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 an inspection method.

Background

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 attach the polarizing plate to the display device, an adhesive layer is laminated on one side of the protective film, and a release film is further laminated on the adhesive layer. In addition, the protective film on the other side is often bonded with a release film (surface protective film) for protecting the surface thereof. The polarizing plate is transported in a state in which the release film is laminated in this manner, and when the polarizing plate is attached to a display device in a manufacturing process of the display device, the release film is peeled off.

However, in the polarizing plate, foreign matter or residual air bubbles may be mixed between the polarizing plate and the protective film at the stage of its production, or if the protective film has a function of a retardation film, there may be an alignment defect (hereinafter, these foreign matter, air bubbles, and alignment defect may be collectively referred to as "defect"). When a defective polarizing plate is attached to a display device, a defective portion may be visually recognized as a bright point or an image distortion may be observed at the defective portion. In particular, a defect visually recognized as a bright point is easily visually recognized when the display device displays black.

Therefore, in the stage before the polarizing plate is bonded to the display device (the polarizing plate having a release film), inspection for detecting defects of the polarizing plate is performed. The inspection of the defect is generally an optical inspection using a 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 the polarizing filter is rotated in a plane direction so that the respective polarization axis directions are in a specific relationship. When the polarization axis directions are orthogonal to each other (that is, when the arrangement of crossed nicols (japanese technology) コ is configured), the linearly polarized light passing through the polarizing filter cannot pass through the polarizing plate. However, if the polarizing plate has a defect, linearly polarized light is transmitted at that portion, and therefore the presence of the defect is recognized by detecting the light. On the other hand, when the polarization plate and the polarization filter have polarization axis directions parallel to each other, the linearly polarized light passing through the polarization filter is transmitted through the polarization 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 recognized by failing to detect the light. The inspector can visually detect the light transmitted through the polarizing plate or automatically detect the light by an image analysis processing value obtained by combining the CCD camera and the image processing device, thereby checking whether the polarizing plate is defective or not.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 9-229817

Disclosure of Invention

Problems to be solved by the invention

When the polarizing plate is a circular polarizing plate and the release film includes polyethylene terephthalate resin (PET resin), a phase difference filter (corresponding to the polarizing filter) that matches the wavelength dispersion of the PET resin to a certain extent is used for inspection of the polarizing plate. Here, in the case where the circularly polarizing plate and the phase difference filter are arranged so as to constitute a crossed nicols, the defect is visually recognized as a bright point according to the principle described above, but in the region where the phase difference value such as an alignment defect or a pinhole of the phase difference film included in the circularly polarizing plate is low, the bright point defect is visually recognized as a black point, and in this case, detection and judgment are more difficult than detection as a bright point. In particular, when the circularly polarizing plate contains a retardation film containing a cured product of a polymerizable liquid crystal compound, this tendency is remarkable.

The principle of the inspection method disclosed in patent document 1 is to observe light transmitted through an object to be inspected. In this principle, when a deformation defect (for example, a wrinkle generated at the time of cutting of the circularly polarizing plate) is present in the object to be inspected, the optical path length is hardly changed between the normal portion and the deformation defect portion, and therefore it is difficult to optically detect the deformation defect.

In addition, as described above, in the case where the polarizing plate includes the release film, the polarization characteristics of the circular polarizing plate are hindered by the birefringence of the release film, and therefore, defects such as bright spots present in the polarizing plate cannot be detected with good accuracy by the conventional inspection apparatus.

Accordingly, an object of the present invention is to provide a reflection type inspection method capable of easily judging whether or not a circularly polarizing plate is defective.

Means for solving the problems

The present invention provides an inspection method for judging whether a film-like object to be inspected is defective, wherein the object to be inspected comprises a circular polarizing plate in which a polarizing film and a phase difference film are laminated, and a release film which is laminated on the phase difference film side of the circular polarizing plate and contains polyethylene terephthalate resin, wherein a light source, a band-pass filter which transmits light of a predetermined wavelength, a 1 st polarizing portion, and an object to be inspected in which the release film side is oriented to the 1 st polarizing portion side are arranged in this order on the optical path of light emitted from the light source, and the 1 st polarizing portion and the 2 nd polarizing portion which constitutes a cross nicol prism are arranged on the optical path of light reflected by the object to be inspected, and when the 1 st polarizing portion and the 2 nd polarizing portion are observed from the light source side, the absorption axis of the polarizing film provided in the 1 st polarizing portion and the absorption axis of the polarizing film provided in the 2 nd polarizing portion are oriented to mutually orthogonal directions, and the light of the light source is made incident to the filter, and the change in the incident angle of light to the incident on the object to be inspected has a small influence on the polarizing plate to be inspected from the optical path of the object to be inspected, and the 1 st polarizing portion is the object to be inspected has a small influence on the polarization of the polarization to be observed.

In this inspection method, since the 1 st polarizing portion and the 2 nd polarizing portion are arranged so as to constitute crossed nicols, light reflected by a normal portion of the object to be inspected (for example, light reflected by the surface of the release film) is blocked by the 2 nd polarizing portion, and thus the observation field of view can be made sufficiently dark, and when a defective portion exists, it is easy to observe it as a bright spot. Since the phase difference between the light reflected from the defective portion generated in the object and the light reflected from the defective portion after passing through the defective portion is deviated from the ideal (becomes an undesired elliptical polarized light) due to the defect, only the 2 nd polarized light is transmitted to the extent of the deviation, and the light can be detected as the defective portion of the object. Here, it is expected that the retardation of the release film increases the brightness of the entire observation field of view, which is an obstacle to defect detection, but in this inspection method, the incidence angle of light with respect to the object to be inspected is changed so as to reduce the influence of the retardation of the release film, that is, the incidence angle of light is changed so that the retardation exhibited by the release film approaches an integer multiple of the wavelength of the incident light, and therefore, even when the release film has the retardation, the observation field of view can be made sufficiently dark. In addition, since the optical path in the object to be inspected is longer than that in the transmission type inspection method, the deformation defect which is difficult to detect by the transmission type inspection method can be easily detected. For the above reasons, the inspection method of the present invention can easily determine whether or not the circularly polarizing plate is defective.

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

In this inspection method, it is preferable that the circularly polarizing plate and the 2 nd polarizing portion included in the object to be inspected are arranged so as to form an crossed nicols. In this way, the observation field can be made darker.

The retardation film may contain a cured product of a polymerizable liquid crystal compound. When the retardation film contains a cured product of a polymerizable liquid crystal compound, the retardation film is generally thin and thick, and thus the possibility of black spot defect is increased. And thus is suitable as an object to which the present invention is applied.

Effects of the invention

According to the present invention, it is possible to provide a reflection type inspection method capable of easily judging whether or not a circularly polarizing plate is defective.

Drawings

Fig. 1 is a configuration diagram of an inspection apparatus for performing the inspection method according to embodiment 1.

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

Fig. 3 (a) and (B) are graphs each 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 for explaining the influence of the phase difference of the release film.

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

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In each of the drawings, the same or corresponding portions are denoted by the same reference numerals, and overlapping description is omitted.

Definitions of terms and symbols

The definitions of terms and symbols in the present specification are as follows.

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

"nx" is a refractive index in a direction in which the refractive index in the plane reaches the maximum (i.e., the slow axis direction), "ny" is a direction orthogonal to the slow axis in the plane, and "nz" is a refractive index in the thickness direction.

(2) In-plane phase difference value

The in-plane phase difference value (Re (λ)) refers to the in-plane phase difference value of the film at 23℃and wavelength λ (nm). Re (λ) is obtained by Re (λ) = (nx-ny) x d when the film thickness is d (nm).

Inspection apparatus and inspected object

The inspection apparatus of the present embodiment inspects the surface of the circularly polarizing plate, between layers constituting the circularly polarizing plate, or inside each layer for the presence of defects. As shown in fig. 1, the inspection apparatus 100 is provided with a light source 4, a band-pass filter 2, and a phase difference filter 3 in this order. The inspection apparatus 100 further includes an inspection stage 20 on which the object 10 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 in which an object 10 to be inspected is mounted on an inspection table 20. The phase difference filter 3 is configured by disposing two wide-band circularly polarizing plates 3A, 3B adjacent to each other on a substantially same plane, the two circularly polarizing plates respectively constituting: the 1 st polarization portion 3A, which is a region into which light transmitted through the band pass filter 2 is incident, and the 2 nd polarization portion 3B, which is a region into which light reflected by the object 10, which will be described later, is incident. The 1 st polarization part 3A and the 2 nd polarization part 3B are both left-handed circular polarization plates or right-handed circular polarization plates. The 1 st polarization unit 3A and the 2 nd polarization unit 3B are arranged as follows: the absorption axis of the polarizing film of the 1 st polarizing portion 3A and the absorption axis of the polarizing film of the 2 nd polarizing portion 3B are oriented in directions orthogonal to each other (crossed nicols) when viewed from the light source 4 side. The 1 st polarization portion 3A and the 2 nd polarization portion 3B are so-called defect-free polarization portions.

As shown in fig. 2, the object 10 is in a film shape, and includes a circularly polarizing plate 1 as a subject of inspection, and a release film 16a laminated on the circularly polarizing plate 1 via an adhesive layer 15. The circularly polarizing plate 1 is formed by laminating protective films 12a and 12b on both sides of a polarizing film 11, and further forming a retardation film 14 on the protective film 12a on the side provided with a release film 16a via an adhesive layer 13. Further, a surface protective film 16b is laminated on the surface of the circularly polarizing plate 1 on the side not provided with the release film 16a. The circularly polarizing plate 1 is generally used for display devices, such as liquid crystal display devices and organic EL display devices, and is attached to the display device via an adhesive layer 15 by peeling off a release film 16a when in use.

The polarizing film 11 is a film that converts light incident from the surface protective film 16b side into linearly polarized light. Examples of the polarizing film 11 include: a polarizing film obtained by adsorbing iodine and a dichroic dye to a polyvinyl alcohol film and aligning the film; a polarizing film in which a dichroic dye is adsorbed to a material obtained by aligning and polymerizing a polymerizable liquid crystal compound and is aligned.

The protective films 12a, 12b serve to protect the polarizing film 11. As the protective films 12a, 12b, for the purpose of obtaining a polarizing plate having appropriate mechanical strength, protective films widely used in the technical field of polarizing plates are used. Typically, this is: cellulose ester-based films such as triacetyl cellulose (TAC) films; a cyclic olefin film; polyester films such as polyethylene terephthalate (PET) films: and (meth) acrylic films such as polymethyl methacrylate (PMMA) films. 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 control of the retardation value and the like are required. As the protective film 12a, a protective film having an extremely small phase difference value is typically preferably used. The protective films 12a and 12b are bonded to the polarizing film 11 with an adhesive.

The phase difference film 14 is a film that converts light, which is incident from the surface protection film 16b side and is converted into linearly polarized light by the polarizing film 11, into circularly polarized light. The phase difference film 14 is a film that converts circularly polarized light incident from the peeling film 16a side into linearly polarized light when viewed from the peeling film 16a side. Therefore, the retardation film 14 has at least a λ/4 film. The retardation film 14 may further be laminated with a lambda/2 film. In this case, the order of the λ/2 film and the λ/4 film may be from the side close to the polarizing film 11.

The retardation film 14 preferably contains a cured product of a polymerizable liquid crystal compound. The retardation film 14 containing a cured product of a polymerizable liquid crystal compound is generally thin in thickness to the extent of 0.2 μm to 10 μm, and when a foreign substance or the like is contained, the phase difference value is liable to change in that portion. In such a position, it is impossible to convert linearly polarized light into circularly polarized light which matches ideal, and becomes unwanted elliptically polarized light. As described later, the light spot defect is observed as a black spot although it should be observed during the inspection.

Examples of the polymerizable liquid crystal compound capable of forming the retardation film 14 include: a polymerizable liquid crystal compound disclosed in japanese patent application laid-open publication No. 2009-173893, japanese patent application laid-open publication No. 2010-31223, WO2012/147904, WO2014/10325, and WO 2017-43438. The polymerizable liquid crystal compounds described in these publications can form a retardation film having so-called reverse wavelength dispersibility, which can realize the same polarization conversion in a wide wavelength range. For example, by applying a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution) to an appropriate substrate and performing photopolymerization, an extremely thin retardation film can be formed as described above, and therefore, a circularly polarizing plate having the above retardation film can be formed into a circularly polarizing plate having an extremely thin thickness. In this way, a circularly polarizing plate having an extremely thin thickness is advantageous as a circularly polarizing plate for flexible display materials which have been attracting attention in recent years.

As a substrate to which the polymerizable liquid crystal compound solution is applied, a substrate described in the above publication is exemplified. The substrate may be provided with an alignment film for aligning the polymerizable liquid crystal compound. The alignment film may be any of an alignment film that is photo-aligned by polarized light irradiation and an alignment film that is mechanically aligned by rubbing treatment. The alignment film is also described in the above publication.

However, when a foreign substance or the like is present in a substrate to which the polymerizable liquid crystal compound solution is applied, or when a flaw or the like is present in the substrate itself, a defect may occur in the coating film itself obtained by applying the polymerizable liquid crystal compound solution. In addition, when the alignment film is subjected to rubbing treatment, the scraps of the rubbing cloth remain on the alignment film, which may cause 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 to be extremely thin, there is a factor of generating defects. Further, as described later, defects of the retardation film may be observed as black spots. The inspection method of the present embodiment is particularly useful for detecting whether or not an object to be inspected having a circularly polarizing plate and a release film has defects (defects observed as black dots), and the circularly polarizing plate has such defects.

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 thus produced is bonded to the adhesive layer 13 formed on the protective film 12a together with the base material, and then the base material is peeled off, whereby the retardation film 14 can be transferred to the protective film 12 a.

In the inspection method of the present embodiment, when the circularly polarizing plate used as the 1 st polarizing portion 3A and the 2 nd polarizing portion 3B is used based on the phase difference value of the release film 16a, the rotation direction (left-handed or right-handed) is determined to be the same as or different from the rotation direction of the circularly polarizing plate 1 in the object 10. Details will be described later.

When the release film 16a is attached to the display device, it is peeled off from the circularly polarizing plate 1, and the peeled release film 16a is usually discarded. Therefore, unlike the protective films 12a, 12b, strict management of the phase difference value is not required. Therefore, in the case of using a commercially available film as the release film 16a, if the phase difference value is not compensated, malfunction may be caused in the inspection of the defect. That is, in the defect inspection of the circularly polarizing plate 1 to which the release film 16a having a non-strictly controlled phase difference value is attached in this manner, the phase difference of the release film 16a may cause a decrease in the inspection accuracy of the inspection apparatus 100.

As described in the background art, in the circularly polarizing plate 1, the surface protection film 16b, which is one type of the release film, is often provided on the opposite surface of the release film 16a. In the circularly polarizing plate 1 shown in fig. 2, a surface protective film 16b is attached to the protective film 12b side. The surface protective film 16b is also peeled off from the circularly polarizing plate 1 normally when attached to the display device, and strict control of the retardation value is not required unlike the protective films 12a and 12 b. In fig. 2, the protective film 12b and the surface protective film 16b may be bonded by an appropriate adhesive layer or pressure-sensitive adhesive layer (in fig. 2, the adhesive layer or pressure-sensitive adhesive layer is not shown).

In the present embodiment, the release film 16a includes PET resin. The surface protective film 16b also uses a film containing PET resin. Films containing PET resins (PET resin films) are widely used as release films and have the advantage of being inexpensive. On the other hand, the low-cost PET resin film does not require strict control of the phase difference value as described above. Thus, for example, the phase difference value sometimes varies from one product lot to another. In addition, even in the same PET resin film, there is a case where the phase difference value is deviated in the surface. Even in the case of a circularly polarizing plate bonded with such a low-cost PET resin film as a release film, the presence or absence of defects can be detected with good accuracy by the inspection method of the present embodiment.

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

Here, a method for determining Re (550) of the release film 16a is shown in advance. As described above, these release films are PET resin films, and such films are readily available on the market. Pieces of a size of, for example, 40mm×40mm are obtained from the film (obtained by dividing a long film by using an appropriate cutting tool). Re (550) of the sheet was measured 3 times to determine the average value of Re (550). Re (550) of the sheet was measured at a measurement temperature of about room temperature (25 ℃) using a phase difference measuring apparatus KOBRA-WPR (manufactured by Wako measuring instruments Co., ltd.). In the case where Re (550) of the surface protective film 16b is obtained, the same test may be performed.

Various commercially available products such as a laser beam and the like (including a light similar to the straight line light) can be used for the light source 4. The light emitted from the light source 4 is unpolarized light, and passes through a 1 st polarization unit 3A described later to become circularly polarized light.

In order to observe the light reflected from the object 10, a detection unit 5 including a CCD camera or the like may be disposed on the optical path of the reflected light at a position on the side where the light source 4 is located among the two sides of the 2 nd polarization portion 3B. For example, the inspection of the object to be inspected can be performed by automatically performing detection by image processing analysis obtained by combining a CCD camera with an image processing apparatus. Alternatively, the detection unit 5 may be a member, but a person visually observes the 2 nd polarized portion 3B. In addition, a spacer plate may be appropriately provided between the light source 4 and the CCD camera.

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 incident angle θ of the light with respect to the object 10 to be inspected 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 adjusted to be suitable for inspection.

< checking method >)

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

(wavelength selection Process)

Before starting the inspection of the object 10 including the circularly polarizing plate 1, an inspection wavelength is selected. In the present embodiment, for the purpose of detecting defects in the retardation film 14, the inspection light is selected based on the optical characteristics of the retardation film. When the retardation film 14 includes 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, inspection light may be selected for the retardation film (for example, a λ/4 film) to be subjected to defect inspection. The wavelength dependence of the interference reflected light in the front direction can be generally calculated for the retardation film based on the average refractive index and thickness in the plane thereof. An example of this calculation is shown in fig. 3. FIG. 3 (A) shows the wavelength dependence of the reflection intensity index of a lambda/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 lambda/4 film having an average refractive index in the plane of 1.62 and a thickness of 2.10. Mu.m, at a wavelength of 550 nm. Any graph is a waveform, and a plurality of lambda/4 films show a tendency to trace such a waveform.

In the inspection method of the present embodiment, since reflected light from a plurality of films is captured, it is advantageous to use a wavelength at which interference of reflected light in the phase difference film 14 becomes relatively strong as the inspection light for defect detection. From this point of view, in the present embodiment, a wavelength having a high reflection intensity index is used for inspection. For example, in the graphs of fig. 3 (a) and (B), the reflection intensity index is commonly increased in the vicinity of 540nm and 580nm, and therefore, these wavelengths are preferably used. In particular, these wavelengths are preferable because they have high visibility and are also in the range of 500nm to 600nm, which is a design wavelength of the retardation film. It is determined that the wavelength within.+ -. 20nm, within.+ -. 10nm, or within.+ -. 5nm of these wavelengths is used as the wavelength of the inspection light. That is, for example, a bandpass filter transmitting light of 540nm and a bandpass filter transmitting light of 580nm are prepared.

(defect inspection Process)

In the defect inspection step, the incidence angle of light is adjusted so that the influence of the phase difference of the release film 16a becomes small. At this time, the incident angle θ of the light to the object 10 (the angle based on the perpendicular to the surface of the object 10) is preferably adjusted to 30 ° or less. Further preferably, the temperature is adjusted to 20 ° or less. If the incident angle θ of the light to the object 10 exceeds 30 °, the optical path length passing through the release film 16a becomes longer, and the interference of the wavelength determined as the inspection light becomes weaker, so that the inspection sensitivity may be lowered. Therefore, as the defect inspection step, any one of the two conditions ([ 1] and [2 ]) described below is selected for inspection based on the phase difference value of the release film 16a. By this selection, inspection in a range where the incident angle θ does not exceed 30 ° is easy.

[1] Inspection in the case of adjusting the phase difference value of the peeling film 16a to be an integral multiple of the inspection wavelength

The inspection was performed using a band-pass filter that transmits light of the wavelength found in the wavelength selection step. Fig. 4 is a diagram showing the arrangement relationship of each polarizing film and each retardation film. In the figure, the two-headed arrow indicates the absorption axis of the polarizing film or the slow axis of the phase difference film. As shown in fig. 4, a case is considered in which the retardation film 14 includes only the λ/4 film 14a as the retardation film. When the phase difference value of the release film 16a can be adjusted to an integer multiple of the inspection wavelength, as described above, the absorption axis of the polarizing film 3A of the 1 st polarizing portion 3A and the absorption axis of the polarizing film 3c of the 2 nd polarizing portion 3B are arranged so as to be oriented in directions orthogonal to each other, and the relationship between the 1 st polarizing portion 3A (including the polarizing film 3A and the phase difference film 3B.) and the circular polarizing plate 1 in the inspected object 10 is arranged so as to be a parallel nicol prism (japanese i.e. コ l), and the relationship between the circular polarizing plate 1 and the 2 nd polarizing portion 3B (including the polarizing film 3c and the phase difference film 3 d.) is arranged so as to be a cross nicol prism. In this case, when the circularly polarizing plate 1 in the object 10 is a right-handed circularly polarizing plate, left-handed circularly polarizing plates are used as the 1 st polarizing portion 3A and the 2 nd polarizing portion 3B (see two-headed arrow in fig. 4). In contrast, when the circularly polarizing plate 1 in the object 10 is a left-handed circularly polarizing plate, both the 1 st and 2 nd polarizing portions 3A and 3B are right-handed circularly polarizing plates.

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

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

The light emitted from the light source 4 is transmitted through the band-pass filter 2, then enters the 1 st polarization unit 3A, and is transmitted therethrough to become circularly polarized light (optical path 9 a). The transmitted light is then incident on the object 10. Then, the light is transmitted through the release film 16a in the test object 10, and is desirably converted into linearly polarized light by the phase difference film 14 constituting the circularly polarizing plate 1, and is finally absorbed by the polarizing film 11 (end of the optical path 9 a). Here, a part of the light transmitted through the 1 st polarization unit 3A is reflected on the surface of the release film 16a in the object 10 (optical path 9 b). The reflected light is blocked by the 2 nd polarization unit 3B (end of the optical path 9B) because the 1 st polarization unit 3A and the 2 nd polarization unit 3B constitute a crossed nicol prism. The inspection light is thus absorbed and blocked, and the observation field of view by the 2 nd polarization portion 3B of the detection unit 5 becomes dark.

On the other hand, when the object 10 has a defect D (for example, a defect existing at the interface between the retardation film 14 and the polarizing film 11, or a defect existing in the retardation film 14), the reflection becomes strong at that portion (optical path 9 c). The reflected light has a phase difference (which is an undesired elliptically polarized light) different from the ideal due to the defect D. These reflected lights are transmitted without being blocked by the 2 nd polarization portion 3B. If it is observed from the detection unit 5 side, the defective portion is observed as a bright point.

Here, the retardation (in-plane retardation) of the release film 16a may be an obstacle to the inspection. That is, when the phase difference exhibited by the release film 16a becomes an integral multiple of the wavelength of the light transmitted through the band-pass filter 2, the polarization state of the circularly polarized light incident on the release film 16a is not disturbed, but in many cases, is not an integral multiple, and therefore, the polarization state of the circularly polarized light is disturbed, and is not converted into linearly polarized light by the phase difference film 14, and is hardly absorbed by the polarizing film 11, and reflected light is generated at the interface thereof (the optical path 9d of fig. 5). Therefore, the amount of transmitted light transmitted through the 2 nd polarization portion 3B increases, and the brightness of the observation field increases. As a result, the bright spots of the defect portion to be observed are buried by the brightness of the entire view field, and the discrimination of the defect becomes difficult.

To solve this problem, the present embodiment has two countermeasures. First, in the present embodiment, since the circular polarizing plate 1 and the 2 nd polarizing portion 3B are arranged so as to be crossed nicols, most of the reflected light (optical path 9d in fig. 1) is absorbed in the 2 nd polarizing portion 3B, and thus, it is difficult to be a defect observation obstacle.

Second, in the inspection method of the present embodiment, the incidence angle θ of the light with respect to the object 10 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 is changed, and therefore, by finding the incident angle θ that is "integer multiple" as described above, the observation field of view can be made darker. Here, in order to change the incident angle θ, the object 10 may be tilted or rotated in various ways (may be moved along with the inspection stage 20), or the light source 4, the band-pass filter 2, and the phase difference filter 3 may be tilted or rotated in various ways. By adjusting the relative positional relationship of the members constituting the inspection apparatus 100 in this manner, it is possible to search for an angle at which the influence of the phase difference of the release film 16a becomes small while changing the incident angle θ in various ways. In the case of tilting the object 10 side, the slow axis direction of the circularly polarizing plate 1 may be tilted as the axis direction, or the fast axis direction may be tilted as the axis direction. The inclination angle is preferably 20 ° or less. In the case where the inclination angle must exceed 20 °, the band-pass filter 2 is preferably replaced with another type of band-pass filter found by the wavelength selection process.

According to the inspection method shown above, the presence or absence of a defect in the circularly polarizing plate can be easily determined. Further, since this inspection method is a reflection type inspection method, the optical path in the object 10 to be inspected is longer than that in a transmission type inspection method, and deformation defects such as wrinkles, which are difficult to detect by the transmission type inspection method, can be easily detected. Although fig. 1 shows a case where the retardation film 14 in the circularly polarizing plate 1 has a defect, even when the polarizing film 11 has a defect, the defect can be detected by the inspection method of the present embodiment.

In order to improve the detection sensitivity, the inspection method of the present embodiment is preferably performed in a state where external light such as a darkroom is blocked. In addition, from the viewpoint of suppressing as much as possible reflected light reflected by the inspection table 20 from light transmitted through the inspection object 10, it is preferable to perform low reflection processing on the mounting surface of the inspection object 10 on the inspection table 20.

[2] Inspection in the case of adjusting the phase difference value of the peeling film 16a to (integer multiple +λ/2) of the inspection wavelength

The inspection was performed using a band-pass filter that transmits light of the wavelength found in the wavelength selection step. Fig. 6 is a diagram showing the arrangement relationship of each polarizing film and each retardation film. In the figure, the two-headed arrow indicates the absorption axis of the polarizing film or the slow axis of the phase difference film. As shown in fig. 6, a case is considered in which the retardation film 14 includes only the λ/4 film 14a as the retardation film. When the phase difference value of the release film 16a can be adjusted to (integer multiple+λ/2) the inspection wavelength, as described above, the absorption axis of the polarizing film 3A of the 1 st polarizing portion 3A and the absorption axis of the polarizing film 3c of the 2 nd polarizing portion 3B are arranged so as to be oriented in directions orthogonal to each other, and the relationship between the 1 st polarizing portion 3A (including the polarizing film 3A and the phase difference film 3B) and the circular polarizing plate 1 in the object 10 is arranged so as to be parallel nicol prisms, and the relationship between the circular polarizing plate 1 and the 2 nd polarizing portion 3B (including the polarizing film 3c and the phase difference film 3 d.) is arranged so as to be orthogonal nicol prisms. In this case, when the circularly polarizing plate 1 in the object 10 is a right-handed circularly polarizing plate, the right-handed circularly polarizing plate is used as the 1 st polarizing portion 3A and the 2 nd polarizing portion 3B (see the two-headed arrow in fig. 6). In contrast, when the circularly polarizing plate 1 in the object 10 is a left-handed circularly polarizing plate, both the 1 st polarizing section 3A and the 2 nd polarizing section 3B are left-handed circularly polarizing plates.

The examination was performed in the same manner as in the case of the above-mentioned [1 ]. However, in the present embodiment, when the phase difference exhibited by the release film 16a is "integer multiple+ (λ/2)" of the wavelength of the light transmitted through the band-pass filter 2 when the incident angle θ of the light to the object 10 is changed, the polarization state of the circularly polarized light incident on the release film 16a is not disturbed, and the observation field of view can be made darker.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments.

Industrial applicability

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

Description of the reference numerals

1 … circular polarizing plate, 2 … bandpass filter, 3 … phase difference filter, 3a … 1 st polarizing part, 3B … 2 nd polarizing part, 3a, 3c … polarizing film, 3B, 3D … phase difference film, 4 … light source, 5 … detection unit, 9 (9 a, 9B, 9c, 9D) … optical path, 10 … inspected object, 11 … polarizing film, 12a, 12B … protective film, 13 … adhesive layer, 14 … phase difference film, 14a … lambda/4 film, 15 … adhesive layer, 16a … release film, 16B … surface protective film, 20 … inspection table, 100 … inspection apparatus, D … defect, θ … incident angle.

Claims (4)

1. An inspection method for judging whether a film-like object to be inspected is defective,

the object to be inspected includes: a circularly polarizing plate in which a polarizing film and a retardation film are laminated, and a release film which is laminated on the retardation film side of the circularly polarizing plate and contains a polyethylene terephthalate resin,

a light source, a band-pass filter transmitting light of a predetermined wavelength, a 1 st polarizing unit, and the object to be inspected having the peeling film side directed to the 1 st polarizing unit are sequentially arranged on a light path of light emitted from the light source, and

the 1 st polarization part and the 2 nd polarization part forming a crossed Nicole prism are arranged on the optical path of the light reflected by the inspected object,

the 1 st polarizing portion and the 2 nd polarizing portion are both left-handed circular polarizing plates or right-handed circular polarizing plates, and when the 1 st polarizing portion and the 2 nd polarizing portion are viewed from the light source side, an absorption axis of a polarizing film provided in the 1 st polarizing portion and an absorption axis of a polarizing film provided in the 2 nd polarizing portion face directions orthogonal to each other,

causing light from the light source to be incident on the band-pass filter,

the incidence angle of the light with respect to the inspected object is changed so as to reduce the influence of the phase difference of the peeling film,

the light reflected by the object to be inspected is observed from the 2 nd polarization portion side to judge whether the circularly polarizing plate is defective.

2. The inspection method according to claim 1, wherein

Before the said examination is carried out,

the wavelength dependence of the interference reflected light in the front direction is calculated from the average refractive index and thickness of the retardation film, the wavelength at which the reflection intensity reaches the maximum in the wavelength range of 500nm to 600nm is obtained, and the wavelength within + -20 nm is determined as the predetermined wavelength.

3. The inspection method according to claim 1 or 2, wherein,

the circular polarizing plate and the 2 nd polarizing portion included in the object to be inspected are arranged so as to form an crossed nicol prism.

4. The inspection method according to claim 1 to 3, wherein,

the retardation film contains a cured product of a polymerizable liquid crystal compound.