CN116420101A - Inspection method - Google Patents

Abstract

The present invention is a method for inspecting whether or not a film-like object (10) is defective, the object being provided with a circularly polarizing plate (1) comprising a polarizing film (11) and a retardation film (14), and a release film (16 a) comprising a polyethylene terephthalate resin, the release film being laminated on the retardation film (14) side of the circularly polarizing plate (1). A light source (4), a bandpass filter (2) that transmits light of a predetermined wavelength, a first polarizing section (3A), an object (10) to be inspected, and a second polarizing section (3B) are disposed, and the incident angle (theta) of the light to the object (10) to be inspected is changed so that the influence of the phase difference of the release film (16 a) is reduced. The light reflected by the inspected object (10) is observed from the second polarization part (3B) side, thereby judging 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 by sandwiching a polarizing plate between two protective films. In order to attach the polarizing plate to the display device, an adhesive layer is laminated on one of the protective films, and a release film is further laminated on the adhesive layer. In addition, in the case of the optical fiber, a release film (surface protective film) for protecting the surface of the other protective film is often bonded to the other protective film. The polarizing plate is transported in a state in which the release film is laminated in this way, and the release film is peeled off when the display device is bonded in the manufacturing process of the display device.

However, in the polarizing plate, there are cases where foreign substances are mixed between the polarizing plate and the protective film, bubbles remain, or alignment defects are present inside when the protective film has a function of a retardation film in its manufacturing stage (hereinafter, these foreign substances, bubbles, and alignment defects may be collectively referred to as "defects"). When a defective polarizing plate is attached to a display device, a portion having the defect is visually recognized as a bright point, and an image appears to be distorted at the defective portion. In particular, a defect visually recognized as a bright point is easily visually recognized at the time of black display of the display device.

Therefore, in the stage before the polarizing plate is attached to the display device (the polarizing plate in a state of having a release film), inspection for detecting a defect 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 then the polarizing plate or the polarizing filter is rotated in a plane direction, whereby the respective polarization axis directions are set to have a specific relationship. When the polarization axis directions are orthogonal to each other (that is, when the arrangement of the cross nicols (japanese) system コ ol) is made, the linearly polarized light that has passed through the polarization filter does not pass through the polarization plate. However, if the polarizing plate has a defect, linearly polarized light is transmitted through the portion, and thus the light is detected, and the presence of the defect is known. 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 passes through the polarization plate. However, if the polarizing plate has a defect, the linearly polarized light is blocked at that portion, and therefore the light is not detected, and the presence of the defect is known. The presence or absence of the polarizing plate can be inspected by visually detecting light transmitted through the polarizing plate by an inspector or automatically detecting an image analysis processing value obtained by combining a CCD camera and an image processing device.

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 is made of 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 the inspection of the polarizing plate. Here, in the case where the circularly polarizing plate and the phase difference filter are arranged so as to form a crossed nicols state, the defect is visually recognized as a bright point according to the principle described above, but in some cases, the bright point defect in a region where the phase difference value such as an alignment defect or a pinhole of the phase difference film of the circularly polarizing plate is low 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 includes a retardation film composed of 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 the case where the inspected object has a deformation defect (for example, a wrinkle generated at the time of cutting of the circularly polarizing plate) in this principle, the optical path length hardly changes in the normal portion and the deformation defect portion, and therefore it is difficult to optically detect the deformation defect.

In addition, in the case where the polarizing plate includes the release film as described above, since the polarization characteristics of the circularly polarizing plate are hindered by the birefringence of the release film, it is difficult to detect defects such as bright spots existing in the polarizing plate with high accuracy by using a conventional inspection apparatus.

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

Means for solving the problems

A method for inspecting a film-like object to be inspected, which comprises a circularly polarizing plate comprising a polarizing film and a retardation film, and a release film comprising a polyethylene terephthalate resin, laminated on the retardation film side of the circularly polarizing plate, wherein a light source, a bandpass filter transmitting light of a predetermined wavelength, a first polarizing portion, and the object to be inspected having the release film side directed to the first polarizing portion are sequentially arranged on the optical path of the light emitted from the light source, and a second polarizing portion forming a cross nicol state with the first polarizing portion is arranged on the optical path of the light reflected by the object to be inspected, the light of the light source is made incident on the bandpass filter, and the incident angle of the light to the object to be inspected is changed so that the influence of the retardation of the release film is reduced, and the light reflected by the object to be inspected is observed from the second polarizing portion side, thereby judging that the circularly polarizing plate is defective.

In the inspection method, since the first polarizing portion and the second polarizing portion are arranged so as to form a crossed nicols state, light reflected at a normal portion of the object to be inspected (for example, light reflected at the surface of the release film) is blocked by the second polarizing portion, and thus the observation field can be sufficiently darkened, and when a defective portion exists, the defective portion is easily observed as a bright point. Since the phase difference of the light reflected by the defective portion generated in the object or the light reflected by the defective portion is deviated from the ideal (becomes unwanted elliptical polarized light) due to the defect, the amount of the deviation is transmitted through the second polarizing portion, and the defective portion of the object can be detected. Here, it is expected that the brightness of the entire observation field of view increases due to the phase difference of the release film, and this becomes an obstacle to defect detection, but in the present inspection method, the incident angle of light to the object to be inspected is changed so that the influence of the phase difference of the release film becomes small, that is, the incident angle of light is changed so that the phase difference appearing by the release film approaches an integer multiple of the wavelength of the incident light, and therefore, even when the release film has a phase difference, the observation field of view can be sufficiently darkened. Further, since the optical path in the object to be inspected is longer in such a reflection type inspection method than in a transmission type inspection method, it is also possible to easily detect a deformation defect which is difficult to detect by the transmission type inspection method. From the above, the presence or absence of a defect in the circularly polarizing plate can be easily determined by the inspection method of the present invention.

In the present inspection method, it is preferable that after the inspection is performed using the bandpass filter, the inspection is performed using the bandpass filter that transmits light having a wavelength different from that of the light that is most easily transmitted by the bandpass filter. Thus, for example, it is possible to check whether or not two defects are present, such as a case where the phase difference value is a defect larger than a predetermined value (blue is mostly observed when the defect is visually recognized, and hence, referred to as blue dot patch hereinafter) and a case where the phase difference value is a defect smaller than a predetermined value (red is mostly observed when the defect is visually recognized, and hence, red dot patch hereinafter).

In the inspection method of the present invention, it is preferable that before the inspection, a light source and two test pieces of a circular polarizing plate having the same structure as the circular polarizing plate provided in the object to be inspected are prepared, the two test pieces are arranged such that the two test pieces face each other on the phase difference film side and the angle between the slow axes of the phase difference films is an angle other than 90 ° when viewed from the optical path direction of the light source, light of various wavelengths is incident from either side of the polarizing film of the test piece such that the optical path passes through the defect-free region on the test piece, and the polarizing film is observed from the other side thereof, and a wavelength (hereinafter referred to as "minimum wavelength") at which the transmitted light amount is minimum is determined, and it is preferable that at least one wavelength of wavelengths 5nm to 50nm larger than the wavelength and wavelengths 5nm to 50nm smaller than the wavelength is used as a predetermined wavelength. When at least one of the wavelength of 5nm to 50nm larger than the minimum wavelength and the wavelength of 5nm to 50nm smaller than the minimum wavelength is used for the inspection, blue spot or red spot is emphasized and made visible while the brightness of the entire view field is sufficiently suppressed. Specifically, by performing the inspection twice using both the light having the wavelength of 5nm to 50nm smaller than the minimum wavelength and the light having the wavelength of 5nm to 50nm smaller than the minimum wavelength, it is possible to perform the inspection under the condition that the blue dot patch and the red dot patch are emphasized, respectively. Here, the inspection using light of a predetermined wavelength means that a bandpass filter transmitting light of the predetermined wavelength is used.

In the inspection method of the present invention, the first polarizing portion and the second polarizing portion may be both circular polarizing plates or both linear polarizing plates. In the case of the circular polarizing plate, the circular polarizing plate may be formed by a single common circular polarizing plate.

The retardation film may be formed of a cured product of a polymerizable liquid crystal compound. When the retardation film is composed of a cured product of a polymerizable liquid crystal compound, the possibility of black spot defect is increased due to its usual thinness. 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 reflective inspection method capable of easily determining whether or not a circularly polarizing plate is defective.

Drawings

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

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

Fig. 3 is a diagram showing the arrangement of each member in the wavelength selection step based on the transmitted light measurement.

Fig. 4 (a) is a diagram showing a relationship between slow axes in two test pieces. Fig. 4 (B) is a view when fig. 4 (a) is viewed from the optical path side.

Fig. 5 is a diagram for explaining the influence of the phase difference of the release film in the inspection method according to the first embodiment.

Fig. 6 is a structural diagram of an inspection apparatus for performing the inspection method according to the second embodiment.

Detailed Description

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

< definition of terms and symbols >

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

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

"nx" is the refractive index in the direction in which the refractive index in the plane is maximum (i.e., the slow axis direction), "ny" is the direction orthogonal to the slow axis in the plane, and "nz" is the 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) was obtained by Re (λ) = (nx-ny) x d when the film thickness was d (nm).

< first embodiment >

The inspection method of the first embodiment will be described.

(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 the presence or absence of defects inside the circularly polarizing plate. As shown in fig. 1, the inspection apparatus 100 is provided with a light source 4, a bandpass filter 2, and a phase difference filter 3 in this order. The inspection apparatus 100 also 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 inspection table 20 is processed to suppress reflection of light on its surface.

Fig. 1 shows a case where an inspection object 10 is placed on an inspection table 20. The phase difference filter 3 is a circular polarizing plate having a wide band wider than the band pass filter 2, and has both functions of a first polarizing portion 3A as a region into which light transmitted through the band pass filter 2 is incident and a second polarizing portion 3B as a region into which light reflected from an object to be inspected 10, which will be described later, is incident. That is, the first polarization portion 3A and the second polarization portion 3B are constituted by a single circular polarization plate in common, and the first polarization portion 3A and the second polarization portion 3B are located on the same plane.

As shown in fig. 2, the object 10 has a film shape, and includes a circular polarizing plate 1 as a subject of inspection, and a release film 16a laminated on the circular polarizing plate 1 via an adhesive layer 15. In the circularly polarizing plate 1, the protective films 12a and 12b are bonded to both surfaces of the polarizing film 11, and the retardation film 14 is formed on the protective film 12a on the side having the release film 16a via the pressure-sensitive 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 a display device, such as a liquid crystal display device or an organic EL display device, and is peeled off from a release film 16a at the time of use and attached to the display device via an adhesive layer 15.

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

The polarizing film 11 is a film that converts light incident from the surface protective film 16a side into linearly polarized light or absorbs it. Examples of the polarizing film 11 include a film in which iodine or a dichroic dye is adsorbed and oriented to a polyvinyl alcohol film; or a film formed by adsorbing and aligning a dichroic dye to an alignment layer and polymerizing a polymerizable liquid crystal compound.

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 an appropriate mechanical strength, protective films commonly used in the technical field of polarizing plates are used. Typically, there are cellulose ester films such as triacetyl cellulose (TAC) films, polyester films such as cyclic olefin films and polyethylene terephthalate (PET) films: and (meth) acrylic films such as polymethyl methacrylate (PMMA) films. In addition, additives commonly used in the technical field of polarizing plates may be contained in the protective film.

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, and therefore strict control of the phase difference value and the like are required. As the protective film 12a, a film having a very small phase difference value is typically preferably used. In addition, as the protective film 12b, for example, a film having a phase difference of λ/4 or a film having an extremely small phase difference value is used in consideration of the ease of viewing the display device through polarized sunglasses. The protective films 12a and 12b are bonded to the polarizing film 11 via an adhesive.

The phase difference film 14 is a film that converts light reflected from the surface protection film 16b side and converted into linearly polarized light by the polarizing film 11 into circularly polarized light. When viewed from the release film 16a side, the phase difference film 14 is a film that converts circularly polarized light incident from the release film 16a side into linearly polarized light. The retardation film 14 is not particularly limited as long as it has a retardation, and may be a film in which a λ/2 film and a λ/4 film are laminated. In this case, the film may be a λ/2 film or a λ/4 film in order from the side closer to the polarizing film 11.

The retardation film 14 is preferably composed of a cured product of a polymerizable liquid crystal compound. The retardation film 14 made of a cured product of a polymerizable liquid crystal compound is generally thin to a thickness of about 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 region, the linearly polarized light cannot be completely converted into ideal circularly polarized light, but becomes unwanted elliptically polarized light. As will be described later, a portion that should be observed as a bright point defect during inspection may be observed as a black point.

Examples of the polymerizable liquid crystal compound capable of forming the retardation film 14 include compounds 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 convert the same polarized light in a wide wavelength range. For example, a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution) is applied to an appropriate substrate and subjected to photopolymerization, whereby an extremely thin retardation film can be formed as described above, and therefore a circularly polarizing plate having such a retardation film can be formed into an extremely thin circularly polarizing plate. Such a circularly polarizing plate having an extremely small thickness is used as a circularly polarizing plate for flexible display materials, which has 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-mentioned publication can be cited. An alignment film may be provided on such a substrate for aligning the polymerizable liquid crystal compound. The alignment film may be an alignment film that is photo-aligned by polarized light irradiation or an alignment film that is mechanically aligned by rubbing treatment. Such an 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 the substrate itself is damaged, the coating film itself obtained by applying the polymerizable liquid crystal compound solution may have defects. In addition, when the alignment film is subjected to rubbing treatment, there are cases where 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). In this way, although a retardation film formed of a polymerizable liquid crystal compound can be formed to have an extremely thin thickness, there is a factor of generating defects. As will be described later, defects in 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, and the circularly polarizing plate has a retardation film having such defects.

The retardation film 14 can be produced by: the composition for forming an alignment film is coated on a substrate, and further a composition for forming a liquid crystal cured film containing a polymerizable liquid crystal compound is coated thereon. The thus-produced retardation film 14 is bonded to the pressure-sensitive adhesive layer 13 formed on the protective film 12a together with the base material, and then the base material is peeled off, whereby the retardation film 14 can be transferred to the protective film 12 a.

The release film 16a is peeled from the circularly polarizing plate 1 when attached to the display device, and the peeled release film 16a is discarded. Therefore, unlike the protective films 12a, 12b, strict management of the phase difference value is not required. Therefore, when a commercially available film is used as the release film 16a, if the phase difference value is not compensated, malfunction may occur 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 such a phase difference value that is not strictly controlled is attached, 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, the circularly polarizing plate 1 is often provided with a surface protective film 16b, which is one type of release film, 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 in general at the time of bonding to the display device, and thus, unlike the protective films 12a, 12b, strict management of the retardation value is not required. In fig. 2, the protective film 12b and the surface protective film 16b may be bonded via 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 is made of PET resin. The surface protective film 16b is also made of a PET resin. A film made of a PET resin (PET resin film) is commonly used as a release film, and has an advantage of low cost. On the other hand, as described above, the low-cost PET resin film does not require strict management of the phase difference value. For this reason, for example, there is a case where the phase difference value varies for each product lot. In addition, even in the same PET resin film, there is a case where the phase difference value is deviated in the plane. Even in the case of a circularly polarizing plate in which such an inexpensive PET resin film is bonded as a release film, the inspection method of the present embodiment can detect the presence of defects with high accuracy.

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 obtaining Re (550) of the release film 16a is first shown. As described above, these release films are PET resin films, and such films can be easily put into the market. Sheets having a size of, for example, about 40mm×40mm are separated from the film (e.g., separated from a long film by using an appropriate cutting tool). Re (550) of the sheet was measured 3 times, and the average value of Re (550) was obtained. 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 of obtaining Re (550) of the surface protective film 16b, the same test may be performed.

Various commercially available products can be used as the light source 4, but a straight line light such as a laser (including a light close to a straight line light) is advantageous. The light emitted from the light source 4 is unpolarized light, and is circularly polarized light by a first polarization unit 3A described later.

In the first embodiment, the first polarizing section 3A and the second polarizing section 3B are both wide-band circularly polarizing plates, and each have a polarizing film for converting linearly polarized light into circularly polarized light and a phase difference film for converting linearly polarized light into circularly polarized light. The first polarization unit 3A and the second polarization unit 3B always form a crossed nicols state when the object 10 is inspected. In order to form the crossed nicols state using the circularly polarizing plate, when the slow axis of the phase difference film included in the first polarizing portion 3A and the slow axis of the phase difference film included in the second polarizing portion 3B are substantially parallel to each other as viewed from the light source side, the absorption axis of the polarizing film included in the first polarizing portion 3A and the absorption axis of the polarizing film included in the second polarizing portion 3B may be disposed so as to be substantially parallel to each other (arrangement α). In addition, as another configuration, when the slow axis of the phase difference film included in the first polarization unit 3A and the slow axis of the phase difference film included in the second polarization unit 3B are substantially orthogonal to each other as viewed from the light source side, the arrangement may be such that the absorption axis of the polarization film included in the first polarization unit 3A and the absorption axis of the polarization film included in the second polarization unit 3B are substantially orthogonal to each other (arrangement β). When the crossed nicols state is formed by the former arrangement α, the first polarization portion 3A and the second polarization portion 3B can be formed using one circular polarization plate. The phase difference filter 3 constituting the first polarization portion 3A and the second polarization portion 3B is a so-called defect-free phase difference filter.

In order to observe the light reflected from the object 10, a detection mechanism 5 including a CCD camera or the like may be disposed at a position on the light path of the reflected light on the side where the light source 4 is located out of both sides of the second polarization portion 3B. For example, the inspection of the object to be inspected can be performed by automatically performing detection by image processing analysis by combining a CCD camera and an image processing device. Alternatively, the detection means 5 may be a member other than the detection means, and the second polarization portion 3B may be visually observed by a person. In addition, a partition plate may be provided between the light source 4 and the CCD camera as appropriate.

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 bandpass filter 2, and the phase difference filter 3 so that the incident angle θ of the light to the object 10 changes. By moving the above mechanism, the phase difference developed by the peeling film 16a can be adjusted, and the brightness of the observation field can be adjusted to be dark to be suitable for inspection.

(inspection method)

Hereinafter, an inspection method of the circularly polarizing plate using the inspection apparatus 100 will be described. The inspection method of the present embodiment includes a step of selecting two wavelengths as light used for inspection (wavelength selecting step) and a step of performing inspection using the light of the wavelengths (defect inspecting step).

Wavelength selection step

Before starting the inspection of the object 10 including the circularly polarizing plate 1, the wavelength of light used in the inspection is selected. As described below, the wavelength of light used in the examination can be selected using the transmitted light of the circularly polarizing plate prepared as the test piece.

The wavelength selection step based on the transmitted light measurement (hereinafter, simply referred to as "transmitted light measurement") can be performed using a spectrophotometer (for example, V7100 manufactured by japan spectroscopy). Such a spectrophotometer includes a light source (transmission system light source) and a transmission light amount measuring mechanism, and is capable of measuring the amount of light (transmitted light) transmitted through the sample by placing the sample on an optical path connecting the transmission system light source and the transmission light amount measuring mechanism and irradiating the sample from the transmission system light source. The transmitted light measurement will be described with reference to fig. 3 and 4. As shown in fig. 3, the measuring instrument 500 used for the transmitted light measurement includes a transmission system light source 4A and a transmitted light amount measuring mechanism 5A. As a sample used for the transmitted light measurement, two test pieces ( test pieces 1A and 1B) each having a circular polarizing plate having the same structure as the circular polarizing plate 1 included in the object to be inspected 10 were prepared. Here, "the same structure" means that the material, thickness, and laminated structure are substantially the same. Test piece 1A includes polarizing film 11A and phase difference film 14A, and test piece 1B includes polarizing film 11B and phase difference film 14B.

The two test pieces are arranged so that the retardation films 14A and 14B face each other and the slow axes p and q thereof form an angle other than 90 ° when viewed from the optical path direction of the transmission system light source 4A. Fig. 4 (a) is a schematic perspective view showing a main part of the placement of the test pieces 1A and 1B. Fig. 4 (B) is a diagram schematically showing an angle θ1 formed by the slow axes p and q when the test pieces 1A and 1B are observed from the optical path 9 direction, and the angle θ1 formed by the slow axes of the phase difference films 14A and 14B is other than 90 °. The angle θ1 is preferably 10 ° to 80 °, more preferably 20 ° to 70 °, and still more preferably 30 °. 60 deg.. By disposing at such an angle θ1, a wavelength useful for defect inspection can be easily found.

Then, light of various wavelengths was incident from either one of the polarizing films 11A and 11B of the test pieces 1A and 1B so that the optical path 9 passed through the defect-free region on the test pieces 1A and 1B, and the polarizing films 11A and 11B were observed from the other side thereof, to determine the wavelength at which the transmitted light amount was the minimum. Such a commercially available spectrophotometer can change the wavelength of the transmission system light source in various ways, and can automatically analyze the amount of light absorbed when light of various wavelengths is emitted, so that the minimum wavelength can be obtained more easily.

The investigation of this wavelength is preferably carried out between 500 and 600 nm. Then, after the minimum wavelength (the wavelength at which the transmitted light amount is the minimum) is obtained, two wavelengths, that is, a wavelength 5nm to 50nm larger than the wavelength and a wavelength 5nm to 50nm smaller than the wavelength, are used as the wavelengths of light used in the examination. For example, when the minimum wavelength is 565nm, both 535nm and 595nm are used as wavelengths of light used for the inspection as ±30 nm. That is, it was determined that two bandpass filters, i.e., a bandpass filter transmitting light with a wavelength of 535nm and a bandpass filter transmitting light with a wavelength of 595nm, were used for the examination. The half-value width of the spectrum of the wavelength of the transmitted light is preferably ±10nm, more preferably ±5nm, with respect to the bandpass filter. The bandpass filters are different in spectrum from each other, and the most easily transmitted light is different in wavelength from each other. The half-value width of the light of the wavelength (peak wavelength) that is most easily transmitted is preferably ±10nm, more preferably ±5nm, with respect to the bandpass filter.

Defect inspection step

After determining the wavelength of light used for inspection, the object 10 is inspected for defects.

As shown in fig. 1, an object 10 to be inspected is placed on an inspection table 20 in an inspection apparatus 100. At this time, the side of the object 10 provided with the release film 16a or the retardation film 14 faces the light source 4 side, and the angle formed by the slow axis of the retardation film 14 of the circular polarizing plate 1 and the slow axis of the retardation film provided with the retardation filter 3 is 10 ° to 80 ° when viewed from the light source 4 side. The angle is preferably 15 ° to 50 °, more preferably 20 ° to 40 °. In the present embodiment, the first polarization unit 3A and the second polarization unit 3B are configured by the same circular polarizing plate (phase difference filter 3), and therefore the first polarization unit 3A and the second polarization unit 3B are disposed in a cross nicols state with respect to the light reflected from the object 10.

The bandpass filter 2, which is one of the two bandpass filters found in the wavelength selection step, is prepared and placed in the inspection apparatus 100. Light is incident from the light source 4 to the bandpass filter 2. In this case, the incident angle θ with respect to the object 10 (angle with respect to the perpendicular to the surface of the object 10) may be set to, for example, 3 ° to 30 °, or 5 ° to 20 °. When the light emitted from the light source 4 is light having low directivity, the reflection angle from the object 10 (or the observation angle by the detection means 5) is preferably within the above-described angle range.

The light emitted from the light source 4 passes through the bandpass filter 2, enters the first polarizer 3A, and passes through the first polarizer 3A to be circularly polarized light (optical path 9 a). The light transmitted through the first polarization portion 3A is then incident on the object 10. Then, the light is transmitted through the release film 16a in the test object 10, 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 first polarization portion 3A is reflected on the surface of the release film 16a in the object 10 (optical path 9 b). Since the first polarization portion 3A and the second polarization portion 3B form a crossed nicols state and are blocked by the second polarization portion 3B (the end of the optical path 9B), the observation field of view by the second polarization portion 3B of the detection mechanism 5 becomes dark.

On the other hand, a part of the light incident on the object 10 is reflected by a part of the defect (for example, the defect D existing at the interface between the retardation film 14 and the polarizing film 11 or the defect D') existing in the retardation film 14) existing in the object 10 (optical path 9 c). Since the phase difference of the reflected light is deviated from ideal (becomes unwanted elliptical polarized light) due to the defect D, the reflected light cannot be absorbed by the polarizing film, and reflected light at the interface is generated. The reflected light is transmitted without being blocked by the second polarization portion 3B. When it is observed from the detection mechanism 5 side, a 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 is an integral 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 is not disturbed, but in many cases, the phase difference exhibited by the release film 16a is not an integral multiple of the wavelength of the light transmitted through the bandpass filter 2, and therefore the polarization state of the circularly polarized light is disturbed, and as shown in fig. 5, the circularly polarized light cannot be converted into linearly polarized light by the phase difference film 14 and cannot be absorbed by the polarization film, and thus reflected light at the interface (optical path 9 d) is generated. Therefore, the amount of transmitted light passing through the second polarization portion 3B increases, and the observation field becomes bright. As a result, the bright spots of the defect portion that is to be observed are buried in the brightness of the entire observation field, and the discrimination of the defect becomes difficult. In addition, defects that should be observed as bright spots may be observed as black spots due to in-plane deviation of the phase difference value of the release film 16a or deviation per batch.

In order to solve this problem, in the inspection method of the present embodiment, the incidence angle θ of the light to the object 10 is changed, so that the influence of the phase difference of the release film 16a is reduced. That is, when the incident angle θ is changed, the phase difference that appears by the release film 16a is changed, so that the observation field of view can be further darkened by finding the incident angle θ that is "integer multiple" of the above. Here, in order to change the incident angle θ, the object 10 may be tilted or rotated variously (or may be moved together with the inspection table 20), or the light source 4, the bandpass filter 2, and the phase difference filter 3 may be tilted or rotated variously. In this way, the angle of incidence θ is changed variously by adjusting the relative positional relationship of the members constituting the inspection apparatus 100, and the angle at which the influence of the phase difference of the release film 16a is reduced is found. In the case of tilting the object 10 side, the slow axis direction of the circularly polarizing plate 1 may be used as the axis direction, or the fast axis direction may be used as the axis direction.

After the inspection is completed, the bandpass filter 2 is replaced with the other bandpass filter of the two bandpass filters found in the wavelength selection step, and the same inspection is performed again. By performing the inspection twice, light having a wavelength of 5nm to 50nm larger than the light transmitted by the second polarization portion 3B and light having a wavelength of 5nm to 50nm smaller than the light transmitted by the second polarization portion 3B are used in the inspection, and therefore blue spots are emphasized and visible in one band pass filter and red spots are emphasized and visible in the other band pass filter. Therefore, it is possible to check the presence or absence of both blue dot speckles and red dot speckles while suppressing the brightness of the entire observation field to be sufficiently dark.

According to the inspection method described above, the presence or absence of defects 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 to be inspected 10 is longer than that in the transmission type inspection method, and thus deformation defects such as wrinkles, which are difficult to detect by the transmission type inspection method, can be easily detected. In fig. 1, a case where the retardation film 14 in the circularly polarizing plate 1 has a defect is shown, but in a case where the polarizing film 11 has a defect, the defect can be detected by the inspection method of the present embodiment.

The inspection method of the present invention is preferably performed in a state where external light such as a darkroom is blocked in order to improve the detection sensitivity. In addition, the mounting surface of the inspection object 10 on the inspection table 20 is preferably subjected to a low reflection treatment in order to suppress as much as possible the reflected light reflected by the inspection table 20 from the light transmitted through the inspection object 10.

< second embodiment >

The inspection method of the second embodiment will be described. The inspection method of the second embodiment is different from the inspection method of the first embodiment in that a linear polarizing plate is used instead of the circular polarizing plates of the first polarizing portion 3A and the second polarizing portion 3B.

(inspection apparatus and inspected object)

As shown in fig. 6, the inspection apparatus 200 is configured as follows: the light source 4, the bandpass filter 2, and the first linear polarization plate 7A are disposed in this order, and the second linear polarization plate 7B is disposed so as to be arranged beside the first linear polarization plate 7A. The first linear polarization plate (first polarization portion) 7A and the second linear polarization plate (second polarization portion) 7B are arranged on substantially the same plane so that the planes are parallel to each other. The other structures in the inspection apparatus 200 are the same as those of the inspection apparatus 100 in the first embodiment.

When the object 10 is inspected, the first linear polarization plate 7A and the second linear polarization plate 7B are oriented so as to always form an orthogonal nicols state. At this time, note that the light incident on the second linear polarization plate 7B is reflected light reflected at the object 10. The first linear polarization plate 7A and the second linear polarization plate 7B are so-called defect-free linear polarization plates.

(inspection method)

Hereinafter, an inspection method of the circularly polarizing plate using the inspection apparatus 200 will be described. Before starting the inspection of the object 10 including the circularly polarizing plate, the wavelength of light used in the inspection is selected.

Wavelength selection step

The wavelength selection process is the same as in the first embodiment.

Defect inspection step

After determining the wavelength of light used for inspection, the object 10 is inspected for defects.

The inspection method using the inspection apparatus 200 is as follows. First, in the inspection apparatus 100, an object to be inspected 10 is placed on the inspection table 20. Then, the object 10 is disposed on the opposite side of the first linear polarization plate 7A and the second linear polarization plate 7B as viewed from the light source 4. At this time, the side of the object 10 provided with the release film 16a or the phase difference film 14 is oriented toward the light source 4 side, and the angle formed by the absorption axis of the polarizing film 11 and the absorption axis of the first linear polarizing plate 7A is 45 ° when viewed from the light source 4 side. The angle may be a value of 0 ° or more and 90 ° or less, and an angle exceeding 90 ° is a value of 0 ° or more and 90 ° or less. Here, the positional relationship between the light source 4 and the detection mechanism 5 is adjusted so that the first linear polarization plate 7A transmits light before the light enters the object 10, and the second linear polarization plate 7B allows light reflected by the object 10 to enter. The first linear polarization plate 7A and the second linear polarization plate 7B are adjusted so as to form a crossed nicols state.

The bandpass filter 2, which is one of the two bandpass filters found in the wavelength selection step, is prepared and placed in the inspection apparatus 200. Light is incident from the light source 4 to the bandpass filter 2. In this case, the incident angle θ with respect to the object 10 (angle with respect to the perpendicular to the surface of the object 10) may be set to, for example, 3 ° to 30 °, or 5 ° to 20 °. When the light emitted from the light source 4 is light having low directivity, the reflection angle from the object 10 (or the observation angle by the detection means 5) is preferably within the above-described angle range.

The light emitted from the light source 4 passes through the bandpass filter 2, enters the first linear polarization plate 7A, and passes through the first linear polarization plate 7A to become linearly polarized light (optical path 9 a). Then, the light enters the object 10 to be inspected (light path 9 a). Then, the phase difference film 14 constituting the circularly polarizing plate 1 is converted into circularly polarized light through the release film 16a in the object 10, and the absorption axis direction component of the circularly polarized light is absorbed by the polarizing film 11 (the end of the optical path 9 a). Here, a part of the light transmitted through the first linear polarization plate 7A is reflected on the surface of the release film 16a in the object 10 to be inspected (optical path 9 b). The reflected light is blocked by the second linear polarization plate 7B (the end of the optical path 9B) because the first linear polarization plate 7A and the second linear polarization plate 7B are arranged so as to form a crossed nicols state. Therefore, the observation field of view based on the second linear polarization plate 7B of the detection mechanism 5 becomes dark to such an extent that defects can be observed.

On the other hand, a part of the light incident on the object 10 is reflected by a part of the defect (for example, the defect D existing at the interface between the retardation film 14 and the polarizing film 11 or the defect D') existing in the retardation film 14) existing in the object 10 (optical path 9 c). Since the phase difference of the reflected light is deviated from ideal (becomes unwanted elliptical polarized light) due to the defect D, D', the amount of light absorbed at the polarizing film 11 or the amount of light absorbed by the second linear polarizing plate 7B is reduced by the deviation amount compared to the normal portion, and the light is transmitted through the second linear polarizing plate. When it is observed from the detection mechanism 5 side, a defective portion is observed as a bright point.

In this embodiment, the method of reducing the influence of the phase difference of the release film 16a or the principle of the effect of this embodiment is the same as that in the first embodiment.

The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments at all. For example, in the first embodiment, one phase difference filter 3 is used as the first polarization portion 3A and the second polarization portion 3B, but the first polarization portion 3A and the second polarization portion 3B may be prepared as different phase difference filters.

In the wavelength selection step of the above embodiment, the minimum wavelength is obtained by using the transmitted light, but alternatively, the minimum wavelength may be obtained by using the reflected light. For example, a laminate in which a circularly polarizing plate 1 is arranged on a reflecting plate such as a mirror is prepared, and light of an arbitrary wavelength is incident on the laminate from a light source. The transmitted light amount is confirmed by observing the light reflected from the laminate using a detection mechanism. Then, the light of the changed wavelength was irradiated, and the amount of transmitted light was confirmed. Thus, the transmitted light amount can be measured using light whose wavelength has been variously changed, and the wavelength at which the transmitted light amount is the smallest can be obtained.

Industrial applicability

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

Description of the reference numerals

1 … circular polarizing plate; 1A, 1B … test pieces (circular polarizing plates); 2 … bandpass filters; 3 … phase difference filter; 3a … first polarizing portions; 3B … second polarizing portions; 4 … light source; 4a … transmissive system light source; 5 … detection mechanism; 5A … transmitted light quantity measuring means; 7a … first linear polarizing plate (first polarizing portion); 7B … second linear polarizing plate (second polarizing portion); 9 (9 a, 9b, 9 c) … optical path; 10 … inspected object; 11 (11A, 11B) … polarizing films; 12a, 12b … protective films; 13 … adhesive layer; 14 (14A, 14B) … phase difference films; 15 … adhesive layer; 16a … release film; 16b … surface protective film; 20 … inspection station; 100. 200 … inspection device; 500 … meter; D. d' … defect; slow axis direction of p, q … phase difference film; θ … an incident angle; the slow axis of θ1 … is at an angle to each other.

Claims (7)

1. An inspection method for judging whether or not a film-like object to be inspected, which is a circularly polarizing plate comprising a polarizing film and a retardation film laminated on each other, and a release film comprising a polyethylene terephthalate resin laminated on the retardation film side of the circularly polarizing plate, is defective,

a light source, a bandpass filter for transmitting light of a predetermined wavelength, a first polarizing unit, and the object to be inspected having the release film side directed to the first polarizing unit side are sequentially arranged on the optical path of the light emitted from the light source, and a second polarizing unit in a cross nicol state with the first polarizing unit is arranged on the optical path of the light reflected by the object to be inspected,

causing light from the light source to enter the bandpass filter,

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

and observing the light reflected by the inspected object from the second polarization part side, thereby judging whether the circular polarization plate has a defect.

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

after the inspection using the bandpass filter, the inspection is performed using a bandpass filter that transmits light having a wavelength different from that of the light that is most easily transmitted by the bandpass filter.

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

before the said examination is carried out,

preparing a light source and two test pieces having the same circular polarization plate as the circular polarization plate of the inspected object,

the two test pieces are arranged such that the two test pieces face each other on the phase difference film side and the angle formed by the slow axes of the phase difference films is an angle other than 90 DEG when viewed from the optical path direction of the light source,

the light of various wavelengths is incident from either side of the polarizing film of the test piece so that the optical path passes through the defect-free region on the test piece, and the polarizing film is observed from the other side thereof to determine the wavelength at which the transmitted light amount is smallest, and at least one of the wavelength 5nm to 50nm larger than the wavelength and the wavelength 5nm to 50nm smaller than the wavelength is determined to be used as the predetermined wavelength.

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

the first polarizing portion and the second polarizing portion are both circularly polarizing plates.

5. The inspection method according to any one of claims 1 to 4, wherein,

the first polarizing portion and the second polarizing portion are formed of a single circular polarizing plate.

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

the first polarizing portion and the second polarizing portion are both linear polarizing plates.

7. The inspection method according to any one of claims 1 to 6, wherein,

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

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