JP7413210B2 - 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

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, the principle of the inspection method shown in Patent Document 1 is to observe light transmitted through an object to be inspected. According to this principle, if there is a deformation defect (for example, wrinkles caused when cutting a circularly polarizing plate) on the object to be inspected, the optical path length will hardly change between the normal part and the deformed defective part, so the deformation defect can be detected optically. difficult to do.

In addition, as mentioned above, when a polarizing plate is provided with a release film, the birefringence of this release film inhibits the polarization characteristics of the circularly polarizing plate, so conventional inspection equipment detects bright spots, etc., present on the polarizing plate. Defects could not be detected accurately.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reflection-type inspection method that can easily determine the presence or absence of a defect in a circularly polarizing plate.

The present invention provides a circularly polarizing plate formed by laminating a polarizing film and a retardation film, and a polyethylene terephthalate resin (hereinafter sometimes referred to as "PET resin") laminated on the retardation film side of the circularly polarizing plate. ) is an inspection method for determining the presence or absence of defects in a film-like inspection object, which comprises a release film consisting of a light source, a first phase difference filter, and an in-plane retardation value (hereinafter referred to as , the in-plane retardation value for light with a wavelength of 550 nm is sometimes referred to as "Re (550)") is approximately the same as the Re (550) of the release film, and compensates for the birefringence that the release film has. The first retardation plate, which is a retardation film, and the object to be inspected, with the release film side facing the first retardation plate side, are arranged in this order on the optical path of the light emitted by the light source. ) is substantially the same as Re (550) of the first retardation plate and compensates for the birefringence of the first retardation plate, and the first retardation plate. The filter and a second phase difference filter constituting a crossed nicol are arranged in this order on the optical path of the light reflected by the object to be inspected, and the light from the light source is incident on the first phase difference filter, The presence or absence of a defect in the circularly polarizing plate is determined by observing the light reflected by the object to be inspected from the second retardation filter side, and the first retardation plate and the second retardation plate are heated to Re(550). Re(550) is 50 to 100 nm larger than the release film's Re(550) and is replaced with a third retardation plate and a fourth retardation plate, which compensate for the birefringence of the release film, and after the replacement, the An inspection method is provided in which light is incident on a first phase difference filter, and the light reflected by an object to be inspected is observed from the second phase difference filter side to determine the presence or absence of a defect in a circularly polarizing plate. 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, the first phase difference filter and the second phase difference filter are arranged so as to form a crossed nicol configuration, so that the light reflected from the normal part of the object to be inspected (for example, from the release film) Since the light reflected on the surface is blocked by the second phase difference filter, the observation field can be sufficiently darkened, making it easier to observe the defective part. On the other hand, the phase difference of the light reflected from a defect inside the inspected object is shifted from the ideal one due to the defect (it becomes unintended elliptically polarized light), so The second phase difference filter is transmitted through the second phase difference filter, and can be detected as a defective portion of the object to be inspected. Here, the light reflected at the defective part will pass through the release film twice, and the retardation of the release film may be an obstacle to defect detection, but the first retardation plate is the one that the release film has. Since it compensates for birefringence, the birefringence of the release film is suppressed from becoming an obstacle to defect detection. In addition, for areas observed as black defects in the inspection using the first retardation plate and the second retardation plate, each of these retardation plates is replaced with a third retardation plate and a fourth retardation plate. By replacing it with , it is possible to adjust the phase difference so that it can be observed as a bright spot defect. In addition, in this type of reflective inspection method, the optical path through the inspected object is longer than in the transmission type inspection method, so it is easier to detect deformed defects that are difficult to detect with the transmission type inspection method. be able to. From the above, the inspection method of the present invention can easily determine the presence or absence of a defect in a circularly polarizing plate.

In this testing method, the retardation film may be 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, the possibility that black spot defects will be observed increases due to its general thinness. Therefore, it is suitable as an object to which the present invention is applied.

Further, 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 phase difference filters may be tilted so that they face each other at different angles, or may be rotated in a direction perpendicular to the optical path. 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 within the same member. Moreover, the first retardation plate and the second retardation plate may be arranged in the same member.

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

FIG. 1 is a diagram showing an inspection device according to a first embodiment. FIG. 3 is a cross-sectional view of the object to be inspected. FIG. 3 is a plan view of a retardation plate.

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.

(Inspection equipment and inspected object)
The inspection device of this embodiment inspects the presence or absence of defects on the surface of a circularly polarizing plate, between the layers constituting the circularly polarizing plate, or inside the circularly polarizing plate. As shown in FIG. 1, the inspection apparatus 100 includes a light source 2, a first phase difference filter 3A, and a first phase difference plate 4A arranged in this order, and a light source 2, a first phase difference filter 3A, and a first phase difference plate 4A. A second phase difference filter 3B and a second phase difference plate 4B are arranged next to the phase difference plate 4A. The surfaces of the first phase difference filter 3A and the second phase difference filter 3B are parallel to each other and are arranged on substantially the same plane, and the surfaces of the first phase difference filter 4A and the second phase difference plate 4B are parallel to each other. They are arranged parallel to each other and approximately on the same plane.

As shown in FIG. 2, the object to be inspected 10 is in the form of a film, and includes a circularly polarizing plate 1, which is the main body of the object to be inspected, and a release film laminated to the circularly polarizing plate 1 via an adhesive layer 15. 16a. 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.

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.

The retardation film 14 is a film that converts light incident from the surface protection film 16b side and linearly polarized by the polarizing film 11 into circularly polarized light. When viewed from the release film 16a side, the retardation film 14 is a film that converts circularly polarized light incident from the release film 16a side into linearly 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. In such areas, linearly polarized light is not completely converted into ideal circularly polarized light, resulting in unintended elliptically polarized light. Furthermore, as will be described later, when the birefringence of the release film 16a is compensated for by the retardation plate 4, the defect may be observed as a black spot even though it should originally be observed as a bright spot defect. .

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 method of this embodiment is particularly useful for determining the presence or absence of defects in an object to be inspected that has a circularly polarizing plate and a release film that include a retardation film that has 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 100. 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. 2, 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. . In addition, in FIG. 2, 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. 2, 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.

Here, we will show how to obtain Re(550) of the release film 16a. 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 broadband 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. At this time, it should be noted that the light incident on the second phase difference filter 3B is the reflected light reflected by the object to be inspected 10. 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 first retardation plate 4A compensates for the birefringence of light caused by the release film 16a included in the inspection object 10. The materials constituting the first retardation plate 4A are not particularly limited as long as they compensate for the birefringence of light due to the release film 16a made of PET resin. The first retardation plate 4A 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 first retardation plate 4A having a desired Re (550) can be obtained from the Re (550) of the laminated retardation plates. The second retardation plate 4B cancels out the phase difference of the first retardation plate 4A, and preferably has the same configuration as the first retardation plate 4A. 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 set of two, a third retardation plate 4C and a fourth retardation plate 4D, each having a Re (550) larger than that of Re(550) by 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 4C and the fourth retardation plate It has the same Re (550) as 4D. 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 similar to the above. It means that it is 5 nm or less.

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 4C. Next, the state of this retardation plate will be explained.

FIG. 3 schematically shows a series of retardation plates 4 in which retardation plates having different in-plane retardation differences are integrated. As shown in FIG. 3, the retardation plate 4 has two rows of regions having different in-plane retardation values arranged in one direction in a single holding member 41 forming a frame. It may be something like that. That is, if we pay attention to one row of the retardation plates 4 (in the vertical direction in the figure), the area located at the end is the area _a1 corresponding to the first retardation plate 4A, and Re(550) is, for example, 1720 nm, the region next to it is region _a3 corresponding to the third retardation plate 4C and has Re (550) of 1790 nm, and the region next to it is region a3 corresponding to the third retardation plate 4C, and the region next to it is the region a3 corresponding to the third retardation plate 4C, and the region next to it is the region This is a region _a5 corresponding to the retardation plate 4E, and has a Re (550) of 1860 nm. In the retardation plate 4, the number of regions per row is arbitrary, and FIG. 3 shows up to the n-th region _a2n-1 . Then, in another row _of the retardation plate 4 _, regions (a _{2 , a 4} , a ₆ , ..., a _2n ) are arranged in pairs. That is, the area corresponding to the first retardation plate 4A (a ₁ ) is the second retardation plate 4B (a 2 ), and the area corresponding to the third retardation plate 4C (a ₃ ) is the fourth retardation plate 4B (a ₂ ). The region corresponding to the fifth retardation plate 4E (a _{5 )} is the sixth retardation plate 4F (a ₆ ). 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.

Since each region of this retardation plate 4 is configured in one holding member 41 as described above, regions having the same Re (550) can be used in pairs in the inspection device 100. . In other words, the retardation plate 4 has a configuration suitable for simultaneously providing the first retardation plate 4A and the second retardation plate 4B. The first retardation plate 4A and the second retardation plate 4B are used as a pair, and then by sliding the retardation plate 4, the third retardation plate 4C and the fourth retardation plate 4D are used as a pair. Furthermore, the fifth retardation plate 4E and the sixth retardation plate 4F can be used as a pair.

In order to observe the light reflected by the defective part inside the inspection object 10, a CCD camera or the like is installed on the optical path of the reflected light and at a position on the side where the light source 2 is located on both sides of the second phase difference filter 3B. You may arrange the detection means 5 containing. 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. Further, a partition plate may be provided between the light source 2 and the CCD camera as appropriate.

The inspection apparatus 100 also includes an object to be inspected 10, a first retardation plate 4A, a second retardation plate 4B, a third retardation plate 4C, a fourth retardation plate 4D, and a first retardation filter. 3A and the second phase difference filter 3B so that they face each other at different angles or rotate in a direction perpendicular to the optical path 9 of the light. ) is preferable. By tilting these, the retardation of the release film 16a made of PET resin, the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, and the fourth retardation plate 4D can be adjusted. Since it can be finely adjusted, a wider range of inspections is possible. In addition, by rotating these, the release film 16a made of PET resin, the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, and the fourth retardation plate 4D can be separated. Axis alignment becomes easy.

(Inspection method)
The inspection method using the inspection device 100 is as follows. First, the object to be inspected 10 is placed inside the inspection apparatus 100 on the other side of the first retardation plate 4A and the second retardation plate 4B when viewed from the light source 2. 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 and the retardation film 14 faces the light source 2 side, and the circularly polarizing plate 1 and the first The phase difference filter 3A is arranged so as to form a crossed Nicol configuration. Here, as the first retardation plate 4A and the second retardation plate 4B, the retardation plate 4 shown in FIG. 3 is used. The second retardation plate 4B is arranged so that the light before it is incident on the inspection object 10 is transmitted therethrough, and the second retardation plate 4B is arranged so that the light reflected by the object to be inspected 10 is incident thereon.

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 100 is equipped with the above movable device, 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.

Light is input from the light source 2 to the first phase difference filter 3A. At this time, the angle of incidence on the object to be inspected 10 (angle based on the perpendicular to the surface of the object to be inspected 10) is preferably 3° to 30°, more preferably 5° to 20°. When the light emitted by the light source 2 has low directivity, it is preferable that the angle of reflection from the object to be inspected 10 (or the angle of observation by the detection means 5) falls within the above angle range.

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 (optical path 9a). The light that has passed through the first retardation plate 4A then enters the object to be inspected 10. The light then passes through the release film 16a in the inspection object 10, is converted into linearly polarized light by the retardation film 14 constituting the circularly polarizing plate 1, and is finally absorbed by the polarizing film 11 (at the end of the optical path 9a). . Here, a part of the light transmitted through the first retardation plate 4A is reflected on the surface of the release film 16a in the object to be inspected 10 (optical path 9b). Since the first phase difference filter 3A and the second phase difference filter 3B are arranged to form a crossed nicol, this reflected light is blocked by the second phase difference filter 3B (on the optical path 9b). Therefore, the observation field of the second phase difference filter 3B by the detection means 5 is dark.

On the other hand, a part of the light incident on the object to be inspected 10 is caused by defects existing in the object to be inspected 10 (defects D existing at the interface between the retardation film 14 and the polarizing film 11, and defects existing in the retardation film 14). Reflection becomes stronger at the defect D') (optical path 9c). The phase difference of this reflected light is shifted from the ideal due to the defects D and D' (unintended elliptically polarized light), so it is not absorbed by the polarizing film, and the reflected light at the interface is arise. This reflected light is transmitted through the second phase difference filter without being blocked. When this is observed from the detection means 5 side, the defective portion is observed as a bright spot.

In addition, the first retardation plate 4A 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, the third retardation plate 4C 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. and a fourth retardation plate 4D. Specifically, the holding member 41 constituting the retardation plate 4 is slid in its surface direction, and a third retardation plate 4C is inserted in place of the first retardation plate 4A and the second retardation plate 4B. And the fourth retardation plate 4D is positioned on the optical path 9. 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 pair of the third retardation plate 4C and the fourth retardation plate 4D, the holding member 41 is further replaced with the fifth retardation plate 4E and the sixth retardation plate. Slide it onto the pair of retardation plates 4F and perform the third inspection.

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 100 includes a movable device.

Furthermore, in the inspection method of the present invention, by using, for example, light with a single wavelength or light with a narrow wavelength range as the light from the light source 2, defects in which the phase difference value is locally shifted can also be detected. It becomes possible. Specifically, as a light source, the transmission axis of the polarizing film of the circularly polarizing plate 1 included in the object to be inspected 10 and the transmission axis of the polarizing plate that converts into linearly polarized light included in the phase difference filter are not arranged in a crossed Nicol arrangement. Uses light of a wavelength that minimizes the amount of transmitted light when placed at . At this time, the first phase difference filter 3A and the phase difference film 14 are arranged to face each other. When there are multiple wavelengths, it is particularly preferable to select a wavelength in the range of 500 to 600 nm. Furthermore, inspection accuracy is improved by using a light source with a half-width of the intensity peak of 30 nm or less.

According to the inspection method described above, a portion where a black defect was observed in the inspection using the pair of the first retardation plate 4A and the second retardation plate 4B is transferred to the third retardation plate 4C and the fourth retardation plate 4B. By inspecting using the retardation plate 4D, it is possible to adjust the retardation so that this can be observed as a bright spot defect. In addition, since this inspection method is a reflection type inspection method, the optical path in the inspected object 10 is longer than that in a transmission type inspection method, and deformations such as wrinkles, which are difficult to detect with the transmission type inspection method, can occur. Defects can also be easily detected. From the above, the inspection method of the present invention can easily determine the presence or absence of a defect in a circularly polarizing plate.

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.

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 (9a, 9b, 9c)... 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, 41...Holding member, 100...Inspection device, a...Region, D, D'...Defect.

Claims (5)

A method for detecting defects in a film-like object to be inspected, comprising a circularly polarizing plate formed by laminating a polarizing film and a retardation film, and a release film made of a polyethylene terephthalate resin and laminated on the retardation film side of the circularly polarizing plate. An inspection method for determining the presence or absence of
a light source and
a first phase difference filter;
A first position whose in-plane retardation value for light with a wavelength of 550 nm is approximately the same as the in-plane retardation value of the release film for light with a wavelength of 550 nm, and which compensates for the birefringence of the release film. A retardation plate,
the object to be inspected, with the release film side facing the first retardation plate side, are lined up in this order on the optical path of the light emitted by the light source, and
The in-plane retardation value for light with a wavelength of 550 nm is approximately the same as the in-plane retardation value of the first retardation plate for light with a wavelength of 550 nm, and the birefringence of the first retardation plate is compensated for. a second retardation plate that
The first phase difference filter and a second phase difference filter forming a crossed nicol are arranged in this order on the optical path of the light reflected by the object to be inspected,
The light from the light source is incident on the first phase difference filter, and the light reflected by the object to be inspected is observed from the second phase difference filter side 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 for light with a wavelength of 550 nm that is 50 to 100 nm larger than an in-plane retardation value of the release film for light with a wavelength of 550 nm, and , replaced with a third retardation plate and a fourth retardation plate that compensate for the birefringence of the release film, respectively,
After the replacement, light is incident on the first phase difference filter, and the light reflected by the object to be inspected is observed from the second phase difference filter side to determine whether there is a defect in the circularly polarizing plate. ,Inspection method. 2. The inspection method according to claim 1, wherein the retardation film is 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, and the second retardation plate. 3. The inspection method according to claim 1, wherein at least one of the phase difference filters is tilted so that they face each other at different angles, or rotated in a direction perpendicular to the optical path. 4. The inspection method according to claim 1, wherein the first retardation plate and the third retardation plate are arranged in the same member. 5. The inspection method according to claim 1, wherein the first retardation plate and the second retardation plate are arranged in the same member.

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