JP2020160421A - Inspection method and inspection apparatus - Google Patents

Abstract

To provide: an inspection method capable of easily determining the presence or absence of a defect in a circular polarizing plate; and an inspection apparatus.SOLUTION: In an inspection method, a film-like inspection object 10 comprising a circular polarizing plate 1 and a release film 16a made of a polyethylene terephthalate-based resin, a phase difference plate 4, and a phase difference filter 3 composing a cross Nicol with the circular polarizing plate 1 are disposed so as to be arranged in this order, light is made incident from one of the inspection object 10 side and the phase difference filter 3 side, and the presence or absence of a defect in the circular polarizing plate 1 is determined when observed from the other side. In the inspection, a first phase difference plate and a second phase difference plate with an in-plane phase difference different from that of the first phase difference plate are used in this order as the phase difference plate 4.SELECTED DRAWING: Figure 1

Description

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

A polarizing plate used in a liquid crystal display device, an organic EL display device, or the like is generally composed of a polarizing element sandwiched between two protective films. In order to attach the polarizing plate to the display device, an adhesive layer is laminated on one of the protective films, and a release film is further laminated on the adhesive layer. In addition, a release film that protects the surface of the other protective film is often attached. The polarizing plate is distributed and transported in a state where the release films are laminated in this way, and the release film is peeled off when the polarizing plate is attached to the display device in the manufacturing process of the display device.

By the way, in the manufacturing stage of the polarizing plate, if foreign matter is mixed between the polarizing element and the protective film, bubbles remain, or if the protective film has the function of a retardation film, an orientation defect is inherent. (Hereinafter, these foreign substances, bubbles and orientation defects are collectively referred to as "defects"). When a polarizing plate having a defect is attached to a display device, the defective portion may be visually recognized as a bright spot, or the image may appear distorted at the defective portion. In particular, defects that are visually recognized as bright spots are easily visible when the display device displays black.

Therefore, an inspection for detecting defects in the polarizing plate is performed before the polarizing plate is attached to the display device (the polarizing plate with the release film provided). The inspection of this defect 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 the plane direction. Each of these polarization axis directions has a specific relationship. When the polarization axis directions are orthogonal to each other (that is, in the case of the arrangement forming the cross Nicol), the linearly polarized light that has passed through the polarizing filter does not pass through the polarizing plate. However, if a defect is present in the polarizing plate, linearly polarized light is transmitted at the portion, and the presence of the defect can be determined by detecting the light. On the other hand, when the polarizing plate and the polarizing filter are parallel to each other in the polarization axis direction, the linearly polarized light that has passed through the polarizing filter passes through the polarizing plate. However, if a defect is present in the polarizing plate, linearly polarized light is blocked at that portion, and the presence of the defect can be determined by not detecting the light. The inspector visually detects the light transmitted through the polarizing plate, or automatically detects it by the image analysis processing value obtained by combining the CCD camera and the image processing device to inspect the polarizing plate for defects. It can be carried out.

Japanese Unexamined Patent Publication No. 9-229817

However, when the polarizing plate is provided with a release film as described above, the polarization characteristics of the polarizing plate are impaired by the birefringence of the release film, so that defects such as bright spots existing in the polarizing plate in the conventional inspection apparatus are present. Could not be detected accurately.

When the polarizing plate is a circular polarizing plate and the release film is made of polyethylene terephthalate resin (PET resin), a retardation filter (corresponding to the above polarizing filter) suitable for the wavelength dispersion of the PET resin to some extent is used. Use. Here, when the circular polarizing plate and the retardation filter are arranged so as to form a cross Nicol, the defect is visually recognized as a bright spot according to the above principle, but the retardation film of the circular polarizing plate has. In a region where the phase difference value is low, such as an orientation defect or a pinhole, the bright spot defect may be visually recognized as a black spot, and in that case, it is more difficult to determine the detection than to detect it as a bright spot. In particular, this tendency is remarkable when the circularly polarizing plate contains a retardation film made of a cured product of a polymerizable liquid crystal compound.

An object of the present invention is to provide an inspection method and an inspection apparatus capable of easily determining the presence or absence of defects in a circularly polarizing plate.

The present invention is an inspection method for determining the presence or absence of defects in a film-shaped inspected object including a circular polarizing plate and a release film made of PET-based resin, and has an in-plane phase difference between the inspected object and the in-plane phase difference at a wavelength of 550 nm. It comprises a first retardation plate whose value is substantially the same as the in-plane retardation value of the release film at a wavelength of 550 nm and which compensates for the birefringence of the release film, a circular polarizing plate, and a cross Nicol. The retardation filters are arranged so as to be arranged in this order, light is incident from either the inspected object side or the retardation filter side, and the retardation filter or the inspected object is observed from the other side to form a circle. The presence or absence of defects in the polarizing plate is determined, and the first retardation plate may be referred to as an in-plane retardation value at a wavelength of 550 nm (hereinafter, the in-plane retardation value at this wavelength of 550 nm is referred to as “Re (550)”. ) Is 50 to 100 nm larger than Re (550) of the release film and is replaced with a second retardation plate that compensates for the birefringence of the release film, and is on the side to be inspected or the retardation filter side. Provided is an inspection method in which light is incident from either one side and the retardation filter or the object to be inspected is observed from the other side to determine the presence or absence of defects in the circular polarizing plate.

In this inspection method, by inspecting a portion where a black defect is observed in the inspection using the first retardation plate using the second retardation plate, it is possible to observe this as a bright spot defect. Become. According to this, it is possible to easily determine the presence or absence of defects in the circularly polarizing plate.

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

In the inspection method of the present invention, at least one of the object to be inspected, the first retardation plate, the second retardation plate, and the retardation filter may be tilted so as to face each other at different angles, or , May be rotated in a direction perpendicular to the optical axis of light. By tilting these, the phase difference of the release film or the retardation plate can be finely adjusted, so that a wider range of inspection becomes possible. Further, by rotating these, the release film and the retardation plate can be easily aligned with each other.

The first retardation plate and the second retardation plate may be configured by being arranged in the same member as each other.

The present invention is an inspection apparatus for determining the presence or absence of defects in a circularly polarizing plate by injecting light onto a film-shaped object to be inspected including a circularly polarizing plate and a release film made of a PET-based resin. A retardation filter that emits light emitted from a light source and converted into circularly polarized light by an object to be inspected, and a side farther from the light source than the place where the object to be inspected is placed and a place where the retardation filter is placed. The first retardation plate is provided with a retardation plate which is arranged on the side close to the light source and allows circularly polarized light to pass through, and the Re (550) of the retardation plate is substantially the same as the Re (550) of the release film. And a second retardation plate in which Re (550) is 50 to 100 nm larger than Re (550) of the release film, and the first retardation plate and the second retardation plate are duplicates of the release film. Provided is an inspection device that compensates for polarization.

Further, the present invention is an inspection device for determining the presence or absence of defects in a circularly polarizing plate by injecting circularly polarized light into a film-shaped object to be inspected including a circularly polarizing plate and a release film made of a PET-based resin. A light source, a retardation filter that converts the light emitted by the light source into circularly polarized light, and a side closer to the light source than the place where the object to be inspected is placed, and a side farther from the light source than the place where the retardation filter is placed. The retardation plate comprises a retardation plate which is arranged and allows circularly polarized light to pass through, and the retardation plate includes a first retardation plate in which Re (550) is substantially the same as Re (550) of the release film, and Re (550). Includes a second retardation plate that is 50 to 100 nm larger than the Re (550) of the release film, and the first retardation plate and the second retardation plate compensate for the double polarization of the release film. Provide an inspection device.

The retardation plate in these inspection devices may be configured by arranging the first retardation plate and the second retardation plate in the same member.

According to the present invention, it is possible to provide an inspection method and an inspection apparatus capable of easily determining the presence or absence of defects in a circularly polarizing plate.

It is a figure which shows the inspection apparatus of 1st Embodiment. It is sectional drawing of the object to be inspected. It is a figure which shows an example of a retardation plate. It is a figure which shows another example of the retardation plate. It is a figure which shows the inspection apparatus of the 2nd Embodiment.

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

<First Embodiment>
The inspection device and the inspection method of the first embodiment will be described.

(Inspection device and object to be inspected)
The inspection device of the present embodiment inspects the presence or absence of surface defects of the circularly polarizing plate. As shown in FIG. 1, in the inspection device 100A, the light source 2, the retardation plate 4, and the retardation filter 3 are arranged in this order.

As shown in FIG. 2, the film-shaped object 10 to be inspected is laminated on the circularly polarizing plate 1 which is the main body of the inspection target and the circularly polarizing plate 1 via the adhesive layer 15. It also includes a release film 16a. In the circular polarizing plate 1, protective films 12a and 12b are bonded to both sides of the polarizing film 11, and a retardation film 14 is further formed on the protective film 12a on the side provided with the release film 16a via an adhesive layer 13. It is formed. Then, another release film 16b is laminated on the surface of the circularly polarizing plate 1 on the side not provided with the release film 16a. The circularly polarizing plate 1 is generally used in a display device, for example, a liquid crystal display device or an organic EL display device. At the time of use, the release film 16a is peeled off and attached to the display device via the adhesive layer 15. ..

In the present specification, the term "circularly polarized light" includes a circularly polarizing plate and an elliptical polarizing plate. Further, "circularly polarized light" includes circularly polarized light and elliptically polarized light.

The 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 in which iodine and a dichroic dye are adsorbed and oriented, and a film in which a polymerizable liquid crystal compound is oriented and polymerized, and a dichroic dye is adsorbed and oriented. Can be mentioned.

The protective films 12a and 12b are for protecting the polarizing film 11. As the protective films 12a and 12b, those widely used in the technical field of polarizing plates are used for the purpose of obtaining a polarizing plate having an appropriate mechanical strength. Typically, cellulose ester films such as triacetyl cellulose (TAC) films; cyclic olefin films; polyester films such as polyethylene terephthalate (PET) films: (meth) acrylic films such as polymethyl methacrylate (PMMA) films. It is a film or the like. Further, an additive widely used in the technical field of the polarizing plate may be contained in the protective film.

Since the protective films 12a and 12b are attached to the display device together with the polarizing film 11 as a component of the circularly polarizing plate 1, strict control of the retardation value and the like are required. As the protective films 12a and 12b, those having an extremely small retardation value are typically preferably used. The protective films 12a and 12b are attached to the polarizing film 11 via an adhesive.

In the inspection device 100A, the retardation film 14 is a film that converts light linearly polarized by the polarizing film 11 into circularly polarized light. The retardation film 14 is not particularly limited as long as it is a film having a retardation, but it is preferably 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 usually has a thin thickness of about 0.2 μm to 10 μm, and when foreign matter or the like is contained, the retardation value tends to decrease at that portion. In such a portion, as will be described later, when the birefringence of the release film 16a is compensated by the retardation plate 4, it is observed as a black spot even though it should be observed as a bright spot defect. May occur.

The polymerizable liquid crystal compounds capable of forming the retardation film 14 are described in, for example, JP-A-2009-173893, JP-A-2010-31223, WO2012 / 147904, WO2014 / 10325 and WO2017-43438. The disclosed ones can be mentioned. The polymerizable liquid crystal compounds described in these publications can form a retardation film having so-called inverse wavelength dispersibility, which enables 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) on an appropriate substrate and photopolymerizing it, an extremely thin retardation film can be formed as described above. A circularly polarizing plate having such a retardation film can form a circularly polarizing plate having an extremely thin thickness. Such a circularly polarizing plate having an extremely thin thickness is advantageous as a circularly polarizing plate for flexible display materials, which has been attracting attention in recent years.

Examples of the base material on 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 orienting the polymerizable liquid crystal compound. The alignment film may be either photo-aligned by polarization irradiation or mechanically oriented by rubbing treatment. The alignment film is also described in the above publication.

However, when foreign matter or the like is present on the base material on which the polymerizable liquid crystal compound solution is applied, or the base material itself is scratched, the coating film itself obtained by applying the polymerizable liquid crystal compound solution is coated. Defects may occur. Further, when the alignment film is rubbed, debris of the rubbing cloth remains on the alignment film, which may cause a defect in the coating film of the polymerizable liquid crystal compound solution (composition for forming a liquid crystal cured film). As described above, the retardation film formed from the polymerizable liquid crystal compound can form a retardation film having an extremely thin thickness, but there is a factor that causes defects. Then, as described above, the defect of the retardation film may cause a defect observed as a black spot. The inspection device and inspection method of the present embodiment are particularly useful in detecting the presence or absence of defects in an object to be inspected having a circularly polarizing plate having a retardation film having such defects and a release film.

The retardation film 14 can be produced by applying a composition for forming an alignment film on a base material, and further applying a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound on the composition. The retardation film 14 thus produced is attached to the pressure-sensitive adhesive layer 13 formed on the protective film 12a together with the base material, 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 the display device, and the peeled release film 16a is usually discarded. Therefore, unlike the protective films 12a and 12b, strict control of the phase difference value is not required. Therefore, when a commercially available film is used as the release film 16a, if the retardation value is not compensated, a malfunction may occur in the defect inspection using the retardation filter 3. That is, in the defect inspection of the circularly polarizing plate 1 to which the release films 16a and 16b whose retardation values are not strictly controlled are adhered, the phase difference of the release film 16a lowers the inspection accuracy of the inspection device 100A. It can be a cause of causing.

As described in the background technique, in the circularly polarizing plate 1, another release film 16b is often provided on the opposite surface of the release film 16a. In the circularly polarizing plate 1 shown in FIG. 2, a release film 16b is bonded to the protective film 12b side. This release film 16b is also usually peeled off from the circularly polarizing plate 1 when it is attached to a display device, and unlike the protective films 12a and 12b, strict control of the retardation 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 (that is, Re (550) of the release film 16b is obtained in advance, and then the inspection is performed. The inspection method of the present embodiment may be carried out by using the inspection device 100A with the direction of the object 10 reversed (the release film 16b is installed so as to face the retardation plate 4). , The protective film 12b and the release film 16b may be bonded to each other via an appropriate adhesive layer or adhesive layer (in FIG. 2, the adhesive layer or adhesive layer is not shown). Absent).

In the present embodiment, the release film 16a is made of a PET-based resin. When the inspection method of the present embodiment is carried out by compensating for the phase difference value of the release film 16b, the release film 16b is also made of PET resin. A film made of a PET-based resin (PET-based resin film) has an advantage that it is versatile as a release film and is inexpensive. On the other hand, as described above, the inexpensive PET-based resin film does not require strict control of the phase difference value. Therefore, for example, the phase difference value may vary from product lot to product lot. Further, even if the same PET resin film is used, there may be variations in the phase difference value in the plane. Even with a circularly polarizing plate in which such an inexpensive PET resin-based film is bonded as a release film, the presence or absence of defects can be accurately detected by the inspection method of the present embodiment.

Here, a method of obtaining Re (550) of the release film 16a will be shown. As described above, these release films are films made of PET-based resin, and such films are easily available on the market. For example, a piece having a size of about 40 mm × 40 mm is separated from this film (from a long film, separated by using an appropriate cutting tool, etc.). Re (550) of this piece is measured three times, and the average value of Re (550) is obtained. One piece of Re (550) can be measured at a measurement temperature of room temperature (about 25 ° C.) using a phase difference measuring device KOBRA-WPR (manufactured by Oji Measuring Instruments Co., Ltd.). The same test may be performed when Re (550) of the release film 16b is obtained.

As the light source 2, various commercially available products can be used, but it is advantageous that the light source 2 is, for example, linear light such as laser light (including one that approximates linear light). The light emitted by the light source 2 is unpolarized, passes through the polarizing film 11 to be polarized in a predetermined direction, and further passes through the retardation film 14 to be circularly polarized. That is, when unpolarized light passes through the circular polarizing plate 1, it becomes circularly polarized light.

The retardation filter 3 is a circular polarizing plate, and a layer having a retardation is arranged toward the light source 2. When the inspected object 10 is inspected, the orientation of the retardation filter 3 is adjusted so as to always form the circular polarizing plate 1 and the cross Nicol in the inspected object 10. Then, as the polarizing plate and the retardation plate (which form the layer having the retardation) constituting the retardation filter 3, so-called defect-free ones are adopted.

The retardation plate 4 compensates for the birefringence of light due to the release film 16a included in the object 10 to be inspected. The material constituting the retardation plate 4 is not particularly limited as long as it compensates for the birefringence of light due to the release film 16a made of PET-based resin. A commercially available retardation plate having a diameter of 100 to 200 nm can be prepared, and a plurality of these retardation plates can be laminated to form a retardation plate 4 so as to obtain a desired retardation value. Since Re (550) is usually additive, a desired Re (550) retardation plate 4 can be obtained from the laminated retardation plates Re (550). Since the release film 16a made of PET resin usually has a large variation in the in-plane retardation value and the slow axis, a plurality of types of retardation plates are prepared so that a plurality of retardation values can be selected at the time of inspection. It is preferable to keep it. In the present embodiment, the first retardation plate having substantially the same retardation value as the Re (550) of the release film 16a and the Re (550) having a phase difference value 50 to 100 nm larger than the Re (550) of the release film 16a. At least two types of retardation plates with the two retardation plates are used. The retardation value substantially the same as Re (550) of the release film 16a means that the absolute value of the difference between Re (550) of the release film 16a and Re (550) of the retardation plate is 20 nm or less. To say.

Further, considering the variation in the phase difference value of the release film, it is preferable that the retardation plate exhibits a phase difference in the range of about ± 300 nm with respect to Re (550) of the release film. Within the range of this phase difference, it is preferable to further change the release film in the in-plane direction in increments of 50 nm to 100 nm. It is preferable to prepare various retardation plates showing these retardation. That is, in addition to the first retardation plate and the second retardation plate, it is preferable to prepare a third retardation plate and a fourth retardation plate having different retardations.

The outline of a typical example of the retardation plate 4 is shown in FIGS. 3 and 4. As shown in FIGS. 3 and 4, regions having different retardation values may be continuously arranged in one retardation plate member. That is, at least the first retardation plate and the second retardation plate may be configured in the same member.

As shown in FIG. 3, the retardation plate 4A may be formed by connecting regions having different in-plane retardation values in one direction. That is, the region located at the end (first region a ₁ ; corresponding to the first retardation plate) is a region where Re (550) is, for example, 1720 nm, and a region adjacent to the region (second region). region _{a 2;} corresponding to the second retardation plate) is a region Re (550) is 1790Nm, further areas in contact with the next (third region _{a 3;} the third retardation plate Correspondingly) is a region where Re (550) is 1860 nm. In the retardation plate 4A, the number of the regions is arbitrary, and FIG. 3 shows up to the _nth region an. In each region, the phase difference value in the thickness direction can be adjusted by the width of the visual field region to be observed in one region.

Further, as shown in FIG. 4, the retardation plate 4B may have a configuration in which regions having different Re (550) are arranged in an annular shape. That is, the disk-shaped retardation plate 4B is divided into a plurality of regions having different retardation values with a virtual line extending radially from the center as a boundary, and a certain region (first region b ₁ ; first position). corresponding to phase difference plate) is, Re (550) is a region that is 1720nm example, areas in contact with the next (second region _{b 2;} corresponding to the second retardation plate) is, Re (550) There is an area which is 1790Nm, regions, further contact with its neighbors (third region _{b 3;} corresponding to the third phase difference plate) is, Re (550) is a region that is 1860Nm. In the phase difference plate 4B, the number of the area is optional, shows a disc-shaped phase plate present to the region b ₆ of 6 in FIG.

In order to observe the light that has passed through the object 10 to be inspected, the retardation plate 4, and the retardation filter 3, the position on the optical axis 9 and on both sides of the retardation filter 3 opposite to the side where the light source 2 is located. The detection means 5 including a CCD camera or the like may be arranged therein. For example, it can be automatically detected by image processing analysis in which a CCD camera and an image processing device are combined, thereby inspecting the object to be inspected. Alternatively, the detecting means 5 may be a human being visually observing the phase difference filter 3 instead of the member.

Further, the inspection device 100A tilts at least one of the object to be inspected 10, the retardation plate 4, and the retardation filter 3 so that they face each other at different angles, or rotates in a direction perpendicular to the optical axis 9 of light. It is preferable to have a movable device (not shown) that enables the operation. By tilting these, the phase difference of the release film 16a made of PET resin and the retardation plate 4 can be finely adjusted, so that a wider range of inspections can be performed. Further, by rotating these, the release film 16a made of PET-based resin and the retardation plate 4 can be easily aligned with each other.

(Inspection method)
The inspection method using the inspection device 100A is as follows. First, the object 10 to be inspected is inserted between the light source 2 and the retardation plate 4 inside the inspection device 100A. At this time, the surface of the object 10 to be inspected, the retardation plate 4, and the retardation filter 3 are all parallel to each other, and the side of the object 10 to be provided with the release film 16a is opposite to the light source 2. The circularly polarizing plate 1 and the retardation filter 3 are arranged so as to form a cross Nicol while facing the side. When the inspection device 100A is provided with the movable device, after inserting the inspected object 10 in an arbitrary direction, the relative positional relationship between the inspected object 10 and the phase difference filter 3 is changed by the movable device. It may be cross Nicol.

The light emitted by the light source 2 enters the object to be inspected 10 and passes through the object to be inspected 10 to become circularly polarized light. By arranging the cross Nicol between the object 10 to be inspected and the retardation filter 3, the circular polarization generated by passing through the object 10 to be inspected is blocked by the retardation filter 3. At this time, if a defect exists in the circularly polarizing plate 1 in the object to be inspected 10, the defective portion cannot be normally blocked, and the defective portion is a bright spot in the eyes of the inspection worker in the detection means 5, the CCD camera, or the like. Observed as.

However, when the release film 16a has a phase difference, the circularly polarized light generated by passing through the object 10 to be inspected is affected, and the amount of light transmitted through the retardation filter 3 increases (for example, 10% of the light amount of the light source or It will exceed 15%), and the detection accuracy of defects such as bright spots existing in the circular polarizing plate 1 will decrease. Here, by arranging the retardation plate 4 between the object 10 to be inspected and the retardation filter 3, the retardation value of the release film 16a in the object 10 to be inspected is canceled, and the light from the release film 16a is canceled. Compensates for birefringence.

Further, the retardation plate 4 is designed so that the retardation value and the wavelength dispersion characteristics of the release film 16a match as much as possible in order to effectively compensate for the birefringence of light due to the release film 16a. Due to the in-plane variation of the phase difference value of 16a, it is difficult to sufficiently block light in the entire inspection field for inspection. In such a case, the optical compensation is matched at the portion of the circular polarizing plate 1 where the retardation value of the retardation film 14 is lowered, and defects that should be originally observed as bright spots are observed as black spots. It can happen. Normally, sunspot defects have a smaller effect on visibility than bright spot defects, so even if the defect size is larger than the bright spot defects, it is often acceptable. Therefore, it is judged that there is no problem as a result. It may end up. However, if the black spot defect should originally be observed as a bright spot defect caused by a portion where the retardation value of the retardation film 14 is lowered, it has a great influence on visibility and becomes a problem.

Therefore, in the present embodiment, a second retardation plate is used for the defect portion visually recognized as a black spot (for example, the second region of the retardation plates 4A and 4B illustrated in FIGS. 3 and 4). a _{2, b 2)} is used. For example, in the initial inspection performed using the first region a ₁ (first retardation plate) of the retardation plate 4A, the second region a ₂ (second) with respect to the defect portion visually recognized as a black spot. The second inspection is performed using the retardation plate). In this way, when the defect is observed as a bright spot defect by inspecting it a plurality of times using retardation plates having different in-plane retardation values, it is easy to correctly recognize the defect. Incidentally, when it is visually recognized as black spots in the inspection using the second region a _{2 (second} retardation plate), the inspection is continuously performed to the third region a _{3 (third} retardation plate).

During the inspection, at least one of the object 10 to be inspected, the retardation plate 4 and the retardation filter 3 may be tilted so as to face each other at different angles, or may be rotated in a direction perpendicular to the optical axis 9 of light. May be good. By tilting, the phase difference between the release film 16a and the retardation plate 4 can be finely adjusted, so that a wider range of inspections can be performed. Further, by rotating these, the release film 16a made of PET-based resin and the retardation plate 4 can be easily aligned with each other. These operations can be performed particularly easily when the inspection device 100A includes a movable device.

<Second embodiment>
The inspection device and the inspection method of the second embodiment will be described. As shown in FIG. 5, the inspection device 100B of the second embodiment differs from the inspection device 100B of the first embodiment in that the place where the object to be inspected 10 is placed and the place where the phase difference filter 3 is placed. Is the opposite. That is, in the inspection device 100B, the light source 2, the retardation filter 3, and the retardation plate 4 are arranged in this order, and the inspected object 10 has the release film 16a facing the light source 2 side at the time of inspection. Therefore, it is arranged at a position farther from the light source than the retardation plate 4. In the same manner as in the first embodiment, when the release film 16b is attached to the circularly polarizing plate 1 to compensate for the retardation value of the release film 16b, the release film 16b is used as a retardation plate in the inspection device 100B. The object to be inspected 10 may be installed so as to face 4.

In the inspection of the object to be inspected 10 using the inspection device 100B, the presence or absence of defects in the circularly polarizing plate 1 can be easily inspected by the same principle as in the first embodiment.

Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

Hereinafter, the content of the present invention will be described in more detail with reference to experimental examples. The present invention is not limited to the following experimental examples. In the following description, "part" and "%" indicating the content or the amount used are based on weight unless otherwise specified.

Each physical property was measured by the following method.
(1) Method for measuring film thickness The film thickness was measured using a digital micrometer MH-15M manufactured by Nikon Corporation.
(2) Method for measuring the phase difference value The measurement was performed using the phase difference measuring device KOBRA-WPR (manufactured by Oji Measuring Instruments Co., Ltd.). In the following notation, similarly to the above-mentioned Re (550), the in-plane phase difference with respect to light having a wavelength of 450 nm and a wavelength of 650 nm is referred to as “Re (450)” and “Re (650)”, respectively.
(3) Measurement of transmittance of light transmitted through a phase difference filter A spectroradiometer (SR-UL1 manufactured by Topcon Techno House Co., Ltd.) is installed 1 m away from the measurement surface and has a measurement angle of 2 °. The brightness was measured. It was calculated what percentage of the light was passing through the phase difference filter with respect to the brightness of the light source.
(4) Measurement of polarization degree and simple substance transmittance of circular polarizing plate:
The measurement was performed using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation; 2 degree field of view; C light source].

[Preparation of linear polarizing plate]
A 30 μm-thick polyvinyl alcohol film (average degree of polymerization of about 2400, saponification degree of 99.9 mol% or more) was uniaxially stretched about 4 times by dry stretching, and pure water at 40 ° C. was further maintained in a tense state. Was immersed in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.052 / 5.7 / 100 for 40 seconds, and then immersed in an aqueous solution at 28 ° C. for 30 seconds for dyeing. Then, it was immersed in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 11.0 / 6.2 / 100 at 70 ° C. for 120 seconds. Subsequently, after washing with pure water at 8 ° C. for 15 seconds, while holding at a tension of 300 N, the iodine was adsorbed and oriented on the polyvinyl alcohol film by drying at 60 ° C. for 50 seconds and then at 75 ° C. for 20 seconds. An absorption type polarizer having a thickness of 12 μm was obtained.

A protective film (triacetyl cellulose (TAC) film (trade name: KC2UAW, thickness) is applied to both sides of the obtained polarizing film while applying a polyvinyl alcohol-based adhesive so that the thickness of the adhesive layer is 0.1 μm. : 25 μm, manufactured by Konica Minolta Co., Ltd.) and then dried at 80 ° C. for 2 minutes to prepare a linear polarizing plate. The obtained linear polarizing plate had a degree of polarization of 99.995% and a single transmission rate. It was 42.5%.

[Preparation of retardation film made of cured product of multi-layer liquid crystal compound]
Five parts of a photo-oriented material having the following chemical structure (weight average molecular weight: 30,000) and 95 parts of cyclopentanone (solvent) are mixed as components, and the obtained mixture is stirred at 80 ° C. for 1 hour for orientation. A film-forming composition was obtained.

（重合性液晶化合物Ｂ）

1.0 part of a leveling agent (F-556; manufactured by DIC) and polymerization of a mixture of the polymerizable liquid crystal compound A and the polymerizable liquid crystal compound B shown below at a mass ratio of 90:10. Six parts of 2-dimethylamino-2-benzyl-1- (4-morpholinophenyl) butane-1-one (“Irgacure 369 (Irg369)”, manufactured by BASF Japan Ltd.) as an initiator was added. Further, N-methyl-2-pyrrolidone (NMP) was added so that the solid content concentration was 13%, and the mixture was stirred at 80 ° C. for 1 hour to obtain a composition for forming a liquid crystal cured film. Here, the polymerizable liquid crystal compound A was produced by the method described in JP-A-2010-31223. Further, the polymerizable liquid crystal compound B was produced according to the method described in JP-A-2009-173893. The molecular structure of each is shown below.
(Polymerizable liquid crystal compound A)

(Polymerizable liquid crystal compound B)

[Manufacture of a laminate consisting of a base material, an alignment film, and a layer obtained by curing a polymerizable liquid crystal compound]
After corona treatment is performed on a cycloolefin film having a thickness of 50 μm as a base material [trade name “ZF-14-50” manufactured by Nippon Zeon Co., Ltd.], the above composition for forming an alignment film is applied with a bar coater. It is applied, dried at 80 ° C. for 1 minute, and using a polarized UV irradiation device [trade name "SPOT CURE SP-9" of Ushio Denki Co., Ltd.], the integrated light intensity at a wavelength of 313 nm: 100 mJ / cm2 and an axial angle of 45 °. Polarized UV exposure was carried out at. Subsequently, the above composition for forming a liquid crystal cured film is applied to the alignment film using a bar coater, dried at 120 ° C. for 1 minute, and then a high-pressure mercury lamp [Ushio Denki Co., Ltd. trade name: "Unicure". By irradiating with ultraviolet rays (integrated light amount at a wavelength of 365 nm under a nitrogen atmosphere: 500 mJ / cm2) using VB-15201BY-A], a layer in which the polymerizable liquid crystal compound was cured was formed. As a result, a laminate composed of a base material, an alignment film, and a layer in which the polymerizable liquid crystal compound was cured was obtained.

The in-plane retardation value Re (λ) of the layer on which the polymerizable liquid crystal compound produced by the above method was cured was bonded to glass via an adhesive, and then the cycloolefin-based film as a base material was peeled off. It was measured later. The measurement results of the phase difference value Re (λ) at each wavelength are Re (450) = 121 nm, Re (550) = 142 nm, Re (650) = 146 nm, Re (450) / Re (550) = 0.85, Re (650) / Re (550) = 1.03.

[Preparation of circularly polarizing plate and object to be inspected]
An adhesive layer was formed on one side of the above-mentioned linear polarizing plate, and a layer made of a cured product of a polymerizable liquid crystal compound, that is, a retardation film was bonded. At this time, they were bonded so that the angle formed by the slow axis of the retardation film and the absorption axis of the linear polarizing plate was 45 ° (45 ° clockwise when viewed from the linear polarizing plate side). Then, an adhesive image was further formed on the retardation film, and a PET film having a retardation value of 2000 nm was bonded as a release film to prepare an object to be inspected.

[Making a phase difference filter]
The above linear polarizing plate is prepared separately, an adhesive layer is formed on one side thereof, and the angle between the slow axis of the retardation film and the absorption axis of the linear polarizing plate is −45 ° (viewed from the linear polarizing plate side). A retarding film was attached so that the temperature would be 45 ° counterclockwise) to prepare a retardation filter.

[Making a retardation plate]
As the retardation plate, 4Z-Y004 (manufactured by Toray Industries, Inc., Re (550) of 150 nm to 180 nm) was used. The produced retardation value was set in 70 nm increments from 1720 nm to 2350 nm. Table 1 shows a list of the produced retardation plates. In the view of this table, the leftmost column shows the phase difference value (in-plane phase difference value) in each phase difference region. For example, it is shown that the region having a retardation value of 1720 nm was prepared by laminating 10 retardation plates having a retardation value of 155 nm and one retardation plate having a retardation value of 170 nm (155 nm × 10 + 170 nm = 1720 nm). .. The phase difference value in the thickness direction of each region was about 4.8 times the in-plane retardation value.

[Inspection of the object to be inspected]
The inspection device manufactured above was used to inspect the object to be inspected for defects. The optical system was configured in the order of backlight (light source) / object to be inspected (arranged so that the release film side faces the opposite side of the light source) / retardation plate / retardation filter. For the retardation plate, a retardation region having in-plane retardation values of 2000 nm and 2070 nm was used. When the brightness in the darkest state was measured in this way, the bright spot defect could be detected without any problem, but the defect observed as a black spot whose brightness was about 11.5% of the incident light amount was also confirmed.

Next, when the in-plane retardation value of the retardation plate was changed to 2070 nm and the black spot portion was inspected, the defect observed as the above black spot could be correctly detected as a bright spot defect.

In this example, as shown in FIG. 1, an experimental example of an inspection device 100A assembled so that the light from the backlight is transmitted in the order of the object to be inspected 10, the retardation plate 4, and the retardation filter 3 is shown. However, as shown in FIG. 5, the inspection device 100B assembled so that the light from the backlight is transmitted in the order of the retardation filter 3, the retardation plate 4, and the object to be inspected 10 also has black spots. Observed defects can be correctly detected as bright spot defects.

The present invention can be used for quality inspection of circularly polarizing plates.

1 ... circular polarizing plate, 2 ... light source, 3 ... retardation filter, 4 (4A, 4B) ... retardation plate, 5 ... detection means, 9 ... optical axis, 10 ... inspected object, 11 ... polarizing film, 12a, 12b ... protective film, 13 ... adhesive layer, 14 ... retardation film, 15 ... adhesive layer, 16a, 16b ... release film, 100A, 100B ... inspection device, a ₁ , b ₁ ... first region (first region) retardation plate), _{a 2,} b _{2 ...} second region (second retardation plate), a n _... n-th area (retardation film of the n).

Claims (7)

This is an inspection method for determining the presence or absence of defects in a film-shaped object to be inspected, which includes a circularly polarizing plate and a release film made of polyethylene terephthalate resin.
With the object to be inspected
A first retardation plate having an in-plane retardation value at a wavelength of 550 nm substantially the same as the in-plane retardation value of the release film at a wavelength of 550 nm and compensating for birefringence of the release film.
The circularly polarizing plate and the phase difference filter constituting the cross Nicol are arranged in this order.
Light is incident from either the inspected object side or the retardation filter side, and the retardation filter or the inspected object is observed from the other side to determine the presence or absence of defects in the circular polarizing plate. ,
The first retardation plate has an in-plane retardation value at a wavelength of 550 nm larger than the in-plane retardation value at a wavelength of 550 nm of the release film by 50 to 100 nm, and compensates for the birefringence of the release film. Replaced with the second retardation plate,
An inspection method in which light is incident from either one of the inspected object side or the retardation filter side, and the retardation filter or the inspected object is observed from the other side. The inspection method according to claim 1, wherein the circularly polarizing plate has a retardation film made of a cured product of a polymerizable liquid crystal compound. At least one of the object to be inspected, the first retardation plate, the second retardation plate, and the retardation filter is tilted so as to face each other at different angles, or the optical axis of the light. The inspection method according to claim 1 or 2, wherein the inspection method is rotated in a direction perpendicular to the optic axis. The inspection method according to any one of claims 1 to 3, wherein the first retardation plate and the second retardation plate are arranged and configured in the same member. An inspection device for determining the presence or absence of defects in the circularly polarizing plate by injecting light onto a film-shaped object to be inspected including a circularly polarizing plate and a release film made of a polyethylene terephthalate resin.
Light source and
A phase difference filter that incidents light emitted from the light source and converted into circularly polarized light by the object to be inspected.
A retardation plate arranged on the side farther from the light source than the place where the object to be inspected is placed and on the side closer to the light source than the place where the retardation filter is placed and to pass the circularly polarized light. With
The retardation plate has a first retardation plate in which the in-plane retardation value at a wavelength of 550 nm is substantially the same as the in-plane retardation value at a wavelength of 550 nm of the release film, and the in-plane retardation value at a wavelength of 550 nm. The first retardation plate and the second retardation plate include a second retardation plate that is 50 to 100 nm larger than the in-plane retardation value at a wavelength of 550 nm of the release film. An inspection device that compensates for refraction. An inspection device for determining the presence or absence of defects in the circularly polarizing plate by injecting circularly polarized light into a film-shaped object to be inspected including a circularly polarizing plate and a release film made of a polyethylene terephthalate resin.
Light source and
A phase difference filter that converts the light emitted by the light source into the circularly polarized light,
A retardation plate arranged on the side closer to the light source than the place where the object to be inspected is placed and on the side farther from the light source than the place where the retardation filter is placed and to pass the circularly polarized light. With
The retardation plate has a first retardation plate in which the in-plane retardation value at a wavelength of 550 nm is substantially the same as the in-plane retardation value at a wavelength of 550 nm of the release film, and the in-plane retardation value at a wavelength of 550 nm. The first retardation plate and the second retardation plate include a second retardation plate that is 50 to 100 nm larger than the in-plane retardation value at a wavelength of 550 nm of the release film. An inspection device that compensates for refraction. The inspection device according to claim 5 or 6, wherein the retardation plate is configured by arranging the first retardation plate and the second retardation plate in the same member.

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