JP7645095B2 - Defect inspection method and defect inspection device - Google Patents

Description

The present invention relates to a defect inspection method and device for linear polarizing plates, in which an optical film is used as the inspection object.

A polarizing plate used in a display device such as a liquid crystal display device or an organic EL display device is generally constructed 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 oriented 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 below, 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". Furthermore, linear polarizers that have protective films on one or both sides are generally called "linear polarizing plates."

Defects can occur in polarizing plates and polarizers during the manufacturing process. For example, defects can occur such as foreign matter being mixed in between the polarizer and the protective film, or air bubbles remaining. Furthermore, uneven coating during manufacturing can cause unevenness in the optical properties of liquid crystal polarizers.

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 placing a polarizing filter between the polarizing plate to be inspected and a light source, and then rotating the polarizing plate or polarizing filter in a planar direction to set the polarization axis directions of each of these in a specific relationship. When the polarization axis directions are perpendicular to each other (i.e., when they are arranged to form a crossed Nicol), linearly polarized light that passes through the polarizing filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light passes through that location, and the presence of the defect is revealed by detecting that light.

On the other hand, when the polarization axes of the polarizing plate and the polarizing filter are parallel, 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 becomes apparent because the light is not detected. 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 image processing device.

Japanese Patent Application Publication No. 9-229817

The method described in Patent Document 1 can detect localized defects with optical properties that differ greatly from the surrounding area, such as foreign objects or air bubbles, but it is difficult to detect unevenness in optical properties.

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

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 the linear polarizing plate.

The present invention provides the following defect inspection method and defect inspection apparatus.
[1] A method for inspecting a defect in a linearly 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 an angle between the alignment axis and an 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,
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°;
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.

[2] A method for inspecting a defect in a linear polarizing plate, comprising the steps of: inspecting an optical film having a linear polarizing plate, the method 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 an angle between the alignment axis and an 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:
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°;
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.

[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 phase difference plate is placed between the first filter and the optical film.

[7] A defect inspection apparatus for a linearly 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 an angle between the alignment axis and an 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,
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°;
A defect inspection device arranged to satisfy the above.

[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 an angle between the alignment axis and an 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,
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°;
A defect inspection device arranged to satisfy the above.

The defect inspection method and defect inspection device of the present invention can detect unevenness in the optical properties of a linear polarizer when the object to be inspected is an optical film in which a protective film and a release film are laminated on both sides of the linear polarizer.

1 is a cross-sectional view that illustrates an optical film that is an example of an object to be inspected in this embodiment. 1 is a schematic diagram of a defect inspection apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a defective area in an optical film. 1 is a cross-sectional view that illustrates a schematic diagram of an optical film that is an example of an object to be inspected in a first application example.

The present invention relates to a method and apparatus for inspecting a linear polarizing plate, the 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°.

A defect inspection method in which an optical film A is inspected (hereinafter referred to as "defect inspection method A") comprises the steps of:
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°;
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.

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 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 the range of 90°±5°.

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,
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°;
are arranged so as to satisfy

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 process, 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 the range of 90°±5°.

Embodiments of the defect inspection device and defect inspection method of the present invention will be described below with reference to the drawings. Identical elements are given the same reference numerals, and duplicate explanations will be omitted. The dimensional ratios in the drawings do not necessarily match those in the description.

This article describes a defect inspection device and defect inspection method according to one embodiment of the present invention.

[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 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.

(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.

A typical method for manufacturing a liquid crystal polarizer is briefly described below. 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 dye is applied onto the alignment film and dried to form a coating layer containing a polymerizable liquid crystal compound on the alignment film. The coating layer is then 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 manufactured using the transparent resin film as a protective film.

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 oriented, and may have a polymerizable group in the molecule. In addition, as described in WO 2011/024891, 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.

The thickness of the liquid crystal polarizer is, for example, 0.2 μm to 10 μm. Liquid crystal polarizers can 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 this embodiment can detect such uneven optical properties.

Next, a brief description of PVA-based polarizing films will be given. PVA-based polarizing films can be produced, for example, by a method including 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 boric acid solution (crosslinking process); and a step of washing with water after the treatment with the crosslinking liquid (cleaning process).

As the PVA-based resin, a saponified polyvinyl acetate-based resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as 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.

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

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

A film made from such a PVA-based resin is used as a raw film (PVA-based resin film) for manufacturing a polarizer. The method for making a PVA-based resin film is not particularly limited, and a known method can be used. There are no particular limitations on the thickness of the PVA-based resin film, but in order to make the thickness of the PVA-based polarizing film 15 μm or less, it is preferable to use one with 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 final PVA-based polarizing film has the desired thickness.

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

In the case of 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 with 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. This stretching ratio can also be selected so that the final PVA-based polarizing film has the desired thickness.

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.

As a crosslinking treatment after dyeing with a dichroic dye, a method such as immersing the dyed PVA-based resin film in an aqueous solution containing boric acid is usually adopted. When iodine is used as the dichroic dye, it is preferable that the aqueous solution containing boric acid contains potassium iodide.

Thus, a PVA-based polarizing film is obtained. As with the liquid crystal polarizer, the thickness of the PVA-based polarizing film is preferably thinner, preferably 15 μm or less, more preferably 13 μm or less, even more 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.

The linear polarizer can be used alone as a linear polarizing plate, or, as described above, can generally be 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.

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

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-based 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.

The thickness of the protective film is preferably 3 μm or more, and 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 even more preferably 30 μm or less. The above upper and lower limit values can be combined in any combination.

The protective film is attached to the display device together with the polarizer 112 as a component of the linear polarizing plate, so strict control of the phase difference value is required. Typically, a protective film with an extremely small phase difference value is used.

(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.

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

The protective film is peeled off together with its adhesive layer after the optical film is attached to a display device or other optical components, and the peeled protective film is usually discarded. Therefore, unlike a protective film, strict management of the phase difference value is not required. The defect inspection method of this embodiment (defect inspection methods A and B) can detect defects in a linear polarizing plate by eliminating the influence of the phase difference of the protective film, even when the inspected object is an optical film equipped with a protective film for which strict management of the phase difference value is not required.

The protective film is usually made of resin. The resin constituting the protective film is not particularly specified, but examples thereof include polyethylene terephthalate resin (PET resin), polybutylene terephthalate resin, polycarbonate resin, polyarene resin, etc., among which PET resin is preferably used. Films made of PET resin have the advantage that they are versatile as protective films and are inexpensive. On the other hand, as mentioned above, inexpensive PET resin films do not require strict management of the retardation value. Therefore, for example, there is variation in the retardation value for each product lot. In addition, even the same PET resin film may have variation in the in-plane retardation value (in-plane retardation value) and the orientation axis.

In order to accurately detect the presence or absence of defects using the inspection method of this embodiment, it is preferable to use a protective film with an orientation axis variation of 60° or less, and it is more preferable to use a protective film with an orientation axis variation of 50° or less. The variation in the orientation axis of the protective film is the maximum value of the angle made by the different orientation axes.

In this specification, we will show how to determine the in-plane retardation value Re(550) of the protective film at a wavelength of 550 nm. Take a piece of 40 mm x 40 mm in size so that the center of the entire protective film is the center (e.g., take it from a long film using an appropriate cutting tool). Measure the Re(550) of this piece three times and calculate the average value of Re(550). The Re(550) of the piece can be measured using a retardation measuring device KORBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.) at room temperature (approximately 25°C).

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

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). For the optical film 100, the angle between the absorption axis of the polarizer 112 and the orientation axis of the protective film is in the above range, so that the variation in the effect of the birefringence of the protective film 141 on the light that passes 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.

(Release film)
The release film 133 is provided releasably on the adhesive layer 132 and is used to cover and protect the surface of the 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.

The release film 133 is peeled off from the adhesive layer 132 when it is attached to the display device, and is usually discarded after being peeled off. Therefore, unlike a protective film, strict management of the phase difference value is not required.

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 the same PET resin film is used, there may be variations in the retardation value (in-plane retardation value) and the orientation 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 orientation axis in the release film is not particularly limited, and for example, a film having an orientation axis of 135° or less can be used. The release film 133 is usually removed and discarded during the manufacturing process, so strict control of the phase difference value is not required, as is the case with the protective film.

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 protection 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.

[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 the linear polarizing plate 110 of the 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, local defects, and the like. 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.

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, the 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.

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 can be, for example, a metal halide lamp, a halogen transmission light, a fluorescent lamp, etc.

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

In the defect inspection apparatus 1, a placement step is first performed. In the placement step, the optical film 100 to be inspected is placed between the retardation compensation plate 4 and the second polarizer 5 with the surface on the release film 133 side facing the retardation compensation plate 4. In the placement step, the placement angles 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°.

Hereinafter, the absorption axis of the linear polarizer 110 will be referred to as the "absorption axis PA0", the absorption axis of the first polarizer of the first filter 3 as the "absorption axis PA1", and the absorption axis of the second polarizer of the second filter 5 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°.

In the above arrangement process, it is preferable that the angles θ1 and θ2 are adjusted so that the field of view is darkest within a range that satisfies the above conditions. Such adjustments can be made even after the arrangement process by appropriately adjusting the arrangement angles of the first filter 3, the phase difference compensation plate 4, the optical film 100, and the second filter 5. The defect inspection device 1 may be equipped with a movable device (not shown) that enables the first filter 3, the phase difference compensation plate 4, the optical film 100, and the second filter 5 to be rotated in a direction perpendicular to the optical axis 9.

In the defect inspection device 1, a detection process is performed after the placement 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 that order, and reaches the detection unit 6. In the detection unit 6, a judgment process is performed in which a judgment is made about defects in the linear polarizer 110 based on the detection results of the light that has reached the detection unit 6.

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

The phase difference compensation plate 4 is provided in advance with a phase difference that cancels the phase difference caused by the birefringence of the peel-off 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 with the effect of the phase difference caused by transmission through the peel-off film 133 canceled. Since the angle θ1 between the absorption axis PA1 of the first filter 3 that was 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.

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

Defect region B, which has an absorption axis PA3 that does not coincide with absorption axis PA0, transmits the first polarized light. The light that passes through linear polarizer 110 is polarized light in a direction that corresponds to the absorption axis of defect region B of linear polarizer 110. If the absorption axis of the defect region of linear polarizer 110 does not have one direction, the light that passes 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 they form with the first polarized light.

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

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

The inventors noticed that the degree of polarization of the light that passed through the first filter and the optical film was substantially low. They discovered 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 greatly improved.

As described above, the light transmission characteristics of the linear polarizer 110 differ between the normal area A and the defective area B, and the light transmission characteristics of the second filter 5 differ depending on the absorption axis direction in the defective area B. The detection unit 6 detects light that reflects these transmission characteristics, so it is possible to detect the presence or absence of defects in the orthogonal polarizer 110 and the presence or absence of unevenness in the absorption axis direction in the defective area B. Unevenness in the absorption axis direction in the linear polarizer 110 corresponds to unevenness in the optical characteristics.

By having the first filter 3 and the second filter 5, the defect inspection device 1 can efficiently detect unevenness in the optical characteristics of the linear polarizer 110. Therefore, the manufacturing method for the optical film 100 that includes the above-mentioned defect inspection method can efficiently produce the optical film 100 as a product that does not contain defects.

<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) like 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 detailed description of the polarizing film is the same as that of the polarizing film in the above-mentioned polarizer 112. The first polarizer and the second polarizer are defect-free.

<Retardation 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-based 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 so as 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 starting from the thinnest part, 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 object to be inspected.

The retardation compensation plate 4 is preferably rectangular or square with a side length ranging from 1 cm to 30 cm.

The retardation compensation plate 4 can be made of inorganic materials such as minerals that exhibit 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.

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 positive 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 reverse dispersion. When using such a retardation film, the retardation film is laminated to the surface of the quartz.

Examples of reverse dispersion retardation films include "Pure Ace WR-S", "Pure Ace WR-W", and "Pure Ace WR-M" manufactured by Teijin Limited, and "NRF" manufactured by Nitto Denko Corporation. Examples of normal dispersion retardation films include films made of polycarbonate resins and polypropylene resins.

Examples of the cycloolefin resin include a resin obtained by ring-opening metathesis polymerization using norbornene or its derivative obtained by the Diels-Alder reaction of cyclopentadiene and olefins as a monomer, followed by hydrogenation; a resin obtained by ring-opening metathesis polymerization using tetracyclododecene or its derivative obtained by the Diels-Alder reaction of dicyclopentadiene and olefins or methacrylic acid esters as a monomer, followed by hydrogenation; a resin obtained by 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.

Cycloolefin resins are readily available commercially. Examples of commercially available products include 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.).

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

The phase difference compensator 4 may be used by preparing two phase difference compensators with a wedge-shaped cross section, stacked together with the directions in which the phase difference value increases continuously being opposite to each other. In this case, the phase difference value of the phase difference 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 phase difference compensators, the optical birefringence of the release film 133 can be compensated for over a wide range, so the inspection area can be expanded and inspection can be performed efficiently.

More specifically, the phase difference of the entire phase difference compensation plate can be changed by shifting at least one of the two phase difference compensation plates in the direction in which the thickness changes. The degree of change is gentler than when there is only one phase difference compensation plate, because the thicknesses are arranged in the opposite directions. As a result, in a defect inspection device using two phase difference compensation plates, the area in which the birefringence of the release film 133 can be cancelled is wider than in a defect inspection device using only one phase difference compensation plate. In addition, inspection can be performed in the same way even if three or four phase difference compensation plates are used. In addition, multiple phase difference compensation plates may be prepared, and the most suitable phase difference compensation plate for cancelling the birefringence of the release film 133 may be placed on the optical axis 9 each time.

The defect inspection device 1 may be used to inspect the optical film 100, which is the object to be inspected, by first specifying the area to be inspected, and then inspecting that area. By scanning the light source 2 and the phase difference compensation plate 4, it is possible to inspect a wider area of the optical film 100. At this time, the detection unit 6 is also moved as necessary.

<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.

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. The layer structure of the optical film 200 is, as shown in FIG. 4, 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/phase difference body 120 [first phase difference layer 121/adhesive layer 124/second phase difference 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 given 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, so the description thereof will be omitted.

The optical film 200 includes, as the retarder 120, a λ/4 retardation layer that imparts a phase difference of 1/4 wavelength to the transmitted light, and may further include a λ/2 retardation layer that imparts a phase difference of 1/2 wavelength to the 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, and a combination of a λ/4 retardation layer and a positive C layer.

The retardation layer can 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 that has been applied to a substrate and oriented to exhibit optical anisotropy.

Examples of stretched films include films obtained by stretching 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 their original size.

As the polymerizable liquid crystal compound for forming the cured 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 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) the 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 layer. The retardation layer forming composition may contain a polymerization initiator, a reactive additive, a leveling agent, a polymerization inhibitor, etc., in addition to the above-mentioned polymerizable liquid crystal compound and solvent. The liquid crystal compound, solvent, polymerization initiator, reactive additive, leveling agent, polymerization inhibitor, etc., can be appropriately used.

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 object to be inspected for defects is a circular polarizer, a λ/4 retardation plate is placed between the first filter 3 and the retardation compensation plate 4 in the arrangement process. This λ/4 retardation plate provides 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 effect of the phase difference due to transmission through the λ/4 retardation layer is canceled. The first filter 3 may be configured to have a λ/4 retardation plate on the optical film 200 side rather than the first polarizer.

In addition, only when the object to be inspected is the optical film 200 (i.e., only when it is a circular polarizing plate), the 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 the 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 the optical film 200 are all arranged parallel to each other.

In the first application example, defects of the circular polarizer that can be detected by the defect inspection device 1 include unevenness in the optical characteristics of the linear polarizer 110, local defects, etc., as in the case where the object to be inspected 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, in addition to the above-mentioned defects, defects in the retarder 120 can also be detected. When the purpose 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 more accurately.

1 Defect inspection device, 2 Light source, 3 First filter, 4 Retardation 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 (6)

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 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,
In the detection step,
The phase difference compensating plate compensates for birefringence of the release film. 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 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,
In the detection step,
The phase difference compensating plate compensates for birefringence of the release film. The defect inspection method according to claim 1 or 2, wherein the release film is made of a polyethylene terephthalate resin. 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. 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 . 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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