Defect inspection method for λ / 4 plate

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, first λ / 4 plate, second λ / 4 plate, and second polarizer in the described order; allowing light to enter from a first polarizer-side surface to observe appearance of a second polarizer-side surface and detecting a defect of the first λ / 4 plate as a bright defect, and adjusting retardation of the second λ / 4 plate according to retardation at the defective portion of the first 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 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 detecting defects in a λ / 4 plate with high sensitivity.

Means for Solving the Problems

[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, and making light incident from the surface on the first polarizer side, observing the appearance of the surface on the second polarizer side, and detecting a defect in the first λ / 4 plate as a clear defect, adjusting the retardation of the second λ / 4 plate according to the retardation of the defective portion of the first λ / 4 plate, and switching between the following state A, state B-1, and state B-2. State A: The absorption axis of the first polarizer is parallel to the absorption axis of the second polarizer, the slow axes of the first λ / 4 plate and the second λ / 4 plate are parallel, 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°; State B-1: The absorption axis of the first polarizer is orthogonal to the absorption axis of the second polarizer, the slow axes of the first λ / 4 plate and the second λ / 4 plate are orthogonal, 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°; State B-2: The absorption axis of the first polarizer is orthogonal to the absorption axis of the second polarizer, and the slow axes of the first λ / 4 plate and the second λ / 4 plate are parallel. The absorption axis of the first polarizer is parallel to the slow axis of the first λ / 4 plate, 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°. In one embodiment, the retardation of the defective portion of the first λ / 4 plate is smaller than the retardation of the normal portion of the first λ / 4 plate; when the retardation (Rp) of the normal portion of the first λ / 4 plate, the retardation (Rd) of the defective portion of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate satisfy the relationship of |Rp - Rf| < |Rd - Rf|, the defect detection of the first λ / 4 plate is performed in the above State B-1 or State B-2. In one embodiment, Rf - Rp is 0 nm or more. In one embodiment, the retardation of the defective portion of the first λ / 4 plate is smaller than the retardation of the normal portion of the first λ / 4 plate; when the retardation (Rp) of the normal portion of the first λ / 4 plate, the retardation (Rd) of the defective portion of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate satisfy the relationship of |Rp - Rf| ≥ |Rd - Rf|, the defect detection of the first λ / 4 plate is performed in the above State A. In one embodiment, Rp - Rf is 2 nm or more. In one embodiment, the phase difference of the defective portion of the first λ / 4 plate is larger than the phase difference of the normal portion of the first λ / 4 plate; when the phase difference (Rp) of the normal portion of the first λ / 4 plate, the phase difference (Rd) of the defective portion of the first λ / 4 plate, and the phase difference (Rf) of the second λ / 4 plate satisfy the relationship of |Rp - Rf| ≦ |Rd - Rf|, the defect of the first λ / 4 plate is detected in the above state B-1 or state B-2. In one embodiment, Rp - Rf is 0 nm or more. In one embodiment, the phase difference of the defective portion of the first λ / 4 plate is larger than the phase difference of the normal portion of the first λ / 4 plate; when the phase difference (Rp) of the normal portion of the first λ / 4 plate, the phase difference (Rd) of the defective portion of the first λ / 4 plate, and the phase difference (Rf) of the second λ / 4 plate satisfy the relationship of |Rp - Rf| > |Rd - Rf|, the defect of the first λ / 4 plate is detected in the above state A. In one embodiment, Rf - Rp is from -5 nm to 5 nm.

Advantages of the Invention

[0006] According to the present invention, it is possible to provide a defect detection method capable of sensitively inspecting defects of an optical laminate including a λ / 4 plate.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0008] A. Defect inspection method The method for inspecting defects of a λ / 4 plate according to 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, and making light incident from the surface on the first polarizer side, observing the appearance of the surface on the second polarizer side, and detecting the defects of the first λ / 4 plate as obvious defects. The method for inspecting defects of a λ / 4 plate according to the present invention includes adjusting the phase difference of the second λ / 4 plate according to the phase difference of the defective part of the first λ / 4 plate, and switching between the following state A, state B-1, and state B-2. State A: The absorption axis of the first polarizer and the absorption axis of the second polarizer are parallel, the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are parallel, 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° (Fig. 1); State B-1: The absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal, the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are orthogonal, 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° (Fig. 2); State B-2: The absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal, and the slow axis of the first λ / 4 plate and the slow axis of the second λ / 4 plate are parallel, the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate are parallel, 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° (Fig. 3). As long as the effects of the present invention can be obtained, as long as 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. For example, another retardation film (for example, a positive C plate) may be interposed between the first polarizer and the first λ / 4 plate. In addition, in this specification, the state in which the absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal to each other may be collectively referred to as "state B". For the sake of convenience, the state of observing the appearance of the second polarizer from above is illustrated, but actually, the inspection system may be configured with the top and bottom reversed. When referring to an angle in this specification, unless otherwise specified, the angle includes angles in both the clockwise and counterclockwise directions.

[0009] In this specification, "parallel" includes a substantially parallel state. "Substantially parallel" includes the case where the angle formed by two directions is 0° ± 7°, preferably 0° ± 5°, and more preferably 0° ± 3°. "Orthogonal" includes a substantially orthogonal state. "Substantially orthogonal" includes the case where the angle formed by two directions is 90° ± 7°, preferably 90° ± 5°, and more preferably 90° ± 3°. When referring to an angle in this specification, it includes both clockwise and counterclockwise directions with respect to the reference direction. Also, "observing the appearance of the surface on the second polarizer side" means observing the presence and amount of light transmitted through the second polarizer. In addition, in this specification, the retardation means the in-plane retardation.

[0010] Figures 1 and 2 are schematic perspective views for explaining an inspection method according to one embodiment of the present invention. In Figure 1, in the above state A, 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 directions of the light transmitted through each layer are shown. In Figure 2, in the above state B-1, 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 directions of the light transmitted through each layer are shown. In the state shown in Figure 1, a phase difference is given to the polarized light a generated by passing through the first polarizer 11 by two λ / 4 plates (the first λ / 4 plate 21 and the 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 that a phase difference is given to the polarized light a to rotate the polarization direction by approximately 90°, and the polarized light b thus generated reaches the second polarizer 12 as normal light. In the state shown in Figure 2, the polarized light a generated by passing through the first polarizer 11 passes through the first and second λ / 4 plates and becomes polarized light b having the same polarization direction as the polarized light a, and 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 b reaches the second polarizer 12 as normal light. In the present invention, the light that reaches the second polarizer 12 without a normal phase difference being given in the first λ / 4 plate is regarded as abnormal light that has passed through the defect of the first λ / 4 plate, and by passing the abnormal light through the second polarizer, the defect of the first λ / 4 plate is detected as an obvious defect (a point having a higher luminance than the normal portion in the periphery). As shown in Figure 3, also in the state B-2, in the present invention, the light that reaches the second polarizer 12 without a normal phase difference being given in the first λ / 4 plate is regarded as abnormal light that has passed through the defect of the first λ / 4 plate, and by passing the abnormal light through the second polarizer, the defect of the first λ / 4 plate is detected as an obvious defect (a point having a higher luminance than the normal portion in the periphery).

[0011] In the present invention, according to the phase difference of the defective portion of the first λ / 4 plate, the phase difference of the second λ / 4 plate is adjusted, and by switching between the above state A, state B-1, and state B-2, it becomes possible to detect even a defect whose difference from the phase difference of the normal portion is small and which is difficult to detect by the conventional technique. The inspection method of the present invention can detect a defect as an obvious defect regardless of what value the phase difference of the defect is. In such an inspection system, it is advantageous in that the effect of improving the defect detection sensitivity by increasing the inspection light amount is remarkable.

[0012] FIG. 4 is a schematic cross-sectional view showing an example of a defect occurring in a λ / 4 plate made of a liquid crystal material. Examples of defects that can occur in a λ / 4 plate made of a liquid crystal material include, for example, a defect having a thickness thinner than that of a normal portion as shown in FIG. 4(a), a defect having a thickness thicker than that of a normal portion as shown in FIG. 4(b), and the like. A defect having a thickness thinner than that of the normal portion has a smaller phase difference than that of the normal portion. Also, a defect having a thickness thicker than that of the normal portion has a larger phase difference than that of the normal portion.

[0013] Typically, the first polarizer and the second polarizer are applied as a polarizing plate together with a protective film.

[0014] 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 suitable other layer and / or film. Examples of the other layer and the other film include, for example, an adhesive layer, an adhesive layer, a substrate, and the like. The other layer and the other film are preferably optically isotropic.

[0015] 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 to be inspected. The present invention is advantageous in that it can inspect even minor defects of a λ / 4 plate made of a liquid crystal material with high sensitivity.

[0016] 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. 5, 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 this embodiment can be adopted, for example, for the inspection of the λ / 4 plate (first λ / 4 plate) provided in a predetermined product before being incorporated into the product.

[0017] In one embodiment, the first λ / 4 plate 21 is made of a liquid crystal material. As schematically shown in FIG. 6, 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 an inspection target. 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 appropriate 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, an alignment film of a polyimide-based film and a polyvinyl alcohol-based film subjected to a rubbing treatment is preferably used. Also, an optical alignment film may be used. The laminate A may be in a long shape. The inspection method of this embodiment can be adopted, for example, for the inspection of the λ / 4 plate (first λ / 4 plate) provided in a predetermined product before being incorporated into the product.

[0018] In another embodiment, the first λ / 4 plate 21 is made of a liquid crystal material. As schematically shown in FIG. 7, 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 target. 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 adopted for the inspection of the optical laminate B (circular polarizing plate) as a product.

[0019] For example, for the purpose of detecting a plurality of types of defects due to differences in phase difference, etc., the above inspection method may be performed multiple times in one line. Specifically, in the embodiments shown in FIGS. 6 and 7, a plurality of components composed of (second polarizer) / (second λ / 4 plate) may be arranged with respect to the long laminated bodies A and B. At this time, the second λ / 4 plates in the (second polarizer) / (second λ / 4 plate) components may have different phase differences for each component. In the embodiment shown in FIG. 6, corresponding to the (second polarizer) / (second λ / 4 plate) component, a plurality of first polarizers may be arranged, or a long first polarizer may be arranged.

[0020] The light incident on the surface on the first polarizer side is generated by any suitable light source. In one embodiment, a white LED is used as the light source.

[0021] The external appearance observation of the surface on the second polarizer side can be performed 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 processing to detect defects.

[0022] (Method for detecting a defect with a phase difference smaller than that of a normal part) In one embodiment, the phase difference (Rd) of the defective part of the first λ / 4 plate is smaller than the phase difference (Rp) of the normal part of the first λ / 4 plate; when the phase difference (Rp) of the normal part of the first λ / 4 plate, the phase difference (Rd) of the defective part of the first λ / 4 plate, and the phase difference (Rf) of the second λ / 4 plate have the relationship of |Rp - Rf| < |Rd - Rf|, the defect of the first λ / 4 plate is detected in the above state B (that is, state B-1 or state B-2). In such an embodiment, it is preferable to increase the phase difference (Rf) of the second λ / 4 plate.

[0023] In the above case, that is, when the retardation (Rd) of the defective portion of the first λ / 4 plate is smaller than the retardation (Rp) of the normal portion of the first λ / 4 plate; the retardation (Rp) of the normal portion of the first λ / 4 plate, the retardation (Rd) of the defective portion of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate have the relationship of |Rp - Rf| < |Rd - Rf|, and when the defect detection of the first λ / 4 plate is performed in the above state B, the retardation (Rf) of the second λ / 4 plate is preferably 125 nm or more, more preferably 140 nm or more. The upper limit of the retardation of the second λ / 4 plate is, for example, 175 nm. Also, Rf - Rp is preferably 0 nm or more, more preferably 2 nm or more, still more preferably 4 nm or more. The upper limit of Rf - Rp is, for example, 10 nm.

[0024] In one embodiment, when the retardation (Rd) of the defective portion of the first λ / 4 plate is smaller than the retardation (Rp) of the normal portion of the first λ / 4 plate; and the retardation (Rp) of the normal portion of the first λ / 4 plate, the retardation (Rd) of the defective portion of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate have the relationship of |Rp - Rf| ≥ |Rd - Rf|, the defect detection of the first λ / 4 plate is performed in the above state A. In such an embodiment, it is preferable to reduce the retardation (Rf) of the second λ / 4 plate.

[0025] In the above case, that is, when the retardation (Rd) of the defective portion of the first λ / 4 plate is smaller than the retardation (Rp) of the normal portion of the first λ / 4 plate; and the retardation (Rp) of the normal portion of the first λ / 4 plate, the retardation (Rd) of the defective portion of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate have the relationship of |Rp - Rf| ≥ |Rd - Rf|, and when the defect detection of the first λ / 4 plate is performed in the above state A, the retardation (Rf) of the second λ / 4 plate is preferably 100 nm to 175 nm, more preferably 140 nm to 150 nm. Also, Rp - Rf is preferably 2 nm or more, more preferably 4 nm or more, still more preferably 6 nm or more, and particularly preferably 8 nm or more. The upper limit of Rp - Rf is, for example, 20 nm.

[0026] (Method for detecting a defect having a phase difference larger than the phase difference of the normal part) In one embodiment, the phase difference (Rd) of the defective portion of the first λ / 4 plate is larger than the phase difference (Rp) of the normal portion of the first λ / 4 plate; when the phase difference (Rp) of the normal portion of the first λ / 4 plate, the phase difference (Rd) of the defective portion of the first λ / 4 plate, and the phase difference (Rf) of the second λ / 4 plate satisfy the relationship |Rp - Rf| ≦ |Rd - Rf|, in the above state B (that is, state B-1 or state B-2), the defect of the first λ / 4 plate is detected. In such an embodiment, it is preferable to reduce the phase difference (Rf) of the second λ / 4 plate.

[0027] In the above case, that is, the phase difference (Rd) of the defective portion of the first λ / 4 plate is larger than the phase difference (Rp) of the normal portion of the first λ / 4 plate; the phase difference (Rp) of the normal portion of the first λ / 4 plate, the phase difference (Rd) of the defective portion of the first λ / 4 plate, and the phase difference (Rf) of the second λ / 4 plate satisfy the relationship |Rp - Rf| ≦ |Rd - Rf|, and when the defect of the first λ / 4 plate is detected in the above state B, the phase difference (Rf) of the second λ / 4 plate is preferably 125 nm to 150 nm, more preferably 140 nm to 150 nm. Also, Rp - Rf is preferably 0 nm or more, more preferably 2 nm or more, and even more preferably 4 nm or more. The upper limit of Rp - Rf is, for example, 10 nm.

[0028] In one embodiment, the phase difference (Rd) of the defective portion of the first λ / 4 plate is larger than the phase difference (Rp) of the normal portion of the first λ / 4 plate; when the phase difference (Rp) of the normal portion of the first λ / 4 plate, the phase difference (Rd) of the defective portion of the first λ / 4 plate, and the phase difference (Rf) of the second λ / 4 plate satisfy the relationship |Rp - Rf| > |Rd - Rf|, in the above state A, the defect of the first λ / 4 plate is detected. In such an embodiment, it is preferable to increase the phase difference (Rf) of the second λ / 4 plate.

[0029] In the above case, that is, when the retardation (Rd) of the defective portion of the first λ / 4 plate is greater than the retardation (Rp) of the normal portion of the first λ / 4 plate; the retardation (Rp) of the normal portion of the first λ / 4 plate, the retardation (Rd) of the defective portion of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate have the relationship of |Rp - Rf| > |Rd - Rf|, and in the above state A, when the defective portion of the first λ / 4 plate is detected, the retardation (Rf) of the second λ / 4 plate is preferably 125 nm to 150 nm, more preferably 140 nm to 150 nm. Also, Rf - Rp is preferably -5 nm to 5 nm, more preferably -3 nm to 3 nm, and even more preferably -1 nm to 1 nm.

[0030] B. First polarizer, second polarizer As the above polarizer, any appropriate polarizer can be used. For example, a hydrophilic polymer film such as a polyvinyl alcohol-based film, a partially formalized polyvinyl alcohol-based film, an ethylene-vinyl acetate copolymer-based partially saponified film, etc., to which a dichroic substance such as iodine or a dichroic dye is adsorbed and uniaxially stretched, a polyene-based oriented film such as a dehydrated product of polyvinyl alcohol or a dehydrochlorinated product of polyvinyl chloride, etc. Among these, a polarizer obtained by adsorbing a dichroic substance such as iodine on a polyvinyl alcohol-based film and uniaxially stretching it has a high polarization dichroism ratio and is particularly preferred. The thickness of the polarizer is preferably 0.5 μm to 80 μm.

[0031] A polarizer obtained by adsorbing iodine on a polyvinyl alcohol-based film and uniaxially stretching it is typically produced by immersing polyvinyl alcohol in an aqueous iodine solution for dyeing and stretching it to 3 to 7 times its original length. The stretching may be performed after dyeing, may be performed while dyeing, or may be performed after stretching and then dyeing. In addition to stretching and dyeing, for example, treatments such as swelling, crosslinking, adjustment, washing with water, and drying are performed for production.

[0032] As described above, in one embodiment, the first polarizer and the second polarizer (these may also be collectively referred to as polarizers) are applied as a polarizing plate together with a protective film.

[0033] As the protective film, any appropriate film can be used. Specific examples of the material that is the main component of such a film include cellulose resins such as triacetyl cellulose (TAC), and transparent resins such as (meth)acrylic, polyester, polyvinyl alcohol, polycarbonate, polyamide, polyimide, polyethersulfone, polysulfone, polystyrene, polynorbornene, polyolefin, acetate, etc. Also, thermosetting resins or ultraviolet curable resins such as acrylic, urethane, acrylic urethane, epoxy, silicone, etc. can be mentioned. In addition to these, for example, glassy polymers such as siloxane-based polymers can also be mentioned. Also, the polymer film described in JP-A-2001-343529 (WO01 / 37007) can be used. As the material of this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used. For example, a resin composition having an alternating copolymer composed of isobutene and N-methylmaleimide and an acrylonitrile-styrene copolymer can be mentioned. The polymer film can be, for example, an extruded product of the above resin composition.

[0034] In one embodiment, as the second polarizer, a polarizer having a light transmittance of 42% or more is used. By using such a second polarizer, the detection sensitivity can be improved. The light transmittance of the second polarizer is more preferably 43% or more, and even more preferably 44% or more. Also, 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.

[0035] C. First λ / 4 plate, second λ / 4 plate The first λ / 4 plate and the second λ / 4 plate (these may also be collectively referred to as the λ / 4 plate) can convert linearly polarized light of a certain specific wavelength into circularly polarized light (or circularly polarized light into linearly polarized light).

[0036] The above 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 a refractive index ellipsoid with 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 obtained 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 slow axis direction), ny is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and d (nm) is the thickness of the film. Also, 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.

[0037] (λ / 4 plate composed 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 employed as the liquid crystal material. For example, polymerizable mesogenic compounds described in JP-T-2002-533742 (WO00 / 37585), EP358208 (US5211877), EP66137 (US4388453), WO93 / 22397, EP0261712, DE19504224, DE4408171, GB2280445, etc. can be used. Specific examples of such polymerizable mesogenic compounds include, for example, LC242 (trade name of BASF), E7 (trade name of Merck), and LC-Sillicon-CC3767 (trade name of Wacker-Chem).

[0038] The λ / 4 plate composed of a liquid crystal material can be obtained, for example, by aligning the liquid crystal material and solidifying or curing it while fixing the alignment state. Specifically, it can be formed by applying a liquid crystal composition containing a liquid crystal material onto a long alignment substrate to align the liquid crystal material, and then 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 a direction substantially the same as the alignment treatment direction of the substrate. As a specific example of the method for forming the retardation layer, the formation method described in JP-A-2006-178389 can be mentioned. The thickness of the λ / 4 plate composed of a liquid crystal material is preferably 0.5 μm to 1.8 μm, more preferably 1 μm to 1.6 μm.

[0039] In one embodiment, a thermotropic liquid crystal that exhibits liquid crystallinity upon heating can be used as the liquid crystal material. The thermotropic liquid crystal undergoes phase transitions among a crystal phase, a liquid crystal phase, and an isotropic phase due to a temperature change.

[0040] (λ / 4 plate composed of a stretched film) The λ / 4 plate composed of a stretched film can be obtained, for example, by stretching a polymer film in a predetermined direction.

[0041] As the resin for forming the above polymer film, any suitable resin can be used. Specific examples include resins constituting positive birefringent films such as cycloolefin resins such as polynorbornene, polycarbonate resins, cellulose resins, polyvinyl alcohol resins, and polysulfone resins. Among them, norbornene resins and polycarbonate resins are preferred.

[0042] The above-mentioned polynorbornene refers to a (co)polymer obtained by using a norbornene-based monomer having a norbornene ring as part or all of the starting material (monomer). Examples of the norbornene-based monomer include norbornene, and its alkyl and / or alkylidene substitution products, 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 polar group substitution products such as those with halogen, etc.; dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; dimethanooctahydronaphthalene, its alkyl and / or alkylidene substitution products, and polar group substitution products such as those with halogen, etc., such as 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-1,4,4a,5,6,7,8,8a-octahydronaphthalene, etc.; trimers to tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene, 4,11:5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene, etc.

[0043] Various products of the above-mentioned polynorbornene are commercially available. Specific examples include the products with the trade names "ZEONEX" and "ZEONOR" manufactured by Zeon Corporation, "Arton" manufactured by JSR Corporation, "TOPAS" manufactured by Ticona, and "APEL" manufactured by Mitsui Chemicals, Inc.

[0044] As the above polycarbonate resin, preferably, an aromatic polycarbonate is used. An aromatic polycarbonate can typically be obtained by the reaction of a carbonate precursor and an aromatic dihydric phenol compound. Specific examples of the carbonate precursor include phosgene, bischloroformate of dihydric phenols, diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, dinaphthyl carbonate, and the like. Among these, phosgene and diphenyl carbonate are preferred. Specific examples of the aromatic dihydric phenol compound 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, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, and the like. These may be used alone 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 both 2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

[0045] Examples of stretching methods include, for example, uniaxial stretching in the horizontal direction, fixed-end biaxial stretching, and sequential biaxial stretching. As a specific example of fixed-end biaxial stretching, there is a method of stretching a polymer film in the short side direction (lateral direction) while running it in the longitudinal direction. This method may seemingly be uniaxial stretching in the horizontal direction. Also, diagonal stretching can be employed. By employing diagonal stretching, a long stretched film having an orientation axis (slow axis) at a predetermined angle with respect to the width direction can be obtained. A method of manufacturing a λ / 4 plate by diagonal stretching is described, for example, in JP-A-2013-54338, JP-A-2014-194482, JP-A-2014-238524, JP-A-2014-194484, etc. The descriptions in the said publications are incorporated herein by reference.

[0046] 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.

[0047] In one embodiment, a λ / 4 plate composed of a stretched film (preferably a λ / 4 plate obtained by diagonal stretching) can be used as an alignment substrate when creating a λ / 4 plate composed of the above liquid crystal material.

Examples

[0048] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. The measurement and evaluation methods in the examples are as follows.

[0049] [Reference Example 1] A photopolymerizable liquid crystal compound (BASF's "Paliocolor LC242") showing a nematic liquid crystal phase was dissolved in cyclopentanone to prepare a solution having a solid content concentration of 30% by weight. To this solution, a surfactant (BIG CHEMIE's "BYK-360") and a photopolymerization initiator (IGM Resins' "Omnirad907") were added to prepare a liquid crystalline composition solution. The addition amounts of the leveling agent and the polymerization initiator were 0.01 part by weight and 3 parts by weight, respectively, with respect to 100 parts by weight of the photopolymerizable liquid crystal compound. An obliquely stretched norbornene-based film (ZEONOR film (ZD12) manufactured by Nippon Zeon Co., Ltd., thickness: 23 μm, in-plane retardation: 140 nm) was prepared. On the above-mentioned obliquely stretched norbornene-based film, the above liquid crystalline composition was applied by a bar coater so that the thickness after drying was 1.15 μm, and heated at 100 °C for 3 minutes to orient the liquid crystal. After cooling to room temperature, in a nitrogen atmosphere, ultraviolet rays with an integrated light quantity of 400 mJ / cm 2 were irradiated to perform photocuring, and a homogeneous alignment liquid crystal layer (first λ / 4 plate, in-plane retardation Rp: 150 nm) was obtained on the obliquely stretched norbornene-based film. Also, on the above-mentioned obliquely stretched norbornene-based film, the above liquid crystalline composition was applied by a bar coater so that the thickness after drying was 1.08 μm, and heated at 100 °C for 3 minutes to orient the liquid crystal. After cooling to room temperature, in a nitrogen atmosphere, ultraviolet rays with an integrated light quantity of 400 mJ / cm 2 were irradiated to perform photocuring, and a homogeneous alignment liquid crystal layer (second λ / 4 plate, in-plane retardation Rf: 141 nm) was obtained on the obliquely stretched norbornene-based film. A first polarizing plate including a first polarizer (single transmittance: 45%), the above first λ / 4 plate, the above second λ / 4 plate, and a second polarizing plate including a second polarizer (single transmittance: 45%) were laminated. At this time, the axial directions of the respective layers were set to the following state B-2. State B-2: The absorption axis of the first polarizer and the absorption axis of the second polarizer are orthogonal to each other, and the slow axes of the first λ / 4 plate and the second λ / 4 plate are parallel, the absorption axis of the first polarizer and the slow axis of the first λ / 4 plate are parallel, 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°. A light source and an imaging device were arranged on both sides of the above configuration, and in the first λ / 4 plate, a defect (defect retardation Rd: about 148 nm) having a thickness thinner and a retardation smaller than that of the normal portion was set as a detection target, and a defect inspection by transmission inspection was performed. As a result, a defect having a thickness thinner and a retardation smaller than that of the normal portion was detected as a dark defect.

[0050] [Reference Example 2] Except that the thickness of the first quarter-wave plate was set to 1.12 μm and the thickness of the second quarter-wave plate was set to 1.11 μm, in the same manner as in Reference Example 1, a first polarizer including a first polarizer, the first quarter-wave plate (retardation Rp: 146 nm), the second quarter-wave plate (retardation Rf: 145 nm), and a second polarizer including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (retardation Rd of the defect: about 144 nm). As a result, defects having a thickness thinner and a retardation smaller than those of the normal portion were detected as dark defects.

[0051] [Example 1] Except that it was set to the following State A instead of State B-2, in the same manner as in Reference Example 1, a first polarizer including a first polarizer, the first quarter-wave plate, the second quarter-wave plate, and a second polarizer including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (retardation Rd of the defect: about 148 nm). State A: The absorption axis of the first polarizer and the absorption axis of the second polarizer are parallel, the slow axes of the first quarter-wave plate and the second quarter-wave plate are parallel, the angle formed by the absorption axis of the first polarizer and the slow axis of the first quarter-wave plate is 35° to 55°, and the angle formed by the absorption axis of the second polarizer and the slow axis of the second quarter-wave plate is 35° to 55°. As a result of the above defect inspection, defects having a thickness thinner and a retardation smaller than those of the normal portion, that is, the defects detected as dark defects in Reference Example 1 were detected as bright defects.

[0052] [Example 2] Except that it was set to State A instead of State B-2, in the same manner as in Reference Example 2, a first polarizer including a first polarizer, the first quarter-wave plate, the second quarter-wave plate, and a second polarizer including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (retardation Rd of the defect: about 144 nm). As a result, defects having a thickness thinner and a retardation smaller than those of the normal portion, that is, the defects detected as dark defects in Reference Example 1 were detected as bright defects.

[0053] [Example 3] Except that the thickness of the second λ / 4 plate was set to 1.15 μm, in the same manner as in Reference Example 2, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate (retardation Rf: 150 nm), and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (retardation Rd of the defect: about 144 nm). As a result, defects having a smaller thickness and a smaller retardation than the normal portion, that is, the defects detected as dark defects in Reference Example 1 were detected as bright defects.

[0054] [Example 4] Except that the thickness of the second λ / 4 plate was set to 1.08 μm, in the same manner as in Example 2, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate (retardation Rf: 141 nm), and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (retardation Rd of the defect: about 144 nm). As a result, defects having a smaller thickness and a smaller retardation than the normal portion, that is, the defects detected as dark defects in Reference Example 1 were detected as brighter bright defects than in Example 2.

[0055] The configurations and inspection results of Reference Examples 1 and 2 and Examples 1 to 4 are summarized in Table 1.

[0056]

Table 1

[0057] As is clear from Table 1, according to the present invention, it is possible to inspect the λ / 4 plate by using bright spots as defects. Further, as is clear from Example 3, in the detection of defects having a smaller retardation than the retardation of the normal portion, when the retardation Rp of the normal portion of the first λ / 4 plate, the retardation Rd of the defective portion of the first λ / 4 plate, and the retardation Rf of the second λ / 4 plate have a relationship of |Rp - Rf| < |Rd - Rf|, it is preferable that the first polarizer, the first λ / 4 plate, the second λ / 4 plate, and the second polarizer are arranged in the "State B". Also, as is clear from Examples 1, 2, and 4, in the detection of defects with a phase difference smaller than that of the normal part, when the relationship is |Rp - Rf| ≧ |Rd - Rf|, the first polarizer, the first λ / 4 plate, the second λ / 4 plate, and the second polarizer are preferably arranged in the "State A". Further, in such a case, as is clear from the comparison between Examples 2 and 4, it is preferable to reduce the phase difference Rf of the second λ / 4 plate.

[0058] [Reference Example 3] Except for setting it to State A instead of State B-2 and setting the thickness of the first λ / 4 plate to 1.08 μm, in the same manner as in Reference Example 1, a first polarizing plate including a first polarizer, the first λ / 4 plate (phase difference Rp: 141 nm), the second λ / 4 plate, and a second polarizing plate including a second polarizer were arranged in this order. A light source and an imaging device were arranged on both sides of the above configuration, and a defect inspection by transmission inspection was performed with a defect having a greater thickness and a greater phase difference than the normal part (phase difference Rd of the defect: about 143 nm) as the detection target. As a result, a defect having a greater thickness and a greater phase difference than the normal part was detected as a dark defect.

[0059] [Reference Example 4] Except for setting the thickness of the first λ / 4 plate to 1.12 μm and the thickness of the second λ / 4 plate to 1.11 μm, in the same manner as in Reference Example 3, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate, and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 3 was performed (phase difference Rd of the defect: about 148 nm). As a result, a defect having a greater thickness and a greater phase difference than the normal part was detected as a dark defect.

[0060] [Example 5] Except for setting it to State B-2 instead of State A, in the same manner as in Reference Example 3, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate, and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 3 was performed (phase difference Rd of the defect: about 143 nm). As a result of the above defect inspection, a defect having a greater thickness and a greater phase difference than the normal portion, that is, the defect detected as a dark defect in Reference Example 3, was detected as a bright defect.

[0061] [Example 6] Except for setting the state to State B-2 instead of State A, in the same manner as in Reference Example 4, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate, and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 3 was performed (phase difference Rd of the defect: about 148 nm). As a result of the above defect inspection, a defect having a greater thickness and a greater phase difference than the normal portion, that is, the defect detected as a dark defect in Reference Example 4, was detected as a bright defect.

[0062] [Example 7] Except for setting the thickness of the second λ / 4 plate to 1.08 μm, in the same manner as in Example 6, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate (phase difference Rf: 141 nm), and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (phase difference Rd of the defect: about 148 nm). As a result of the above defect inspection, a defect having a greater thickness and a greater phase difference than the normal portion, that is, the defect detected as a dark defect in Reference Example 4, was detected as a bright defect.

[0063] [Example 8] Except for setting the thickness of the second λ / 4 plate to 1.15 μm, in the same manner as in Reference Example 4, a first polarizing plate including a first polarizer, the first λ / 4 plate, the second λ / 4 plate (phase difference Rf: 150 nm), and a second polarizing plate including a second polarizer were arranged in this order, and the same defect inspection as in Reference Example 1 was performed (phase difference Rd of the defect: about 148 nm). As a result of the above defect inspection, a defect having a greater thickness and a greater phase difference than the normal portion, that is, the defect detected as a dark defect in Reference Example 4, was detected as a bright defect.

[0064] The configurations and inspection results of Reference Examples 3 and 4, and Examples 5 to 8 are summarized in Table 2.

[0065]

Table 2

[0066] As is clear from Table 2, according to the present invention, inspection of the λ / 4 plate can be performed with bright spots regarded as defects. Also, as is clear from Examples 5 to 7, in the detection of defects having a larger phase difference than that of the normal part, when the relationship is |Rp - Rf| ≦ |Rd - Rf|, the first polarizer, the first λ / 4 plate, the second λ / 4 plate, and the second polarizer are preferably arranged in the "state B". Further, in such a case, as is clear from the comparison between Examples 6 and 7, it is preferable to reduce the phase difference Rf of the second λ / 4 plate. Also, as is clear from Example 8, in the detection of defects having a larger phase difference than that of the normal part, when the relationship is |Rp - Rf| > |Rd - Rf|, the first polarizer, the first λ / 4 plate, the second λ / 4 plate, and the second polarizer are preferably arranged in the "state A".

Explanation of Reference Signs

[0067] 11 First polarizer 12 Second polarizer 21 First λ / 4 plate 22 Second λ / 4 plate 30 Isotropic substrate

Claims

1. Arranging a first polarizer, a first λ / 4 plate, a second λ / 4 plate, and a second polarizer in this order, and including the steps of making light incident from the surface on the first polarizer side, observing the appearance of the surface on the second polarizer side, and detecting the defect of the first λ / 4 plate as an obvious defect; A method for inspecting defects of a λ / 4 plate, including adjusting the retardation of the second λ / 4 plate according to the retardation of the defective part of the first λ / 4 plate, and switching among the following state A, state B-1, and state B-2; State A: The absorption axis of the first polarizer is parallel to the absorption axis of the second polarizer, the slow axis of the first λ / 4 plate is parallel to the slow axis of the second λ / 4 plate, 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°; State B-1: The absorption axis of the first polarizer is orthogonal to the absorption axis of the second polarizer, the slow axis of the first λ / 4 plate is orthogonal to the slow axis of the second λ / 4 plate, 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°; State B-2: The absorption axis of the first polarizer is orthogonal to the absorption axis of the second polarizer, and the slow axis of the first λ / 4 plate is parallel to the slow axis of the second λ / 4 plate. The absorption axis of the first polarizer is parallel to the slow axis of the first λ / 4 plate, and the absorption axis of the second polarizer is orthogonal to the slow axis of the second λ / 4 plate.

2. When the retardation of the defective part of the first λ / 4 plate is smaller than the retardation of the normal part of the first λ / 4 plate; and when the retardation (Rp) of the normal part of the first λ / 4 plate, the retardation (Rd) of the defective part of the first λ / 4 plate, and the retardation (Rf) of the second λ / 4 plate have the relationship of |Rp - Rf| < |Rd - Rf|, the defect detection of the first λ / 4 plate is performed in state B-1 or state B-2. The method for inspecting defects of a λ / 4 plate according to Claim 1.

3. The method for inspecting defects of a λ / 4 plate according to Claim 2, wherein Rf - Rp is 0 nm or more.

4. The retardation of the defective portion of the first quarter-wave plate is smaller than the retardation of the normal portion of the first quarter-wave plate; when the retardation (Rp) of the normal portion of the first quarter-wave plate, the retardation (Rd) of the defective portion of the first quarter-wave plate, and the retardation (Rf) of the second quarter-wave plate satisfy the relationship |Rp - Rf| ≥ |Rd - Rf|, in the state A, the defect detection of the first quarter-wave plate is performed. The method for inspecting defects of a quarter-wave plate according to claim 1.

5. The method for inspecting defects of a quarter-wave plate according to claim 4, wherein Rp - Rf is 2 nm or more.

6. The retardation of the defective portion of the first quarter-wave plate is larger than the retardation of the normal portion of the first quarter-wave plate; when the retardation (Rp) of the normal portion of the first quarter-wave plate, the retardation (Rd) of the defective portion of the first quarter-wave plate, and the retardation (Rf) of the second quarter-wave plate satisfy the relationship |Rp - Rf| ≤ |Rd - Rf|, in the state B-1 or state B-2, the defect detection of the first quarter-wave plate is performed. The method for inspecting defects of a quarter-wave plate according to claim 1.

7. The method for inspecting defects of a quarter-wave plate according to claim 6, wherein Rp - Rf is 0 nm or more.

8. The retardation of the defective portion of the first quarter-wave plate is larger than the retardation of the normal portion of the first quarter-wave plate; when the retardation (Rp) of the normal portion of the first quarter-wave plate, the retardation (Rd) of the defective portion of the first quarter-wave plate, and the retardation (Rf) of the second quarter-wave plate satisfy the relationship |Rp - Rf| > |Rd - Rf|, in the state A, the defect detection of the first quarter-wave plate is performed. The method for inspecting defects of a quarter-wave plate according to claim 1.

9. The method for inspecting defects of a quarter-wave plate according to claim 8, wherein Rf - Rp is -5 nm to 5 nm.

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