JP7413209B2 - Inspection method - Google Patents

Description

The present invention relates to an inspection method.

Polarizing plates used in liquid crystal display devices, organic EL display devices, and the like are generally configured such that a polarizer is sandwiched between two protective films. In order to attach a polarizing plate to a display device, an adhesive layer is laminated on one of the protective films, and a release film is further laminated on the adhesive layer. Further, a release film (surface protection film) for protecting the surface of the other protective film is often laminated to the other protective film. The polarizing plate is transported in a state in which a release film is laminated in this manner, and the release film is peeled off when it is bonded to a display device in the display device manufacturing process.

By the way, during the manufacturing process of polarizing plates, foreign objects or air bubbles may remain between the polarizer and the protective film, or if the protective film functions as a retardation film, orientation defects may occur. (Hereinafter, these foreign substances, bubbles, and orientation defects may be collectively referred to as "defects"). When a polarizing plate with a defect is attached to a display device, the defective location may be visually recognized as a bright spot, or the image may appear distorted at the defective location. In particular, defects that are visible as bright spots are easily visible when the display device displays black.

Therefore, before the polarizing plate is bonded to the display device (the polarizing plate is provided with a release film), an inspection is performed to detect defects in the polarizing plate. This defect inspection is generally an optical inspection using the polarization axis of a polarizing plate. Specifically, as shown in Patent Document 1, a polarizing filter is provided between a polarizing plate that is an object to be inspected and a light source, and this polarizing plate or polarizing filter is rotated in a plane direction. The directions of these respective polarization axes are set in a specific relationship. When the directions of polarization axes are orthogonal to each other (that is, in the case of a crossed Nicols arrangement), the linearly polarized light that has passed through the polarizing filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light will be transmitted through that location, and the presence of the defect will be revealed by detecting that light. On the other hand, when the polarization axes of the polarizing plate and the polarizing filter are parallel to each other, the linearly polarized light that has passed through the polarizing filter is transmitted through the polarizing plate. However, if a defect exists in the polarizing plate, linearly polarized light is blocked at that location, so the fact that the light is not detected reveals the presence of the defect. The presence or absence of defects in the polarizing plate can be inspected by visually detecting the light that has passed through the polarizing plate, or by automatically detecting it using image analysis processing using a combination of a CCD camera and an image processing device. It can be carried out.

Japanese Patent Application Publication No. 9-229817

However, as mentioned above, when a polarizing plate is provided with a release film, the polarizing properties of the polarizing plate are inhibited by the birefringence of this release film, so conventional inspection equipment can detect defects such as bright spots on the polarizing plate. could not be detected accurately.

If the polarizing plate is a circularly polarizing plate and the release film is made of polyethylene terephthalate resin (PET resin), a retardation filter (equivalent to the above polarizing filter) that matches the wavelength dispersion of the PET resin to some extent is used. use Here, if the circularly polarizing plate and the retardation filter are arranged to form a crossed nicol, defects will be visually recognized as bright spots according to the above principle, but the retardation film of the circularly polarizing plate will In areas where the retardation value is low, such as orientation defects and pinholes, bright spot defects may be visually recognized as black spots, and in this case, detection and judgment were more difficult than detecting them as bright spots. This tendency is particularly noticeable when the circularly polarizing plate includes a retardation film made of a cured product of a polymerizable liquid crystal compound.

Furthermore, for reasons of design of the display device, the circularly polarizing plate may have an irregular shape. For example, a concave portion may be provided on the outer periphery of the circularly polarizing plate, the corners of the outer periphery may be rounded, or a through hole may be provided. When a circularly polarizing plate of an irregular shape is subjected to the above inspection, it is necessary to prepare a light shielding plate of the same shape as the irregular shape, and when the irregularly shaped polarizing plate is moved during defect inspection, the shielding plate and the irregularly shaped polarizing plate may be Since the inspection light leaks strongly at irregularly shaped parts where misalignment is likely to occur, the observation field of view becomes too bright, which sometimes becomes a hindrance to detecting minute defects.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inspection method that can easily determine the presence or absence of defects in irregularly shaped circularly polarizing plates.

The present invention provides an inspection method for determining the presence or absence of defects in a film-like object to be inspected, which includes a circularly polarizing plate and a release film made of polyethylene terephthalate resin (hereinafter sometimes referred to as "PET resin"). The object to be inspected has a shape with a rectangle as a reference and has a concave portion recessed from the side of the rectangle toward the inside of the rectangle, or has a shape with curved corners of the rectangle, or has a shape of a rectangle with a curved corner. The shape has a through hole at a position away from the side, and the in-plane retardation value at a wavelength of 550 nm between the light source, the first retardation filter, the first retardation plate, and the object to be inspected is the same as that of the release film. Something that is approximately the same as the in-plane retardation value at a wavelength of 550 nm (hereinafter, this in-plane retardation value at a wavelength of 550 nm may be referred to as "Re (550)"), and that compensates for the birefringence that the release film has. A second retardation plate, and a second retardation filter forming a crossed nicol with the first retardation filter and the circularly polarizing plate are arranged in this order on the optical path of the light emitted by the light source. , the first retardation plate has Re (550) that is approximately the same as Re (550) of the second retardation plate, and compensates for the birefringence of the second retardation plate, Light is incident on the object to be inspected from the light source, observed from the opposite side of the light source to determine whether there is a defect in the circularly polarizing plate, and the first retardation plate and the second retardation plate are Replaced with a third retardation plate and a fourth retardation plate that are 50 to 100 nm larger than Re (550) of the release film and compensate for the birefringence of the release film, and after the replacement, the test object To provide an inspection method in which the presence or absence of a defect in a circularly polarizing plate is determined by injecting light into an object and observing it from the opposite side of the light source. Note that "substantially the same" in Re(550) here means that the difference in Re(550) is only about ±5 nm.

In this inspection method, for a portion where a black defect is observed in an inspection using a first retardation plate and a second retardation plate, each of these retardation plates is replaced with a third retardation plate and a fourth retardation plate. By replacing it with a retardation plate and inspecting it, it becomes possible to adjust the retardation so that it can be observed as a bright spot defect. In addition, in this inspection method, the first phase difference filter and the second phase difference filter are arranged so as to form a crossed nicol, so when there is no object to be inspected on the optical path, the light from the light source is The light is blocked by the second phase difference filter. Therefore, light leakage from the irregularly shaped portion of the object to be inspected is significantly suppressed, and does not become a hindrance when inspecting the vicinity of the irregularly shaped portion. From the above, the inspection method of the present invention can easily determine the presence or absence of a defect in an irregularly shaped circularly polarizing plate.

Here, the object to be inspected further includes a surface protection film made of PET resin on the side opposite to the side on which the release film is provided with respect to the circularly polarizing plate, and the first retardation plate and the object to be inspected are connected to each other. A high retardation plate having Re(550) of 5000 nm or more may be further disposed between the two. When the object to be inspected includes a surface protection film, the in-plane retardation of the surface protection film may cause a rainbow-colored pattern to appear in the observation field of view, which may impede defect observation. In this case, by using a high retardation plate having a high in-plane retardation, the iridescent light can be converted into white light so that it does not interfere with observation.

Moreover, at that time, it is preferable to arrange the slow axis of the surface protection film and the slow axis of the high retardation plate to be substantially parallel. Since the in-plane phase difference is additive, by making the slow axes substantially parallel to each other, rainbow-colored light can be reliably converted to white light.

The circularly polarizing plate may have a retardation film made of a cured product of a polymerizable liquid crystal compound. When the retardation film is made of a cured product of a polymerizable liquid crystal compound, there is a high possibility that it will be observed as a black spot defect due to its general thinness. Therefore, it is suitable as an object to which the present invention is applied.

In addition, in this inspection method, the inspection object, the first retardation plate, the second retardation plate, the third retardation plate, the fourth retardation plate, the first retardation filter, and the second retardation plate are used. At least one of the retardation filter, the first retardation plate, and the second retardation plate may be tilted so that they face each other at different angles, or may be rotated in a direction perpendicular to the optical path. good. By tilting these, the retardation of the release film, the first and second retardation plates, etc. can be finely adjusted, making it possible to inspect a wider range. Moreover, by rotating these, it becomes easy to align the axes of each component.

The first retardation plate and the third retardation plate may be arranged and configured in the same member.

According to the present invention, it is possible to provide an inspection method that can easily determine the presence or absence of a defect in an irregularly shaped circularly polarizing plate.

FIG. 1 is a diagram showing an inspection device according to a first embodiment. FIG. 3 is a plan view of the object to be inspected. FIG. 3 is a sectional view taken along III-III of the object to be inspected. FIG. 3 is a diagram showing an example of a retardation plate. It is a figure showing the inspection device of a 2nd embodiment.

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.

<First embodiment>
The inspection method of the first embodiment will be explained.

(Inspection equipment and inspected object)
The inspection device of this embodiment inspects the presence or absence of surface defects on a circularly polarizing plate. As shown in FIG. 1, the inspection apparatus 100A includes a light source 2, a first phase difference filter 3A, a first phase difference plate 4A, a second phase difference plate 4B, and a second phase difference filter 3B. are arranged in this order.

As shown in FIG. 2, the film-like object 10 to be inspected is an irregularly shaped circularly polarizing plate with a rectangular shape as a reference, and a concave portion is formed from one side of the rectangle toward the inside of the object 10. It has a recess R. Here, "based on a rectangle" means that the shape of the object to be inspected 10 is rectangular, assuming that the recess R does not exist. Further, the corners of the object to be inspected 10 are processed into curves. In this specification, the term "abnormal shape" refers to a partially deformed shape such as a polygon, a perfect circle, or an ellipse. Deformation refers to providing a recess on the outer periphery, rounding a corner, making a curve straight, or providing a through hole.

As shown in FIG. 3, the inspected object 10 includes a circularly polarizing plate 1, which is the main body to be inspected, and a release film 16a laminated to the circularly polarizing plate 1 via an adhesive layer 15. ing. In the circularly polarizing plate 1, protective films 12a and 12b are laminated on both sides of a polarizing film 11, and a retardation film 14 is further placed on the protective film 12a on the side provided with the release film 16a via an adhesive layer 13. It is something that is formed. A surface protection film 16b is laminated on the side of the circularly polarizing plate 1 that is not provided with the release film 16a. The circularly polarizing plate 1 is generally used in a display device, such as a liquid crystal display device or an organic EL display device, and when used, the release film 16a is peeled off and the plate is attached to the display device via the adhesive layer 15. .

Note that in this specification, the term "circularly polarizing plate" includes a circularly polarizing plate and an elliptically polarizing plate. Furthermore, "circularly polarized light" includes circularly polarized light and elliptically polarized light.

In the inspection apparatus 100A, the polarizing film 11 is a film that converts light incident from the surface protection film 16b side into linearly polarized light. The polarizing film 11 may be, for example, a polyvinyl alcohol film on which iodine or a dichroic dye is adsorbed and oriented, or a polyvinyl alcohol film on which a dichroic dye is adsorbed and oriented on a polymerizable liquid crystal compound oriented and polymerized. Can be mentioned.

The protective films 12a and 12b are for protecting the polarizing film 11. As the protective films 12a and 12b, those commonly used in the technical field of polarizing plates are used for the purpose of obtaining polarizing plates 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.

Since the protective films 12a and 12b are attached to the display device together with the polarizing film 11 as constituent elements of the circularly polarizing plate 1, strict control of the retardation value is required. Typically, a protective film 12a having an extremely small retardation value is preferably used. Further, as the protective film 12b, for example, a film having a retardation of λ/4 or a film having a small retardation value is used for ease of viewing when viewing the display device through polarized sunglasses. The protective films 12a and 12b are bonded to the polarizing film 11 via an adhesive.

In the inspection apparatus 100A, the retardation film 14 is a film that converts the light linearly polarized by the polarizing film 11 into circularly polarized light. The retardation film 14 is not particularly limited as long as it has a retardation, but may be a laminate of a λ/2 film and a λ/4 film. In this case, the λ/2 film and the λ/4 film may be arranged in that order from the one closest to the polarizing film 11.

Moreover, it is preferable that the retardation film 14 is made of a cured product of a polymerizable liquid crystal compound. The retardation film 14 made of a cured product of a polymerizable liquid crystal compound is usually thin, about 0.2 μm to 10 μm, and when it contains foreign matter, the retardation value tends to decrease in that part. As will be described later, in such areas, when the birefringence of the release film 16a is compensated for by the retardation plate 4, the defect is observed as a black spot, even though it should originally be observed as a bright spot defect. There may be cases where

Polymerizable liquid crystal compounds that can form the retardation film 14 are described in, for example, JP2009-173893A, JP2010-31223A, WO2012/147904, WO2014/10325, and WO2017-43438. Those disclosed can be mentioned. The polymerizable liquid crystal compounds described in these publications can form a retardation film having so-called reverse wavelength dispersion, which is capable of uniform polarization conversion in a wide wavelength range. For example, by applying a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution) onto a suitable base material and photopolymerizing it, an extremely thin retardation film can be formed as described above. A circularly polarizing plate having such a retardation film can be extremely thin. A circularly polarizing plate having such a very thin thickness is advantageous as a circularly polarizing plate for flexible display materials, which have been attracting attention in recent years.

Examples of the base material to which the polymerizable liquid crystal compound solution is applied include those described in the above-mentioned publications. Such a base material 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. Note that such an alignment film is also described in the above publication.

However, if there are foreign substances on the substrate to which the polymerizable liquid crystal compound solution is applied, or if the substrate itself has scratches, defects may occur in the coating film itself obtained by applying the polymerizable liquid crystal compound solution. may occur. 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). As described above, a retardation film formed from a polymerizable liquid crystal compound can be extremely thin, but there are factors that cause defects. As described later, defects in the retardation film may be observed as black spots. The inspection apparatus and inspection method of this embodiment are particularly useful in detecting the presence or absence of a defect in an object to be inspected that includes a circularly polarizing plate and a release film having a retardation film having such defects.

The retardation film 14 can be produced by applying a composition for forming an alignment film onto a base material, and further applying a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound thereon. The retardation film 14 created in this way is laminated together with the base material to the adhesive layer 13 formed on the protective film 12a, and then the base material is peeled off to attach the retardation film 14 to the protective film 12a. can be transferred onto.

The release film 16a is peeled off from the circularly polarizing plate 1 when it is attached to a display device, and the peeled release film 16a is normally discarded. Therefore, unlike the protective films 12a and 12b, strict control of the retardation value is not required. Therefore, when a commercially available film is used as the release film 16a, if the retardation value is not compensated for, malfunctions may occur during defect inspection. That is, in the defect inspection of the circularly polarizing plate 1 to which the release film 16a whose retardation value is not strictly controlled is bonded, the retardation of the release film 16a is the cause of reducing the inspection accuracy of the inspection device 100A. It can be.

Note that, as described in the above background art, in the circularly polarizing plate 1, a surface protection film 16b, which is a type of release film, is often provided on the opposite surface of the release film 16a. In the circularly polarizing plate 1 shown in FIG. 3, a surface protection film 16b is bonded to the protection film 12b side. This surface protection film 16b is also usually peeled off from the circularly polarizing plate 1 when it is attached to a display device, and unlike the protection films 12a and 12b, strict control of the retardation value is not required. . Furthermore, a case in which coloring of observation light due to light interference caused by the retardation value of the surface protection film 16b is suppressed will be described in a second embodiment described later. In addition, in FIG. 3, the protective film 12b and the surface protection film 16b may be bonded together via a suitable adhesive layer or pressure-sensitive adhesive layer (in FIG. 3, this adhesive layer or pressure-sensitive adhesive layer (not shown).

In this embodiment, the release film 16a is made of PET resin. Furthermore, the surface protection film 16b is also made of PET resin. A film made of PET resin (PET resin film) has the advantage of being versatile as a release film and being inexpensive. On the other hand, as mentioned above, the inexpensive PET resin film does not require strict control of the retardation value. Therefore, for example, there may be variations in phase difference values from product lot to product lot. Further, even if the PET resin film is the same, there may be variations in the retardation value within the plane. Even in the case of a circularly polarizing plate 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. In addition, in the test object 10, it is preferable that the slow axis of the release film 16a and the slow axis of the surface protection film 16b are bonded together so that they are substantially parallel to each other.

Here, how to obtain Re(550) of the release film 16a will be explained. As mentioned above, these release films are PET resin films, and such films are easily available on the market. For example, pieces of about 40 mm x 40 mm are separated from this film (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 (about 25° C.) using a phase difference measuring device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.). Note that a similar test may be performed when determining Re(550) of the surface protection film 16b.

Although various commercially available products can be used as the light source 2, it is advantageous to use a straight light beam (including one that approximates a straight light beam) such as a laser beam, for example. The light emitted by the light source 2 is non-polarized, passes through a first phase difference filter 3A, which will be described later, and becomes polarized in a predetermined direction.

The first phase difference filter 3A and the second phase difference filter 3B are both circularly polarizing plates. When the object to be inspected 10 is inspected, the direction of the second phase difference filter 3B is always adjusted so that it forms a crossed nicol configuration with the first phase difference filter 3A. The polarizing plate and the retardation plate (constituting a layer having a retardation) constituting the first and second retardation filters 3A and 3B are so-called defect-free ones.

The second retardation plate 4B compensates for the birefringence of light caused by the release film 16a of the object to be inspected 10. The material constituting the second retardation plate 4B is not particularly limited as long as it compensates for the birefringence of light caused by the release film 16a made of PET resin. The second retardation plate 4B can also be formed by preparing a commercially available retardation plate having a wavelength of 100 to 200 nm and stacking a plurality of these to obtain a desired retardation value. Since Re(550) usually has additivity, the second retardation plate 4B having a desired Re(550) can be obtained from the Re(550) of the laminated retardation plates. The first retardation plate 4A cancels out the phase difference of the second retardation plate 4B, and preferably has the same configuration as the second retardation plate 4B. Since the release film 16a made of PET resin usually has large variations in retardation values and slow axes in the in-plane direction, multiple types of retardation plates are prepared so that multiple retardation values can be selected during inspection. It is preferable to leave it there. In this embodiment, a two-sheet set of a first retardation plate 4A and a second retardation plate 4B having substantially the same retardation value as Re(550) of the release film 16a, and a Re(550) of the release film 16a are used. ) At least two types of retardation plates are used: a third retardation plate and a fourth retardation plate having a Re (550) larger than that of 50 to 100 nm. Here, the first retardation plate 4A and the second retardation plate 4B used as a pair have the same Re (550), and the third retardation plate and the fourth retardation plate have the same Re(550). Note that a retardation value that is substantially the same as Re (550) of the release film 16a means that the absolute value of the difference between Re (550) of the release film 16a and Re (550) of the retardation plate is 20 nm or less. means.

Furthermore, considering the variation in the retardation value of the release film, the first and second retardation plates 4A and 4B exhibit a retardation in the range of about ±300 nm with respect to Re (550) of the release film. It is preferable that Within this range of retardation, it is further preferable to change the retardation in increments of 50 nm to 100 nm in the in-plane direction of the release film. It is preferable to prepare various types of retardation plates that exhibit these phase differences. That is, as a series of retardation plates that change the retardation, it is preferable to prepare a retardation plate having a different retardation in addition to the first retardation plate 4A and the third retardation plate. Next, the state of this retardation plate will be explained.

FIG. 4 schematically shows a series of retardation plates 4 in which retardation plates having different phase differences are integrated. As shown in FIG. 4, the retardation plate 4 may be configured such that regions having different in-plane retardation values are continuous in one direction in a single retardation plate member. good. That is, the region located at the end (first region a ₁ ; corresponding to the first retardation plate) is a region in which Re (550) is, for example, 1720 nm, and the region adjacent to it (second region a 1 ; corresponding to the first retardation plate) The region a ₂ ; corresponding to the third retardation plate) is a region with Re (550) of 1790 nm, and the region adjacent to it (the third region a ₃ ; corresponding to the fifth retardation plate) is a region where Re (550) is 1790 nm. (equivalent) is a region where Re (550) is 1860 nm. In the retardation plate 4, the number of regions is arbitrary, and FIG. 4 shows up to the nth region a _n . Note that in each region, the retardation value in the thickness direction can be adjusted depending on the width of the visual field to be observed in one region.

This retardation plate 4 can be used not only as a first retardation plate 4A disposed next to the first retardation filter 3A when viewed from the light source 2 side, but also as a first retardation plate 4A disposed next to the first retardation filter 3A when viewed from the light source 2 side. It is simultaneously used as the second retardation plate 4B disposed in . On the side of the second retardation plate 4B, the first area a ₁ , the second area a ₂ , and the third area a ₃ are the second retardation plate, the fourth retardation plate, and the sixth retardation plate, respectively. It becomes a retardation plate. When two retardation plates 4, 4 are used as the first and second retardation plates 4A, 4B, regions having the same Re (550) (for example, the first region _a1 , the second area _a2 ) are used as a pair.

In order to observe the light that has passed through the object to be inspected 10, a detection device including a CCD camera or the like is installed on the optical path 9 and at a position opposite to the side where the light source 2 is located on both sides of the second phase difference filter 3B. Means 5 may be arranged. For example, the object to be inspected can be inspected by automatically detecting it by image processing analysis using a combination of a CCD camera and an image processing device. Alternatively, the detection means 5 may not be a member, but may be a person who visually observes the second phase difference filter 3B.

The inspection apparatus 100A also arranges at least one of the object to be inspected 10, the first and second retardation plates 4A and 4B, and the first and second retardation filters 3A and 3B such that the angle at which they face each other is Preferably, it is provided with a movable device (not shown) which allows it to be tilted differently or rotated in a direction perpendicular to the optical path 9 of the light. By tilting these, the retardation of the release film 16a made of PET resin and the first and second retardation plates 4A, 4B can be finely adjusted, making it possible to inspect a wider range. Moreover, by rotating these, it becomes easy to align the axes of the release film 16a made of PET resin and the first and second retardation plates 4A, 4B.

(Inspection method)
The inspection method using the inspection device 100A is as follows. First, the object to be inspected 10 is inserted between the first retardation plate 4A and the second retardation plate 4B inside the inspection apparatus 100A. At this time, the surfaces of each of these films are parallel to each other, and the side of the object to be inspected 10 provided with the release film 16a faces the side opposite to the light source 2, and the circularly polarizing plate 1 and the second retardation are The filter 3B is arranged so as to form a crossed nicol structure. Here, as the first retardation plate 4A and the second retardation plate 4B, the retardation plate 4 shown in FIG. ₄ is used. It is located so that it is located at

Then, the first phase difference filter 3A and the second phase difference filter 3B are adjusted so as to form a crossed nicol configuration. When the inspection apparatus 100A is equipped with the movable device described above, after inserting the object 10 to be inspected in an arbitrary direction, the relative positional relationship of each film may be changed by the movable device to form a crossed nicol configuration.

The light emitted by the light source 2 enters the first phase difference filter 3A, passes through this, becomes circularly polarized light, and then passes through the first phase difference plate 4A. When the inspected object 10 is moved in any in-plane direction for inspection, the portion of the inspected object 10 at the recess R passes through the first phase difference filter 3A and the first phase difference plate 4A. The light enters the second retardation plate 4B as it is, and is blocked by the first retardation filter 3A and the second retardation filter 3B, which is in a crossed nicol configuration. When this is observed from the detection means 5 side, the surface of the second phase difference filter 3B is dark.

On the other hand, in a portion of the object to be inspected 10 other than the concave portion, the light that has passed through the first phase difference filter 3A and the first phase difference plate 4A enters the object to be inspected 10, is transmitted, and then passes through the second phase difference filter 3A and the first phase difference plate 4A. The light enters the retardation plate 4B and is blocked by the second phase difference filter 3B, which is in a crossed nicol configuration with the object to be inspected 10. At this time, if there is a defect in the circularly polarizing plate 1 in the object to be inspected 10, proper blocking cannot be performed at this defective portion, and when this is observed from the detection means 5 side, the defective portion is observed as a bright spot.

Here, if the release film 16a has a phase difference, the circularly polarized light that has passed through the object to be inspected 10 is affected, and the amount of light that passes through the second phase difference filter 3B increases (for example, 5% or 5% of the amount of light from the light source). (exceeds 10%), and the detection accuracy of defects such as bright spots present in the circularly polarizing plate 1 decreases. Here, by disposing the second retardation plate 4B between the object to be inspected 10 and the second phase difference filter 3B, the retardation value of the release film 16a in the object to be inspected 10 is canceled. , to compensate for the birefringence of light due to the release film 16a.

Further, the second retardation plate 4B is designed to match the retardation value and wavelength dispersion characteristics of the release film 16a as much as possible in order to effectively compensate for the birefringence of light caused by the release film 16a. Due to in-plane variations in the retardation value of the release film 16a, it is difficult to perform an inspection while sufficiently blocking light over the entire inspection field. In such a case, the optical compensation is matched in the portion of the circularly polarizing plate 1 where the retardation value of the retardation film 14 is decreased, and defects that should originally be observed as bright spots are observed as black spots. Things can happen. Normally, black spot defects have a smaller effect on visibility than bright spot defects, so it is often accepted that the defect size is larger than that of bright spot defects, so in the end it is determined that there is no problem. Sometimes I put it away. However, if the black spot defect should originally be observed as a bright spot defect caused by a portion of the retardation film 14 where the retardation value decreases, the influence on visibility is large and becomes a problem.

For this reason, in this embodiment, a third retardation plate having an in-plane retardation different from that of the first retardation plate 4A and the second retardation plate 4B is used for a defect site visually recognized as a black spot. A fourth retardation plate is used. Specifically, both the retardation plates 4 and 4 are slid in the in-plane direction, and in both cases, the second region a ₂ (third retardation plate, fourth retardation plate) is positioned on the optical path 9. I'll do what I do. A second inspection will be conducted with this arrangement.

In this way, by performing multiple inspections using retardation plates with different in-plane retardation values, the possibility that defects will be observed as bright spot defects increases, making it easier to correctly recognize defects. Note that if a black spot is visually recognized again even in the inspection using the second area a ₂ (third retardation plate, fourth retardation plate), the two retardation plates 4 and 4 are further replaced with the third retardation plate. The third retardation plate is slid to area a ₃ (fifth retardation plate, sixth retardation plate), and a third inspection is performed.

During the inspection, at least one of the inspected object 10, the first and second phase difference plates 4A, 4B, and the first and second phase difference filters 3A, 3B are tilted so that they face each other at different angles. Alternatively, it may be rotated in a direction perpendicular to the optical path 9 of the light. By tilting, it is possible to finely adjust the retardation of the release film 16a and the first and second retardation plates 4A and 4B, thereby enabling inspection over a wider range. Moreover, by rotating these, it becomes easy to align the axes of the release film 16a made of PET resin and the first and second retardation plates 4A, 4B. These operations can be performed particularly easily when the inspection device 100A is equipped with a movable device.

According to the above-described inspection method, a portion where a black defect is observed in an inspection using a pair of the first retardation plate 4A and the second retardation plate 4B is transferred to the third retardation plate (a ₂ ). By inspecting using the fourth retardation plate (a ₂ ), it is possible to adjust the retardation so that this can be observed as a bright spot defect. In addition, in this inspection method, the first phase difference filter 3A and the second phase difference filter 3B are arranged so as to form a crossed nicol, so that when the object to be inspected 10 is not present on the optical path, Light from the light source is blocked by the second phase difference filter. Therefore, light leakage from the irregularly shaped portion of the object to be inspected 10 is significantly suppressed, and does not become a hindrance when inspecting the vicinity of the irregularly shaped portion. From the above, the inspection method of this embodiment can easily determine whether there is a defect in the irregularly shaped circularly polarizing plate 1.

<Second embodiment>
The inspection method of the second embodiment will be explained. The difference between the inspection method of the second embodiment and the inspection method of the first embodiment is that, as shown in FIG. The point is that a high retardation plate 20 is placed between them.

The high retardation plate 20 is a film having the same shape as the object 10 to be inspected, and has a similar recess R' at a position corresponding to the recess R of the object 10 to be inspected. Since the high retardation plate 20 complements the retardation value of the surface protection film 16b, it is preferably made of the same material as the surface protection film 16b, and preferably made of polyethylene terephthalate resin.

The Re(550) of the high retardation plate 20 is preferably 5000 nm or more, more preferably 7000 nm or more, even more preferably 8000 nm or more, and particularly preferably 10000 nm or more. Moreover, it is preferable that the high retardation plate 20 is arranged so that its slow axis is substantially parallel to the slow axis of the surface protection film 16b.

According to the inspection using the high retardation plate 20, in addition to the effects produced by the inspection method of the first embodiment, coloring of observation light due to light interference caused by the retardation of the surface protection film 16b is suppressed. be able to. That is, due to the in-plane retardation of the surface protection film 16b, a rainbow-colored pattern may appear in the observation field of inspection, which may hinder defect observation, but since the high retardation plate 20 has a high in-plane retardation value, , it is possible to convert the rainbow-colored light into white light so that it does not interfere with observation. In particular, when the slow axis of the high retardation plate 20 and the slow axis of the surface protection film 16b are arranged substantially parallel, the iridescent light is converted into light outside of visible light due to the additivity of the in-plane retardation. can be converted reliably.

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 first retardation filter 3A and the first retardation plate 4A are shown as separate products, but they constitute one film as a laminate stacked on each other. Good too. Similarly, the second phase difference filter 3B and the second phase difference plate 4B may be formed into one laminate.

In the above embodiment, the two retardation plates 4 (first retardation plate 4A, second retardation plate 4B) include a first region a ₁ and a second region a with different Re (550). Although the retardation plate used is one in which _{the second} and the like are arranged in a straight line, this retardation plate may have a structure in which regions having different Re(550) are arranged in an annular shape. For example, a disc-shaped film is divided into a plurality of regions having different retardation values using virtual lines extending radially from the center as boundaries, and one region (first region; equivalent to the first retardation plate) has a Re (550) is, for example, 1720 nm, and the adjacent region (second region; equivalent to the second retardation plate) is a region where Re (550) is 1790 nm, and The adjacent region (third region; equivalent to the third retardation plate) may have Re(550) of 1860 nm. The number of regions is arbitrary, and can be, for example, four, six, eight, etc.

INDUSTRIAL APPLICATION This invention can be utilized for the quality inspection of a circularly polarizing plate.

DESCRIPTION OF SYMBOLS 1... Circularly polarizing plate, 2... Light source, 3A... First phase difference filter, 3B... Second phase difference filter, 4... Phase difference plate, 4A... First phase difference plate, 4B... Second phase difference Plate, 5... Detection means, 9... Optical path, 10... Test object, 11... Polarizing film, 12a, 12b... Protective film, 13... Adhesive layer, 14... Retardation film, 15... Adhesive layer, 16a... Peeling Film, 16b...Surface protection film, 20...High retardation plate, 100A, 100B...Inspection device, _a1 ...First region (first retardation plate, second retardation plate), _a2 ...Second retardation plate region (third retardation plate, fourth retardation plate), an _... n-th region, R, R'...recess.

Claims (6)

An inspection method for determining the presence or absence of defects in a film-like inspection object comprising a circularly polarizing plate and a release film made of polyethylene terephthalate resin, the method comprising:
The object to be inspected has a shape with a rectangle as a reference and has a concave portion recessed from the side of the rectangle toward the inside of the rectangle, or has a shape with curved corners of the rectangle, or has a shape of a rectangle. It has a shape with a through hole located away from the sides,
a light source and
a first phase difference filter;
a first retardation plate;
The object to be inspected;
a second retardation plate whose in-plane retardation value at a wavelength of 550 nm is approximately the same as the in-plane retardation value at a wavelength of 550 nm of the release film, and which compensates for the birefringence of the release film;
The first phase difference filter and the second phase difference filter forming a crossed nicol with the circularly polarizing plate are arranged in this order on the optical path of the light emitted by the light source,
The first retardation plate has an in-plane retardation value at a wavelength of 550 nm that is approximately the same as the in-plane retardation value at a wavelength of 550 nm of the second retardation plate, and the second retardation plate has an in-plane retardation value at a wavelength of 550 nm. It compensates for the birefringence that it has,
Injecting light into the object to be inspected and observing it from the opposite side of the light source to determine whether there is a defect in the circularly polarizing plate,
The first retardation plate and the second retardation plate have an in-plane retardation value at a wavelength of 550 nm that is 50 to 100 nm larger than an in-plane retardation value at a wavelength of 550 nm of the release film, and the release film Replaced with a third retardation plate and a fourth retardation plate that compensate for the birefringence of
After the replacement, light is incident on the object to be inspected, and the object is observed from the opposite side of the light source to determine whether or not there is a defect in the circularly polarizing plate. The object to be inspected further includes a surface protection film made of polyethylene terephthalate resin on a side opposite to the side where the release film is provided with respect to the circularly polarizing plate,
2. The inspection method according to claim 1, further comprising disposing a high retardation plate having an in-plane retardation value of 5000 nm or more at a wavelength of 550 nm between the first retardation plate and the object to be inspected. 3. The inspection method according to claim 2, wherein the slow axis of the surface protection film and the slow axis of the high retardation plate are arranged to be substantially parallel. 4. The inspection method according to claim 1, wherein the circularly polarizing plate has a retardation film made of a cured product of a polymerizable liquid crystal compound. the object to be inspected, the first retardation plate, the second retardation plate, the third retardation plate, the fourth retardation plate, the first phase difference filter, the second phase difference plate; Claim: At least one of the retardation filter, the first retardation plate, and the second retardation plate is tilted so that the angles at which they face each other are different, or rotated in a direction perpendicular to the optical path. The inspection method described in any one of 1 to 4. 6. The inspection method according to claim 1, wherein the first retardation plate and the third retardation plate are arranged in the same member.

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