WO2021176797A1

WO2021176797A1 - Inspection method

Info

Publication number: WO2021176797A1
Application number: PCT/JP2020/047107
Authority: WO
Inventors: 信次小林; 尚人田岡; 麻耶尾崎; 里恵曽我部
Original assignee: 住友化学株式会社
Priority date: 2020-03-04
Filing date: 2020-12-17
Publication date: 2021-09-10
Also published as: JP2021139999A; JP7374815B2; TW202134636A

Abstract

The object to be inspected comprising a first polarizing plate and a first retardation film that is formed from a cured product of a polymerizable crystal liquid compound and is formed on one face of the first polarizing plate is irradiated with inspection light to determine the presence/absence of a defect in the first retardation film. The aforementioned are disposed such that the angle formed by the slow axis of the fist retardation film and the slow axis of a second retardation film becomes 10°-80°. The in-plane phase difference values at a wavelength of 550 nm of the first retardation film and the second retardation film are approximately the same. The inspection light has an intensity peak with the half width of 30 nm or less and has a wavelength at which the amount of light transmitted by the object to be inspected and a retardation filter is minimized within a wavelength range of 500-600 nm.

Description

Inspection method

The present invention relates to an inspection method.

Since the retardation film can convert linearly polarized light into circularly polarized light or elliptically polarized light, and conversely, it can convert circularly polarized light or elliptically polarized light into linearly polarized light, this retardation film and linearly polarizing plate are combined (elbow). Circular polarizing plates are applied to organic EL display devices and reflective liquid crystal display devices. Among the retardation films, the retardation film obtained by orienting and curing a polymerizable liquid crystal compound is an extremely thin film, and has been attracting attention in manufacturing a thin display device (for example, patent documents). 1).

It is also important that the manufactured (elliptical) circularly polarized light can be inspected for defects before it is shipped as a product. Generally, as an inspection method of an optical film, an optical film as an object to be inspected is irradiated with inspection light and detected as a bright spot defect or a dark spot defect in a dark mode or a white mode (for example,). See Patent Document 2).

Japanese Unexamined Patent Publication No. 2006-58546 Japanese Unexamined Patent Publication No. 2015-13831

In the inspection method of Patent Document 2, it is necessary to use light of a plurality of wavelengths (plurality of light sources). Further, the defect portion actually has a small difference in the amount of transmitted light from the normal portion, and the difference is not so large that automatic detection can be reliably performed. Therefore, the present invention is an inspection method for determining the presence or absence of defects in the retardation film, and can use a single wavelength and increase the difference in the amount of transmitted light of the inspection light between the normal portion and the defective portion. The purpose is to provide an inspection method.

In the present invention, inspection light is applied to a film-shaped object to be inspected including a first polarizing plate and a first retardation film made of a cured product of a polymerizable liquid crystal compound formed on one side of the first polarizing plate. This is an inspection method for determining the presence or absence of defects in the first retardation film when incident, and is a second phase difference formed on one side of an object to be inspected and a second polarizing plate and a second polarizing plate. A retardation filter including a film is provided so that the first retardation film side of the object to be inspected faces the retardation filter side and the second retardation film side of the retardation filter faces the object to be inspected. Moreover, the angle formed by the slow axis of the first retardation film and the slow axis of the second retardation film is 10 ° to 80 ° when viewed from the optical axis direction of the inspection light. The in-plane retardation value of the first retardation film at a wavelength of 550 nm and the in-plane retardation value of the second retardation film at a wavelength of 550 nm are substantially the same as each other. Light having a half-value width of 30 nm or less and a wavelength in which the amount of transmitted light of the object to be inspected and the retardation filter is minimized within the range of a wavelength of 500 to 600 nm, and is the first polarizing plate side or position of the object to be inspected. Inspection light is incident from either side of the second polarizing plate side of the phase difference filter so that the optical axis passes through a predetermined inspection region on the object to be inspected, and the second polarizing plate or the second polarizing plate or the second polarizing plate is incident from the other side. An inspection method for observing the polarizing plate of No. 1 is provided.

In this inspection method, as the inspection light, light having a wavelength that minimizes the amount of transmitted light of the object to be inspected and the retardation filter is used. At the wavelength at which the amount of transmitted light in the normal portion is minimized, the amount of transmitted light in the portion (defective portion) of the first retardation film whose retardation value deviates from the desired value tends to be large, and in particular, the wavelength is 500 to 500 to. When the wavelength is in the range of 600 nm, even if the phase difference value of the defective part is deviated to be larger than the phase difference value of the normal part or deviated to be smaller than the normal part, it is more transparent than the normal part. Since the amount of light is large, it is easy to detect as a defect. Further, since the light having the half width of the intensity peak of 30 nm or less is used as the inspection light, the contrast ratio between the normal portion and the defective portion becomes high, and the defective portion can be easily recognized as a difference in brightness.

In the present invention, before the inspection, the third polarizing plate having the same configuration as the first polarizing plate and the first retardation film formed on one side of the third polarizing plate have the same configuration. A film-shaped test piece having the retardation film of 3 is prepared, and the test piece and the retardation filter are arranged so that the third retardation film side of the test piece faces the retardation filter side and the retardation filter. The angle formed by the slow axis of the third retardation film and the slow axis of the second retardation film is the optical axis of the inspection light so that the second retardation film side of the filter faces the test piece side. Arranged so that the angle is other than 90 ° when viewed from the direction, the optical axis is on the test piece from either the third polarizing plate side of the test piece or the second polarizing plate side of the retardation filter. Light of various wavelengths is incident so as to pass through the defect-free region of the above, and the second polarizing plate or the first polarizing plate is observed from the other side to obtain the wavelength that minimizes the amount of transmitted light. It is preferable to decide to use light of a wavelength as the inspection light.

In the defect inspection of the present invention, in order to find a portion (defect portion) of the first retardation film to be inspected whose retardation value deviates from the desired retardation value, the amount of transmitted light of the defect portion is small. However, it is desirable to use light with a larger wavelength. Therefore, it is preferable to find the optimum wavelength prior to the inspection and decide to adopt it as the inspection light. In the process of finding the wavelength, the angle formed by the slow axis of the second retardation film and the slow axis of the third retardation film (= the slow axis of the first retardation film 7A later) is defined as described above. When the angle is set to, the amount of change in the amount of transmitted light with respect to the degree of change in wavelength is large, and it is easy to find a wavelength useful for defect inspection.

According to the present invention, it is an inspection method for determining the presence or absence of defects in the retardation film, and it is possible to use a single wavelength and increase the difference in the amount of transmitted light of the inspection light between the normal portion and the defective portion. It is possible to provide an inspection method that can be performed.

It is a figure which shows the arrangement of each member in the defect inspection process in the inspection method of this embodiment. It is a figure which shows the arrangement of each member in the light source wavelength selection process in the inspection method of this embodiment. FIG. (A) is a diagram showing the relationship between the slow axis of the third retardation film in the test piece and the slow axis of the second retardation film in the retardation filter. (B) is a view of (A) viewed from the optical axis side. FIG. (A) is a diagram showing the relationship between the slow axis of the first retardation film in the object to be inspected and the slow axis of the second retardation film in the retardation filter. (B) is a view of (A) viewed from the optical axis side. It is a figure which shows the arrangement of each member in the defect inspection process of another embodiment.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same parts or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted.

<Definition of terms and symbols>
Definitions of terms and symbols herein are as follows.
(1) Refractive index (nx, ny, nz)
"Nx" is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), "ny" is the direction orthogonal to the slow-phase axis in the in-plane, and "nz" is the thickness direction. Refractive index.
(2) In-plane retardation value The in-plane retardation value (Re (λ)) refers to the in-plane retardation value of the film at 23 ° C. and a wavelength of λ (nm). Re (λ) is obtained by Re (λ) = (nx−ny) × d, where d (nm) is the thickness of the film.
(3) Phase difference value in the thickness direction The phase difference value in the thickness direction (Rth (λ)) refers to the phase difference value in the thickness direction of the film at 23 ° C. and a wavelength of λ (nm). Rth (λ) is obtained by Rth (λ) = ((nx + ny) / 2-nz) × d, where d (nm) is the thickness of the film.

<Inspection equipment and objects to be inspected>
The inspection device of the present embodiment inspects the presence or absence of surface defects of the retardation film. As shown in FIG. 1, the inspection device 1A includes a light source 2, a phase difference filter 4, and a camera (detecting means) 6 arranged in this order. The inspection device 1A is provided with a place for arranging the inspected object 10 to be inspected between the light source 2 and the phase difference filter 4, and FIG. 1 shows a state in which the inspected object 10 is arranged there. I'm drawing.

First, the film-shaped object 10 to be inspected will be described. The object 10 to be inspected is a long circular polarizing plate (phase difference plate), and is formed by laminating a first polarizing plate 3A and a first retardation film 7A which is a main body to be inspected. Here, both are bonded so that the absorption axis of the first polarizing plate 3A and the slow axis of the first retardation film 7A are at 45 ° to each other. In the present specification, the term "circularly polarized light" includes a circularly polarizing plate and an elliptical polarizing plate. Further, "circularly polarized light" includes circularly polarized light and elliptically polarized light.

The first retardation film 7A is, for example, a λ / 4 plate. In the present embodiment, the first retardation film 7A is made of a cured product of a polymerizable liquid crystal compound. The first retardation film 7A made of a cured product of a polymerizable liquid crystal compound usually has a thin thickness of about 0.2 μm to 10 μm, and when a foreign substance or the like is contained, the retardation value tends to decrease at that portion.

The polymerizable liquid crystal compounds capable of forming the first retardation film 7A are, for example, JP-A-2009-173893, JP-A-2010-31223, WO2012 / 147904, WO2014 / 10325 and WO2017-43438. Examples thereof include those disclosed in the publication. The polymerizable liquid crystal compounds described in these publications can form a retardation film having so-called anti-wavelength dispersibility, which enables uniform polarization conversion in a wide wavelength range.

As a method for forming the first retardation film 7A, a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution; liquid composition) is applied (coated) on the base film to form a coating film. By photopolymerizing this, an extremely thin substance can be formed as described above. Such a base film may be provided with an alignment film for orienting the polymerizable liquid crystal compound.
The alignment film may be either photo-aligned by polarized light irradiation or mechanically oriented by rubbing treatment. As a specific example of such an alignment film, those described in the above publication can be used. The first retardation film 7A formed in this way is attached to the first polarizing plate 3A together with the base film, and then the base film is peeled off to form the first retardation film 7A. It can be transferred onto the first polarizing plate 3A. Alternatively, the first retardation film 7A may be formed by directly applying a solution containing the polymerizable liquid crystal compound onto the first polarizing plate 3A.

When the first retardation film 7A is formed, foreign matter is present on the base film to which the polymerizable liquid crystal compound solution is applied, or the base film or the first polarizing plate 3A itself is scratched. In addition, a defect may occur in the coating film itself obtained by applying the polymerizable liquid crystal compound solution.
For example, the phase difference value fluctuates due to uneven thickness of the coating film.

Further, when the alignment film is rubbed, debris of the rubbing cloth remains on the alignment film, which may cause a defect in the coating film of the polymerizable liquid crystal compound solution (composition for forming a liquid crystal cured film). In this way, when a retardation film is formed from a polymerizable liquid crystal compound, it is possible to form a retardation film having an extremely thin thickness, but the above-mentioned debris and scratches cause optical defects in the retardation film. May become.

In the inspection device 1A, the first polarizing plate 3A is a film that converts light incident from the light source 2 into linearly polarized light, and is formed by laminating a protective film on at least one surface of the polarizing film. Examples of the polarizing film include a polyvinyl alcohol film in which iodine and a dichroic dye are adsorbed and oriented, and a film in which a polymerizable liquid crystal compound is oriented and polymerized and a dichroic dye is adsorbed and oriented. Be done.

The first polarizing plate 3A has an absorption axis in a transmission axis direction for emitting linearly polarized light and in a direction orthogonal to the transmission axis direction. In the present embodiment, for convenience, the direction in which linearly polarized light is emitted is defined as the transmission axis direction, and the direction in which linearly polarized light is emitted is defined as the absorption axis direction, but the polarizing film in which the polarized light in the blocking direction is reflected is not excluded. ..

Here, the protective film is for protecting the polarizing film. As the protective film, a film widely used in the technical field of polarizing plates is used for the purpose of obtaining a polarizing plate having appropriate mechanical strength. Typically, cellulose ester films such as triacetyl cellulose (TAC) films; cyclic olefin films; polyester films such as polyethylene terephthalate (PET) films: (meth) acrylic films such as polymethyl methacrylate (PMMA) films. It is a film or the like. Further, an additive widely used in the technical field of the polarizing plate may be contained in the protective film. The phase difference of the protective film used for the linear polarizing plate is preferably small. For example, in Re (550), 10 nm or less is preferable, and 5 nm or less is particularly preferable.

The object 10 to be inspected may further have a positive C plate on the first retardation film 7A. The thickness direction retardation value (Rth (550)) of the positive C plate may be appropriately selected according to the thickness direction retardation value of the first retardation film 7A to be inspected.

Various commercially available products can be used as the light source 2, but it is advantageous that the light source 2 is, for example, linear light such as laser light (including one that approximates linear light). The light emitted by the light source 2 is unpolarized, passes through the first polarizing plate 3A and becomes polarized light in a predetermined direction, and further passes through the first retardation film 7A and becomes circularly polarized light. That is, unpolarized light passes through the first polarizing plate 3A and the first retardation film 7A, resulting in circularly polarized light.

The retardation filter 4 includes a second polarizing plate 3B and a second retardation film 7B laminated on the second polarizing plate 3B. Here, both are bonded so that the absorption axis of the second polarizing plate 3B and the slow axis of the second retardation film 7B are at 45 ° to each other. As the retardation filter 4, the in-plane retardation value at a wavelength of 550 nm is substantially the same as the in-plane retardation value of the first retardation film 7A to be inspected at a wavelength of 550 nm. The in-plane phase difference value is, for example, λ / 4. Here, "λ" is a measurement wavelength (here, 550 nm). In order to determine the optical defect from the luminance (brightness) information ΔL *, it is preferable to use a film having the same configuration as the object 10 to be inspected for the retardation filter 4.

Further, the phase difference filter 4 may further include a positive C plate. The positive C plate may be provided on the surface facing the first retardation film 7A, or may be provided on the surface opposite to the first retardation film 7A. The inspection area can be expanded by using the positive C plate. The thickness direction retardation value (Rth (550)) of the positive C plate may be appropriately selected according to the thickness direction retardation value of the first retardation film 7A to be inspected. For example, the first retardation film may be selected. When 7A is a λ / 4 plate, the effect can be easily obtained by using a phase difference value (Rth (550)) in the thickness direction of -50 nm to −300 nm.

The retardation filter 4 may include a second retardation film 7B and a base film on which the second retardation film 7B is laminated. It is preferable to use a base film having a substantially zero in-plane retardation value (Re (550)) so as not to impair the optical characteristics of the second retardation film 7B. Here, when the in-plane phase difference is substantially zero, it means that the in-plane phase difference value (Re (550)) is 3 nm or less.

Here, how to obtain the in-plane retardation value (Re (550)) and the thickness direction retardation value (Rth (550)) at a wavelength of 550 nm will be shown. As described above, for example, a piece having a size of about 40 mm × 40 mm is separated from the film to be measured (from a long film, separated by using an appropriate cutting tool, etc.). Re (550) of this piece is measured three times, and the average value of Re (550) is obtained. One piece of Re (550) can be measured at a measurement temperature of room temperature (23 ° C.) using a phase difference measuring device KOBRA-WPR (manufactured by Oji Measuring Instruments Co., Ltd.).

The configuration and material of the second polarizing plate 3B are the same as those of the first polarizing plate 3A.

In the inspection device 1A of the present embodiment, in order to observe the light that has passed through the object 10 to be inspected and the retardation filter 4, the side of the optical axis 9 and both sides of the retardation filter 4 where the light source 2 is located is A camera (detection means) 6 is arranged at a position on the opposite side. The camera 6 is, for example, a CCD camera. In this case, the camera 6 is automatically detected by image processing analysis in which the CCD camera and the image processing device are combined, whereby the object 10 to be inspected can be inspected.

<Inspection method>
Hereinafter, a method for inspecting a circularly polarizing plate using the inspection device 1A will be described. Before starting the inspection with the circularly polarizing plate as the object 10 to be inspected, the wavelength of the light emitted by the light source 2 is set. To set the wavelength, use a test piece to select the wavelength.

(Light source wavelength selection process)
The wavelength of the light emitted by the light source 2 can be selected as follows.

First, as shown in FIG. 2, in the inspection device 1A, the test piece 20 is placed at the place where the object 10 to be inspected is placed. The test piece 20 is a circularly polarizing plate (phase difference plate), and includes a third polarizing plate 3C and a third retardation film 7C laminated on one surface thereof. The test piece 20 is a part of a long object to be inspected 10 cut out, and has substantially the same structure as the object to be inspected 10. That is, the test piece 20 is a laminated body having substantially the same material, thickness, and laminated structure as the object 10 to be inspected.

The test piece 20 is arranged in the inspection device 1A so that the third retardation film 7C faces the retardation filter 4 side. At this time, as shown in FIG. 3, the slow axis p of the third retardation film 7C included in the test piece 20 and the slow axis q of the second retardation film 7B included in the retardation filter 4 The angle θ ₁ between the two is arranged so as to be an angle other than 90 ° when viewed from the direction of the optical axis 9. This angle is preferably 10 ° to 80 °, more preferably 20 ° to 70 °, and even more preferably 30 ° to 60 °. Here, the angle θ ₁ can take a value of 0 ° or more and 90 ° or less, and an angle exceeding 90 ° is expressed by a value of 0 ° or more and 90 ° or less. By arranging at such an angle, it becomes easy to find a wavelength useful for defect inspection. That is, in the defect inspection, in the first retardation film 7A to be inspected, the amount of transmitted light of the defective portion is small in order to find the portion (defective portion) whose retardation value deviates from the desired retardation value. However, it is desirable to use light with a larger wavelength. Here, the angle formed by the slow axis q of the second retardation film 7B and the slow axis p of the third retardation film 7C (= the slow axis r of the first retardation film 7A later) is When the angle is the above, the amount of change in the amount of transmitted light with respect to the degree of change in wavelength is large, and it becomes easy to find a wavelength useful for defect inspection.

Of the surface of the test piece 20, a normal portion presumed to have no defect in the third retardation film 7C is positioned on the optical axis, and the normal portion is irradiated with light of an arbitrary wavelength from the light source 2. The amount of transmitted light is measured by using the camera 6 from the opposite side across the phase difference filter 4. Next, light with a different wavelength is irradiated, and the amount of transmitted light is measured. In this way, the amount of transmitted light is measured with light having various wavelengths, and the wavelength at which the amount of transmitted light is minimized is determined. The wavelength that minimizes the amount of transmitted light is used as the inspection light.

The examination of the wavelength is preferably performed in the range of 500 to 600 nm. The wavelength used as the inspection light may be, for example, 520 to 590 nm, 530 to 580 nm, or 540 to 570 nm. Within these wavelength ranges, the amount of transmitted light of the inspection light at the defective part tends to be larger than the amount of transmitted light of the inspection light at the normal part, which is advantageous for detecting the presence or absence of defects.

(Defect inspection process)
After determining the wavelength of the inspection light, the defect inspection of the object 10 to be inspected is performed next. As shown in FIG. 1, the object to be inspected 10 is arranged between the light source 2 of the inspection device 1A and the phase difference filter 4. At this time, the first retardation film 7A is arranged so as to face the retardation filter 4 side. Further, as shown in FIG. 4, the slow axis r of the first retardation film 7A included in the object 10 to be inspected and the slow axis q of the second retardation film 7B included in the retardation filter 4 The angle θ ₂ formed is 10 ° to 80 ° when viewed from the direction of the optical axis 9. This angle is preferably 20 ° to 70 °, more preferably 30 ° to 60 °. Here, the angle θ ₂ can take a value of 0 ° or more and 90 ° or less, and an angle exceeding 90 ° is expressed by a value of 0 ° or more and 90 ° or less. By arranging at such an angle, the retardation value of the first retardation film 7A deviates from the desired value at the wavelength at which the amount of transmitted light in the normal portion is minimized, which is determined in the light source wavelength selection step. The amount of transmitted light in the existing part (defective part) tends to increase. In particular, when the wavelength used is a wavelength in the range of 500 to 600 nm, even if the phase difference value of the defective portion is shifted to be larger than the phase difference value of the normal portion, it is shifted to be smaller. However, the amount of transmitted light is larger than that of the normal part, and it is easy to detect it as a defect. In other wavelength regions, only one of the cases where the phase difference value of the defective part is shifted to be larger than the phase difference value of the normal part or the phase difference value is shifted to be smaller than the normal part is larger than the normal part. The amount of transmitted light is often large, and in this case, it is necessary to perform the inspection using inspection lights of two types of wavelengths corresponding to each. However, in the present embodiment, by finding the optimum wavelength for the inspection, the defect inspection can be performed using only the inspection light having a single wavelength.

After arranging the object 10 to be inspected, the light source 2 irradiates a predetermined inspection area of the object 10 to be inspected with light having a wavelength determined in the light source wavelength selection step. At this time, the inspection light used has a half width of the intensity peak of 30 nm or less. The inspection light may have a half width of 20 nm or less, or may have a half width of 10 nm or less. By using such inspection light, the contrast ratio between the normal part and the defective part becomes high, the brightness of the defective part recognized as a part whose color is different from that of the normal part becomes stronger, and the defective part is determined by the difference in brightness. It becomes easy to recognize.

As described above, the retardation filter 4 uses an in-plane retardation value at a wavelength of 550 nm which is substantially the same as the in-plane retardation value of the first retardation film 7A to be inspected at a wavelength of 550 nm. When the phase difference filter 4 is observed with the camera 6, the normal portion of the object 10 to be inspected is recognized as dark. Where the defective portion is recognized as having a different color from the normal portion, it is detected in a state where the brightness is high because the inspection light having the above half-value width is used. Therefore, according to the inspection method of the present embodiment, it is possible to easily determine the presence or absence of defects in the first retardation film 7A in the object to be inspected 10.

After completing the inspection of the predetermined inspection area of the inspected object 10, the inspected object 10 can be transported and inspected in the next inspection area.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment. For example, in the above embodiment, the inspection light emitted by the light source 2 is incident on the object 10 to be inspected and the retardation filter 4 in this order, and the inspection light emitted from the retardation filter 4 is captured by the camera 6. The positions of 2 and the camera 6 may be reversed. That is, as shown in FIG. 5, the inspection light emitted by the light source 2 is incident on the phase difference filter 4 and the inspected object 10 in this order, and the inspection light emitted from the inspected object 10 is captured by the camera 6 (inspection). It may be the device 1B).

Further, although the above-described embodiment shows that the object to be inspected is a long one, the object to be inspected may be, for example, a rectangular single-wafered object.

The present invention can be used for an inspection for determining the presence or absence of defects in the retardation film.

1A, 1B ... inspection device, 2 ... light source, 3A ... first polarizing film, 3B ... second polarizing film, 3C ... third polarizing film, 4 ... retardation filter, 6 ... camera (detection means), 7A ... 1st retardation film, 7B ... 2nd retardation film, 7C ... 3rd retardation film, 9 ... optical axis, 10 ... object to be inspected, 20 ... test piece, p ... third retardation film Slow axis of, q ... Slow axis of the second retardation film, r ... Slow axis of the first retardation film, θ ₁ , θ ₂ ... Angle.

Claims

Inspection light is incident on a film-shaped object to be inspected, which includes a first polarizing plate and a first retardation film made of a cured product of a polymerizable liquid crystal compound formed on one side of the first polarizing plate. This is an inspection method for determining the presence or absence of defects in the first retardation film.
A retardation filter including the object to be inspected and a second polarizing plate and a second retardation film formed on one surface of the second polarizing plate is provided with a first retardation film of the object to be inspected. The side faces the retardation filter side, the second retardation film side of the retardation filter faces the object to be inspected, and the slow axis and the first retardation of the first retardation film. Arranged so that the angle formed by the retarding axis of the retardation film 2 with the slow axis is 10 ° to 80 ° when viewed from the optical axis direction of the inspection light.
The in-plane retardation value of the first retardation film at a wavelength of 550 nm and the in-plane retardation value of the second retardation film at a wavelength of 550 nm are substantially the same.
The inspection light is light having a wavelength in which the half width of the intensity peak is 30 nm or less and the amount of transmitted light of the object to be inspected and the retardation filter is minimized within the wavelength range of 500 to 600 nm.
The optical axis passes through a predetermined inspection region on the inspected object from either the first polarizing plate side of the inspected object or the second polarizing plate side of the retardation filter. An inspection method in which the inspection light is incident on the surface and the second polarizing plate or the first polarizing plate is observed from the other side.
Before performing the above inspection
A third polarizing plate having the same configuration as the first polarizing plate and a third retardation film having the same configuration as the first retardation film formed on one surface of the third polarizing plate are formed. Prepare a film-shaped test piece to prepare
With respect to the test piece and the retardation filter, the third retardation film side of the test piece faces the retardation filter side, and the second retardation film side of the retardation filter is the test piece side. The angle formed by the slow axis of the third retardation film and the slow axis of the second retardation film is other than 90 ° when viewed from the optical axis direction of the inspection light. Arrange so that the angle is
Various so that the optical axis passes through a defect-free region on the test piece from either the third polarizing plate side of the test piece or the second polarizing plate side of the retardation filter. Light of a different wavelength is incident, the second polarizing plate or the first polarizing plate is observed from the other side, a wavelength that minimizes the amount of transmitted light is obtained, and the light of that wavelength is adopted as the inspection light. The inspection method according to claim 1, which determines that.