Defect inspection method and defect inspection device

Abstract

To provide a defect inspection method and a defect inspection device that, when taking an optical film in which a protect film and a release film are laminated on a linearly polarizing plate as an object to be inspected, can detect unevenness of optical characteristics of the linearly polarizing plate.SOLUTION: An optical film has a release film, a linearly polarizing plate, and a protect film in this order and are laminated such that an angle formed by an orientation axis of the protect film and an absorption axis of the linearly polarizing plate falls within a range of 0° ± 30°. A defect inspection method has an arrangement step of arranging, along an optical axis, a first filter having a first polarizer, a phase difference compensation plate, an optical film, and a second filter having a second polarizer in this order such that, in a direction in which a surface of the optical film on the release film side faces the phase difference compensation plate, (b1) an angle formed by an absorption axis of the second polarizer and the orientation axis of the protect film falls within a range of 90° ± 5°.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a defect inspection method and apparatus for a linear polarizing plate in which an optical film is used as an inspection object. [Background technology]

[0002] A polarizing plate used in a display device such as a liquid crystal display device or an organic EL display device is generally configured by sandwiching a polarizer between two protective films. In order to attach the polarizing plate to a display device, an adhesive layer is laminated on one protective film, and a protective film may be laminated on the other protective film to prevent scratches on the surface of the protective film during distribution. A release film is usually laminated on the adhesive layer. Specific examples of polarizers include a PVA-based polarizing film in which a dichroic dye such as iodine or a dichroic dye is adsorbed and aligned on a uniaxially stretched polyvinyl alcohol (PVA-based) resin film, and a polarizer (hereinafter also referred to as a "liquid crystal polarizer") made of a liquid crystal cured layer containing a polymer of a polymerizable liquid crystal compound and a dichroic dye. A liquid crystal polarizer is usually formed by applying a composition containing a polymerizable liquid crystal compound on a substrate film and curing it, and has the advantage of being able to produce a thin polarizer. As described later, such a PVA-based polarizing film and liquid crystal polarizer have the effect of passing linearly polarized light of a specific vibration plane, and are called "linear polarizers". Moreover, a linear polarizer having a protective film on one or both sides thereof is generally called a "linear polarizing plate."

[0003] Polarizing plates and polarizers can have defects during their manufacturing process. For example, defects such as foreign matter being mixed in between the polarizer and the protective film or air bubbles remaining can occur. In addition, liquid crystal polarizers can have uneven optical properties due to uneven coating during manufacturing.

[0004] Therefore, before the polarizing plate is incorporated into the display device, an inspection is performed to detect defects in the polarizing plate. As shown in JP-A-9-229817 (Patent Document 1), this defect inspection involves providing a polarizing filter between the polarizing plate to be inspected and a light source, and then rotating the polarizing plate or the polarizing filter in a planar direction to set the directions of their respective polarization axes in a specific relationship. When the directions of the polarization axes are perpendicular to each other (i.e., when they are arranged to form a crossed Nicol), linearly polarized light that has passed through the polarizing filter does not pass through the polarizing plate. However, if a defect exists in the polarizing plate, linearly polarized light passes through that portion, and the presence of the defect is revealed by detecting the light.

[0005] On the other hand, when the polarization axes of the polarizing plate and the polarizing filter are parallel to each other, the linearly polarized light that passes through the polarizing filter is transmitted through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light is blocked at that location, and the presence of the defect is revealed by not detecting the light. The presence or absence of defects in the polarizing plate can be inspected by an inspector visually detecting the light that has passed through the polarizing plate, or by automatically detecting it using image analysis processing values ​​that combine a CCD camera and an image processing device. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-229817 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the method described in Patent Document 1, it is possible to detect local defects whose optical properties differ greatly from those of the surrounding area, such as foreign matter or air bubbles, but it is difficult to detect unevenness in the optical properties.

[0008] In addition, when the protective film and the release film are laminated, it is difficult to detect defects in the polarizing plate due to the influence of birefringence of the protective film and the release film.

[0009] The present invention aims to provide a defect inspection method and defect inspection device capable of detecting unevenness in the optical characteristics of a linear polarizing plate when the object to be inspected is an optical film in which a protective film and a release film are laminated to a linear polarizing plate. [Means for solving the problem]

[0010] The present invention provides the following defect inspection method and defect inspection apparatus. [1] A method for inspecting a defect in a linear polarizing plate, comprising the steps of: The optical film is The polarizing plate has a release film, the linear polarizing plate, and a protective film in this order, the protective film has an alignment axis and is laminated such that the angle between the alignment axis and the absorption axis of the linear polarizer is in the range of 0°±30°; The defect inspection method includes: a step of arranging a first filter having a first polarizer, a phase difference compensation plate, the optical film, and a second filter having a second polarizer in this order along an optical axis, with the optical film facing the release film in a direction opposite to the phase difference compensation plate; a detection step of irradiating light along the optical axis from one of the first filter side and the second filter side and detecting light emitted from the other side; a determination step of determining a defect in the optical film based on a detection result in the detection step, In the placing step, Condition a and condition b1 below: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b1) an angle between the absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 90°±5°; The arrangement is made so as to satisfy the following: In the detection step, The phase difference compensating plate compensates for birefringence of the release film.

[0011] [2] A method for inspecting a defect in a linear polarizing plate, comprising the steps of: The optical film is The polarizing plate has a release film, the linear polarizing plate, and a protective film in this order, the protective film has an alignment axis and is laminated such that the angle between the alignment axis and the absorption axis of the linear polarizer is within a range of 90°±30°; The defect inspection method includes: a step of arranging a first filter having a first polarizer, a phase difference compensation plate, the optical film, and a second filter having a second polarizer in this order along an optical axis, with the optical film facing the release film in a direction opposite to the phase difference compensation plate; a detection step of irradiating light along the optical axis from one of the first filter side and the second filter side and detecting light emitted from the other side; a determination step of determining a defect in the optical film based on a detection result in the detection step, The placing step includes: Condition a and condition b2 below: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b2) an angle between the absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 0°±5°; The arrangement is made so as to satisfy the following: In the detection step, The phase difference compensating plate compensates for birefringence of the release film.

[0012] [3] The defect inspection method according to [1] or [2], wherein the release film is made of a polyethylene terephthalate resin. [4] The defect inspection method according to any one of [1] to [3], wherein the protective film is made of a polyethylene terephthalate resin. [5] The defect inspection method according to any one of [1] to [4], wherein the linear polarizing plate has a polarizer containing a cured product of a polymerizable liquid crystal compound. [6] The optical film further includes a λ / 4 retardation layer between the linear polarizer and the release film, The defect inspection method according to any one of [1] to [5], wherein in the positioning step, a λ / 4 retardation plate is positioned between the first filter and the optical film.

[0013] [7] A defect inspection apparatus for a linear polarizing plate, the apparatus comprising: The optical film is The polarizing plate has a release film, the linear polarizing plate, and a protective film in this order, the protective film has an alignment axis and is laminated such that the angle between the alignment axis and the absorption axis of the linear polarizer is in the range of 0°±30°; The defect inspection device includes: a first filter having a first polarizer, a retardation compensation plate capable of compensating for birefringence of the release film, and a second filter having a second polarizer, in this order along an optical axis, and further comprising a light source capable of irradiating light along the optical axis from the first filter side or the second filter side; a defect inspection is performed after a positioning step in which the optical film is positioned such that the surface on the release film side faces the retardation compensation plate; In the placing step, Condition a and condition b1 below: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b1) an angle between the absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 90°±5°; A defect inspection device arranged to satisfy the above.

[0014] [8] A defect inspection apparatus for a linear polarizing plate, the apparatus comprising: The optical film is The polarizing plate has a release film, the linear polarizing plate, and a protective film in this order, the protective film has an alignment axis and is laminated such that the angle between the alignment axis and the absorption axis of the linear polarizer is within a range of 90°±30°; The defect inspection device includes: a first filter having a first polarizer, a retardation compensation plate capable of compensating for birefringence of the release film, and a second filter having a second polarizer, in this order along an optical axis, and further comprising a light source capable of irradiating light along the optical axis from the first filter side or the second filter side; a defect inspection is performed after a positioning step in which the optical film is positioned such that the surface on the release film side faces the retardation compensation plate; In the placing step, Condition a and condition b2 below: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b2) an angle between the absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 0°±5°; A defect inspection device arranged to satisfy the above. Effect of the Invention

[0015] According to the defect inspection method and defect inspection apparatus of the present invention, when the object to be inspected is an optical film having a protective film and a release film laminated on each side of a linear polarizing plate, unevenness in the optical properties of the linear polarizing plate can be detected. [Brief description of the drawings]

[0016] [Figure 1]1 is a cross-sectional view that illustrates an optical film that is an example of an object to be inspected in this embodiment. [Diagram 2] 1 is a schematic diagram of a defect inspection apparatus according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing an example of a defective area in an optical film. [Figure 4] 1 is a cross-sectional view that typically shows an optical film that is an example of an object to be inspected in a first application example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention relates to a defect inspection method and apparatus for a linear polarizing plate, the defect inspection method and apparatus being configured to inspect an optical film having a linear polarizing plate as an object to be inspected. Examples of the object to be inspected in the defect inspection method and apparatus of the present invention include optical film A and optical film B. Optical film A has a release film, the linear polarizing plate, and a protective film in that order, and the protective film has an alignment axis and is laminated so that the angle between the alignment axis and the absorption axis of the linear polarizing plate is in the range of 0°±30°. Optical film B has a release film, the linear polarizing plate, and a protective film, in that order, and the protective film has an alignment axis and is laminated so that the angle between the alignment axis and the absorption axis of the linear polarizing plate is in the range of 90°±30°.

[0018] A defect inspection method in which optical film A is inspected (hereinafter referred to as "defect inspection method A") is a step of arranging a first filter having a first polarizer, a phase difference compensation plate, the optical film, and a second filter having a second polarizer in this order along an optical axis, with the optical film facing the release film in a direction opposite to the phase difference compensation plate; a detection step of irradiating light along the optical axis from one of the first filter side and the second filter side and detecting light emitted from the other side; a determination step of determining a defect in the optical film based on a detection result in the detection step, In the placing step, Condition a and condition b1 below: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b1) an angle between the absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 90°±5°; The arrangement is made so as to satisfy the following: In the detection step, The retardation compensation plate compensates for the birefringence of the release film.

[0019] A defect inspection method in which optical film B is the object to be inspected (hereinafter referred to as "defect inspection method B") differs from defect inspection method A only in that, in the arrangement step, the optical film B is arranged so as to satisfy the following condition b2 instead of the above condition b1. (b2) The angle between the absorption axis of the second polarizer and the alignment axis of the protective film is within a range of 90°±5°.

[0020] The defect inspection apparatus for inspecting optical film A as an object to be inspected can be used in defect inspection method A, a first filter having a first polarizer, a retardation compensation plate capable of compensating for birefringence of the release film, and a second filter having a second polarizer, in this order along an optical axis, and further comprising a light source capable of irradiating light along the optical axis from the first filter side or the second filter side; a defect inspection is performed after a positioning step in which the optical film is positioned such that the surface on the release film side faces the retardation compensation plate; In the placing step, Condition a and condition b1 below: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b1) an angle between the absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 90°±5°; are arranged so as to satisfy

[0021] A defect inspection apparatus in which optical film B is the object to be inspected can be used in defect inspection method B, and differs from defect inspection apparatus B only in that, in the placement step, the optical film B is placed so as to satisfy the following condition b2 instead of the above condition b1. (b2) The angle between the absorption axis of the second polarizer and the alignment axis of the protective film is within a range of 90°±5°.

[0022] Hereinafter, an embodiment of a defect inspection apparatus and a defect inspection method of the present invention will be described with reference to the drawings. The same elements are given the same reference numerals, and duplicated explanations will be omitted. The dimensional ratios in the drawings do not necessarily match those in the description.

[0023] A defect inspection apparatus and a defect inspection method according to an embodiment of the present invention will be described.

[0024] [Optical film] The optical films A and B, which are the objects to be inspected in this embodiment, will now be described. Fig. 1 is a cross-sectional view that typically shows an optical film 100, which is an example of the optical films A and B. As shown in Fig. 1, the layer structure of the optical film 100 is a protection film 141 / linear polarizing plate 110 [first protection film 111 / adhesive layer 114 / polarizer 112 / adhesive layer 114 / second protection film 113] / adhesive layer 132 / release film 133.

[0025] (Polarizer) The polarizer 112 may be an absorptive polarizer that absorbs linearly polarized light having a vibration plane parallel to its absorption axis and transmits linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). Representative polarizers include a liquid crystal polarizer containing a cured product of a polymerizable liquid crystal compound, a polarizing film in which a dichroic dye is adsorbed and aligned on a uniaxially stretched polyvinyl alcohol-based resin film, and the like.

[0026] A typical method for producing a liquid crystal polarizer will be briefly described. First, a suitable support is prepared. Then, an alignment film is formed on the surface of the support. Then, a liquid composition containing a liquid composition containing a polymerizable liquid crystal compound and a dichroic dye is applied onto the alignment film and dried to form a coating layer containing a polymerizable liquid crystal compound on the alignment film. Then, the coating layer is polymerized and cured by light irradiation to obtain a liquid crystal polarizer on the support. If a transparent resin film is used as the support, a polarizer can be produced using the transparent resin film as a protective film.

[0027] The liquid crystal polarizer may be, for example, one described in JP 2016-170368 A. The dichroic dye may have absorption in the wavelength range of 380 to 800 nm, and it is preferable to use an organic dye. The dichroic dye may, for example, be an azo compound. The liquid crystal compound is a liquid crystal compound that can be polymerized while remaining aligned, and can have a polymerizable group in the molecule. In addition, as described in WO2011 / 024891, a polarizer may be formed from a dichroic dye having liquid crystallinity. Note that after polymerization (after the formation of a polarizer made of a liquid crystal cured layer), the liquid crystal compound no longer needs to exhibit liquid crystallinity.

[0028] The thickness of the liquid crystal polarizer is, for example, 0.2 μm to 10 μm. The liquid crystal polarizer may have uneven optical properties due to uneven application of the liquid composition during the manufacturing process. The defect inspection method and defect inspection device of the present embodiment can detect such uneven optical properties.

[0029] Next, the PVA-based polarizing film will be briefly described. The PVA-based polarizing film can be produced by a method including, for example, a step of uniaxially stretching a PVA-based resin film, a step of dyeing the PVA-based resin film with a dichroic dye to adsorb the dichroic dye (dyeing process), a step of treating the PVA-based resin film with the adsorbed dichroic dye with a crosslinking liquid such as an aqueous solution of boric acid (crosslinking process), and a step of washing with water after the treatment with the crosslinking liquid (washing process).

[0030] As the PVA-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of the polyvinyl acetate-based resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers that can be copolymerized with vinyl acetate. Examples of other monomers that can be copolymerized with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

[0031] In this specification, "(meth)acrylic" means at least one selected from acrylic and methacrylic. The same applies to "(meth)acryloyl", "(meth)acrylate", etc.

[0032] The saponification degree of the PVA resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can be used. The average polymerization degree of the PVA resin is usually 1000 to 10000, preferably 1500 to 5000. The average polymerization degree of the PVA resin can be determined in accordance with JIS K 6726.

[0033] Such a PVA-based resin is used as a raw film (PVA-based resin film) for manufacturing a polarizer. The method for forming a PVA-based resin film is not particularly limited, and a known method is used. The thickness of the PVA-based resin film is not particularly limited, but in order to make the thickness of the PVA-based polarizing film 15 μm or less, it is preferable to use one having a thickness of 5 to 35 μm. More preferably, it is 20 μm or less. The thickness of such a PVA-based resin film can be selected so that the PVA-based polarizing film finally obtained has a desired thickness.

[0034] The uniaxial stretching of the PVA-based resin film may be performed before, simultaneously with, or after the dyeing treatment with a dichroic dye. When the uniaxial stretching is performed after the dyeing treatment, the uniaxial stretching may be performed before or during the crosslinking treatment. Moreover, the uniaxial stretching may be performed multiple times at the stages of these multiple treatments.

[0035] In the uniaxial stretching, when a long PVA-based resin film is used, for example, the PVA-based resin film may be stretched uniaxially between rolls by varying the peripheral speed of the rolls, or may be stretched uniaxially using a heated roll. The uniaxial stretching may be dry stretching in which stretching is performed in the atmosphere, or wet stretching in which stretching is performed in a state in which the PVA-based resin film is swollen using a solvent or water. The stretching ratio is usually 3 to 8 times. When the PVA-based resin film is stretched by multiple uniaxial stretchings, the stretching ratio is usually set to 3 to 8 times the original length. The stretching ratio can also be selected so that the PVA-based polarizing film finally obtained has a desired thickness.

[0036] A typical method for dyeing a PVA-based resin film with a dichroic dye (dyeing process) is to immerse the PVA-based resin film in an aqueous solution containing the dichroic dye. Iodine or a dichroic organic dye is used as the dichroic dye. It is preferable to immerse the PVA-based resin film in water before the dyeing process.

[0037] As a crosslinking treatment after dyeing with a dichroic dye, a method of immersing the dyed PVA resin film in an aqueous solution containing boric acid is usually adopted. When iodine is used as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide.

[0038] Thus, a PVA-based polarizing film is obtained. The thickness of the PVA-based polarizing film is preferably thinner, similar to the liquid crystal polarizer, and is preferably 15 μm or less, more preferably 13 μm or less, further preferably 10 μm or less, and particularly preferably 8 μm or less. The thickness of the polarizing film is usually 2 μm or more, and preferably 3 μm or more.

[0039] The linear polarizer can be used alone as a linear polarizing plate, or, as described above, can be generally used as a linear polarizing plate by laminating a protective film on one or both sides of the linear polarizer. In this specification, the absorption axis of the linear polarizing plate is assumed to coincide with the absorption axis of the polarizer 112.

[0040] (Protective film) The protective films (for example, first protective film 111 and second protective film 113) laminated on one or both sides of polarizer 112 are made of a film formed from a thermoplastic resin.

[0041] Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins such as nylon and aromatic polyamide, polyimide resins, polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymers, cyclic polyolefin resins having cyclo- and norbornene structures (also called norbornene resins), (meth)acrylic resins, polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof. When protective films are laminated on both sides of the polarizer, the resin compositions of the two protective films may be the same or different.

[0042] The thickness of the protective film is preferably 3 μm or more, more preferably 5 μm or more. The thickness of the protective film is usually 100 μm or less. The thickness of this protective film is also preferably thinner, for example, 70 μm or less, more preferably 50 μm or less, and more preferably 30 μm or less. The above upper limit and lower limit can be combined arbitrarily.

[0043] The protective film is attached to the display device together with the polarizer 112 as a component of the linear polarizing plate, and therefore requires strict management of the retardation value, etc. Typically, a protective film having an extremely small retardation value is used.

[0044] (adhesive layer) The adhesive layer (e.g., adhesive layer 114, 124) can be formed by curing a curable component in the adhesive. The adhesive for forming the adhesive layer is an adhesive other than a pressure-sensitive adhesive (adhesive), and examples thereof include water-based adhesives such as polyvinyl alcohol adhesives and active energy ray curable adhesives such as ultraviolet curable adhesives. The thickness of the adhesive layer is selected according to the type of adhesive, and is, for example, 0.05 μm or more, may be 0.1 μm or more, may be 0.5 μm or more, may be 1 μm or more, may be 3 μm or more, and is usually 20 μm or less, may be 15 μm or less, may be 10 μm or less, or may be 8 μm or less.

[0045] (Protection film) Protective film 141 is provided removably on linear polarizer 110 and is used to cover and protect the surface of the linear polarizer. An example of a protective film is one that is composed of a base film formed using a resin and an adhesive layer laminated thereon.

[0046] The protective film is peeled off together with the adhesive layer of the protective film after the optical film is attached to a display device or other optical components, and the peeled protective film is usually discarded. Therefore, unlike the protective film, strict management of the retardation value is not required. The defect inspection method of this embodiment (defect inspection methods A and B) can detect defects in the linear polarizing plate by eliminating the influence of the retardation of the protective film, even when the optical film to be inspected is an optical film provided with a protective film that does not require strict management of the retardation value.

[0047] The protective film is usually made of resin, and the resin forming the protective film is not particularly specified, but may be polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, polyarene resin, etc., among which PET resin is preferably used. A film made of PET resin has an advantage that it is versatile as a protective film and is inexpensive. On the other hand, as described above, an inexpensive PET resin film does not require strict management of the retardation value. Therefore, for example, the retardation value varies depending on the product lot. In addition, even if the same PET resin film is used, there may be variations in the in-plane retardation value (in-plane retardation value) and the orientation axis.

[0048] In order to accurately detect the presence or absence of defects by the inspection method of this embodiment, the variation in the orientation axis of the protective film is preferably 60° or less, and more preferably 50° or less. The variation in the orientation axis of the protective film is defined as the maximum value of the angle between different orientation axes.

[0049] In this specification, the method for determining the in-plane retardation value Re(550) of the protective film at a wavelength of 550 nm will be described. A piece of 40 mm x 40 mm in size is cut out so that the center of the entire protective film is the center (e.g., cut out from a long film using an appropriate cutting tool). The Re(550) of this piece is measured three times, and the average value of Re(550) is obtained. The Re(550) of the piece can be measured using a retardation measuring device KORBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.) at a measurement temperature of room temperature (about 25°C).

[0050] The in-plane retardation value Re(550) of the protective film 141 is, for example, 1000 nm to 2500 nm. This means that the in-plane retardation value Re(550) is 1000 nm to 2500 nm for any arbitrary piece of the protective film 141. In the protective film 141, the in-plane retardation value Re(550) usually differs depending on the piece at the time of measurement.

[0051] In the optical film 100, the polarizer 112 and the protective film 141 are laminated so that the angle between the absorption axis of the linear polarizer 110 and the orientation axis of the protective film 141 is 0°±30° (optical film A) or 90°±30° (optical film B). In the optical film 100, the angle between the absorption axis of the polarizer 112 and the orientation axis of the protective film is within the above range, so that the variation in the influence of the birefringence of the protective film 141 on the light that is transmitted continuously through the polarizer 112 and the protective film 141 can be reduced. In other words, it is possible to suppress a decrease in the accuracy of defect detection due to the birefringence of the protective film 141.

[0052] (Release film) Release film 133 is provided releasably on adhesive layer 132 and is used to cover and protect the surface of adhesive layer 132. An example of the release film is a film in which a base film formed using a resin has been subjected to a release treatment. The release treatment applied to the base film may be a known release treatment, but a method in which a release agent such as a fluorine compound or a silicone compound is coated on the base film is preferred.

[0053] The release film 133 is peeled off from the adhesive layer 132 when the display device is attached, and the peeled off release film is usually discarded. Therefore, unlike the protective film, strict management of the retardation value is not required.

[0054] The resin constituting the base film is not particularly limited, but examples thereof include polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, polyarene resin, etc., among which PET resin is preferably used. A film made of PET resin has the advantage that it is versatile as a release film and is inexpensive. On the other hand, as described above, an inexpensive PET resin film does not require strict management of the retardation value. Therefore, for example, the retardation value may vary for each product lot. In addition, even if it is the same PET resin film, there may be variations in the retardation value (in-plane retardation value) and the alignment axis in the plane. Even in an optical film in which such an inexpensive PET resin film is laminated as a release film, the presence or absence of defects can be accurately detected by the inspection method of this embodiment. The variation in the alignment axis in the release film is not particularly limited, and for example, one having an angle of 135° or less can be used. Since the release film 133 is usually removed and discarded during the manufacturing process, strict management of the retardation value is not required as with the protective film.

[0055] In this specification, the method for determining the in-plane retardation value Re(550) of the release film at a wavelength of 550 nm is the same as the method for determining the in-plane retardation value Re(550) of the protect film at a wavelength of 550 nm. The in-plane retardation value Re(550) of the release film 133 is, for example, 1000 nm to 2500 nm.

[0056] [Defect inspection device and defect inspection method] FIG. 2 is a schematic diagram of a defect inspection device according to the present embodiment. As shown in FIG. 2, the defect inspection device 1 detects defects in a linear polarizing plate 110 included in an optical film 100 as an object to be inspected. Examples of defects in the linear polarizing plate 110 that can be detected by the defect inspection device 1 include unevenness in the optical characteristics of the linear polarizing plate 110 and local defects. In the linear polarizing plate 110, when the polarizer 112 is a liquid crystal polarizer, the linear polarizing plate 110 may have unevenness in the optical characteristics due to uneven coating during the manufacturing process. In addition, if air bubbles or foreign matter are mixed in or unevenness occurs during the manufacturing process of the linear polarizing plate 110, local defects will occur.

[0057] In the defect inspection device 1, a first filter 3 having a first polarizer, a phase difference compensation plate 4, and a second filter 5 having a second polarizer are arranged in this order along an optical axis 9. The defect inspection device 1 has a light source 2 capable of irradiating light along the optical axis 9 from the first filter 3 side or the second filter 5 side. In FIG. 2, the light source 2 is arranged at a position where it can irradiate light from the first filter 3 side. In the following, a form in which the light source 2 irradiates light from the first filter 3 side will be described in detail, but defects can also be detected in the same manner in which the light source 2 irradiates light from the second filter 5 side. The defect inspection device 1 has a detection unit 6 arranged at a position where the light irradiated from the light source 2 is incident after passing through each member.

[0058] The light source 2 is not limited as long as it is unpolarized and can output light that does not affect the composition and properties of the optical film 100. The light source 2 is, for example, a metal halide lamp, a halogen transmission light, or a fluorescent lamp.

[0059] In the detection unit 6, the defect may be judged by detecting (observing) the detection light with the naked eye, or the defect may be judged based on the captured image of the detection light. Examples of the imaging means include a CCD camera. In the following, unless otherwise specified, the form in which the detection light is detected with the naked eye will be described. The same applies to other embodiments.

[0060] In the defect inspection apparatus 1, a positioning step is first performed. In the positioning step, the optical film 100 to be inspected is positioned between the retardation compensator 4 and the second polarizer 5 with the surface on the release film 133 side facing the retardation compensator 4. In the positioning step, the positions of the first filter 3, the optical film 100, and the second filter 5 are adjusted so as to satisfy the following condition a, and also to satisfy the following condition b1 when the optical film 100 is optical film A, or to satisfy the following condition b2 when the optical film 100 is optical film B. (a) The angle θ1 between the absorption axis of the first polarizer of the first filter 3 and the absorption axis of the linear polarizer 110 is within the range of 90°±5°. (b1) The angle θ2 between the absorption axis of the second polarizer of the second filter 5 and the alignment axis of the protective film 141 is within the range of 90°±5°. (b2) The angle θ2 between the absorption axis of the second polarizer of the second filter 5 and the alignment axis of the protective film 141 is within the range of 0°±5°.

[0061] Hereinafter, the absorption axis of the linear polarizer 110 will also be referred to as the "absorption axis PA0", the absorption axis of the first polarizer of the first filter 3 will also be referred to as the "absorption axis PA1", and the absorption axis of the second polarizer of the second filter 5 will also be referred to as the "absorption axis PA2". Satisfying the above condition b1 or condition b2 also means that the angle between the absorption axis PA2 of the second filter 5 and the absorption axis PA0 of the linear polarizer 110 is within the range of 90°±35°.

[0062] In the above-mentioned arrangement step, the angles θ1 and θ2 are preferably adjusted so that the field of view becomes the darkest within a range that satisfies the above-mentioned conditions. Such adjustments can be made even after the arrangement step by appropriately adjusting the arrangement angles of the first filter 3, the phase difference compensator 4, the optical film 100, and the second filter 5. The defect inspection device 1 may include a movable device (not shown) that can rotate the first filter 3, the phase difference compensator 4, the optical film 100, and the second filter 5 in a direction perpendicular to the optical axis 9.

[0063] In the defect inspection apparatus 1, a detection process is performed after the arrangement process. In the detection process, light is emitted from the light source 2, and passes along the optical axis 9 through the first filter 3, the phase difference compensation plate 4, the optical film 100, and the second filter 5 in this order, and reaches the detection unit 6. In the detection unit 6, a determination process is performed in which a defect in the linear polarizing plate 110 is determined based on the detection result of the light that has reached the detection unit 6.

[0064] The first filter 3 transmits only light having a specific polarization direction (hereinafter also referred to as "first polarized light") from the unpolarized light emitted from the light source 2. Light having a polarization direction perpendicular to the first polarized light is also referred to as "second polarized light."

[0065] The phase difference compensator 4 is provided in advance with a phase difference that cancels the phase difference caused by the birefringence of the release film 133 that is transmitted in the subsequent stage. The light that is incident on the optical film 100 is incident on the linear polarizer 110 in a state in which the effect of the phase difference caused by transmission through the release film 133 is canceled. Since the angle θ1 between the absorption axis PA1 of the first filter 3 that has previously transmitted and the absorption axis PA0 of the linear polarizer 110 satisfies the above condition a, the first polarized light that is incident on the linear polarizer 110 is almost entirely absorbed in areas without defects.

[0066] However, linear polarizer 110 may have a defect region whose absorption axis does not coincide with absorption axis PA0. FIG. 3 shows an example of defect region B in linear polarizer 110, and the absorption axis in defect region B is indicated by double-headed arrows. Defect region B has an absorption axis (hereinafter referred to as "absorption axis PA3") that does not coincide with absorption axis PA0. When the defect in defect region B is unevenness in optical characteristics, it can be assumed that the angle between absorption axis PA3 in defect region B and absorption axis PA0 changes continuously as shown in FIG. 3. In linear polarizer 110, the region having absorption axis PA0 is referred to as normal region A.

[0067] Defect area B, which has absorption axis PA3 that does not coincide with absorption axis PA0, transmits the first polarized light. The light that transmits through linear polarizer 110 is polarized light in a direction corresponding to the absorption axis of defect area B of linear polarizer 110. If the absorption axis of the defect area of ​​linear polarizer 110 does not have one direction, the light that transmits through it contains polarized light in multiple directions. Hereinafter, these will be collectively referred to as third polarized light, and some of the multiple polarized light beams contained in the third polarized light will be referred to as 3a polarized light, 3b polarized light, 3c polarized light, ... in order of the angle that they form with the first polarized light, which is smallest.

[0068] The third polarized light that has exited linear polarizer 110 is affected by the phase difference due to the birefringence of protective film 141 and enters second filter 5. Second filter 5 has a filtering function of absorbing and exiting the third polarized light according to the polarization direction. The proportion of light absorbed by second filter 5 decreases in the order of 3a polarized light, 3b polarized light, 3c polarized light, ...

[0069] The angle between the absorption axis PA2 of the second filter 5 and the absorption axis PA0 of the linear polarizer 110 is within the range of 90°±35°, and the angle θ2 between the absorption axis PA2 of the second filter 5 and the alignment axis of the protect film 141 is also adjusted by satisfying the above condition b1 or b2. Therefore, it is possible to suppress a decrease in detection accuracy caused by a phase difference caused by the birefringence of the protect film 141.

[0070] The inventors have noticed that the degree of polarization of light transmitted through the first filter and the optical film is substantially low, and have found that by passing such light through a second filter, the contrast ratio between the first polarized light region and the third polarized light region can be increased, and the detection sensitivity can be significantly improved.

[0071] As described above, the light transmission characteristics of linear polarizer 110 differ between normal region A and defective region B, and the light transmission characteristics of second filter 5 differ depending on the absorption axis direction in defective region B. Since detection unit 6 detects light reflecting these transmission characteristics, it is possible to detect the presence or absence of defects in crossed polarizer 110 and the presence or absence of unevenness in the absorption axis direction in defective region B. Unevenness in the absorption axis direction of linear polarizer 110 corresponds to unevenness in the optical characteristics.

[0072] The defect inspection apparatus 1, having the first filter 3 and the second filter 5, can efficiently detect unevenness in the optical properties of the linear polarizing plate 110. Therefore, the manufacturing method for the optical film 100 including the above-described defect inspection method can efficiently produce the optical film 100 as a product that does not contain defects.

[0073] <First filter, second filter> The first filter 3 has a first polarizer, and the second filter 5 has a second polarizer. The first polarizer and the second polarizer can be absorption-type polarizers that absorb linearly polarized light having a vibration plane parallel to the absorption axis and transmit linearly polarized light having a vibration plane perpendicular to the absorption axis (parallel to the transmission axis), similar to the above-mentioned polarizer 112. A representative polarizer is a polarizing film in which a dichroic dye is adsorbed and aligned on a uniaxially stretched polyvinyl alcohol-based resin film. The polarizing film is described in detail in the above-mentioned polarizing film 112. The first polarizer and the second polarizer are defect-free.

[0074] <Phase difference compensation plate> The shape of the retardation compensation plate 4 is not particularly limited as long as it can compensate for the birefringence of light in the release film 133. However, since the release film 133 made of a PET resin has a large variation in the in-plane retardation value and the slow axis, it is preferable that the retardation value is adjustable during inspection. As shown in FIG. 2, the thickness of the retardation compensation plate 4 is not uniform, but changes continuously to have thin and thick parts. Since the thickness changes continuously, the retardation value also changes continuously according to the thickness. The retardation compensation plate 4 has a thickness that spreads at a predetermined angle from the thinnest part as a starting point, and has a "wedge" shape in cross section. The retardation compensation plate 4 having such a wedge shape can be easily compensated for the birefringence of light caused by the release film 133 by shifting or rotating it within the inspection area of ​​the inspection object.

[0075] The retardation compensation plate 4 is preferably rectangular or square in size with each side having a length in the range of 1 cm to 30 cm.

[0076] The retardation compensation plate 4 can be made of inorganic materials such as minerals exhibiting birefringence, such as quartz and calcite, or a film made of a cycloolefin resin. It is particularly preferable to use such materials with flat wavelength dispersion characteristics. In addition, it is preferable to use minerals such as quartz in terms of ease of processing into a wedge shape and subsequent handling.

[0077] When using a mineral such as quartz, a retardation film may be further used to make the wavelength dispersion characteristics flatter. When the slow axis of the retardation film is arranged perpendicular to the slow axis of the retardation plate made of a mineral such as quartz, it is preferable to use a retardation film with a normal dispersion, and when the slow axis of the retardation film is arranged parallel to the slow axis of the retardation compensator made of a mineral such as quartz, it is preferable to use a retardation film with a reverse dispersion. When using such a retardation film, the retardation film is laminated on the surface of the quartz.

[0078] Examples of the reverse dispersion retardation film include "Pure Ace WR-S", "Pure Ace WR-W", and "Pure Ace WR-M" manufactured by Teijin Ltd., and "NRF" manufactured by Nitto Denko Corp. Examples of the normal dispersion retardation film include a film made of a polycarbonate resin and a film made of a polypropylene resin.

[0079] Examples of the cycloolefin resin include a resin obtained by ring-opening metathesis polymerization using as a monomer norbornene or a derivative thereof obtained by the Diels-Alder reaction of cyclopentadiene and olefins, followed by hydrogenation; a resin obtained by ring-opening metathesis polymerization using as a monomer tetracyclododecene or a derivative thereof obtained by the Diels-Alder reaction of dicyclopentadiene and olefins or methacrylic acid esters, followed by hydrogenation; a resin obtained by similar ring-opening metathesis copolymerization using two or more kinds of norbornene, tetracyclododecene, their derivatives, or other cyclic olefin monomers, followed by hydrogenation; and a resin obtained by addition copolymerization of an aromatic compound having a vinyl group to the above-mentioned norbornene, tetracyclododecene, or their derivatives.

[0080] Cycloolefin resins are readily available as commercially available products, such as Topas (manufactured by Topas Advanced Polymers GmbH), Arton (manufactured by JSR Corporation), Zeonor, Zeonex (all manufactured by Zeon Corporation), and Apel (manufactured by Mitsui Chemicals, Inc.).

[0081] It is preferable to use a retardation compensator 4 having a retardation value in a range (hereinafter sometimes referred to as a "wide compensation range") 500 to 600 nm larger than the Re(550) of the release film 133. By using a retardation compensator 4 having a range shifted by about one wavelength in this way, the transmission spectrum of visible light can be matched with the PET resin film in a wider wavelength range, making retardation compensation possible.

[0082] The retardation compensator 4 may be used by preparing two retardation compensators with a wedge-shaped cross section, stacking them in such a way that the directions in which the retardation value increases continuously are opposite to each other. In this case, the retardation value of the retardation compensator is the total value of the two plates, and the above-mentioned "wide compensation area" is also based on the total value of the two plates. By using two wedge-shaped retardation compensators, the birefringence of light in the release film 133 can be compensated over a wide range, so the inspection area can be expanded and the inspection can be performed efficiently.

[0083] More specifically, the phase difference of the entire phase difference compensator can be changed by shifting at least one of the two phase difference compensators in the direction in which the thickness changes. The degree of change is gentler than that in the case of a single phase difference compensator, because the two phase difference compensators are arranged so that the thickness increases in the opposite directions. This makes it possible for a defect inspection device using two phase difference compensators to have a wider area in which the birefringence of the release film 133 can be cancelled than a defect inspection device using a single phase difference compensator. In addition, inspection can be performed in the same way even if three or four phase difference compensators are used. In addition, a plurality of phase difference compensators may be prepared, and an optimal phase difference compensator for cancelling the birefringence of the release film 133 may be arranged on the optical axis 9 each time.

[0084] The defect inspection device 1 may be used in a method of inspecting an area of ​​the optical film 100 to be inspected by specifying the area to be inspected in advance, and the optical film 100 can be inspected over a wider range by scanning the light source 2 and the retardation compensator 4. At this time, the detection unit 6 is also moved as necessary.

[0085] <First application example> The first application example describes a suitable application example of this embodiment in which the optical films A and B to be inspected further have a λ / 4 retardation layer, and defects in a circular polarizing plate composed of a combination of a linear circular polarizing plate and a λ / 4 retardation layer are inspected.

[0086] The optical films A and B, which are the objects to be inspected in this application example, will be described. FIG. 4 is a cross-sectional view that shows a schematic diagram of an optical film 200, which is an example of the optical films A and B. As shown in FIG. 4, the layer structure of the optical film 200 is a protective film 141 / linear polarizing plate 110 [first protective film 111 / adhesive layer 114 / polarizer 112 / adhesive layer 114 / second protective film 113] / adhesive layer 131 / retardant 120 [first retardation layer 121 / adhesive layer 124 / second retardation layer 122] / adhesive layer 132 / peeling film 133. The same components as those in the layer structure of the optical film 100 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. The description of the adhesive layer 114 is applied to the adhesive layer 124, and the description of the adhesive layer 132 is applied to the adhesive layer 131, and the description thereof will be omitted.

[0087] The optical film 200 includes, as the retarder 120, a λ / 4 retardation layer that imparts a phase difference of 1 / 4 wavelength to transmitted light, and may further include a λ / 2 retardation layer that imparts a phase difference of 1 / 2 wavelength to transmitted light, a positive A plate, and a positive C plate. The retarder 120 of the optical film 200 shown in Fig. 4 includes a first retardation layer 121 and a second retardation layer 122. Examples of combinations of the first retardation layer 121 and the second retardation layer 122 include a combination of a λ / 2 retardation layer and a λ / 4 retardation layer, a combination of a λ / 4 retardation layer and a positive C layer, and the like.

[0088] The retardation layer may be an optical film exhibiting optical anisotropy. Examples of optical films exhibiting optical anisotropy include stretched films obtained by stretching polymer films made of polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride / polymethyl methacrylate, acetyl cellulose, saponified ethylene-vinyl acetate copolymer, polyvinyl chloride, etc., to about 1.01 to 6 times. Among the stretched films, polymer films obtained by uniaxially or biaxially stretching acetyl cellulose, polyester, polycarbonate film, or cycloolefin resin film are preferable. In addition, the retardation layer may be a retardation layer made of a cured product of a polymerizable liquid crystal compound, which is coated and oriented on a substrate to exhibit optical anisotropy.

[0089] Examples of the stretched film include films obtained by stretching a film formed of polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride / polymethyl methacrylate, acetyl cellulose, saponified ethylene-vinyl acetate copolymer, polyvinyl chloride, or the like, by about 1.01 to 6 times.

[0090] As the polymerizable liquid crystal compound for forming the cured product layer of the polymerizable liquid crystal compound, a rod-shaped liquid crystal compound, a discotic liquid crystal compound, and a mixture thereof can be used. The cured product layer can be formed by applying a retardation layer forming composition containing a polymerizable liquid crystal compound, a solvent, and various additives as necessary, onto an alignment film to form a coating film, and solidifying (curing) this coating film. Alternatively, the retardation layer forming composition can be applied onto a substrate layer to form a coating film, and the coating film can be stretched together with the substrate layer to form a cured product layer. The retardation layer forming composition may contain a polymerization initiator, a reactive additive, a leveling agent, a polymerization inhibitor, and the like, in addition to the above-mentioned polymerizable liquid crystal compound and solvent. The liquid crystal compound, the solvent, the polymerization initiator, the reactive additive, the leveling agent, the polymerization inhibitor, and the like can be appropriately used.

[0091] In the defect inspection device 1 shown in FIG. 2, when the object to be inspected is the optical film 200 instead of the optical film 100 and the target to be inspected for defects is a circular polarizer, a λ / 4 retardation plate is arranged between the first filter 3 and the retardation compensation plate 4 in the arrangement step. This λ / 4 retardation plate provides in advance a phase difference that cancels the phase difference of the λ / 4 retardation layer of the optical film 200 that is transmitted in the subsequent stage. The light that is incident on the optical film 200 is incident on the linear polarizer 110 in a state in which the influence of the phase difference due to transmission through the λ / 4 retardation layer is canceled. The first filter 3 may be configured to include a λ / 4 retardation plate on the optical film 200 side rather than the first polarizer.

[0092] In addition, only when the object to be inspected is optical film 200 (i.e., only when it is a circular polarizing plate), a crossed Nicol state can be obtained even if the absorption axis of the first polarizer of the first filter and the absorption axis of the polarizer of optical film 200, and the slow axis of the λ / 4 retardation layer of the first filter and the slow axis of the λ / 4 retardation layer of optical film 200 are all arranged parallel to each other.

[0093] Defects of the circular polarizer that can be detected by the defect inspection device 1 in the first application example include unevenness in the optical properties of the linear polarizer 110, local defects, and the like, as in the case where the inspected object is the optical film 100. Furthermore, in the first application example, when the light source 2 is arranged so that light is incident from the second filter 5 side, defects in the retarder 120 can also be detected in addition to the above-mentioned defects. When the objective is to detect only defects in the linear polarizer 110, it is preferable to use the light source 2 arranged so that light is incident from the first filter 4 side. With such an arrangement, defects in the linear polarizer 110 can be detected with higher accuracy. [Explanation of symbols]

[0094] 1 defect inspection device, 2 light source, 3 first filter, 4 phase difference compensation plate, 5 second filter, 6 detection unit, 100, 200 optical film, 111 first protective film, 112 polarizer, 113 second protective film, 114, 124 adhesive layer, 131, 132 pressure-sensitive adhesive layer, 133 release film, 141 protective film, 120 retardation body, 121 first retardation layer, 122 second retardation layer.

Claims

1. A method for inspecting a defect in a linear polarizing plate, the method comprising the steps of: inspecting an optical film having a linear polarizing plate, the method comprising the steps of: The optical film is A release film, the linear polarizing plate, and a protective film in this order, and further comprising a λ / 4 retardation layer between the linear polarizing plate and the release film; the protective film has an alignment axis and is laminated such that an angle between the alignment axis and an absorption axis of the linear polarizer is in the range of 0°±30°; The protective film is made of a polyethylene terephthalate resin, The alignment axis is a slow axis, The defect inspection method includes: a step of arranging a first filter having a first polarizer, a phase difference compensation plate, the optical film, and a second filter having a second polarizer in this order along an optical axis, with the optical film facing the release film in a direction opposite to the phase difference compensation plate; a detection step of irradiating light along the optical axis from one of the first filter side and the second filter side and detecting light emitted from the other side; a determination step of determining a defect in the optical film based on a detection result in the detection step, In the placing step, The following conditions a and b1: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b1) an angle between an absorption axis of the second polarizer and the orientation axis of the protective film is within a range of 90°±5°; and a λ / 4 retardation plate is disposed between the first filter and the optical film so as to satisfy the above. In the detection step, The phase difference compensating plate compensates for birefringence of the release film.

2. A method for inspecting a defect in a linear polarizing plate, the method comprising the steps of: inspecting an optical film having a linear polarizing plate, the method comprising the steps of: The optical film is A release film, the linear polarizing plate, and a protective film in this order, and further comprising a λ / 4 retardation layer between the linear polarizing plate and the release film; the protective film has an alignment axis and is laminated such that an angle between the alignment axis and an absorption axis of the linear polarizer is within a range of 90°±30°; The protective film is made of a polyethylene terephthalate resin, The alignment axis is a slow axis, The defect inspection method includes: a step of arranging a first filter having a first polarizer, a phase difference compensation plate, the optical film, and a second filter having a second polarizer in this order along an optical axis, with the optical film facing the release film in a direction opposite to the phase difference compensation plate; a detection step of irradiating light along the optical axis from one of the first filter side and the second filter side and detecting light emitted from the other side; a determination step of determining a defect in the optical film based on a detection result in the detection step, The placing step includes: The following condition a and condition b2: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b2) an angle between an absorption axis of the second polarizer and the alignment axis of the protective film is within a range of 0°±5°; and a λ / 4 retardation plate is disposed between the first filter and the optical film so as to satisfy the above. In the detection step, The phase difference compensating plate compensates for birefringence of the release film.

3. 3. The defect inspection method according to claim 1, wherein the release film is made of a polyethylene terephthalate resin.

4. 4. The defect inspection method according to claim 1, wherein the linear polarizing plate has a polarizer containing a cured product of a polymerizable liquid crystal compound.

5. An apparatus for inspecting defects in a linear polarizing plate, the apparatus comprising: The optical film is A release film, the linear polarizing plate, and a protective film in this order, and further comprising a λ / 4 retardation layer between the linear polarizing plate and the release film; the protective film has an alignment axis and is laminated such that an angle between the alignment axis and an absorption axis of the linear polarizer is in the range of 0°±30°; The protective film is made of a polyethylene terephthalate resin, The alignment axis is a slow axis, The defect inspection device includes: a first filter having a first polarizer, a retardation compensation plate capable of compensating for birefringence of the release film, and a second filter having a second polarizer, in this order along an optical axis, and further comprising a light source capable of irradiating light along the optical axis from the first filter side or the second filter side; a defect inspection is performed after a positioning step in which the optical film is positioned such that the surface on the release film side faces the retardation compensation plate; In the placing step, The following conditions a and b1: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b1) A defect inspection device in which the first filter and the optical film are arranged so as to satisfy the following condition: an angle between the absorption axis of the second polarizer and the alignment axis of the protect film is within a range of 90°±5°, and a λ / 4 retardation plate is arranged between the first filter and the optical film.

6. An apparatus for inspecting defects in a linear polarizing plate, the apparatus comprising: The optical film is A release film, the linear polarizing plate, and a protective film in this order, and further comprising a λ / 4 retardation layer between the linear polarizing plate and the release film; the protective film has an alignment axis and is laminated such that an angle between the alignment axis and an absorption axis of the linear polarizer is within a range of 90°±30°; The protective film is made of a polyethylene terephthalate resin, The alignment axis is a slow axis, The defect inspection device includes: a first filter having a first polarizer, a retardation compensation plate capable of compensating for birefringence of the release film, and a second filter having a second polarizer, in this order along an optical axis, and further comprising a light source capable of irradiating light along the optical axis from the first filter side or the second filter side; a defect inspection is performed after a positioning step in which the optical film is positioned such that the surface on the release film side faces the retardation compensation plate; In the placing step, The following condition a and condition b2: (a) the angle between the absorption axis of the first polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±5°; (b2) A defect inspection device in which the first filter and the optical film are arranged so as to satisfy the following condition: an angle between the absorption axis of the second polarizer and the alignment axis of the protect film is within a range of 0°±5°, and a λ / 4 retardation plate is arranged between the first filter and the optical film.

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