CN116577332A

CN116577332A - Defect inspection method for lambda/4 plate

Info

Publication number: CN116577332A
Application number: CN202310088482.XA
Authority: CN
Inventors: 家原惠太; 铃木畅; 深见空斗
Original assignee: Nitto Denko Corp
Current assignee: Nitto Denko Corp
Priority date: 2022-02-10
Filing date: 2023-02-09
Publication date: 2023-08-11
Also published as: TW202336429A; JP2023117236A; KR20230121002A

Abstract

The defect inspection method of the lambda/4 plate of the present invention comprises: sequentially configuring a first polarizer, a first lambda/4 plate, a second lambda/4 plate and a second polarizer; and observing the appearance of the surface of the second polarizer side by incident light from the surface of the first polarizer side, detecting the defect of the first lambda/4 plate, comprising: the absorption axis of the first polarizer and the absorption axis of the second polarizer are set to be parallel, the slow axis of the first lambda/4 plate and the slow axis of the second lambda/4 plate are set to be parallel, the angle formed by the absorption axis of the first polarizer and the slow axis of the first lambda/4 plate is set to be 35 DEG to 55 DEG, the angle formed by the absorption axis of the second polarizer and the slow axis of the second lambda/4 plate is set to be 35 DEG to 55 DEG, and the total value of the phase difference Rp of the normal part of the first lambda/4 plate and the phase difference Rf of the second lambda/4 plate is adjusted according to the phase difference of the defect part of the first lambda/4 plate.

Description

Defect inspection method for lambda/4 plate

Technical Field

The invention relates to a defect inspection method of lambda/4 plates.

Background

In image display devices such as liquid crystal display devices (LCDs) and organic electroluminescence display devices (OLEDs), retardation films are often used for the purpose of improving display characteristics, antireflection, and the like. In the production process of the retardation film, there is a case where defects are generated due to local appearance defects, and a method for inspecting the defects with good sensitivity is required. In particular, as the lambda/4 plate having a retardation film made of a liquid crystal material is not detected by the conventional method, a slight defect is more likely to occur, and an inspection method capable of detecting such a defect is demanded.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open publication No. 2013-15766

Disclosure of Invention

Problems to be solved by the invention

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

Means for solving the problems

In one embodiment, a total value 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 300nm to 321nm.

In one embodiment, a total value 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 269nm to 290nm.

In one embodiment, the first λ/4 plate is made of a liquid crystal material.

Effects of the invention

According to the present invention, a defect inspection method capable of inspecting defects of an optical laminate including a λ/4 plate with good sensitivity can be provided.

Drawings

Fig. 1 is a schematic perspective view illustrating an inspection method according to an embodiment of the present invention.

Fig. 2 is a schematic perspective view illustrating an inspection method according to an embodiment of the present invention.

Fig. 3 is a schematic perspective view illustrating an inspection method according to an embodiment of the present invention.

Fig. 4 is a schematic perspective view illustrating an inspection method according to an embodiment of the present invention.

Fig. 5 is a photograph showing an example of a defect (bright spot) generated in a λ/4 plate composed of a liquid crystal material.

Description of symbols

11 first polarizer

12 second polarizer

21 first lambda/4 plate

22 second lambda/4 plate

30 Isotropic substrates

Detailed Description

A. Defect inspection method

The defect inspection method of the lambda/4 plate of the present invention comprises: sequentially configuring a first polarizer, a first lambda/4 plate, a second lambda/4 plate and a second polarizer; and the light is incident from the surface of the first polarizer side, the appearance of the surface of the second polarizer side is observed, and the defect of the first lambda/4 plate is detected. In the above-described 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 become parallel. Further, the first λ/4 plate and the second λ/4 plate are arranged in such a manner that the slow axis of the first λ/4 plate and the slow axis of the second λ/4 plate become parallel. The first polarizer and the first lambda/4 plate are disposed such that an angle formed between an absorption axis of the first polarizer and a slow axis of the first lambda/4 plate is 35 DEG to 55 deg. The second polarizer and the second lambda/4 plate are disposed such that an angle formed by an absorption axis of the second polarizer and a slow axis of the second lambda/4 plate is 35 DEG to 55 deg. Further, the defect inspection method includes adjusting a total value 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. If the first polarizer, the first λ/4 plate, the second λ/4 plate, and the second polarizer are arranged in this order, other films may be interposed therebetween as long as the effects of the present invention can be obtained. For example, another retardation film (for example, a positive C plate) may be interposed between the first polarizer and the first λ/4 plate. Further, for convenience, the appearance of the second polarizer is illustrated as viewed from above, but in practice, the inspection system may be constructed with upside down.

In the present specification, "parallel" also includes a substantially parallel state. The term "substantially parallel" includes a case where the angle formed by 2 directions is 0 ° ± 7 °, preferably 0 ° ± 5 °, and more preferably 0 ° ± 3 °. "orthogonal" also includes substantially orthogonal states. "substantially orthogonal" includes a case where the angle formed by 2 directions is 90++7°, preferably 90++5°, and more preferably 90++3°. In the present specification, the term "angle" includes both clockwise and counterclockwise with respect to the reference direction. The term "view the appearance of the surface on the second polarizer side" means to view the presence or absence or the amount of light transmitted through the second polarizer. In the present specification, the phase difference refers to an in-plane retardation.

Fig. 1 is a schematic perspective view illustrating an inspection method according to an embodiment of the present invention. Fig. 1 shows a 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, and the polarization direction of light transmitted through each layer. In the inspection method of the present invention, the polarized light a generated by passing through the first polarizer 11 is given a phase difference by two λ/4 plates (first λ/4 plate 21, second λ/4 plate 22). In the state shown in fig. 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 that the polarized light a is rotated by approximately 90 ° by imparting a phase difference to the polarized light, and the polarized light b thus generated reaches the second polarizer 12 as normal light. In the present invention, the light reaching the second polarizer 12 without normally giving a phase difference in the first λ/4 plate 21 is set to be abnormal light that has passed through the defect of the first λ/4 plate, and the defect of the first λ/4 plate is detected as a bright defect (a point with higher luminance than the normal portion of the periphery) by passing the abnormal light through the second polarizer.

In the present invention, by adjusting the total value 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 is possible to detect the disadvantage that the difference between the phase difference Rp and the phase difference Rf of the normal portion is small and difficult to detect by the conventional technique.

In one embodiment, the sum of the phase difference Rp of the normal portion of the first lambda/4 plate and the phase difference Rf of the second lambda/4 plate is preferably 300nm to 321nm, more preferably 307nm to 314nm. If the range is such, an inspection method that can detect the defect of the first lambda/4 plate with good sensitivity can be provided. In particular, although it has been difficult to detect a disadvantage (hereinafter, also referred to as "white streak") that a streak-like unevenness occurs due to a phase difference higher than a normal portion, the disadvantage can be detected by the method of the present invention. In addition, a point defect (hereinafter, also referred to as a bright point) having a very narrow defect range can be detected with good sensitivity.

In another embodiment, the sum of the phase difference Rp of the normal portion of the first lambda/4 plate and the phase difference Rf of the second lambda/4 plate is preferably 269nm to 290nm, more preferably 276nm to 283nm. By setting the range as described above, an inspection method having significantly excellent sensitivity against the disadvantage that the phase difference is lower than the normal portion can be set.

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

The first lambda/4 plate and/or the second lambda/4 plate (in particular the first lambda/4 plate) may also form a laminate together with any suitable further layers and/or films. Examples of the other layer and other film include an adhesive layer, and a substrate. The other layers and other films are preferably optically isotropic.

In one embodiment, the first λ/4 plate or the second λ/4 plate (in particular the first λ/4 plate) is composed of a liquid crystal material. In one embodiment, a first λ/4 plate composed of a liquid crystal material is an inspection object. In the present invention, it is advantageous in that a slight defect of a lambda/4 plate composed of a liquid crystal material can be checked with good sensitivity as well.

In one embodiment, the first λ/4 plate 21 is composed of a liquid crystal material, and the second λ/4 plate 22 may be a stretched film of a polymer film. The second lambda/4 plate 22 can be an oriented substrate when forming the first lambda/4 plate 21. Further, as schematically shown in fig. 2, the first λ/4 plate 21 and the second λ/4 plate 22 may constitute a laminated body. The laminate may be elongated. The inspection method of the present embodiment can be used for an inspection performed before a λ/4 plate (first λ/4 plate) provided in a predetermined product is incorporated into the product.

In one embodiment, the first λ/4 plate 21 is made of a liquid crystal material, and as schematically shown in fig. 3, a laminate a including the first λ/4 plate 21 and the isotropic base material 30 disposed on the first polarizer 11 side surface of the first λ/4 plate 21 is an inspection target. The isotropic substrate has optically isotropic properties. Typically, the isotropic substrate 30 has an alignment layer on the side of the first λ/4 plate 21. The alignment layer may be an alignment film or a layer formed by rubbing treatment. The alignment film may be any suitable film selected according to the type of liquid crystal monomer, the material of the substrate, and the like. As an alignment film for uniformly aligning liquid crystal molecules in a predetermined direction, a film obtained by rubbing an alignment film of a polyimide film and a polyvinyl alcohol film is preferably used. In addition, a photo-alignment film may be used. The laminate a may be elongated. The inspection method of the present embodiment can be used for an inspection performed before a λ/4 plate (first λ/4 plate) provided in a predetermined product is incorporated into the product.

In another embodiment, the first λ/4 plate 21 is made of a liquid crystal material, and 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 an inspection object. The optical layered body B may be elongated. Typically, the optical stack B may be a circular polarizer. The inspection method of the present embodiment can be used for inspecting an optical laminate B (circularly polarizing plate) as a product.

For example, the inspection method may be performed on 1 line a plurality of times for the purpose of detecting various defects due to differences in phase difference. Specifically, in the embodiment shown in fig. 3 and 4, a plurality of constituent bodies including (second polarizer)/(second λ/4 plate) may be arranged with respect to the elongated optical layered body A, B, and in this case, the second λ/4 plate in the (second polarizer)/(second λ/4 plate) constituent body may be set so that the phase difference differs from constituent body to constituent body. In the embodiment shown in fig. 3, a plurality of first polarizers may be provided, or a long first polarizer may be provided, corresponding to the (second polarizer)/(second λ/4 plate) structure.

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

The external 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 an arbitrary suitable camera, and the image is subjected to image processing such as 2-valued processing, thereby performing defect detection.

B. First polarizer, second polarizer

As the polarizer, any suitable polarizer is used. Examples thereof include a polarizer obtained by uniaxially stretching a hydrophilic polymer film such as a polyvinyl alcohol film, a partially formalized polyvinyl alcohol film, or an ethylene/vinyl acetate copolymer partially saponified film by adsorbing a dichroic substance such as iodine or a dichroic dye, a dehydrated product of polyvinyl alcohol, and a multi-functional oriented film such as a desalted product of polyvinyl chloride. Among them, a polarizer obtained by uniaxially stretching a polyvinyl alcohol film with a dichroic substance such as iodine adsorbed thereon is particularly preferable because of its high polarization to color ratio. The thickness of the polarizer is preferably 0.5 μm to 80. Mu.m.

A polarizer obtained by uniaxially stretching a polyvinyl alcohol film by adsorbing iodine is typically produced by immersing polyvinyl alcohol in an aqueous solution of iodine, dyeing the film, and stretching the film to 3 to 7 times the original length. The stretching may be performed after dyeing, stretching may be performed while dyeing, or dyeing may be performed after stretching. In addition to stretching and dyeing, the fiber can be produced by, for example, swelling, crosslinking, conditioning, washing with water, drying, and the like.

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

As the protective film, any suitable film is used. Specific examples of the material that becomes the main component of such a film include cellulose resins such as triacetyl cellulose (TAC), transparent resins such as (meth) acrylic resins, polyester resins, polyvinyl alcohol resins, polycarbonate resins, polyamide resins, polyimide resins, polyether sulfone resins, polysulfone resins, polystyrene resins, polynorbornene resins, polyolefin resins, and acetate resins. Examples of the resin include a thermosetting resin such as an acrylic resin, a urethane resin, an acrylic urethane resin, an epoxy resin, and a silicone resin, and an ultraviolet curable resin. In addition, for example, a vitreous polymer such as a siloxane polymer can be used. Furthermore, a polymer film described in Japanese patent application laid-open No. 2001-343529 (WO 01/37007) may also be used. As a material of the film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in a side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in a side chain, and for example, a resin composition having an alternating copolymer of isobutylene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be used. The polymer film may be, for example, an extrusion molded product of the resin composition.

In one embodiment, as the second polarizer, a polarizer having a light transmittance of 42% or more is used. If such a second polarizer is used, the detection sensitivity can be improved. The light transmittance of the second polarizer is more preferably 43% or more, and still more preferably 44% or more. In the case of using a polarizing plate including the second polarizer, the light transmittance of the polarizing plate is preferably 42% or more, more preferably 43% or more, and further preferably 44% or more.

C. First lambda/4 plate and second lambda/4 plate

The first lambda/4 plate and the second lambda/4 plate (sometimes collectively referred to as lambda/4 plates) can convert linearly polarized light of a particular wavelength into circularly polarized light (or circularly polarized light into linearly polarized light).

The in-plane retardation Re of the lambda/4 plate is preferably 95nm to 180nm, more preferably 110nm to 160nm. The lambda/4 plate preferably has refractive index ellipsoids with nx > ny.gtoreq.nz. In this specification, the in-plane retardation Re means an in-plane retardation at 23 ℃ and a wavelength of 590 nm. When the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction) is given as nx, the refractive index in the direction orthogonal to the slow axis in-plane (i.e., the fast axis direction) is given as ny, and the film thickness is given as d (nm), re is obtained by re= (nx-ny) ×d. In this specification, "ny=nz" includes not only the case where ny is exactly equal to nz but also the case where ny is substantially equal to nz.

In one embodiment, the in-plane retardation Re at the defective portion of the first lambda/4 plate is preferably 141.5nm to 151nm, more preferably 142nm to 146nm. The disadvantage of having such an in-plane retardation Re may be that the retardation is higher than that of the normal portion. In another embodiment, the in-plane retardation Re at the defective portion of the first lambda/4 plate is preferably 140.5nm to 131nm, more preferably 139.5nm to 136nm. The disadvantage of having such an in-plane retardation Re may be that the retardation is lower than that of the normal portion. Further, the difference between the in-plane retardation Re at the normal site of the first λ/4 plate and the in-plane retardation Re at the defective site (in-plane retardation Re at the normal site of the first λ/4 plate—in-plane retardation Re at the defective site) is, for example, -10nm to 10nm. According to the present invention, even if the difference between the in-plane retardation Re at the normal site and the in-plane retardation Re at the defective site is small, the defect detection can be preferably performed.

(lambda/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. As the liquid crystal material, any suitable liquid crystal monomer may be used. For example, the polymerizable mesogenic compounds described in Japanese patent application laid-open No. 2002-533742 (WO 00/37585), EP358208 (US 5211877), EP66137 (US 4388453), WO93/22397, EP0261712, DE19504224, DE4408171, GB2280445 and the like can be used. Specific examples of such a polymerizable mesogenic compound include, for example, a product name LC242 from BASF, a product name E7 from Merck, and a product name LC-Silicon-CC 3767 from Wacker-Chem.

The λ/4 plate made of a liquid crystal material can be obtained, for example, by aligning a liquid crystal material and curing or hardening the liquid crystal material in a state where the alignment state is fixed. Specifically, the liquid crystal material can be aligned by applying a liquid crystal composition containing the liquid crystal material to an elongated alignment substrate; and subjecting the aligned liquid crystal material to a polymerization treatment and/or a crosslinking treatment to form a liquid crystal cured layer. Here, since the liquid crystal material can be aligned according to the alignment treatment direction of the substrate, the slow axis of the retardation layer can be expressed in substantially the same direction as the alignment treatment direction of the substrate. Specific examples of the method for forming the retardation layer include the method described in JP 2006-178389A. The thickness of the lambda/4 plate made of the liquid crystal material is preferably 0.5 μm to 1.8. Mu.m, more preferably 1 μm to 1.6. Mu.m.

In one embodiment, as the liquid crystal material, a thermotropic liquid crystal exhibiting liquid crystallinity by heating may be used. The thermotropic liquid crystal generates phase changes of crystalline phase, liquid crystal phase and isotropic phase by temperature change.

(lambda/4 plate made of stretched film)

The λ/4 plate composed of a stretched film can be obtained by stretching a polymer film in a predetermined direction, for example.

Any suitable resin is used as the resin for forming the polymer film. Specific examples thereof include cycloolefin resins such as polynorbornene, polycarbonate resins, cellulose resins, polyvinyl alcohol resins, polysulfone resins, and other resins constituting the positive birefringent film. Among them, norbornene-based resins and polycarbonate-based resins are preferable.

The polynorbornene refers to a (co) polymer obtained by using a norbornene-based monomer having a norbornene ring in part or all of the starting materials (monomers). Examples of the norbornene monomer include norbornene, and alkyl and/or alkylidene substituents thereof, and polar group substituents such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5-butyl-2-norbornene, 5-ethylidene-2-norbornene, and halogens thereof; dicyclopentadiene, 2, 3-dihydro-dicyclopentadiene, and the like; dimethylbridged octahydronaphthalenes, alkyl and/or alkylidene substituents thereof, polar group substituents such as halogen, e.g., 6-methyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-ethyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-ethylidene-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-chloro-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-cyano-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-pyridinyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, 6-methoxycarbonyl-1, 4:5, 8-dimethylbridge-1, 4a,5,6,7,8 a-octahydronaphthalene, etc.; trimers to tetramers of cyclopentadiene, for example 4,9:5, 8-dimethyl-3 a, 4a,5, 8a,9 a-octahydro-1H-benzidine, 4,11:5,10:6, 9-trimethyl-3 a, 4a, 5a,6, 9a,10 a,11 a-dodecahydro-1H-cyclopentaanthracene, and the like.

As the polynorbornene, various products are commercially available. Specific examples thereof include trade names "ZEONEX", "ZEONOR", and "Arton", and "TOPAS", and "APEL", both manufactured by ZEON corporation, JSR, and TICONA, respectively.

As the polycarbonate resin, an aromatic polycarbonate is preferably used. Typically, the aromatic polycarbonate is obtained by reacting a carbonate precursor with an aromatic dihydric phenol compound. Specific examples of the carbonate precursor include carbonyl chloride, bischloroformates of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, and dinaphthyl carbonate. Among them, carbonyl chloride and diphenyl carbonate are preferable. As a specific example of the aromatic dihydric phenol compound, examples thereof include 2, 2-bis (4-hydroxyphenyl) propane, 2-bis (4-hydroxy-3, 5-dimethylphenyl) propane, bis (4-hydroxyphenyl) methane, 1-bis (4-hydroxyphenyl) ethane, 2-bis (4-hydroxyphenyl) butane 2, 2-bis (4-hydroxy-3, 5-dimethylphenyl) butane, 2-bis (4-hydroxy-3, 5-dipropylphenyl) propane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane and the like. They may be used alone or in combination of 2 or more. Preference is given to using 2, 2-bis (4-hydroxyphenyl) propane, 1-bis (4-hydroxyphenyl) cyclohexane, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane. Particular preference is given to using 2, 2-bis (4-hydroxyphenyl) propane together with 1, 1-bis (4-hydroxyphenyl) -3, 5-trimethylcyclohexane.

Examples of the stretching method include transverse uniaxial stretching, fixed-end biaxial stretching, and sequential biaxial stretching. As a specific example of the biaxial stretching at the fixed end, a method of stretching a polymer film in the short side direction (transverse direction) while advancing the polymer film in the longitudinal direction is exemplified. The process may obviously be transverse uniaxial stretching. In addition, oblique stretching may be employed. By using 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 producing a lambda/4 plate by oblique stretching are described in, for example, japanese patent application laid-open publication No. 2013-54338, japanese patent application laid-open publication No. 2014-194482, japanese patent application laid-open publication No. 2014-238524, japanese patent application laid-open publication No. 2014-194484, and the like. The disclosure of this publication is incorporated by reference into the present specification.

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

In one embodiment, a λ/4 plate (preferably, a λ/4 plate obtained by oblique stretching) composed of a stretched film can be used as an alignment substrate when the λ/4 plate composed of the above-described liquid crystal material is produced.

Examples

Hereinafter, the present invention will be specifically described 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.

Example 1

A photopolymerizable liquid crystal compound (Paliocolor LC242, manufactured by BASF) exhibiting a nematic liquid crystal phase was dissolved in cyclopentanone to prepare a solution having a solid content concentration of 30% by weight. A surfactant (BYK-360, manufactured by BYK-Chemie) and a photopolymerization initiator (Omnirad 907, manufactured by IGM Resins) were added to the solution to prepare a liquid crystal composition solution. The amounts of the leveling agent and the polymerization initiator to be added were set to 0.01 part by weight and 3 parts by weight, respectively, relative to 100 parts by weight of the photopolymerizable liquid crystal compound.

A tilt-stretched norbornene-based FILM (ZEONOR FILM (ZD 12) manufactured by ZEON, japan), thickness: 23 μm, in-plane retardation: 140 nm) was prepared.

The liquid crystal composition was applied to the obliquely-stretched norbornene film by a bar coater so that the thickness after drying became 1.69. Mu.m, and heated at 100℃for 3 minutes to orient the liquid crystal. After cooling to room temperature, the cumulative light amount was 400mJ/cm under a nitrogen atmosphere ² The film was subjected to photo-curing by ultraviolet light to obtain a uniformly aligned liquid crystal layer (first lambda/4 plate, in-plane retardation Rp:141 nm) on the obliquely stretched norbornene film.

The liquid crystal composition was applied to the obliquely-stretched norbornene-based film by a bar coater so that the thickness of the film after drying became 1.54. Mu.m, and the film was heated at 100℃for 3 minutes to orient the liquid crystal. After cooling to room temperature, the cumulative light amount was 400mJ/cm under a nitrogen atmosphere ² The film was cured by ultraviolet light to obtain a uniformly aligned liquid crystal layer (second lambda/4 plate, in-plane retardation Rf:128nm, thickness: 1.54 μm) on the obliquely stretched norbornene film.

The first polarizer including the first polarizer (monomer transmittance: 45%), the first λ/4 plate, the second λ/4 plate, and the second polarizer including the second polarizer (monomer transmittance: 45%) were laminated.

At this time, regarding the axial direction of each layer, the absorption axis of the first polarizer and the absorption axis of the second polarizer are set to be parallel, the slow axis of the first λ/4 plate and the slow axis of the second λ/4 plate are set to be parallel, the angle formed by the absorption axis of the first polarizer and the slow axis of the first λ/4 plate is set to 45 °, and the angle formed by the absorption axis of the second polarizer and the slow axis of the second λ/4 plate is set to 45 °.

The light source and the imaging device were disposed on both sides of the above configuration, and a defect inspection using a transmission inspection was performed on the first λ/4 plate with a rib-like defect (a defect having a phase difference of about 1.5nm smaller than that of the normal portion) having a smaller thickness and a smaller phase difference than that of the normal portion as a detection target. As a result, this disadvantage can be detected.

Example 2

The same defect inspection as in example 1 was performed by arranging a first polarizing plate including a first polarizer, the first lambda/4 plate (phase difference Rp:141 nm), the second lambda/4 plate (phase difference Rf:135 nm), and a second polarizing plate including a second polarizer in this order, in the same manner as in example 1, except that the thickness of the second lambda/4 plate was set to 1.62. Mu.m. As a result, the streak-like disadvantage (disadvantage of having a phase difference of about 1.5nm smaller than that of the normal portion) that the thickness was thin and the phase difference was small compared with that of the normal portion was clearly detected as compared with example 1.

Example 3

The same procedure as in example 1 was followed except that the thickness of the second λ/4 plate was set to 1.70 μm, and the first polarizing plate including 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 polarizing plate including the second polarizer were sequentially arranged, to perform the same defect inspection as in example 1. As a result, the streak-like disadvantage (disadvantage of having a phase difference of about 1.5nm smaller than that of the normal portion) that the thickness was thin and the phase difference was small compared with that of the normal portion was clearly detected as compared with example 1.

Example 4

The same defect inspection as in example 1 was performed by arranging a first polarizing plate including a first polarizer, the first lambda/4 plate (phase difference Rp:141 nm), the second lambda/4 plate (phase difference Rf:149 nm), and a second polarizing plate including a second polarizer in this order, in the same manner as in example 1, except that the thickness of the second lambda/4 plate was set to 1.79. Mu.m. As a result, a streak-like defect (a defect having a phase difference of about 1.5nm smaller than that of the normal portion) having a smaller thickness and a smaller phase difference than that of the normal portion can be detected.

Example 5

The same procedure as in example 1 was followed except that the thickness of the second λ/4 plate was set to 1.91 μm, and the first polarizing plate including 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 polarizing plate including the second polarizer were laminated in this order.

The light source and the imaging device were disposed on both sides of the above configuration, and a defect inspection using a transmission inspection was performed on the first λ/4 plate with a rib-like defect (a defect having a phase difference of about 1.5nm compared with the phase difference of the normal portion) having a larger thickness and a larger phase difference than the normal portion as a detection target. As a result, this disadvantage can be detected.

Example 6

The same procedure as in example 5 was followed except that the thickness of the second λ/4 plate was set to 1.99 μm, and the first polarizing plate including 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 polarizing plate including the second polarizer were sequentially arranged, to perform the same defect inspection as in example 5. As a result, the streak-like disadvantage (disadvantage of having a phase difference of about 1.5nm higher than that of the normal portion) that the thickness was thicker and the phase difference was large compared with that of the normal portion was clearly detected as compared with example 5.

Example 7

The same procedure as in example 5 was followed except that the thickness of the second λ/4 plate was set to 2.08 μm, and the first polarizing plate including 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 polarizing plate including the second polarizer were sequentially arranged, to examine the defects in the same manner as in example 1. As a result, the streak-like disadvantage (disadvantage of having a phase difference of about 1.5nm higher than that of the normal portion) that the thickness was thicker and the phase difference was large compared with that of the normal portion was clearly detected as compared with example 5.

Further, the number of detections in the range of 1.3m×1m was confirmed for the bright spot, and as a result, 4.6 defects were detected. A representative of the appearance of the bright spots is illustrated in fig. 5.

Example 8

The same procedure as in example 5 was followed except that the thickness of the second λ/4 plate was set to 2.16 μm, and the first polarizing plate including 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 polarizing plate including the second polarizer were sequentially arranged, to perform the same defect inspection as in example 5. As a result, a rib-like defect (a defect having a phase difference of about 1.5nm from the phase difference of the normal portion) having a larger thickness and a larger phase difference than the normal portion can be detected.

Comparative example 1

The same procedure as in example 1 was followed except that the thickness of the second λ/4 plate was set to 1.85 μm, and the first polarizing plate including 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 polarizing plate including the second polarizer were laminated in this order.

With the above configuration, the same defect inspection as in example 1 was performed. As a result, the defects detectable in example 1 could not be detected. Further, the same defect inspection as in example 5 was performed. As a result, the defects detectable in example 5 could not be detected.

Further, the first λ/4 plate similar to example 7 (i.e., the λ/4 plate similar to the λ/4 plate in which 4.6 bright spots were detected in example 7) was used as the inspection target, and the number of detected bright spots within a range of 1.3m×1m was checked in the same manner as in example 7, and as a result, 2.4 defects were detected.

The results of examples and comparative examples are summarized in the following table. As also shown in tables 1 and 2, according to the present invention, various disadvantages can be detected with good sensitivity by appropriately setting rp+rf.

TABLE 1

TABLE 2

	Example 7	Comparative example 1
			Second lambda/4 plate phase difference Rf [ nm]	123	141
First lambda/4 plate (article) phase difference Rp [ nm]	141	141
			Rp+Rf[nm]	264	282
The defect (bright spot) can be detected	4.6	2.4

Claims

1. A method of inspecting a lambda/4 plate for defects, comprising: sequentially configuring a first polarizer, a first lambda/4 plate, a second lambda/4 plate and a second polarizer; and the light is incident from the surface of the first polarizer side, the appearance of the surface of the second polarizer side is observed, the defect of the first lambda/4 plate is detected,

it comprises: setting the absorption axis of the first polarizer and the absorption axis of the second polarizer to be parallel, setting the slow axis of the first lambda/4 plate and the slow axis of the second lambda/4 plate to be parallel, setting the angle formed by the absorption axis of the first polarizer and the slow axis of the first lambda/4 plate to be 35-55 DEG, setting the angle formed by the absorption axis of the second polarizer and the slow axis of the second lambda/4 plate to be 35-55 DEG,

the total value of the phase difference Rp of the normal portion of the first lambda/4 plate and the phase difference Rf of the second lambda/4 plate is adjusted according to the phase difference of the defective portion of the first lambda/4 plate.

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

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

4. A defect inspection method of a λ/4 plate according to any one of claims 1 to 3, wherein the first λ/4 plate is composed of a liquid crystal material.