CN114096833B - Method and device for detecting uneven alignment defect of phase difference film - Google Patents
Method and device for detecting uneven alignment defect of phase difference film Download PDFInfo
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Abstract
The invention provides a method and a device for detecting uneven alignment defects of a phase difference film, which can improve the reproducibility of evaluation by detecting and evaluating uneven alignment defects of the phase difference film based on quantitative evaluation of an optical system. The method for detecting defects in the retardation film caused by uneven alignment of the present invention comprises the following steps (1) to (5). (1) The retardation axis of the retardation film is rotatably arranged between 2 polarizing plates arranged in crossed nicols so as to be inclined by-10 DEG to 10 DEG with respect to the absorption axis of the polarizing plate. (2) The retardation film is irradiated with inspection light through one polarizing plate. (3) The phase difference film is imaged through the other polarizing plate to obtain a luminance image. (4) The captured luminance image is subjected to differential (difference) processing in the oblique direction with respect to the slow axis of the phase difference film to emphasize the edge portion. (5) Binarizing the edge-emphasized luminance image with a predetermined threshold value to obtain a bright pixel or a dark pixel, and detecting the orientation unevenness from the pixel.
Description
Technical Field
The present invention relates to a method and an apparatus for detecting defects of uneven alignment of a retardation film. More specifically, the present invention relates to a method for detecting and evaluating uneven alignment defects of a retardation film by quantitatively evaluating the retardation film using an optical system, whereby the burden on an operator can be reduced and the reproducibility of the evaluation result can be improved, and an uneven alignment defect detection device used for the method.
Background
In recent years, liquid crystal display devices have been widely used for televisions, monitors for personal computers, and the like due to features such as power saving, light weight, and thin profile. The liquid crystal display device has the above advantages and also has a problem of viewing angle dependence due to refractive index anisotropy of a liquid crystal cell and a polarizing plate. As a representative method for improving the problem of the viewing angle dependence, there is a method using a retardation film.
In the conventional production of retardation films, even in a strictly controlled production process, it is difficult to completely prevent the occurrence of defects that deteriorate the surface quality of the film.
In recent years, the retardation film used in the liquid crystal display device is required to be thin, and the alignment unevenness defect found in the manufacturing process is remarkable along with the thinning of the liquid crystal display device.
In order to prevent films having such defects from flowing to the market, it is important to inspect the defects of the films, and in quality evaluation of defects of uneven alignment, a grade determination is conventionally performed by visual inspection. However, with such visual qualitative evaluation, the evaluation result greatly depends on the proficiency of the operator, the reproducibility is low, and the result may vary greatly when the operator changes. Further, since the person who can perform evaluation reliably is limited to a skilled person, there is a problem that the workload is biased to a part of the operators and the burden is increased.
As defect inspection of an optical film, a defect inspection method and an inspection apparatus disclosed in patent documents 1 and 2 are known.
In patent document 1, the following method is proposed: a transparent or semitransparent film sheet is used as an object, a light source is arranged on one surface of the conveyed film sheet, a1 st polarizing plate is arranged between the light source and a film, a linear array camera is arranged on the other surface, a2 nd polarizing plate is arranged between the linear array camera and the film, the offset angle of the polarizing directions of the 1 st polarizing plate and the 2 nd polarizing plate is set within +/-20 DEG, and defect information caused by foreign matters is detected from video signals output from the linear array camera.
Patent document 2 discloses a patterned retardation film used in a 3D television, in which 1 st and 2 nd polarizers are disposed so as to sandwich the film, and which includes a light source for irradiating the film with inspection light via the 1 st polarizer, a photographing device for photographing transmitted light of the film via the 2 nd polarizer to obtain a luminance image, and a defect detecting unit for detecting a defect from the luminance image.
The following defect inspection apparatus is proposed: the 1 st and 2 nd polarizing plates are in a state in which one polarization transmission axis is substantially parallel to one optical axis in a plurality of phase difference regions of the patterned phase difference film, and a defect inspection device based mainly on foreign matter and the like adjusts one polarization transmission axis so that "each brightness of a brightness image is at the same level in the vicinity of an extinction state" when a defect-free film is photographed.
However, in the method proposed in patent document 1,2 polarizing plates are largely out of the crossed nicols state, and in this state, the amount of light from the light source transmitting the polarizing plates is large, and it is difficult to capture the change in the polarization state due to the film defect, and there is a problem that information of the alignment unevenness to be obtained cannot be obtained.
Further, in the device proposed in patent document 2, since the captured luminance image is at the same level in the vicinity of the extinction state, there is a problem that a minute change in the polarization state for detecting the misalignment cannot be captured. Further, since the boundary line of the different phase difference regions of the patterned phase difference film is preferentially eliminated from the captured luminance image by the image processing, there is a possibility that the defect portion that is originally desired to be extracted is also eliminated.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 11-30591
Patent document 2: japanese patent laid-open No. 2013-50393
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made in view of the above-described problems and situations, and an object of the present invention is to provide a method for detecting and evaluating uneven alignment defects of a retardation film, which can reduce the load on an operator and improve the reproducibility of the evaluation result by performing quantitative evaluation using an optical system, and an uneven alignment defect detection device used for the method.
Means for solving the problems
In order to solve the above problems, the present inventors have found that, in the course of studying the cause of the above problems and the like, a method for detecting defects in alignment of a retardation film is obtained by using a device comprising 2 polarizing plates, a light irradiation device, an imaging device, and a defect detection unit and employing a method for detecting defects in alignment having a specific procedure, and by performing detection and evaluation of defects in alignment of a retardation film by quantitative evaluation using an optical system, the burden on an operator can be reduced, and reproducibility of evaluation results can be improved.
That is, the above-described problems of the present invention are solved by the following means.
1. A method for detecting defects in alignment unevenness of a retardation film, comprising the steps of (1) to (5),
Step (1): a step of arranging the 1 st and 2 nd polarizing plates, or the phase difference film, in a manner such that the slow axis of the phase difference film is within a range of-10 DEG to 10 DEG (excluding 0 DEG) with respect to the absorption axis of either one of the 1 st and 2 nd polarizing plates when the phase difference film is arranged between the 1 st and 2 nd polarizing plates arranged in a cross nicol manner;
step (2): a step of irradiating the retardation film with inspection light via the 1 st polarizing plate;
Step (3): a step of photographing the phase difference film by a photographing device through the 2 nd polarizing plate to obtain a luminance image;
Step (4): a step of differentiating (differentiating) the captured luminance image in a direction within a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film to obtain a luminance image with an edge portion emphasized; and
Step (5): and a step of binarizing the brightness image subjected to edge emphasis by a predetermined threshold value to obtain a bright pixel having a value equal to or higher than the threshold value and a dark pixel having a value lower than the threshold value, and detecting uneven orientation from the bright pixel or the dark pixel.
2. The method for detecting an uneven alignment defect of a retardation film according to claim 1, further comprising a step (6) of performing an image processing for expanding the binarized luminance image in an oblique direction in a range of 70 ° to 120 ° with respect to a direction of differential (difference) processing of the retardation film to emphasize a component in the oblique direction.
3. The method for detecting defects in alignment of a retardation film according to claim 2, further comprising a step (7) of performing shrinkage processing on the luminance image in the same direction after the expansion processing.
4. The method for detecting an uneven alignment defect of a retardation film according to claim 3, further comprising a step (8) of extracting, as an uneven alignment defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing.
5. The method for detecting an uneven alignment defect of a retardation film according to any one of items 1 to 4, wherein an angle of view θ of the lens calculated from a distance between a lens tip position of the imaging device and the retardation film and a size of a longitudinal direction of an inspection area on the retardation film is 23 ° or less with respect to the longitudinal direction of the retardation film.
6. An uneven alignment defect detection device for a retardation film according to any one of items 1 to 5, characterized in that the uneven alignment defect detection device for a retardation film comprises:
a 1 st polarizing plate and a2 nd polarizing plate disposed so as to be crossed with nicols through the retardation film;
A light source that irradiates the retardation film with inspection light via the 1 st polarizing plate;
a photographing device for photographing the phase difference film through the 2 nd polarizing plate to obtain a brightness image; and
A defect detecting section for detecting a defect from the luminance image,
The defect detection unit includes:
An edge detection circuit that, when the phase difference film is disposed between a1 st polarizing plate and a2 nd polarizing plate disposed in a crossed nicols manner, subjects the 1 st polarizing plate and the 2 nd polarizing plate, or the phase difference film to differential (difference) processing in a direction within a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film so that the slow axis of the phase difference film is within a range of-10 DEG to 10 DEG (excluding 0 DEG) with respect to an absorption axis of either one of the 1 st polarizing plate and the 2 nd polarizing plate, and emphasizes an edge portion when the brightness image that is photographed is disposed rotationally; and
And a binarizing circuit for binarizing the brightness image after edge detection by using a predetermined threshold value, so that each pixel is a bright pixel above the threshold value and a dark pixel below the threshold value.
7. The device for detecting defects in uneven alignment of a retardation film according to claim 6, wherein said defect detecting section comprises an image processing circuit, said image processing circuit
The binarized luminance image is subjected to expansion processing in an oblique direction in a range of 70 DEG to 120 DEG with respect to the differential (difference) processing direction of the phase difference film, and a component in the oblique direction is emphasized.
8. The device for detecting defects in uneven alignment of a retardation film according to claim 7, wherein said defect detecting section comprises an image processing circuit, said image processing circuit
After the expansion processing is performed, the luminance image is subjected to contraction processing in the same direction.
9. The device for detecting defects in uneven alignment of a retardation film according to claim 6, wherein said defect detecting section has a filter circuit
And extracting a portion satisfying a filter condition defined by a representative length of each pixel region as an orientation unevenness defect component in the direction from the luminance image after the shrinkage processing.
10. The device for detecting an uneven alignment defect of a retardation film according to any one of items 6 to 9, wherein an angle of view θ of the lens calculated from a distance between a lens tip position of the imaging device and the retardation film and a size of a longitudinal direction of an inspection area on the retardation film is 23 ° or less with respect to the longitudinal direction of the retardation film.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the means of the present invention, it is possible to provide a method for detecting and evaluating uneven alignment defects of a retardation film, which can reduce the load on an operator and improve the reproducibility of the evaluation result by performing quantitative evaluation using an optical system, and an uneven alignment defect detection device used for the method.
The finding mechanism or the action mechanism of the effect of the present invention is not yet clarified, but is presumed as follows.
It can be assumed that by arranging 2 polarizing plates in a nicol manner and arranging either one of the polarizing plates or the phase difference film so that the slow axis of the phase difference film is in the range of-10 ° to 10 ° (excluding 0 °) with respect to the absorption axis of the polarizing plates, it is possible to emphasize the change in polarization state accompanying the change in slow axis and to improve the detection accuracy of the defective portion (uneven alignment defect).
The differential processing is processing for extracting edges of an image by differential filtering (a portion where brightness in the extracted image changes sharply is referred to as edge extraction), but in the case of an image, since the values are not continuous, the differential processing is processed as an approximation of the differential by taking the difference between pixel values (referred to as "differential" in the present invention).
In order to emphasize the edge of the defective portion, the direction of the differentiation process is designated as a direction within a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG obliquely with respect to the slow phase axis of the phase difference film. In general, when a retardation film is produced, the slow axis is oriented in a certain direction by stretching or the like, but minute orientation irregularities caused by unevenness in width tension applied during stretching or drying are accumulated in addition to the above-described one direction, so that it is presumed that the inclination component of the orientation irregularities is easily extracted by differential processing as a result, and the accuracy of detecting the orientation irregularities can be improved.
Further, binarization of the obtained luminance image is performed to roughly distinguish between a defective portion and a normal region other than the defective portion, and it is estimated that the expansion process and the contraction process further emphasize the defective portion in the binarized image, thereby further improving the detection accuracy of the defect.
It is estimated that only the uneven alignment defect can be detected by extracting, as the uneven alignment defect component in the direction, a portion satisfying the filter condition defined by the representative length of each pixel region from the luminance image after the shrinkage processing, and the above image processing can provide an uneven alignment defect evaluation method with high accuracy and quantification.
Drawings
Fig. 1 is a schematic diagram schematically showing a conventional visual evaluation method of an uneven alignment defect.
Fig. 2 is a schematic diagram illustrating the angle of view of a lens mounted to a camera used in an inspection.
Fig. 3A is a specific example (original luminance image) of an image binarized by a predetermined threshold value.
Fig. 3B is a specific example of an image (binarized image) binarized by a predetermined threshold value.
Fig. 4 is a flowchart of image processing and a specific example of processing an image.
Fig. 5 is a schematic diagram showing an example of an uneven alignment defect detection device for a retardation film according to the present invention.
Fig. 6 is a schematic diagram illustrating a defect detection unit including an edge detection circuit, a binarization circuit, an image processing circuit, and a filter circuit.
Detailed Description
The method for detecting defects in the retardation film caused by uneven alignment of the present invention is characterized by comprising the steps (1) to (5). This feature is a feature of the technology that is common or corresponding in the following embodiments.
As an embodiment of the present invention, from the viewpoint of the effect discovery of the present invention, it is preferable that the method further comprises the step (6) of performing an image processing of expanding the binarized luminance image in an oblique direction in the range of 70 ° to 120 ° with respect to the direction of differential (differential) processing of the phase difference film to emphasize a component in the oblique direction, from the viewpoint of enabling precise and quantitative assessment of the alignment unevenness defect by emphasizing a defective portion.
The step (7) of performing the contraction processing on the luminance image in the same direction after the expansion processing is further included is preferable from the viewpoint of enabling accurate and quantitative assessment of the non-alignment defect by emphasizing the defective portion and reducing noise.
The step (8) of extracting, as an uneven-orientation defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing is further included, and is preferable from the standpoint of determining uneven orientation and enabling accurate and quantitative uneven-orientation defect evaluation.
The angle of view θ of the lens calculated from the distance between the lens front end position of the imaging device and the retardation film and the size of the inspection area on the retardation film in the longitudinal direction is preferably within 23 ° with respect to the longitudinal direction of the retardation film.
The reason for making the angle of view θ fall within the above range, that is, to maintain the distance between the retardation film and the camera so as to be the angle of view θ is to reduce the dependence of the incidence angle of the inspection light and to make the gradation of the image uniform at the center and the corners of the inspection region.
The device for detecting defects in uneven alignment of a retardation film according to the present invention is characterized by comprising: a1 st polarizing plate and a2 nd polarizing plate disposed so as to be crossed with nicols through the retardation film; a light source that irradiates the retardation film with inspection light via the 1 st polarizing plate; a photographing device for photographing the phase difference film through the 2 nd polarizing plate to obtain a brightness image; and a defect detection unit that detects a defect from the luminance image, the defect detection unit including: an edge detection circuit that emphasizes an edge portion of the captured luminance image by performing differential (difference) processing in a direction in a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film, by rotationally disposing the 1 st polarizing plate and the 2 nd polarizing plate or the phase difference film so that the slow axis of the phase difference film is in a range of-10 DEG to 10 DEG (except 0 DEG) with respect to an absorption axis of any one of the 1 st polarizing plate and the 2 nd polarizing plate disposed in a crossed nicol; and a binarization circuit for binarizing the brightness image after edge detection by using a predetermined threshold value, so that each pixel is a bright pixel above the threshold value and a dark pixel below the threshold value.
The defect detection unit preferably includes an image processing circuit that performs expansion processing on the binarized luminance image in an oblique direction in a range of 70 ° to 120 ° with respect to a differential (difference) processing direction of the phase difference film to emphasize a component in the oblique direction, from the viewpoint of enabling accurate and quantitative assessment of the uneven alignment defect.
The defect detection unit further includes an image processing circuit that performs contraction processing on the luminance image in the same direction after performing the expansion processing, and is preferable from the viewpoint of enabling accurate and quantitative assessment of the uneven alignment defect.
The defect detection unit further includes a filter circuit for extracting, as an uneven alignment defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing, and is preferable from the standpoint of determining uneven alignment and enabling accurate and quantitative uneven alignment defect evaluation.
The angle of view θ of the lens calculated from the distance between the lens tip position of the imaging device and the retardation film and the size of the inspection area on the retardation film in the longitudinal direction is preferably within 23 ° with respect to the longitudinal direction of the retardation film, from the viewpoint of enabling evaluation of defects in alignment that are excellent in operation efficiency and quantitative.
The present application and its constituent elements and specific embodiments/aspects are described in detail below. In the present application, "to" is used in the sense that the numerical values described before and after "are included as the lower limit value and the upper limit value.
Summary of the method for detecting defects in uneven alignment of a retardation film according to the present invention
The method for detecting defects in the retardation film caused by uneven alignment of the present invention is characterized by comprising the following steps (1) to (5).
Step (1): and a step of arranging the 1 st polarizing plate and the 2 nd polarizing plate, or the phase difference film, in a manner such that the slow axis of the phase difference film is within a range of-10 DEG to 10 DEG (excluding 0 DEG) with respect to the absorption axis of either one of the 1 st polarizing plate and the 2 nd polarizing plate when the phase difference film is arranged between the 1 st polarizing plate and the 2 nd polarizing plate arranged in a cross nicol manner.
Step (2): and irradiating the retardation film with inspection light via the 1 st polarizing plate.
Step (3): and a step of photographing the phase difference film by a photographing device through the 2 nd polarizing plate to obtain a brightness image.
Step (4): and differentiating (differentiating) the captured luminance image in a direction within a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film to obtain a luminance image with an edge portion emphasized.
Step (5): and a step of binarizing the edge-emphasized luminance image using a predetermined threshold value to obtain a bright pixel having a threshold value or more and a dark pixel having a lower threshold value, and detecting the uneven orientation from the bright pixel or the dark pixel.
Here, the term "retardation film" refers to an optical film that improves the problem of viewing angle dependence of a liquid crystal display device, and is used in VA (VIRTICAL ALIGNMENT, vertical alignment) liquid crystal display devices, for example, and has birefringence. The optical film is a transparent resin film having a specific function based on optical characteristics. The optical film is formed by stretching or the like, and if formed normally, has uniform optical characteristics (birefringence, retardation, or the like) in the plane, but actually generates slight unevenness.
The value of the retardation of the optical film can be generally defined by the following formula.
That is, the retardation Ro in the in-plane direction and the retardation Rt in the thickness direction of the optical film are expressed by the following formulas (1) and (2).
Ro＝(nx-ny)×d…(1)
Rt＝{(nx+ny)/2-nz}×d…(2)
In the formula, n x represents the refractive index in the slow axis direction in the film plane, n y represents the refractive index in the slow axis direction in the film plane, n z represents the refractive index in the thickness direction of the film, and d represents the thickness (nm) of the film.
In addition, the "slow phase axis" refers to an axis at which the traveling speed of light with a phase delay becomes the slowest when the light propagates in the film causing birefringence. That is, the direction in which the refractive index in the plane becomes maximum. The "phase advance axis" refers to an axis in which the traveling speed of light becomes the fastest, and refers to a direction in which the refractive index in the plane becomes the smallest.
The in-plane slow and slow axes of the retardation film can be confirmed by an automatic birefringence meter AxO Scan (AxO Scan Mueller matrix polarimeter: manufactured by Axometrics Co.).
The measurement of Ro and Rt of the retardation film can be performed by the following method.
1) The retardation film was subjected to humidity control at 23℃and 55% RH for 24 hours. The average refractive index of the retardation film was measured by an Abbe refractometer, and the thickness d was measured by a commercially available micrometer.
2) An automatic birefringence meter Axo Scan (Axo Scan Mueller matrix polarimeter: axometrics Inc.) in an environment of 23℃and 55% RH, the retardation Ro and Rt at 550nm of the retardation film after humidity control was measured.
When the retardation film of the present invention is used in the VA mode, for example, the retardation Ro in the in-plane direction measured in an environment of a measurement wavelength of 550nm, 23℃and 55% RH is preferably in the range of 20nm to 120nm, more preferably in the range of 30nm to 100 nm. The retardation Rt of the optical film in the thickness direction is preferably in the range of 70nm to 350nm, more preferably in the range of 100nm to 320 nm.
Further, since the phase difference is a value that varies depending on the wavelength of light to be irradiated to the optical film, the environmental conditions (temperature and humidity) under which measurement is performed, and the like, it is desirable to set these conditions so that the phase difference becomes an arbitrary value depending on the purpose of optical characteristic evaluation, the type of the optical film to be evaluated, and the like.
The term "alignment angle" as used herein refers to an angle formed by the alignment direction of the molecules forming the retardation film with respect to a predetermined reference direction, and generally corresponds to an angle formed by the in-plane slow axis of the retardation film with respect to the predetermined reference direction. The predetermined reference direction generally refers to the direction in which the retardation film extends in the width direction. The "uneven alignment defect" according to the present invention is a defect in which the orientation angle is deviated from the reference direction in the direction of the slow axis at each selected position (for example, in the case where a plurality of positions are selected in the width direction) in the film surface.
The "polarizing plate" is one of polarizing elements, and is generally composed of a polarizer and a protective film. The polarizer is used to change the vibration direction of incident linearly polarized light by rotating the transmission axis direction of the linearly polarized light having a specific vibration direction extracted from natural light (randomly polarized light). The "polarizer" is an element that transmits only light having a polarized wave plane in a certain direction, and is a polyvinyl alcohol-based polarizing film. Among the polyvinyl alcohol-based polarizing films, there are those dyed with iodine and those dyed with dichroic dyes.
The "absorption axis" refers to the direction of the axis of the polarizer that absorbs the vibration of light, and generally refers to an angle that coincides with the direction of extension of the polarizer.
The "1 st polarizing plate and the 2 nd polarizing plate disposed in crossed nicols" means that the "absorption axis" of the polarizer is orthogonal to the 90 ° direction between the 1 st polarizing plate and the 2 nd polarizing plate.
The present application and its constituent elements and specific embodiments/aspects will be described below. In the present application, "to" is used in the sense that the numerical values described before and after "are included as the lower limit value and the upper limit value.
[1] Structure of defect detection method for uneven orientation of phase difference film
The method for detecting defects in the retardation film due to uneven alignment of the present invention comprises the steps (1) to (5), more preferably comprises the steps (6), (7) and (8) following the step (5).
First, a conventional visual evaluation method of the uneven alignment defect will be schematically described.
Fig. 1 is a schematic diagram schematically showing a conventional visual assessment method 10 for uneven alignment defects.
The evaluation of the uneven alignment defect of the retardation film 1 is a method of transmitting the irradiation light L emitted from the lower flat LED illumination 2 in the order of the 1 st polarizing plate 3, the retardation film 1, and the 2 nd polarizing plate 4, and observing the uneven alignment defect of the retardation film 1 by visual observation 5. At this time, the absorption axes of the 1 st polarizing plate 3 and the 2 nd polarizing plate 4 are arranged so as to be crossed nicols, so that the irradiation light L is not transmitted as it is and becomes a dark portion, but the irradiation light L is polarized in the direction of the slow axis of the retardation film and becomes transmitted light by the evaluator slightly rotating the retardation film 1 from the absorption axis direction of the polarizing plate (tilting direction 6 of the arrow in the figure), and is observed as a dark region if there is an uneven alignment defect under the visual observation 5.
Therefore, the evaluation results are affected by the proficiency of the evaluator's method of handling the retardation film and the classification of the evaluator's experience of the uneven alignment defect, and thus are personal and qualitative evaluation methods.
The method for detecting defects in uneven alignment of a retardation film according to the present invention is a method for evaluating the defects by a predetermined procedure using an optical evaluation device, and therefore, it is possible to provide a quantitative evaluation method for evaluating defects which are not personal.
Hereinafter, each step of the method for detecting defects in alignment unevenness of a retardation film of the present invention will be described in detail.
Step (1): and a step of arranging the 1 st polarizing plate and the 2 nd polarizing plate, or the phase difference film, in a manner such that the slow axis of the phase difference film is within a range of-10 DEG to 10 DEG (excluding 0 DEG) with respect to the absorption axis of either one of the 1 st polarizing plate and the 2 nd polarizing plate when the phase difference film is arranged between the 1 st polarizing plate and the 2 nd polarizing plate arranged in a cross nicol manner.
When a film is provided between 2 polarizing plates (1 st polarizing plate and 2 nd polarizing plate) in a crossed nicols state, light is not transmitted and is not observed even if the film is provided so that the slow axis of the film has the same orientation as the absorption axis of the polarizing plates. When the film is slightly rotated with respect to the absorption axis of the polarizing plate, the polarization state of the light passing through the film changes according to the slow axis of the phase difference film (the direction of polarization slightly changes), so that the light is transmitted through the 2 nd polarizing plate and reaches.
Since the brightness change is small in the defect of the uneven alignment as the inspection target of this time, when the polarizing plate or the retardation film is excessively rotated, the light reaching the camera as the imaging device is too strong to be observed. As a result of the study, when either one of the 1 st polarizing plate and the 2 nd polarizing plate or the phase difference film is rotated so that the slow axis of the phase difference film is within a range of-10 ° to 10 ° with respect to the absorption axis of either one of the 1 st polarizing plate and the 2 nd polarizing plate, the phase difference unevenness is most clearly observed, and therefore, the phase difference is defined to be within the range.
In actual operation, in the below-described defect detection device of fig. 5, it is preferable that the retardation film is rotated without rotating the 1 st polarizing plate and the 2 nd polarizing plate, and the absorption axis of the polarizing plate is tilted with respect to the slow axis of the retardation film.
Step (2): and irradiating the retardation film with inspection light via the 1 st polarizing plate.
As an illumination device for irradiating the inspection light, it is preferable that the inspection light is transmitted in the order of the 1 st polarizing plate, the phase difference film, and the 2 nd polarizing plate, a sufficient area is required for photographing the inspection light, and the brightness is as uniform as possible.
The light source of the lighting device is not particularly limited, and an optical fiber type light source using a deuterium lamp, a halogen lamp, or an LED (LIGHT EMITTING Diode) lamp as a light source, or a surface light source using a fluorescent lamp, an LED, or an OLED (Organic LIGHT EMITTING Diode) can be used. Preferably a planar light source (planar light source), preferably using planar LED illumination.
The light quantity of the inspection light is managed by the inspection machine control software Lab VIEW (manufactured by National Instruments corporation), and the in-plane average luminance of the luminance calculation region (for example, rectangular region of the order of 80mm×60mm to 400mm×300 mm) set in the Lab VIEW is measured, and the light quantity of the light source is preferably adjusted so that the luminance value falls within the range of 128±10, so that a sufficient luminance image for evaluation is obtained.
In addition, regarding the luminance calculation region, a phenomenon occurs in which the inspection region becomes darker as it goes to the end of the inspection region due to the influence of the angle of incidence. When the average luminance in the plane is adjusted to be 128±10 even in a dark portion including the desired edge portion, the center portion becomes excessively bright, and key unevenness cannot be detected, so that the luminance calculation region is preferably set narrower than the inspection region. For example, when the inspection area is set to 400mm in length by 300mm in width, the luminance calculation area is preferably set to 90mm in length by 80mm in width.
Step (3): and a step of photographing the phase difference film by a photographing device through the 2 nd polarizing plate to obtain a brightness image.
The imaging device is not particularly limited, and a CCD camera of a field type or a line sensor type can be used. The segment type is used when the inspection region range of the retardation film can be covered by photographing within several times, and the line sensor type is used when a wider range than this is required for photographing, and is preferable in terms of photographing time and accuracy.
For example, models acA to 2500 gm manufactured by BASLER and models H6X8 to 1.0 to II manufactured by APACECOM can be used as cameras of the imaging device.
The inspection area is determined by the angle of view of a lens attached to the camera, the size of the polarizing plate and the size of the retardation film, the distance between the retardation film and the lens attached to the camera, and the like. If the imaging device is configured to be able to move the sample in the width direction, it is possible to measure the sample regardless of the width, as long as the inspection is performed a plurality of times.
For example, in the case where a sample having a length of 450mm and a width of 2500mm is used as a retardation film and an inspection area having a length of 400mm and a width of 300mm, the inspection may be performed by photographing a plurality of times. The length direction is also fixed according to the inspection area of the device. The width is the maximum width that is generally used as a retardation film.
The angle of view θ of the lens attached to the camera is calculated in detail from the distance between the lens front end position of the imaging device and the retardation film, and the size of the inspection area on the retardation film in the longitudinal direction, but is preferably within 23 ° with respect to the longitudinal direction of the retardation film, from the viewpoint of enabling evaluation of defects in alignment that are highly efficient and quantitative.
Fig. 2 is a schematic diagram illustrating a field angle θ of a lens mounted to a camera used in an inspection.
Regarding the distance WD between the front end position of the lens 56 and the retardation film 51 (the working distance is abbreviated as "distance from the front end of the lens to the position where the object is focused"), for example, when WD is 1150mm, the field angle θ of the lens is 22.14 ° when the length 51a of the retardation film is 450mm and the width 51b is 375mm with respect to the conveyance direction 51c of the retardation film 51 in the imaging region of the camera, as the uneven alignment defect inspection device 50 according to the present invention. In addition, when the inspection area is 400mm long and 300mm long, θ is 19.73 °. Can be calculated.
Step (4): and differentiating (differentiating) the captured luminance image in a direction within a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film to obtain a luminance image with an edge portion emphasized.
The general differentiation process aims to emphasize the edge portion of the captured luminance image. The differential processing is processing for extracting edges of an image by differential filtering (a portion where brightness in the extracted image changes sharply is referred to as edge extraction), but in the case of an image, since the values are not continuous, the differential processing is processed as an approximation of the differential by taking the difference between pixel values (referred to as "differential" in the present invention). In the differentiation processing, it is preferable to find and use a core when differentiating a matrix called a core (also called a matrix) in a direction ranging from 35 ° to 55 ° and a core when differentiating a matrix in a direction ranging from-55 ° to-35 ° in the study stage.
The edges refer to portions of the image that are divided into areas of darkness. In the case of emphasizing an edge, it is desirable to perform processing in a direction orthogonal to the direction in which the boundary of the light and the shade extends. The orientation unevenness defect is found along an orientation of about 45 ° with respect to the longitudinal direction (or the width direction), but there is a certain degree of deviation in the angle, and in order to cope with this, it is preferable to make the orientation of the differentiation process to be performed within a range of 35 ° to 55 ° with respect to the slow axis of the retardation film.
The differentiation processing software to be used is not limited, and analytical software NI vision (National Instruments Co.) is preferably used.
Step (5): and binarizing the edge-emphasized luminance image using a predetermined binarization software and a threshold value to obtain a bright pixel having a value equal to or higher than the threshold value and a dark pixel having a value lower than the threshold value, and detecting the orientation unevenness from the bright pixel or the dark pixel.
In the photographed image, the non-uniform orientation defect is observed as a dark region. Therefore, it is desirable to leave a group of elements in the image that appear darker at the time of binarization, so setting a threshold value is performed and only elements having a lower luminance than the threshold value are left.
At this time, the set threshold value is determined while confirming that the uneven portion that can be visually confirmed is clearly left. That is, the threshold value may be determined empirically.
The binarization is preferably performed specifically by the following method.
[A] the captured luminance image was read into a personal computer using analysis software NI vision (manufactured by National Instruments). The brightness image is preferably not manually performed because it changes with adjustment of focus, contrast, and brightness.
[B] Definition setting of black and white is performed.
In the analysis software NI vision, when a tick is made in Black Background, a luminance value 0 is indicated by Black, and a luminance value 255 is indicated by white. When the hook is not in the Black Background, the luminance value 0 is indicated by white, and the luminance value 255 is indicated by Black.
[C] Noise removal of images
Shading (shading) processing is performed. The shading process is a process of removing noise by averaging the brightness within an image.
[D] a band pass filter is applied.
For example, the band pass filter value is recommended to be 20 to 100. The set value is preferably set to be optimal because it depends on the initial luminance image.
[E] Binarization of the luminance image is performed.
The setting is performed with 8 bits, and a threshold value is set. The threshold is preferably adjusted in accordance with analytical software NI vision (National Instruments, inc.).
The threshold value is preferably set by the evaluator without being fixed because it varies according to the contrast of the image.
If the threshold is determined, it becomes a black-and-white image. Binarization is performed using a predetermined threshold value, and a dark pixel having a threshold value or more and a bright pixel lower than the threshold value are obtained, and the orientation unevenness is detected from the bright pixel or the dark pixel.
Fig. 3 is a specific example of an image binarized by a predetermined threshold value.
Fig. 3A is a photographed original luminance image in which dark pixel portions that appear darker are candidates for an uneven orientation defect. Fig. 3B shows a case where the threshold value is determined so as to clearly leave candidates of the uneven alignment defect and binarized as a dark pixel.
The method for detecting an uneven orientation defect of the present invention preferably further comprises the following steps (6), (7) and (8).
Step (6): and performing an image processing for expanding the binarized luminance image in an oblique direction in a range of 70 DEG to 120 DEG with respect to a differential (difference) processing direction of the phase difference film to emphasize a component in the oblique direction.
Since a large amount of noise other than the orientation defect uneven element remains in the image immediately after binarization, the expansion processing is performed to emphasize the defective portion, and the expansion processing is performed to facilitate noise reduction. Here, the "expansion processing" generally refers to processing of a binarized black-and-white image, and is called expansion (expansion) in which 1 pixel is replaced with a white pixel in the vicinity of the pixel of interest. The "shrinkage process" described later refers to a process of replacing a pixel whose periphery is black with a pixel whose 1 pixel is black, which is conversely called shrinkage (error).
In order to leave the orientation defect uneven and remove noise, it is effective to perform processing in a direction in which the unevenness exists. When the differential processing is expressed with reference to the direction of the differential processing, the processing is performed in a direction orthogonal to the differential processing. This is because it is desirable to perform the differentiation in a direction perpendicular to the direction in which the unevenness exists. However, since there is a deviation in the direction of the unevenness, it is preferable to perform the expansion processing in an oblique direction within a range of 70 ° to 120 ° with respect to the direction of the differential (difference) processing in order to cope with the deviation.
Step (7): and a step of performing a contraction process on the luminance image in the same direction after performing the expansion process.
The contraction processing is performed in the next expansion processing to remove noise as much as possible, and similarly, the differential processing is performed in a direction orthogonal to the direction in which the unevenness exists, so that it is preferable to perform the contraction processing in an oblique direction in which the angle of the direction in which the unevenness exists is in the range of 70 ° to 120 ° with respect to the direction in which the differential (differential) processing exists.
The expansion process and the contraction process can be performed using the analysis software NI vision (National Instruments).
Step (8): and extracting a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing as an uneven-orientation defect component in the direction.
This step is also called a filtering process or a filtering process, and the "filtering condition defined by the representative length of each pixel region" refers to a condition empirically required for detecting an uneven alignment defect.
For example, the binarized luminance image is subjected to filtering to remove an element having a shape close to a perfect circle (filtering process 1), to remove an element having a short length (filtering process 2), or to remove an element having an area outside a predetermined range (filtering process 3), and a portion satisfying the filtering condition defined by the representative length of each pixel region is detected as an uneven orientation defect.
Specifically, for example, as the filter processing 1, a round factor H of Haywood (Haywood) is set: when the quotient of the circumference of the pixel region divided by the circumference of the same area is obtained, it is preferable that only the pixel region in the range of 1.5.ltoreq.H.ltoreq.5 remains. The sea wood circle factor H is 1 in the case of perfect circles.
Further, as the filtering process 2, it is preferable to remove a pixel region having a specific length or less from the long side of the uneven alignment.
Further, as the filter processing 2, the stretch factor L is set to: when the quotient of the maximum Feret (Feret) diameter of the pixel region divided by the short side (Feret) of the equivalent rectangle is obtained, it is preferable to detect the uneven alignment defect while leaving only the pixel region in the range of 4.ltoreq.l.ltoreq.13.
The filter processing software used in the filter processing is not limited, and may be performed using the analysis software NI vision (National Instruments).
Fig. 4 shows a flowchart of image processing and a specific example of processing an image.
(P1) capturing an image of the retardation film to obtain a luminance image,
(P2) a shading process of the luminance image (for removing noise by averaging the luminance in the image),
(P3) emphasis of an edge portion based on differential (difference) processing of the luminance image,
(P4) binarization of the luminance image,
(P5) emphasis processing (expansion and contraction processing) of the binarized image,
(P6) filtering processing 1 (removing elements having shapes close to perfect circles) on the binarized image,
(P7) filtering 2 (removing elements with short lengths) of the binarized image,
(P8) filtering processing 3 (removing elements whose areas are outside the specified range) on the binarized image,
(P9) detecting only the orientation unevenness defect from the binarized image by the filtering process.
[2] Device for detecting defect of uneven orientation of phase difference film
The device for detecting uneven alignment defects of a retardation film used in the method for detecting uneven alignment defects of a retardation film according to the present invention is characterized by comprising: a 1 st polarizing plate and a2 nd polarizing plate disposed so as to be crossed with nicols through the retardation film; a light source that irradiates the retardation film with inspection light via the 1 st polarizing plate; a photographing device for photographing the phase difference film through the 2 nd polarizing plate to obtain a brightness image; and a defect detection unit that detects a defect from the luminance image, the defect detection unit including: an edge detection circuit that emphasizes an edge portion of the captured luminance image by performing differential (difference) processing in a direction in a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film, by rotationally disposing the 1 st polarizing plate and the 2 nd polarizing plate or the phase difference film so that the slow axis of the phase difference film is in a range of-10 DEG to 10 DEG (except 0 DEG) with respect to an absorption axis of any one of the 1 st polarizing plate and the 2 nd polarizing plate disposed in a crossed nicol; and a binarization circuit for binarizing the brightness image after edge detection by using a predetermined threshold value, so that each pixel is a bright pixel above the threshold value and a dark pixel below the threshold value.
Fig. 5 is a schematic diagram showing an example of an uneven alignment defect detection device for a retardation film according to the present invention.
The uneven alignment defect detection device 50 for a retardation film according to the present invention is a device that irradiates irradiation light L emitted from a lower flat LED illumination 52 to transmit in the order of a light shielding plate 53, a1 st polarizing plate 54, a retardation film 51, a light shielding plate 53, and a2 nd polarizing plate 55, and photographs uneven alignment defects of the retardation film 51 by a camera 57 equipped with a lens 56. At this time, the absorption axes of the 1 st polarizing plate 54 and the 2 nd polarizing plate 55 are arranged so as to be crossed nicols, so that the irradiation light L is not transmitted as it is and becomes a dark portion, but by slightly rotating (tilting) the phase difference film 51 from the absorption axis direction of the polarizing plates, the irradiation light L is polarized in accordance with the slow phase axis direction of the phase difference film 51, and the uneven alignment is imaged as a dark region in the imaged image.
The misalignment defect detecting apparatus 50 preferably includes a mechanism (not shown) for rotating the 1 st polarizing plate 54 and the 2 nd polarizing plate 55 with respect to the slow axis of the retardation film so that the absorption axis of the polarizing plate is within a range of-10 ° to 10 ° without rotating the retardation film 51.
The dimensions of the respective portions are not particularly limited, and for example, a long sample having a length of 450mm cut in the longitudinal direction and a width of 2000mm cut in the width direction is used as the retardation film for evaluation. The imaging device is preferably configured such that the angle of view θ of the lens calculated from the distance between the lens tip position of the imaging device and the retardation film and the size of the inspection area on the retardation film in the longitudinal direction is within 23 ° with respect to the longitudinal direction of the retardation film, and for example, the inspection device having the structure shown in fig. 2 is preferably mounted for inspecting the area of 400mm in the longitudinal direction and 300mm in the width direction, from the viewpoint of inspection efficiency.
The light source of the lighting device is not particularly limited, and as described above, an optical fiber type light source using a deuterium lamp, a halogen lamp, or an LED lamp as a light source, or a surface light source using a fluorescent lamp, an LED, or an OLED can be used.
The imaging device is not particularly limited, and a CCD camera of a field type or a line sensor type can be used. The segment type is used when the range of the object to be measured of the phase difference film can be covered by photographing within several times, and the line sensor type is used when a wider range than this is required for photographing, and is preferable in terms of photographing time and accuracy.
As a standard example of the camera and the lens, the above description is given.
Further, it is preferable that the defect detecting section has an image processing circuit for expanding the binarized luminance image in an oblique direction in a range of 70 ° to 120 ° with respect to a direction of differential (difference) processing of the phase difference film to emphasize a component of the oblique direction.
In addition, it is preferable that the defect detecting section has an image processing circuit that performs contraction processing on the luminance image in the same direction after performing the expansion processing.
Further, it is preferable that the defect detection unit has a filter circuit for extracting, as the orientation unevenness defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing.
Fig. 6 is a schematic diagram illustrating a defect detection unit including an edge detection circuit, a binarization circuit, an image processing circuit, and a filter circuit.
[ Defect detection section ]
Each structure of the defect detecting unit 100 will be described.
As shown in fig. 6, the defect detecting unit 100 includes a control unit 101, a recording unit 102, a communication unit 103, a data processing unit 104, an operation display unit 105, and the like, and the respective units are communicably connected to each other via a bus 106.
The control unit 101 includes: a CPU (Central Processing Unit ) 101a for controlling the operation of the defect detecting unit 100 as a whole; a RAM (Random Access Memory ) 101b that functions as a work memory for temporarily storing various data when the CPU 101a executes a program; a program memory 101c for storing a program and fixed data read and executed by the CPU 101 a; etc. The program memory 101c is constituted by a ROM or the like.
The recording unit 102 stores and records, in addition to the image data after photographing and image processing, data of various thresholds used in the image processing circuit and irradiation condition data of the illumination device 52.
The communication unit 103 includes an interface for communication such as network I/F, and transmits the measurement conditions input from the operation display unit 105 to the image capturing and adjusting apparatus 120 via a network such as an intranet. The communication unit 103 receives image data transmitted from the imaging device 130.
The data processing unit 104 performs image processing based on the luminance image data received by the communication unit 103 and captured by the imaging device 130 (the lens 56 and the camera 57).
The data processing unit 104 includes various processing circuits used in steps (4) to (8) according to the present invention.
The data processing unit 104 includes a shading processing circuit 104a, an edge detection circuit 104b (step (4)) for performing differential processing in a direction ranging from 35 ° to 55 ° or-55 ° to-35 ° with respect to the slow phase axis of the phase difference film to emphasize an edge portion, a binarization circuit 104c (step (5)) for binarizing the luminance image after edge detection with a predetermined threshold value to make each pixel a bright pixel equal to or higher than the threshold value and a dark pixel lower than the threshold value, an image processing circuit 104d (step (6) and step (7)) for performing expansion processing or contraction processing on the luminance image, and a filter circuit 104e (step (8)) for extracting, as an orientation uneven defect component in the direction, a portion satisfying a filter condition defined by the representative length of each pixel region from the luminance image after the contraction processing.
The operation display unit 105 may be configured by, for example, an LCD (Liquid CRYSTAL DISPLAY), a touch panel provided so as to cover the LCD, various switches, buttons, numeric keys, and an operation key group (not shown). The operation display unit 105 receives an instruction from a user, and outputs an operation signal to the control unit 101. The operation display unit 105 displays various setting screens for inputting various operation instructions and setting information, and an operation screen for displaying various processing results, etc., on the LCD in accordance with the display signal output from the control unit 101.
[ External output device ]
The defect detecting unit 100 may include an external output device 150 communicably connected to the defect detecting unit 100. The external output device 150 may be a general PC (Personal Computer ), an image forming device, or the like. The external output device 150 may function as an operation display unit instead of the operation display unit 105 of the defect detection unit 100.
Examples
The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, "part" or "%" is used, and "part by mass" or "% by mass" is indicated unless otherwise specified.
Example 1
< Preparation of retardation film for evaluation >
A retardation film for evaluation was produced in accordance with the following method.
(Preparation of microparticle Dispersion dilution)
After 10 parts by mass of AEROSIL R812 (manufactured by AEROSIL Co., ltd., primary average particle diameter: 7nm, apparent specific gravity: 50 g/L) and 90 parts by mass of ethanol were mixed in a dissolver with stirring for 30 minutes, they were dispersed by using a high-pressure emulsifying machine (Manton Gorlin) as a high-pressure dispersing machine to prepare a fine particle dispersion.
88 Parts by mass of methylene chloride was added to the obtained fine particle dispersion with stirring, and the mixture was stirred and mixed for 30 minutes in a dissolver, followed by dilution. The obtained solution was filtered through a polypropylene air drum filter TCW-PPS-1N manufactured by ADVANTEC Toyo Co., ltd.
(Modulation of inline (in-line) additive liquid
36 Parts by mass of the fine particle dispersion diluted solution prepared above was added to 100 parts by mass of methylene chloride while stirring, and after stirring for 30 minutes, 6 parts by mass of cellulose acetate propionate (CAP: degree of substitution of acetyl group 2.00, degree of substitution of propionate 0.60, weight average molecular weight 27 ten thousand) was added while stirring, and stirring was further continued for 60 minutes. The obtained solution was filtered through FINEMET NF manufactured by japan fine line (ltd.) to obtain an inline additive solution. As the filter material, a material having a nominal filtration accuracy of 20 μm was used.
(Preparation of coating)
The following components were put into a closed vessel and completely dissolved while heating and stirring. The resulting solution was filtered at 50℃using a filter equipped with a leaf disc filter apparatus to obtain a main dope. As the filter material, a material having a nominal filtration accuracy of 20 μm was used.
< Composition of Main coating >
Cellulose acetate propionate (CAP: degree of substitution of acetyl 2.00, degree of substitution of propionate 0.60, weight average molecular weight 27 ten thousand)
100 Parts by mass
And (2) a plasticizer: a sugar ester; bzSc (benzyl sucrose: average degree of ester substitution=5.5)
12 Parts by mass
Dichloromethane 430 mass portions
11 Parts by mass of methanol
100 Parts by mass of the main paint 1 and 2.5 parts by mass of the inline additive solution were thoroughly mixed by an inline Mixer (Dongli static in-line Mixer Hi-Mixer, SWJ) to obtain a paint.
(Film-forming Process)
The resulting dope was uniformly cast on a stainless steel belt support using a tape casting apparatus under conditions that the liquid temperature of the dope was 35℃and the width was 1950mm and that the final film thickness was 40. Mu.m. After forming a web by evaporating the organic solvent in the resulting coating film until the residual solvent content becomes 100 mass%, the web was peeled off from the stainless steel belt support. After the obtained web was further preliminary dried at 110℃for 5 minutes to set the residual solvent content to 10 mass%, the web was stretched 1.4 times with respect to the original width in the TD direction at 160℃by a tenter, giving the following predetermined phase difference. Regarding the extension speed, extension was performed at a speed of 300%/min.
After stretching by a tenter, the sheet was relaxed at 130℃for 1 minute, and then the sheet was transported through a drying zone by a large number of rolls to terminate drying. The drying temperature was 130℃and the conveying tension was 100N/m. The obtained film was slit at a width of 2000mm, knurled with a width of 10mm and a height of 5 μm was applied to both ends of the film, and the film was wound around a core having an inner diameter of 15.24cm at an initial tension of 220N/m and a final tension of 110N/m, to obtain a retardation film for evaluation having a length of 4000m and a dry film thickness of 40. Mu.m.
As a result of measurement by the above-described measurement method, the phase difference of the above-described phase difference film is Ro:50nm and Rt:120nm.
< Evaluation of uneven orientation Defect >
Using the uneven alignment defect evaluation apparatus shown in fig. 5, uneven alignment defects of the retardation film produced as described above were detected and evaluated by the following steps (1) to (8).
The retardation film for evaluation was cut into a long sample having a length of 450mm and a width of 2000 mm. The imaging device performs imaging a plurality of times in an inspection area of 400mm in the longitudinal direction and 300mm in the width direction by setting the distance between the lens front end position of the imaging device and the phase difference film to 1150mm and setting the angle of view θ of the lens calculated from the distance and the size of the inspection area in the longitudinal direction on the phase difference film to 20 °.
Step (1): and a step of arranging the 1 st polarizing plate and the 2 nd polarizing plate in a rotating manner so that the slow axis of the phase difference film becomes-7 DEG with respect to the absorption axis of the polarizer of the 1 st polarizing plate when the phase difference film is arranged between the 1 st polarizing plate and the 2 nd polarizing plate arranged in a crossed nicols manner.
In the angles shown in table I, the counterclockwise direction is a negative value, and the clockwise direction is a positive value.
Step (2): and a step of irradiating the retardation film with inspection light from a flat-panel LED via the 1 st polarizing plate.
Step (3): and a step of photographing the phase difference film via the 2 nd polarizing plate by a photographing device (camera) to obtain a luminance image.
Step (4): and differentiating (differentiating) the captured luminance image in a direction of 40 DEG with respect to a slow axis of the phase difference film to obtain a luminance image with an edge portion emphasized.
Step (5): and a step of binarizing the brightness image subjected to edge emphasis by a predetermined threshold value to obtain a bright pixel having a value equal to or higher than the threshold value and a dark pixel having a value lower than the threshold value, and detecting uneven orientation from the bright pixel or the dark pixel.
Step (6): and performing an image processing for expanding the binarized luminance image in an oblique direction of 90 DEG with respect to a differential (difference) processing direction of the phase difference film to emphasize a component in the oblique direction.
Step (7): and a step of performing a contraction process on the luminance image in the same direction after performing the expansion process.
Step (8): and extracting, as an orientation unevenness defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing.
(Filtering 1)
Set to sea wood circle factor H: when the quotient of the circumference of the pixel region divided by the circumference of the same area is obtained, only the pixel region in the range of 1.5.ltoreq.H.ltoreq.5 remains.
(Filtering 2)
Setting to the stretch factor L: when the maximum feret diameter of the pixel region is divided by the shorter side (feret) of the equivalent rectangle, only the pixel region in the range of 4.ltoreq.l.ltoreq.13 remains.
Examples 2 to 8
In the evaluation conditions of example 1, the same evaluation was performed by changing the device conditions θ, θf, and θp (each indicating an angle) and the image processing conditions (step (4), step (5), step (6), step (7), step (8) -1: filter 1 and (8) -2: filter 2) described in table I, and examples 2 to 8 were obtained.
Here, θ denotes a field angle of a lens mounted on the camera, θf denotes an angle formed by a slow phase axis of the retardation film and an absorption axis of the polarizing plate, and θp denotes an angle formed by absorption axes of 2 polarizing plates.
Comparative examples 1 to 3
Using the uneven alignment defect evaluation apparatus of fig. 1, the evaluations of comparative examples 1 to 3 were performed by 3 panelists having an evaluation experience of 1 year or more (visual 1), an evaluation experience of half a year or more and less (visual 2), and an evaluation experience of less than half a year (visual 3).
Comparative example 4
Evaluation was carried out according to examples described in Japanese patent application laid-open No. 11-30591 paragraphs [0113] to [0122 ].
Comparative example 5
An evaluation of example 1 described in Japanese patent application laid-open No. 2013-50393 paragraphs [0098] to [0099] was carried out.
Evaluation (evaluation)
(1) Complexity of
The complexity was determined based on the time taken for the evaluation of 1 sample.
And (3) the following materials: less than 1 minute
And (2) the following steps: more than 1 and less than 5 minutes
Delta: more than 5 minutes and less than 10 minutes
X: more than 10 minutes
In the case of good to excellent, it is considered that the method is a complicated and preferable evaluation method.
(2) Detection accuracy
The detection accuracy is classified by the degree of coincidence between the result (customer-side evaluation result) when the quality evaluation is performed after the display device is assembled using the inspected retardation film and the quality evaluation result (in-house evaluation result) in the film state.
And (3) the following materials: the evaluation results of 9 to 10 samples are consistent
And (2) the following steps: the evaluation results of 6 to 8 samples are consistent
Delta: the evaluation results of 3 to 5 samples are consistent
X: the evaluation results of 0 to 2 samples are consistent, and for the detection accuracy, delta or more is required, and good to excellent are preferable. Table I shows the above evaluation methods and evaluation results.
TABLE 1
As is clear from the evaluation results in table I, by using the method and apparatus for detecting uneven alignment defects of a retardation film according to the present invention, the complexity and detection accuracy of uneven alignment defect evaluation of a retardation film are improved compared to visual evaluation.
Therefore, according to the present invention, it is possible to provide a method for detecting an uneven alignment defect of a retardation film and an uneven alignment defect detecting device as follows: by detecting and evaluating the uneven alignment defect of the retardation film based on the quantitative evaluation of the optical system, the evaluation is not personal, and the reproducibility of the evaluation can be improved more easily.
Industrial applicability
The method and device for detecting uneven alignment defects of a retardation film according to the present invention can detect and evaluate uneven alignment defects of a retardation film by quantitative evaluation based on an optical system, and the evaluation is not personal and is suitable for easier evaluation of uneven alignment defects of a retardation film.
Symbol description
1. Retardation film
2. Flat LED illumination
3.1 St polarizing plate
4.2 Nd polarizing plate
5. Visual inspection
6. Direction of inclination
L irradiation light
Angle of view θ
10. Conventional visual evaluation method for uneven alignment defect
50. Uneven orientation defect detection device
51. Retardation film
51A length is long
51B width is long
52. Flat LED illumination
53. Shading plate
54. 1 St polarizing plate
55. 2 Nd polarizing plate
56. Lens
57. Camera with camera body
100. Defect detecting section
101. Control unit
101a CPU
101b RAM
101C program memory
102. Recording unit
103. Communication unit
104. Data processing unit
104A shading processing circuit
104B edge detection circuit
104C binarization circuit
104D image processing circuit
104E filter circuit
105. Operation display unit
120. Photographic adjusting device
130. Image pickup apparatus
150. External output device
Claims (6)
1. A method for detecting defects in alignment unevenness of a retardation film, comprising the steps of (1) to (7),
Step (1): a step of arranging the retardation film between a 1 st polarizing plate and a 2 nd polarizing plate arranged in crossed nicols such that a slow axis of the retardation film is within a range of-10 DEG to 10 DEG and 0 DEG with respect to an absorption axis of any one polarizing plate of the 1 st polarizing plate and the 2 nd polarizing plate, or the retardation film is rotated;
step (2): a step of irradiating the retardation film with inspection light via the 1 st polarizing plate;
Step (3): a step of photographing the phase difference film by a photographing device through the 2 nd polarizing plate to obtain a luminance image;
Step (4): extracting a difference between adjacent pixel values in a direction within a range of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to a slow axis of the phase difference film with respect to the photographed luminance image, thereby obtaining a luminance image with an edge portion emphasized;
step (5): binarizing the edge-emphasized luminance image with a predetermined threshold value to obtain a bright pixel having a threshold value or more and a dark pixel having a lower threshold value, and detecting an orientation unevenness from the bright pixel or the dark pixel;
step (6): performing an image processing of expanding the binarized luminance image in an oblique direction in a range of 70 ° to 120 ° with respect to a direction of the differential processing of the phase difference film to emphasize a component of the oblique direction;
step (7): and a step of performing a contraction process on the luminance image in the same direction after performing the expansion process.
2. The method for detecting defects in alignment of a retardation film according to claim 1, further comprising:
and (8) extracting, as an orientation unevenness defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region from the luminance image after the shrinkage processing.
3. The method for detecting defects in alignment of a retardation film according to claim 1 or 2, wherein,
The angle of view θ of the lens calculated from the distance between the lens front end position of the imaging device and the phase difference film and the size of the inspection area on the phase difference film in the longitudinal direction is within 23 DEG with respect to the length direction of the phase difference film.
4. An uneven alignment defect detection device for a retardation film according to any one of claims 1 to 3, characterized in that the uneven alignment defect detection device for a retardation film comprises:
a 1 st polarizing plate and a2 nd polarizing plate disposed so as to be crossed with nicols through the retardation film;
A light source that irradiates the retardation film with inspection light via the 1 st polarizing plate;
a photographing device for photographing the phase difference film through the 2 nd polarizing plate to obtain a brightness image; and
A defect detecting section for detecting a defect from the luminance image,
The defect detection unit includes:
An edge detection circuit that, when the phase difference film is disposed between a 1 st polarizing plate and a2 nd polarizing plate disposed in a crossed nicols manner, extracts a difference between adjacent pixel values in a direction of 35 DEG to 55 DEG or-55 DEG to-35 DEG with respect to the luminance image captured by rotating the 1 st polarizing plate and the 2 nd polarizing plate or the phase difference film so that the slow axis of the phase difference film is within a range of-10 DEG to 10 DEG and 0 DEG with respect to the absorption axis of either one of the 1 st polarizing plate and the 2 nd polarizing plate, and emphasizes an edge portion;
A binarization circuit binarizing the brightness image after edge detection by using a predetermined threshold value, so that each pixel is a bright pixel above the threshold value and a dark pixel below the threshold value;
An image processing circuit that expands the binarized luminance image in an oblique direction within a range of 70 ° to 120 ° with respect to a direction of differential processing of the phase difference film, and emphasizes a component of the oblique direction; and
And an image processing circuit that performs contraction processing on the luminance image in the same direction after performing the expansion processing.
5. The device for detecting defects in alignment of a retardation film according to claim 4, wherein,
The defect detection unit includes a filter circuit that extracts, as an orientation unevenness defect component in the direction, a portion satisfying a filter condition defined by a representative length of each pixel region, for the luminance image after the contraction processing.
6. The device for detecting defects in alignment of a retardation film according to claim 4 or 5, wherein,
The angle of view θ of the lens calculated from the distance between the lens front end position of the imaging device and the phase difference film and the size of the inspection area on the phase difference film in the longitudinal direction is within 23 DEG with respect to the length direction of the phase difference film.
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| PCT/JP2020/025669 WO2021010157A1 (en) | 2019-07-16 | 2020-06-30 | Method for detecting orientation non-uniformity defect in retardation film and apparatus for detecting orientation non-uniformity defect in retardation film |
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