CN116519711A - Inspection Method - Google Patents

Abstract

The invention provides a reflection type inspection method, which can easily judge whether a circular polarizing plate has defects. An inspection method for judging whether or not a film-like object (10) is defective, wherein the object (10) comprises: a circular polarizing plate (1) in which a polarizing film (11) and a phase difference film (14) are laminated, and a release film (16 a) which is laminated on the phase difference film (14) side of the circular polarizing plate (1) and contains polyethylene terephthalate resin. A light source (4), a band-pass filter (2) transmitting light of a predetermined wavelength, a 1 st polarization unit (3A), an object (10) to be inspected, and a 2 nd polarization unit (3B) are arranged, and the incidence angle [ theta ] of the light to the object (10) to be inspected is changed so as to reduce the influence of the phase difference of a release film (16 a). The light reflected by the inspected object (10) is observed from the 2 nd polarization part (3B) side to judge whether the circular polarization plate (1) has defects.

Description

Inspection Method

technical field

The present invention relates to inspection methods.

Background technique

Polarizing plates used in liquid crystal display devices, organic EL display devices, and the like are generally configured such that a polarizing plate is sandwiched between two protective films. In order to stick the polarizing plate to the display device, an adhesive layer is laminated on one protective film, and a release film is further laminated on the adhesive layer. Moreover, the peeling film (surface protection film) which protects the surface is also bonded to the other protective film in many cases. The polarizing plate is circulated and transported in a state where the release film is laminated in this way, and when it is bonded to the display device in the manufacturing process of the display device, the release film is peeled off.

However, in the production stage of the polarizing plate, foreign substances or residual bubbles may be mixed between the polarizing plate and the protective film, or when the protective film has the function of a retardation film, there may be alignment defects inside (hereinafter, sometimes referred to as These foreign matter, air bubbles, and alignment defects are collectively referred to as "defects"). When a defective polarizing plate is bonded to a display device, the defective site may be visually recognized as a bright spot, or image distortion may be observed at the defective site. In particular, defects that are visually recognized as bright spots are easily visually recognized when the display device displays black.

Therefore, the inspection for detecting the defect of this polarizing plate is performed in the previous stage (polarizing plate of the state provided with the peeling film) of a polarizing plate being bonded to a display device. The inspection of this defect is generally an optical inspection using the polarization axis of a polarizing plate. Specifically, as shown in Patent Document 1, a polarizing filter is provided between a polarizing plate as an object to be inspected and a light source, and the polarizing plate or polarizing filter is rotated in a plane direction so that their respective polarization axes Direction becomes a specific relationship. In the case where the directions of the polarization axes are perpendicular to each other (that is, when crossed Nicols are arranged), the linearly polarized light passing through the polarizing filter cannot pass through the polarizing plate. However, if there is a defect in the polarizing plate, linearly polarized light is transmitted through the portion, so the presence of the defect can be clarified 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, linearly polarized light having passed through the polarizing filter is transmitted through the polarizing plate. However, if there is a defect in the polarizing plate, the linearly polarized light is blocked at that portion, and therefore, the presence of the defect is determined by not detecting the light. Inspectors can inspect the polarizing plate for defects by visually detecting the light transmitted through the polarizing plate, or by automatically detecting an image analysis value obtained by combining a CCD camera and an image processing device.

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. 9-229817

Contents of the invention

The problem to be solved by the invention

In the case where the polarizing plate is a circular polarizing plate and the release film contains a polyethylene terephthalate-based resin (PET-based resin), the retardation filter that matches the wavelength dispersion of the PET-based resin to some extent A sheet (equivalent to the above-mentioned polarizing filter) is used for inspection of the polarizing plate. Here, when the circular polarizing plate and the retardation filter are arranged so as to constitute crossed Nicols, the defect is visually recognized as a bright spot according to the above principle, but the phase of the circular polarizing plate has For areas with low retardation values such as alignment defects and pinholes in the poor film, bright spot defects may be visually recognized as black spots. In this case, detection and judgment are more difficult than detection of bright spots. This tendency is remarkable especially when the circularly polarizing plate includes a retardation film containing a cured product of a polymerizable liquid crystal compound.

In addition, the principle of the inspection method disclosed in Patent Document 1 is to observe light transmitted through the object to be inspected. In this principle, when there are deformation defects in the inspected object (for example, wrinkles generated when the circular polarizing plate is cut), the optical path length will hardly change between the normal part and the deformed defect part. detection of deformation defects.

In addition, as mentioned above, when the polarizing plate is equipped with a release film, the polarization characteristics of the circular polarizing plate are hindered by the birefringence of the release film, so the existing inspection equipment cannot accurately test the polarizing plate. Defects such as bright spots in the

Therefore, an object of the present invention is to provide a reflective inspection method capable of easily determining whether a circularly polarizing plate has a defect.

means of solving problems

The present invention provides an inspection method, which is an inspection method for judging the presence or absence of defects in a film-shaped object to be inspected. A release film made of a polyethylene terephthalate-based resin on the retardation film side, a light source, a band-pass filter that transmits light of a predetermined wavelength, a first polarizer, and the release film side facing the first The objects to be inspected on the polarizer side are arranged sequentially on the optical path of light emitted by the light source, and the first polarizer and the second polarizer constituting a crossed Nicol prism are arranged on the optical path of light reflected by the object to be inspected, Both the 1st polarizer and the 2nd polarizer are left-handed circular polarizers or right-handed circular polarizers, and when the 1st polarizer and the 2nd polarizer are viewed from the light source side, the polarizing film that the 1st polarizer has The absorption axis and the absorption axis of the polarizing film included in the second polarizing part are oriented in directions perpendicular to each other, the light from the light source is incident on the bandpass filter, and the incident angle of the light relative to the object to be inspected is changed so that the peeling film has The influence of the phase difference becomes small, and the light reflected by the object to be inspected is observed from the second polarizing part side to judge whether there is a defect in the circularly polarizing plate.

In this inspection method, the first polarizer and the second polarizer are arranged to constitute a crossed Nicol prism. Therefore, the light reflected by the normal part of the object to be inspected (for example, the light reflected by the surface of the release film) Light) is blocked by the second polarizer, so the observation field can be made sufficiently dark, and when there is a defective part, it is easy to observe it as a bright spot. The light reflected by the defect part generated inside the object to be inspected and the light reflected after passing through the defect part have a phase difference that deviates from the ideal due to the defect (becomes undesired elliptically polarized light). Therefore, only The degree of this deviation can be detected as a defective part of the object to be inspected through the second polarizing part. Here, it is expected that due to the phase difference of the release film, the brightness of the entire observation field will increase, which will hinder defect detection. However, in this inspection method, the incident angle of light with respect to the object to be inspected is changed so that the release film The influence of the phase difference has becomes small, that is, the incident angle of the light is changed so that the phase difference exhibited by the release film is close to an integer multiple of the wavelength of the incident light, so even if the release film has a phase difference, the It can make the observation field dark enough. In addition, such a reflection-type inspection method has a longer optical path in the object to be inspected than a transmission-type inspection method, so deformation defects that are difficult to detect by a transmission-type inspection method can be easily detected. For the above reasons, the presence or absence of defects in the circularly polarizing plate can be easily judged by the inspection method of the present invention.

In this inspection method, since reflected light from various types of films is captured, it is advantageous to use, as inspection light, a wavelength at which the interference of each reflected light becomes relatively strong in defect detection. From this point of view, it is preferable to calculate the wavelength dependence of interference reflected light in the front direction from the average refractive index and thickness of the retardation film before inspection, and obtain the wavelength at which the reflection intensity reaches the maximum in the wavelength range of 500nm to 600nm. , it is decided to adopt the wavelength within ±20nm of the wavelength as the specified wavelength.

In this inspection method, it is preferable that the circularly polarizing plate and the second polarizing unit included in the object to be inspected be arranged so as to constitute a crossed Nicol prism. In this way, the observation field of view can be made darker.

The retardation film may contain a cured product of a polymerizable liquid crystal compound. In the case where the retardation film contains a cured product of a polymerizable liquid crystal compound, the possibility of seeing black spot defects increases due to its general thickness. Therefore, it is suitable as an object to which the present invention is applied.

Invention effect

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

Description of drawings

FIG. 1 is a configuration diagram of an inspection device for performing an inspection method according to a first embodiment.

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

3(A) and (B) are graphs showing the wavelength dependence of the reflection intensity index of the λ/4 film.

FIG. 4 is a diagram showing the arrangement relationship of each polarizing film and each retardation film.

FIG. 5 is a diagram illustrating the influence of the phase difference that a release film has.

FIG. 6 is a diagram showing the arrangement relationship of each polarizing film and each retardation film.

Detailed ways

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code|symbol is attached|subjected to the same part or a corresponding part, and repeated description is abbreviate|omitted.

＜Definition of terms and symbols＞

Definitions of terms and symbols in this specification are as follows.

(1) Refractive index (nx, ny, nz)

"nx" is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow axis direction), "ny" is the in-plane direction perpendicular to the slow axis, and "nz" is the refractive index in the thickness direction.

(2) In-plane phase difference

The in-plane retardation value (Re(λ)) refers to the in-plane retardation value of the film at 23° C. and wavelength λ (nm). Re(λ) is obtained by Re(λ)=(nx-ny)×d when the thickness of the film is d (nm).

＜Inspection equipment and objects to be inspected＞

The inspection device of this embodiment inspects the surface of the circularly polarizing plate, between layers constituting the circularly polarizing plate, or inside each layer for defects. As shown in FIG. 1 , the inspection apparatus 100 is sequentially arranged with a light source 4 , a bandpass filter 2 , and a phase difference filter 3 . In addition, the inspection apparatus 100 further includes an inspection table 20 on which the object 10 to be inspected is placed on the opposite side of the phase difference filter 3 when viewed from the light source 4 . The surface of the inspection table 20 is processed to suppress reflection of light.

FIG. 1 shows a state where an inspection object 10 is placed on an inspection table 20 . The phase difference filter 3 is formed by arranging two wide-band circular polarizing plates 3A and 3B adjacent to each other on substantially the same plane. The two circular polarizing plates respectively constitute: The first polarizer 3A is the region where it enters, and the second polarizer 3B is the region where light reflected by the object 10 to be inspected, which will be described later, enters. A left-handed circular polarizer or a right-handed circular polarizer is used for both the first polarizer 3A and the second polarizer 3B. In addition, the first polarizing part 3A and the second polarizing part 3B are arranged in such a manner that the absorption axis of the polarizing film included in the first polarizing part 3A and the axis of the polarizing film included in the second polarizing part 3B are arranged as viewed from the light source 4 side. The absorption axes are oriented in directions orthogonal to each other (crossed Nicols). The first polarizer 3A and the second polarizer 3B employ so-called defect-free polarizers.

As shown in FIG. 2 , the object 10 to be inspected is in the form of a film, and includes a circularly polarizing plate 1 as a main body to be inspected, and a release film 16 a laminated on the circularly polarizing plate 1 via an adhesive layer 15 . Circularly polarizing plate 1 is formed by bonding protective films 12a and 12b on both sides of a polarizing film 11, and further forming a retardation film 14 via an adhesive layer 13 on the protective film 12a on the side provided with a release film 16a. . Moreover, the surface protection film 16b is laminated|stacked on the surface of the circularly polarizing plate 1 which does not have the peeling film 16a. The circularly polarizing plate 1 is generally used in a display device, such as a liquid crystal display device or an organic EL display device, and the peeling film 16 a is peeled off during use, and is attached to the display device through the adhesive layer 15 .

The polarizing film 11 is a film that converts light incident from the surface protection film 16 b side into linearly polarized light. As the polarizing film 11, for example, a polarizing film obtained by adsorbing iodine and a dichroic dye to a polyvinyl alcohol film and aligning it; The material and the polarizing film obtained by orientation.

The protective films 12a and 12b are used to protect the polarizing film 11 . As the protective films 12a and 12b, for the purpose of obtaining a polarizing plate having moderate mechanical strength, protective films widely used in the technical field of polarizing plates are used. Typical: Cellulose ester film such as cellulose triacetate (TAC) film; Cyclic olefin film; Polyester film such as polyethylene terephthalate (PET) film: Polymethyl methacrylate (PMMA) film and other (meth)acrylic films, etc. In addition, additives widely used in the technical field of polarizing plates may be contained in the protective film.

Since the protective films 12a and 12b are bonded to the display device together with the polarizing film 11 as constituent elements of the circularly polarizing plate 1, strict management of retardation values and the like are required. As the protective film 12a, typically, a protective film having an extremely small retardation value is preferably used. Protective films 12a and 12b are bonded to polarizing film 11 via an adhesive.

The retardation film 14 is a film that converts light that is incident from the surface protection film 16b side and linearly polarized by the polarizing film 11 into circularly polarized light. The retardation film 14 is a film that converts circularly polarized light incident from the release film 16a side into linearly polarized light when viewed from the release film 16a side. Therefore, the retardation film 14 includes at least a λ/4 film. In addition, the retardation film 14 may be further laminated with a λ/2 film. In this case, the order of the λ/2 film and the λ/4 film may be used from the side closer to the polarizing film 11 .

In addition, the retardation film 14 preferably contains a cured product of a polymerizable liquid crystal compound. The retardation film 14 made of a cured product of a polymerizable liquid crystal compound is generally thin, about 0.2 μm to 10 μm in thickness, and if it contains foreign matter, the retardation value tends to change in this portion. In such a portion, the linearly polarized light cannot be converted into the ideal circularly polarized light, and becomes undesired elliptically polarized light. In addition, as will be described later, there may be cases where black spots are observed even though they should be observed as bright spot defects during inspection.

Examples of polymerizable liquid crystal compounds that can form the retardation film 14 include JP-A-2009-173893, JP-A-2010-31223, WO2012/147904, WO2014/10325, and WO2017-43438. A polymerizable liquid crystal compound disclosed in the gazette. The polymerizable liquid crystal compounds described in these gazettes can form a retardation film which can achieve the same polarization conversion over a wide wavelength range and has so-called reverse wavelength dispersion. For example, by coating a solution (polymerizable liquid crystal compound solution) containing this polymerizable liquid crystal compound on a suitable substrate and performing photopolymerization, an extremely thin retardation film can be formed as described above, and therefore has the above-mentioned phase The circular polarizing plate of the poor film can be formed into an extremely thin circular polarizing plate. Thus, an extremely thin circularly polarizing plate is advantageous as a circularly polarizing plate for flexible display materials that has attracted attention in recent years.

Examples of the substrate on which the polymerizable liquid crystal compound solution is applied include those described in the above-mentioned gazettes. An alignment film may be provided on the substrate to align the polymerizable liquid crystal compound. The alignment film may be any of an alignment film that is photo-aligned by irradiation with polarized light, and an alignment film that is mechanically aligned by rubbing. It should be noted that the above-mentioned alignment film is also described in the above-mentioned gazette.

However, when foreign matter or the like is present in the substrate on which the polymerizable liquid crystal compound solution is applied, or the substrate itself has flaws, defects may occur in the coating film itself obtained by applying the polymerizable liquid crystal compound solution. In addition, when the alignment film is rubbed, scraps of the rubbing cloth remain on the alignment film, which also causes defects in the coating film of the polymerizable liquid crystal compound solution (composition for forming a liquid crystal cured film). As described above, although a retardation film formed of a polymerizable liquid crystal compound can be formed with an extremely thin thickness, there is a factor of causing defects. In addition, the defects of the retardation film may be observed as black spots, as will be described later. The inspection method of this embodiment is particularly useful in the inspection for determining the presence or absence of defects in an object to be inspected having a circularly polarizing plate and a release film having defects (defects observed as black spots) retardation film.

The retardation film 14 can be produced by coating a composition for forming an alignment film on a substrate, and further coating a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound thereon. The retardation film 14 produced in this way can be transferred to the protective film 12a by bonding the retardation film 14 produced in this way to the adhesive layer 13 formed on the protective film 12a together with a base material, and peeling the base material.

In the inspection method of this embodiment, according to the retardation value of the peeling film 16a, when using the circular polarizing plate used as the first polarizing part 3A and the second polarizing part 3B, the rotation direction (left-handed or right-handed) and the circular polarizing plate are determined. The rotation directions of the circular polarizing plates 1 in the inspection object 10 are the same or different. Details will be described later.

The release film 16a is peeled from the circularly polarizing plate 1 when it is bonded to the display device, and the peeled release film 16a is usually discarded. Therefore, unlike the protective films 12a and 12b, strict management of the retardation value is not required. Therefore, when a commercially available film is used as the release film 16a, if the retardation value is not compensated, malfunction may be caused in the defect inspection. That is, in the defect inspection of the circularly polarizing plate 1 bonded with the release film 16 a whose retardation value is not strictly controlled, the retardation of the release film 16 a may cause a decrease in the inspection accuracy of the inspection apparatus 100 .

In addition, as described in the said background art, in the circularly polarizing plate 1, the surface protection film 16b which is 1 type of release films is provided on the surface opposite to the release film 16a in many cases. In the circularly polarizing plate 1 shown in FIG. 2 , a surface protective film 16 b is bonded to the protective film 12 b side. This surface protective film 16b is also usually peeled from the circular polarizing plate 1 when it is bonded to the display device, and unlike the protective films 12a and 12b, strict management of the retardation value is not required. It should be noted that, in Fig. 2, the protective film 12b and the surface protective film 16b can be pasted by means of a suitable adhesive layer or adhesive layer (in Fig. 2, the adhesive layer or adhesive layer has not been icon).

In this embodiment, the peeling film 16a contains PET-type resin. In addition, the surface protection film 16b also uses the film containing PET-type resin. Films containing PET-based resins (PET-based resin films) are widely used as release films, and have an advantage of being inexpensive. On the other hand, an inexpensive PET-based resin film does not require strict management of the retardation value as described above. Therefore, for example, the phase difference value sometimes deviates between each product lot. In addition, even with the same PET resin film, there may be variations in the retardation value within the plane. Even a circularly polarizing plate bonded together with such an inexpensive PET resin-based film as a release film can detect the presence or absence of defects with high precision by the inspection method of this embodiment.

The retardation value (Re(550)) of the in-plane direction of the peeling film 16a of this embodiment is, for example, 1500 nm - 3000 nm.

Here, the method of calculating Re(550) of the release film 16a is shown in advance. As mentioned above, these release films are PET-based resin films, and such films are readily available from the market. From this film, pieces having a size of, for example, about 40 mm×40 mm are obtained by dividing (dividing and obtaining from a long film using an appropriate cutting tool, etc.). The Re(550) of this sheet was measured three times, and the average value of Re(550) was calculated|required. Re(550) of the sheet can be measured at a measurement temperature of room temperature (about 25° C.) using a retardation measuring device KOBRA-WPR (manufactured by Oji Scientific Instruments, Ltd.). In addition, when Re(550) of the surface protection film 16b is calculated|required, the same test should just be performed.

Various commercially available products can be used as the light source 4 , for example, linear light (including light similar to linear light) such as laser light is advantageous. The light emitted from the light source 4 is unpolarized light, and passes through a first polarizing unit 3A described later to become circularly polarized light.

In order to observe the light reflected from the object 10 to be inspected, a detection unit 5 including a CCD camera or the like may be arranged on the optical path of the reflected light and on the side where the light source 4 is located on both sides of the second polarizer 3B. For example, the inspection of the object to be inspected can be performed by automatically performing detection through image processing analysis obtained by combining a CCD camera and an image processing device. Alternatively, the detection unit 5 may not be a member, but a person may visually observe the second polarizing unit 3B. In addition, it may be appropriate to have a spacer plate between the light source 4 and the CCD camera.

In addition, the inspection apparatus 100 preferably includes a mechanism for tilting or rotating the inspection table 20, or a mechanism for tilting or rotating the arrangement of the light source 4, the band-pass filter 2, and the phase difference filter 3 so that the light relative to the inspection object 10 The incident angle θ changes. By operating these mechanisms, the phase difference exhibited by the release film 16a can be adjusted, and the brightness of the observation field can be dimmed to be suitable for inspection.

＜Inspection method＞

Hereinafter, a method of inspecting a circularly polarizing plate using the inspection apparatus 100 will be described. The inspection method of this embodiment includes: a step of selecting the wavelength of light (inspection light) used for inspection (hereinafter referred to as "inspection wavelength") (wavelength selection step); and a step of performing inspection using light of the wavelength. (defect inspection process).

(wavelength selection process)

The inspection wavelength is selected before starting the inspection of the inspection object 10 including the circular polarizing plate 1 . In the present embodiment, the inspection light is selected based on the optical characteristics of the retardation film for the purpose of detecting a defect of the retardation film 14 . When the retardation film 14 has a plurality of layers, for example, a λ/2 film and a λ/4 film, or a λ/4 film and a positive C film, the retardation film (for example, λ /4 film) just select the inspection light. For the retardation film, generally, the wavelength dependence of interference reflected light in the front direction can be calculated based on the in-plane average refractive index and thickness thereof. An example of this calculation is shown in FIG. 3 . 3(A) shows the wavelength dependence of the reflection intensity index of a λ/4 film having an in-plane average refractive index ((nx+ny)/2)) of 1.58 and a thickness of 2.85 μm at a wavelength of 550 nm. FIG. 3(B) shows the wavelength dependence of the reflection intensity index of a λ/4 film having an in-plane average refractive index of 1.62 and a thickness of 2.10 μm at a wavelength of 550 nm. Any graph is a waveform, and many λ/4 films tend to draw such a waveform.

In the inspection method of this embodiment, since reflected light from various films is captured, it is advantageous in defect detection to use a wavelength at which interference of reflected light in the retardation film 14 becomes relatively strong as inspection light. From this point of view, in this embodiment, a wavelength with a high reflection intensity index is used for inspection. For example, in the graphs of FIG. 3(A) and (B), since the reflection intensity index increases in common at wavelengths around 540 nm and 580 nm, it is preferable to use these wavelengths. In particular, these wavelengths have high visibility and are preferably within a range from 500 nm to 600 nm, which is also a design wavelength of the retardation film. The wavelengths within ±20 nm, within ±10 nm, or within ±5 nm of these wavelengths are decided to be used as the wavelengths of the inspection light. That is, for example, a band-pass filter that transmits light with a wavelength of 540 nm and a band-pass filter that transmits light with a wavelength of 580 nm are prepared.

(Defect inspection process)

In the defect inspection process, the incident angle of light is adjusted so that the influence of the retardation of the peeling film 16a becomes small. At this time, it is preferable to adjust so that the incident angle θ of light with respect to the inspection object 10 (the angle based on the perpendicular to the surface of the inspection object 10 ) becomes 30° or less. More preferably, it is adjusted to be 20° or less. If the incident angle θ of light on the inspection object 10 exceeds 30°, the length of the optical path passing through the release film 16a becomes longer, and the interference of wavelengths determined as inspection light becomes weaker, which may lower inspection sensitivity. Therefore, as a defect inspection process, according to the retardation value of the peeling film 16a, any one of the two conditions ([1] and [2]) described below is selected and inspected. With this selection, it is easy to perform inspection within a range where the incident angle θ does not exceed 30°.

[1] Inspection when the retardation value of the release film 16a is adjusted to an integer multiple of the inspection wavelength

Inspection is performed using a bandpass filter that transmits light of a wavelength found in the wavelength selection step. FIG. 4 is a diagram showing the arrangement relationship of each polarizing film and each retardation film. The two arrows in the figure indicate the absorption axis of the polarizing film or the slow axis of the retardation film. As shown in FIG. 4 , a case where the retardation film 14 includes only the λ/4 film 14 a as the retardation film is considered. In the case where the retardation value of the peeling film 16a can be adjusted to an integer multiple of the inspection wavelength, as described above, the absorption axis of the polarizing film 3a included in the first polarizing section 3A and the absorption axis of the polarizing film 3a included in the second polarizing section 3B can be adjusted. The absorption axis of the polarizing film 3c is arranged in a direction perpendicular to each other, and the first polarizing part 3A (including the polarizing film 3a and the retardation film 3b.) and the circular polarizing plate 1 in the object 10 to be inspected are arranged The relationship is a parallel Nicol prism (Japanese: パララニコル), and the relationship between the circular polarizing plate 1 and the second polarizer 3B (with a polarizing film 3c and a retardation film 3d.) is a crossed Nicol prism. mode configuration. In this case, when the circular polarizing plate 1 in the inspection object 10 is a right-handed circular polarizing plate, as the first polarizing portion 3A and the second polarizing portion 3B, a left-handed circular polarizing plate is used (refer to FIG. 4's two-arrow symbol). Conversely, when the circular polarizing plate 1 in the inspection object 10 is a left-handed circular polarizing plate, a right-handed circular polarizing plate is used as both the first polarizing portion 3A and the second polarizing portion 3B.

As shown in FIG. 1 , an inspection object 10 is placed on an inspection table 20 inside the inspection apparatus 100 . At this time, the side provided with the release film 16 a and the retardation film 14 in the inspection object 10 is directed toward the light source 4 side.

A band-pass filter 2 that transmits light of a wavelength (for example, 540 nm) found in the wavelength selection step is prepared and placed in the inspection device 100 . Light is made incident on the bandpass filter 2 from the light source 4 .

The light emitted from the light source 4 passes through the bandpass filter 2, and then enters the first polarizing unit 3A, passes therethrough, and becomes circularly polarized light (optical path 9a). The transmitted light then enters the inspection object 10 . Then, it passes through the peeling film 16a in the inspection object 10, ideally passes through the retardation film 14 constituting the circular polarizing plate 1, is converted into linearly polarized light, and is finally absorbed by the polarizing film 11 (end of the optical path 9a). Here, part of the light transmitted through the first polarizer 3A is reflected on the surface of the release film 16 a in the inspection object 10 (optical path 9 b ). The reflected light is blocked by the second polarizer 3B because the first polarizer 3A and the second polarizer 3B constitute a crossed Nicol prism (the end of the optical path 9b). The inspection light is thus absorbed and blocked, whereby the observation field by the second polarizing unit 3B of the detection unit 5 becomes dark.

On the other hand, when there is a defect D (for example, a defect existing at the interface between the retardation film 14 and the polarizing film 11, a defect existing in the retardation film 14) in the inspection object 10, the reflection becomes stronger at this portion. (light path 9c). Due to the defect D, the reflected light deviates from the ideal phase difference (becomes undesired elliptically polarized light). These reflected lights are transmitted without being blocked by the second polarizer 3B. When it is observed from the detection unit 5 side, the defective portion is observed as a bright spot.

Here, the phase difference (in-plane phase difference) of the peeling film 16a may become an obstacle to this inspection. That is, when the phase difference exhibited by the release film 16a becomes an integer multiple of the wavelength of the light transmitted through the bandpass filter 2, the polarization state of the circularly polarized light incident on the release film 16a will not be disturbed, but at In most cases, it does not become an integer multiple, therefore, the polarization state of circularly polarized light is disordered, cannot be converted into linearly polarized light by the retardation film 14, is difficult to be absorbed by the polarizing film 11, and reflected light (optical path 9d of FIG. 5 ) is generated at its interface . Therefore, the amount of transmitted light transmitted through the second polarizer 3B increases, and the brightness of the observation field increases. As a result, the bright spot in the defect portion that is intended to be observed is buried by the brightness of the entire observation field of view, making it difficult to discriminate the defect.

In order to solve this problem, this embodiment has two countermeasures. First, in this embodiment, the relationship between the circularly polarizing plate 1 and the second polarizing unit 3B is arranged as a crossed Nicol prism, so even if this reflected light occurs (optical path 9d in FIG. Part of it is absorbed in the second polarizing part 3B, so it is less likely to become an obstacle to defect observation.

Second, in the inspection method of this embodiment, the incident angle θ of light with respect to the object 10 to be inspected is changed so that the influence of the phase difference of the release film 16a is reduced. That is, if the incident angle θ is changed, the phase difference exhibited by the release film 16a changes, so by finding the incident angle θ which becomes the above-mentioned "integer multiple", the observation field of view can be made darker. Here, in order to change the incident angle θ, the object 10 to be inspected can be tilted or rotated in various ways (it can be moved with the inspection table 20), or the light source 4, the bandpass filter 2, and the phase difference filter 3 sides to tilt or swivel in various ways. In this way, by adjusting the relative positional relationship of the members constituting the inspection apparatus 100 , it is possible to find an angle at which the influence of the retardation of the peeling film 16 a is reduced while varying the incident angle θ in various ways. When tilting the object 10 side to be inspected, the slow axis direction of the circularly polarizing plate 1 may be the axial direction, or the fast axis direction may be the axial direction. The angle of inclination is preferably set to 20° or less. When the angle of inclination must exceed 20°, it is preferable to replace the bandpass filter 2 with another type of bandpass filter found through the wavelength selection process.

According to the inspection method described above, it is possible to easily determine the presence or absence of defects in the circularly polarizing plate. In addition, since this inspection method is a reflective inspection method, compared with a transmission-type inspection method, the optical path in the object 10 to be inspected is longer, and deformation defects such as wrinkles that are difficult to detect by a transmission-type inspection method can be easily detected. detected. It should be noted that in FIG. 1 , the retardation film 14 in the circular polarizing plate 1 is shown to have a defect, but even if the polarizing film 11 has a defect, the inspection method of this embodiment can detect the defect. to test.

The inspection method of this embodiment is preferably carried out in a state where external light is blocked such as in a dark room in order to increase the detection sensitivity. In addition, from the viewpoint of suppressing reflected light reflected by the inspection table 20 from light transmitted through the inspection object 10 as much as possible, it is preferable to perform a low-reflection treatment on the mounting surface of the inspection object 10 of the inspection table 20 .

[2] Inspection when the retardation value of the peeling film 16a is adjusted to (integer multiple + λ/2) of the inspection wavelength

Inspection is performed using a bandpass filter that transmits light of a wavelength found in the wavelength selection step. FIG. 6 is a diagram showing the arrangement relationship of each polarizing film and each retardation film. The two arrows in the figure indicate the absorption axis of the polarizing film or the slow axis of the retardation film. As shown in FIG. 6 , a case where the retardation film 14 includes only the λ/4 film 14 a as the retardation film is considered. In the case where the retardation value of the peeling film 16a can be adjusted to (integer multiple+λ/2) of the inspection wavelength, as described above, the absorption axis of the polarizing film 3a included in the first polarizing unit 3A and the second The absorption axis of the polarizing film 3c included in the polarizing part 3B is arranged in a direction perpendicular to each other, and the first polarizing part 3A (including the polarizing film 3a and the retardation film 3b.) The relationship between the circularly polarizing plate 1 becomes a parallel Nicol prism, and the relationship between the circularly polarizing plate 1 and the second polarizer 3B (with a polarizing film 3c and a retardation film 3d.) becomes a crossed Nicol prism way to configure. In this case, when the circular polarizing plate 1 in the test object 10 is a right-handed circular polarizing plate, as the first polarizing portion 3A and the second polarizing portion 3B, a right-handed circular polarizing plate is used (refer to The two-arrow symbol in Figure 6). Conversely, when the circular polarizing plate 1 in the inspection object 10 is a left-handed circular polarizing plate, a left-handed circular polarizing plate is used as both the first polarizing portion 3A and the second polarizing portion 3B.

The inspection is performed in the same manner as in the case of [1] above. However, in this embodiment, when the incident angle θ of light with respect to the inspection object 10 is changed, the phase difference exhibited in the peeling film 16a becomes "integer multiple + In the case of (λ/2)", the polarization state of the circularly polarized light incident on the peeling film 16a is not disturbed, and the observation field of view can be made darker.

As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment at all.

Industrial availability

The present invention can be utilized in quality inspection of circularly polarizing plates.

Explanation of reference signs

1...circular polarizing plate, 2...bandpass filter, 3...retardation filter, 3A...first polarizing part, 3B...second polarizing part, 3a, 3c...polarizing film, 3b, 3d...retardation film, 4...light source, 5...detection unit, 9(9a, 9b, 9c, 9d)...optical path, 10...object to be inspected, 11...polarizing film, 12a, 12b...protective film, 13...adhesive layer, 14...phase Differential film, 14a...λ/4 film, 15...adhesive layer, 16a...release film, 16b...surface protection film, 20...inspection table, 100...inspection device, D...defect, θ...incident angle.

Claims (4)

1. An inspection method, which is an inspection method for judging the presence or absence of defects in a membranous object to be inspected, The object to be inspected includes: a circular polarizing plate laminated with a polarizing film and a retardation film; peel-off film, A light source, a band-pass filter that transmits light of a predetermined wavelength, a first polarizer, and the object to be inspected with the side of the peeling film facing the first polarizer side are included in the light emitted by the light source. are arranged sequentially on the optical path, and disposing the first polarizer and the second polarizer constituting a crossed Nicol prism on the optical path of the light reflected by the object to be inspected, Both the first polarizer and the second polarizer are left-handed circular polarizers or right-handed circular polarizers, and when the first polarizer and the second polarizer are viewed from the light source side, The absorption axis of the polarizing film included in the first polarizing section and the absorption axis of the polarizing film included in the second polarizing section are oriented in directions perpendicular to each other, making the light from the light source incident on the bandpass filter, changing the incident angle of the light with respect to the object to be inspected so that the influence of the phase difference of the release film is reduced, The presence or absence of a defect in the circularly polarizing plate is determined by observing the light reflected by the object to be inspected from the second polarizing unit side. 2. The inspection method according to claim 1, wherein Before carrying out said inspection, Calculate the wavelength dependence of the interference reflected light in the front direction from the average refractive index and thickness of the retardation film, obtain the wavelength at which the reflection intensity reaches the maximum in the range of wavelength 500nm to 600nm, and decide to use the wavelength within ±20nm. wavelength as the prescribed wavelength. 3. The inspection method according to claim 1 or 2, wherein, The circular polarizing plate and the second polarizing unit included in the inspection object are arranged to constitute a crossed Nicol prism. 4. The inspection method according to any one of claims 1 to 3, wherein: The retardation film includes a cured product of a polymerizable liquid crystal compound.