JP2023171051A - Inspection method - Google Patents

Abstract

To provide an inspection method for determining the presence of defects in a retardation layer, with which it is possible to easily detect not just defects based on phase difference but also defects based on axis deviation.SOLUTION: Provided is an inspection method for applying inspection light to a film-like test object 10 having a first polarizing plate 3A and a first λ/4 retardation layer 9A and determining the presence of defects in the first λ/4 retardation layer 9A. The test object 10 and a retardation filter 4 having a second polarizing plate 3B and a second λ/4 retardation layer 9B are arranged in such a way that the angle formed by the mutual slow axes is 0°±30°. Here, the in-plane retardation values of the first λ/4 retardation layer 9A and second λ/4 retardation layer 9B are differentiated.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inspection method.

A retardation layer can convert linearly polarized light into circularly polarized light, or conversely, convert circularly polarized light into linearly polarized light, so a circularly polarizing plate that combines this retardation layer and a linearly polarizing plate is suitable for organic EL display devices. It is applied to reflective liquid crystal display devices. Among retardation layers, the retardation layer obtained by aligning and curing a polymerizable liquid crystal compound is an extremely thin film, and has therefore been attracting attention for manufacturing thin display devices (for example, Patent Document (see 1).

It is also important that the manufactured circularly polarizing plate can be inspected for defects before being shipped as a product. Generally, as a method for inspecting an optical film, an optical film to be inspected is irradiated with inspection light, and defects are detected based on the difference in the amount of transmitted light (see, for example, Patent Document 2).

Japanese Patent Application Publication No. 2006-58546 Japanese Patent Application Publication No. 2021-139999

In the inspection method of Patent Document 2, when the retardation value of the circularly polarizing plate that is the object to be inspected deviates from the ideal (this is called "phase difference shift"), the defect is detected using colored light (for example, red or red light). blue). However, defects caused by deviation of the slow axis of the retardation layer from the designed axis angle with respect to the absorption axis of the polarizer (this is called "axis deviation") do not cause coloration and only cause a slight change in brightness. Because of this, it is difficult to detect.

SUMMARY OF THE INVENTION Therefore, the present invention provides an inspection method for determining the presence or absence of defects in a retardation layer, which can easily detect not only defects based on phase difference shifts but also defects based on axis misalignment. With the goal.

The present invention detects defects in the first λ/4 retardation layer by making an inspection light incident on a film-like object to be inspected that includes a first polarizing plate and a first λ/4 retardation layer. An inspection method for determining a first λ/4 phase difference between an object to be inspected and a phase difference filter including a second polarizing plate and a second λ/4 phase difference layer. The layer side faces the phase difference filter side, and the second λ/4 phase difference layer side of the phase difference filter faces the object to be inspected, and the slow phase of the first λ/4 phase difference layer The angle between the axis and the slow axis of the second λ/4 retardation layer was 0° ± 30° when viewed from the optical path direction of the inspection light, and the The in-plane retardation value of the first λ/4 retardation layer and the in-plane retardation value of the second λ/4 retardation layer measured with light with a wavelength of 550 nm are different from each other. Inspection light is input from either the first polarizing plate side or the second polarizing plate side of the phase difference filter so that the optical path passes through a predetermined inspection area on the object to be inspected, and the inspection light is input from the other side. The present invention provides an inspection method for observing a second polarizing plate or a first polarizing plate.

According to the present invention, not only defects based on a phase difference shift but also defects based on an axis shift can be easily detected as defects in a retardation layer included in an object to be inspected.

The present invention may include one or more of the following features.

In the present invention, the in-plane retardation value of the second λ/4 retardation layer measured with light with a wavelength of 550 nm is the in-plane retardation value of the first λ/4 retardation layer measured with light with a wavelength of 550 nm. It can be made to differ within a range of ±20 nm. By satisfying this requirement, defects due to axis misalignment can be detected more easily.

The present invention provides a second test using light with a wavelength of 550 nm so that the transmittance of the inspection light for the part of the object to be inspected that has no defects and the phase difference filter is 0.1% to 5%. The in-plane retardation value of the λ/4 retardation layer may be selected. If the transmittance of the inspection light is within this range, the brightness of the observation field will be particularly suitable for inspection, allowing defects to be correctly recognized as defects, and non-defects to not be mistakenly recognized as defects. Increases accuracy.

The first λ/4 retardation layer may be made of a cured product of a polymerizable liquid crystal compound. When this retardation layer is a stretched film, it is easy to predict that overall axis misalignment will occur depending on the stretching condition, but when this retardation layer is made of a cured product of a polymerizable liquid crystal compound, alignment of liquid crystal molecules may be partially disturbed, and defects may occur locally due to axis misalignment caused by this. According to the present invention, locally generated axis misalignment defects can also be easily detected.

In the present invention, the inspection light may be visible light other than a single wavelength. In an inspection method using light of a single wavelength, it is necessary to remove unnecessary wavelength light with a corresponding bandpass filter, resulting in a low light intensity, and therefore it is necessary to increase the light intensity of the light source. On the other hand, if it is possible to use light that includes light of various wavelengths, such as white light, for example, sufficient light for inspection can be incident on the object to be inspected, so there is no need to increase the light intensity of the light source. do not have.

According to the present invention, there is provided an inspection method for determining the presence or absence of defects in a retardation layer, which can easily detect not only defects based on phase difference shifts but also defects based on axis misalignment. be able to.

It is a figure showing arrangement of each member in the inspection method of this embodiment. (A) is a diagram showing the relationship between the slow axis of the first λ/4 phase difference layer included in the test object and the slow axis of the second λ/4 phase difference layer included in the phase difference filter. be. (B) is a diagram of (A) viewed from the optical path side. It is a figure showing arrangement of each member in the inspection method of other embodiments.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same parts or corresponding parts are given the same reference numerals, and overlapping explanations will be omitted.

<Definition of terms and symbols>
Definitions of terms and symbols used 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 maximum (that is, the slow axis direction), "ny" is the direction perpendicular to the slow axis in the plane, and "nz" is the thickness direction is the refractive index of
(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 wavelength λ (nm). Re(λ) is determined by Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the film.
(3) Retardation value in the thickness direction The retardation value in the thickness direction (Rth (λ)) refers to the retardation value in the thickness direction of the film at 23° C. and wavelength λ (nm). Rth(λ) is determined by Rth(λ)=((nx+ny)/2−nz)×d, where d (nm) is the thickness of the film.

<Inspection equipment and inspected object>
The inspection method of this embodiment is a method of inspecting the presence or absence of defects in a retardation layer included in an object to be inspected, and is carried out using a predetermined inspection apparatus. As shown in FIG. 1, the inspection device 1A includes a light source 2, a phase difference filter 4, and a camera 6 arranged in this order. In the inspection apparatus 1A, a place is prepared between the light source 2 and the phase difference filter 4, and a place to place the object to be inspected 10 is shown in FIG. 1. I'm drawing.

[Object to be inspected]
First, the object to be inspected 10 to be inspected will be explained. The object to be inspected 10 is a film-like circularly polarizing plate, and is formed by laminating a first polarizing plate 3A and a first λ/4 retardation layer 9A, which is the main body of the object to be inspected.

- First λ/4 retardation layer The first λ/4 retardation layer 9A may be made of a cured product of a polymerizable liquid crystal compound. In the following, a case where the first λ/4 retardation layer 9A is made of a cured product of a polymerizable liquid crystal compound will be exemplified.

The polymerizable liquid crystal compound that can form the first λ/4 retardation layer 9A is, for example, disclosed in JP2009-173893A, JP2010-31223A, WO2012/147904A, WO2014/10325A, and Examples include those disclosed in WO2017-43438. The polymerizable liquid crystal compounds described in these publications can form a retardation layer capable of uniform polarization conversion in a wide wavelength range. Further, it is possible to form a retardation layer having so-called reverse wavelength dispersion.

As a method for forming the first λ/4 retardation layer 9A, a solution containing a polymerizable liquid crystal compound as a raw material (polymerizable liquid crystal compound solution; liquid composition) is coated (coated) onto each base film. By creating a coating film using the process (processing) and photopolymerizing it, it is possible to form an extremely thin film. Such a base film may be provided with an alignment film for aligning the polymerizable liquid crystal compound. The alignment film may be one that is optically aligned by polarized light irradiation or one that is mechanically aligned by rubbing treatment. In addition, as a specific example of such an alignment film, those described in the above-mentioned publication can be used.

The first λ/4 retardation layers 9A each formed in this manner are, for example, a base film on which the first λ/4 retardation layers 9A are formed, and a base film on which the first λ/4 retardation layers 9A are formed. It can be transferred onto the first polarizing plate 3A by bonding the two layers together via an adhesive layer and then peeling off the base film. In this way, a circularly polarizing plate, which is an object to be inspected, can be manufactured.

The first λ/4 retardation layer 9A made of a cured product of a polymerizable liquid crystal compound is usually thin, about 0.2 μm to 10 μm, and if it contains foreign matter, the retardation value tends to decrease in that part. .

For example, when forming both layers, if there are foreign substances on the base film to which the polymerizable liquid crystal compound solution is applied, or if there are scratches on the base film or the first polarizing plate 3A itself, polymerization may occur. Defects may occur in the coating film itself obtained by coating the liquid crystal compound solution. For example, scratches on the base film are reflected as uneven thickness of the coating film, and the retardation value of that portion varies.

Furthermore, when the alignment film is subjected to a rubbing treatment, scraps of the rubbing cloth remain on the alignment film, which may cause defects in the coating film of the polymerizable liquid crystal compound solution (composition for forming a cured liquid crystal film). In this way, when forming a retardation layer from a polymerizable liquid crystal compound, it is possible to form an extremely thin retardation layer, but the above-mentioned debris and scratches can cause optical defects in the retardation layer. It may be a factor. Defects that occur as described above are "defects based on phase difference shift."

On the other hand, "defects due to axis misalignment" may also occur in the first λ/4 retardation layer 9A. As an example of the design value of the first λ/4 retardation layer 9A, the absorption axis of the first polarizing plate 3A and the slow axis of the first λ/4 retardation layer 9A are set at 45 degrees to each other. . In the first λ/4 retardation layer, a portion that is deviated from this angle due to some reason is a "defect due to axis misalignment."

If the first λ/4 retardation layer 9A is a stretched film, it is easy to predict the occurrence of overall axis misalignment depending on the stretching condition, and it is easy to deal with it. On the other hand, when these retardation layers are made of a cured product of a polymerizable liquid crystal compound, the alignment of liquid crystal molecules may be partially disordered, and defects caused by this (defects due to axis misalignment) may occur locally. It can occur.

According to the inspection method of this embodiment, not only defects based on phase difference shifts but also defects based on locally generated axis shifts can be easily detected.

- First Polarizing Plate The first polarizing plate 3A is a film that converts the light incident from the light source 2 into linearly polarized light, and is formed by pasting a protective film on at least one surface of the polarizing film. Examples of polarizing films include polyvinyl alcohol films with iodine and dichroic dyes adsorbed and oriented, and polymerizable liquid crystal compounds oriented and polymerized with dichroic dyes adsorbed and oriented. It will be done.

The first polarizing plate 3A has an absorption axis in a direction perpendicular to a transmission axis direction from which linearly polarized light is emitted. In this embodiment, for convenience, the direction in which linearly polarized light is emitted is defined as the transmission axis direction, and the direction in which it is blocked is defined as the absorption axis direction, but this does not exclude polarizing films that reflect polarized light in the direction in which it is blocked. .

The protective film is for protecting the polarizing film. As the protective film, those commonly used in the technical field of polarizing plates are 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; Film, etc. Further, additives commonly used in the technical field of polarizing plates may be included in the protective film. The retardation of the protective film is preferably small; for example, for Re(550), it is preferably 10 nm or less, particularly preferably 5 nm or less.

Note that the object to be inspected 10 may further include a positive C plate on the first λ/4 retardation layer 9A. The retardation value (Rth(550)) in the thickness direction of the positive C plate may be appropriately selected depending on the retardation value in the thickness direction of the first λ/4 retardation layer 9A.

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 described. For example, a piece of about 40 mm x 40 mm is separated from the film to be measured (eg, separated from a long film using an appropriate cutting tool). The Re(550) of this piece is measured three times and the average value of Re(550) is determined. The Re(550) of the piece can be measured at room temperature (23° C.) using a phase difference measuring device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.).

[Phase difference filter]
Next, the phase difference filter 4 will be explained. The phase difference filter 4 includes a second polarizing plate 3B and a second λ/4 phase difference layer 9B laminated thereon.

-Second retardation layer The second λ/4 retardation layer 9B has the in-plane retardation value of the first λ/4 retardation layer 9A measured with light with a wavelength of 550 nm and the in-plane retardation value measured with light with a wavelength of 550 nm. A layer having a different in-plane retardation value from the measured second λ/4 retardation layer 9B is selected.

More preferably, the in-plane retardation value of the second λ/4 retardation layer 9B measured with light with a wavelength of 550 nm is the in-plane retardation value of the first λ/4 retardation layer 9A measured with light with a wavelength of 550 nm. The phase difference value is a difference within a range of ±20 nm.

In the above, the numerical range of "±20 nm" may be "±10 nm" or "±5 nm". Further, as long as it is within the numerical range, either a positive or negative numerical range may be adopted. For example, "+5 nm to +15 nm", "-3 nm to -10 nm", "-0.1 nm to -2.0 nm", etc. Further, as long as the value is within the numerical value range, a numerical value range that spans positive and negative values may be adopted. For example, "-10 nm to +12 nm", "-4 nm to +8 nm", etc.

The in-plane retardation value of the second λ/4 retardation layer 9B is the degree of transmission of the inspection light (this is referred to as the "transmittance It is preferable to select the amount of light so that the amount of light before entering the object 10 is 0.1% to 5%. This transmittance value is a value that serves as a standard for determining the presence or absence of defects. In the inspection, the presence or absence of a defect is determined based on whether the measured transmittance is greater than this value. For example, if there is a point where the transmittance is 0.45% when inspected with the transmittance set to 0.3%, that point is determined to be a defect. Furthermore, if there is a point where the transmittance is 1.3% when inspected with the transmittance as 1%, that point is determined to be a defect. When the transmittance of the inspection light is within this range, the brightness of the observation field becomes particularly suitable for the inspection in this embodiment, making it easier to correctly recognize defects as defects, and to identify non-defects. Misrecognition as a defect is prevented.

The selected transmittance value may be between 0.15% and 3%, between 0.2% and 1%, and between 0.25% and 0.6%. To what extent should the retardation value of the second λ/4 retardation layer 9B be different from the retardation value of the first λ/4 retardation layer 9A to be inspected to obtain the transmittance? , Under various assumed conditions for the phase difference of the λ/4 retardation layer, for example, perform a computer simulation that calculates the movement of a point indicating the polarization state on the Poincaré sphere or a computer simulation using a Mueller matrix. It can be estimated by Examples of commercially available software include LCD Master from Shintech Co., Ltd., and the like.

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 λ/4 retardation layer 9A, or may be provided on the surface opposite thereto. By using a positive C plate, the inspection area can be expanded. The retardation value (Rth(550)) in the thickness direction of the positive C plate may be appropriately selected depending on the retardation value in the thickness direction of the first λ/4 retardation layer 9A to be inspected.

-Second polarizing plate The configuration and material of the second polarizing plate 3B are the same as those of the first polarizing plate 3A. Further, the method for forming the second λ/4 retardation layer 9B is also the same as the method for forming the first λ/4 retardation layer 9A.

[light source]
Various commercial products can be used as the light source 2, and for example, a light source that emits white light can be used. Further, the light emitted by the light source 2 may not be completely white light, but may be light that does not include light of a part of the wavelengths in the visible light region. The light emitted by the light source 2 may be single-wavelength visible light, or may be non-single-wavelength visible light. The light emitted by the light source 2 is unpolarized, passes through the first polarizing plate 3A to become polarized light in a predetermined direction, and further passes through the first λ/4 retardation layer 9A to become circularly polarized light. That is, unpolarized light becomes circularly polarized light by passing through the first polarizing plate 3A and the first λ/4 retardation layer 9A.

In conventional inspection methods that use light with a single wavelength, it is necessary to remove unnecessary wavelength light with a corresponding bandpass filter, which reduces the amount of light and causes a decrease in inspection sensitivity. For this reason, it was necessary to increase the light intensity of the light source, but in this embodiment, it is possible to use light including light of various wavelengths, such as white light, so there is no need to increase the light intensity of the light source.

[camera]
In the inspection apparatus 1A of the present embodiment, in order to observe the light that has passed through the inspection object 10 and the phase difference filter 4, the light source 2 is placed on the optical path 12 and opposite to the side where the light source 2 is located on both sides of the phase difference filter 4. A camera 6 as a detection means is arranged at a side position. The camera 6 is, for example, a CCD camera, and in this case, the object to be inspected 10 can be inspected by automatically detecting it by image processing analysis using a combination of a CCD camera and an image processing device. Note that the detection means may be the naked eye instead of a camera.

<Inspection method>
Hereinafter, a method for inspecting a circularly polarizing plate using the inspection apparatus 1A will be described. As shown in FIG. 1, an object to be inspected 10 is placed between the light source 2 and the phase difference filter 4 of the inspection apparatus 1A. At this time, the object to be inspected 10 is arranged so that the first λ/4 phase difference layer 9A faces the phase difference filter 4 side. At this time, the phase difference filter 4 is arranged so that the second λ/4 phase difference layer side 9B faces the inspected object 10 side. Further, as shown in FIG. 2, the slow axis p of the first λ/4 phase difference layer 9A included in the inspection object 10 and the second λ/4 phase difference layer 9B included in the phase difference filter 4 are It is arranged so that the angle θ formed with the slow axis q is 0°±30° when viewed from the direction of the optical path 12. This angle is preferably 0°±20°, more preferably 0°±10°. Here, the angle θ shall be expressed as a value of 0° or more and 90° or less, and an angle exceeding 90° shall be expressed as a value of 0° or more and 90° or less. By arranging it at such an angle, the inspection light is blocked, and the amount of light transmitted through the portion of the first λ/4 retardation layer 9A where the retardation value deviates from the desired value (phase difference shift) is relatively It becomes larger and easier to detect as a defect.

After the object to be inspected 10 is placed, a predetermined inspection area of the object to be inspected 10 is irradiated with inspection light from the light source 2 . When the phase difference filter 4 arranged so as to satisfy the above angle θ is observed with the camera 6 (or with the naked eye) from the opposite side of the light source 2, the normal portion of the inspection object 10 will be determined according to the transmittance selected above. The field of vision is darkened. Here, parts that appear different in color and parts where an amount of light exceeding the selected transmittance is observed are determined to be defects.

With conventional inspection methods, defects caused by phase differences are easy to detect because they appear in a different color from normal parts, but defects caused by axis misalignment are difficult to detect because their colors do not differ from normal parts. In this embodiment, the in-plane retardation value of the first λ/4 retardation layer 9A and the in-plane retardation value of the second λ/4 retardation layer 9B are different from each other, and the transmittance of the inspection light is is appropriately selected, defects due to axis misalignment can be easily recognized from the amount of transmitted light.

Note that if the inspected object 10 and the phase difference filter 4 are arranged in parallel with respect to the phase difference, the phase difference value of the phase difference filter 4 is not adjusted so as to be different from the phase difference value of the inspected object. It can be said that defects based on phase difference shift and axis shift can be detected. However, with this arrangement, highly accurate detection such as detecting a phase difference shift of 2 nm or less cannot be performed. By adjusting the phase difference value of the phase difference filter 4 to be different from the phase difference value of the object to be inspected as in this embodiment, it is possible to perform highly accurate inspection that can detect a phase difference shift of 2 nm or less. Become.

From the above, according to the inspection method of this embodiment, not only defects based on phase difference shift but also defects based on axis misalignment can be easily detected as defects in the retardation layer included in the inspected object. .

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiment, the inspection light emitted by the light source 2 enters the inspection object 10 and the phase difference filter 4 in this order, and the inspection light emitted from the phase difference filter 4 is captured by the camera 6. 2 and camera 6 may be reversed in position. That is, as shown in FIG. 3, the inspection light emitted by the light source 2 enters the phase difference filter 4 and the inspection object 10 in this order, and the inspection light emitted from the inspection object 10 is captured by the camera 6 (inspection It may also be a device 1B).

Further, in the above embodiment, the object to be inspected is a rectangular sheet-shaped object, but the object to be inspected may be, for example, a long object.

INDUSTRIAL APPLICATION This invention can be utilized for the test|inspection which determines the presence or absence of a defect of a retardation layer.

1A, 1B... Inspection device, 2... Light source, 3A... First polarizing plate, 3B... Second polarizing plate, 4... Phase difference filter, 6... Camera, 9A... First λ/4 phase difference layer, 9B ...Second λ/4 retardation layer, 10...Object to be inspected, 12...Optical path, p...Slow axis of first λ/4 retardation layer, q...Slow phase of second λ/4 retardation layer Axis, θ...angle.

Claims (5)

Inspection light is incident on a film-like object to be inspected that includes a first polarizing plate and a first λ/4 retardation layer to determine the presence or absence of a defect in the first λ/4 retardation layer. An inspection method,
The object to be inspected, and a phase difference filter including a second polarizing plate and a second λ/4 retardation layer, such that the first λ/4 retardation layer side of the object to be inspected is the side of the retardation filter. and the second λ/4 phase difference layer side of the phase difference filter faces the object to be inspected, and the slow axis of the first λ/4 phase difference layer and the Arranged so that the angle formed with the slow axis of the second λ/4 retardation layer is 0° ± 30° when viewed from the optical path direction of the inspection light,
What is the in-plane retardation value of the first λ/4 retardation layer measured with light with a wavelength of 550 nm and the in-plane retardation value of the second λ/4 retardation layer measured with light with a wavelength of 550 nm? are different from each other,
The optical path passes through a predetermined inspection area on the object to be inspected from either the first polarizing plate side of the object to be inspected or the second polarizing plate side of the phase difference filter. An inspection method in which the inspection light is incident and the second polarizing plate or the first polarizing plate is observed from the other side. What is the in-plane retardation value of the second λ/4 retardation layer measured with light with a wavelength of 550 nm and the in-plane retardation value of the first λ/4 retardation layer measured with light with a wavelength of 550 nm? The inspection method according to claim 1, wherein the difference is within a range of ±20 nm. The second test beam was measured using light with a wavelength of 550 nm so that the transmittance of the inspection light, which is a combination of the defect-free portion of the object to be inspected and the phase difference filter, is 0.1% to 5%. 3. The inspection method according to claim 1, wherein an in-plane retardation value of the λ/4 retardation layer is selected. 3. The inspection method according to claim 1, wherein the first λ/4 retardation layer is made of a cured product of a polymerizable liquid crystal compound. 3. The inspection method according to claim 1, wherein the inspection light is visible light that is not a single wavelength.

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