Defect inspection method and defect inspection device

Abstract

The present invention is a defect inspection method for an optical film having a linear polarizing plate as an inspected object, wherein the optical film has a peeling film, the linear polarizing plate and a protective film in sequence, and the defect inspection method has a configuration step: a first filter having a first polarizing plate, a first phase difference compensation plate, the optical film, a second phase difference compensation plate and a second filter having a second polarizing plate are configured in sequence along the optical axis, and the optical film is configured in a direction in which the surface of the peeling film side is opposite to the first phase difference compensation plate, the first phase difference compensation plate compensates for the birefringence of the peeling film, and the second phase difference compensation plate compensates for the birefringence of the protective film.

Description

Technical Field

[0001] The present invention relates to a defect inspection method and defect inspection device for a linear polarizing plate using an optical film as an inspection object. Background Art

[0002] The polarizing plate used in display devices such as liquid crystal display devices and organic EL display devices is usually composed of a polarizer sandwiched between two protective films. For the polarizing plate, in order to fit the display device, an adhesive layer is sometimes laminated on a protective film, and a protective film is laminated on another protective film to prevent damage to the surface of the protective film during circulation. A release film is usually laminated on the adhesive layer. As a specific example of a polarizer, a PVA-based polarizing film formed by adsorption and orientation of dichroic pigments such as iodine and dichroic dyes on a uniaxially stretched polyvinyl alcohol (PVA) resin film, and a polarizer (hereinafter also referred to as "liquid crystal polarizer") formed by a polymer containing a polymerizable liquid crystal compound and a liquid crystal solidified layer of dichroic pigments can be cited. The liquid crystal polarizer is usually formed by applying a composition containing a polymerizable liquid crystal compound to a substrate film and curing it, and has the advantage of being able to manufacture a thin polarizer. Such a PVA-based polarizing film and liquid crystal polarizer, as described later, have the effect of allowing linear polarized light of a specific vibration plane to pass through, and are called "linear polarizers". In addition, a linear polarizing plate having a protective film on one or both surfaces thereof is generally referred to as a "linear polarizing plate".

[0003] Polarizing plates and polarizers sometimes have defects in their manufacturing stage. For example, sometimes there are defects such as foreign matter mixed in between the polarizing plate and the protective film, or residual bubbles. In addition, liquid crystal polarizers sometimes produce uneven optical properties of the polarizing plate due to uneven coating during manufacturing.

[0004] Therefore, at the stage before assembling the polarizing plate to the display device, an inspection for detecting defects of the polarizing plate is performed. The inspection of the defects is shown in Japanese Patent Publication No. 9-229817 (Patent Document 1). After a polarizing filter is set between the polarizing plate as the object to be inspected and the light source, the polarizing plate or the polarizing filter is rotated in the plane direction, and the directions of their respective polarization axes are set to a specific relationship. When the directions of the polarization axes are orthogonal to each other (that is, in the case of a configuration forming an orthogonal Nicol prism), the linearly polarized light passing through the polarizing filter does not transmit the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light will be transmitted at that position, so the presence of the defect is determined 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 passing 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 part, so the presence of the defect is determined by not detecting the light.

[0006] The inspector can visually detect the light transmitted through the polarizing plate, or automatically detect the light transmitted through the polarizing plate by performing image analysis processing using a combination of a CCD camera and an image processing device, thereby inspecting the polarizing plate for defects.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Laid-Open No. 9-229817 Summary of the invention

[0010] Problems to be solved by the invention

[0011] According to the method described in Patent Document 1, although local defects such as foreign matter or air bubbles mixed in and having optical characteristics greatly different from those of the surroundings can be detected, it is difficult to detect unevenness in optical characteristics.

[0012] In addition, in a state where the pellicle film and the release film are laminated, it is difficult to detect defects of the polarizing plate due to the influence of the birefringence of the pellicle film and the release film.

[0013] An object of the present invention is to provide a defect inspection method and defect inspection device capable of detecting unevenness in optical characteristics of a linear polarizing plate when an optical film in which a protective film and a release film are laminated on the linear polarizing plate is used as an inspection object.

[0014] Means for solving problems

[0015] The present invention provides a defect inspection method and a defect inspection device as shown below.

[0016] [1] A defect inspection method for a linear polarizing plate, wherein an optical film having a linear polarizing plate is used as an inspection object.

[0017] The optical film comprises a release film, the linear polarizing plate and a protective film in this order.

[0018] The above defect inspection method has the following advantages:

[0019] an arrangement step of sequentially arranging a first optical filter having a first polarizer, a first phase difference compensation plate, the optical film, a second phase difference compensation plate, and a second optical filter having a second polarizer along an optical axis, and arranging the optical film in a direction in which a surface on the side of the release film faces the first phase difference compensation plate;

[0020] a detection step of allowing light to enter from either the first filter side or the second filter side along the optical axis and detecting light emitted from the other side; and

[0021] a judging step of judging the defects of the optical film based on the detection result in the detecting step;

[0022] In the above configuration process, the configuration is performed in a manner that satisfies the following conditions a and b:

[0023] (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°;

[0024] (b) the angle between the absorption axis of the second polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±30°,

[0025] In the above detection process,

[0026] The first phase difference compensation plate compensates for the birefringence of the release film, and the second phase difference compensation plate compensates for the birefringence of the protection film.

[0027] [2] The defect inspection method according to [1], wherein the release film comprises a polyethylene terephthalate-based resin.

[0028] [3] The defect inspection method according to [1] or [2], wherein the pellicle film comprises a polyethylene terephthalate-based resin.

[0029] [4] The defect inspection method according to any one of [1] to (3], wherein the linear polarizing plate has a polarizer comprising a cured product of a polymerizable liquid crystal compound.

[0030] [5] The defect inspection method according to any one of [1] to [4], wherein the optical film further comprises a λ / 4 phase difference layer between the linear polarizing plate and the release film,

[0031] In the arrangement step, a λ / 4 phase difference plate is arranged between the first optical filter and the first phase difference compensation plate.

[0032] [6] A defect inspection device for a linear polarizing plate, wherein the defect inspection device is a defect inspection device for a linear polarizing plate having an optical film having a linear polarizing plate as an object to be inspected,

[0033] The optical film comprises a release film, the linear polarizing plate and a protective film in this order.

[0034] The defect inspection device comprises, in order along the optical axis: a first filter having a first polarizing plate, a first phase difference compensation plate capable of compensating for the birefringence of the release film, a second phase difference compensation plate capable of compensating for the birefringence of the protective film, and a second filter having a second polarizing plate, and further comprises a light source capable of irradiating light along the optical axis from the first filter side or the second filter side, and performs defect inspection after a configuration step of configuring the optical film in a direction in which the surface of the release film side is opposed to the first phase difference compensation plate.

[0035] In the above configuration process, the configuration is performed in a manner that satisfies the following conditions a and b:

[0036] (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°;

[0037] (b) The angle formed by the absorption axis of the second polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±30°.

[0038] Effects of the Invention

[0039] According to the defect inspection method and defect inspection apparatus of the present invention, when an optical film having a pellicle and a release film laminated on both surfaces of a linear polarizing plate is used as an inspection object, unevenness in optical characteristics of the linear polarizing plate can be detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a cross-sectional view schematically showing an optical film as an example of the inspection object according to the present embodiment.

[0041] Figure 2 It is a schematic diagram of the defect inspection device of this embodiment.

[0042] Figure 3 This is a diagram showing an example of a defect region in an optical film.

[0043] Figure 4 1 is a cross-sectional view schematically showing an optical film as an example of the inspection object in the first application example. DETAILED DESCRIPTION

[0044] The present invention relates to a defect inspection method and a defect inspection device for an optical film having a linear polarizing plate as an inspection object. The inspection object in the defect inspection method and the defect inspection device of the present invention can be an optical film having a release film, a linear polarizing plate and a protective film in this order.

[0045] The defect inspection method of the present invention using an optical film as an object to be inspected has the following features:

[0046] an arrangement step of sequentially arranging a first optical filter having a first polarizer, a first phase difference compensation plate, the optical film, a second phase difference compensation plate, and a second optical filter having a second polarizer along an optical axis, and arranging the optical film in a direction in which a surface on the side of the release film faces the first phase difference compensation plate;

[0047] a detection step of allowing light to enter from either the first filter side or the second filter side along the optical axis and detecting light emitted from the other side; and

[0048] a judging step of judging the defects of the optical film based on the detection result in the detecting step;

[0049] In the above configuration process, the configuration is performed in a manner that satisfies the following conditions a and b:

[0050] (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°;

[0051] (b) The angle formed by the absorption axis of the second polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±30°.

[0052] In the detection step, the first phase difference compensation plate compensates for the birefringence of the release film, and the second phase difference compensation plate compensates for the birefringence of the protection film.

[0053] The defect inspection device of the present invention can be used in the above-mentioned defect inspection method.

[0054] The defect inspection device of the present invention comprises, in order along the optical axis: a first filter having a first polarizing plate, a first phase difference compensation plate capable of compensating for the birefringence of the above-mentioned peeling film, a second phase difference compensation plate capable of compensating for the birefringence of the above-mentioned protective film, and a second filter having a second polarizing plate, and further comprises a light source capable of irradiating light along the above-mentioned optical axis from the above-mentioned first filter side or the above-mentioned second filter side, and performs defect inspection after a configuration step of configuring the above-mentioned optical film in a direction in which the surface of the above-mentioned peeling film side is opposite to the above-mentioned first phase difference compensation plate.

[0055] In the above configuration process,

[0056] Configure in a way that satisfies the following conditions a and b:

[0057] (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°;

[0058] (b) The angle formed by the absorption axis of the second polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±30°.

[0059] Hereinafter, embodiments of the defect inspection device and defect inspection method of the present invention will be described with reference to the accompanying drawings. The same elements are denoted by the same reference numerals, and repeated descriptions are omitted. The dimensional ratios in the drawings are not necessarily the same as the dimensional ratios in the description.

[0060] A defect inspection device and a defect inspection method according to an embodiment of the present invention will be described.

[0061] [Optical film]

[0062] An optical film as an inspection object according to the present embodiment will be described. Figure 1 1 is a cross-sectional view schematically showing an optical film 100 as an example of an optical film. Figure 1 As shown, the layer structure of the optical film 100 is: 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 132 / release film 133 .

[0063] (Polarizing Plate)

[0064] The polarizer 112 may be an absorption-type polarizer having the property of absorbing linear polarized light having a vibration plane parallel to its absorption axis and transmitting linear polarized light having a vibration plane orthogonal 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 obtained by adsorbing and orienting a dichroic dye on a uniaxially stretched polyvinyl alcohol resin film, and the like.

[0065] A typical method for manufacturing a liquid crystal polarizer is briefly described. First, a suitable support is prepared. Next, an alignment film is formed on the surface of the support. Next, a liquid composition containing a polymerizable liquid crystal compound and a dichroic pigment is applied to the alignment film and dried, thereby forming 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. As the support, if a transparent resin film is used, a polarizer with the transparent resin film as a protective film can be manufactured.

[0066] As a liquid crystal polarizer, for example, it can be a liquid crystal polarizer described in Japanese Patent Gazette No. 2016-170368. As a dichroic pigment, a dichroic pigment having absorption in the range of wavelength 380 to 800 nm can be used, preferably an organic dye. As a dichroic pigment, for example, an azo compound can be cited. The liquid crystal compound is a liquid crystal compound that can be polymerized while maintaining an orientation, and can have a polymerizable group in the molecule. In addition, as described in WO201I / 024891, a polarizer can be formed by a dichroic pigment having liquid crystal properties. It should be noted that after polymerization (after the polarizer including the liquid crystal solidification layer is formed), the liquid crystal compound no longer needs to show liquid crystal properties.

[0067] 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 coating of the liquid composition in the manufacturing process. In the defect inspection method and defect inspection device based on this embodiment, such uneven optical properties can also be detected.

[0068] Next, the PVA polarizing film is briefly described. The PVA polarizing film can be manufactured, for example, by a method including the following steps: a step of uniaxially stretching a PVA resin film; a step of dyeing the PVA resin film with a dichroic dye to adsorb the dichroic dye (dyeing treatment); a step of treating the PVA resin film adsorbed with the dichroic dye with a crosslinking liquid such as an aqueous boric acid solution (crosslinking treatment); and a step of washing with water after the treatment with the crosslinking liquid (cleaning treatment).

[0069] As the PVA resin, a PVA resin obtained by saponifying a polyvinyl acetate resin can be used. As the polyvinyl acetate resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, copolymers of vinyl acetate and other copolymerizable monomers can be cited. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

[0070] In the present specification, "(meth)acrylic acid" means at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acryloyl", "(meth)acrylate" and the like.

[0071] The saponification degree of PVA resin is usually 85 to 100 mol%, preferably 98 mol% or more. PVA resin can be modified, for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The average polymerization degree of PVA resin is usually 1000 to 10000, preferably 1500 to 5000. The average polymerization degree of PVA resin can be calculated according to JIS K 6726.

[0072] The film made of such a PVA-based resin can be used as a raw material film (PVA-based resin film) for manufacturing polarizers. The method of making a PVA-based resin film is not particularly limited, and a known method can be used. The thickness of the PVA-based resin film is not particularly limited. In order to make the thickness of the polarizing film less than 15 μm, a PVA-based resin film of 5 to 35 μm is preferably used. More preferably, it is less than 20 μm. The thickness of the PVA-based resin film can be selected in such a way that the PVA-based polarizing film finally obtained becomes the desired thickness.

[0073] The uniaxial stretching of PVA based resin film can be carried out before the dyeing process utilizing the dichroic pigment, can also be carried out simultaneously with the dyeing process, can also be carried out after the dyeing process. Under the situation of carrying out uniaxial stretching after the dyeing process, the uniaxial stretching can be carried out before the crosslinking process, can also be carried out in the crosslinking process. In addition, it is also possible to be divided into and carry out uniaxial stretching for many times in the stage of these multiple processes.

[0074] During uniaxial stretching, when using a long strip of PVA resin film, for example, the PVA resin film can be laid on a roller so that the circumferential speed of the roller is different, thereby performing uniaxial stretching between the rollers, or a hot roller can be used for uniaxial stretching. In addition, uniaxial stretching can be dry stretching in the atmosphere, or wet stretching in which the PVA resin film is swollen using a solvent or water. The stretching ratio is generally 3 to 8 times. When the PVA resin film is stretched by multiple uniaxial stretchings, the stretching ratio compared to the original length is generally set to 3 to 8 times. It should be noted that the stretching ratio can also be selected in such a way that the final PVA polarizing film has the desired thickness.

[0075] As a method for dyeing the PVA resin film with a dichroic pigment (dyeing treatment), typically, a method is adopted in which the PVA resin film is immersed in an aqueous solution containing a dichroic pigment. As the dichroic pigment, iodine or a dichroic organic dye can be used. It should be noted that the PVA resin film is preferably immersed in water before the dyeing treatment.

[0076] As a crosslinking treatment after dyeing with a dichroic dye, a method of immersing the dyed PVA-based resin film in an aqueous solution containing boric acid is generally adopted. When iodine is used as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide.

[0077] In this way, a PVA-based polarizing film can be obtained. The thickness of the PVA-based polarizing film is also preferably thinner, as with the liquid crystal polarizer, 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, preferably 3 μm or more.

[0078] The linear polarizer can also be made into a linear polarizing plate alone. As described above, the linear polarizing plate can be made into 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 coincides with the absorption axis of the polarizer 112 .

[0079] (Protective film)

[0080] As the protective film (for example, the first protective film 111 and the second protective film 113 ) laminated on one or both surfaces of the polarizing plate 112 , a film made of a thermoplastic resin is used.

[0081] 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 a ring system and a norbornene structure (also referred to as norbornene resins); (meth) acrylic resins; polyarylate resins; polystyrene resins; polyvinyl alcohol resins, and mixtures thereof. In the case where protective films are laminated on both sides of the polarizer, the resin compositions of the two protective films may be the same or different.

[0082] The thickness of the protective film is preferably 3 μm or more, more preferably 5 μm or more. In addition, the thickness of the protective film is usually 100 μm or less. The thickness of the protective film is preferably thinner, for example, it can be 70 μm or less, more preferably 50 μm or less, and more preferably 30 μm or less. It should be noted that the above upper limit and lower limit can be arbitrarily combined.

[0083] The protective film is attached to the display device together with the polarizing plate 112 as a component of the linear polarizing plate, and therefore requires strict management of the retardation value, etc. As the protective film, a protective film having an extremely small retardation value can be typically used.

[0084] (Adhesive layer)

[0085] The adhesive layer (e.g., adhesive layer 114, 124) can be formed by curing the curable component in the adhesive. As the adhesive used to form the adhesive layer, it is an adhesive other than a pressure-sensitive adhesive (adhesive), for example, water-based adhesives such as polyvinyl alcohol-based adhesives, and active energy ray-curing adhesives such as ultraviolet-curing adhesives. The thickness of the adhesive layer is selected according to the type of adhesive, for example, it is 0.05 μm or more, can be 0.1 μm or more, can be 0.5 μm or more, can be 1 μm or more, can be 3 μm or more, usually 20 μm or less, can be 15 μm or less, can be 10 μm or less, and can be 8 μm or less.

[0086] (Protective film)

[0087] The protective film 141 is provided to be removable from the linear polarizing plate 110 and covers and protects the surface of the linear polarizing plate. Examples of the protective film include a base film formed of a resin and a pressure-sensitive adhesive layer laminated thereon.

[0088] The protective film is a film that is peeled off together with the adhesive layer it has after the optical film is attached to a display device or other optical components. The peeled protective film is usually discarded. Therefore, unlike the protective film, strict management of the phase difference value is not required. The defect inspection method of this embodiment can eliminate the influence of the phase difference of the protective film and detect the defects of the linear polarizing plate even when an optical film having such a protective film that does not require strict management of the phase difference value is used as the inspection object.

[0089] The pellicle is usually made of resin. The resin forming the pellicle is not particularly limited, and examples thereof include polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, polyarylate resin, etc. Among them, PET resin can be preferably used. A film containing PET resin is versatile as a pellicle and has the advantage of being inexpensive.

[0090] On the other hand, as mentioned above, the cheap PET resin film does not require strict management of the phase difference value. Therefore, for example, there is a deviation in the phase difference value in each product batch. In addition, even for the same PET resin film, there is sometimes a deviation in the in-plane phase difference value (in-plane phase difference value) and the orientation axis.

[0091] In this specification, a method for determining the in-plane phase difference value Re(550) of the protective film at a wavelength of 550nm is described. A piece of 40mm×40mm is cut with the center of the entire protective film as the center (using an appropriate cutting tool to cut from a long film, etc.). The Re(550) of the piece is measured three times, and the average value of Re(550) is calculated. The Re(550) of the piece can be measured in a measurement temperature chamber (about 25°C) using a phase difference measuring device KORBRA-WPR (manufactured by Oji Measurement Instruments Co., Ltd.).

[0092] The in-plane retardation value Re(550) of the pellicle 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 one of the sheets of the pellicle 141. In the pellicle 141, the in-plane retardation value Re(550) usually differs depending on the sheet at the time of measurement.

[0093] (Release film)

[0094] The release film 133 is provided to be releasable relative to the adhesive layer 132, and is used to cover and protect the surface of the adhesive layer 132. As the release film, there can be mentioned a film obtained by subjecting a substrate film formed using a resin to a release treatment. As the release treatment applied to the substrate film, a known release treatment can be performed, and a method of applying a release agent such as a fluorine compound or an organic silicon compound to the substrate film is preferred.

[0095] The release film 133 is peeled off from the pressure-sensitive adhesive layer 132 when the display device is attached, and the peeled release film is usually discarded. Therefore, unlike a protective film, strict management of the phase difference value is not required.

[0096] The resin that becomes the base film is not particularly limited, for example, polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, polyarylate resin, etc. can be cited, among which PET resin is preferably used. The film containing PET resin is universal as a release film and has the advantage of being cheap. On the other hand, as described above, the cheap PET resin film does not require strict management of the phase difference value. Therefore, for example, sometimes there is a deviation in the phase difference value in each product batch. In addition, even for the same PET resin film, there is sometimes a deviation in the phase difference value (in-plane phase difference value) and the orientation axis in the surface. Even if such a cheap PET resin film is bonded as a release film, the inspection method of this embodiment can detect the presence or absence of its defects with high precision. The deviation of the orientation axis in the release film is not particularly limited, for example, a release film below 135° can be used. The release film 133 is usually peeled off and discarded in the manufacturing process, so strict management of the phase difference value is not required like the protective film.

[0097] In this specification, the method for obtaining the in-plane retardation value Re(550) of the release film at a wavelength of 550 nm is the same as the method for obtaining the in-plane retardation value Re(550) of the pellicle 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.

[0098] [Defect inspection device and defect inspection method]

[0099] Figure 2 Schematic diagram of the defect inspection device of this embodiment. Figure 2 As shown, the defect inspection apparatus 1 detects defects of a linear polarizing plate 110 of the optical film 100 using the optical film 100 as an inspection object. Defects of the linear polarizing plate 110 that can be detected by the defect inspection apparatus 1 include uneven optical characteristics of the linear polarizing plate 110 and local defects.

[0100] In the linear polarizing plate 110, when the polarizing plate 112 is a liquid crystal polarizing plate, there may be uneven optical properties due to uneven coating during the manufacturing process. In addition, if bubbles or foreign matter are mixed or unevenness is generated during the manufacturing process of the linear polarizing plate 110, it will become a local defect.

[0101] The defect inspection device 1 is provided with a first filter 3 having a first polarizing plate, a first phase difference compensation plate 4, a second phase difference compensation plate 7, and a second filter 5 having a second polarizing plate 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. Figure 2 In the embodiment, the light source 2 is arranged at a position where light can be irradiated from the first filter 3 side. Hereinafter, the method 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 method in which the light source 2 irradiates light from the second filter 5 side. The defect inspection device 1 includes a detection unit 6 arranged at a position where light irradiated from the light source 2 is incident after passing through each component.

[0102] The light source 2 is non-polarized light and is not limited as long as it 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 lamp, a fluorescent lamp, or the like.

[0103] In the detection unit 6, the defect can be determined by detecting (observing) the detection light with the naked eye, or the defect can be determined based on the captured image by photographing the detection light. As a photographing mechanism, a CCD camera or the like can be cited. In the following, unless otherwise specified, the method of detecting the detection light with the naked eye is described. The same is true in other embodiments.

[0104] In the defect inspection device 1, the arrangement process is first performed. In the arrangement process, the optical film 100 of the inspection object is arranged between the first phase difference compensation plate 4 and the second phase difference compensation plate 7, and arranged in a direction in which the surface on the side of the release film 133 faces the first phase difference compensation plate 4. In the arrangement process, the arrangement angles of the first optical filter 3, the optical film 100, and the second optical filter 5 are adjusted so as to satisfy the following conditions a and b.

[0105] (a) An angle θ1 formed between the absorption axis of the first polarizer of the first optical filter 3 and the absorption axis of the linear polarizing plate 110 is within the range of 90°±5°.

[0106] (b) An angle θ2 formed by the absorption axis of the second polarizer of the second filter 5 and the absorption axis of the linear polarizing plate 110 is within the range of 90°±30°.

[0107] Hereinafter, the absorption axis of the linear polarizing plate 110 is also referred to as “absorption axis PA0”, the absorption axis of the first polarizer of the first filter 3 is also referred to as “absorption axis PA1”, and the absorption axis of the second polarizer of the second filter 5 is also referred to as “absorption axis PA2”.

[0108] In the above configuration step, the angle θ1 and the angle θ2 are preferably adjusted to have the darkest field of view within the range satisfying the above conditions. This adjustment can be performed by appropriately adjusting the configuration angles of the first optical filter 3, the first phase difference compensation plate 4, the optical film 100, the second phase difference compensation plate 7, and the second optical filter 5 even after the configuration step. The defect inspection device 1 may include a movable device (not shown) capable of rotating the first optical filter 3, the first phase difference compensation plate 4, the optical film 1, the second phase difference compensation plate 7, and the second optical filter 5 in a direction perpendicular to the optical axis 9.

[0109] In the defect inspection device 1, a detection process is performed after the configuration process. In the detection process, light is emitted from the light source 2, and the light sequentially transmits the first optical filter 3, the first phase difference compensation plate 4, the optical film 100, the second phase difference compensation plate 7, and the second optical filter 5 along the optical axis 9, and reaches the detection unit 6. In the detection unit 6, a determination process is performed to determine a defect in the linear polarization plate 110 based on the detection result of the light that has arrived.

[0110] The first filter 3 transmits only light of a specific polarization direction (hereinafter also referred to as “first polarization light”) among the unpolarized light emitted from the light source 2. Light of a polarization direction orthogonal to the first polarization light is also referred to as “second polarization light”.

[0111] The first phase difference compensation plate 4 is provided with a phase difference that cancels the phase difference caused by the birefringence of the release film 133 transmitted in the later stage. The light incident on the optical film 100 is incident on the linear polarizing plate 110 in a state where the influence of the phase difference caused by the transmission of the release film 133 is canceled. Since the angle θ1 formed by the absorption axis PA1 of the first optical filter 3 transmitted first and the absorption axis PA0 of the linear polarizing plate 110 satisfies the above-mentioned condition a, the first polarized light incident on the linear polarizing plate 110 is almost absorbed in the region without defects.

[0112] However, the linear polarizing plate 110 may have a defective region where the absorption axis does not coincide with the absorption axis PA0. Figure 3 FIG. 1 shows an example of a defect region B in the linear polarizing plate 110, and the absorption axis in the defect region B is indicated by arrows at both ends. In the defect region B, there is an absorption axis (hereinafter referred to as "absorption axis PA3") that is inconsistent with the absorption axis PA0. When the defect in the defect region B is an optical property unevenness, as the absorption axis PA3 in the defect region B, Figure 3 As shown in FIG. 1 , a state in which the angle with the absorption axis PA0 changes continuously can be assumed.

[0113] The first polarized light is transmitted in the defective region B having an absorption axis PA3 that is inconsistent with the absorption axis PA0. The light transmitted through the linear polarizing plate 110 is polarized light in a direction corresponding to the absorption axis of the defective region B of the linear polarizing plate 110. In the case where the absorption axis of the defective region of the linear polarizing plate 110 is not in a single direction, the light transmitted therein includes polarized light in multiple directions. Hereinafter, they are collectively referred to as the third polarized light, and a portion of the multiple polarized light included in the third polarized light is referred to as 3a polarized light, 3b polarized light, 3c polarized light, etc. in the order of the angle formed with the first polarized light from small to large.

[0114] The third polarized light emitted from the linear polarizing plate 110 is incident on the second optical filter 5 in a state where the influence of the phase difference caused by the birefringence of the protective film 141 is offset by the second phase difference compensation plate 7. The second optical filter 5 has a filtering function of absorbing and emitting the third polarized light according to the polarization direction. The proportion of light absorbed by the second optical filter 5 decreases in the order of 3a polarized light, 3b polarized light, 3c polarized light, ...

[0115] The inventors of the present invention focused on the fact that the polarization degree of light transmitted through the first filter and the optical film is substantially reduced, and found that by allowing such light to further pass through the second filter, the contrast between the first polarized light region and the third polarized light region can be increased, and the detection sensitivity can be greatly improved.

[0116] As described above, the transmission characteristics of light in the linear polarizing plate 110 are different between the normal region A and the defect region B, and the transmission characteristics of light in the second optical filter 5 are different depending on the absorption axis direction in the defect region B. The detection unit 6 detects light reflecting these transmission characteristics, so it is possible to detect the presence or absence of defects in the orthogonal polarizing plate 110 and the presence or absence of unevenness in the absorption axis direction in the defect region B. The unevenness in the absorption axis direction in the linear polarizing plate 110 corresponds to unevenness in optical characteristics.

[0117] The defect inspection device 1 includes the first filter 3 and the second filter 5, so that the unevenness of the optical characteristics of the linear polarizing plate 110 can be effectively detected. Therefore, in the method for manufacturing the optical film 100 including the defect inspection method, the optical film 100 can be efficiently produced as a product without defects.

[0118] <First filter, second filter>

[0119] The first filter 3 has a first polarizer, and the second filter 5 has a second polarizer. The first polarizer and the second polarizer, like the above-mentioned polarizer 112, can be absorption-type polarizers having the property of absorbing linear polarized light having a vibration plane parallel to the absorption axis and transmitting linear polarized light having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). As a representative polarizer, a polarizing film obtained by adsorbing and orienting a dichroic pigment on a uniaxially stretched polyvinyl alcohol resin film can be cited. The detailed description of the polarizing film can be applied to the description of the polarizing film in the above-mentioned polarizer 112. The first polarizer and the second polarizer are defect-free.

[0120] <First Phase Compensation Plate, Second Phase Compensation Plate>

[0121] The shapes of the first phase difference compensation plate 4 and the second phase difference compensation plate 7 (hereinafter, they are collectively referred to as "phase difference compensation plates") are not particularly limited as long as they can compensate for the birefringence of light of the release film 133 or the protective film 141. However, since the release film 133 and the protective film 141 made of PET resin have large deviations in the phase difference value and the slow axis in the plane, it is preferable to set them to a shape that can adjust the phase difference value during inspection. As for the shape, Figure 2 As shown, the shape in which the thickness is different and the thickness changes continuously in a manner having a thin part and a thick part can be cited. Since the thickness changes continuously, the phase difference value also changes continuously according to the thickness. The phase difference compensation plate 4 has the thinnest part as the starting point, and the thickness expands at a predetermined angle, forming a "wedge (Japanese: くさび)" shape in the cross-sectional view. Such a wedge-shaped phase difference compensation plate can easily compensate for the birefringence of light caused by the peeling film 133 or the protective film 141 by staggering or rotating in the inspection area of ​​the inspected object.

[0122] The size of the phase difference compensation plate is preferably a rectangle or a square with a side length in the range of 1 cm to 30 cm.

[0123] As the phase difference compensation plate, inorganic materials such as minerals showing birefringence such as quartz and calcite, and films containing cycloolefin resins can be used. It is particularly preferred to use such materials with flat wavelength dispersion characteristics. In addition, from the perspective of ease of processing into a wedge shape and subsequent handling, it is preferred to use minerals such as quartz.

[0124] In the case of using minerals such as quartz, in order to make the wavelength dispersion characteristics flatter, a phase difference film can be further used. In the case where the slow axis of the phase difference film is arranged orthogonally to the slow axis of the phase difference plate containing minerals such as quartz, it is preferred to use a positive dispersion phase difference film, and in the case where the slow axis of the phase difference film is arranged parallel to the slow axis of the phase difference compensation plate containing minerals such as quartz, it is preferred to use a reverse dispersion phase difference film. In the case of using such a phase difference film, the phase difference film is bonded to the surface of the quartz.

[0125] Examples of the reverse dispersion retardation film include "PURE-ACE WR-S", "PURE-ACE WR-W", and "PURE-ACE WR-M" manufactured by Teijin Co., Ltd. and "NRF" manufactured by Nitto Denko Co., Ltd. Examples of the positive dispersion retardation film include films containing polycarbonate resins and films containing polypropylene resins.

[0126] Examples of the cycloolefin resin include a resin obtained by ring-opening metathesis polymerization of norbornene or its derivatives obtained by Diels-Alder reaction between cyclopentadiene and olefins, followed by hydrogenation; a resin obtained by ring-opening metathesis polymerization of tetracyclododecene or its derivatives obtained by Diels-Alder reaction between dicyclopentadiene and olefins or methacrylates, followed by hydrogenation; a resin obtained by similarly ring-opening metathesis copolymerization of norbornene, tetracyclododecene, their derivatives, or other cycloolefin monomers, followed by hydrogenation; a resin obtained by addition copolymerization of norbornene, tetracyclododecene, or their derivatives with an aromatic compound having a vinyl group, and the like.

[0127] Cycloolefin resins are readily available in the market, for example, Topas (manufactured by Topas Advanced Polymers GmbH), ARTON (manufactured by JSR Corporation), ZEONOR, ZEONEX (manufactured by Nippon ZEON Corporation), and APEL (manufactured by Mitsui Chemicals, Inc.) are listed as trade names.

[0128] As the phase difference value of the first phase difference compensation plate 4, it is preferred to use a phase difference value having a region that is 500 to 600 nm larger than the Re (550) of the release film 133 (hereinafter sometimes referred to as a "wide compensation region"). As the phase difference value of the second phase difference compensation plate 7, it is preferred to use a phase difference value having a region that is 500 to 600 nm larger than the Re (550) of the protective film 141 (hereinafter sometimes referred to as a "wide compensation region"). In this way, by using a phase difference compensation plate 4 having a region that is offset by about 1 wavelength, the transmission spectrum of visible light can be matched with the PET-based resin film in a wider wavelength range, and phase difference compensation can be performed.

[0129] Regarding the phase difference compensation plate, two phase difference compensation plates having a wedge-shaped cross-sectional view may be prepared and used in a state where they are overlapped in directions in which the phase difference value continuously increases in opposite directions.

[0130] In this case, the phase difference value of the phase difference compensation plate refers to 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 phase difference compensation plates, the birefringence of light of the peeling film 133 or the protective film 141 can be compensated in a wide range, so the inspection area can be expanded and the inspection can be performed efficiently.

[0131] In more detail, by staggering at least one of the two phase difference compensation plates in the direction in which the thickness thereof changes, the phase difference of the phase difference compensation plate as a whole can be changed. The degree of this change is gentler than when there is only one phase difference compensation plate by configuring the directions of thickness increase in opposite directions. Thus, in a defect inspection device using two phase difference compensation plates, the area in which the birefringence of the peeling film 133 or the protective film 141 can be offset is further increased compared to a defect inspection device using only one phase difference compensation plate. In addition, the inspection can be performed in the same manner by setting the number of phase difference compensation plates used to three, four, etc. In addition, a plurality of phase difference compensation plates can be prepared, and each time the best phase difference compensation plate is configured on the optical axis 9 to offset the birefringence of the peeling film 133 or the protective film 141.

[0132] The defect inspection device 1 can also be used for a method of inspecting the vicinity of an optical film 100 to be inspected after a region to be inspected is determined in advance, and the optical film 100 can be inspected over a wider range by scanning the light source 2, the first phase difference compensation plate 4, and the second phase difference compensation plate 7. At this time, the detection unit 6 is also moved as needed.

[0133] In addition, as a method of further expanding the inspection field of view, it is also effective to further configure a λ / 2 phase difference layer between the second phase difference compensation plate and the second filter. In this case, the absorption axis of the polarizer of the optical film 100 is arranged in parallel with the absorption axis of the polarizer of the second filter, and the angle formed by the slow axis of the λ / 2 phase difference layer and the absorption axis of the polarizer of the second filter is arranged to be approximately 45°.

[0134] <First application example>

[0135] As a first application example, a suitable application example of the present embodiment will be described for a case where an optical film as an inspection object further includes a λ / 4 retardation layer and a circular polarization plate composed of a combination of a linear circular polarization plate and a λ / 4 retardation layer is inspected for defects.

[0136] An optical film as an inspection object in this application example will be described. Figure 4 2 is a cross-sectional view schematically showing an optical film 200 as an example of an optical film. Figure 4 As shown, the layer structure of the optical film 200 is protective film 141 / linear polarizing plate 110 [first protective film 111 / adhesive layer 114 / polarizing plate 112 / adhesive layer 114 / second protective film 113] [ / adhesive layer 131 / phase difference body 120 [first phase difference layer 121 / adhesive layer 124 / second phase difference layer 122] / adhesive layer 132 / peeling film 133. Figure 1 The same components in the layer structure of the optical film 100 shown are denoted by the same reference numerals, and the description thereof will be omitted.

[0137] The description of the adhesive layer 114 applies to the adhesive layer 124 , and the description of the adhesive layer 132 applies to the adhesive layer 131 , and thus these descriptions are omitted.

[0138] The optical film 200 includes a λ / 4 retardation layer that imparts a retardation of 1 / 4 wavelength to transmitted light as the retardation body 120 , and may further include a λ / 2 retardation layer that imparts a retardation of 1 / 2 wavelength to transmitted light, a positive A plate, and a positive C plate. Figure 4 The retardation body 120 of the optical film 200 shown includes a first retardation layer 121 and a second retardation layer 122. Examples of the combination 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, and a combination of a λ / 4 retardation layer and a positive C layer.

[0139] The phase difference layer can be an optical film showing optical anisotropy. As an optical film showing optical anisotropy, for example, a stretched film obtained by stretching a polymer film containing polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride / polymethyl methacrylate, acetyl cellulose, ethylene-vinyl acetate copolymer saponification, polyvinyl chloride, etc. to about 1.01 to 6 times can be cited. Among the stretched films, preferably, a polymer film obtained by uniaxially stretching or biaxially stretching acetyl cellulose, polyester, polycarbonate film, and cycloolefin resin film. In addition, the phase difference layer can also be a phase difference layer of a cured product containing a polymerizable liquid crystal compound that exhibits optical anisotropy by coating the polymerizable liquid crystal compound on a substrate and orienting it.

[0140] Examples of stretched films include films obtained by stretching a film made of polyvinyl alcohol, polycarbonate, polyester, polyarylate, polyimide, polyolefin, polycycloolefin, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride / polymethyl methacrylate, acetyl cellulose, ethylene-vinyl acetate copolymer saponification product, polyvinyl chloride, etc. to about 1.01 to 6 times.

[0141] As a polymerizable liquid crystal compound for forming a cured product layer of a polymerizable liquid crystal compound, a rod-shaped liquid crystal compound, a disc-shaped liquid crystal compound and a mixture thereof can be used. With regard to the above-mentioned cured product layer, a phase difference layer forming composition comprising a polymerizable liquid crystal compound and a solvent, and various additives as needed is applied to the alignment film to form a coating film, and the coating film is solidified (hardened), thereby being able to form a cured product layer of a polymerizable liquid crystal compound. Alternatively, a phase difference layer forming composition can also be applied to a substrate layer to form a coating film, and the coating film is stretched together with the substrate layer to form a cured product layer. In addition to the above-mentioned polymerizable liquid crystal compound and solvent, the phase difference layer forming composition may also include a polymerization initiator, a reactive additive, a leveling agent, an inhibitor, etc. Liquid crystal compounds, solvents, polymerization initiators, reactive additives, leveling agents, inhibitors, etc. can appropriately use known substances.

[0142] exist Figure 2In the defect inspection device 1 shown, when the object to be inspected is an optical film 200 instead of the optical film 100 and the object to be inspected for defects is a circular polarizing plate, in the arrangement process, a λ / 4 phase difference plate is arranged between the first optical filter 3 and the first phase difference compensation plate 4. The λ / 4 phase difference plate is used to preliminarily provide a phase difference that cancels the phase difference of the λ / 4 phase difference layer of the optical film 200 transmitted in the later stage. The light incident on the optical film 200 is incident on the linear polarizing plate 110 in a state where the influence of the phase difference caused by the transmission of the λ / 4 phase difference layer is canceled. As the first optical filter 3, a filter having a configuration of a λ / 4 phase difference plate on the optical film 200 side closer to the first polarizing plate may be used.

[0143] It should be noted that, limited to the case where the inspection object is the optical film 200 (i.e., limited to the case where the circular polarization plate is used), even if the absorption axis of the first polarizer of the first filter, the absorption axis of the polarizer of the optical film 200, the slow axis of the λ / 4 phase difference layer of the first filter, and the slow axis of the λ / 4 phase difference layer of the optical film 200 are all arranged to be parallel, the state of orthogonal Nicol prisms can be obtained.

[0144] As defects of the circular polarizing plate that can be detected by the defect inspection device 1 in the first application example, as in the case where the object to be inspected is the optical film 100, unevenness of the optical characteristics of the linear polarizing plate 110, local defects, etc. can be cited. In addition, in the first application example, when the light source 2 is configured to be incident from the second filter 5 side, in addition to the above-mentioned defects, defects in the phase difference body 120 can also be detected. When the purpose is to detect only defects of the linear polarizing plate 110, it is preferred to configure the light source 2 to be incident from the first filter 3 side. With this configuration, defects of the linear polarizing plate 110 can be detected with higher accuracy.

[0145] Description of Reference Numerals

[0146] 1: defect inspection device, 2: light source, 3: first optical filter, 4: first phase difference compensation plate, 5: second optical filter, 6: detection unit, 7: second phase difference compensation plate, 100, 200: optical film, 111: first protective film, 112: polarizer, 113: second protective film, 114, 124: adhesive layer, 131, 132: adhesive layer, 133: peeling film, 141: protective film, 120: phase difference body, 121: first phase difference layer, 122: second phase difference layer.

Claims

1. A defect inspection method, which is a defect inspection method for a linear polarizing plate, wherein an optical film having a linear polarizing plate is used as an inspection object, The optical film comprises a release film, the linear polarizing plate, and a protective film in this order, and the optical film further comprises a λ / 4 phase difference layer between the linear polarizing plate and the release film. The defect inspection method has the following features: an arrangement step of sequentially arranging a first optical filter having a first polarizer, a λ / 4 phase difference plate, a first phase difference compensation plate, the optical film, a second phase difference compensation plate, and a second optical filter having a second polarizer along an optical axis, and arranging the optical film in a direction in which a surface on the release film side faces the first phase difference compensation plate; a detection step of injecting light along the optical axis from either the first filter side or the second filter side and detecting light emitted from the other side; as well as a judging step of judging the defects of the optical film based on the detection result in the detecting step, In the configuration step, the configuration is performed in a manner that satisfies the following conditions a and b: (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°; (b) the angle between the absorption axis of the second polarizer and the absorption axis of the linear polarizing plate is within the range of 90°±30°, In the detection process, The first phase difference compensation plate compensates for the birefringence of the release film, and the second phase difference compensation plate compensates for the birefringence of the protective film.

2. The defect inspection method according to claim 1, wherein: The release film includes a polyethylene terephthalate-based resin.

3. The defect inspection method according to claim 1, wherein: The protective film includes a polyethylene terephthalate-based resin.

4. The defect inspection method according to claim 2, wherein: The protective film includes a polyethylene terephthalate-based resin.

5. The defect inspection method according to any one of claims 1 to 4, wherein: The linear polarizing plate includes a polarizer including a cured product of a polymerizable liquid crystal compound.

6. A defect inspection device, which is a defect inspection device for a linear polarizing plate, wherein an optical film having a linear polarizing plate is used as an inspection object, The optical film comprises a release film, the linear polarizing plate, and a protective film in this order, and the optical film further comprises a λ / 4 phase difference layer between the linear polarizing plate and the release film. The defect inspection device comprises, in order along the optical axis: a first filter having a first polarizing plate, a λ / 4 phase difference plate, a first phase difference compensation plate capable of compensating for the birefringence of the peeling film, a second phase difference compensation plate capable of compensating for the birefringence of the protective film, and a second filter having a second polarizing plate, and further comprises a light source capable of irradiating light along the optical axis from the first filter side or the second filter side, and performs defect inspection after a configuration step of configuring the optical film in a direction in which the surface of the peeling film side is opposed to the first phase difference compensation plate. In the configuration step, the configuration is performed in a manner that satisfies the following conditions a and b: (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°; (b) An angle formed between the absorption axis of the second polarizer and the absorption axis of the linear polarizing plate is within a range of 90°±30°.

Images