JP2020160422A - 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 10A comprising a polarizing plate 1A and a release film 16a made of a polyethylene terephthalate-based resin, a phase difference plate 4 including a region with an in-plane phase difference value at a wavelength of 550 nm being larger than the in-plane phase difference value of the release film 16a at a wavelength of 550 nm by 500 to 600 nm, and compensating for the birefringence that the release film 16a has, and a polarizing filter 3A composing a cross Nicol with the polarizing plate 1A are disposed so as to be arranged in this order, light is made incident from one of the inspection object 10A side and the polarizing filter 3A side so that an optical axis 9 passes through the region, and the presence/absence of a defect in the polarizing plate 1A is determined when observing the polarizing filter 3A or the inspection object 10A from the other side.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.

That is, when the polarizing plate and the polarizing 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 bright spot defect is a black spot depending on the defect condition of the polarizing plate. In that case, it was more difficult to determine the detection than to detect it as a bright spot. This situation is the same regardless of whether the polarizing plate is a linearly polarized plate or a circular polarizing plate.

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 polarizing plate.

The present invention is an inspection method for determining the presence or absence of defects in film-shaped inspected grains including a polarizing plate and a release film made of a polyethylene terephthalate resin (PET resin), wherein the object to be inspected and a wavelength of 550 nm are present. In-plane retardation value (hereinafter, the in-plane retardation value at this wavelength of 550 nm is referred to as “Re (550)”) includes a region 500 to 600 nm larger than Re (550) of the release film, and the release film The retardation plate for compensating for the birefringence and the polarizing filter constituting the polarizing plate and the cross Nicol are arranged in this order, and from either the inspection object side or the polarizing filter side, Provided is an inspection method in which light is incident so that the optical axis passes through a region, and a polarizing filter or an object to be inspected 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 with the release film in a wider wavelength range, so that the entire observation field of view can be further darkened. At this time, the defective portion of the polarizing plate observed as a bright spot becomes more prominent in the observation field of view. Therefore, according to the present invention, the presence or absence of defects in the polarizing plate can be easily determined.

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. Further, in the present invention, the polarizing plate may be a circular polarizing plate, and the polarizing filter may be a retardation filter. In either case, the present invention can be applied.

The retardation plate may be one in which the in-plane retardation value is continuously changed. In this case, since one retardation plate has various in-plane retardation values, the one retardation plate can compensate for the retardation of various release films.

In the present invention, the retardation plate may be composed of a plurality of plates, and may be arranged so that the in-plane retardation values increase in opposite directions. In the plurality of retardation plates arranged in this way, the change in the retardation value according to the location in the retardation plate is gradual as compared with the case where there is only one retardation plate. Therefore, when a plurality of retardation plates are used, the region where the retardation of the release film can be compensated becomes wider than when the retardation plate is one.

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 as to face each other at different angles, or may be rotated in a direction perpendicular to the optical axis of light. Good. 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.

Further, the present invention is an inspection device for determining the presence or absence of defects in a polarizing plate by injecting light onto a film-shaped object to be inspected including a polarizing plate and a release film made of a PET-based resin. A polarizing filter that emits light emitted from the light source and passes through the object to be inspected, and a polarizing filter that is located farther from the light source than the place where the object to be inspected is placed and closer to the light source than the place where the polarizing filter is placed. It is provided with a retardation plate for passing light that has passed through the object to be inspected, and the retardation plate includes a region where Re (550) is 500 to 600 nm larger than Re (550) of the release film, and is peeled off. Provided is an inspection device that compensates for the birefringence of a film.

Further, the present invention is an inspection device for determining the presence or absence of defects in a polarizing plate by injecting light onto a film-shaped object to be inspected including a polarizing plate and a release film made of a PET-based resin. A polarizing filter that allows light emitted by the light source to pass through, and a polarizing filter that is placed closer to the light source than the place where the object to be inspected is placed and farther from the light source than the place where the polarizing filter is placed, and passed through the polarizing filter. A retardation plate for passing light is provided, and the retardation plate includes a region where the wave Re (550) is 500 to 600 nm larger than the Re (550) of the release film, and compensates for the double polarization of the release film. Provide an inspection device, which is to be used.

In the inspection apparatus of the present invention, the polarizing plate may be a linear polarizing plate, and the polarizing filter may be a linear polarizing filter. Further, in the present invention, the polarizing plate may be a circular polarizing plate, and the polarizing filter may be a retardation filter. In either case, the present invention can be applied.

Also in the inspection apparatus of the present invention, the retardation plate may be one in which the in-plane retardation value is continuously changed. Further, the retardation plate may be composed of a plurality of plates and may be arranged so that the in-plane retardation value increases in opposite directions. Further, the retardation plate may be made of an inorganic material or a cycloolefin resin.

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

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 the polarizing plate.

It is a figure which shows the inspection apparatus of 1st Embodiment. It is sectional drawing of the object to be inspected in 1st Embodiment. It is a figure which shows an example of a retardation plate. It is a figure which shows the inspection apparatus of the modification of 1st Embodiment. It is a figure which shows the situation which scans a retardation plate. It is a figure which shows the inspection apparatus of the 2nd Embodiment. It is a figure which shows the inspection apparatus of 3rd Embodiment. It is sectional drawing of the object to be inspected in 3rd Embodiment. It is a figure which shows the inspection apparatus of 4th 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 linear polarizing plate. As shown in FIG. 1, in the inspection device 100A, the light source 2, the retardation plate 4, and the linear polarizing filter (polarizing filter) 3A are arranged in this order.

As shown in FIG. 2, the film-shaped object to be inspected 10A to be inspected is laminated on the linear polarizing plate 1A which is the main body of the inspection target and the linear polarizing plate 1A via the pressure-sensitive adhesive layer 15. It also includes a release film 16a. The linear polarizing plate 1A is formed by laminating protective films 12a and 12b on both sides of the polarizing film 11. Then, another release film 16b is laminated on the surface of the linear polarizing plate 1A on the side not provided with the release film 16a. The linear polarizing plate 1A 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 pressure-sensitive adhesive layer 15. ..

In the present specification, the "linear polarizing plate" refers to a polarizing plate for converting arbitrary 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 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 linear polarizing plate 1A, 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.

The release films 16a and 16b are peeled off from the linear polarizing plate 1A when they are attached to the display device, and the peeled release films 16a and 16b are 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 phase difference value is not compensated, a malfunction may occur in the defect inspection using the linear polarizing filter 3A. That is, in the defect inspection of the linear polarizing plate 1A 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 reduces the inspection accuracy of the inspection device 100A. It can be a cause of causing.

As described in the background technique, in the polarizing plate 1A, another release film 16b is often provided on the opposite surface of the release film 16a. In the polarizing plate 1A shown in FIG. 2, a release film 16b is attached to the protective film 12b side. This release film 16b is also usually peeled off from the linear polarizing plate 1A when it is attached to the 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 10A 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 the adhesive layer is not shown). ..

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, the in-plane retardation value (in-plane retardation value) may vary. Even with a 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, and is polarized in a predetermined direction.

The linear polarizing filter 3A is a linear polarizing plate. When inspecting the object to be inspected 10A, the direction of the linear polarizing filter 3A is adjusted so as to form a cross Nicol with the linear polarizing plate 1A in the object to be inspected 10A. The linear polarizing plate of the linear polarizing filter 3A is defect-free.

The retardation plate 4 compensates for the birefringence of light due to the release film 16a. When the polarization axes of the linear polarizing filter 3A and the linear polarizing plate 1A are orthogonal to each other (that is, when cross Nicol is formed), the linearly polarized light converted by the linear polarizing plate 1A does not pass through the linear polarizing filter 3A at all. If a defect is present in the linear polarizing plate 1A, it may be visually recognized as a bright spot.

However, as the release film 16a, an optically transparent material is used, and usually, a material having birefringence such as a PET resin is often used. When linearly polarized light passes through such a material, it is converted into elliptically polarized light. Therefore, even though the linearly polarized light filter 3A and the linearly polarizing plate 1A form a cross Nicol, the amount of light transmitted through the linearly polarized light filter 3A is large. , The amount of light of the light source exceeds 15%, and the detection accuracy of bright spots derived from defects existing in the linear polarizing plate 1 is significantly lowered. When the release film 16b is used, an optically transparent material is used for the same reason.

Therefore, by arranging the retardation plate 4 between the linear polarizing filter 3A and the linear polarizing plate 1A to be inspected, the change in the transmittance of the release film 16a is canceled, so that the birefringence of light by the release film 16a is performed. Compensate.

The shape of the retardation plate 4 is not particularly limited as long as it can compensate for the birefringence of the light of the release film 16a, but the release film 16a made of PET-based resin has an in-plane retardation value and a slow phase. Since there is a large variation in the shaft, it is preferable to have a shape in which the phase difference value can be adjusted during inspection. As the shape thereof, as shown in FIG. 3, the thickness is not uniform, and the thickness is continuously changed so as to have a thin portion and a thick portion. Since the thickness is continuously changing, the phase difference value is also continuously changing according to the thickness. The retardation plate 4 starts from the thinnest portion and expands in thickness at a predetermined angle α, and has a “wedge” shape in cross-sectional view. The wedge-shaped retardation plate 4 can be easily compensated for the birefringence of light by the release film 16a by shifting or rotating the retardation plate 4 within the inspection region of the object to be inspected 10A. ..

The size of the retardation plate 4 is preferably a rectangle or a square having a side length in the range of 1 cm to 30 cm.

As the retardation plate 4, an inorganic material such as a mineral exhibiting birefringence such as quartz or calcite, or a film made of a cycloolefin resin can be used. It is particularly preferable to use a material having such flat wavelength dispersion characteristics. Further, it is preferable to use a mineral such as quartz from the viewpoint of ease of processing into a wedge shape and subsequent handling.

When a mineral such as quartz is used, a retardation film may be further used in order to make the wavelength dispersion characteristics flatter. When the slow axis of the retardation film is arranged orthogonally to the slow axis of the retardation plate made of mineral such as quartz, the retardation film of positive dispersion is used, and the slow phase of the retardation plate made of mineral such as quartz is used. When the slow axis of the retardation film is arranged parallel to the shaft, it is preferable to use a reverse dispersion retardation film. When such a retardation film is used, the retardation film is bonded to the surface of quartz.

Examples of the reverse-dispersive retardation film include the product names "Pure Ace WR-S", "Pure Ace WR-W", "Pure Ace WR-M" manufactured by Teijin Limited, and the product name "Pure Ace WR-M" manufactured by Nitto Denko Corporation. NRF ”. Examples of the positively dispersible retardation film include a film made of a polycarbonate resin and a film made of a polypropylene resin.

As the above-mentioned cycloolefin-based resin, for example, dicyclopentadiene, a resin obtained by ring-opening metathesis polymerization using norbornene obtained by a deal alder reaction from cyclopentadiene and olefins or a derivative thereof as a monomer and subsequently hydrogenated. Ring-opening metathesis polymerization is carried out using tetracyclododecene or a derivative thereof obtained by the deal alder reaction from olefins or methacrylic acid esters as a monomer, followed by resin, norbornene, tetracyclododecene, and the like. Ring-opening metathesis copolymerization is carried out in the same manner using two or more kinds of derivatives of the above, or other cyclic olefin monomers, and the resin obtained by subsequent water addition, the above-mentioned norbornene, tetracyclododecene, or a derivative thereof. Examples thereof include a resin obtained by addition-copolymerizing an aromatic compound having a vinyl group or the like.

Commercially available products of the cycloolefin-based resin can be easily obtained. Examples of these commercially available products include Topas (manufactured by Topas Advanced Polymers GmbH), Arton (manufactured by JSR Corporation), Zeonoa, Zeonex (manufactured by Nippon Zeon Corporation), and Appel (manufactured by Mitsui Chemicals, Inc.) under their respective trade names. ) Etc. can be mentioned.

Further, as the retardation value of the retardation plate 4, a film having a region larger than Re (550) of the release film 16a by 500 to 600 nm (hereinafter, may be referred to as a “wide compensation region”) is used. By using the retardation plate 4 having a region shifted by about one wavelength in this way, the transmission spectrum of visible light can be matched with the PET resin film in a wider wavelength range, and the retardation compensation becomes possible.

In order to observe the light passing through the object to be inspected 10A, the retardation plate 4 and the linear polarizing filter 3A, the position on the optical axis 9 and on both sides of the linear polarizing filter 3A 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 linear polarizing filter 3A instead of the member.

Further, the inspection device 100A tilts at least one of the object to be inspected 10A, the retardation plate 4 and the linear polarizing filter 3A so as to face each other at different angles, or rotates in a direction perpendicular to the optical axis 9 of light. It is preferable to provide 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, in the inside of the inspection device 100A, the object to be inspected 10A is inserted between the light source 2 and one wedge-shaped retardation plate 4. At this time, the surface of the object to be inspected 10A, the retardation plate 4, and the linear polarizing filter 3A are all parallel to each other, and the side of the object to be inspected 10A provided with the release film 16a is opposite to the light source 2. The linear polarizing plate 1A and the linear polarizing filter 3A are arranged so as to form a cross Nicol while facing the side. When the inspection device 100A is provided with the above-mentioned movable device, after inserting the inspected object 10A in an arbitrary direction, the relative positional relationship between the inspected object 10A and the linear polarizing filter 3A 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 10A, passes through the object to be inspected 10A, and becomes linearly polarized light. When the object to be inspected 10A and the linearly polarized light filter 3A are arranged in a cross Nicol, the linearly polarized light generated by passing through the object to be inspected 10A is blocked by the linearly polarized light filter 3A. At this time, if there is a defect in the linear polarizing plate 1A in the object to be inspected 10A, 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 linearly polarized light generated by passing through the object to be inspected 10A is affected, and the amount of light transmitted through the linearly polarizing filter 3A increases (for example, 10% of the amount of light of the light source or It becomes more than 15%), and the detection accuracy of defects such as bright spots existing in the linear polarizing plate 1A is lowered. Here, by arranging the retardation plate 4 between the object to be inspected 10A and the linear polarizing filter 3A, the retardation value of the release film 16a in the object to be inspected 10A is canceled, and the light from the release film 16a is canceled. Compensates for birefringence.

During the inspection, the optical axis of the light emitted by the light source 2 is made to pass through the "wide compensation region" of the retardation plate 4. As a result, the transmitted spectrum of visible light can be matched with the PET-based resin film in a wider wavelength range, and the compensation for the phase difference becomes more effective. That is, since the thickness of the retardation plate 4 changes continuously, and therefore the retardation value also changes continuously, in a part of the thickness portion of the various thicknesses of the retardation plate 4, , The birefringence of the release film 16a is cancelled.

Further, during the inspection, at least one of the object to be inspected 10A, the retardation plate 4 and the linear polarizing filter 3A 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. You may let me. 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.

The inspection device and inspection method of the first embodiment have been described above. This inspection device and inspection method can also be implemented by modifying a part of the configuration or inspection procedure as follows.

As shown in FIG. 4, two retardation plates 4 having a wedge-shaped cross-sectional view are prepared, and these are used in a state of being overlapped with the directions in which the retardation values continuously increase are opposite to each other. You may. In this case, as the phase difference value of the retardation plate, the total value of the two sheets is inserted, and the above "wide compensation area" is also based on the total value of the two sheets. By using two wedge-shaped retardation plates 4, the birefringence of the light of the release film 16a can be compensated for in a wide range, so that the inspection area can be expanded and the inspection can be performed efficiently.

More specifically, the phase difference of the two retardation plates 4 and 4 as a whole is changed by shifting at least one of the two retardation plates 4 and 4 in the direction in which the thickness changes (the left-right direction in the drawing). be able to. The degree of the change is gradual as compared with the case where the retardation plate 4 is one, because the thickness increases in the directions opposite to each other. According to this, in the inspection device 100A'(FIG. 4) using two retardation plates 4 and 4, the birefringence of the release film 16a is higher than that in the inspection apparatus 100 having one retardation plate 4. The area that can be canceled becomes wider. Further, the same inspection can be performed even if the retardation plates 4 to be used are three, four, or the like.

Alternatively, the retardation plate does not have to have a wedge-shaped cross-sectional view. Since the retardation plate only needs to have the above-mentioned "wide compensation region", the phase difference of the release films 16a and 16b is measured in advance, and the retardation plate has the corresponding phase difference and has a thickness of one. A different retardation plate may be used.

Further, the first embodiment is particularly useful as a method of inspecting the area of the object to be inspected 10A after specifying the place to be inspected in advance, but as shown in FIG. 5, the light source 2 and the position By scanning the phase difference plate 4, the object to be inspected 10A can be inspected over a wider range. In this case, as shown in FIG. 5, the retardation plate 4 is moved so as to scan the entire area of the surface of the object to be inspected 10A. The direction of movement is preferably a direction in which the thicknesses of the retardation plates 4 are different. Speaking of the relationship between FIGS. 1 and 5, since the thickness of the retardation plate 4 is different in the left-right direction shown, it is preferable that the movement direction of the retardation plate 4 is the left-right direction shown. At this time, the light source 2 and the detecting means 5 are also moved as needed.

<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 object to be inspected 10A is placed and the place where the linear polarizing filter 3A is placed. Is the opposite. That is, in the inspection device 100B, the light source 2, the linear polarizing filter 3A, and the retardation plate 4 are arranged in this order, and the inspected object 10A 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 2 than the retardation plate 4. In the same manner as in the first embodiment, when the release film 16b is attached to the polarizing plate 1A to compensate for the retardation value of the release film 16b, the release film 16b is used as the retardation plate 4 in the inspection device 100B. The object to be inspected 10A may be installed so as to face the surface.

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

<Third embodiment>
The inspection device and the inspection method of the third embodiment will be described.

(Inspection device and object to be inspected)
Unlike the first embodiment, the inspection device of the present embodiment inspects the presence or absence of surface defects of the circularly polarizing plate. The difference from the first embodiment is that the film-shaped object to be inspected 10B to be inspected includes the circular polarizing plate 1B, and the retardation filter 3B is used instead of the linear polarizing filter 3A accordingly. Is to use. Hereinafter, the differences from the first embodiment will be described.

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

As shown in FIG. 8, the film-shaped object to be inspected 10B to be inspected is laminated on the circularly polarizing plate 1B which is the main body of the inspection target and the circularly polarizing plate 1B via the adhesive layer 15. It also includes a release film 16a. In the circular polarizing plate 1B, protective films 12a and 12b are bonded to both sides of the polarizing film 11, and further, a retardation film 14 is 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 1B on the side not provided with the release film 16a. The circularly polarizing plate 1B 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 pressure-sensitive 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 retardation film 14 is a film that converts light linearly polarized by the polarizing film 11 into circularly polarized light in the inspection device 100C (for example, a λ / 4 plate). 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 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 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.

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, unpolarized light passes through the circular polarizing plate 1B to become circularly polarized light.

The retardation filter 3B is a circular polarizing plate, and a layer having a retardation is arranged toward the light source 2. When inspecting the object to be inspected 10B, the phase difference filter 3B is always adjusted in its orientation so as to form a cross-nicol with the circularly polarizing plate 1B in the object to be inspected 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 surface of the object to be inspected 10B, the retardation plate 4, and the retardation filter 3B are all parallel to each other, and the side of the object to be inspected 10B provided with the release film 16a is opposite to the light source 2. The circularly polarizing plate 1B and the retardation filter 3B are arranged so as to form a cross Nicol while facing the side. When the inspection device 100C is provided with the movable device, after inserting the inspected object 10B in an arbitrary direction, the relative positional relationship between the inspected object 10B and the phase difference filter 3B 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 10B, passes through the object to be inspected 10B, and becomes circularly polarized light. By arranging the cross Nicol between the object to be inspected 10B and the retardation filter 3B, the circular polarization generated by passing through the object to be inspected 10B is blocked by the retardation filter 3B. At this time, if there is a defect in the circularly polarizing plate 1B in the object to be inspected 10B, this 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 circular polarization generated by passing through the object to be inspected 10B is affected, and the amount of light transmitted through the retardation filter 3B increases (for example, 10% of the light amount of the light source or It becomes more than 15%), and the detection accuracy of defects such as bright spots existing in the circular polarizing plate 1B is lowered. Here, by arranging the retardation plate 4 between the object to be inspected 10B and the retardation filter 3B, the retardation values of the release films 16a and 16b in the object to be inspected 10B are canceled, and the release film 16a is canceled. Compensates for birefringence of light due to.

During the inspection, the optical axis of the light emitted by the light source 2 is made to pass through the wide compensation region of the retardation plate 4. As a result, the transmitted spectrum of visible light can be matched with the PET-based resin film in a wider wavelength range, and the compensation for the phase difference becomes more effective. That is, since the thickness of the retardation plate 4 changes continuously, and therefore the retardation value also changes continuously, in a part of the thickness portion of the various thicknesses of the retardation plate 4, , The birefringence of the release film 16a is cancelled.

Further, during the inspection, at least one of the object to be inspected 10B, the retardation plate 4 and the retardation filter 3B 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. It is the same as the first embodiment. In the same manner as in the first embodiment, when the release film 16b is attached to the circularly polarizing plate 1B 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 100C. The object to be inspected 10A may be installed so as to face 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 object to be inspected 10B is placed and the place where the phase difference filter 3B is placed. Is the opposite. That is, in the inspection device 100D, the light source 2, the retardation filter 3B, and the retardation plate 4 are arranged in this order, and the inspected object 10B 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 2 than the retardation plate 4.

In the inspection of the object to be inspected 10B using the inspection device 100D, the presence or absence of defects in the circularly polarizing plate 1B can be easily inspected by the same principle as in the third embodiment. In the same manner as in the first embodiment, when the release film 16b is attached to the object to be inspected 10B 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 100D. The object to be inspected 10B may be installed so as to face 4.

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

Hereinafter, the contents of the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples. In the following description, "part" and "%" indicating the content or the amount used are based on weight unless otherwise specified. Further, in the following description, the reference numerals of the "polarizing filter 1" and the "phase difference plate 1" represent the reference numerals used in the experiment, and are different from the reference numerals on the drawings.

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.).
(3) Measurement of transmittance of light transmitted through a polarizing filter A spectroradiometer (SR-UL1 manufactured by Topcon Techno House Co., Ltd.) was installed 1 m away from the measurement surface, and the measurement angle was 2 °. The brightness was measured. It was calculated what percentage of the light was passing through the polarizing filter with respect to the brightness of the light source.
(4) Measurement of polarization degree and simple transmittance of 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 the object to be inspected]
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)) was applied to both sides of the obtained polarizing film while applying a polyvinyl alcohol-based adhesive so that the thickness of the adhesive layer was 0.1 μm. After laminating (25 μm, manufactured by Konica Minolta), the film was dried at 80 ° C. for 2 minutes to prepare a polarizing plate 1. The degree of polarization of the obtained polarizing plate 1 was 99.995%, which was transparent to a single substance. The rate was 42.5%.

An adhesive layer was formed on one side of the polarizing plate 1, and a PET film having a retardation value of 2000 nm was bonded as a release film to prepare 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 quartz wedge-shaped inspection plates were used as the retardation plate 1. In both of the two wedge-shaped inspection plates, the retardation value was continuously changed from 500 nm to 2000 nm.

[Example 1]
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 to the backlight) / retardation plate 1 / polarizing plate 1 (polarizing filter). The retardation plates 1 were arranged by superimposing the two quartz inspection plates so that the directions in which the retardation values increase were opposite to each other. By sliding the retardation plate 1, the retardation value (Re (550)) is set to 2550 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 1.4%, and the bright spot defect could be detected without any problem in the inspection.

[Comparative Example 1]
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 to the backlight) / retardation plate 1 / polarizing plate 1 (polarizing filter). The retardation plates 1 were arranged by superimposing the two quartz inspection plates so that the directions in which the retardation values increase were opposite to each other. By sliding the retardation plate 1, the retardation value (Re (550)) is set to 2000 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 11.7%, and the bright spot defect could not be detected.

[Example 2]
The optical system was similarly configured except that the PET film (release film) included in the object to be inspected in Example 1 was changed to a PET film having a retardation value of 2300 nm. By sliding the retardation plate 1, the retardation value (Re (550)) is set to 2850 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 2.0%, and the bright spot defect could be detected without any problem in the inspection.

[Comparative Example 2]
In Example 2, the optical system was similarly configured except that the retardation plate 1 was slid so that the retardation value (Re (550)) was set to 2300 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 12.7%, and the bright spot defect could not be detected.

[Example 3]
The optical system was similarly configured except that the PET film (release film) included in the object to be inspected in Example 1 was changed to a PET film having a retardation value (Re (550)) of 2600 nm. By sliding the retardation plate 1, the retardation value becomes 3150 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 3.7%, and the bright spot defect could be detected without any problem in the inspection.

[Comparative Example 3]
In the third embodiment, the optical system was similarly configured except that the retardation plate 1 was slid so that the retardation value (Re (550)) was 2600 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 14.4%, and the bright spot defect could not be detected.

[Example 4]
The optical system was similarly configured except that the PET film (release film) included in the object to be inspected in Example 1 was changed to a PET film having a retardation value (Re (550)) of 1700 nm. By sliding the retardation plate 1, the retardation value becomes 2250 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 2.1%, and the bright spot defect could be detected without any problem in the inspection.

[Comparative Example 4]
In Example 3, the optical system was similarly configured except that the retardation plate 1 was slid so that the retardation value (Re (550)) was set to 1700 nm in the optical axis portion. When the brightness in the darkest state was measured in this way, it was 10.5%, and the bright spot defect could not be detected.

[Example 5]
Bright spot defects are also 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) / retardation plate 1 / inspected object. can do.

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

1A ... linear polarizing plate (polarizing plate), 1B ... circular polarizing plate (plate plate), 2 ... light source, 3A ... linear polarizing filter (polarizing filter), 3B ... retardation filter (polarizing filter), 4 ... retardation 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 (15)

It is an inspection method for determining the presence or absence of defects in a film-like object to be inspected, which includes a polarizing plate and a release film made of polyethylene terephthalate resin.
With the object to be inspected
A retardation plate that 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 at a wavelength of 550 nm of the release film and that compensates for the birefringence of the release film. ,
The polarizing plate and the polarizing filter constituting the cross Nicol are arranged in this order.
An inspection method in which light is incident from either the side of the object to be inspected or the side of the polarizing filter so that the optical axis passes through the region, and the polarizing filter or the object to be inspected is observed from the other side. .. 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.
The inspection method according to claim 1, wherein the polarizing filter is a retardation filter. The inspection method according to any one of claims 1 to 3, wherein the in-plane retardation value of the retardation plate is continuously changed. The inspection method according to claim 4, wherein the retardation plate is composed of a plurality of plates, and the in-plane retardation values are arranged in opposite directions to each other. The inspection method according to any one of claims 1 to 5, wherein the retardation plate is made of an inorganic material or a cycloolefin resin. Claims 1 to claim that at least one of the object to be inspected, the retardation plate, and the polarizing filter is tilted so as to face each other at different angles, or is rotated in a direction perpendicular to the optical axis of the light. The inspection method according to any one of 6. An inspection device for determining the presence or absence of defects in the polarizing plate by injecting light onto a film-shaped object to be inspected including a polarizing plate and a release film made of a polyethylene terephthalate resin.
Light source and
A polarizing filter for incident light emitted from the light source and passing through the object to be inspected,
It is 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 polarizing filter is placed so that the light passing through the object to be inspected can pass through. With a phase difference plate,
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 at a wavelength of 550 nm of the release film, and compensates for the birefringence of the release film. Is an inspection device. An inspection device for determining the presence or absence of defects in the polarizing plate by injecting light onto a film-shaped object to be inspected including a polarizing plate and a release film made of a polyethylene terephthalate resin.
Light source and
A polarizing filter that allows light emitted by the light source to pass through,
A phase difference that is arranged closer to the light source than the place where the object to be inspected is placed and farther from the light source than the place where the polarizing filter is placed, and allows light that has passed through the polarizing filter to pass through. With a board,
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 at a wavelength of 550 nm of the release film, and compensates for the birefringence of the release film. Is an inspection device. The polarizing plate is a linear polarizing plate.
The inspection device according to claim 8 or 9, wherein the polarizing filter is a linear polarizing filter. The polarizing plate is a circular polarizing plate.
The inspection device according to claim 8 or 9, wherein the polarizing filter is a retardation filter. The inspection device according to any one of claims 8 to 11, wherein the retardation plate has an in-plane retardation value continuously changing. The inspection device according to claim 12, wherein the retardation plate is composed of a plurality of plates 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 8 to 13, wherein the retardation plate is made of an inorganic material or a cycloolefin resin. The inspection device according to any one of claims 8 to 14, wherein the retardation plate is arranged at a position where the optical axis of light passes through the region.

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