardation film sides face each other, and the angle between the slow axes of the phase retardation films is an angle other than 90° when viewed from the light path direction of the light source. Light of various wavelengths is incident from either side of the polarization film of the test piece, allowing the light path to pass through a defect-free area on the test piece. The polarization film is observed from the other side, and the wavelength with the minimum transmitted light (hereinafter referred to as the "minimum wavelength") is determined. Preferably, at least one wavelength selected from wavelengths 5 nm to 50 nm larger than the minimum wavelength and wavelengths 5 nm to 50 nm smaller than the minimum wavelength is chosen as the specified wavelength. By using light of at least one wavelength selected from wavelengths 5 nm to 50 nm larger than the minimum wavelength and wavelengths 5 nm to 50 nm smaller than the minimum wavelength during inspection, blue or red speckles are highlighted and visible when the overall brightness of the observation field is sufficiently suppressed. Specifically, by performing two inspections using light with a wavelength 5 nm to 50 nm larger than the minimum wavelength and light with a wavelength 5 nm to 50 nm smaller than the minimum wavelength, it is possible to inspect for both blue and red speckles, respectively. It should be noted that, here, using light of the specified wavelength means using a bandpass filter that transmits light of that wavelength.

[0018] In the inspection method of the present invention, both the first polarization section and the second polarization section can be circular polarizers or linear polarizers. Furthermore, if they are circular polarizers, they can be constructed from a single, common circular polarizer.

[0019] The retardation film can also be composed of a cured polymeric liquid crystal compound. When the retardation film is composed of a cured polymeric liquid crystal compound, the likelihood of observing black spot defects increases due to its typically thin thickness. Therefore, it is suitable as an object of application of the present invention.

[0020] Invention Effects

[0021] According to the present invention, an inspection method is provided, which is a reflective inspection method, and can easily determine whether there are defects in a circular polarizing plate. Attached Figure Description

[0022] Figure 1 This is a structural diagram of an inspection apparatus used for performing the inspection method of the first embodiment.

[0023] Figure 2 It is a cross-sectional view of the object being inspected.

[0024] Figure 3 This is a diagram showing the configuration of each component in the wavelength selection process based on transmitted light measurement.

[0025] Figure 4 (A) is a graph showing the relationship between the slow axes in the two test pieces. Figure 4 (B) is observed from the light path side. Figure 4 The graph at (A).

[0026] Figure 5 This is a diagram illustrating the effect of the phase difference of the stripping film in the inspection method of the first embodiment.

[0027] Figure 6 This is a structural diagram of an inspection apparatus used for performing the inspection method of the second embodiment. Detailed Implementation

[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 used to label the same or equivalent parts in the various figures, and repeated descriptions are omitted.

[0029] <Definitions of Terms and Symbols>

[0030] The terms and symbols used in this specification are defined as follows.

[0031] (1) Refractive index (nx, ny, nz)

[0032] “nx” is the refractive index in the direction of maximum in-plane refractive index (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis in-plane, and “nz” is the refractive index in the thickness direction.

[0033] (2) In-plane phase difference

[0034] The in-plane phase difference (Re(λ)) refers to the in-plane phase difference of the film at 23℃ and wavelength λ (nm). Re(λ) is calculated by setting the film thickness to d (nm) using Re(λ) = (nx - ny) × d.

[0035] <First Implementation Method>

[0036] The inspection method of the first embodiment will be described.

[0037] (Inspection device and the object being inspected)

[0038] The inspection device of this embodiment inspects the surface of the circular polarizing plate, the layers constituting the circular polarizing plate, or the presence or absence of defects. For example... Figure 1 As shown, the inspection apparatus 100 is sequentially configured with a light source 4, a bandpass filter 2, and a phase difference filter 3. Furthermore, the inspection apparatus 100 also has an inspection stage 20 for placing the object to be inspected 10 on the opposite side of the phase difference filter 3 when viewed from the light source 4. The inspection stage 20 has a surface treated to suppress light reflection.

[0039] Figure 1 The diagram shows the object 10 to be inspected placed on the inspection table 20. The phase difference filter 3 is a wideband circular polarizer wider than the bandpass filter 2, serving as both a first polarizing section 3A for light passing through the bandpass filter 2 and a second polarizing section 3B for light reflected from the object 10 to be inspected (described later). Specifically, the first polarizing section 3A and the second polarizing section 3B are formed by a common circular polarizer, and are located on the same plane.

[0040] like Figure 2 As shown, the object to be inspected 10 is a film, comprising a circular polarizing plate 1 as the main body of the object to be inspected, and a release film 16a laminated to the circular polarizing plate 1 via an adhesive layer 15. For the circular polarizing plate 1, protective films 12a and 12b are adhered to both sides of the polarizing film 11, and a phase retardation film 14 is formed on the protective film 12a on the side with the release film 16a via an adhesive layer 13. Furthermore, a surface protective film 16b is laminated on the side of the circular polarizing plate 1 that does not have the release film 16a. The circular polarizing plate 1 is typically used in display devices, such as liquid crystal display devices or organic EL display devices. In use, the release film 16a is peeled off and adhered to the display device via the adhesive layer 15.

[0041] It should be noted that in this specification, "circular polarizing plate" includes both circularly polarized plates and elliptically polarized plates. Additionally, "circularly polarized light" includes both circularly polarized light and elliptically polarized light.

[0042] The polarizing film 11 is a film that converts light incident from the surface protective film 16a side into linearly polarized light or absorbs it. Examples of polarizing films 11 include films formed by adsorbing or oriented iodine or dichroic pigments onto a polyvinyl alcohol film; or films formed by adsorbing or oriented dichroic pigments onto a compound in which a polymeric liquid crystal compound has been polymerized.

[0043] Protective films 12a and 12b are used to protect the polarizing film 11. As protective films 12a and 12b, protective films commonly used in the field of polarizing film technology are used for the purpose of obtaining a polarizing plate with appropriate mechanical strength. Typically, these include cellulose ester films such as triacetyl cellulose (TAC) films, cyclic olefin films, polyester films such as polyethylene terephthalate (PET) films, and (meth)acrylic films such as polymethyl methacrylate (PMMA) films. Furthermore, additives commonly used in the field of polarizing film technology may also be included in the protective films.

[0044] Protective films 12a and 12b are attached to the display device together with the polarizing film 11 as components of the circular polarizer 1, thus requiring strict management of the phase difference. Typically, a film with an extremely small phase difference is preferred for protective film 12a. Furthermore, for protective film 12b, for example, considering ease of observation when visually recognizing the display device through polarized sunglasses, a film with a phase difference of λ / 4 or a film with an extremely small phase difference is used. Protective films 12a and 12b are attached to the polarizing film 11 using an adhesive.

[0045] The phase retardation film 14 is a film that converts light reflected from the surface protective film 16b side and converted into linearly polarized light by the polarizing film 11 into circularly polarized light. When viewed from the stripping film 16a side, the phase retardation film 14 is a film that converts circularly polarized light incident from the stripping film 16a side into linearly polarized light. The phase retardation film 14 is not particularly limited as long as it is a film with a phase difference; it can be a film composed of stacked λ / 2 and λ / 4 films. In this case, the films can be λ / 2 and λ / 4 films sequentially from the side closest to the polarizing film 11.

[0046] Furthermore, the phase retardation film 14 is preferably composed of a cured polymeric liquid crystal compound. For the phase retardation film 14 composed of a cured polymeric liquid crystal compound, the thickness is typically thin, around 0.2 μm to 10 μm. In the presence of foreign matter, the phase difference value can easily change in this area. In such areas, linearly polarized light cannot be completely converted to ideal circularly polarized light, and instead becomes undesirable elliptically polarized light. Additionally, as described later, sometimes even areas that should be observed as bright spots during inspection may be observed as dark spots.

[0047] For example, compounds disclosed in Japanese Patent Application Publication Nos. 2009-173893, 2010-31223, WO2012 / 147904, WO2014 / 10325, and WO2017-43438 can be cited as examples of polymeric liquid crystal compounds capable of forming the retardation film with so-called inverse wavelength dispersion, which can perform the same polarization conversion over a wide wavelength range. For example, by coating a solution containing the polymeric liquid crystal compound (polymeric liquid crystal compound solution) onto a suitable substrate and photopolymerizing it, an extremely thin retardation film can be formed as described above. Therefore, a circular polarizer with such a retardation film can be formed into an extremely thin circular polarizer. Such an extremely thin circular polarizer is used as a circular polarizer for flexible display materials that have attracted attention in recent years.

[0048] As a substrate for coating a polymerizable liquid crystal compound solution, the substrates described in the aforementioned publication can be cited. 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 photo-aligned by polarized light irradiation or an alignment film mechanically aligned by rubbing. It should be noted that such alignment films are also described in the aforementioned publication.

[0049] However, when foreign matter or damage exists in the substrate on which the polymeric liquid crystal compound solution is coated, defects may sometimes occur in the coating film itself. Furthermore, when the alignment film is rubbed, debris from the rubbing cloth may remain on the alignment film, which can also cause defects in the coating film of the polymeric liquid crystal compound solution (composition for forming a liquid crystal curable film). Thus, although the phase retardation film formed from the polymeric liquid crystal compound can achieve an extremely thin phase retardation film, factors that can lead to defects still exist. Moreover, as described later, defects in the phase retardation film can sometimes manifest as black spots. The inspection method of this embodiment is particularly useful in determining whether an inspected object having a circular polarizer and a release film has defects, where the circular polarizer has a phase retardation film with such defects.

[0050] The retardation film 14 can be manufactured by coating an alignment film forming composition onto a substrate, and further coating a liquid crystal curing film forming composition containing a polymerizable liquid crystal compound onto it. The retardation film 14 thus manufactured is then bonded together with the substrate to the adhesive layer 13 formed on the protective film 12a, and then the substrate is peeled off, thereby transferring the retardation film 14 onto the protective film 12a.

[0051] The release film 16a is peeled off from the circular polarizer 1 during bonding to the display device, and is typically discarded after peeling. Therefore, unlike the protective films 12a and 12b, strict management of the phase difference is not required. Consequently, if a commercially available film is used as the release film 16a, failure to compensate for its phase difference may lead to malfunctions during defect inspection. That is, in defect inspection of the circular polarizer 1 with a release film 16a whose phase difference is not strictly managed, the phase difference of the release film 16a can reduce the inspection accuracy of the inspection device 100.

[0052] It should be noted that, as described in the background section above, in the circular polarizer 1, a surface protective film 16b, which is a type of release film, is usually provided on the opposite side of the release film 16a. Figure 2 In the circular polarizer 1 shown, a surface protective film 16b is attached to the protective film 12b side. This surface protective film 16b is also typically peeled off from the circular polarizer 1 during bonding to the display device, thus unlike the protective films 12a and 12b, it does not require strict management of the phase difference. It should be noted that... Figure 2 In this process, the protective film 12b and the surface protective film 16b can also be bonded together via a suitable adhesive layer or bonding agent layer (in... Figure 2 (The adhesive layer or bonding agent layer is not shown in the figure).

[0053] In this embodiment, the release film 16a is made of PET-based resin. Additionally, the surface protective film 16b also uses a film made of PET-based resin. Films made of PET-based resin (PET-based resin films) are commonly used as release films and have the advantage of being inexpensive. On the other hand, as mentioned above, inexpensive PET-based resin films do not require strict management of phase difference values. Therefore, for example, sometimes the phase difference value varies from batch to batch. Furthermore, even with the same PET-based resin film, sometimes there are deviations in the in-plane phase difference value. Even with a circular polarizer that has been laminated using such an inexpensive PET-based resin film as a release film, the inspection method of this embodiment can detect defects with high precision.

[0054] The phase difference (Re(550)) in the in-plane direction of the release film 16a in this embodiment is, for example, 1500 nm to 3000 nm.

[0055] Here, the method for obtaining the Re(550) of the release film 16a is first shown. As mentioned above, these release films are PET-based resin films, which are readily available from the market. A sheet of approximately 40mm x 40mm in size is taken from this film (using a suitable cutting tool from a long strip of film, etc.). The Re(550) of this sheet is measured three times, and the average value of the Re(550) is obtained. The Re(550) of the sheet can be measured using a phase difference measuring device KOBRA-WPR (manufactured by Oji Measurement Equipment Co., Ltd.) at a measurement temperature of room temperature (approximately 25°C). It should be noted that the same test can be performed when obtaining the Re(550) of the surface protective film 16b.

[0056] The light source 4 can use various commercially available products, but linear light (including light that is close to linear light) such as lasers is advantageous. The light emitted by the light source 4 is unpolarized light, which becomes circularly polarized light after passing through the first polarization section 3A described later.

[0057] In the first embodiment, both the first polarizing section 3A and the second polarizing section 3B are broadband circular polarizers, having a polarizing film that converts linearly polarized light into linearly polarized light and a phase retardation film that converts linearly polarized light into circularly polarized light. The first polarizing section 3A and the second polarizing section 3B are always configured in a crossed Nicol state when inspecting the object 10. To achieve this crossed Nicol state using circular polarizers, when observed from the light source side, the slow axis of the phase retardation film in the first polarizing section 3A is approximately parallel to the slow axis of the phase retardation film in the second polarizing section 3B. This can be achieved by arranging the polarizers in the first polarizing section 3A and the second polarizing section 3B in a manner that makes their absorption axes approximately parallel (configuration α). Alternatively, as another structure, when observed from the light source side, the slow axis of the retardation film contained in the first polarization section 3A is approximately orthogonal to the slow axis of the retardation film contained in the second polarization section 3B. This can be achieved by arranging the absorption axis of the polarization film in the first polarization section 3A and the absorption axis of the polarization film contained in the second polarization section 3B in a manner that is approximately orthogonal (arrangement β). When the orthogonal Nicol state is achieved through the former arrangement α, a single circular polarizer can be used to construct the first polarization section 3A and the second polarization section 3B. The retardation filter 3 constituting the first polarization section 3A and the second polarization section 3B is a so-called defect-free retardation filter.

[0058] To observe the light reflected from the object 10 being inspected, a detection mechanism 5, including a CCD camera, can be positioned on the side of the light source 4 on both sides of the second polarization section 3B, along the optical path of the reflected light. For example, detection can be performed automatically by image processing and analysis combining the CCD camera and an image processing device, thereby enabling the inspection of the object. Alternatively, the detection mechanism 5 may not be a component, and the second polarization section 3B can be visually observed by a person. Furthermore, a partition plate can be appropriately provided between the light source 4 and the CCD camera.

[0059] Furthermore, the inspection device 100 preferably includes a mechanism for tilting or rotating the inspection table 20, or a mechanism for tilting or rotating the arrangement of the light source 4, bandpass filter 2, and phase difference filter 3, so as to change the incident angle θ of the light relative to the object 10 being inspected. By moving the aforementioned mechanism, the phase difference manifested by the peeling film 16a can be adjusted, thereby making the brightness of the observation field darker to suit the inspection.

[0060] (Inspection Method)

[0061] The following describes the inspection method for a circularly polarized plate using the inspection apparatus 100. The inspection method of this embodiment includes a step of selecting two wavelengths as light used in the inspection (wavelength selection step) and a step of performing the inspection using light of those wavelengths (defect inspection step).

[0062] Wavelength selection process

[0063] Before starting the inspection of the object 10 including the circular polarizer 1, the wavelength of the light to be used in the inspection is selected. As explained below, the wavelength of the light to be used in the inspection can be selected using the transmitted light from the circular polarizer prepared as a test piece.

[0064] The wavelength selection process based on transmitted light measurement (hereinafter referred to as "transmitted light measurement") can be performed using a spectrophotometer (e.g., the "V7100" manufactured by Nippon Spectrophotometer Co., Ltd.). Such a spectrophotometer includes a light source (transmission system light source) and a transmitted light quantity measurement mechanism. By placing a sample in the optical path connecting the transmission system light source and the transmitted light quantity measurement mechanism, and irradiating the sample from the transmission system light source, the amount of light transmitted through the sample (transmitted light) can be measured. (See reference...) Figure 3 as well as Figure 4 The measurement of transmitted light is explained. For example... Figure 3As shown, the measuring instrument 500 used in the transmitted light measurement includes a transmission system light source 4A and a transmitted light quantity measuring mechanism 5A. As samples used in the transmitted light measurement, two test pieces (test pieces 1A and 1B) are prepared, each having the same structure as the circular polarizer 1 of the object under inspection 10. Here, "same structure" means that the materials, thickness, and layering structure are substantially the same. Test piece 1A has a polarizing film 11A and a phase retardation film 14A, and test piece 1B has a polarizing film 11B and a phase retardation film 14B.

[0065] The two test pieces are arranged such that the phase retardation films 14A and 14B face each other, and the angle between their slow axes p and q is other than 90° when viewed from the light path direction of the light source 4A of the transmission system. Figure 4 (A) is a schematic perspective view showing the main parts of the mounting of test pieces 1A and 1B. Furthermore, Figure 4 (B) is a schematic diagram illustrating the angle θ1 formed by the slow axes p and q of the test pieces 1A and 1B when observed from the direction of optical path 9, where the angle θ1 is other than 90°, to show the angle formed by the slow axes of the phase retardation films 14A and 14B. This angle θ1 is preferably 10° to 80°, more preferably 20° to 70°, and even more preferably 30° to 60°. By configuring the image with such an angle θ1, it is easy to find wavelengths useful for defect inspection.

[0066] Then, light of various wavelengths is incident from either side of the polarizing films 11A and 11B on test pieces 1A and 1B, such that the light path 9 passes through the defect-free areas on the test pieces 1A and 1B, and the polarizing films 11A and 11B are observed from the other side to determine the wavelength at which the transmitted light is minimal. Such a commercially available spectrophotometer can vary the wavelength of the light source in the transmission system and can automatically analyze the absorbed light at various wavelengths, thus making it easier to determine the minimum wavelength.

[0067] The wavelength study is preferably conducted between 500 and 600 nm. Then, after determining the minimum wavelength (the wavelength with the minimum transmitted light), two wavelengths are used as the wavelengths of light used in the inspection: one 5 nm to 50 nm larger than this wavelength, and the other 5 nm to 50 nm smaller. For example, if the minimum wavelength is 565 nm, 535 nm and 595 nm are used as ±30 nm as the wavelengths of light used in the inspection. That is, two bandpass filters are determined: one that transmits light at a wavelength of 535 nm, and another that transmits light at a wavelength of 595 nm. For the aforementioned bandpass filters, the half-width of the spectrum of the transmitted light wavelength is preferably ±10 nm, more preferably ±5 nm. For the aforementioned bandpass filters, the transmitted light spectrum is different for each filter, and the wavelengths of the light most easily transmitted are also different for each filter. For the aforementioned bandpass filters, the half-width of the light at the wavelength most easily transmitted (peak wavelength) is preferably ±10 nm, more preferably ±5 nm.

[0068] • Defect inspection process

[0069] After determining the wavelength of the light to be used in the inspection, the next step is to inspect the defect of the object 10.

[0070] like Figure 1 As shown, inside the inspection apparatus 100, the object to be inspected 10 is placed on the inspection table 20. At this time, the object to be inspected 10 is configured such that the side of the object to be inspected 10 equipped with the release film 16a or the retardation film 14 faces the light source 4, and the angle between the slow axis of the retardation film 14 of the circular polarizer 1 and the slow axis of the retardation film of the retardation filter 3 is 10° to 80° when viewed from the light source 4. This angle is preferably 15° to 50°, and more preferably 20° to 40°. It should be noted that in this embodiment, the first polarizing section 3A and the second polarizing section 3B are composed of the same circular polarizer (retardation filter 3), therefore the first polarizing section 3A and the second polarizing section 3B are configured in an orthogonal Nicol configuration with respect to the light reflected from the object to be inspected 10.

[0071] A bandpass filter 2, which is prepared as one of the two bandpass filters identified in the wavelength selection process, is placed within the inspection apparatus 100. Light is incident from the light source 4 onto the bandpass filter 2. At this time, the angle of incidence relative to the object 10 (the angle based on the perpendicular line to the surface of the object 10) θ can be set, for example, to 3° to 30°, or to 5° to 20°. If the light emitted by the light source 4 is low-directivity light, it is preferable that the reflection angle from the object 10 (or the observation angle based on the detection mechanism 5) is within the aforementioned angle range.

[0072] Light emitted from light source 4 passes through bandpass filter 2 and then enters the first polarization section 3A, becoming circularly polarized light (light path 9a). The light passing through the first polarization section 3A then enters the object under inspection 10. It then passes through the release film 16a in the object under inspection 10 and is ideally converted into linearly polarized light by the phase difference film 14 constituting the circular polarizer 1, and is finally absorbed by the polarization film 11 (end of light path 9a). Here, a portion of the light passing through the first polarization section 3A is reflected at the surface of the release film 16a in the object under inspection 10 (light path 9b). This reflected light is blocked by the second polarization section 3B (end of light path 9b) because the first polarization section 3A and the second polarization section 3B form an orthogonal Nicol state. Therefore, the observation field of view based on the second polarization section 3B of the detection mechanism 5 becomes darker.

[0073] On the other hand, a portion of the light incident on the object under inspection 10 is strongly reflected by defects present in the object under inspection 10 (e.g., defect D at the interface between the retardation film 14 and the polarization film 11, or defect D' in the retardation film 14) (light path 9c). For this reflected light, since the phase difference deviates from the ideal due to defects D and D' (becoming undesirable elliptically polarized light), it cannot be absorbed by the polarization film, thus generating reflected light at the interface. This reflected light is not blocked by the second polarization section 3B and passes through. When observed from the inspection mechanism 5 side, the defective portion is observed as a bright spot.

[0074] Here, the phase difference (in-plane phase difference) of the release film 16a can sometimes become an obstacle to the inspection. That is, when the phase difference exhibited by the release film 16a is an integer multiple of the wavelength of the light transmitted through the bandpass filter 2, the polarization state of the circularly polarized light incident on the release film 16a will not be disturbed. However, in most cases, the phase difference exhibited by the release film 16a is not an integer multiple of the wavelength of the light transmitted through the bandpass filter 2, thus disturbing the polarization state of the circularly polarized light, such as... Figure 5 As shown, the phase difference film 14 cannot convert the light into linearly polarized light, and therefore the light cannot be absorbed by the polarization film, resulting in reflected light at the interface (light path 9d). Consequently, the amount of transmitted light through the second polarization section 3B increases, and the viewing field becomes brighter. As a result, the bright spot of the defect that was originally intended to be observed will be obscured by the overall brightness of the viewing field, making defect identification difficult. In addition, due to the in-plane deviation of the phase difference value of the release film 16a or the deviation of each batch, defects that should be observed as bright spots may be observed as black spots.

[0075] To solve this problem, in the inspection method of this embodiment, the incident angle θ of light relative to the object 10 to be inspected is changed, thereby reducing the influence of the phase difference of the release film 16a. That is, if the incident angle θ is changed, the phase difference manifested by the release film 16a changes, and therefore, by finding an incident angle θ that is an integer multiple of the above-mentioned, the field of view can be further darkened. Here, in order to change the incident angle θ, the object 10 to be inspected can be tilted or rotated in various ways (or the inspection table 20 can be moved together), and the light source 4, bandpass filter 2, and phase difference filter 3 can also be tilted or rotated in various ways. In this way, while adjusting the relative positional relationship of the components constituting the inspection device 100 to change the incident angle θ in various ways, the angle at which the influence of the phase difference of the release film 16a is reduced is found. When tilting the object 10 to be inspected, it can be tilted with the slow axis direction of the circular polarizer 1 as the axis direction, or it can be tilted with the fast axis direction as the axis direction.

[0076] After the inspection is completed, bandpass filter 2 is replaced with the other of the two bandpass filters selected in the wavelength selection process, and the same inspection is performed again. By performing this double inspection, using light with a wavelength 5nm to 50nm larger than the wavelength with the minimum light intensity transmitted by the second polarizing section 3B, and light with a wavelength 5nm to 50nm smaller than the wavelength with the minimum light intensity transmitted by the second polarizing section 3B, the blue speckle pattern is emphasized and visible in one bandpass filter, and the red speckle pattern is emphasized and visible in the other bandpass filter. Therefore, by suppressing the overall brightness of the observation field sufficiently, the presence or absence of both blue and red speckle patterns can be checked.

[0077] Based on the inspection method described above, it is easy to determine whether the circular polarizing plate has defects. Furthermore, since this inspection method is a reflective method, the optical path in the inspected object 10 is longer compared to a transmission method, thus making it easier to detect deformation defects such as wrinkles that are difficult to detect using transmission methods. It should be noted that in... Figure 1 The diagram shows a case where the phase difference film 14 in the circular polarizer 1 has a defect, but the defect can also be detected by the inspection method of this embodiment when the polarizer 11 has a defect.

[0078] In order to improve its detection sensitivity, the inspection method of the present invention is preferably performed in a dark room or other state where external light is blocked. In addition, from the viewpoint of suppressing reflected light caused by light transmitted through the object 10 being reflected at the inspection table 20, the surface on which the object 10 is placed on the inspection table 20 is preferably treated with low reflectivity.

[0079] <Second Implementation Method>

[0080] The inspection method of the second embodiment will be described. The difference between the inspection method of the second embodiment and the inspection method of the first embodiment is that a linear polarizing plate is used instead of the circular polarizing plate of the first polarizing part 3A and the second polarizing part 3B.

[0081] (Inspection device and the object being inspected)

[0082] like Figure 6 As shown, the inspection device 200 is configured such that a light source 4, a bandpass filter 2, and a first linear polarizer 7A are arranged sequentially, and a second linear polarizer 7B is arranged next to the first linear polarizer 7A. The first linear polarizer (first polarization section) 7A and the second linear polarizer (second polarization section) 7B are arranged on approximately the same plane with their surfaces parallel to each other. The other structures in the inspection device 200 are the same as those in the inspection device 100 of the first embodiment.

[0083] The first linear polarizer 7A and the second linear polarizer 7B are oriented in a manner that always forms an orthogonal Nicol pattern when inspecting the object 10. Note that the light incident on the second linear polarizer 7B is reflected light that is reflected from the object 10. Furthermore, the first linear polarizer 7A and the second linear polarizer 7B are so-called defect-free linear polarizers.

[0084] (Inspection Method)

[0085] The following describes the inspection method using the circular polarizing plate of the inspection device 200. Before starting the inspection of the object 10 including the circular polarizing plate, the wavelength of the light to be used in the inspection is selected.

[0086] Wavelength selection process

[0087] The wavelength selection process is the same as in the first embodiment.

[0088] • Defect inspection process

[0089] After determining the wavelength of the light to be used in the inspection, the next step is to inspect the defect of the object 10.

[0090] The inspection method using the inspection device 200 is as follows. First, inside the inspection device 100, the object to be inspected 10 is placed on the inspection table 20. Then, the object to be inspected 10 is positioned on the side opposite to the first linear polarizer 7A and the second linear polarizer 7B when viewed from the light source 4. At this time, the object to be inspected 10 is positioned such that the side of the object to be inspected 10 having the release film 16a or the phase difference film 14 faces the light source 4, and the angle formed by the absorption axis of the polarizer 11 and the absorption axis of the first linear polarizer 7A is 45° when viewed from the light source 4. This angle can be a value of 0° or more and 90° or less, and angles exceeding 90° are expressed as a value of 0° or more and 90° or less. Here, the positional relationship between the light source 4 and the detection mechanism 5 is adjusted such that the first linear polarizer 7A transmits light before it is incident on the object to be inspected 10, and the second linear polarizer 7B receives light reflected from the object to be inspected 10. Furthermore, the adjustment is performed such that the first linear polarizer 7A and the second linear polarizer 7B form an orthogonal Nicol configuration.

[0091] A bandpass filter 2, which is prepared as one of the two bandpass filters identified in the wavelength selection process, is placed within the inspection apparatus 200. Light is incident from the light source 4 onto the bandpass filter 2. At this time, the angle of incidence relative to the object 10 (the angle based on the perpendicular line to the surface of the object 10) θ can be set, for example, to 3° to 30°, or to 5° to 20°. If the light emitted by the light source 4 is low-directivity light, it is preferable that the reflection angle from the object 10 (or the observation angle based on the detection mechanism 5) is within the aforementioned angle range.

[0092] Light emitted from light source 4 passes through bandpass filter 2 and then enters the first linear polarizer 7A, becoming linearly polarized light (light path 9a). It then enters the object under inspection 10 (light path 9a). Next, it passes through the release film 16a in the object under inspection 10 and is converted into circularly polarized light by the phase difference film 14 constituting the circular polarizer 1. The absorption axis component of this circularly polarized light is absorbed by the polarizing film 11 (end of light path 9a). Here, a portion of the light that passed through the first linear polarizer 7A is reflected at the surface of the release film 16a in the object under inspection 10 (light path 9b). This reflected light is blocked by the second linear polarizer 7B because the first linear polarizer 7A and the second linear polarizer 7B are configured in an orthogonal Nicol configuration (end of light path 9b). Therefore, the observation field of view based on the second linear polarizer 7B of the detection mechanism 5 is darkened to a level where defects can be observed.

[0093] On the other hand, a portion of the light incident on the object under inspection 10 is strongly reflected by defects present in the object under inspection 10 (e.g., defect D at the interface between the phase retardation film 14 and the polarization film 11, or defect D' in the phase retardation film 14) (light path 9c). For this reflected light, since the phase difference deviates from the ideal due to defects D and D' (becoming undesirable elliptically polarized light), the amount of light absorbed at the polarization film 11 or the amount of light absorbed by the second linear polarizer 7B is reduced by the amount of this deviation compared to the normal portion, thus allowing the light to pass through the second linear polarizer. When observed from the inspection mechanism 5 side, the defective portion is observed as a bright spot.

[0094] In this embodiment, the method for reducing the influence of the phase difference of the stripping film 16a, or the principle that achieves the effect of this embodiment, is the same as in the first embodiment.

[0095] The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments in any way. For example, in the first embodiment, a single phase difference filter 3 is used as the first polarization section 3A and the second polarization section 3B, but the first polarization section 3A and the second polarization section 3B may also be prepared as different phase difference filters.

[0096] Furthermore, in the wavelength selection process of the above embodiment, the minimum wavelength is determined using transmitted light, but it is also possible to determine the minimum wavelength using reflected light as an alternative. For example, prepare a laminate in which a circular polarizer 1 is arranged on a reflective plate such as a mirror, and incident light of any wavelength onto the laminate from a light source. Use a detection mechanism to observe the light reflected from the laminate and confirm the amount of transmitted light. Then, irradiate light with a changed wavelength and confirm its amount of transmitted light. In this way, it is possible to use light with various wavelength changes to measure the amount of transmitted light, thereby determining the wavelength with the minimum amount of transmitted light.

[0097] Industrial applicability

[0098] This invention can be used for quality inspection of circular polarizing plates.

[0099] Explanation of reference numerals in the attached figures

[0100] 1… Circular polarizer; 1A, 1B… Test piece (circular polarizer); 2… Bandpass filter; 3… Phase difference filter; 3A… First polarizing section; 3B… Second polarizing section; 4… Light source; 4A… Transmission system light source; 5… Detection mechanism; 5A… Transmitted light measurement mechanism; 7A… First linear polarizer (first polarizing section); 7B… Second linear polarizer (second polarizing section); 9 (9a, 9b, 9c)… Optical path; 10… Subject to inspection Object; 11 (11A, 11B)...polarizing film; 12a, 12b...protective film; 13...adhesive layer; 14 (14A, 14B)...phase reversal film; 15...adhesive layer; 16a...release film; 16b...surface protective film; 20...inspection table; 100, 200...inspection device; 500...measuring device; D, D'...defect; p, q...slow axis direction of phase reversal film; θ...incident angle; θ1...angle between slow axes.

Claims

1. An inspection method for judging whether there are defects in a film-like object to be inspected, comprising a circular polarizing plate having a stacked polarizing film and a phase retardation film, and a release film made of polyethylene terephthalate resin stacked on the phase retardation film side of the circular polarizing plate, wherein, A light source, a bandpass filter that transmits light of a predetermined wavelength, a first polarizing section, and the object to be inspected with the stripping film side facing the first polarizing section are arranged sequentially in the optical path of the light emitted by the light source. A second polarizing section, which is orthogonal to the first polarizing section, is positioned in the optical path of the light reflected by the object to be inspected. The light from the light source is directed toward the bandpass filter. The angle of incidence of light onto the object being inspected is changed in a way that minimizes the effect of the phase difference present in the release film. The light reflected by the object under inspection is observed from the second polarizing section side to determine whether the circular polarizing plate has defects. Before performing the aforementioned inspection, Prepare a light source and two test pieces with the same structure as the circular polarizing plate on the object under inspection. The two test pieces are arranged such that their phase retardation film sides face each other, and the angle between the slow axes of the phase retardation films is other than 90° when viewed from the optical path direction of the light source. Light of various wavelengths is incident from either side of the polarizing film of the test piece in such a way that the light path passes through a defect-free area on the test piece, and the polarizing film is observed from the other side to determine the wavelength with the minimum amount of transmitted light. At least one wavelength is selected from wavelengths that are 5 nm to 50 nm larger than the specified wavelength and wavelengths that are 5 nm to 50 nm smaller than the specified wavelength.

2. The inspection method according to claim 1, wherein, After inspection using the bandpass filter, an inspection is performed using a bandpass filter with a wavelength that is different from the wavelength of light that the bandpass filter is most likely to transmit.

3. The inspection method according to claim 1 or 2, wherein, Both the first polarizing section and the second polarizing section are circular polarizing plates.

4. The inspection method according to claim 1 or 2, wherein, The first polarization section and the second polarization section are both composed of a common circular polarizing plate.

5. The inspection method according to claim 1 or 2, wherein, Both the first polarization section and the second polarization section are linear polarizing plates.

6. The inspection method according to claim 1 or 2, wherein, The phase retardation film is composed of a cured polymeric liquid crystal compound.

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