JP2022172803A - Inspection method - Google Patents

Abstract

To provide an inspection method that can easily determine the presence or absence of color unevenness defects in an optical laminate that has a phase difference film indicating optical characteristics with reverse wavelength dispersive properties.SOLUTION: An inspection method is to determine the presence or absence of color unevenness defects in an optical laminate 1 obtained by laminating a first polarization film on a first phase difference film 5A indicating optical characteristics with reverse wavelength dispersive properties. The method includes: arranging the optical laminate 1 and a phase difference filter 6 having a second polarization film and a second phase difference film 5B under a condition in which an angle formed by their slow axes becomes 0°±5°; making inspection light incident in an inspection area A of the optical laminate 1 from either one side of the optical laminate 1 or the phase difference filter 6, and photographing the inspection area through which the inspection light passes with a color camera 8 from the other side. The method includes determining the presence or absence of color unevenness defects in the optical laminate 1 based on an image obtained by photographing the optical laminate with the color camera 8.SELECTED DRAWING: Figure 2

Description

The present invention relates to an inspection method.

Since the retardation film can convert linearly polarized light into circularly polarized light, or vice versa, circularly polarized light can be converted into linearly polarized light. and reflective liquid crystal display devices. Among the retardation films, the retardation film obtained by aligning and curing a polymerizable liquid crystal compound is extremely thin, so it has been attracting attention in manufacturing a thin display device (for example, patent documents 1).

In the manufacturing stage of the circularly polarizing plate, foreign matter may be mixed between the polarizer and the protective film, air bubbles may remain, or orientation defects may be present (hereinafter, these foreign matter, air bubbles, and Orientation defects may be collectively referred to as "defects"). When a circularly polarizing plate having a defect is attached to a display device, the defective portion may be visually recognized as a bright spot, or an image may appear distorted at the defective portion.

Therefore, before bonding the circularly polarizing plate to the display device, an inspection for the presence or absence of defects is performed. Patent document 2 shows an example of optical inspection using the polarization axis of a general polarizing plate. Here, a non-defective polarizing plate is used as a filter together with the polarizing plate to be inspected, and a portion where inspection light is not normally transmitted or blocked is detected as a defect.

JP-A-2006-58546 JP-A-9-229817

Circularly polarizing plates have defects due to external physical factors such as foreign matter, scratches, and bubbles, as well as defects that appear reddish or bluish due to a different phase difference compared to normal parts (hereinafter referred to as " (referred to as "uneven color defect") may also occur. According to the findings of the present inventors, such a color unevenness defect is likely to occur in a retardation film exhibiting so-called reverse wavelength dispersion optical characteristics. In the inspection of a circularly polarizing plate, it is necessary to be able to detect such color unevenness defects, but even with color unevenness defects, the difference in color tone (difference in phase difference) is slight compared to the normal part, and the brightness is almost the same. Therefore, conventionally, it was difficult to detect color unevenness defects. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an inspection method capable of easily determining the presence or absence of color unevenness defects in an optical laminate having a retardation film exhibiting optical characteristics of reverse wavelength dispersion.

The present invention is an inspection method for determining the presence or absence of color unevenness defects in an optical laminate in which a first retardation film and a first polarizing film exhibiting reverse wavelength dispersion optical characteristics are laminated, A retardation filter having a laminate, a second polarizing film, and a second retardation film having an in-plane retardation value for light with a wavelength of 550 nm that is substantially the same as the in-plane retardation value of the first retardation film. The first retardation film and the second retardation film are positioned to face each other, and the angle formed by the slow axes is 0 ° ± 5 °, and the optical laminate or Inspection light is incident on a predetermined inspection area of the optical laminate from one side of the retardation filter, and the inspection area through which the inspection light passes is photographed from the other side with a color camera. Provided is an inspection method for determining the presence or absence of a color unevenness defect in an optical laminate based on an obtained image.

In this inspection method, the optical layered body and the retardation filter are arranged such that the retardation films face each other and the angle formed by the slow axes is 0°±5°. For this reason, the phase difference between the two retardation films is added, and if there is a color unevenness defect, the image is emphasized.

Determining the presence or absence of color unevenness defects is performed by processing an image captured by a color camera with a differential filter, and processing the image obtained by processing with a differential filter as an object, and then using the image obtained by processing with the differential filter as an object, It may include determining whether there is a portion where the output value is greater than or equal to the first threshold value or less than or equal to the second threshold value, with reference to the output value of the portion where there is no . When the image is processed with a differential filter, an image is obtained in which the boundary of the portion where the color changes is emphasized. In this image, it is determined whether or not there is a portion exceeding the predetermined first and second thresholds based on the output value of the portion with little color change (portion without color unevenness defect). , facilitating the detection of uneven color defects.

The first retardation film may contain a cured product of a polymerizable liquid crystal compound, and may have a thickness of 0.5 μm to 10 μm.

When performing the inspection, the optical layered body may be inspected continuously in the length direction while being transported in the length direction of the optical layered body. Moreover, at this time, a plurality of inspection areas may be provided in the width direction of the optical layered body.

ADVANTAGE OF THE INVENTION According to this invention, the inspection method which can judge easily the presence or absence of the color unevenness defect of the optical laminated body which has the retardation film which shows the optical characteristic of reverse wavelength dispersion can be provided.

FIG. 3 is a cross-sectional view of an optical layered body; It is a figure which shows the test|inspection method of an optical laminated body.

Preferred embodiments of the present invention will be described in detail below with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted.

(Optical laminate)
First, an optical laminate to be inspected will be described. As shown in FIG. 1, the optical layered body 1 is formed by laminating a linear polarizing plate 4A and a retardation film (first retardation film) 5A via an adhesive or pressure-sensitive adhesive. The linear polarizing plate 4A has protective films 3, 3 on both sides of a polarizing film (first polarizing film) 2. As shown in FIG. One example of the optical layered body 1 is a circularly polarizing plate used in a liquid crystal display device or an organic EL display device. In addition, although FIG. 1 shows a mode in which the protective films 3 are provided on both sides of the polarizing film 2 as the linear polarizing plate 4A, a mode in which the protective film 3 is provided only on one side of the polarizing film 2 may be employed.

As the polarizing film 2, for example, a polyvinyl alcohol film in which iodine or a dichroic dye is adsorbed and oriented, or a polymerizable liquid crystal compound in which a dichroic dye is adsorbed and oriented is oriented and polymerized. mentioned. The thickness of the polarizing film 2 may be 1 μm to 40 μm, or may be 5 μm to 20 μm.

The protective films 3 , 3 are for protecting the polarizing film 2 . As the protective films 3, 3, those commonly used in the technical field of polarizing plates are used for the purpose of obtaining a polarizing plate having appropriate mechanical strength. Typically, cellulose ester films such as triacetyl cellulose (TAC) films; cyclic olefin films; polyester films such as polyethylene terephthalate (PET) films; (meth)acrylic films such as polymethyl methacrylate (PMMA) films film and the like. In addition, the protective film may contain additives commonly used in the technical field of polarizing plates. The retardation of the protective films 3, 3 is preferably small. For example, the in-plane retardation value (Re(550)) for light with a wavelength of 550 nm is preferably 10 nm or less, particularly preferably 5 nm or less. Each of the protective films 3, 3 may have a thickness of 5 μm to 30 μm, 10 μm to 28 μm, or 15 μm to 25 μm.

In this embodiment, the retardation film 5A functions as a λ/4 plate that converts linearly polarized light into circularly polarized light. The retardation film 5A of the present embodiment has a low retardation value for light with a short wavelength and a high retardation value for light with a long wavelength, which is a so-called reverse wavelength dispersion optical characteristic. Polarization conversion is possible. The retardation film 5A preferably contains a cured product of a polymerizable liquid crystal compound.

The polymerizable liquid crystal compound forming the retardation film 5A is disclosed in, for example, JP-A-2009-173893, JP-A-2010-31223, WO2012/147904, WO2014/10325 and WO2017-43438. can be mentioned. According to the polymerizable liquid crystal compounds described in these publications, it is possible to form a retardation film exhibiting reverse wavelength dispersion optical characteristics. Moreover, it is possible to form a thin retardation film. The retardation film 5A may have a thickness of 0.5 μm to 10 μm or 1 μm to 5 μm.

As a method for forming the retardation film 5A, a solution containing the polymerizable liquid crystal compound (polymerizable liquid crystal compound solution; liquid composition) is applied (coated) onto a separately prepared base film to form a coating film. , and photopolymerization thereof. At this time, the substrate film may be provided in advance with an alignment film for orienting the polymerizable liquid crystal compound. The alignment film may be one that is photo-aligned by irradiating polarized light, or one that is mechanically oriented by rubbing. As specific examples of the alignment film, those described in the above publications can be used. The retardation film 5A thus formed is attached together with the base film to another film, and then the base film is peeled off to transfer the retardation film 5A onto the other film. can be done. In this embodiment, the retardation film 5A can be transferred and laminated on the linear polarizing plate 4A.

In the formation of the retardation film 5A, if the base film to which the polymerizable liquid crystal compound solution is applied has foreign matter or the like, or if the base film itself has scratches or the like, the polymerizable liquid crystal compound solution is applied. Defects may occur in the coating film itself obtained by the process. In addition, when the alignment film is subjected to a rubbing treatment, 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 cured liquid crystal film). Thus, when forming a retardation film from a polymerizable liquid crystal compound, it is possible to form an extremely thin retardation film. can be In addition, unevenness in the thickness of the retardation film 5A also causes color unevenness defects.

As another layer that the optical laminate 1 may have, a temporary protective film may be provided on the surface on the linear polarizing plate 4A side. A positive C plate may be provided on the surface of the retardation film 5A. Other layers that may be provided are preferably layers that do not affect the retardation of the optical layered body 1 .

(Inspection methods)
An inspection method according to this embodiment will be described. A phase difference filter 6 having the same or substantially the same configuration as the optical laminate 1 with respect to phase difference is prepared. That is, the retardation filter 6 is formed by laminating a linear polarizing plate 4B and a retardation film (second retardation film) 5B via an adhesive or an adhesive, and the linear polarizing plate 4B is a polarizing film. (Second polarizing film) is provided with protective films on both sides thereof. The retardation film 5B in the retardation filter 6 also functions as a λ/4 plate. The difference between the retardation film 5A and the retardation film 5B is preferably 10 nm or less, more preferably 5 nm or less.

The retardation filter 6 may be manufactured separately by the same method as the optical layered body 1, or may be a part of the optical layered body 1 cut out. As the phase difference filter 6, a filter whose entire surface is known to be defect-free is used. The phase difference filter 6 may have the same structure as the optical layered body 1 with respect to phase difference, and may include other layers that are not involved in the phase difference. Alternatively, if the optical layered body 1 includes any layer such as the temporary protective film described above, the retardation filter 6 may not include this.

As shown in FIG. 2, the optical laminate 1 and the retardation filter 6 are arranged so that their surfaces are parallel to each other and are spaced apart from each other. At this time, the retardation film 5A and the retardation film 5B are arranged so as to face each other and the angle formed by their slow axes is 0°±5°. A light source 7 is arranged on one side of the arrangement of the optical laminate 1 and the retardation filter 6 facing each other, and a color camera 8 is arranged on the other side. In FIG. 2, the light source 7 is arranged on the optical laminate 1 side and the color camera 8 is arranged on the retardation filter 6 side, but this arrangement may be reversed.

Various commercial products can be used as the light source 7 . It may be one that emits light including all wavelengths of light in the visible light region, and may be, for example, a white LED. Alternatively, linear light such as laser light (including light that approximates linear light) may be used. The light emitted by the light source 7 may be unpolarized.

The color camera 8 captures an image in the visible light region, and is, for example, a CCD camera. In this case, it is preferable to detect by image processing analysis using a combination of a CCD camera and an image processing device. This makes it possible to automate image processing and detection of color unevenness defects, which will be described later. Further, the use of the color camera 8 instead of the monochrome camera is advantageous in detecting color unevenness defects because high brightness and contrast ratio can be obtained.

In the optical layered body 1, an inspection area A is formed in the vicinity of the intersection of the optical path 9 of the inspection light emitted by the light source 7, that is, the line connecting the light source 7 and the color camera 8. FIG. Here, the inspection area A is a three-dimensional concept including not only the surface of the optical layered body 1 but also the interior extending in the thickness direction. In the inspection, inspection light is incident on the inspection area A from the light source 7 and the inspection area A through which the inspection light passes is photographed by the color camera 8 . Based on the image obtained by this photographing, the presence or absence of the color unevenness defect of the optical layered body 1 is determined.

In making the determination, an image obtained by photographing with the color camera 8 may be processed with a differential filter. A differential filter is a kind of spatial filter, and is a process of obtaining a difference between adjacent pixels for all pixels in an image. In the resulting image, portions with hue changes are emphasized. Processing by the differential filter may be performed in only one of the MD direction and the TD direction.

Next, two thresholds (a first threshold and a second threshold) are set with reference to a normal portion (a portion with little change in hue) that is considered to have no uneven color defect. Then, it is determined whether or not there is a portion where the output value based on the image obtained by processing with the differential filter is greater than or equal to the first threshold value or less than or equal to the second threshold value. A bright threshold (first threshold) is set on the side where the output value is higher than the reference, and a dark threshold (second threshold) is set on the side where the output value is lower than the reference.

Then, the image obtained by processing with the differential filter is searched over the entire inspection area to see if there is a portion where the output value is above the bright threshold or below the dark threshold. If there is a portion where the output value is above the light threshold or below the dark threshold, that portion is determined to be a color unevenness defect. After finishing the inspection in the inspection area A, the inspection area A is moved to another part of the optical layered body 1 and inspection is performed in the same procedure. As described above, it is possible to determine whether or not there is a color unevenness defect in the entire area of the optical layered body 1 as an inspection object.

Since the difference in brightness between a portion with a color unevenness defect and a normal portion is small, it was difficult to detect the color unevenness defect by an inspection method using a monochrome camera. In the inspection method of the present embodiment, the retardation film 5A provided in the optical layered body 1 and the retardation film 5B provided in the retardation filter 6 are arranged so that the angle formed by their slow axes is 0°±5°. (so-called paranicol arrangement). Therefore, the phase difference due to both the retardation films 5A and 5B is added (total λ/2), and if there is a color unevenness defect, the image is emphasized and the image is displayed with light in the visible light region. Since this can be detected, the color unevenness defect can be photographed with high sensitivity by capturing it with the color camera 8 .

The inspection method of the present embodiment can be suitably applied even when the retardation film 5A exhibiting the optical characteristics of reverse wavelength dispersion is provided, or the thickness of the retardation film 5A is thin, like the optical layered body 1. can. When the retardation film included in the optical layered body 1 is a retardation film exhibiting optical characteristics of positive wavelength dispersion, the ideal value of retardation (λ/ Since the deviation from 4) is large, the entire inspection area looks bright, and even if there is a defect that should be seen as a color unevenness defect, it is difficult to detect the difference in hue. On the other hand, when the retardation film provided in the optical layered body 1 is a retardation film exhibiting optical characteristics of reverse wavelength dispersion, generally the ideal value of the retardation (λ/4) over the wavelengths of the entire visible light region is Since the deviation is small, the entire inspection area looks dark, and if there is a defect that should be seen as a color unevenness defect, it is easy to detect it as a red or blue color unevenness.

(Continuous inspection method)
The inspection method of the present embodiment can be carried out continuously in the length direction while fixing the locations of the light source, the color camera, and the phase difference filter and conveying the long optical laminate in the length direction. can. At this time, in order to inspect the entire width of the optical layered body, it is preferable to arrange a plurality of light sources, color cameras, and retardation filters in the width direction of the optical layered body to form a plurality of inspection areas. In this continuous inspection method, in addition to the inspection according to the present embodiment, an inspection using a conventional monochrome camera is also performed at another location on the transfer line, so that external physical factors such as foreign matter, scratches, and bubbles can be detected. Defects can also be inspected.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, in the above embodiment, a method of processing an image obtained by photographing with a color camera with a differential filter has been shown, but other means for emphasizing changes in hue may be used.

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

DESCRIPTION OF SYMBOLS 1... Optical laminated body, 2... Polarizing film, 3... Protective film, 4A, 4B... Linear polarizing plate, 5A, 5B... Retardation film, 6... Retardation filter, 7... Light source, 8... Color camera, 9... Optical path , A . . . inspection area.

Claims (6)

An inspection method for determining the presence or absence of color unevenness defects in an optical laminate obtained by laminating a first retardation film and a first polarizing film exhibiting reverse wavelength dispersion optical characteristics,
The optical laminate, the second polarizing film, and a second retardation film having an in-plane retardation value for light with a wavelength of 550 nm that is substantially the same as the in-plane retardation value of the first retardation film. and a retardation filter is arranged under the condition that the first retardation film and the second retardation film face each other and that the angle formed by the slow axes thereof is 0°±5°. ,
Inspection light is incident on a predetermined inspection area of the optical laminate from either one side of the optical laminate or the retardation filter, and the inspection area through which the inspection light passes is photographed from the other side with a color camera,
An inspection method for determining whether or not there is a color unevenness defect in the optical layered body based on an image obtained by photographing with the color camera. Determining the presence or absence of the color unevenness defect,
Processing the image obtained by photographing with the color camera with a differential filter,
For the image obtained by processing with the differential filter, the output value is equal to or greater than the first threshold value or equal to or less than the second threshold value, with reference to the output value of the portion without color unevenness defect in the photographed inspection area. 2. The inspection method of claim 1, comprising determining whether there is a portion that is covered. 3. The inspection method according to claim 1, wherein said first retardation film comprises a cured product of a polymerizable liquid crystal compound. 4. The inspection method according to claim 1, wherein the first retardation film has a thickness of 0.5 μm to 10 μm. The inspection method according to any one of claims 1 to 4, wherein the optical laminate is inspected continuously in the length direction while being conveyed in the length direction of the optical laminate. 6. The inspection method according to claim 5, wherein a plurality of said inspection areas are provided in the width direction of said optical layered body.

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