Inspection method for retardation laminate, inspection method for circular polarization plate including retardation laminate, and production method for circular polarization plate

Abstract

To provide an inspection method capable of inspecting the presence or absence of abnormality in a thin-film bonding layer that a retardation laminate has, an inspection method for a circular polarization plate including the retardation laminate, and a production method for the circular polarization plate.SOLUTION: Provided is an inspection method for a retardation laminate having a first liquid crystal retardation layer, a second liquid crystal retardation layer, and a thin-film bonding layer, the method comprising: a wavelength determination step of determining an inspection wavelength; an irradiation step of irradiating the retardation laminate with inspection light having the inspection wavelength from the second liquid crystal retardation layer side; and a determination step of determining the presence or absence of an abnormal portion by observing the retardation laminate, which has been irradiated with the inspection light, from the second liquid crystal retardation layer side. In the wavelength determination step, a wavelength within an inspection wavelength range, which includes a predetermined wavelength at which interference states of a first interference spectral characteristic for a first thin-film, serving as a model of a normal portion in the thin-film bonding layer, and a second interference spectral characteristic for a second thin-film, serving as a model of an abnormal portion in the thin-film bonding layer, are reversed, is determined as an inspection wavelength.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for inspecting a retardation laminate, a method for inspecting a circular polarizing plate including the retardation laminate, and a method for manufacturing a circular polarizing plate.

Background Art

[0002] Patent Document 1 discloses a technique for detecting defects (foreign matters, air bubbles, etc.) in a circular polarizing plate using a reflection-type optical system.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A circular polarizing plate has a linear polarizing plate and a retardation plate laminated on the linear polarizing plate. As the retardation plate, a configuration in which two liquid crystal retardation films are joined by a thin film joining layer is known. Since the thin film joining layer sandwiched between the two liquid crystal retardation films is a thin film, thin film interference occurs. If a region (hereinafter referred to as an "abnormal portion") where the thickness deviates from the desired thickness occurs in the thin film joining layer, the interference state of the abnormal portion is different from the interference state of the region formed with the desired thickness (hereinafter referred to as a "normal portion"). Therefore, for example, the abnormal portion appears as a black dot. Thus, for example, when the circular polarizing plate is applied to an image display device, image quality deterioration occurs.

[0005] Therefore, an object of the present invention is to provide an inspection method capable of inspecting the presence or absence of abnormalities in the thin film joining layer of a retardation laminate including two liquid crystal retardation films and a thin film joining layer for joining them, an inspection method for a circular polarizing plate including the retardation laminate, and a manufacturing method for the circular polarizing plate.

Means for Solving the Problems

[0006] [1] The inspection method according to one embodiment is an inspection method for a retardation laminate having a first liquid crystal retardation layer, a second liquid crystal retardation layer, and a thin film bonding layer bonding the first liquid crystal retardation layer and the second liquid crystal retardation layer, the method comprising: a wavelength determination step of determining an inspection wavelength; an irradiation step of irradiating the laminate with inspection light having the inspection wavelength determined in the wavelength determination step from the second liquid crystal retardation layer side; and a determination step of determining the presence or absence of an abnormal portion by observing the laminate irradiated with the inspection light from the second liquid crystal retardation layer side. In the wavelength determination step, within a wavelength range including a predetermined wavelength at which the interference state is inverted between a first interference spectrum characteristic with respect to a first thin film that is a model of a normal portion in the thin film bonding layer and a second interference spectrum characteristic with respect to a second thin film that is a model of an abnormal portion in the thin film bonding layer, a wavelength within the range is determined as the inspection wavelength. The wavelength range is in the range of λa ± 5 [nm] when the predetermined wavelength is λa [nm]. The thickness of the first thin film is within a first thickness range of 3.0 μm or more and 10.0 μm or less, and the thickness of the second thin film is within a second thickness range such that the difference in thickness from the first thin film is 0.05 μm or more and 0.2 μm or less.

[0007] In the inspection method described in [1] above, the laminate is inspected by irradiating the laminate with inspection light having the inspection wavelength. In the inspection light having the inspection wavelength, when an abnormal portion exists in the thin film bonding layer, in the thin film interference caused by the thin film bonding layer, the interference state at the portion of the abnormal portion is inverted with respect to the interference state at the portion of the normal portion. As a result, the presence or absence of an abnormal portion can be determined based on the thin film interference caused by the thin film bonding layer. That is, in the inspection method described in [1] above, it is possible to inspect the presence or absence of an abnormality in the thin film bonding layer.

[0008] [2] In the inspection method for the retardation laminate described in [1] above, the first interference spectrum characteristic may be represented by a first interference spectrum group constituted by first interference spectra of a plurality of the first thin films having different thicknesses, and the second interference spectrum characteristic may be represented by a second interference spectrum group constituted by second interference spectra of a plurality of the second thin films having different thicknesses.

[0009] In this case, inspection light having the same inspection wavelength can be used to inspect the presence or absence of abnormalities in thin film bonding layers having different thicknesses.

[0010] [3] In the inspection method of the retardation laminate according to [1] above, the second interference spectrum characteristic may be represented by a second interference spectrum group constituted by second interference spectra of a plurality of the second thin films having different thicknesses.

[0011] [4] In the inspection method of the retardation laminate according to any one of [1] to [3] above, the predetermined wavelength may be a wavelength at which the first interference spectrum characteristic has a maximum peak and the second interference spectrum characteristic has a minimum peak, or a wavelength at which the first interference spectrum characteristic has a minimum peak and the second interference spectrum characteristic has a maximum peak.

[0012] [5] In the inspection method of the retardation laminate according to any one of [1] to [4] above, in the irradiation step, the inspection light output from the light source unit is irradiated onto the laminate through a first linear polarizing unit, and in the determination step, the laminate may be observed through a second linear polarizing unit arranged in cross Nicol with respect to the first linear polarizing unit.

[0013] From the laminate, reflected light other than the reflected light contributing to thin film interference of the thin film bonding layer is background light in the observation of thin film interference. In the inspection method described in [5] above, the influence of the background light can be reduced by the arrangement relationship between the first linear polarizing unit and the second linear polarizing unit, so that thin film interference is easier to observe.

[0014] [6] In the inspection method of the retardation laminate according to [5] above, the first linear polarizing unit may be arranged such that the polarization axis of the first linear polarizing unit is shifted with respect to the slow axis of the second liquid crystal retardation layer.

[0015] [7] In the inspection method of the retardation laminate according to [6] above, the laminate has a resin film laminated in the opposite direction to the first liquid crystal retardation layer with respect to the second liquid crystal retardation layer, and in the first linearly polarized light portion, the polarization axis of the first linearly polarized light portion may be arranged parallel or orthogonal to the slow axis of the resin film.

[0016] [8] In the inspection method of the retardation laminate according to any one of [5] to [7] above, the light source portion may have a white light source and a band-pass filter that selectively passes light of the inspection wavelength among the light output from the white light source.

[0017] [9] In the inspection method of the retardation laminate according to any one of [1] to [8] above, the direction of the alignment axis of the first liquid crystal retardation layer on the surface of the first liquid crystal retardation layer in contact with the bonding layer in the first liquid crystal retardation layer and the direction of the alignment axis of the second liquid crystal retardation layer on the surface of the second liquid crystal retardation layer in contact with the bonding layer in the second liquid crystal retardation layer may be the same.

[0018]

[10] An inspection method of a circularly polarizing plate according to another aspect of the present invention is an inspection method of a circularly polarizing plate having a laminate including a first liquid crystal retardation layer, a second liquid crystal retardation layer, and a thin film bonding layer bonding the first liquid crystal retardation layer and the second liquid crystal retardation layer, and a linearly polarizing plate laminated in the opposite direction to the thin film bonding layer with respect to the first liquid crystal retardation layer, the method including a step of inspecting the laminate included in the circularly polarizing plate by the inspection method according to any one of [1] to [9] above.

[0019] In the inspection method of the circularly polarizing plate according to

[10] above, the laminate included in the circularly polarizing plate is inspected by the inspection method according to any one of [1] to [9] above. Therefore, it is possible to inspect the presence or absence of abnormalities in the thin film bonding layer included in the circularly polarizing plate.

[0020]

[11] A manufacturing method of a circularly polarizing plate according to another aspect of the present invention includes a step of inspecting the circularly polarizing plate by the inspection method of the circularly polarizing plate according to

[10] above.

[0021] In the method for manufacturing a circularly polarizing plate described in the above

[11] , the method includes a step of inspecting the circularly polarizing plate by the inspection method for the circularly polarizing plate described in the above

[10] . Therefore, it is possible to manufacture a circularly polarizing plate provided with a thin film bonding layer having no abnormal portion.

Advantages of the Invention

[0022] According to the present invention, it is possible to provide an inspection method capable of inspecting the presence or absence of abnormality in the thin film bonding layer included in a retardation laminate including two liquid crystal retardation films and the thin film bonding layer for bonding them, an inspection method for a circularly polarizing plate including the retardation laminate, and a method for manufacturing the circularly polarizing plate.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same parts or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0025] First, a laminate 2 including a retardation plate (retardation laminate) inspected by an inspection apparatus and an inspection method according to an embodiment will be described. FIG. 1 is a schematic diagram for explaining the configuration of a laminate 2 including a retardation plate inspected by an inspection apparatus and an inspection method according to an embodiment.

[0026] The laminate 2 is a film-like laminate. The laminate 2 includes a circular polarizing plate 1 and a release film 31 laminated on the circular polarizing plate 1. Therefore, the laminate 2 is a circular polarizing plate with a release film. The release film 31 is laminated on the circular polarizing plate 1 via an adhesive layer 42. The laminate 2 may have a surface protection film 32 on the side opposite to the release film 31 when viewed from the circular polarizing plate 1. Hereinafter, a form in which the laminate 2 has a surface protection film 32 will be described.

[0027] The circular polarizing plate 1 is used, for example, in an image display device. Examples of the image display device include a liquid crystal display device and an organic EL display device. When the circular polarizing plate 1 is used, after the release film 31 of the laminate 2 is peeled off, the circular polarizing plate 1 is attached to the image display device via the adhesive layer 42. The circular polarizing plate 1 has a retardation plate (retardation laminate) 10 and a linear polarizing plate 20. The retardation plate 10 is laminated on the linear polarizing plate 20.

[0028] The linear polarizing plate 20 has a polarizer 21. The polarizer 21 is a film that converts light incident from the surface protection film 32 side into linearly polarized light. Examples of the polarizer 21 include a film in which iodine, a dichroic dye, etc. are adsorbed and oriented on a polyvinyl alcohol film, and a film in which a dichroic dye is adsorbed and oriented on a film obtained by orienting and polymerizing a polymerizable liquid crystal compound. An example of the thickness of the polarizer 21 is 1 μm or more and 50 μm or less.

[0029] The linear polarizing plate 20 may have protective films 22 and 23. The protective films 22 and 23 are films for protecting the polarizer 21. The protective film 22 may be provided on one surface of the polarizer 21, and the protective film 23 may be provided on the other surface of the polarizer 21. Also, the protective films 22 and 23 are bonded to the polarizer 21 via an adhesive. An example of the thickness of the protective films 22 and 23 is 1 μm or more and 200 μm or less.

[0030] Although the case where the linear polarizing plate 20 has the protective films 22 and 23 has been described, the linear polarizing plate 20 may be configured to have only one of the protective films 22 and 23. That is, another form of the linear polarizing plate 20 may be constituted by a polarizer 21 and a protective film (for example, the protective film 22) provided only on one of the two surfaces of the polarizer 21.

[0031] The protective films 22 and 23 are used for the purpose of obtaining a polarizing plate having appropriate mechanical strength. As the protective films 22 and 23, those commonly used in the technical field of polarizing plates are used. Typically, cellulose ester films such as triacetyl cellulose (TAC) films; cyclic olefin films; polyester films such as polyethylene terephthalate (PET) films; (meth)acrylic films such as polymethyl methacrylate (PMMA) films, etc. can be used as the protective films 22 and 23. Additives commonly used in the technical field of polarizing plates may be included in the protective films 22 and 23.

[0032] Since the protective films 22 and 23 are bonded to the display device together with the polarizer 21 as components of the circular polarizing plate 1, strict management of the retardation value and the like is required. As the protective films 22 and 23, typically, those having an extremely small retardation value are preferably used.

[0033] The retardation plate 10 is laminated on the protective film 22 via the bonding layer 41. As the adhesive constituting the bonding layer 41, any appropriate adhesive can be used. As the adhesive, an aqueous adhesive, an active energy ray-curable adhesive, etc. can be used. An example of the thickness of the bonding layer 41 is 0.01 μm or more and less than 3.0 μm.

[0034] Examples of the aqueous adhesive include an aqueous solution of a polyvinyl alcohol-based resin, an aqueous two-component urethane-based emulsion adhesive, etc.

[0035] The above-mentioned active energy ray curable adhesive is an adhesive containing a curable compound that cures upon irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays, and is preferably an ultraviolet curable adhesive.

[0036] The above-mentioned curable compound can be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of the cationically polymerizable curable compound include epoxy compounds (compounds having one or more epoxy groups in the molecule), oxetane compounds (compounds having one or more oxetane rings in the molecule), or combinations thereof. Examples of the radically polymerizable curable compound include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule), other vinyl compounds having a radically polymerizable double bond, or combinations thereof. A cationically polymerizable curable compound and a radically polymerizable curable compound may be used in combination. The active energy ray curable adhesive usually further contains at least one of a cationic polymerization initiator and a radical polymerization initiator for initiating the curing reaction of the above-mentioned curable compound.

[0037] In order to enhance adhesiveness, a surface activation treatment may be performed on at least one of the bonding surfaces of the bonding layer and the layer to be bonded to the bonding layer. Examples of the surface activation treatment include dry treatments such as corona treatment, plasma treatment, discharge treatment (such as glow discharge treatment), ozone treatment, UV ozone treatment, and ionizing active ray treatment (such as ultraviolet treatment and electron beam treatment). These surface activation treatments may be performed alone or in combination of two or more. Among them, corona treatment is preferred. The corona treatment can be performed, for example, with an output of 1 kJ / m 2 or more and 50 kJ / m 2 or less. The time for performing the corona treatment may be, for example, 1 second or more and 1 minute or less.

[0038] The retardation plate 10 is a film that enters from the surface protection film 32 side and converts the light linearly polarized by the polarizer 21 of the linear polarizer 20 into circularly polarized light.

[0039] The retardation plate 10 has a first liquid crystal retardation layer 11, a second liquid crystal retardation layer 12, and a thin film bonding layer 13 that bonds them. The retardation plate 10 is a laminate in which the first liquid crystal retardation layer 11, the thin film bonding layer 13, and the second liquid crystal retardation layer 12 are laminated in this order. The first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 have a function of imparting a retardation to incident light so that the laminated structure of the retardation plate 10 and the linear polarizer 20 functions as a circular polarizer 1. For example, the second liquid crystal retardation layer 12 functions as a λ / 4 film, and the first liquid crystal retardation layer 11 functions as a λ / 2 film. As another example, for example, the second liquid crystal retardation layer 12 functions as a positive C-plate film, and the first liquid crystal retardation layer 11 functions as a λ / 4 film.

[0040] Examples of the thicknesses of the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 are 0.5 μm or more and 5 μm or less. Each of the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 is formed, for example, from a cured product of a polymerizable liquid crystal compound.

[0041] As the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12, for example, the liquid crystal retardation layers disclosed in JP-A-2009-173893, JP-A-2010-31223, WO2012 / 147904, WO2014 / 10325, WO2017 / 43438, WO2021 / 060378, WO2021 / 132616, and WO2021 / 132624 can be used. The liquid crystal retardation layers described in these publications can have so-called inverse wavelength dispersion, which enables uniform polarization conversion in a wide wavelength range. Therefore, depending on the characteristics of the retardation plate 10, it is also possible to configure one of the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 to have inverse wavelength dispersion.

[0042] Examples of the substrate for forming the liquid crystal retardation layer include those described in the above-mentioned publication. Such a substrate may be provided with an alignment film for aligning the polymerizable liquid crystal compound. The alignment film may be either one that is photo-aligned by polarized light irradiation or one that is mechanically aligned by rubbing treatment. Such an alignment film is also described in the above-mentioned publication.

[0043] Each of the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 can be produced by applying a composition for forming an alignment film on a substrate and then applying a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound thereon. Each of the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 may also be produced by applying a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound on a substrate without using an alignment film.

[0044] The produced first liquid crystal retardation layer 11 and second liquid crystal retardation layer 12 can be joined by a thin film joining layer 13 to produce a retardation plate 10. Then, the substrate on the first liquid crystal retardation layer 11 side is peeled off, placed on, for example, a protective film 22 coated with an ultraviolet curable resin, and the ultraviolet curable resin is cured to form a joining layer 41. Then, by peeling off the substrate on the second liquid crystal retardation layer 12 side, the retardation plate 10 can be transferred onto the protective film 22.

[0045] The thin film joining layer 13 is a layer that joins the first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12. The thickness of the thin film joining layer 13 is 3.0 μm or more and 10.0 μm or less. An adhesive layer is used for the thin film joining layer 13.

[0046] The adhesive layer can be composed of an adhesive composition mainly composed of a resin such as a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin. Among them, an adhesive composition based on a (meth)acrylic resin having excellent transparency, weather resistance, heat resistance, etc. as a base polymer is preferable. The adhesive composition may be an active energy ray curable type or a thermosetting type.

[0047] As the (meth)acrylic resin (base polymer) used in the adhesive composition, for example, a polymer or copolymer having as a monomer one or more of (meth)acrylic esters such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate is preferably used. It is preferable to copolymerize a polar monomer with the base polymer. Examples of the polar monomer include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group, etc., such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

[0048] The adhesive composition may contain only the above base polymer, but usually further contains a crosslinking agent. Examples of the crosslinking agent include polyvalent metal ions that form a metal carboxylate with a carboxyl group; polyamine compounds that form an amide bond with a carboxyl group; polyepoxy compounds and polyols that form an ester bond with a carboxyl group; and polyisocyanate compounds that form an amide bond with a carboxyl group. Among them, polyisocyanate compounds are preferable.

[0049] The thickness of the adhesive layer as the thin film bonding layer 13 is preferably 3.0 μm or more and 7.0 μm or less. The refractive index of the thin film bonding layer 13 is 1.2 or more and 1.9 or less, and preferably 1.4 or more and 1.7 or less.

[0050] The first liquid crystal retardation layer 11 and the second liquid crystal retardation layer 12 are laminated at a predetermined angle α formed by the direction of the alignment axis of the first liquid crystal retardation layer 11 on the surface 11a in contact with the thin film bonding layer 13 in the first liquid crystal retardation layer 11 and the direction of the alignment axis of the second liquid crystal retardation layer 12 on the surface 12a in contact with the thin film bonding layer 13 in the second liquid crystal retardation layer 12. For example, when the second liquid crystal retardation layer 12 functions as a λ / 4 film and the first liquid crystal retardation layer 11 functions as a λ / 2 film, the predetermined angle α is 0° or more and 65° or less. In particular, when this predetermined angle α is 0° or more and 5° or less, the intensity of the interference light becomes maximum and defects are likely to be visually recognized. However, by using this inspection method, defects can be detected even when the predetermined angle α exceeds 5°. When the predetermined angle α is 0° or more and 5° or less, it corresponds to the case where the direction of the alignment axis of the first liquid crystal retardation layer 11 on the surface 11a in contact with the thin film bonding layer 13 in the first liquid crystal retardation layer 11 and the direction of the alignment axis of the second liquid crystal retardation layer 12 on the surface 12a in contact with the thin film bonding layer 13 in the second liquid crystal retardation layer 12 are substantially the same direction.

[0051] The release film 31 is laminated on the protective film 22 via the adhesive layer 42. The release film 31 is peeled off from the circular polarizing plate 1 when it is attached to an image display device (such as an organic EL display device).

[0052] The release film 31 is a film temporarily adhered to protect the surface of the adhesive until it is attached to an image display device, other optical members, etc. The release film 31 is usually composed of a thermoplastic resin film having a release treatment on one side with a release agent such as a silicone-based or fluorine-based release agent, and the release-treated surface is bonded to the adhesive layer.

[0053] The thermoplastic resin constituting the release film 31 is, for example, a polyethylene-based resin such as polyethylene, a polypropylene-based resin such as polypropylene, a polyester-based resin such as polyethylene terephthalate or polyethylene naphthalate, etc. The thickness of the release film 31 is, for example, 10 μm or more and 100 μm or less. If the thickness of the release film 31 is 100 μm or less, it is advantageous for peeling because the force caused when peeling the release film 31 can be kept low. If it is 10 μm or more, it is possible to suppress the formation of indentations in the adhesive layer due to foreign matter during processing, which is preferable.

[0054] The film made of a polyester-based resin may or may not be stretched, but a stretched film is preferable from the viewpoint of improving strength, and it may be uniaxially stretched or biaxially stretched.

[0055] The release film 31 can include an antistatic layer. The antistatic layer may be provided, for example, on the surface of the release film 31 opposite to the surface where the adhesive layer is laminated.

[0056] The surface protection film 32 is provided on the opposite surface of the release film 31 in the circular polarizing plate 1. In the form shown in FIG. 1, the surface protection film 32 is adhered to the protection film 23.

[0057] The surface protection film 32 is provided on the circular polarizing plate 1 for the purpose of preventing dirt and scratches on the circular polarizing plate 1. The surface protection film 32 may be a resin film for surface protection film with an adhesive layer formed thereon, or may be formed of a self-adhesive film alone. The thickness of the surface protection film 32 can be, for example, 30 μm or more and 200 μm or less, preferably 30 μm or more and 150 μm or less, and more preferably 30 μm or more and 120 μm or less.

[0058] The surface protection film 32 is peeled off together with the adhesive layer it has, for example, after the circular polarizing plate 1 with the surface protection film is attached to an image display device (such as an organic EL display device) or other optical members.

[0059] The laminate 2 is manufactured, for example, as follows. First, a retardation plate 10 is formed on the linear polarizing plate 20 to form a circular polarizing plate 1 (circular polarizing plate forming step). A release film 31 is attached to the linear polarizing plate 20 of the circular polarizing plate 1 via an adhesive layer 42 (release film attaching step). When manufacturing the laminate 2 having the surface protection film 32, the surface protection film 32 is attached to the protective film 23 of the circular polarizing plate 1 (surface protection film attaching step). When the manufacturing method of the laminate 2 has a surface protection film attaching step, the order of the release film attaching step and the surface protection film attaching step is not limited.

[0060] An example of the method for forming the retardation plate 10 in the circular polarizing plate forming step is as described above. The circular polarizing plate forming step may have a step of forming the linear polarizing plate 20. The linear polarizing plate 20 is formed by attaching protective films 22 and 23 to the polarizer 21. The polarizer 21 is formed by stretching a film (for example, a polyvinyl alcohol film) to be the polarizer 21 and adsorbing and orienting iodine, dichroic dyes, etc.

[0061] The manufacturing method of the laminate 2 has a step of inspecting the circular polarizing plate 1 to which the release film 31 is attached (inspection step).

[0062] In the inspection step, the retardation plate 10 constituting a part of the circular polarizing plate 1 is inspected. Specifically, in the inspection step, the thin film bonding layer 13 of the retardation plate 10 is inspected.

[0063] FIG. 2 is a schematic diagram of an example of the thin film bonding layer. Specifically, FIG. 2 is a schematic diagram of the thin film bonding layer 13 when it has a region where the thickness deviates from the desired thickness. In the thin film bonding layer 13, the region with a thickness of the desired thickness d1 [μm] is referred to as the normal portion 131, and the region where the thickness deviates from the desired thickness d1 is referred to as the abnormal portion 132. An example of the desired thickness d1 is 3.0 μm or more and 10 μm or less as described above. When the thickness of the abnormal portion 132 is d2, the difference Δd between d1 and d2 is 0.05 μm or more and 0.2 μm or less. In FIG. 2, the abnormal portion 132 is shown emphasized, but the abnormal portion 132 is a minute region. As shown in FIG. 2, when the thickness of the abnormal portion 132 varies within the abnormal portion 132, the thickness d2 is the thickness of the portion where the difference Δd from the thickness d1 of the normal portion 131 is the largest. The abnormal portion 132 may be a portion thicker than the normal portion 131.

[0064] Since the thin film bonding layer 13 is a thin film, thin film interference occurs. As shown in FIG. 2, if the thin film bonding layer 13 has the abnormal portion 132, the state of thin film interference in the abnormal portion 132 is different from the state of thin film interference in the normal portion 131. Therefore, in a display device to which the circularly polarizing plate 1 is applied, for example, the location of the abnormal portion 132 may appear as a black dot on the screen, and the image quality may deteriorate. Therefore, in the inspection process, the presence or absence of the abnormal portion 132 is inspected. In the inspection process, when the presence of the abnormal portion 132 is confirmed, an adjustment process for adjusting the manufacturing conditions of the laminate 2 may be performed, or the inspected laminate may be discarded as a defective product. When performing the above adjustment process, the formation conditions of the thin film bonding layer 13 may be adjusted.

[0065] By manufacturing the laminate 2, the circularly polarizing plate 1 to be bonded to a display device or the like is manufactured. Therefore, the manufacturing method of the above laminate 2 can also be referred to as a manufacturing method of a circularly polarizing plate.

[0066] The inspection apparatus used in the above inspection process and the inspection method using the inspection apparatus will be described. Unless otherwise stated, a form in which the laminate 2 has the surface protection film 32 will be described.

[0067] FIG. 3 is a schematic diagram for explaining the schematic configuration of an inspection apparatus according to an embodiment. As described above, the inspection apparatus 50 is an apparatus for inspecting a retardation plate (specifically, the thin film bonding layer 13).

[0068] The inspection apparatus 50 includes an inspection table 51 on which the laminate 2 is placed. The laminate 2 is placed on the inspection table 51 with the surface protection film 32 in contact with the inspection table 51.

[0069] The inspection apparatus 50 includes a light source unit 52 for inspecting the laminate 2 placed on the inspection table 51. The inspection apparatus 50 may include a first linear polarizer (first linear polarization unit) 53A and a second linear polarizer (second linear polarization unit) 53B. Hereinafter, the inspection apparatus 50 including the first linear polarizer 53A and the second linear polarizer 53B will be described.

[0070] The light source unit 52 is disposed on the side opposite to the inspection table 51 with respect to the laminate 2. In other words, the light source unit 52 is disposed with respect to the laminate 2 such that the inspection light 3 output from the light source unit 52 enters the laminate 2 from the side of the release film 31. The light source unit 52 outputs inspection light 3 for inspecting the circular polarizer 1. The inspection light 3 output from the light source unit 52 is, for example, unpolarized light. The wavelength of the inspection light 3 is referred to as the inspection wavelength λd [nm].

[0071] The light source unit 52 includes a white light source 52A that outputs white light, and a band-pass filter 52B that selectively passes light having the inspection wavelength λd among lights of various wavelengths included in the white light. The white light source 52A may be a three-color LED light source including a red LED, a blue LED, and a green LED.

[0072] The first linear polarizer 53A is an optical component that selectively passes light that is polarized in the direction of the polarization axis of the first linear polarizer 53A among the incident light. The first linear polarizer 53A is disposed on the optical path of the inspection light 3 output from the light source unit 52 between the light source unit 52 and the laminate 2.

[0073] The second linear polarizing plate 53B is an optical component that selectively transmits the light polarized in the direction of the polarization axis of the second linear polarizing plate 53B among the incident light. The second linear polarizing plate 53B is disposed on the optical path of the reflected light from the laminate 2 in order to observe the laminate 2 irradiated with the inspection light 3 through the second linear polarizing plate 53B.

[0074] The second linear polarizing plate 53B is arranged so as to be absorbed by the second linear polarizing plate 53B when the linearly polarized inspection light 3 output from the first linear polarizing plate 53A toward the laminate 2 is reflected while maintaining the polarization state and then enters the second linear polarizing plate 53B. That is, the second linear polarizing plate 53B is arranged in a cross-Nicol state with respect to the first linear polarizing plate 53A.

[0075] The observation of the laminate 2 irradiated with the inspection light 3 may be carried out by the inspector directly visually recognizing the laminate 2 through the second linear polarizing plate 53B, or may be carried out by the imaging unit imaging the laminate 2 through the second linear polarizing plate 53B. In the form in which the inspector visually recognizes the laminate 2 and observes the laminate 2 without using the imaging unit, a polarizing sunglass (second linear polarizing part) may be used instead of the second linear polarizing plate 53B.

[0076] The inspection device 50 may have an optical system 54 for expanding the inspection light 3 on the optical path of the inspection light 3 between the first linear polarizing plate 53A and the laminate 2. The optical system 54 may be a single lens or may be configured by a combination of a plurality of lenses.

[0077] Next, an example of a method for inspecting the circular polarizing plate 1 using the inspection device 50 having the configuration shown in FIG. 3 will be described. The method for inspecting the circular polarizing plate 1 (or the method for inspecting the retardation plate 10) includes a wavelength determination step of determining the inspection wavelength λd, an irradiation step of irradiating the laminate 2 with the inspection light 3 having the inspection wavelength λd determined in the wavelength determination step, and a determination step of determining the presence or absence of the abnormal portion 132 by observing the laminate 2 irradiated with the inspection light 3 from the second linear polarizing plate 53B side.

[0078] [Wavelength determination step] In the wavelength determination step, in the first interference spectral characteristic for the first thin film which is a model of the normal part 131 in the thin film bonding layer 13 and the second interference spectral characteristic for the second thin film which is a model of the abnormal part 132 in the thin film bonding layer 13, a wavelength within the inspection wavelength range including a predetermined wavelength λa [nm] at which the interference state is inverted is determined as the inspection wavelength λd. The inspection wavelength range is in the range of the predetermined wavelength λa ± 5 [nm].

[0079] For the sake of convenience of explanation, the meaning that the interference state is inverted at a certain wavelength is explained by referring to the wavelength at which the interference state is inverted as the "predetermined wavelength λa" as described above. That the interference state is inverted at the predetermined wavelength λa means that at the predetermined wavelength λa, there exists a maximum peak (the top of the mountain part) of the first interference spectral characteristic and a minimum peak (the bottom of the valley part) of the second interference spectral characteristic, or there exists a minimum peak (the bottom of the valley part) of the first interference spectral characteristic and a maximum peak (the top of the mountain part) of the second interference spectral characteristic.

[0080] The thickness of the first thin film corresponds to the thickness d1 shown in FIG. 2. Therefore, the thickness of the first thin film is a thickness within the range of 3.0 μm or more and 10 μm or less (hereinafter referred to as the "first thickness range"). The thickness of the second thin film is a thickness within the second thickness range in which the difference in thickness from the first thin film is the above difference Δd. Therefore, the thickness of the second thin film is a thickness within the second thickness range in which the difference in thickness Δd from the first thin film is 0.05 μm or more and 0.2 μm or less.

[0081] In the wavelength determination step, the first interference spectral characteristic and the second interference spectral characteristic may be obtained by an experiment using the actually fabricated first thin film and second thin film, or the first interference spectral characteristic and the second interference spectral characteristic may be obtained by optical calculation.

[0082] In the wavelength determination step, for example, the predetermined wavelength λa may be determined using any one of the following Case A and Case B.

[0083] (Case A) Case A is a case where a predetermined wavelength λa is determined in a form in which the thickness d1 of the first thin film is fixed to one value and the absolute value of the difference Δd is fixed to one value.

[0084] An example of a method for determining the predetermined wavelength λa will be described with reference to FIG. 4. FIG. 4 is a drawing for explaining the case of determining the predetermined wavelength λa in Case A. FIG. 4 shows an example of the first interference spectrum characteristic and the second interference spectrum characteristic. The horizontal axis of FIG. 4 indicates the wavelength [nm], and the vertical axis indicates the reflectance [%].

[0085] The solid line shown in FIG. 4 is the calculation result of the first interference spectrum for the first thin film with a thickness d1 of 5 μm. That is, in FIG. 4, the first interference spectrum characteristic is composed of one first interference spectrum. In the calculation of the first interference spectrum, the refractive index of the first thin film was 1.477 at a wavelength of 550 nm.

[0086] The dashed line shown in FIG. 4 is the calculation result of the second interference spectrum of the second thin film with a thickness d2 of 4.9 μm. The alternate long and short dash line shown in FIG. 4 is the calculation result of the second interference spectrum of the second thin film with a thickness d2 of 5.1 μm. In the calculation of the second interference spectrum, the refractive index of the second thin film was the same as that of the first thin film.

[0087] That is, in FIG. 4, the second interference spectrum characteristic is composed of two second interference spectra. Specifically, the second interference spectrum characteristic shown in FIG. 4 is a second interference spectrum group composed of the second interference spectrum of the second thin film when Δd is 0.1 μm with respect to the thickness d1 and the second interference spectrum of the second thin film when Δd is -0.1 μm with respect to the thickness d1.

[0088] In FIG. 4, at wavelength m1, the interference states of the first interference spectral characteristic and the second interference spectral characteristic are inverted. Specifically, at wavelength m1, the first interference spectrum indicated by the solid line has a minimum peak, and the second interference spectra indicated by the dashed line and the alternate long and short dash line respectively have maximum peaks. Therefore, based on the calculation results in FIG. 4, wavelength m1 is the predetermined wavelength λa.

[0089] (Case B) Case B is a case where the predetermined wavelength λa is determined based on at least one of the case where the first interference spectral characteristic is constituted by a first interference spectrum group (a bundle of a plurality of first interference spectra) including a plurality of first interference spectra and the case where the second interference spectral characteristic is constituted by a second interference spectrum group (a bundle of a plurality of second interference spectra) including a plurality of second interference spectra.

[0090] FIG. 5 is a drawing for explaining another example of a method for determining a predetermined wavelength. In FIG. 5, it is a graph plotting the difference between the calculation result of the first interference spectrum of the first thin film with a thickness of d1 and the calculation result of the second interference spectrum of the second thin film with a thickness d2 of (d1 - Δd). The horizontal axis indicates the wavelength [nm], and the vertical axis indicates the difference (interference spectrum difference) between the interference spectrum value [%] of the second interference spectrum and the interference spectrum value [%] of the first interference spectrum. In FIG. 5, Δd is fixed at 0.1 μm, and the results when the thickness d1 is changed to 4.8 μm, 4.9 μm, 5 μm, 5.1 μm, and 5.2 μm are shown with different line types. For the sake of illustration, the difference in line types is distinguished by the difference in thickness d1. For example, in the solid line in FIG. 5, it shows the difference between the second interference spectrum for the second thin film with a thickness d2 of 4.9 μm (5.0 μm - 0.1 μm) and the first interference spectrum for the first thin film with a thickness of 4.8 μm. FIG. 5 corresponds to a drawing for explaining an example of a method for determining a predetermined wavelength in the case where the first interference spectral characteristic is a first interference spectrum group and the second interference spectral characteristic is a second interference spectrum group.

[0091] In FIG. 5, the difference between the second interference spectrum and the first interference spectrum is plotted. Therefore, each maximum peak and each minimum peak in FIG. 5 respectively mean that the interference state between the second interference spectrum and the first interference spectrum is inverted. And at wavelength m2, maximum peaks and minimum peaks occur in the graphs of the differences between all the second interference spectra and the first interference spectra when the thickness d1 is changed to 4.8 μm, 4.9 μm, 5 μm, 5.1 μm, and 5.2 μm. Therefore, at wavelength m2, in the combination of the thicknesses of the first thin film and the second thin film used in the calculation, it means that the interference state between the first interference spectrum characteristic and the second interference spectrum characteristic is inverted.

[0092] After determining the predetermined wavelength λa as described above, a wavelength within the inspection wavelength range is determined as the inspection wavelength λd. For example, within the inspection wavelength range, a wavelength that coincides with the transmission wavelength of the band-pass filter 52B may be adopted as the inspection wavelength λd.

[0093] [Irradiation step] Referring to FIG. 3 again, an example of the inspection method of the circular polarizing plate 1 will be further described. In the irradiation step, the inspection light 3 having the inspection wavelength λd determined in the inspection wavelength determination step is irradiated onto the laminate 2. Specifically, as the band-pass filter 52B included in the light source unit 52, a band-pass filter that selectively passes light of the inspection wavelength λd is set, and light is output from the white light source 52A. As a result, among the light output from the white light source 52A, the light having the inspection wavelength λd selectively passes through the band-pass filter 52B. As a result, the inspection light 3 having the inspection wavelength λd is output from the light source unit 52. The inspection light 3 output from the light source unit 52 is irradiated onto the laminate 2 through the first linear polarizing plate 53A. Therefore, the laminate 2 is irradiated with linearly polarized inspection light. When the inspection apparatus 50 has the optical system 54, the inspection light 3 is enlarged and irradiated onto the laminate 2. In this case, since the observation region is widened, the inspection can be performed efficiently.

[0094] [Judgment step] In the determination step, the laminate 2 irradiated with the inspection light 3 as described in the irradiation step is observed through the second linear polarizing plate 53B. Specifically, the thin film interference generated by the thin film bonding layer 13 is observed. The observation may be performed using the imaging unit or may be visually recognized by the inspector.

[0095] As shown in FIG. 3, the reflected light from the first surface 13a of the thin film bonding layer 13 is referred to as reflected light 3a, and the reflected light from the second surface 13b of the thin film bonding layer 13 is referred to as reflected light 3b. The first surface 13a is the surface in contact with the second liquid crystal retardation layer 12, and the second surface 13b is the surface in contact with the first liquid crystal retardation layer 11. The second surface 13b is located opposite to the first surface 13a. The reflected lights 3a and 3b are the reflected lights contributing to the thin film interference.

[0096] After the reflected lights 3a and 3b enter the laminate 2 from the release film 31, the inspection light 3 that has passed through the second liquid crystal retardation layer 12 is reflected by the first surface 13a and the second surface 13b of the thin film bonding layer 13, passes through the second liquid crystal retardation layer 12 again, and then is output from the release film 31. Since the reflected lights 3a and 3b are the lights that have passed through the second liquid crystal retardation layer 12 in this way, they are different from the linear polarization characteristics of the inspection light 3 output from the first linear polarizing plate 53A and irradiated to the laminate 2. Therefore, even if the second linear polarizing plate 53B is arranged in a cross-Nicol state with respect to the first linear polarizing plate 53A, the reflected lights 3a and 3b pass through the second linear polarizing plate 53B. Thus, even when observing the laminate 2 through the second linear polarizing plate 53B, the thin film interference generated by the thin film bonding layer 13 can be observed.

[0097] When the inspection light 3 is irradiated to the laminate 2, there are also reflected lights other than the above-mentioned reflected lights 3a and 3b. Such reflected lights other than the reflected lights 3a and 3b are background lights in the observation of the thin film interference. In the configuration of the inspection apparatus 50 shown in FIG. 3, by arranging the first linear polarizing plate 53A and the second linear polarizing plate 53B as illustrated, a part of the reflected lights other than the reflected lights 3a and 3b can be blocked by the second linear polarizing plate 53B.

[0098] For example, the reflected light from the surface 31a of the release film 31 (hereinafter referred to as "reflected light 3c") has the same linearly polarized light characteristics as the inspection light 3. Therefore, the reflected light 3c is blocked by the second linear polarizing plate 53B. Here, the reflected light 3c from the surface 31a of the release film 31 has been exemplified and described. However, since the reflected light from the back surface 31b of the release film 31 also does not pass through the second liquid crystal retardation layer 12, it is blocked by the second linear polarizing plate 53B in the same manner as the reflected light 3c. Since the reflected light on the surface 31a and the back surface 31b of the release film 31 is blocked by the second linear polarizing plate 53B in this way, by arranging the first linear polarizing plate 53A and the second linear polarizing plate 53B as exemplified, it is easy to observe the thin film interference by the thin film bonding layer 13.

[0099] In the determination step, when observing the thin film interference by the thin film bonding layer 13, the presence or absence of the abnormal portion 132 is determined according to the difference in the interference state between the normal portion 131 and the abnormal portion 132. For example, when the abnormal portion 132 is observed as a black dot, the presence or absence of the abnormal portion 132 is determined by the presence or absence of the black dot. When the abnormal portion 132 exists, the laminate 2 in which the abnormal portion 132 exists is determined as a defective product.

[0100] In the above inspection method, the incident angle θ of the inspection light 3 on the laminate 2 (see FIG. 3) may be appropriately adjusted. The incident angle θ is the angle between the lamination direction n of the plurality of layers constituting the laminate 2 and the inspection light 3 (specifically, the principal ray of the inspection light 3). The incident angle θ can be adjusted, for example, by changing the inclination state of the laminate 2 with respect to the inspection light 3. The inclination state of the laminate 2 can be adjusted, for example, by using an inspection table 51 provided with a mechanism that rotates around a direction perpendicular to the plane including the principal ray (or optical axis) of the inspection light 3 incident on the laminate 2 and the reflected light.

[0101] In the form of irradiating the laminate 2 with the inspection light 3 through the first linear polarizing plate 53A, the first linear polarizing plate 53A may be arranged such that the polarization axis of the first linear polarizing plate 53A is parallel or orthogonal to the slow axis of the release film 31. For example, the angle between the polarization axis of the first linear polarizing plate 53A and the slow axis of the release film 31 as viewed from the light source unit 52 side is -5° or more and 5° or less, or 85° or more and 95° or less. Thereby, the reflected light from the back surface 31b of the release film 31 is also blocked by the second linear polarizing plate 53B, similarly to the reflected light 3c. As a result, thin film interference is easier to observe, so that the abnormal portion 132 can be detected with higher accuracy.

[0102] The inspection light 3 may be irradiated onto the laminate 2 while (or while changing) the orientation of the laminate 2 with respect to the direction of the polarization axis of the first linear polarizing plate 53A so that the direction of the polarization axis of the first linear polarizing plate 53A is in a direction in which thin film interference is easier to observe with respect to the direction of the slow axis of the release film 31. Thereby, the abnormal portion 132 can be detected with higher accuracy. The adjustment of the arrangement relationship between the polarization axis of the first linear polarizing plate 53A and the slow axis of the release film 31 can be carried out by rotating the laminate 2 around the stacking direction n. In order to carry out such rotation, the inspection table 51 may have a mechanism for rotating the inspection table 51 around the stacking direction n. In the above inspection method, after rotating the laminate 2 around the stacking direction n and specifying a position where thin film interference can be more clearly observed, the presence or absence of the abnormal portion 132 may be determined.

[0103] The above inspection method includes an inspection wavelength determination step, and the laminate 2 is inspected using the inspection wavelength λd determined in the inspection wavelength determination step. At the inspection wavelength λd, since the interference states in the normal portion 131 and the abnormal portion 132 of the thin film bonding layer 13 are inverted, the abnormal portion 132 can be detected by inspecting the laminate 2 using the inspection wavelength λd. Therefore, it is possible to determine the quality of the laminate 2 (specifically, the retardation plate 10). As a result, when the circular polarizing plate 1 included in the laminate 2 is applied to, for example, a liquid crystal display device, image degradation caused by the abnormal portion 132 in the thin film bonding layer 13 can be prevented.

[0104] When determining the inspection wavelength λd (in the case of Case B above) using at least one of the first interference spectrum characteristics composed of a first interference spectrum group (a bundle of a plurality of first interference spectra) including a plurality of first interference spectra and the second interference spectrum characteristics composed of a second interference spectrum group (a bundle of a plurality of second interference spectra) including a plurality of second interference spectra, the presence or absence of the abnormal portion 132 can be detected even if at least one of the thickness of the normal portion 131 and the thickness of the abnormal portion 132 changes. Therefore, in the case of Case B, the versatility of the inspection wavelength λd is improved.

[0105] Particularly, in a form where the incident angle θ of the inspection light 3 to the laminate 2 is changed so as to more easily observe thin film interference, the optical path length of the light passing through the thin film bonding layer 13 changes according to the incident angle θ (in other words, the inclined state of the laminate 2). Even in this case, if the inspection wavelength λd is determined by the method described in Case B, the interference states of the normal portion 131 and the abnormal portion 132 are inverted at the inspection wavelength λd. As a result, the presence or absence of the abnormal portion 132 can be determined.

[0106] When determining a predetermined wavelength λa (in the case of Case A above) in a form where the thickness d1 of the first thin film is fixed to one value and the absolute value of the difference Δd is fixed to one value, the interference state is inverted at the position of the abnormal portion 132 whether the thickness of the abnormal portion 132 is thicker or thinner than the thickness of the normal portion 131. Therefore, the presence or absence of the abnormal portion 132 can be determined.

[0107] In the case of a form where the light source unit 52 has a white light source 52A and a band - pass filter 52B, the inspection wavelength λd can be easily changed by changing the band - pass filter 52B. Therefore, even when inspecting circular polarizing plates 1 (or retardation plates 10) having different thicknesses d1 of the thin film bonding layer 13, inspection can be performed using the same inspection apparatus 50 by changing the band - pass filter 52B. When the white light source 52A is composed of the above three - color LEDs, since a certain intensity or more can be maintained over a relatively wide wavelength range, the interference intensity is easily ensured. As a result, it is easy to determine the presence or absence of the abnormal portion 132.

[0108] Although various embodiments of the present invention have been described above, the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0109] An embodiment in which the circular polarizing plate 1 (or the retardation plate 10) is inspected with the release film 31 provided has been illustrated. However, the circular polarizing plate 1 (or the retardation plate 10) may be inspected without the release film 31. In this case, the inspection light 3 is directly incident on the second liquid crystal retardation layer 12. In the form in which the inspection light 3 is directly incident on the second liquid crystal retardation layer 12 through the first linear polarizing plate 53A, the first linear polarizing plate 53A may be arranged such that the polarization axis of the first linear polarizing plate 53A is deviated from the slow axis of the second liquid crystal retardation layer 12. For example, the angle between the polarization axis of the first linear polarizing plate 53A and the slow axis of the second liquid crystal retardation layer 12 as viewed from the light source unit 52 side is 5° or more and 85° or less. Thereby, the reflected lights 3a and 3b from the thin film bonding layer 13 easily pass through the second linear polarizing plate 53B. As a result, since the thin film interference is easier to observe, the presence or absence of the abnormal portion 132 can be determined more accurately.

[0110] When determining the inspection wavelength, the first interference spectrum characteristic may be composed of one first interference spectrum, and the second interference spectrum characteristic may be composed of one second interference spectrum. That is, the thickness d1 of the thin film bonding layer may be used as the thickness of the first thin film, and the inspection wavelength may be determined with the thickness (d1 + Δd) or (d1 - Δd) as the thickness of the second thin film from the thickness d1.

[0111] The light source unit is not limited to the illustrated configuration as long as it can output inspection light having an inspection wavelength λd.

[0112] The various forms exemplified so far may be appropriately combined without departing from the spirit of the present invention.

Explanation of Reference Numerals

[0113] 1... Circular polarizing plate, 2... Laminate, 3... Inspection light, 10... Retardation plate (retardation laminate), 11... First liquid crystal retardation layer, 11a, 11b, 12a... Surfaces, 12... Second liquid crystal retardation layer, 13... Thin film bonding layer, 20... Linear polarizing plate, 41... Bonding layer, 52... Light source unit, 52A... White light source, 52B... Band pass filter, 53A... First linear polarizing plate (first linear polarization part), 53B... Second linear polarizing plate (second linear polarization part), 131... Normal part, 132... Abnormal part.

Claims

1. An inspection method for a retardation laminate having a first liquid crystal retardation layer, a second liquid crystal retardation layer, and a thin film bonding layer that bonds the first liquid crystal retardation layer and the second liquid crystal retardation layer, comprising: a wavelength determination step of determining an inspection wavelength; an irradiation step of irradiating the laminate with inspection light having the inspection wavelength determined in the wavelength determination step from the second liquid crystal retardation layer side; a determination step of determining the presence or absence of an abnormal portion by observing the laminate irradiated with the inspection light from the second liquid crystal retardation layer side; characterized in that: in the wavelength determination step, within a wavelength range including a predetermined wavelength at which the interference state is inverted between a first interference spectrum characteristic for a first thin film that is a model of a normal portion in the thin film bonding layer and a second interference spectrum characteristic for a second thin film that is a model of an abnormal portion in the thin film bonding layer, a wavelength is determined as the inspection wavelength; the wavelength range is in the range of λa ± 5 [nm] when the predetermined wavelength is λa [nm]; the thickness of the first thin film is within a first thickness range of 3.0 μm or more and 10.0 μm or less; the thickness of the second thin film is within a second thickness range in which the difference in thickness from the first thin film is 0.05 μm or more and 0.2 μm or less. An inspection method for a retardation laminate.

2. The first interference spectrum characteristic is represented by a first interference spectrum group constituted by first interference spectra of a plurality of the first thin films having different thicknesses; the second interference spectrum characteristic is represented by a second interference spectrum group constituted by second interference spectra of a plurality of the second thin films having different thicknesses. The inspection method for a retardation laminate according to Claim 1.

3. The second interference spectrum characteristic is represented by a second interference spectrum group constituted by second interference spectra of a plurality of the second thin films having different thicknesses. The inspection method for a retardation laminate according to Claim 1.

4. The predetermined wavelength is a wavelength at which the first interference spectrum characteristic has a maximum peak and the second interference spectrum characteristic has a minimum peak, or a wavelength at which the first interference spectrum characteristic has a minimum peak and the second interference spectrum characteristic has a maximum peak. The inspection method for a retardation laminate according to Claim 1.

5. In the irradiation step, the inspection light output from a light source unit is passed through a first linearly polarizing unit and irradiated onto the laminate. In the determination step, the laminate is observed through a second linearly polarizing part arranged in a cross Nicol configuration with respect to the first linearly polarizing part. The method for inspecting a retardation laminate according to claim 1.

6. The first linearly polarizing part is arranged such that the polarization axis of the first linearly polarizing part is offset with respect to the slow axis of the second liquid crystal retardation layer. The method for inspecting a retardation laminate according to claim 5.

7. The laminate has a resin film laminated on the second liquid crystal retardation layer in a manner opposite to the first liquid crystal retardation layer. The first linearly polarizing part is arranged such that the polarization axis of the first linearly polarizing part is orthogonal or parallel to the slow axis of the resin film. The method for inspecting a retardation laminate according to claim 5.

8. The light source part a white light source, a band-pass filter that selectively passes light of the inspection wavelength among the light output from the white light source, and has The method for inspecting a retardation laminate according to claim 5.

9. The direction of the alignment axis of the first liquid crystal retardation layer on the surface of the first liquid crystal retardation layer in contact with the bonding layer in the first liquid crystal retardation layer is the same as the direction of the alignment axis of the second liquid crystal retardation layer on the surface of the second liquid crystal retardation layer in contact with the bonding layer in the second liquid crystal retardation layer. The method for inspecting a retardation laminate according to claim 1.

10. A method for inspecting a circular polarizing plate having a laminate having a first liquid crystal retardation layer, a second liquid crystal retardation layer, and a thin film bonding layer bonding the first liquid crystal retardation layer and the second liquid crystal retardation layer, and a linear polarizing plate laminated on the first liquid crystal retardation layer in a manner opposite to the thin film bonding layer, comprising a step of inspecting the laminate included in the circular polarizing plate by the inspection method according to any one of claims 1 to 9. The method for inspecting a circular polarizing plate.

11. A method for manufacturing a circular polarizing plate, having a step of inspecting the circular polarizing plate by the inspection method for a circular polarizing plate according to claim 9.

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