λ / 4 plate defect inspection method

Abstract

To provide a defect inspection method which enables highly sensitive inspection for defects of λ / 4 plates.SOLUTION: A λ / 4 plate defect inspection method of the present invention comprises: arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in the described order; and allowing light to enter from a first polarizer-side surface, and observing appearance of a second polarizer-side surface to detect a defect of the first λ / 4 plate, where an absorption axis of the first polarizer and an absorption axis of the second polarizer are orthogonal to each other, a slow axis of the first λ / 4 plate and a slow axis of the second λ / 4 plate are orthogonal to each other, an angle between the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate is 35-55°, an angle between the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate is 35-55°, and |Rp-Rf| is 5-26 nm, where Rp represents a phase difference in a normal portion of the first λ / 4 plate and Rf represents a phase difference of the second λ / 4 plate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting defects in a λ / 4 plate. [Background technology]

[0002] Retardation films are widely used in image display devices such as liquid crystal displays (LCDs) and organic electroluminescence displays (OLEDs) for the purposes of improving display characteristics, preventing reflection, etc. During the manufacturing process of retardation films, defects due to localized appearance defects can occur, and a method capable of sensitively inspecting such defects is required. In particular, retardation films made of λ / 4 plates made of liquid crystal materials are prone to developing minor defects that cannot be detected by conventional methods, and an inspection method capable of detecting such defects is required. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-15766 Summary of the Invention [Problem to be solved by the invention]

[0004] The present invention has been made to solve the above problems, and an object of the present invention is to provide a defect inspection method capable of inspecting defects in a λ / 4 plate with high sensitivity. [Means for solving the problem]

[0005] The method for inspecting defects in a λ / 4 plate of the present invention includes arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in this order, irradiating light from the surface on the first polarizer side, observing the appearance of the surface on the second polarizer side, and detecting defects in the first λ / 4 plate, wherein the absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal to each other, and the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are orthogonal to each other. the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate are orthogonal to each other, the angle between the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate is 35° to 55°, and the angle between the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate is 35° to 55°, and where Rp is the phase difference of the normal portion of the first λ / 4 plate and Rf is the phase difference of the second λ / 4 plate, |Rp−Rf| is 5 nm to 26 nm. In one embodiment, when the phase difference of the normal portion of the first λ / 4 plate is Rp and the phase difference of the second λ / 4 plate is Rf, Rp−Rf is set to 5 nm to 26 nm. In one embodiment, when the phase difference of the normal portion of the first λ / 4 plate is Rp and the phase difference of the second λ / 4 plate is Rf, Rp−Rf is set to −5 nm to −26 nm. In one embodiment, the first λ / 4 plate is made of a liquid crystal material. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a defect inspection method capable of inspecting defects in an optical laminate including a λ / 4 plate with high sensitivity. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 2] 1 is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 3] 1 is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 4] 1 is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 5] FIG. 1 is a photograph showing an example of a defect (bright spot) that occurs in a λ / 4 plate made of a liquid crystal material. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. Defect inspection method A defect inspection method for a λ / 4 plate of the present invention includes arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in this order, illuminating light from the surface on the first polarizer side, observing the appearance of the surface on the second polarizer side, and detecting defects in the first λ / 4 plate. In the defect inspection method, the first polarizer and the second polarizer are arranged so that the absorption axis of the first polarizer and the absorption axis of the second polarizer are perpendicular to each other. The first λ / 4 plate and the second λ / 4 plate are also arranged so that the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are perpendicular to each other. The first polarizer and the first λ / 4 plate are also arranged so that the angle between the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate is 35° to 55°. The second polarizer and the second λ / 4 plate are arranged so that the angle between the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate is 35° to 55°. Furthermore, in the defect inspection method, when the phase difference of the normal portion of the first λ / 4 plate is Rp and the phase difference of the second λ / 4 plate is Rf, |Rp−Rf| is 5 nm to 26 nm. As long as the effects of the present invention are obtained, other films may be interposed between the first polarizer, the first λ / 4 plate, the second λ / 4 plate, and the second polarizer as long as they are arranged in this order. For example, other retardation films (e.g., positive C plates) may be interposed between the first polarizer and the first λ / 4 plate. For convenience, the illustration shows the appearance of the second polarizer observed from above, but in practice, the inspection system may be configured upside down.

[0009] In this specification, "orthogonal" also includes a state in which the two directions are substantially orthogonal. "Substantially orthogonal" includes a case in which the angle between the two directions is 90°±7°, preferably 90°±5°, and more preferably 90°±3°. Furthermore, when an angle is referred to in this specification, it includes both clockwise and counterclockwise directions relative to the reference direction. Furthermore, "observing the appearance of the surface on the second polarizer side" means observing the presence or absence and amount of light transmitted through the second polarizer. Furthermore, in this specification, "phase difference" refers to in-plane phase difference.

[0010] Fig. 1 is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. Fig. 1 shows a configuration in which a first polarizer 11, a first λ / 4 plate 21, a second λ / 4 plate 22, and a second polarizer 12 are arranged in this order, and the polarization direction of light transmitted through each layer. In the inspection method of the present invention, the first polarizer 11, the first λ / 4 plate 21, the second λ / 4 plate 22, and the second polarizer 12 are arranged so that polarized light a generated by transmission through the first polarizer 11 passes through the first λ / 4 plate 21 and the second λ / 4 plate 22 to become polarized light b having the same polarization direction as polarized light a, and polarized light b reaches the second polarizer 12 as normal light. In the present invention, light that reaches the second polarizer 12 without being given a normal phase difference by the first λ / 4 plate 21 is treated as abnormal light that has passed through a defect in the first λ / 4 plate, and by transmitting this abnormal light through the second polarizer, the defect in the first λ / 4 plate is detected as a bright defect (a point that is brighter than the surrounding normal parts).

[0011] As described above, by setting |Rp-Rf| to 5 nm to 26 nm, defects in the first λ / 4 plate can be detected with high sensitivity. In particular, defects in which the phase difference is higher than that of normal portions and results in streak-like irregularities (hereinafter also referred to as white streaks) have been difficult to detect in the past, but the method of the present invention makes it possible to detect such defects. Furthermore, defects in which the phase difference is lower than that of normal portions and point defects with a very narrow defect range (hereinafter also referred to as bright spots) can also be detected with high sensitivity. When the phase difference of the normal portions of the first λ / 4 plate is Rp and the phase difference of the second λ / 4 plate is Rf, |Rp-Rf| is preferably 8 nm to 23 nm, and more preferably 12 nm to 19 nm. Within this range, the above-mentioned effects are significant.

[0012] In one embodiment, when the phase difference of the normal portion of the first λ / 4 plate is Rp and the phase difference of the second λ / 4 plate is Rf, Rp-Rf is preferably 5 nm to 26 nm, more preferably 8 nm to 23 nm, and even more preferably 12 nm to 19 nm. By setting Rp-Rf within the above range, in other words, by making the phase difference Rf of the second λ / 4 plate appropriately small relative to the phase difference Rp of the first λ / 4 plate to be inspected, an inspection method with significantly excellent sensitivity to white streaks and bright spots can be achieved.

[0013] In one embodiment, when the phase difference of the normal portion of the first λ / 4 plate is Rp and the phase difference of the second λ / 4 plate is Rf, Rp-Rf is preferably -5 nm to -26 nm, more preferably -8 nm to -23 nm, and even more preferably -12 nm to -19 nm. By setting Rp-Rf within the above range, an inspection method with significantly excellent sensitivity to defects with a phase difference lower than that of the normal portion can be achieved.

[0014] Typically, the first polarizer and the second polarizer are applied as a polarizing plate together with a protective film.

[0015] The first λ / 4 plate and / or the second λ / 4 plate (particularly the first λ / 4 plate) may form a laminate together with any appropriate other layers and / or films. Examples of the other layers and films include a pressure-sensitive adhesive layer, an adhesive layer, a substrate, etc. The other layers and films are preferably optically isotropic.

[0016] In one embodiment, the first λ / 4 plate or the second λ / 4 plate (particularly the first λ / 4 plate) is made of a liquid crystal material. In one embodiment, the first λ / 4 plate made of a liquid crystal material is the object of inspection. The present invention is advantageous in that it can sensitively inspect even minor defects in a λ / 4 plate made of a liquid crystal material.

[0017] In one embodiment, the first λ / 4 plate 21 may be made of a liquid crystal material, and the second λ / 4 plate 22 may be a stretched polymer film. This second λ / 4 plate 22 may be an alignment substrate used when forming the first λ / 4 plate 21. As shown schematically in FIG. 2, the first λ / 4 plate 21 and the second λ / 4 plate 22 may form a laminate. The laminate may also be long. The inspection method of this embodiment may be used, for example, to inspect a λ / 4 plate (first λ / 4 plate) provided in a specific product before it is incorporated into the product.

[0018] In one embodiment, the first λ / 4 plate 21 is made of a liquid crystal material. As shown in FIG. 3 , the laminate A to be inspected includes the first λ / 4 plate 21 and an isotropic substrate 30 disposed on the surface of the first λ / 4 plate 21 facing the first polarizer 11. The isotropic substrate has optically isotropic properties. Typically, the isotropic substrate 30 has an alignment layer on the surface facing the first λ / 4 plate 21. The alignment layer may be an alignment film or a layer formed by rubbing. Any appropriate alignment film may be selected depending on the type of liquid crystalline monomer, the material of the substrate, and the like. As the alignment film for homogeneously aligning the liquid crystal molecules in a predetermined direction, a rubbed alignment film of a polyimide film or a polyvinyl alcohol film is preferably used. Alternatively, a photo-alignment film may be used. The laminate A may be in a long shape. The inspection method of this embodiment can be used, for example, to inspect a λ / 4 plate (first λ / 4 plate) provided in a given product before the plate is incorporated into the product.

[0019] In another embodiment, the first λ / 4 plate 21 is made of a liquid crystal material, and as shown schematically in FIG. 4, an optical laminate B including a first polarizer 11 (preferably a polarizing plate including the first polarizer) and the first λ / 4 plate 21 is inspected. The optical laminate B may be in a long shape. Typically, the optical laminate B may be a circular polarizing plate. The inspection method of this embodiment can be used to inspect the optical laminate B (circular polarizing plate) as a product.

[0020] For example, the above inspection method may be performed multiple times on one line to detect multiple types of defects with different phase differences. Specifically, in the embodiments shown in FIGS. 3 and 4, multiple (second polarizer) / (second λ / 4 plate) structures may be arranged for the long optical laminates A and B, and the second λ / 4 plates in the (second polarizer) / (second λ / 4 plate) structures may have different phase differences for each structure. In the embodiment shown in FIG. 3, multiple first polarizers may be arranged corresponding to the (second polarizer) / (second λ / 4 plate) structures, or a long first polarizer may be arranged.

[0021] The light incident on the first polarizer surface can be generated by any suitable light source, in one embodiment a white LED is used as the light source.

[0022] The appearance of the surface on the second polarizer side can be observed by any suitable method. Typically, an image of the inspection area is obtained by any suitable camera, and the image is subjected to image processing such as binarization to detect defects.

[0023] B. First polarizer, second polarizer Any appropriate polarizer can be used as the polarizer. Examples include hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and partially saponified ethylene-vinyl acetate copolymer films, which are uniaxially stretched after adsorbing a dichroic substance such as iodine or a dichroic dye; and oriented polyene films such as dehydrated polyvinyl alcohol films and dehydrochlorinated polyvinyl chloride films. Among these, polarizers obtained by adsorbing a dichroic substance such as iodine into polyvinyl alcohol films and uniaxially stretching them are particularly preferred, as they have a high polarization dichroic ratio. The thickness of the polarizer is preferably 0.5 μm to 80 μm.

[0024] A polarizer obtained by uniaxially stretching a polyvinyl alcohol film after iodine adsorption is typically produced by dyeing the polyvinyl alcohol by immersing it in an aqueous iodine solution and stretching it to 3 to 7 times its original length. The stretching may be performed after dyeing, while dyeing, or after stretching. In addition to stretching and dyeing, the polarizer may also be produced by performing treatments such as swelling, crosslinking, conditioning, washing with water, and drying.

[0025] As described above, in one embodiment, the first polarizer and the second polarizer (sometimes collectively referred to as polarizers) are applied as a polarizing plate together with a protective film.

[0026] Any suitable film can be used as the protective film. Specific examples of materials that can be used as the main component of such films include cellulose-based resins such as triacetyl cellulose (TAC), and transparent resins such as (meth)acrylic, polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, and acetate. Other examples include thermosetting or ultraviolet-curing resins such as acrylic, urethane, acrylic urethane, epoxy, and silicone. Other examples include glassy polymers such as siloxane polymers. Polymer films described in JP 2001-343529 A (WO 01 / 37007) can also be used. Examples of materials that can be used for this film include a resin composition containing a thermoplastic resin having substituted or unsubstituted imide groups in its side chains and a thermoplastic resin having substituted or unsubstituted phenyl and nitrile groups in its side chains, such as a resin composition containing an alternating copolymer of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer.The polymer film can be, for example, an extrusion molded product of the resin composition.

[0027] In one embodiment, a polarizer having a light transmittance of 42% or more is used as the second polarizer. Use of such a second polarizer can improve detection sensitivity. The light transmittance of the second polarizer is more preferably 43% or more, and even more preferably 44% or more. Furthermore, when a polarizing plate including the second polarizer is used, the light transmittance of the polarizing plate is preferably 42% or more, more preferably 43% or more, and even more preferably 44% or more.

[0028] C. First λ / 4 plate, second λ / 4 plate The first λ / 4 plate and the second λ / 4 plate (sometimes collectively referred to as λ / 4 plates) can convert linearly polarized light of a certain wavelength into circularly polarized light (or circularly polarized light into linearly polarized light).

[0029] The λ / 4 plate preferably has an in-plane retardation Re of 95 nm to 180 nm, more preferably 110 nm to 160 nm. The λ / 4 plate preferably has an index ellipsoid such that nx>ny≧nz. In this specification, the in-plane retardation Re refers to the in-plane retardation value at 23°C and a wavelength of 590 nm. Re is calculated by the formula Re=(nx−ny)×d, where nx is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), ny is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and d (nm) is the thickness of the film. In this specification, "ny=nz" not only refers to the case where ny and nz are strictly equal, but also encompasses the case where ny and nz are substantially equal.

[0030] In one embodiment, the in-plane retardation Re at the defect portion of the first λ / 4 plate is preferably 141.5 nm to 151 nm, more preferably 142 nm to 146 nm. A defect having such an in-plane retardation Re may have a higher retardation than the in-plane retardation Re at a normal portion. In another embodiment, the in-plane retardation Re at the defect portion of the first λ / 4 plate is preferably 140.5 nm to 131 nm, more preferably 139.5 nm to 136 nm. A defect having such an in-plane retardation Re may have a lower retardation than the in-plane retardation Re at a normal portion. Furthermore, the difference between the in-plane retardation Re at a normal portion of the first λ / 4 plate and the in-plane retardation Re at the defect portion (the in-plane retardation Re at a normal portion of the first λ / 4 plate minus the in-plane retardation Re at the defect portion) is, for example, −10 nm to 10 nm. According to the present invention, even if the difference between the in-plane phase difference Re at a normal portion and the in-plane phase difference Re at a defective portion is small, defect detection can be preferably performed.

[0031] (λ / 4 plate made of liquid crystal material) As described above, in one embodiment, the first λ / 4 plate is made of a liquid crystal material. Any appropriate liquid crystal monomer can be used as the liquid crystal material. For example, polymerizable mesogen compounds described in JP-A-2002-533742 (WO 00 / 37585), EP 358208 (US 5,211,877), EP 66137 (US 4,388,453), WO 93 / 22397, EP 0261712, DE 19504224, DE 4408171, and GB 2280445 can be used. Specific examples of such polymerizable mesogen compounds include LC242 (product name) by BASF, E7 (product name) by Merck, and LC-Sillicon-CC3767 (product name) by Wacker-Chem.

[0032] A λ / 4 plate made of a liquid crystal material can be obtained, for example, by orienting the liquid crystal material and solidifying or curing it while maintaining the orientation. Specifically, the plate can be formed by applying a liquid crystal composition containing the liquid crystal material to a long alignment substrate to align the liquid crystal material, and then subjecting the aligned liquid crystal material to a polymerization and / or crosslinking treatment to form a cured liquid crystal layer. Since the liquid crystal material can be oriented in accordance with the alignment treatment direction of the substrate, the slow axis of the retardation layer can be formed in a direction substantially identical to the alignment treatment direction of the substrate. A specific example of a method for forming a retardation layer is the method described in JP 2006-178389 A. The thickness of the λ / 4 plate made of a liquid crystal material is preferably 0.5 μm to 1.8 μm, more preferably 1 μm to 1.6 μm.

[0033] In one embodiment, the liquid crystal material may be a thermotropic liquid crystal that exhibits liquid crystallinity upon heating. Thermotropic liquid crystals undergo phase transitions between a crystalline phase, a liquid crystal phase, and an isotropic phase upon temperature change.

[0034] (λ / 4 plate made of stretched film) A λ / 4 plate made of a stretched film can be obtained, for example, by stretching a polymer film in a predetermined direction.

[0035] Any appropriate resin can be used as the resin for forming the polymer film. Specific examples include resins that form positive birefringence films, such as cycloolefin resins such as polynorbornene, polycarbonate resins, cellulose resins, polyvinyl alcohol resins, and polysulfone resins. Of these, norbornene resins and polycarbonate resins are preferred.

[0036] The polynorbornene refers to a (co)polymer obtained by using a norbornene-based monomer having a norbornene ring as a part or all of the starting material (monomer). Examples of the norbornene-based monomer include norbornene and its alkyl and / or alkylidene substituted derivatives such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and polar group substituted derivatives thereof such as halogen; dicyclopentadiene, 2,3-dihydrodicyclopentadiene; di ... Octahydronaphthalene, its alkyl and / or alkylidene substituted derivatives, and polar group substituted derivatives such as halogen, for example, 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7 ,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl-1,4:5,8-dimethano 1H-cyclopentadiene trimers and tetramers thereof, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene and 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene.

[0037] Various polynorbornene products are commercially available, including, for example, "Zeonex" and "Zeonor" manufactured by Zeon Corporation, "Arton" manufactured by JSR Corporation, "Topas" manufactured by TICONA, and "APEL" manufactured by Mitsui Chemicals, Inc.

[0038] As the polycarbonate resin, an aromatic polycarbonate is preferably used. Aromatic polycarbonates can typically be obtained by reacting a carbonate precursor with an aromatic dihydric phenol compound. Specific examples of carbonate precursors include phosgene, bischloroformates of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, and dinaphthyl carbonate. Among these, phosgene and diphenyl carbonate are preferred. Specific examples of aromatic dihydric phenol compounds include 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)butane, 2,2-bis(4-hydroxy-3,5-dipropylphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. These may be used alone or in combination. 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are preferred. In particular, it is preferable to use 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane together.

[0039] Examples of stretching methods include transverse uniaxial stretching, fixed-end biaxial stretching, and sequential biaxial stretching. A specific example of fixed-end biaxial stretching is a method in which a polymer film is stretched in the short direction (transverse direction) while running in the longitudinal direction. This method may appear to be transverse uniaxial stretching. Oblique stretching can also be employed. By employing oblique stretching, a long stretched film having an orientation axis (slow axis) at a predetermined angle relative to the width direction can be obtained. Methods for producing a λ / 4 plate by oblique stretching are described, for example, in JP 2013-54338 A, JP 2014-194482 A, JP 2014-238524 A, and JP 2014-194484 A. The disclosures of these publications are incorporated herein by reference.

[0040] The thickness of the stretched film is typically 5 μm to 80 μm, preferably 15 μm to 60 μm, and more preferably 25 μm to 45 μm.

[0041] In one embodiment, a λ / 4 plate made of a stretched film (preferably a λ / 4 plate obtained by oblique stretching) can be used as an alignment substrate when producing a λ / 4 plate made of the above liquid crystal material. [Example]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Measurement and evaluation methods in the examples are as follows.

[0043] [Example 1] A photopolymerizable liquid crystal compound exhibiting a nematic liquid crystal phase (BASF's "Paliocolor LC242") was dissolved in cyclopentanone to prepare a solution with a solids concentration of 30% by weight. A surfactant (BYK-Chemie's "BYK-360") and a photopolymerization initiator (IGM Resins' "Omnirad907") were added to this solution to prepare a liquid crystal composition solution. The amounts of the leveling agent and polymerization initiator added were 0.01 parts by weight and 3 parts by weight, respectively, per 100 parts by weight of the photopolymerizable liquid crystal compound. An obliquely stretched norbornene-based film (Zeon Corporation's "Zeonorfilm (ZD12)", thickness: 23 μm, in-plane retardation: 140 nm) was prepared. The liquid crystal composition was applied to the obliquely stretched norbornene film using a bar coater so that the thickness after drying would be 1.69 μm, and the film was heated at 100° C. for 3 minutes to align the liquid crystals. After cooling to room temperature, the film was irradiated with an integrated light dose of 400 mJ / cm 2 in a nitrogen atmosphere. 2 The film was photocured by irradiating it with ultraviolet light, to obtain a homogeneously aligned liquid crystal layer (first λ / 4 plate, in-plane retardation Rp: 141 nm) on the obliquely stretched norbornene-based film. The liquid crystal composition was applied to the obliquely stretched norbornene film using a bar coater so that the thickness after drying would be 2 μm, and the film was heated at 100° C. for 3 minutes to align the liquid crystals. After cooling to room temperature, the film was irradiated with an integrated light dose of 400 mJ / cm under a nitrogen atmosphere. 2 The film was photocured by irradiating it with ultraviolet light, to obtain a homogeneously aligned liquid crystal layer (second λ / 4 plate, in-plane retardation Rf: 167 nm, thickness: 2 μm) on the obliquely stretched norbornene-based film. A first polarizing plate including a first polarizer (single transmittance: 45%), the first λ / 4 plate, the second λ / 4 plate, and a second polarizing plate including a second polarizer (single transmittance: 45%) were laminated. In this case, the axial directions of the layers were such that the absorption axis of the first polarizer and the absorption axis of the second polarizer were perpendicular, the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate were parallel, the angle between the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate was 45°, and the angle between the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate was 45°. A light source and an imaging device were placed on both sides of the above configuration, and a defect inspection was performed by transmission inspection on the first λ / 4 plate, targeting a streak-like defect that was thinner and had a smaller phase difference than the normal part (a defect with a phase difference approximately 1.5 nm smaller than the phase difference of the normal part). As a result, the defect was successfully detected.

[0044] [Example 2] Except for the fact that the thickness of the second λ / 4 plate was set to 1.92 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 160 nm), and a second polarizing plate including a second polarizer were arranged in this order in the same manner as in Example 1, and a defect inspection was performed in the same manner as in Example 1. As a result, streak-like defects that were thinner and had a smaller phase difference than normal portions (defects having a phase difference that was approximately 1.5 nm smaller than the phase difference of normal portions) were detected more clearly than in Example 1.

[0045] [Example 3] Except for the fact that the thickness of the second λ / 4 plate was set to 1.84 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 153 nm), and a second polarizing plate including a second polarizer were arranged in this order in the same manner as in Example 1, and a defect inspection was performed in the same manner as in Example 1. As a result, streak-like defects that were thinner and had a smaller phase difference than normal portions (defects having a phase difference that was approximately 1.5 nm smaller than the phase difference of normal portions) were detected more clearly than in Example 1.

[0046] [Example 4] Except for the fact that the thickness of the second λ / 4 plate was set to 1.75 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 146 nm), and a second polarizing plate including a second polarizer were arranged in this order in the same manner as in Example 1, and a defect inspection was performed in the same manner as in Example 1. As a result, a streak-like defect that was thinner and had a smaller phase difference than a normal portion (a defect having a phase difference that was approximately 1.5 nm smaller than the phase difference of the normal portion) could be detected.

[0047] [Example 5] In the same manner as in Example 1, except that the thickness of the second λ / 4 plate was set to 1.63 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 136 nm), and a second polarizing plate including a second polarizer were laminated in this order. A light source and an imaging device were placed on both sides of the above configuration, and a defect inspection was performed by transmission inspection to detect a streak-like defect in the first λ / 4 plate that was thicker than the normal part and had a large phase difference (a defect with a phase difference approximately 1.5 nm larger than the phase difference of the normal part).As a result, the defect was successfully detected.

[0048] [Example 6] Except for the fact that the thickness of the second λ / 4 plate was set to 1.55 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 129 nm), and a second polarizing plate including a second polarizer were arranged in this order in the same manner as in Example 1, and a defect inspection was carried out in the same manner as in Example 5. As a result, streak-like defects that were thicker and had a larger phase difference than normal portions (defects having a phase difference that was approximately 1.5 nm larger than the phase difference of normal portions) were detected more clearly than in Example 5.

[0049] [Example 7] Except for the fact that the thickness of the second λ / 4 plate was set to 1.48 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 123 nm), and a second polarizing plate including a second polarizer were arranged in this order in the same manner as in Example 1, and a defect inspection was carried out in the same manner as in Example 5. As a result, streak-like defects that were thicker and had a larger phase difference than normal portions (defects having a phase difference that was approximately 1.5 nm larger than the phase difference of normal portions) were detected more clearly than in Example 5. Furthermore, when the number of bright spots detected within a 1.3m x 1m area was checked, 4.7 defects were detected. Figure 5 shows a typical example of the appearance of a bright spot.

[0050] [Example 8] Except for the fact that the thickness of the second λ / 4 plate was set to 1.38 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 115 nm), and a second polarizing plate including a second polarizer were arranged in this order in the same manner as in Example 1, and a defect inspection was performed in the same manner as in Example 5. As a result, a streak-like defect that was thicker and had a larger phase difference than the normal portion (a defect having a phase difference that was approximately 1.5 nm larger than the phase difference of the normal portion) could be detected.

[0051] [Comparative Example 1] In the same manner as in Example 1, except that the thickness of the second λ / 4 plate was set to 1.69 μm, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 141 nm), and a second polarizing plate including a second polarizer were laminated in this order. For the above configuration, a defect inspection similar to that in Example 1 was performed. As a result, defects that could be detected in Example 1 could not be detected. Furthermore, a defect inspection similar to that in Example 5 was performed. As a result, defects that could be detected in Example 5 could not be detected. Furthermore, a first λ / 4 plate similar to that used in Example 7 (i.e., the same λ / 4 plate as that used in Example 7 in which 4.7 bright spots were detected) was used as the inspection object, and the number of bright spots detected within a range of 1.3 m x 1 m was confirmed in the same manner as in Example 7, and 2.6 defects were detected.

[0052] The results of the Examples and Comparative Examples are summarized in the following Tables: As is clear from Tables 1 to 3, according to the present invention, by appropriately setting Rp-Rf, various defects can be detected with high sensitivity.

[0053] [Table 1]

[0054] [Table 2]

[0055] [Table 3] [Explanation of symbols]

[0056] 11 First polarizer 12 Second polarizer 21 First λ / 4 plate 22 Second λ / 4 plate 30 Isotropic substrate

Claims

1. The method includes arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in this order, allowing light to be incident on the surface on the first polarizer side, and observing the appearance of the surface on the second polarizer side, thereby detecting defects in the first λ / 4 plate; the absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal to each other, the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are orthogonal to each other, the angle formed by the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate is 35° to 55°, and the angle formed by the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate is 35° to 55°; where Rp is a phase difference of a normal portion of the first λ / 4 plate and Rf is a phase difference of the second λ / 4 plate, and |Rp−Rf| is set to 5 nm to 26 nm; the first λ / 4 plate and the second λ / 4 plate are each made of a common material; A method for inspecting defects in λ / 4 plates.

2. 2. The method for inspecting defects in a quarter-wave plate according to claim 1, wherein Rp is a phase difference of a normal portion of the first quarter-wave plate, and Rf is a phase difference of the second quarter-wave plate, and Rp-Rf is 5 nm to 26 nm.

3. 2. The method for inspecting defects in a quarter-wave plate according to claim 1, wherein Rp is a phase difference of a normal portion of the first quarter-wave plate, and Rf is a phase difference of the second quarter-wave plate, and Rp-Rf is set to be −5 nm to −26 nm.

4. 4. The method for inspecting defects in a λ / 4 plate according to claim 1, wherein the first λ / 4 plate is made of a liquid crystal material.

Images