JP7474569B2 - Inspection method and inspection device - Google Patents

Description

The present invention relates to an inspection method and an inspection device.

Polarizing plates used in liquid crystal displays, organic EL displays, etc., generally consist of a polarizer sandwiched between two protective films. To attach the polarizing plate to a display device, an adhesive layer is laminated onto one of the protective films, and a release film is further laminated onto the adhesive layer. In many cases, a release film is also attached to the other protective film to protect its surface. Polarizing plates are transported and distributed with the release film laminated in this manner, and the release film is peeled off when the polarizing plate is attached to a display device during the display device manufacturing process.

During the manufacturing process of polarizing plates, foreign matter may be mixed in between the polarizer and the protective film, air bubbles may remain, or, if the protective film functions as a retardation film, alignment defects may be present (hereinafter, these foreign matter, air bubbles, and alignment defects may be collectively referred to as "defects"). When a polarizing plate with defects is attached to a display device, the defective area may be visible as a bright spot, or the image may appear distorted at the defective area. In particular, defects that are visible as bright spots are easily visible when the display device is displaying black.

Therefore, before the polarizing plate is attached to the display device (the polarizing plate with the 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 the polarizing plate. Specifically, as shown in Patent Document 1, a polarizing filter is provided between the polarizing plate to be inspected and the light source, and then the polarizing plate or the polarizing filter is rotated in a planar direction to set the polarization axis directions of these plates in a specific relationship. When the polarization axis directions are perpendicular to each other (i.e., when the arrangement forms a cross Nicol), the linearly polarized light that passes through the polarizing filter does not pass through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light passes through the corresponding part, and the presence of the defect is identified by detecting the light. On the other hand, when the polarization axis directions of the polarizing plate and the polarizing filter are parallel to each other, the linearly polarized light that passes through the polarizing filter passes through the polarizing plate. However, when there is a defect in the polarizing plate, the linearly polarized light is blocked at the corresponding part, and the presence of the defect is identified by not detecting the light. The presence or absence of defects in the polarizing plate can be inspected by an inspector either visually detecting the light that has passed through the polarizing plate or automatically detecting it using image analysis processing values that combine a CCD camera and image processing device.

Japanese Patent Application Laid-Open No. 9-229817

However, as mentioned above, when a release film is provided on a polarizing plate, the birefringence of the release film impairs the polarization characteristics of the polarizing plate, making it impossible to accurately detect defects such as bright spots on the polarizing plate using conventional inspection devices.

In other words, when a polarizing plate and a polarizing filter are arranged to form a crossed Nicol, the defect will be seen as a bright spot according to the above principle, but depending on the defect condition of the polarizing plate, the bright spot defect may be seen as a black spot, in which case it is more difficult to detect than if it were a bright spot. This situation is the same whether the polarizing plate is a linear polarizing plate or a circular polarizing plate.

The objective of the present invention is to provide an inspection method and inspection device that can easily determine whether or not a polarizing plate has a defect.

The present invention provides an inspection method for determining the presence or absence of defects in a film-like inspection particle comprising a polarizing plate and a release film made of polyethylene terephthalate resin (PET resin), in which the inspection object, a retardation plate that includes a region in which the in-plane retardation value at a wavelength of 550 nm (hereinafter, the in-plane retardation value at a wavelength of 550 nm is referred to as "Re(550)") is 500 to 600 nm greater than the Re(550) of the release film and compensates for the birefringence of the release film, and a polarizing filter that forms a crossed Nicol with the polarizing plate are arranged in this order, and light is incident from either the inspection object side or the polarizing filter side so that the optical axis passes through the region, and the polarizing filter or inspection object is observed from the other side to determine the presence or absence of defects in the polarizing plate.

According to this inspection method, by using the retardation plate, the transmission spectrum of visible light can be matched to the release film over a wider wavelength range, making the entire observation field darker. In this case, defective parts of the polarizing plate, which are observed as bright spots, become more prominent in the observation field. Therefore, according to the present invention, it is easy to determine whether or not there is a defect in the polarizing plate.

In the inspection method of the present invention, the polarizing plate may be a linear polarizing plate, and the polarizing filter may be a linear polarizing filter. Also, in the present invention, the polarizing plate may be a circular polarizing plate, and the polarizing filter may be a phase difference filter. The present invention can be applied in either case.

The retardation plate may have an in-plane retardation value that changes continuously. In this case, a single retardation plate has various in-plane retardation values, and therefore the retardation of various release films can be compensated for by the single retardation plate.

In the present invention, the retardation plate may be made up of multiple sheets, and may be arranged so that the directions in which the in-plane retardation value increases are opposite to each other. In the case of multiple retardation plates arranged in this manner, the change in the retardation value according to the location in the retardation plate is more gradual than when there is only one retardation plate. Therefore, when multiple retardation plates are used, the region in which the retardation of the release film can be compensated for is wider than when there is only one retardation plate.

The retardation plate may be made of an inorganic material or a cycloolefin resin.

In the present invention, at least one of the object to be inspected, the retardation plate, and the polarizing filter may be tilted so that they face each other at different angles, or may be rotated in a direction perpendicular to the optical axis of the light. By tilting these, the phase difference of the release film and the retardation plate can be finely adjusted, making it possible to inspect a wider range. In addition, by rotating these, it becomes easier to align the axes of the release film and the retardation plate.

The present invention also provides an inspection device that judges the presence or absence of defects in a polarizing plate by irradiating light onto a film-like inspection object that includes a polarizing plate and a release film made of a PET resin, the inspection device comprising a light source, a polarizing filter that allows the light emitted from the light source and passed through the inspection object to enter, and a retardation plate that is arranged on a side farther from the light source than the inspection object and closer to the light source than the polarizing filter, and that allows the light that has passed through the inspection object to pass, the retardation plate including a region in which Re(550) is 500 to 600 nm greater than the Re(550) of the release film, and that compensates for the birefringence of the release film.

The present invention also provides an inspection device that judges the presence or absence of defects in a polarizing plate by irradiating light onto a film-like inspection object that includes a polarizing plate and a release film made of a PET resin, the inspection device comprising a light source, a polarizing filter that passes light emitted by the light source, and a retardation plate that passes light that has passed through the polarizing filter and is placed closer to the light source than the object to be inspected and farther from the light source than the polarizing filter, the retardation plate including a region in which the wave Re(550) is 500-600 nm larger than the Re(550) of the release film, and that compensates for birefringence of the release film.

In the inspection device of the present invention, the polarizing plate may be a linear polarizing plate, and the polarizing filter may be a linear polarizing filter. Also, in the present invention, the polarizing plate may be a circular polarizing plate, and the polarizing filter may be a phase difference filter. The present invention can be applied in either case.

In the inspection device of the present invention, the retardation plate may have an in-plane retardation value that changes continuously. The retardation plate may be made of multiple sheets, and may be arranged so that the directions in which the in-plane retardation value increases are opposite to each other. The retardation plate may be made of an inorganic material or a cycloolefin resin.

In the inspection device of the present invention, the retardation plate may be positioned at a position where the optical axis of the light passes through the region.

The present invention provides an inspection method and inspection device that can easily determine whether or not a polarizing plate has a defect.

FIG. 1 is a diagram illustrating an inspection device according to a first embodiment. 2 is a cross-sectional view of an object to be inspected in the first embodiment. FIG. FIG. 2 is a diagram showing an example of a retardation plate. FIG. 13 is a diagram showing an inspection device according to a modified example of the first embodiment. FIG. 13 is a diagram showing a situation in which a retardation plate is scanned. FIG. 13 is a diagram illustrating an inspection device according to a second embodiment. FIG. 13 is a diagram illustrating an inspection device according to a third embodiment. FIG. 11 is a cross-sectional view of an object to be inspected in a third embodiment. FIG. 13 is a diagram illustrating an inspection device according to a fourth embodiment.

Below, a preferred embodiment of the present invention will be described in detail with reference to the drawings. Note that the same or corresponding parts in each drawing are given the same reference numerals, and duplicated explanations will be omitted.

First Embodiment
An inspection device and an inspection method according to a first embodiment will be described.

(Inspection equipment and inspection object)
The inspection device of this embodiment is for inspecting the presence or absence of surface defects on a linear polarizing plate. As shown in Fig. 1, the inspection device 100A includes a light source 2, a retardation plate 4, and a linear polarizing filter (polarizing filter) 3A arranged in this order.

As shown in FIG. 2, the film-shaped test object 10A to be inspected comprises a linear polarizer 1A, which is the main body of the test object, and a release film 16a laminated to the linear polarizer 1A via an adhesive layer 15. The linear polarizer 1A is formed by laminating protective films 12a and 12b to both sides of a polarizing film 11. A separate release film 16b is laminated to the side of the linear polarizer 1A that does not have the release film 16a. The linear polarizer 1A is generally used in display devices, such as liquid crystal display devices and organic EL display devices, and when in use, the release film 16a is peeled off and the linear polarizer is attached to the display device via the adhesive layer 15.

In this specification, the term "linear polarizing plate" refers to a polarizing plate for converting any light, for example unpolarized light, into linearly polarized light.

The polarizing film 11 is a film that converts the light incident from the light source 2 into linearly polarized light in the inspection device 100A. Examples of the polarizing film 11 include a polyvinyl alcohol film on which iodine or a dichroic dye is adsorbed and oriented, and a polymerizable liquid crystal compound on which a dichroic dye is adsorbed and oriented.

The protective films 12a and 12b are intended to protect the polarizing film 11. For the purpose of obtaining a polarizing plate having appropriate mechanical strength, protective films that are commonly used in the technical field of polarizing plates are used as the protective films 12a and 12b. Typical examples include cellulose ester-based films such as triacetyl cellulose (TAC) film; cyclic olefin-based films; polyester-based films such as polyethylene terephthalate (PET) film; and (meth)acrylic films such as polymethyl methacrylate (PMMA) film. The protective films may also contain additives that are commonly used in the technical field of polarizing plates.

The protective films 12a and 12b are attached to the display device together with the polarizing film 11 as components of the linear polarizing plate 1A, so strict control of the phase difference value is required. Typically, protective films 12a and 12b with an extremely small phase difference value are preferably used. The protective films 12a and 12b are attached to the polarizing film 11 via an adhesive.

The release films 16a and 16b are peeled off from the linear polarizer 1A when it is attached to a display device, and the peeled off release films 16a and 16b are usually discarded. Therefore, unlike the protective films 12a and 12b, strict management of the phase difference value is not required. Therefore, if a commercially available film is used as the release film 16a, if the phase difference value is not compensated for, it may cause malfunctions in defect inspection using the linear polarizing filter 3A. In other words, in defect inspection of the linear polarizer 1A to which the release films 16a and 16b, whose phase difference values are not strictly controlled, are attached, the phase difference of the release film 16a may cause a decrease in the inspection accuracy of the inspection device 100A.

As described in the Background Art above, in polarizing plate 1A, another release film 16b is often provided on the opposite side of release film 16a. In polarizing plate 1A shown in Figure 2, release film 16b is attached to the protective film 12b side. This release film 16b is also usually peeled off from linear polarizing plate 1A when it is attached to a display device, and unlike protective films 12a and 12b, strict management of the phase difference value is not required. When compensating for the phase difference value of the release film 16b, the release film 16a is replaced with the release film 16b in the inspection device 100A (i.e., the Re (550) of the release film 16b is obtained in advance, and then the direction of the inspection object 10A is reversed (the release film 16b is placed so that it faces the retardation film 4), and the inspection method of this embodiment is carried out using the inspection device 100A. Note that in FIG. 2, the protective film 12b and the release film 16b may be bonded together via an appropriate adhesive layer or pressure-sensitive adhesive layer (this adhesive layer or pressure-sensitive adhesive layer is not shown in FIG. 2).

In this embodiment, the release film 16a is made of a PET resin. When the phase difference value of the release film 16b is compensated for and the inspection method of this embodiment is carried out, the release film 16b is also made of a PET resin. A film made of a PET resin (PET resin film) has the advantage that it is versatile as a release film and is inexpensive. On the other hand, as described above, strict management of the phase difference value is not required for an inexpensive PET resin film. Therefore, for example, the phase difference value may vary for each product lot. In addition, even if the same PET resin film is used, the phase difference value (in-plane phase difference value) may vary within the plane. Even if such an inexpensive PET resin film is attached as a release film to a polarizing plate, the presence or absence of defects can be accurately detected by the inspection method of this embodiment.

Here, we will show how to determine the Re(550) of the release film 16a. As mentioned above, these release films are made of PET resin, and such films are easily available on the market. For example, a piece of about 40 mm x 40 mm in size is taken from this film (e.g., from a long film using an appropriate cutting tool). The Re(550) of this piece is measured three times, and the average Re(550) is calculated. 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.). The same test can be performed to determine the Re(550) of the release film 16b.

The light source 2 can be any commercially available product, but it is advantageous to use linear light (including light that approximates linear light) such as laser light. The light emitted by the light source 2 is unpolarized and becomes polarized in a predetermined direction as it passes through the polarizing film 11.

The linear polarizing filter 3A is a linear polarizing plate. When inspecting the object 10A, the orientation of the linear polarizing filter 3A is adjusted so that it always forms a crossed Nicol with the linear polarizing plate 1A in the object 10A. The linear polarizing plate of the linear polarizing filter 3A is defect-free.

The retardation plate 4 compensates for the birefringence of light caused by the peel-off film 16a. When the polarization axes of the linear polarizing filter 3A and the linear polarizing plate 1A are perpendicular (i.e., when they form a crossed Nicol), the linearly polarized light converted by the linear polarizing plate 1A does not pass through the linear polarizing filter 3A at all, but if there is a defect in the linear polarizing plate 1A, it may be visible as a bright spot.

However, an optically transparent material is used for the release film 16a, and a material with birefringence such as a PET resin is usually used. When linearly polarized light passes through such a material, it is converted into elliptically polarized light. Therefore, even though the linear polarizing filter 3A and the linear polarizing plate 1A form a crossed Nicol configuration, the amount of light transmitted through the linear polarizing filter 3A exceeds 15% of the amount of light from the light source, and the detection accuracy of bright spots resulting from defects in the linear polarizing plate 1 is significantly reduced. For the same reason, an optically transparent material is used when using the release film 16b.

Therefore, by placing a retardation plate 4 between the linear polarizing filter 3A and the linear polarizing plate 1A to be inspected, the change in transmittance of the peel-off film 16a is canceled, thereby compensating for the birefringence of light caused by the peel-off film 16a.

The shape of the retardation plate 4 is not particularly limited as long as it can compensate for the birefringence of light in the release film 16a, but since the release film 16a made of PET-based resin has a large variation in the in-plane retardation value and slow axis, it is preferable that the retardation value be adjusted during inspection. As shown in FIG. 3, the thickness of the retardation plate 4 is not uniform, but changes continuously to have thin and thick parts. Since the thickness changes continuously, the retardation value also changes continuously according to the thickness. The retardation plate 4 has a thickness that spreads at a predetermined angle α from the thinnest part as a starting point, and has a "wedge" shape in cross section. The wedge-shaped retardation plate 4 can be easily shifted or rotated within the inspection area of the test object 10A to compensate for the birefringence of light caused by the release film 16a.

The retardation film 4 is preferably a rectangle or square with a side length ranging from 1 cm to 30 cm.

The retardation plate 4 can be made of inorganic materials such as minerals that exhibit birefringence, such as quartz and calcite, or a film made of a cycloolefin resin. It is particularly preferable to use such materials with flat wavelength dispersion characteristics. In addition, it is preferable to use minerals such as quartz in terms of ease of processing into a wedge shape and subsequent handling.

When using a mineral such as quartz, a retardation film may be further used to make the wavelength dispersion characteristics flatter. When the slow axis of the retardation film is arranged perpendicular to the slow axis of the retardation plate made of a mineral such as quartz, it is preferable to use a retardation film with normal dispersion, and when the slow axis of the retardation film is arranged parallel to the slow axis of the retardation plate made of a mineral such as quartz, it is preferable to use a retardation film with reverse dispersion. When using such a retardation film, the retardation film is laminated to the surface of the quartz.

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

Examples of the cycloolefin resin include a resin obtained by ring-opening metathesis polymerization using norbornene or its derivative obtained by the Diels-Alder reaction of cyclopentadiene and olefins as a monomer, followed by hydrogenation; a resin obtained by ring-opening metathesis polymerization using tetracyclododecene or its derivative obtained by the Diels-Alder reaction of dicyclopentadiene and olefins or methacrylic acid esters as a monomer, followed by hydrogenation; a resin obtained by ring-opening metathesis copolymerization using two or more types of norbornene, tetracyclododecene, their derivatives, or other cyclic olefin monomers, followed by hydrogenation; and a resin obtained by addition copolymerization of an aromatic compound having a vinyl group to the above-mentioned norbornene, tetracyclododecene, or their derivatives.

Cycloolefin resins are readily available commercially. Examples of commercially available products include Topas (manufactured by Topas Advanced Polymers GmbH), Arton (manufactured by JSR Corporation), Zeonor, Zeonex (all manufactured by Zeon Corporation), and Apel (manufactured by Mitsui Chemicals, Inc.).

The retardation value of the retardation plate 4 has a region (hereinafter sometimes referred to as the "wide compensation region") that is 500 to 600 nm larger than the Re (550) of the release film 16a. By using a retardation plate 4 with a region shifted by approximately one wavelength in this way, the transmission spectrum of visible light can be matched with the PET resin film over a wider wavelength range, making retardation compensation possible.

To observe the light that has passed through the object 10A, the retardation plate 4, and the linear polarizing filter 3A, a detection means 5 including a CCD camera or the like may be disposed on the optical axis 9 and on one side of the linear polarizing filter 3A opposite the side where the light source 2 is located. For example, the object can be automatically detected by image processing analysis that combines a CCD camera and an image processing device, thereby inspecting the object. Alternatively, the detection means 5 may not be a component, but may be a human being who visually observes the linear polarizing filter 3A.

The inspection device 100A also preferably includes a movable device (not shown) that allows at least one of the object to be inspected 10A, the retardation film 4, and the linear polarizing filter 3A to be tilted so that they face each other at different angles, or to be rotated in a direction perpendicular to the optical axis 9 of the light. Tilting these allows the phase difference of the release film 16a made of PET resin and the retardation film 4 to be finely adjusted, making it possible to inspect a wider range. Rotating these also makes it easier to align the axes of the release film 16a made of PET resin and the retardation film 4.

(Inspection method)
The inspection method using the inspection device 100A is as follows. First, the object to be inspected 10A is inserted between the light source 2 and one wedge-shaped retardation plate 4 inside the inspection device 100A. At this time, the object to be inspected 10A, the retardation plate 4, and the linear polarizing filter 3A are arranged so that their surfaces are all parallel, the side of the object to be inspected 10A having the release film 16a faces the opposite side to the light source 2, and the linear polarizing plate 1A and the linear polarizing filter 3A form a crossed Nicol. If the inspection device 100A is provided with the above-mentioned movable device, the object to be inspected 10A may be inserted in an arbitrary direction, and then the relative positional relationship between the object to be inspected 10A and the linear polarizing filter 3A may be changed by the movable device to form a crossed Nicol.

The light emitted by the light source 2 is incident on the object 10A to be inspected, passes through the object 10A, and becomes linearly polarized light. The object 10A and the linear polarizing filter 3A are arranged in a crossed Nicol configuration, so that the linearly polarized light generated by passing through the object 10A is blocked by the linear polarizing filter 3A. If there is a defect in the linear polarizing plate 1A in the object 10A, the defective part cannot be blocked normally, and the defective part is observed as a bright spot by the eyes of the inspection operator or a CCD camera, etc., in the detection means 5.

However, if the release film 16a has a phase difference, the linearly polarized light generated by passing through the object under inspection 10A is affected, and the amount of light transmitted through the linear polarizing filter 3A increases (for example, exceeding 10% or 15% of the amount of light from the light source), reducing the accuracy of detecting defects such as bright spots present in the linear polarizing plate 1A. Here, by disposing the phase difference plate 4 between the object under inspection 10A and the linear polarizing filter 3A, the phase difference value of the release film 16a in the object under inspection 10A is canceled, compensating for the birefringence of light caused by the release film 16a.

During the inspection, the optical axis of the light emitted by the light source 2 passes through the "wide compensation region" of the retardation film 4. This allows the visible light transmission spectrum to be matched with the PET resin film over a wider wavelength range, making compensation for the retardation more effective. In other words, the thickness of the retardation film 4 changes continuously, and therefore the retardation value also changes continuously, so that the birefringence of the release film 16a is canceled in some thickness portions among the various thicknesses of the retardation film 4.

During inspection, at least one of the object to be inspected 10A, the retardation film 4, and the linear polarizing filter 3A may be tilted so that they face each other at different angles, or may be rotated in a direction perpendicular to the optical axis 9 of the light. By tilting, the phase difference of the release film 16a and the retardation film 4 can be finely adjusted, making it possible to inspect a wider range. Furthermore, by rotating these, it becomes easier to align the axes of the release film 16a made of PET resin and the retardation film 4. These operations can be performed particularly easily when the inspection device 100A is equipped with a movable device.

The above describes the inspection device and inspection method of the first embodiment. This inspection device and inspection method can also be implemented by modifying some of the configuration or inspection procedure as follows.

As shown in FIG. 4, two retardation plates 4 with a wedge-shaped cross section may be prepared and used in a stacked state with the directions in which the retardation value increases continuously being opposite to each other. In this case, the retardation value of the retardation plate is the total value of the two plates, and the above-mentioned "wide compensation area" is also based on the total value of the two plates. By using two wedge-shaped retardation plates 4, the birefringence of light in the release film 16a can be compensated over a wide range, so the inspection area can be expanded and inspection can be performed efficiently.

More specifically, the phase difference of the retardation plates 4, 4 as a whole can be changed by shifting at least one of the two retardation plates 4, 4 in the direction in which its thickness changes (left and right direction in the figure). The degree of change is gentler than when there is only one retardation plate 4, because the retardation plates 4, 4 are arranged so that the directions in which their thickness increases are opposite to each other. As a result, in the inspection device 100A' (Figure 4) using two retardation plates 4, 4, the area in which the birefringence of the release film 16a can be canceled is wider than in the inspection device 100 using only one retardation plate 4. In addition, inspection can be performed in the same way even if three or four retardation plates 4 are used.

Alternatively, the retardation plate does not have to be wedge-shaped in cross section. It is sufficient for the retardation plate to have the above-mentioned "wide compensation region," so the retardation of the release films 16a and 16b can be measured in advance, and a retardation plate having a corresponding retardation and a uniform thickness can be used.

The first embodiment is particularly useful as a method for inspecting an area of the object 10A to be inspected after identifying the area to be inspected in advance, but as shown in FIG. 5, the object 10A can be inspected over a wider range by scanning the light source 2 and the retardation plate 4. In this case, as shown in FIG. 5, the retardation plate 4 is moved so as to scan the entire surface area of the object 10A to be inspected. The direction of movement is preferably the direction in which the thickness of the retardation plate 4 differs. In terms of the relationship between FIG. 1 and FIG. 5, since the thickness of the retardation plate 4 differs in the left and right directions in the figure, the movement direction of the retardation plate 4 is preferably the left and right direction in the figure. At this time, the light source 2 and the detection means 5 are also moved as necessary.

Second Embodiment
The inspection device and the inspection method of the second embodiment will be described. As shown in FIG. 6, the inspection device 100B of the second embodiment is different from the inspection device 100A of the first embodiment in that the place where the inspection object 10A is arranged and the place where the linear polarizing filter 3A is arranged are reversed. That is, the inspection device 100B is configured by arranging the light source 2, the linear polarizing filter 3A, and the retardation plate 4 in this order, and the inspection object 10A is arranged at a position farther from the light source 2 than the retardation plate 4 so that the release film 16a faces the light source 2 during inspection. Note that, as in the first embodiment, when the release film 16b is attached to the polarizing plate 1A to compensate for the phase difference value of this release film 16b, the inspection object 10A may be placed in the inspection device 100B so that the release film 16b faces the retardation plate 4.

When inspecting the object 10A using the inspection device 100B, the linear polarizer 1A can be easily inspected for defects using the same principles as in the first embodiment.

Third Embodiment
An inspection device and an inspection method according to the third embodiment will be described.

(Inspection equipment and inspection object)
The inspection device of this embodiment is different from the first embodiment in that it inspects the presence or absence of surface defects on a circular polarizer. The difference from the first embodiment is that the film-like inspection object 10B to be inspected includes a circular polarizer 1B, and accordingly, a phase difference filter 3B is used instead of the linear polarizer filter 3A. The differences from the first embodiment are described below.

As shown in FIG. 7, the inspection device 100C is configured with a light source 2, a retardation plate 4, and a retardation filter (polarizing filter) 3B arranged in this order.

As shown in FIG. 8, the film-shaped test object 10B to be inspected includes a circular polarizer 1B, which is the main body of the test object, and a release film 16a laminated to the circular polarizer 1B via an adhesive layer 15. The circular polarizer 1B has protective films 12a and 12b attached to both sides of a polarizing film 11, and further has a retardation film 14 formed on the protective film 12a on the side having the release film 16a via an adhesive layer 13. Another release film 16b is laminated on the side of the circular polarizer 1B that does not have the release film 16a. The circular polarizer 1B is generally used in display devices, such as liquid crystal display devices and organic EL display devices, and is attached to the display device via the adhesive layer 15 after the release film 16a is peeled off when in use.

In this specification, the term "circular polarizing plate" includes circular polarizing plates and elliptically polarizing plates. In addition, "circularly polarized light" includes circularly polarized light and elliptically polarized light.

The retardation film 14 is a film (e.g., a λ/4 plate) that converts the light that has been linearly polarized by the polarizing film 11 into circularly polarized light in the inspection device 100C. There are no particular limitations on the retardation film 14 as long as it is a film that has a phase difference, but it is preferable that it is made of a cured polymerizable liquid crystal compound. The retardation film 14 made of a cured polymerizable liquid crystal compound usually has a thickness of about 0.2 μm to 10 μm.

The retardation film 14 can be produced by applying a composition for forming an alignment film onto a substrate, and then applying a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound onto the composition. The retardation film 14 thus produced is attached together with the substrate to the adhesive layer 13 formed on the protective film 12a, and then the substrate is peeled off, allowing the retardation film 14 to be transferred onto the protective film 12a.

The light source 2 is advantageously a linear light (including light approximating linear light) such as a laser beam. The light emitted by the light source 2 is unpolarized, passes through the polarizing film 11 and becomes polarized in a predetermined direction, and then passes through the retardation film 14 and becomes circularly polarized. In other words, the unpolarized light becomes circularly polarized by passing through the circular polarizing plate 1B.

The phase difference filter 3B is a circular polarizer, and is arranged with the layer having phase difference facing the light source 2. When inspecting the object 10B, the orientation of the phase difference filter 3B is adjusted so that it always forms a crossed Nicol with the circular polarizer 1B in the object 10B.

(Inspection method)
The inspection method using the inspection device 100C is as follows. First, the object to be inspected 10B is inserted between the light source 2 and the retardation plate 4 inside the inspection device 100C. At this time, the object to be inspected 10B, the retardation plate 4, and the retardation filter 3B are arranged so that their surfaces are all parallel, the side of the object to be inspected 10B having the release film 16a faces the opposite side to the light source 2, and the circular polarizer 1B and the retardation filter 3B form a crossed Nicol. When the inspection device 100C is provided with the above-mentioned movable device, the object to be inspected 10B may be inserted in an arbitrary direction, and then the relative positional relationship between the object to be inspected 10B and the retardation filter 3B may be changed by the movable device to form a crossed Nicol.

The light emitted by the light source 2 is incident on the object to be inspected 10B, passes through the object to be inspected 10B, and becomes circularly polarized light. The object to be inspected 10B and the phase difference filter 3B are arranged in a crossed Nicol configuration, so that the circularly polarized light generated by passing through the object to be inspected 10B is blocked by the phase difference filter 3B. At this time, if there is a defect in the circular polarizer 1B in the object to be inspected 10B, the defective part cannot be blocked normally, and the defective part is observed as a bright spot by the eyes of the inspection operator or a CCD camera, etc., in the detection means 5.

However, if the release film 16a has a phase difference, the circularly polarized light generated by passing through the inspection object 10B is affected, and the amount of light transmitted through the phase difference filter 3B increases (for example, exceeding 10% or 15% of the amount of light from the light source), reducing the accuracy of detecting defects such as bright spots present in the circular polarizer 1B. Here, by disposing the phase difference plate 4 between the inspection object 10B and the phase difference filter 3B, the phase difference value of the release films 16a and 16b in the inspection object 10B is canceled, compensating for the birefringence of light caused by the release film 16a.

During inspection, the optical axis of the light emitted by the light source 2 passes through the wide compensation region of the retardation film 4. This allows the visible light transmission spectrum to be matched with the PET resin film over a wider wavelength range, making compensation for the phase difference even more effective. In other words, the thickness of the retardation film 4 changes continuously, and therefore the phase difference value also changes continuously, so that the birefringence of the release film 16a is canceled in some thickness portions among the various thicknesses of the retardation film 4.

As in the first embodiment, during inspection, at least one of the object to be inspected 10B, the retardation plate 4, and the retardation filter 3B may be tilted so that the angles at which they face each other are different, or may be rotated in a direction perpendicular to the optical axis 9 of the light. As in the first embodiment, when a release film 16b is attached to the circular polarizer 1B and the phase difference value of this release film 16b is compensated, the object to be inspected 10A may be placed in the inspection device 100C so that the release film 16b faces the retardation plate 4.

Fourth Embodiment
The inspection device and the inspection method of the fourth embodiment will be described. As shown in Fig. 9, the inspection device 100D of the fourth embodiment is different from the inspection device 100C of the third embodiment in that the place where the inspection object 10B is arranged and the place where the phase difference filter 3B is arranged are reversed. That is, the inspection device 100D is configured such that the light source 2, the phase difference filter 3B, and the phase difference plate 4 are arranged in this order, and the inspection object 10B is arranged at a position farther from the light source 2 than the phase difference plate 4, with the release film 16a facing the light source 2 side during inspection.

When inspecting the object 10B using the inspection device 100D, the presence or absence of defects in the circular polarizer 1B can be easily inspected using the same principle as in the third embodiment. As in the first embodiment, when a release film 16b is attached to the object 10B and the phase difference value of this release film 16b is compensated, the object 10B can be placed in the inspection device 100D so that the release film 16b faces the phase difference plate 4.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the inspection device and inspection method using two retardation plates 4 shown as a modified example of the first embodiment can be applied to any of the second to fourth embodiments.

The present invention will be described in more detail below with reference to examples and comparative examples. Note that the present invention is not limited to the following examples. In the following description, "parts" and "%" representing the content or amount used are by weight unless otherwise specified. In the following description, the symbols "polarizing plate 1" and "retardation plate 1" are symbols used to identify the items used in the experiment, and are different from the symbols on the drawings.

The physical properties were measured by the following methods.
(1) Method for Measuring Film Thickness Measurement was performed using a digital micrometer MH-15M manufactured by Nikon Corporation.
(2) Method for Measuring Retardation Value The retardation value was measured using a retardation measurement device KOBRA-WPR (manufactured by Oji Scientific Instruments).
(3) Measurement of the transmittance of light transmitted through a polarizing filter A spectroradiometer (SR-UL1, manufactured by Topcon Technohouse Corporation) was placed 1 m away from the measurement surface, and the luminance was measured with a measurement angle of 2°. The percentage of light transmitted through the polarizing filter relative to the luminance of the light source was calculated.
(4) Measurement of polarization degree and single transmittance of polarizing plate:
The measurement was carried out using a spectrophotometer equipped with an integrating sphere ("V7100" manufactured by JASCO Corporation, 2-degree field of view; C light source).

[Preparation of specimen]
A 30 μm thick polyvinyl alcohol film (average polymerization degree about 2400, saponification degree 99.9 mol% or more) was uniaxially stretched about 4 times by dry stretching, and then immersed in pure water at 40 ° C. for 40 seconds while maintaining tension, and then immersed in an aqueous solution of iodine / potassium iodide / water with a weight ratio of 0.052 / 5.7 / 100 at 28 ° C. for 30 seconds to perform a dyeing treatment. Then, immersed in an aqueous solution of potassium iodide / boric acid / water with a weight ratio of 11.0 / 6.2 / 100 at 70 ° C. for 120 seconds. Subsequently, after washing with pure water at 8 ° C. for 15 seconds, it was dried at 60 ° C. for 50 seconds and then at 75 ° C. for 20 seconds while holding it under a tension of 300 N, to obtain an absorption type polarizer of 12 μm in which iodine is adsorbed and aligned in the polyvinyl alcohol film.

A polyvinyl alcohol-based adhesive was applied to both sides of the obtained polarizing film so that the thickness of the adhesive layer was 0.1 μm, and a protective film (triacetyl cellulose (TAC) film (product name: KC2UAW, thickness: 25 μm, manufactured by Konica Minolta) was laminated thereon, followed by drying at 80°C for 2 minutes to produce polarizing plate 1. The polarization degree of the obtained polarizing plate 1 was 99.995%, and the single transmittance was 42.5%.

An adhesive layer was formed on one side of this polarizing plate 1, and a PET film with a phase difference value of 2000 nm was attached as a release film to produce a linear polarizing plate to be inspected. This PET film is a film made of PET and is one of the PET-based resin films.

[Preparation of retardation plate]
Two wedge-shaped quartz test plates were used as the retardation plate 1. The retardation value of each of the two wedge-shaped test plates changed continuously from 500 nm to 2000 nm.

[Example 1]
The optical system was configured in the following order: backlight (light source)/test object (placed so that the release film side faces the opposite side to the backlight)/phase difference plate 1/polarizing plate 1 (polarizing filter). The phase difference plate 1 was placed by overlapping the above two quartz test plates so that the directions in which the phase difference value increases were opposite to each other. The phase difference plate 1 was slid so that the phase difference value (Re (550)) was 2550 nm at the optical axis portion. When the luminance in the darkest state was measured in this way, it was 1.4%, and the bright spot defect was detected without any problems in the inspection.

[Comparative Example 1]
The optical system was configured in the following order: backlight (light source)/test object (placed so that the release film side faces the opposite side to the backlight)/phase difference plate 1/polarizing plate 1 (polarizing filter). The phase difference plate 1 was placed by overlapping the above two quartz test plates so that the directions in which the phase difference value increases were opposite to each other. The phase difference plate 1 was slid so that the phase difference value (Re (550)) was 2000 nm at the optical axis portion. When the brightness in the darkest state was measured in this way, it was 11.7%, and no bright spot defects could be detected.

[Example 2]
An optical system was constructed in the same manner as in Example 1, except that the PET film (release film) of the specimen in Example 1 was replaced with a PET film with a phase difference value of 2300 nm. The phase difference value (Re(550)) was set to 2850 nm at the optical axis portion by sliding the phase difference plate 1. When the luminance in the darkest state was measured in this way, it was 2.0%, and the bright point defect could be detected without any problems in the inspection.

[Comparative Example 2]
The optical system was constructed in the same manner as in Example 2, except that the retardation value (Re(550)) was set to 2300 nm at the optical axis portion by sliding the retardation plate 1. When the luminance in the darkest state was measured in this way, it was 12.7%, and no bright spot defects could be detected.

[Example 3]
An optical system was constructed in the same manner as in Example 1, except that the PET film (release film) of the specimen in Example 1 was changed to a PET film with a phase difference value (Re(550)) of 2600 nm. The phase difference value was set to 3150 nm at the optical axis portion by sliding the retardation plate 1. When the luminance in the darkest state was measured in this way, it was 3.7%, and the bright point defect could be detected without any problems in the inspection.

[Comparative Example 3]
An optical system was constructed in the same manner as in Example 3, except that the retardation value (Re(550)) was set to 2600 nm at the optical axis portion by sliding the retardation plate 1. When the luminance in the darkest state was measured in this way, it was 14.4%, and no bright spot defects could be detected.

[Example 4]
An optical system was constructed in the same manner as in Example 1, except that the PET film (release film) of the specimen in Example 1 was changed to a PET film with a phase difference value (Re(550)) of 1700 nm. The phase difference value was set to 2250 nm at the optical axis portion by sliding the retardation plate 1. When the luminance in the darkest state was measured in this way, it was 2.1%, and the bright point defect could be detected without any problems in the inspection.

[Comparative Example 4]
An optical system was constructed in the same manner as in Example 3, except that the retardation value (Re(550)) was set to 1700 nm at the optical axis portion by sliding the retardation plate 1. When the luminance in the darkest state was measured in this way, it was 10.5%, and no bright spot defects could be detected.

[Example 5]
Bright spot defects can also be detected by using an inspection device in which the optical system of Example 1 is changed to an optical system in the order of backlight (light source)/polarizing plate 1 (polarizing filter)/phase difference plate 1/inspection object.

The present invention can be used to inspect the quality of polarizing plates.

1A...linear polarizing plate (polarizing plate), 1B...circular polarizing plate (polarizing plate), 2...light source, 3A...linear polarizing filter (polarizing filter), 3B...phase difference filter (polarizing filter), 4...phase difference plate, 5...detection means, 9...optical axis, 10A, 10B...object to be inspected, 11...polarizing film, 12a, 12b...protective film, 13...adhesive layer, 14...phase difference film, 15...adhesive layer, 16a, 16b...release film, 100A, 100B, 100C, 100D...inspection device.

Claims (13)

1. An inspection method for determining whether or not there is a defect in a film-like inspection object having a polarizing plate and a release film made of a polyethylene terephthalate resin, comprising:
The test object;
a retardation plate including a region in which an in-plane retardation value at a wavelength of 550 nm is 500 to 600 nm larger than the in-plane retardation value at a wavelength of 550 nm of the release film, compensating for birefringence possessed by the release film, and the in-plane retardation value changes continuously;
the polarizing plate and the polarizing filter forming a crossed Nicol are arranged in this order, and the inspection object is arranged such that the release film side faces the retardation plate side;
An inspection method comprising: irradiating light from either the object to be inspected or the polarizing filter side so that the optical axis passes through the region; and observing the polarizing filter or the object to be inspected from the other side to detect bright spot defects. The polarizing plate is a linear polarizing plate,
The inspection method according to claim 1 , wherein the polarizing filter is a linear polarizing filter. the polarizing plate is a circular polarizing plate having a polarizing film and a retardation film,
the release film is laminated on the retardation film side of the circular polarizer,
the polarizing filter is a phase difference filter,
The inspection method according to claim 1 , wherein the retardation filter is arranged such that, of a polarizing plate and a layer having a phase difference included in the retardation filter, the layer having the phase difference faces the retardation plate. The inspection method according to any one of claims 1 to 3, wherein the retardation plate is made up of multiple sheets, and the sheets are arranged so that the directions in which the in-plane retardation value increases are opposite to each other. The inspection method according to any one of claims 1 to 4, wherein the retardation plate is made of an inorganic material or a cycloolefin resin. The inspection method according to any one of claims 1 to 5, wherein at least one of the object to be inspected, the retardation plate, and the polarizing filter is tilted so that they face each other at different angles, or rotated in a direction perpendicular to the optical axis of the light. An inspection device for detecting the presence or absence of defects in a film-like inspection object including a polarizing plate and a release film made of a polyethylene terephthalate resin by irradiating light from the polarizing plate side to the film -like inspection object, the inspection device comprising:
A light source;
a polarizing filter that receives light emitted from the light source and transmitted through the object to be inspected;
a retardation plate that is disposed on a side farther from the light source than a position where the object to be inspected is disposed and closer to the light source than a position where the polarizing filter is disposed, and that transmits light that has passed through the object to be inspected,
the retardation plate includes a region in which the in-plane retardation value at a wavelength of 550 nm is 500 to 600 nm larger than the in-plane retardation value of the release film at a wavelength of 550 nm, compensates for the birefringence of the release film, and the in-plane retardation value changes continuously ;
An inspection device that detects bright point defects by irradiating light from the object to be inspected so that the optical axis passes through the region and observing the polarizing filter from the polarizing filter side . An inspection device for detecting the presence or absence of defects in a film-like inspection object including a polarizing plate and a release film made of a polyethylene terephthalate resin by irradiating light from the release film side to the film-like inspection object, comprising:
A light source;
a polarizing filter that passes light emitted by the light source;
a retardation plate that is disposed on a side closer to the light source than a location where the object to be inspected is disposed and on a side farther from the light source than a location where the polarizing filter is disposed, and that transmits light that has passed through the polarizing filter,
the retardation plate includes a region in which the in-plane retardation value at a wavelength of 550 nm is 500 to 600 nm larger than the in-plane retardation value of the release film at a wavelength of 550 nm, compensates for the birefringence of the release film, and the in-plane retardation value changes continuously ;
An inspection apparatus that causes light to be incident from the polarizing filter side so that the optical axis passes through the region, and observes the object to be inspected from the object to be inspected side to detect bright point defects . The polarizing plate is a linear polarizing plate,
9. The inspection apparatus according to claim 7, wherein the polarizing filter is a linear polarizing filter. the polarizing plate is a circular polarizing plate having a polarizing film and a retardation film,
the release film is laminated on the retardation film side of the circular polarizer,
the polarizing filter is a phase difference filter,
9. The inspection device according to claim 7, wherein the retardation filter is arranged such that a layer having a retardation, out of a polarizing plate and a layer having a retardation, of the retardation filter faces the retardation plate. The inspection device according to any one of claims 7 to 10, wherein the retardation plate is made up of multiple sheets, and is arranged so that the directions in which the in-plane retardation value increases are opposite to each other. The inspection device according to any one of claims 7 to 11, wherein the retardation plate is made of an inorganic material or a cycloolefin resin. The inspection device according to any one of claims 7 to 12, wherein the retardation plate is disposed at a position where the optical axis of the light passes through the region.

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