TW202217285A - Inspection method - Google Patents

Abstract

The present invention provides an inspection method of reflection type capable of easily determining the presence or absence of defects in a circularly polarizing plate. The inspection method provided in the present invention determines the presence or absence of defects in a film-shaped inspected object 10 which has a circular polarizing plate 1 and a separating film 16a made of a polyethylene terephthalate resin. A light source 2, a first phase differential filter 3A, a first phase differential plate 4A, the inspected object 10, a second phase differential plate 4B and a second phase differential filter 3B are arranged as a predetermined configuration, and the presence or absence of defects in the circular polarizing plate 1 is determined by observing the light reflected by the inspected object 10. Then, the first phase differential plate 4A and the second phase differential plate 4B are respectively replaced with a third phase differential plate and a fourth phase differential plate that have different in-plane retardation values with respect to a light having a wavelength of 550 nm, and the light is incident again to determine the presence or absence of defects in the circular polarizing 1. By this inspection method, deformation defects that are difficultly to be detected by inspection methods of transmission type can be easily detected.

Description

Inspection Method

The present invention relates to an inspection method.

A polarizer used for a liquid crystal display device, an organic EL display device, or the like is generally constituted by sandwiching a polarizer between two protective films. In order to attach the polarizing plate to the display device, an adhesive layer (pressure sensitive adhesive) is laminated on one protective film, and then a release film is laminated on the adhesive layer. Moreover, the peeling film (surface protective film) for protecting the surface is also usually bonded to the other protective film. The polarizing plate is conveyed and conveyed in the state where the release film is laminated as described above, and the release film is peeled off when it is attached to the display device in the manufacturing process of the display device.

Here, in the manufacturing process of the polarizer, foreign matter and residual air bubbles may be mixed between the polarizer and the protective film, or, when the protective film has the function of a retardation film, there may be alignment defects (hereinafter, also referred to as Such foreign matter, air bubbles, and alignment defects may be collectively referred to as "defects"). When a defective polarizing plate is bonded to a display device, the defective portion may be observed as a bright spot, or an image may be distorted and displayed at the defective portion. In particular, when the display device displays black, it is easy to visually recognize defects that are visually recognized as bright spots.

On the other hand, the inspection for detecting the defect of this polarizing plate is performed at the stage before the polarizing plate is to be bonded to the display device (the polarizing plate in the state of peeling off the film). The inspection of this defect is generally performed by using Optical inspection of the polarizing axis of the polarizing plate. Specifically, as shown in Patent Document 1, a polarizing filter is provided between a polarizing plate as an object to be inspected and a light source, and the polarizing plate or the polarizing filter is rotated in the plane direction, and the polarizing plate or the polarizing filter is rotated. The respective polarization axis directions have a specific relationship. When the directions of the polarization axes are perpendicular to each other (that is, when the cross-polarized light is configured), the linearly polarized light passing through the polarizing filter does not pass through the polarizing plate. However, when there is a defect in the polarizing plate, the linearly polarized light will pass through the defect, so the presence of the defect can be determined by detecting the light. On the other hand, when the polarizing axis directions of the polarizing plate and the polarizing filter are parallel to each other, the linearly polarized light passing through the polarizing filter passes through the polarizing plate. However, when there is a defect in the polarizing plate, the linearly polarized light is blocked by the defective portion, so that the presence of the defect can be determined by not detecting the light. The light passing through the polarizing plate can be detected visually by an inspector, or can be automatically detected by combining the image analysis processing value of a CCD camera and an image processing device, thereby enabling inspection of the polarizing plate for defects.

(prior art literature)

(patent literature)

Patent Document 1: Japanese Patent Publication No. Hei 9-229817

When the polarizing plate is a circular polarizing plate and the release film is made of a polyethylene terephthalate-based resin (PET-based resin), a retardation filter (equivalent to a certain degree of wavelength dispersion matching with the PET-based resin) is used. on the polarizing filter above). Here, when the circularly polarizing plate and the retardation filter are arranged so as to form crossed polarized light, the defects are observed and confirmed as bright spots according to the above-mentioned principle, but the circularly polarizing plate has alignment defects of the retardation film, pins and needles. In areas with low phase difference values such as holes, bright spot defects are observed If it is confirmed as a black spot, the detection judgment is more difficult than the detection of a bright spot. This tendency is more remarkable when the circularly polarizing plate contains the retardation film which consists of the hardened|cured material of a polymerizable liquid crystal compound especially.

In addition, the principle of the inspection method disclosed in Patent Document 1 is to observe the light passing through the inspection object. When inspected by this principle, if the inspected object has deformation defects (for example, wrinkles generated when cutting a circular polarizing plate), the optical path length in the normal part and the deformation defect part hardly changes, so it is difficult to use optical methods. Deformation defects are detected.

Furthermore, as described above, when the polarizing plate is provided with a release film, since the polarization characteristics of the circular polarizing plate are hindered by the birefringence of the release film, the conventional inspection apparatus cannot accurately detect the bright spots and the like present in the polarizing plate. Defects.

In view of this, an object of the present invention is to provide a reflection-type inspection method that can easily determine the presence or absence of defects in a circularly polarizing plate.

The present invention provides an inspection method for determining whether a film-like inspection object is defective or not, the inspection object comprising a circular polarizing plate on which a polarizing film and a retardation film are laminated, and a retardation film laminated on the circular polarizing plate and A release film composed of a polyethylene terephthalate-based resin (hereinafter, also referred to as a "PET-based resin"), the inspection method consists of a light source, a first retardation filter, a first retardation plate, and the object to be inspected are arranged in this order on the optical path of the light emitted by the light source, and the second phase difference plate and the second phase difference filter are arranged in this order to be reflected by the object to be inspected On the optical path of the light, the in-plane retardation value of the first retardation plate for light with a wavelength of 550 nm (hereinafter, the in-plane retardation value for light with a wavelength of 550 nm is also referred to as "Re(550 )") is approximately the same as the Re(550) of the release film, and compensates for the birefringence of the release film; the side of the release film of the object to be inspected faces the first retardation plate side; the second phase The Re(550) of the difference plate is the same as that of the first retardation plate. Re(550) is approximately the same, and compensates the birefringence of the first phase difference plate; the second phase difference filter and the first phase difference filter form orthogonally polarized light; and the inspection method is to use the light source The light is incident on the first phase difference filter, and the light reflected by the object to be inspected is observed from the side of the second phase difference filter to determine whether the circularly polarizing plate is defective; and the first phase difference plate and the second phase difference The plates are replaced with a third retardation plate and a fourth retardation plate respectively. The Re(550) of the third retardation plate and the fourth retardation plate are 50 to 100 nm larger than the Re(550) of the peeling film, and are compensated The birefringence of the peeling film; after replacement, the light is incident on the first retardation filter, and the light reflected by the object to be inspected is observed from the second retardation filter side to determine whether the circularly polarizing plate is defective. In addition, the term "substantially the same" in Re(550) here means that the difference in Re(550) is only about ±5 nm.

In this inspection method, since the first retardation filter and the second retardation filter are arranged to constitute crossed polarized light, the light reflected by the normal part of the inspection object (for example, the light reflected by the surface of the peeling film) It is blocked by the second phase difference filter, so that the observation field can be sufficiently darkened, and the observation of the defective part can be facilitated. On the other hand, the light reflected by the defective portion generated in the object under inspection has a phase difference deviated from the ideal (undesired elliptically polarized light) due to the defect, so only the reflected light corresponding to the deviation passes through. The second phase difference filter can detect the defective part of the object to be inspected. Here, the light reflected by the defective part will pass through the release film again, and the retardation of the release film can also be considered as an obstacle to defect detection, but the first retardation plate compensates for the birefringence of the release film, so The birefringence of the release film can be suppressed from hindering defect detection. In addition, with regard to the parts of the black defect observed in the inspection using the first retardation plate and the second retardation plate, the retardation plates were replaced with the third retardation plate and the fourth retardation plate, respectively. By inspection, the portion where the phase difference can be adjusted to become the black defect is observed as a bright spot defect. Moreover, compared with the penetrating inspection method, the optical path of the reflective inspection method increases in the object to be inspected, so even the penetrating inspection method Deformation defects that are difficult to detect in the method can also be easily detected. According to the above description, the inspection method of the present invention can easily determine the presence or absence of defects in the circularly polarizing plate.

In this inspection method, the retardation film may be formed of a cured product of a polymerizable liquid crystal compound. When the retardation film is composed of a cured product of a polymerizable liquid crystal compound, the possibility of observing black spot defects increases due to its general thinness. Therefore, it is suitable as a subject to which the present invention is applied.

In addition, in this inspection method, the inspection object, the first phase difference plate, the second phase difference plate, the third phase difference plate, the fourth phase difference plate, the first phase difference filter, and the first phase difference plate can be used in the inspection. At least one of the two phase difference filters is inclined so that the angles facing each other are different, or, during inspection, the inspection object, the first phase difference plate, the second phase difference plate, and the third phase difference plate may be At least one of the plate, the fourth phase difference plate, the first phase difference filter, and the second phase difference filter rotates in a direction perpendicular to the optical path. By such an inclination, the retardation of the peeling film, the first retardation plate, the second retardation plate, and the like can be finely adjusted, and a wider range of inspection can be performed. In addition, by such rotation, the axes of the respective structures can be easily aligned.

The first retardation plate and the third retardation plate may also be arranged in the same member. Furthermore, the first retardation plate and the second retardation plate may be arranged in the same member.

According to the present invention, a reflection-type inspection method can be provided, which can easily determine the presence or absence of defects in a circularly polarizing plate.

1: Circular polarizer

2: light source

3A: First phase difference filter

3B: Second phase difference filter

4: Phase difference plate

4A: The first phase difference plate

4B: Second retardation plate

4C: The third phase difference plate

4D: Fourth retardation plate

4E: Fifth retardation plate

4F: Sixth retardation plate

5: Detection means

9,9a,9b,9c: Optical path

10: Object to be inspected

11: polarizing film

12a, 12b: Protective film

13: Adhesive layer

14: retardation film

15: Adhesive layer

16a: Release film

16b: Surface protection film

41: Keeping Components

100: Inspection device

a1,a2,a3,a4,a5,a6,a _2n-1 ,a _2n : area

D, D': Defect

FIG. 1 is a diagram showing the inspection apparatus of the first embodiment.

Fig. 2 is a cross-sectional view of the object to be inspected.

FIG. 3 is a plan view showing the retardation plate.

Hereinafter, the preferred embodiments of the present invention will be described in detail with reference to the drawings. Here, the same reference numerals are attached to the same parts or corresponding parts in the respective drawings, and overlapping descriptions are omitted.

(Inspection device and object to be inspected)

The inspection apparatus of the present embodiment inspects the surface of the circular polarizing plate, the layers constituting the polarizing plate, or whether there is any defect in the interior. As shown in FIG. 1, the inspection apparatus 100 arranges the light source 2, the first phase difference filter 3A, and the first phase difference plate 4A in this order, and arranges the second phase difference filter 3B and the second phase difference plate 4B respectively It is arranged so as to be adjacent to the first phase difference filter 3A and the first phase difference plate 4A. The surfaces of the first phase difference filter 3A and the second phase difference filter 3B are arranged on substantially the same plane with their surfaces parallel to each other, and the surfaces of the first phase difference plate 4A and the second phase difference plate 4B are arranged in substantially the same plane with their surfaces parallel to each other. on flat surface.

As shown in FIG. 2 , the object to be inspected 10 is in the form of a film, and includes: a circular polarizing plate 1 serving as a main body of the inspection object; . The circular polarizing plate 1 has protective films 12a and 12b attached to both sides of the polarizing film 11, and a retardation film 14 is formed on the protective film 12a on the side provided with the release film 16a through an adhesive layer 13, thereby A circular polarizing plate 1 is formed. Moreover, the surface protection film 16b is laminated|stacked on the surface of the side which does not have the peeling film 16a of the circularly polarizing plate 1. As shown in FIG. Generally speaking, the circular polarizing plate 1 is used in display devices, such as liquid crystal display devices, organic EL display devices, etc., and the release film 16a is peeled off and attached to the display device through the adhesive layer 15 during use.

In addition, in this specification, the "circular polarizing plate" refers to what includes a circular polarizing plate and an elliptical polarizing plate. In addition, "circular polarization" includes circular polarization and elliptical polarization.

The polarizing film 11 is a film that converts light incident from the surface protection film 16b side into linearly polarized light. The polarizing film 11 includes, for example, a polyvinyl alcohol film adsorbed and aligned by iodine or a dichroic dye, and a polymerizable liquid crystal compound is oriented and a polymerized material adsorbed and aligned by a dichroic dye.

The protective films 12a and 12b are used to protect the polarizing film 11 . The protective films 12a and 12b are widely used in the technical field where a polarizing plate can be used in order to obtain a polarizing plate having an appropriate mechanical strength. Typical cellulose ester films such as triacetate cellulose (TAC) films, cyclic olefin films, polyester films such as polyethylene terephthalate (PET) films, polymethyl methacrylate (PMMA) Films, etc. (meth)acrylic films, etc. In addition, the protective film may contain additives widely used in the technical field of polarizing plates.

The protective films 12a and 12b are attached to the display device together with the polarizing film 11 as a constituent element of the circularly polarizing plate 1, so there is a need to strictly control the retardation value and the like. As for the protective film 12a, it is typically preferable to use a film with a very small retardation value. In addition, for the protective film 12b, for example, a protective film having a λ/4 retardation or a protective film having a small retardation value can be used for easy viewing when viewing the display device with polarized sunglasses. The protective films 12a and 12b are bonded to the polarizing film 11 by an adhesive.

The retardation film 14 is a film that converts the light incident from the surface protection film 16b side and converted into linearly polarized light by the polarizing film 11 into circularly polarized light. When viewed from the release film 16a side, the retardation film 14 is a film that converts circularly polarized light incident from the release film 16a side into linearly polarized light. The retardation film 14 is not particularly limited as long as it is a film having a retardation, and may be a laminate of a λ/2 film and a λ/4 film. At this time, from the side close to the polarizing film 11 , the λ/2 film and the λ/4 film may be laminated in this order.

In addition, the retardation film 14 is preferably made of a cured product of a polymerizable liquid crystal compound. The retardation film 14 composed of the cured product of the 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 included, the retardation value of the part thereof tends to decrease. In such a portion, the linearly polarized light cannot be completely converted into ideal circularly polarized light, and becomes undesired elliptically polarized light. Moreover, as As will be described later, when the retardation plate 4 compensates for the birefringence of the release film 16a, a portion that should be observed as a bright spot defect may be observed as a black spot.

The polymerizable liquid crystal compounds that can form the retardation film 14 include, for example, Japanese Patent Laid-Open Publication No. 2009-173893, Japanese Patent Laid-Open Publication No. 2010-31223, WO2012/147904, WO2014/10325, and The one disclosed in WO2017-43438. The polymerizable liquid crystal compound described in these publications is a retardation film having so-called reverse wavelength dispersion, which can be formed into a so-called reverse wavelength dispersion capable of performing uniform polarization conversion in a wide frequency range. For example, a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution) can be coated on an appropriate substrate and subjected to photopolymerization, thereby forming an extremely thin retardation film as described above, and thus has this A circular polarizer with a retardation film can form a very thin circular polarizer. In this way, an extremely thin circularly polarizing plate is useful as a circularly polarizing plate for flexible display materials that has attracted attention in recent years.

As a base material to which the polymerizable liquid crystal compound solution is applied, the base material described in the above-mentioned gazette is mentioned. In order to align the polymerizable liquid crystal compound, the base material may also be provided with an alignment film. The alignment film may be photo-aligned by polarized light irradiation or mechanically aligned by brushing treatment. Here, as the alignment film, those described in the above-mentioned publications can be used.

However, if the substrate to which the polymerizable liquid crystal compound solution is to be coated has foreign matter or the like, or the substrate itself is damaged, defects may occur in the coating film itself obtained by applying the polymerizable liquid crystal compound solution. situation. In addition, when the alignment film is brushed, debris from the brushed cloth may remain on the alignment film, resulting in defects in the coating film of the polymerizable liquid crystal compound solution (the composition for forming a liquid crystal cured film). situation. In this way, the retardation film formed of the polymerizable liquid crystal compound can be formed into an extremely thin retardation film, but there is a cause of defects. In addition, as will be described later, the defects of the retardation film may There are cases where defects observed as black spots occur. The inspection method of the present embodiment is particularly advantageous for the inspection to determine whether there is such a defect in the inspection object of the circularly polarizing plate and the release film provided with the retardation film.

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

The peeling film 16a is a film to be peeled off from the circular polarizing plate 1 when it is attached to a display device, and the peeled peeling film 16a is usually discarded. Therefore, unlike the protective films 12a, 12b, there is no need to strictly manage the phase difference value. Therefore, when a commercially available film is used as the release film 16a, if the phase difference value is not compensated, it is difficult to ensure that malfunction is not caused in the defect inspection. That is, in the defect inspection of the circularly polarizing plate 1 to which the release film 16a whose retardation value is not strictly controlled is attached, the retardation of the release film 16a may reduce the inspection accuracy of the inspection apparatus 100. reason.

In addition, as described in the above-mentioned prior art, the surface protective film 16b which is a kind of peeling film is usually provided on the opposite side of the peeling film 16a of the circularly polarizing plate 1 . In the circularly polarizing plate 1 shown in FIG. 2, the surface protective film 16b is attached to the protective film 12b side. The surface protection film 16b is usually torn off from the circular polarizer 1 when it is attached to the display device. Unlike the protection films 12a and 12b, there is no requirement to strictly manage the retardation value. In addition, in FIG. 2, the protective film 12b and the surface protective film 16b can also be bonded together by an appropriate adhesive layer or adhesive layer (the adhesive layer or adhesive layer is omitted in FIG. 2).

In the embodiment, the release film 16a is made of a PET-based resin. In addition, the surface protection film 16b which consists of PET-type resin is also used. Films made of PET-based resins (PET-based resin films) are widely used release films and have the advantage of being inexpensive. On the other hand, the inexpensive PET-based resin film is as described above, and there is no need to strictly control the retardation value. Therefore, there will be a phase difference value that varies depending on the product batch. deviations. Furthermore, even the same PET resin-based film may have phase difference value unevenness in the plane. The presence or absence of defects can be accurately detected by the inspection method of the present embodiment even in a circularly polarizing plate to which such an inexpensive PET resin-based film is bonded as a release film.

Here, first, a method for obtaining Re(550) of the release film 16a will be described. As described above, these release films are PET-based resin films, and such films can be easily purchased from the market. From this film, for example, a sheet having a size of about 40 mm×40 mm is collected (separated from a long film using an appropriate cutting tool). The Re(550) of this tablet was measured three times, and the average value of Re(550) was obtained. The Re(550) of the sheet can be measured at room temperature (about 25°C) using a phase difference measuring apparatus KOBRA-WPR (manufactured by Oji Scientific Instruments Inc.). In addition, when the Re(550) of the surface protection film 16b is requested|required, the same test can be performed.

Various commercially available products can be used as the light source 2 , but it is advantageous to use linear light such as laser light (including those similar to linear light), for example. The light emitted from the light source 2 is unpolarized light, and becomes polarized light in a predetermined direction after passing through the first phase difference filter 3A described later.

Both the first phase difference filter 3A and the second phase difference filter 3B are circular polarizers with a wide frequency range. In the state where the inspection object 10 is inspected, the second phase difference filter 3B is maintained to be adjusted so that the orientation thereof and the first phase difference filter 3A constitute orthogonal polarization. At this time, it should be noted that the light incident on the second phase difference filter 3B is reflected light reflected by the object to be inspected 10 . In addition, the polarizing plate and the retardation plate (forming a layer having a phase difference) constituting the first phase difference filter 3A and the second phase difference filter 3B are so-called defect-free ones.

The first retardation plate 4A compensates for the birefringence of light caused by the release film 16 a included in the test object 10 . The material constituting the first retardation plate 4A is not particularly limited as long as it can compensate for birefringence of light caused by the release film 16a made of a PET-based resin. Also be prepared to have 100 A commercially available retardation plate with Re (550) of 200 nm is used, and a plurality of retardation plates are laminated to obtain a desired retardation value to form the first retardation plate 4A. Re(550) is generally additive, so the first retardation plate 4A with a desired Re(550) can be obtained from the Re(550) of the laminated retardation plate. The second phase difference plate 4B is one that cancels the phase difference of the first phase difference plate 4A, and preferably adopts the same structure as the first phase difference plate 4A. The release film 16a made of a PET-based resin generally has large differences in retardation values in the in-plane direction, slow axis, and the like. Therefore, it is preferable to prepare a plurality of retardation plates during inspection so that the retardation values can be selected from a plurality of retardation values. In this embodiment, at least the following two types of retardation plates are used: the first retardation plate 4A and the second retardation plate 4B of the two-piece group having substantially the same retardation value as the Re(550) of the release film 16a A retardation plate; and a retardation plate of a two-piece group of the third retardation plate 4C and the fourth retardation plate 4D having a Re(550) greater than that of the release film 16a by 50 to 100 nm. Here, the first retardation plate 4A and the second retardation plate 4B used in pairs have substantially the same Re (550), and the third retardation plate 4C and the fourth retardation plate 4D used in pairs The plates have approximately the same Re(550). Here, the substantially same retardation value as Re(550) of the release film 16a means that the absolute value of the difference between the Re(550) of the release film 16a and the Re(550) of the retardation plate is 5 nm or less as described above. .

In addition, when the unevenness of the retardation value of the release film is considered, the first retardation plate 4A and the second retardation plate 4B show the retardation in the range of about ±300 nm with respect to the Re(550) of the release film, respectively. whichever is better. In addition, within the range of this retardation, it is preferable to change in units of 50 nm to 100 nm in the in-plane direction of the release film. It is preferable to prepare various retardation plates showing such retardation in advance. That is, as the relevant retardation plate for changing the phase difference, in addition to the first retardation plate 4A and the third retardation plate 4C, it is preferable to prepare a retardation plate with different retardation. Hereinafter, the state of this retardation plate will be described.

FIG. 3 shows an outline of a related retardation plate 4 in which retardation plates having different in-plane retardations are assembled. As shown in FIG. 3 , the retardation plate 4 may also be configured such that regions with different retardation values in the in-plane direction are arranged in two rows and connected in one direction in the holding member 41 , which is one piece of the frame. That is, when focusing on one row of the retardation plate 4 (one row in the vertical direction in the figure), the region located at the end corresponds to the region a1 of the _first retardation plate 4A, and Re(550) is, for example, 1720 nm. region, the region located adjacent to it is a region corresponding to the region a ₃ of the third retardation plate 4C and the Re(550) is 1790nm, and the region located adjacent to it is the region corresponding to the fifth retardation plate 4E a ₅ and Re(550) is a region of 1860 nm. In the retardation plate 4, the number of the regions in one column is arbitrary, and the nth region a _2n-1 is shown in FIG. 3 . In addition, in the other row of the _retardation plate 4, regions (a ₁ , a ₃ , a ₅ , . a ₂ , a ₄ , a ₆ , ..., a _2n ). That is, the area corresponding to the first phase difference plate 4A(a ₁ ) is the second phase difference plate 4B(a ₂ ), and the area corresponding to the third phase difference plate 4C(a ₃ ) is the fourth phase difference plate In the plate 4D(a ₄ ), the region corresponding to the fifth phase difference plate 4E(a ₅ ) is the sixth phase difference plate 4F(a ₆ ). Here, in each area, the retardation value in the thickness direction can be adjusted according to the width of the visual field area to be observed in one area.

Since the retardation plate 4 constitutes each region in a single holding member 41 as described above, in the inspection apparatus 100, regions having the same Re (550) can be used in pairs. That is, the retardation plate 4 is formed in a structure suitable for simultaneously providing the first retardation plate 4A and the second retardation plate 4B. By using the paired first retardation plate 4A and the second retardation plate 4B, and then sliding the retardation plate 4, the paired third retardation plate 4C and the fourth retardation plate 4D can be used, and further Paired fifth retardation plate 4E and sixth retardation plate 4F.

In order to observe the light reflected by the defective part inside the object to be inspected 10, a CCD camera or the like may be arranged on the optical path of the reflected light and at a position on the light source 2 side on both sides of the second phase difference filter 3B. detection means 5. For example, the inspection of the object to be inspected can be performed by automatic detection by image processing analysis performed by a combination of a CCD camera and an image processing device. Alternatively, the detection means 5 may be The second phase difference filter 3B is to be visually observed by a person rather than a device member. In addition, a partition plate may be appropriately provided between the light source 2 and the CCD camera.

Further, the inspection apparatus 100 preferably includes a movable device (not shown) that can move the object 10 to be inspected, the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, the third retardation plate 4C, and the At least one of the four-phase difference plate 4D, the first phase-difference filter 3A, and the second phase-difference filter 3B is inclined so that the angles facing each other are different, or the inspection object 10, the first phase-difference plate 4A, At least one of the second phase difference plate 4B, the third phase difference plate 4C, the fourth phase difference plate 4D, the first phase difference filter 3A, and the second phase difference filter 3B is perpendicular to the optical path 9 of the light direction rotation. These inclinations can finely adjust the retardation of the release film 16a made of PET-based resin, the first retardation film 4A, the second retardation film 4B, the third retardation film 4C, and the fourth retardation film 4D. , and a wider range of checks can be performed. Moreover, by these rotations, the axis of the release film 16a made of PET-based resin, the first retardation plate 4A, the second retardation plate 4B, the third retardation plate 4C, and the fourth retardation plate 4D can be adjusted. Easy to align.

(Inspection Method)

The inspection method using the inspection apparatus 100 is as follows. First, the object to be inspected 10 is placed inside the inspection apparatus 100 on the side facing the first retardation plate 4A and the second retardation plate 4B when viewed from the light source 2 . At this time, the surfaces of these films are arranged in parallel, and the side of the inspection object 10 with the release film 16 a or the retardation film 14 is directed to the side of the light source 2 , and the circular polarizer 1 and the first retardation filter are The device 3A constitutes crossed polarized light. Here, for the first retardation plate 4A and the second retardation plate 4B, the retardation plate 4 shown in FIG. 3 is used, and the light before incident on the object to be inspected 10 passes through the first retardation plate 4A and the light reflected by the inspection object 10 is incident on the second retardation plate 4B.

Next, the first phase difference filter 3A and the second phase difference filter 3B are adjusted to constitute orthogonally polarized light. When the inspection apparatus 100 is provided with the above-mentioned movable device, after the object 10 to be inspected is inserted in an arbitrary direction, the relative positional relationship of each film can be changed by the movable device so as to be orthogonally polarized.

The light train enters the first phase difference filter 3A from the light source 2 . At this time, the incident angle of the object to be inspected 10 (an angle based on the vertical line of the surface of the object to be inspected 10 ) is preferably 3° to 30°, more preferably 5° to 20°. When the light emitted from the light source 2 is light with low directivity, it is preferable that the reflection angle reflected from the test object 10 (or the observation angle detected by the detection means 5 ) falls within the above-mentioned angle range.

The light emitted from the light source 2 is incident on the first phase difference filter 3A, passes through the first phase difference filter 3A, becomes circularly polarized light, and then passes through the first phase difference plate 4A (optical path 9a). The light passing through the first retardation plate 4A is then incident on the object to be inspected 10 , passes through the release film 16 a in the object to be inspected 10 , and is converted into linearly polarized light by the retardation film 14 constituting the circular polarizer 1 , and finally The polarizing film 11 absorbs (the end of the optical path 9a). Here, part of the light passing through the first retardation plate 4A is reflected by the surface of the release film 16a in the object to be inspected 10 (optical path 9b). Since the first phase difference filter 3A and the second phase difference filter 3B are arranged to constitute orthogonally polarized light, the reflected light is blocked by the second phase difference filter 3B (the end of the optical path 9b). Therefore, the detection means 5 The observed field of view of the second phase difference filter 3B becomes dark.

On the other hand, part of the light incident on the object to be inspected 10 is due to defects existing in the object to be inspected 10 (defect D existing in the interface between the retardation film 14 and the polarizing film 11 , defects existing in the retardation film 14 Defect D' etc.) to enhance reflection (optical path 9c). Since the phase difference deviates from the ideal state (undesired elliptical polarization) due to the defects D and D', the reflected light is not absorbed by the polarizing film, and the reflected light at the interface is generated. The reflected light passes through the second phase difference filter without being blocked by the second phase difference filter. When viewed from the detection means 5 side, the defective portion is observed as a bright spot.

In addition, the first retardation plate 4A is designed to effectively compensate the birefringence of light caused by the peeling film 16a to make the retardation value and the wavelength dispersion characteristic of the peeling film 16a as consistent as possible, however, due to peeling The in-plane unevenness of the retardation value of the film 16a makes it difficult to sufficiently block light in the entire inspection field to perform inspection. In this case, in the circularly polarizing plate 1 , the part where the retardation value of the retardation film 14 is reduced is matched by optical compensation, which may cause defects that should be observed as bright spots to be observed as black spots. In general, since black spot defects have less influence on viewing confirmation than bright spot defects, even if the defect size of black spot defects is larger than that of bright spot defects, it is acceptable in many cases, and it is judged that there is no problem. However, if the black spot defect should be observed as a bright spot defect in the retardation value-decreasing portion of the retardation film 14 , the influence on the visibility is increased and becomes a problem.

Therefore, in the present embodiment, the third retardation plate 4C having an in-plane retardation different from that of the first retardation plate 4A and the second retardation plate 4B is used for the defect portion confirmed as a black spot by observation. and the fourth retardation plate 4D. Specifically, the holding member 41 constituting the retardation plate 4 is slid along the surface direction thereof, and the third retardation plate 4C and the fourth retardation plate 4D are positioned on the optical path 9 instead of the first retardation plate 4A and the second retardation plate 4B. A second check is performed with this configuration.

In this way, by performing a plurality of inspections using retardation plates with different in-plane retardation values, the possibility of observing defects as bright spot defects increases, and it becomes easy to accurately identify defects. Here, even if the paired third retardation plate 4C and the fourth retardation plate 4D are used for inspection, if the black spot is confirmed by re-observation, the holding member 41 is moved further toward the paired fifth retardation plate 4E and the second retardation plate 4E. The six retardation plate 4F is slid, and the third inspection is performed.

During inspection, at least one of the object 10 , the first phase difference plate 4A, the second phase difference plate 4B, and the first phase difference filter 3A and the second phase difference filter 3B may be inclined so as to face each other. The angle of the inspection object 10, the first retardation plate 4A, the second retardation plate 4B, And at least one of the first phase difference filter 3A and the second phase difference filter 3B rotates in a direction perpendicular to the optical path 9 of the light. By inclination, the retardation of the peeling film 16a, the 1st retardation plate 4A, the 2nd retardation plate 4B, etc. can be finely adjusted, and inspection of a wider range can be performed. Moreover, by these rotations, the release film 16a made of PET-based resin can be easily aligned with the axes of the first retardation plate 4A and the second retardation plate 4B. Such operations can be performed particularly easily when the inspection apparatus 100 is provided with a movable apparatus.

In addition, in the inspection method of the present invention, as for the light from the light source 2, for example, light with a single wavelength or light with a narrow wavelength width is used, whereby defects in which the retardation value is partially shifted can also be detected. Specifically, when the light source uses the transmission axis of the polarizing film of the circularly polarizing plate 1 included in the test object 10 and the transmission axis of the polarizing plate included in the retardation filter that converts the polarizing plate into linearly polarized light, and the transmission axis is arranged so as not to form crossed polarized light , the light of the wavelength at which the amount of transmitted light becomes the smallest. At this time, the first phase difference filter 3A and the phase difference film 14 are arranged to face each other. When there are plural wavelengths, it is preferable to select a wavelength in the range of 500 to 600 nm. Furthermore, when the light source has a half-value width of an intensity peak of 30 nm or less, the inspection accuracy can be improved.

According to the inspection method shown above, the third retardation plate 4C and the fourth retardation plate 4D are used to inspect the black defect observed in the inspection using the paired first retardation plate 4A and the second retardation plate 4B. By this, the phase difference can be adjusted so that the part where the black defect is observed can be observed as a bright spot defect. In addition, since this inspection method is a reflection type inspection method, the optical path length in the object to be inspected 10 is longer than that of the transmission type inspection method, so that wrinkles which are difficult to be detected even in the transmission type inspection method Equal deformation defects can also be easily detected. In summary, the inspection method of the present embodiment can easily determine whether the circularly polarizing plate has defects.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to any of the above embodiments. For example, the above-mentioned embodiment shows the first phase difference filter 3A and the first phase difference plate 4A They are independent items, however, the first phase difference filter 3A and the first phase difference plate 4A may be a laminated body laminated with each other to form a single film.

[Industrial availability]

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

1: Circular polarizer

2: light source

3A: First phase difference filter

3B: Second phase difference filter

4: Phase difference plate

4A: The first phase difference plate

4B: Second retardation plate

5: Detection means

9,9a,9b,9c: Optical path

10: Object to be inspected

11: polarizing film

14: retardation film

16a: Release film

16b: Surface protection film

100: Inspection device

D, D': Defect

Claims (5)

An inspection method for judging whether a film-shaped inspected object is defective or not, the inspected object is provided with a circular polarizing plate laminated with a polarizing film and a retardation film, and the circular polarizing plate is laminated on the retardation film side of the circular polarizing plate and is formed by the polarizing film. Release film composed of ethylene terephthalate resin, In the inspection method, a light source, a first retardation filter, a first retardation plate, and the object to be inspected are arranged in this order on the optical path of the light emitted by the light source, and the second retardation plate is placed on the optical path of the light emitted by the light source. , and a second phase difference filter, arranged in this order on the optical path of the light reflected by the object to be inspected, wherein, The in-plane retardation value of the first retardation plate for light with a wavelength of 550 nm is approximately the same as the in-plane retardation value of the peeling film for light with a wavelength of 550 nm, and the birefringence of the peeling film is compensated; The side of the peeling film of the object to be inspected is directed to the side of the first retardation plate; The in-plane retardation value of the second retardation plate for light with a wavelength of 550 nm is approximately the same as the in-plane retardation value of the first retardation plate for light with a wavelength of 550 nm, and it compensates the first retardation plate. have birefringence; The second phase difference filter and the first phase difference filter form orthogonally polarized light; and, In the inspection method, the light of the light source is incident on the first phase difference filter, and the light reflected by the object to be inspected is observed from the side of the second phase difference filter to determine whether the circularly polarizing plate is defective or not. ; Replace the first retardation plate and the second retardation plate with a third retardation plate and a fourth retardation plate respectively, and the surfaces of the third retardation plate and the fourth retardation plate for light with a wavelength of 550 nm internal phase The difference is 50 to 100 nm larger than the in-plane retardation of the aforementioned peeling film for light with a wavelength of 550 nm, and compensates for the birefringence of the aforementioned peeling film; After replacement, light is incident on the first phase difference filter, and the light reflected by the object to be inspected is observed from the second phase difference filter side to determine whether the circularly polarizing plate is defective. The inspection method according to claim 1, wherein the retardation film includes a cured product of a polymerizable liquid crystal compound. The inspection method according to claim 1 or 2, wherein in the inspection, the object to be inspected, the first retardation plate, the second retardation plate, the third retardation plate, and the fourth retardation plate are At least one of the plate, the first phase difference filter, and the second phase difference filter is inclined so that the angles facing each other are different, or, during inspection, the inspection object, the first phase difference plate, the At least one of the second phase difference plate, the third phase difference plate, the fourth phase difference plate, the first phase difference filter, and the second phase difference filter rotate in a direction perpendicular to the optical path . The inspection method according to any one of claims 1 to 3, wherein the first retardation plate and the third retardation plate are arranged in the same member. The inspection method according to any one of claims 1 to 4, wherein the first retardation plate and the second retardation plate are arranged in the same member.

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