Defect inspection method for λ / 4 boards

Abstract

To provide a defect inspection method that can sensitively inspect defects in λ / 4 plates. [Solution] The present invention provides a method for inspecting defects in a λ / 4 plate, comprising arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in this order, and detecting defects in the first λ / 4 plate by irradiating light from the surface on the first polarizer side and observing the appearance of the surface on the second polarizer side, wherein the absorption axis of the first polarizer and the absorption axis of the second polarizer are parallel, and the slow axis of the first λ / 4 plate and the second polarizer are parallel. The method includes setting the slow axis of the second λ / 4 plate parallel to the absorption axis of the first polarizer, setting the angle between the absorption axis of the first λ / 4 plate and the slow axis of the first λ / 4 plate to 35° to 55°, and setting the angle between the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate to 35° to 55°, and adjusting the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate according to the phase difference of the defective portion of the first λ / 4 plate.

Description

Technical Field

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

Background Art

[0002] In image display devices such as liquid crystal display devices (LCDs) and organic electroluminescence display devices (OLEDs), a retardation film is frequently used for the purpose of improving display characteristics, anti-reflection, etc. In the manufacturing process of the retardation film, defects may occur due to local appearance defects, and a method capable of detecting such defects with high sensitivity is required. In particular, a λ / 4 plate composed of a liquid crystal material is likely to have extremely 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

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0005] The present invention provides a method for inspecting defects in a λ / 4 plate, comprising: 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 side of the first polarizer, observing the appearance of the side of the second polarizer, 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 parallel, and the slow axis of the first λ / 4 plate and the second λ The method includes setting the lagging axis of the λ / 4 plate parallel to the absorption axis of the first polarizer, setting the angle between the absorption axis of the first λ / 4 plate and the lagging axis of the first λ / 4 plate to 35° to 55°, and setting the angle between the absorption axis of the second polarizer and the lagging axis of the second λ / 4 plate to 35° to 55°, and adjusting the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate according to the phase difference of the defective portion of the first λ / 4 plate. In one embodiment, the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate is 300 nm to 321 nm. In one embodiment, the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate is 269 nm to 290 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, a defect inspection method can be provided that can sensitively inspect defects in an optical laminate including a λ / 4 plate. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 2] This is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 3] This is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 4] This is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. [Figure 5]This is a photographic diagram showing an example of defects (bright spots) that occur in a λ / 4 plate made of liquid crystal material. [Modes for carrying out the invention]

[0008] A. Methods for inspecting defects The present invention provides a method for inspecting defects in a λ / 4 plate, which includes arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in that order, and detecting defects in the first λ / 4 plate by illuminating the surface on the first polarizer side with light and observing the appearance of the surface on the second polarizer side. In the above defect inspection method, the first polarizer and the second polarizer are arranged such that the absorption axis of the first polarizer and the absorption axis of the second polarizer are parallel. The first λ / 4 plate and the second λ / 4 plate are arranged such that the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are parallel. The first polarizer and the first λ / 4 plate are arranged such that the angle between the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate is between 35° and 55°. Furthermore, the second polarizer and the second λ / 4 plate are arranged such that the angle between the absorption axis of the second polarizer and the slow axis of the second λ / 4 plate is between 35° and 55°. In addition, the above defect inspection method includes adjusting the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate according to the phase difference of the defective portion of the first λ / 4 plate. As long as the effects of the present invention are obtained, the first polarizer, the first λ / 4 plate, the second λ / 4 plate, and the second polarizer are arranged in this order, but other films may be interposed between them. For example, another phase difference film (e.g., a positive C plate) may be interposed between the first polarizer and the first λ / 4 plate. Also, for convenience, the diagram shows the appearance of the second polarizer being observed from above, but in reality, the inspection system may be configured with the top and bottom reversed.

[0009] In this specification, “parallel” includes substantially parallel states. “Substantially parallel” includes the case where the angle between the two directions is 0°±7°, preferably 0°±5°, and more preferably 0°±3°. “Orthogonal” also includes substantially orthogonal states. “Substantially orthogonal” includes the case where the angle between the two directions is 90°±7°, preferably 90°±5°, and more preferably 90°±3°. Furthermore, when angles are referred to in this specification, both clockwise and counterclockwise directions with respect to the reference direction are included. Furthermore, “observing the appearance of the second polarizer side surface” means observing the presence and amount of light transmitted through the second polarizer. Furthermore, in this specification, phase difference means in-plane phase difference.

[0010] Figure 1 is a schematic perspective view illustrating an inspection method according to one embodiment of the present invention. In Figure 1, the configuration in which the first polarizer 11, the first λ / 4 plate 21, the second λ / 4 plate 22, and the second polarizer 12 are arranged in this order is shown, as well as the polarization direction of the light transmitted through each layer. In the inspection method of the present invention, a phase difference is given to the polarization a generated by transmitting through the first polarizer 11 by the two λ / 4 plates (first λ / 4 plate 21, second λ / 4 plate 22). In the state shown in Figure 1, the first polarizer 11, the first λ / 4 plate 21, the second λ / 4 plate 22, and the second polarizer 12 are arranged so as to give a phase difference to the polarization a and rotate the polarization direction by approximately 90°, and so as to allow the polarization b thus generated to reach the second polarizer 12 as normal light. In this invention, light that reaches the second polarizer 12 without a normal phase difference being applied in the first λ / 4 plate 21 is considered abnormal light that has passed through a defect in the first λ / 4 plate, and by passing this abnormal light through the second polarizer, the defect in the first λ / 4 plate is detected as a bright defect (a point with higher brightness than the surrounding normal area).

[0011] In this invention, by adjusting the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate according to the phase difference of the defective portion of the first λ / 4 plate, it becomes possible to detect defects that have a small difference from the phase difference of the normal portion and are difficult to detect with conventional techniques.

[0012] In one embodiment, the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate is preferably 300 nm to 321 nm, and more preferably 307 nm to 314 nm. Within this range, an inspection method can be provided that can sensitively detect defects in the first λ / 4 plate. In particular, defects that have a higher phase difference than the normal portion and appear as streaky unevenness (hereinafter also referred to as white streaks) have conventionally been difficult to detect, but the method of the present invention makes it possible to detect such defects as well. Furthermore, point defects (hereinafter also referred to as bright spots) with a very narrow defect range can also be detected sensitively.

[0013] In another embodiment, the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate is preferably 269 nm to 290 nm, and more preferably 276 nm to 283 nm. By setting it within this range, an inspection method can be made that is remarkably sensitive to defects with a phase difference lower than that of the normal portion.

[0014] Typically, the first and second polarizers are used as polarizers together with a protective film.

[0015] The first λ / 4 plate and / or the second λ / 4 plate (in particular the first λ / 4 plate) may constitute a laminate together with any other suitable layers and / or films. Examples of other layers and other films include adhesive layers, bonding layers, substrates, etc. The other layers and other 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 liquid crystal material is the object of inspection. The present invention is advantageous in that even minor defects in the λ / 4 plate made of liquid crystal material can be inspected with high sensitivity.

[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 film of a polymer film. This second λ / 4 plate 22 may be an alignment substrate when forming the first λ / 4 plate 21. Also, as schematically shown in FIG. 2, the first λ / 4 plate 21 and the second λ / 4 plate 22 may form a laminate. Further, the laminate may be in a long shape. The inspection method of the present embodiment can be adopted, for example, for the inspection of the λ / 4 plate (the first λ / 4 plate) provided in a predetermined product before being incorporated into the product.

[0018] In one embodiment, the first λ / 4 plate 21 is made of a liquid crystal material. As schematically shown in FIG. 3, a laminate A including the first λ / 4 plate 21 and an isotropic substrate 30 disposed on the surface of the first λ / 4 plate 21 on the side of the first polarizer 11 is the inspection object. The isotropic substrate has optically isotropic properties. Typically, the isotropic substrate 30 has an alignment layer on the surface on the side of the first λ / 4 plate 21. The alignment layer may be an alignment film or a layer formed by a rubbing treatment. The alignment film may be any suitable one depending on the type of liquid crystal monomer, the material of the substrate, etc. As an alignment film for homogeneously aligning liquid crystal molecules in a predetermined direction, a rubbed alignment film of a polyimide-based film and a polyvinyl alcohol-based film is preferably used. Also, a photo-alignment film may be used. The laminate A may be in a long shape. The inspection method of the present embodiment can be adopted, for example, for the inspection of the λ / 4 plate (the first λ / 4 plate) provided in a predetermined product before being incorporated into the product.

[0019] In another embodiment, the first λ / 4 plate 21 is made of a liquid crystal material. As schematically shown in FIG. 4, an optical laminate B including the first polarizer 11 (preferably, a polarizing plate including the first polarizer) and the first λ / 4 plate 21 is the inspection object. 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 the present embodiment can be adopted for the inspection of the optical laminate B (circular polarizing plate) as a product.

[0020] For example, the above inspection method may be performed multiple times on a single line for purposes such as detecting multiple types of defects due to differences in phase difference. Specifically, in the embodiments shown in Figures 3 and 4, multiple structures consisting of (second polarizer) / (second λ / 4 plate) may be arranged on elongated optical laminates A and B, in which case the second λ / 4 plate in the (second polarizer) / (second λ / 4 plate) structure may have different phase differences for each structure. In the embodiment shown in Figure 3, multiple first polarizers may also be arranged corresponding to the (second polarizer) / (second λ / 4 plate) structures, or an elongated first polarizer may be arranged.

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

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

[0023] B. First polarizer, second polarizer Any suitable polarizer can be used as the polarizer described above. For example, hydrophilic polymer films such as polyvinyl alcohol-based films, partially formalized polyvinyl alcohol-based films, and partially saponified ethylene-vinyl acetate copolymer films, on which dichroic substances such as iodine or dichroic dyes are adsorbed and then uniaxially stretched are used, as well as polyene-based oriented films such as dehydrated polyvinyl alcohol or dehydrochlorinated polyvinyl chloride. Among these, polarizers made by adsorbing dichroic substances such as iodine onto a polyvinyl alcohol-based film and then uniaxially stretching them are particularly preferred because they have a high dichroic polarization ratio. The thickness of the polarizer is preferably 0.5 μm to 80 μm.

[0024] Polarizers made by uniaxially stretching a polyvinyl alcohol-based film with iodine adsorbed onto it are typically produced by dyeing the polyvinyl alcohol by immersing it in an aqueous iodine solution and then stretching it to 3 to 7 times its original length. Stretching may be performed after dyeing, while dyeing, or after stretching. In addition to stretching and dyeing, other processes such as swelling, crosslinking, conditioning, washing, and drying may also be performed during production.

[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 make up the main component of such films include cellulosic resins such as triacetylcellulose (TAC), and transparent resins such as (meth)acrylic, polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, and acetate. Thermosetting resins or UV-curing resins such as acrylic, urethane, acrylic-urethane, epoxy, and silicone can also be used. In addition, glassy polymers such as siloxane polymers can also be used. Furthermore, polymer films described in Japanese Patent Application Publication No. 2001-343529 (WO01 / 37007) can also be used. As materials for this film, for example, 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 groups and nitrile groups in its side chains can be used. Examples include a resin composition having an alternating copolymer of isobutene and N-methylmaleimide, and an acrylonitrile-styrene copolymer. The polymer film may be, for example, an extruded product of the above resin composition.

[0027] In one embodiment, a polarizer with a light transmittance of 42% or more is used as the second polarizer. Using 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 containing 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 the λ / 4 plate) can convert linearly polarized light of a certain wavelength to circularly polarized light (or circularly polarized light to linearly polarized light).

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

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

[0031] (λ / 4 plate made of liquid crystal material) As described above, in one embodiment, the first λ / 4 plate is composed of a liquid crystal material. Any suitable liquid crystal monomer can be used as the liquid crystal material. For example, polymerizable mesogenic compounds described in JP 2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, and GB2280445 can be used. Specific examples of such polymerizable mesogenic compounds include, for example, BASF's trade name LC242, Merck's trade name E7, and Wacker-Chem's trade name LC-Silicon-CC3767.

[0032] A λ / 4 plate made of liquid crystal material can be obtained, for example, by oriented the liquid crystal material and then solidifying or curing it while fixing the orientation. Specifically, it can be formed by applying a liquid crystalline composition containing liquid crystal material to a long oriented substrate to orient the liquid crystal material, and then applying polymerization and / or crosslinking treatment to the oriented liquid crystal material to form a liquid crystal cured layer. Here, since the liquid crystal material can be oriented according to the orientation treatment direction of the substrate, the slow phase axis of the phase difference layer can be made to appear in substantially the same direction as the orientation treatment direction of the substrate. A specific example of a method for forming the phase difference layer is the method described in Japanese Patent Application Publication No. 2006-178389. The thickness of the λ / 4 plate made of liquid crystal material is preferably 0.5 μm to 1.8 μm, and more preferably 1 μm to 1.6 μm.

[0033] In one embodiment, a thermotropic liquid crystal, which exhibits liquid crystalline properties upon heating, may be used as the liquid crystal material. Thermotropic liquid crystals undergo phase transitions between a crystalline phase, a liquid crystal phase, and an isotropic phase in response to temperature changes.

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

[0035] Any suitable resin can be used to form the polymer film described above. Specific examples include cycloolefin resins such as polynorbornene, polycarbonate resins, cellulose resins, polyvinyl alcohol resins, and polysulfone resins, which constitute positive birefringence films. Among these, norbornene resins and polycarbonate resins are preferred.

[0036] The above polynorbornene refers to a (co)polymer obtained using a norbornene-based monomer having a norbornene ring in 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, etc., and their halogen- and other polar group substituted derivatives; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc. Tanooctahydronaphthalene, its alkyl and / or alkylidene substituted derivatives, and polar group substituted derivatives such as halogens, e.g., 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 Examples include tano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, and tripers and tetramers of cyclopentadiene, 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 products containing the above-mentioned polynorbornene are commercially available. Specific examples include the product names "Zeonex" and "Zeonor" from Nippon Zeon Corporation, "Arton" from JSR Corporation, "Topas" from TICONA Corporation, and "APEL" from Mitsui Chemicals Corporation.

[0038] Preferably, aromatic polycarbonates are used as the polycarbonate resins mentioned above. Aromatic polycarbonates can typically be obtained by the reaction of a carbonate precursor with an aromatic divalent phenol compound. Specific examples of carbonate precursors include phosgene, divalent phenols such as bischloroformates, 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 divalent 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 individually or in combination of two or more. Preferably, 2,2-bis(4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane are used. 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 being moved in the longitudinal direction. This method can 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 with respect to the width direction can be obtained. Methods for manufacturing λ / 4 plates by oblique stretching are described, for example, in Japanese Patent Publication No. 2013-54338, Japanese Patent Publication No. 2014-194482, Japanese Patent Publication No. 2014-238524, and Japanese Patent Publication No. 2014-194484. The descriptions in these publications are incorporated herein by reference.

[0040] The thickness of the stretched film described above 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 orientation substrate when creating a λ / 4 plate made of the liquid crystal material. [Examples]

[0042] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The 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 solid content of 30% by weight. A surfactant (Bic Chemie's "BYK-360") and a photopolymerization initiator (IGM Resins' "Omnirad907") were added to this solution to prepare a liquid crystalline 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. A diagonally oriented norbornene-based film (Zeonor Film (ZD12) manufactured by Nippon Zeon, thickness: 23 μm, in-plane phase difference: 140 nm) was prepared. The above-mentioned liquid crystalline composition was applied to the obliquely stretched norbornene-based film using a bar coater to a dry thickness of 1.69 μm, and the liquid crystals were oriented by heating at 100°C for 3 minutes. After cooling to room temperature, the film was subjected to a nitrogen atmosphere with an integrated light intensity of 400 mJ / cm². 2 By irradiating with ultraviolet light, photocuring was performed to obtain a homogeneous oriented liquid crystal layer (first λ / 4 plate, in-plane phase difference Rp: 141 nm) on an obliquely stretched norbornene-based film. Furthermore, the above-mentioned liquid crystalline composition was applied to the obliquely stretched norbornene-based film using a bar coater to a dry thickness of 1.54 μm, and the liquid crystals were oriented by heating at 100°C for 3 minutes. After cooling to room temperature, the film was subjected to a nitrogen atmosphere with an integrated light intensity of 400 mJ / cm². 2 By irradiating with ultraviolet light, photocuring was performed to obtain a homogeneous oriented liquid crystal layer (second λ / 4 plate, in-plane phase difference Rf: 128 nm, thickness: 1.54 μm) on an obliquely stretched norbornene-based film. A first polarizing plate containing a first polarizer (single-unit transmittance: 45%), the first λ / 4 plate, the second λ / 4 plate, and a second polarizing plate containing a second polarizer (single-unit transmittance: 45%) were laminated together. In this configuration, the axial directions of each layer were such that the absorption axis of the first polarizer was parallel to the absorption axis of the second polarizer, the slow axis of the first λ / 4 plate was parallel to the slow axis of the second λ / 4 plate, 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°. Light sources and imaging devices were placed on both sides of the above configuration. In the first λ / 4 plate, a streak-like defect (a defect with a phase difference approximately 1.5 nm smaller than that of the normal portion) was targeted for detection, and a defect inspection was performed by transmission inspection. As a result, the defect was successfully detected.

[0044] [Example 2] Except for setting the thickness of the second λ / 4 plate to 1.62 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 135 nm), and the second polarizer plate containing the second polarizer were arranged in the same order as in Example 1, and a defect inspection was performed in the same manner as in Example 1. As a result, streak-like defects with a thinner thickness and smaller phase difference than the normal portion (defects with a phase difference approximately 1.5 nm smaller than the phase difference of the normal portion) were detected more clearly than in Example 1.

[0045] [Example 3] Except for setting the thickness of the second λ / 4 plate to 1.70 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 142 nm), and the second polarizer plate containing the second polarizer were arranged in the same order as in Example 1, and a defect inspection was performed in the same manner as in Example 1. As a result, streak-like defects with a thinner thickness and smaller phase difference than the normal portion (defects with a phase difference approximately 1.5 nm smaller than the phase difference of the normal portion) were detected more clearly than in Example 1.

[0046] [Example 4] Except for setting the thickness of the second λ / 4 plate to 1.79 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 149 nm), and the second polarizer plate containing the second polarizer were arranged in the same order as in Example 1, and a defect inspection was performed in the same manner as in Example 1. As a result, streak-like defects with a thinner thickness and smaller phase difference than the normal portion (defects with a phase difference approximately 1.5 nm smaller than the phase difference of the normal portion) were detected.

[0047] [Example 5] Except for setting the thickness of the second λ / 4 plate to 1.91 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 159 nm), and the second polarizer plate containing the second polarizer were stacked in the same order as in Example 1. Light sources and imaging devices were placed on both sides of the above configuration. In the first λ / 4 plate, a streak-like defect with a greater thickness and larger phase difference than the normal portion (a defect with a phase difference approximately 1.5 nm larger than that of the normal portion) was targeted for detection, and a defect inspection was performed by transmission inspection. As a result, the defect was successfully detected.

[0048] [Example 6] Except for setting the thickness of the second λ / 4 plate to 1.99 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 166 nm), and the second polarizer plate containing the second polarizer were arranged in the same order as in Example 1, and a defect inspection similar to that in Example 5 was performed. As a result, streak-like defects with a greater thickness and larger phase difference than the normal portion (defects with a phase difference approximately 1.5 nm larger than the phase difference of the normal portion) were detected more clearly than in Example 5.

[0049] [Example 7] Except for setting the thickness of the second λ / 4 plate to 2.08 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 173 nm), and the second polarizer plate containing the second polarizer were arranged in the same order as in Example 1, and a defect inspection similar to that in Example 5 was performed. As a result, streak-like defects with a greater thickness and larger phase difference than the normal portion (defects with a phase difference approximately 1.5 nm larger than the phase difference of the normal portion) were detected more clearly than in Example 5. Furthermore, when examining the number of bright spots detected within a 1.3m x 1m area, 4.6 defects were found. A representative example of the appearance of the bright spots is shown in Figure 5.

[0050] [Example 8] Except for setting the thickness of the second λ / 4 plate to 2.16 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 180 nm), and the second polarizer plate containing the second polarizer were arranged in the same order as in Example 1, and a defect inspection similar to that in Example 5 was performed. As a result, streak-like defects with a greater thickness and larger phase difference than the normal portion (defects with a phase difference approximately 1.5 nm larger than the phase difference of the normal portion) were detected.

[0051] [Comparative Example 1] Except for setting the thickness of the second λ / 4 plate to 1.85 μm, the first polarizer plate containing the first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate (phase difference Rf: 154 nm), and the second polarizer plate containing the second polarizer were stacked in the same order as in Example 1. A defect inspection similar to that in Example 1 was performed on the above configuration. As a result, the defects that were detectable in Example 1 could not be detected. Furthermore, a defect inspection similar to that in Example 5 was performed. As a result, the defects that were detectable in Example 5 could not be detected. Furthermore, using the same first λ / 4 plate as in Example 7 (i.e., the same λ / 4 plate from which 4.6 bright spots were detected in Example 7) as the subject of inspection, the number of bright spots detected within a 1.3m × 1m area was checked, similar to Example 7, and 2.4 defects were detected.

[0052] The results of the examples and comparative examples are summarized in the table below. As is clear from Tables 1 and 2, according to the present invention, various defects can be detected with high sensitivity by appropriately setting Rp+Rf.

[0053] [Table 1]

[0054] [Table 2] [Explanation of symbols]

[0055] 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, and illuminating the surface on the side of the first polarizer, observing the appearance of the surface on the side of the second polarizer, and detecting defects in the first λ / 4 plate. The absorption axis of the first polarizer and the absorption axis of the second polarizer are made parallel, the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are made parallel, the angle between the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate is set to 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 set to 35° to 55°. This includes adjusting the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate, according to the phase difference of the defective portion of the first λ / 4 plate. A method for inspecting defects in λ / 4 plates.

2. The defect inspection method for a λ / 4 plate according to claim 1, wherein the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate is 300 nm to 321 nm.

3. The defect inspection method for a λ / 4 plate according to claim 1, wherein the sum of the phase difference Rp of the normal portion of the first λ / 4 plate and the phase difference Rf of the second λ / 4 plate is 269 nm to 290 nm.

4. The method for inspecting defects in a λ / 4 plate according to any one of claims 1 to 3, wherein the first λ / 4 plate is made of a liquid crystal material.

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