CN114096833A

CN114096833A - Method and apparatus for detecting defect of uneven alignment of retardation film

Info

Publication number: CN114096833A
Application number: CN202080050402.6A
Authority: CN
Inventors: 桥本翔太; 增田修; 南条崇
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2019-07-16
Filing date: 2020-06-30
Publication date: 2022-02-25
Anticipated expiration: 2040-06-30
Also published as: JP7476897B2; CN114096833B; TW202122787A; KR20220018599A; TWI757776B; KR102676825B1; JPWO2021010157A1; WO2021010157A1

Abstract

The invention provides a method and a device for detecting orientation unevenness defects of a phase difference film, which can improve evaluation reproducibility by detecting and evaluating the orientation unevenness defects of the phase difference film based on quantitative evaluation of an optical system. The method for detecting an orientation unevenness defect of a retardation film of the present invention includes the following steps (1) to (5). (1) The retardation film is disposed between 2 crossed nicols polarizers in such a manner that the retardation axis of the retardation film is inclined at-10 DEG to 10 DEG with respect to the absorption axis of the polarizers. (2) The retardation film is irradiated with inspection light through one polarizing plate. (3) The retardation film was photographed through the other polarizing plate to obtain a luminance image. (4) The edge portion is emphasized by differentiating (differentiating) the captured luminance image in an oblique direction with respect to the slow axis of the phase difference film. (5) The edge-emphasized luminance image is binarized by a predetermined threshold value to obtain a bright pixel or a dark pixel, and the alignment unevenness is detected from the pixel.

Description

Method and apparatus for detecting defect of uneven alignment of retardation film

Technical Field

The present invention relates to a method and an apparatus for detecting an orientation unevenness defect of a retardation film. More specifically, the present invention relates to a method for detecting an orientation unevenness defect of a retardation film and an orientation unevenness defect detection apparatus used for the method, which can reduce the burden on the operator and improve the reproducibility of the evaluation result by performing detection and evaluation of the orientation unevenness defect of the retardation film by quantitative evaluation using an optical system.

Background

In recent years, liquid crystal display devices have been widely used for televisions, monitors for personal computers, and the like because of their features such as power saving, light weight, and thin profile. The liquid crystal display device has the above-described 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 dependency, there is a method using a retardation film.

In the conventional production of retardation films, it is difficult to completely prevent the occurrence of defects that impair the surface quality of the film, even in the case of strictly controlled production processes.

In addition, in recent years, as the thickness of liquid crystal display devices has been reduced, the retardation film used therein is also required to be reduced in thickness, and accordingly, defects of uneven alignment, which are found in the manufacturing process, become remarkable.

In order to prevent a film having such defects from being distributed to the market, inspection of the defects of the film is important, and conventionally, in quality evaluation of the defects of uneven alignment, a grade determination is performed by visual inspection. However, such qualitative evaluation by visual observation has a large dependency on the skill of the operator, and the evaluation result has low reproducibility and may greatly change when the operator changes. Further, since the person who can be evaluated reliably is limited to the skilled person, there is a problem that the workload is biased to a part of the operators, and the burden is increased.

As a defect inspection of an optical film, a defect inspection method and an inspection apparatus disclosed in patent documents 1 and 2 are known.

Patent document 1 proposes the following method: a transparent or translucent film sheet is used as an object, a light source is arranged on one surface of the film sheet to be conveyed, a 1 st polarizing plate is arranged between the light source and the film, a linear array camera is arranged on the other surface of the film sheet, a2 nd polarizing plate is arranged between the linear array camera and the film, the deviation angle of the polarization directions of the 1 st polarizing plate and the 2 nd polarizing plate is set within +/-20 degrees, and defect information caused by foreign matters is detected from a video signal output from the linear array camera.

Patent document 2 discloses a device for detecting defects in a 3D television set, which includes a light source for irradiating a film with inspection light through a 1 st polarizing plate, a photographing device for photographing transmitted light of the film through a2 nd polarizing plate to obtain a luminance image, and a defect detecting unit for detecting defects from the luminance image, wherein 1 st and 2 nd polarizing plates are arranged so as to cross nicols (cross-nicols) with a film interposed therebetween, and a patterned retardation film used in the 3D television set is used as a target.

The following defect inspection apparatus is proposed: the 1 st and 2 nd polarizing plates are defect inspection apparatuses mainly based on foreign matter or the like, in which one polarization transmission axis is substantially parallel to one optical axis in a plurality of retardation regions of a patterned retardation film, and one polarization transmission axis is adjusted so that "each brightness is at the same level in the vicinity of an extinction state" of a brightness image when a defect-free film is photographed.

However, the method proposed in patent document 1 has a problem that 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 defect of the film, and information on the orientation unevenness to be obtained cannot be obtained.

In the device proposed in patent document 2, the captured luminance image is at the same level in the vicinity of the extinction state, and therefore, there is a problem that a minute change in polarization state for detecting orientation unevenness cannot be captured. In addition, 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 defective portion which is originally desired to be extracted is also eliminated.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 11-30591

Patent document 2: japanese patent laid-open publication No. 2013-50393

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above problems and situations, and an object of the present invention is to provide a method for detecting an orientation unevenness defect of a retardation film and an orientation unevenness defect detection apparatus used for the method, which can reduce the burden on the operator and improve the reproducibility of the evaluation result by performing detection and evaluation of the orientation unevenness defect of the retardation film by quantitative evaluation using an optical system.

Means for solving the problems

In order to solve the above problems, the present inventors have found, in the course of studying the causes of the above problems and the like, that a method for detecting an orientation unevenness defect of a retardation film, which can reduce the burden on the operator and improve the reproducibility of the evaluation result, can be obtained by detecting and evaluating the orientation unevenness defect of the retardation film by quantitative evaluation using an optical system by using an orientation unevenness defect detection method having a specific procedure using an apparatus composed of 2 polarizing plates, a light irradiation apparatus, an image pickup apparatus, and a defect detection unit.

That is, the above problem according to the present invention is solved by the following means.

1. A method for detecting defects of orientation unevenness of a retardation film, comprising the following steps (1) to (5),

step (1): a step of disposing the retardation film between a 1 st polarizing plate and a2 nd polarizing plate disposed orthogonally nicols, wherein the 1 st polarizing plate and the 2 nd polarizing plate, or the retardation film is disposed so as to be rotated such that a retardation axis of the retardation film is in a range of-10 ° to 10 ° (excluding 0 °) with respect to an absorption axis of either the 1 st polarizing plate or the 2 nd polarizing plate;

step (2): irradiating the retardation film with inspection light via the 1 st polarizing plate;

and (3): a step of obtaining a luminance image by photographing the retardation film through the 2 nd polarizing plate by a photographing device;

and (4): a step of obtaining a luminance image with an edge portion emphasized by differentiating (differentiating) the captured luminance image in a direction within a range of 35 ° to 55 ° or-55 ° to-35 ° with respect to a slow axis of the retardation film; and

and (5): and binarizing the edge-emphasized luminance image by using a predetermined threshold value to obtain bright pixels each having a threshold value or more and dark pixels each having a threshold value or less, and detecting orientation unevenness from the bright pixels or the dark pixels.

2. The method for detecting an orientation unevenness defect of a retardation film according to claim 1, further comprising a step (6) of performing image processing for emphasizing a component in an oblique direction by performing expansion processing on the luminance image after binarization in the oblique direction within a range of 70 ° to 120 ° with respect to a direction of differentiation (difference) processing of the retardation film.

3. The method for detecting an orientation unevenness defect of a retardation film according to claim 2, further comprising a step (7) of performing a shrinking process on the luminance image in the same direction after the swelling process is performed.

4. The method for detecting an orientation unevenness defect of a retardation film according to claim 3, further comprising a step (8) of 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 shrinking process.

5. The method of detecting an orientation unevenness defect of a retardation film according to any one of claims 1 to 4, wherein a field angle θ of the lens calculated from a distance between a lens tip position of the imaging device and the retardation film and a size in a longitudinal direction of an inspection area on the retardation film is within 23 ° with respect to the longitudinal direction of the retardation film.

6. An apparatus for detecting an orientation unevenness defect of a retardation film, the apparatus being used in the method for detecting an orientation unevenness defect of a retardation film according to any one of items 1 to 5, the apparatus comprising:

a 1 st polarizing plate and a2 nd polarizing plate orthogonally disposed in nicols with the retardation film interposed therebetween;

a light source that irradiates inspection light to the retardation film via the 1 st polarizing plate;

an imaging device for imaging the retardation film through the 2 nd polarizing plate to obtain a luminance image; and

a defect detecting section for detecting a defect from the luminance image,

the defect detection unit includes:

an edge detection circuit configured to, when the retardation film is disposed between a 1 st polarizing plate and a2 nd polarizing plate disposed orthogonally to each other, rotationally dispose the 1 st polarizing plate and the 2 nd polarizing plate or the retardation film such that a slow axis of the retardation film is in a range of-10 ° to 10 ° (excluding 0 °) with respect to an absorption axis of either the 1 st polarizing plate or the 2 nd polarizing plate, and differentiate (differentiate) the captured luminance image in a direction in a range of 35 ° to 55 ° or-55 ° to-35 ° with respect to the slow axis of the retardation film to emphasize an edge portion; and

and a binarization circuit for binarizing the luminance image after the edge detection by using a predetermined threshold value so that each pixel becomes a bright pixel equal to or more than the threshold value and a dark pixel lower than the threshold value.

7. The apparatus according to claim 6, wherein the defect detector includes an image processing circuit, and the image processing circuit includes a light source and a light source

The binarized luminance image is subjected to dilation processing in an oblique direction in the range of 70 ° to 120 ° with respect to the direction of differentiation (difference) processing of the retardation film, and the component in the oblique direction is emphasized.

8. The apparatus according to claim 7, wherein the defect detector includes an image processing circuit, and the image processing circuit includes a light source and a light source

After the expansion processing is performed, the contraction processing is performed on the luminance image in the same direction.

9. The apparatus for detecting defect of uneven alignment of retardation film according to claim 6, wherein the defect detecting unit includes a filter circuit having a plurality of filter elements

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 orientation unevenness defect component in the direction.

10. The apparatus according to any one of claims 6 to 9, wherein a field angle θ of the lens calculated from a distance between a lens tip position of the imaging device and the retardation film and a size in a longitudinal direction of an inspection area on the retardation film is within 23 ° with respect to the longitudinal direction of the retardation film.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the above-described means of the present invention, it is possible to provide a method for detecting an orientation unevenness defect of a retardation film and an orientation unevenness defect detection apparatus used for the method, which can reduce the burden on the operator and improve the reproducibility of the evaluation result by performing detection and evaluation of the orientation unevenness defect of the retardation film by quantitative evaluation using an optical system.

The mechanism for finding the effect of the present invention or the mechanism for acting the same is not clear, but is presumed as described below.

It is presumed that by disposing 2 polarizing plates orthogonally to each other and disposing one of the polarizing plate and the retardation film in a rotational manner so that the slow axis of the retardation film is in the range of-10 ° to 10 ° (excluding 0 °) with respect to the absorption axis of the polarizing plate, the change in polarization state due to the change in slow axis can be emphasized, and the detection accuracy of the defect portion (misorientation defect) can be improved.

The differential processing is processing for extracting an edge of an image by differential filtering (a portion where brightness rapidly changes in the extracted image is referred to as edge extraction), but in the case of an image, the difference between pixel values (referred to as "difference" in the present invention) is taken to approximate the differential.

In order to emphasize the edge of the above-described defective portion, the direction of the differentiation process is specified as a direction in the range of 35 ° to 55 ° or-55 ° to-35 ° obliquely to the slow axis of the retardation film. In general, when a retardation film is produced, a slow axis is oriented in one direction by stretching or the like, but minute orientation unevenness due to unevenness of width tension applied during stretching or drying accumulates in other than the one direction, and it is estimated that as a result, a gradient component of the orientation unevenness is easily extracted by a differential process, and the detection accuracy of the orientation unevenness can be improved.

The reason why the obtained luminance image is binarized is to roughly distinguish a defective portion from other normal regions, and it is estimated that the detection accuracy of the defect can be further improved by further emphasizing the defective portion in the binarized image in the expansion process and the contraction process.

It is presumed that by 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 contraction processing, only an orientation unevenness defect can be detected, and by the above image processing, an orientation unevenness defect evaluation method with high accuracy and a quantitative amount can be provided.

Drawings

Fig. 1 is a schematic view showing a conventional visual evaluation method for an alignment unevenness defect.

Fig. 2 is a schematic diagram illustrating the angle of view of a lens attached to a camera used in an inspection.

Fig. 3A shows a specific example (original luminance image) of an image binarized by a predetermined threshold value.

Fig. 3B shows a specific example of an image binarized with a predetermined threshold value (binarized image).

Fig. 4 is a flowchart of image processing and a specific example of processing an image.

Fig. 5 is a schematic view showing an example of the alignment unevenness defect detecting apparatus of the retardation film of 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 a defect in uneven alignment of a retardation film of the present invention is characterized by comprising the above-described steps (1) to (5). This feature is a feature of a common or corresponding technique in the embodiments described below.

As an embodiment of the present invention, from the viewpoint of finding the effect of the present invention, the method further includes a step (6) of performing image processing in which the luminance image after binarization is subjected to dilation processing in an oblique direction in a range of 70 ° to 120 ° with respect to the direction of differentiation (difference) processing of the retardation film to emphasize a component in the oblique direction, and is preferable from the viewpoint of enabling accurate and quantitative evaluation of the orientation unevenness defect by emphasizing a defective portion.

The method further includes a step (7) of performing a contraction process on the luminance image in the same direction after the expansion process is performed, and is preferable in that the defect portion is emphasized and noise is reduced, so that the defect evaluation of the alignment unevenness can be performed with high accuracy and quantitatively.

The method further includes a step (8) of 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, and is preferable in terms of determining orientation unevenness and enabling accurate and quantitative evaluation of orientation unevenness defects.

It is preferable 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 region on the retardation film in the longitudinal direction is within 23 ° with respect to the longitudinal direction of the retardation film.

The reason why the angle of view θ is made to converge to the above range, that is, the distance between the retardation film and the camera is maintained so as to be the angle of view θ is to reduce the incident angle dependency of the inspection light and to make uniform the difference in the image density at the center and the corner of the inspection region.

The device for detecting alignment unevenness of a retardation film according to the present invention includes: a 1 st polarizing plate and a2 nd polarizing plate orthogonally disposed in nicols with the retardation film interposed therebetween; a light source that irradiates inspection light to the retardation film via the 1 st polarizing plate; an imaging device for imaging the retardation film through the 2 nd polarizing plate to obtain a luminance image; and a defect detection unit that detects a defect from the luminance image, the defect detection unit including: an edge detection circuit that rotationally disposes the 1 st polarizing plate and the 2 nd polarizing plate or the retardation film so that a slow axis of the retardation film is in a range of-10 ° to 10 ° (excluding 0 °) with respect to an absorption axis of either the 1 st polarizing plate or the 2 nd polarizing plate disposed orthogonally to the nicol, and performs a differential (difference) process in a direction in a range of 35 ° to 55 ° or-55 ° to-35 ° with respect to the slow axis of the retardation film on the captured luminance image to emphasize an edge portion; and a binarization circuit for binarizing the luminance image after the edge detection by using a predetermined threshold value so that each pixel becomes a bright pixel equal to or more than the threshold value and a dark pixel lower than the threshold value.

The defect detecting section 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 the direction of differentiation (difference) processing of the retardation film to emphasize a component in the oblique direction, and is preferable from the viewpoint of enabling accurate and quantitative evaluation of the orientation unevenness defect.

The defect detection unit preferably further includes an image processing circuit that performs a contraction process on the luminance image in the same direction after the expansion process is performed, and is preferable in that the defect detection unit can perform a precise and quantitative evaluation of the alignment unevenness defect.

The defect detection unit may further include a filter circuit for 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, and is preferable in terms of determining orientation unevenness and enabling accurate and quantitative evaluation of orientation unevenness defects.

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 the alignment unevenness defect with good work efficiency and in a quantitative manner.

The present invention and its constituent elements and specific embodiments/aspects are described in detail below. In the present application, "to" is used in the sense of including numerical values described before and after the "to" as the lower limit value and the upper limit value.

Outline of method for detecting defects due to orientation unevenness of retardation film of the present invention

The method for detecting a defect in uneven alignment of a retardation film of the present invention is characterized by comprising the following steps (1) to (5).

Step (1): and a step of disposing the retardation film between a 1 st polarizing plate and a2 nd polarizing plate disposed orthogonally to each other, wherein the 1 st polarizing plate and the 2 nd polarizing plate, or the retardation film is disposed so as to be rotated so that a retardation axis of the retardation film is in a range of-10 ° to 10 ° (excluding 0 °) with respect to an absorption axis of either one of the 1 st polarizing plate and the 2 nd polarizing plate.

Step (2): and irradiating the retardation film with inspection light via the 1 st polarizing plate.

And (3): and a step of obtaining a luminance image by photographing the retardation film through the 2 nd polarizing plate by a photographing device.

And (4): and obtaining a luminance image with an edge portion emphasized by differentiating (differentiating) the captured luminance image in a direction within a range of 35 ° to 55 ° or-55 ° to-35 ° with respect to a slow axis of the retardation film.

And (5): and a step of binarizing the edge-emphasized luminance image by using a predetermined threshold value to obtain a bright pixel in which each pixel is equal to or more than the threshold value and a dark pixel which is lower than the threshold value, and detecting the orientation unevenness from the bright pixel or the dark pixel.

Here, the "retardation film" refers to an optical film that improves the problem of the viewing angle dependence of a liquid crystal display device, and is, for example, an optical film having birefringence used in a VA (vertical Alignment) type liquid crystal display device. 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 it is formed normally, it has uniform optical characteristics (birefringence, retardation, or the like) in the plane, but in practice, slight unevenness occurs.

The retardation value of the optical film can be generally defined by the following formula.

That is, the in-plane direction retardation Ro and the thickness direction retardation Rt of the optical film are expressed by the following formulas (1) and (2).

Ro＝(n_x-n_y)×d…(1)

Rt＝{(n_x+n_y)/2-n_z}×d…(2)

Further, in the formula, n_xShowing the slow axis direction in the film planeRefractive index of_yRefractive index n in the film plane in the phase advance axis direction_zThe refractive index in the thickness direction of the film is shown, and d represents the thickness (nm) of the film.

The "slow axis" refers to an axis in which the traveling speed of light with a phase retardation becomes the slowest when the light propagates through the film causing birefringence. That is, the direction in which the in-plane refractive index becomes maximum is referred to. The "phase advancing axis" refers to an axis along which the traveling speed of light becomes the highest, and refers to a direction along which the in-plane refractive index becomes the smallest.

The in-plane retardation axis and the phase advancing axis of the retardation film can be confirmed by an automatic birefringence meter Axo Scan (Axo Scan Mueller matrix polarimeter, manufactured by Axometrics).

The Ro and Rt of the retardation film can be measured by the following method.

1) The phase difference 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) Using an automatic birefringence meter Axo Scan (Axo Scan Mueller matrix polarimeter: axometrics corporation) was measured at 23 ℃ and 55% RH, and the retardation Ro and Rt at a measurement wavelength of 550nm of the retardation film after humidity control was measured.

When the retardation film according to the present invention is used for a VA mode, for example, the in-plane retardation Ro measured in an environment with 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 in the thickness direction of the optical film is preferably in the range of 70nm to 350nm, more preferably in the range of 100nm to 320 nm.

The retardation is a value that varies depending on the wavelength of light irradiated to the optical film, the environmental conditions (temperature and humidity) under which measurement is performed, and the like, and therefore it is desirable to set these conditions so that the retardation becomes an arbitrary value depending on the purpose of optical characteristic evaluation, the type of optical film to be evaluated, and the like.

Here, the "orientation angle" refers to an angle formed by an orientation direction in which molecules forming the retardation film are oriented with respect to a predetermined reference direction, and generally coincides with an angle formed by an in-plane retardation axis of the retardation film with respect to the predetermined reference direction. The predetermined reference direction generally refers to a direction in which the retardation film extends in the width direction. The "orientation unevenness defect" according to the present invention is a defect in which the orientation angle varies from the reference direction at each selected portion (for example, when a plurality of portions 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 azimuthally rotate a transmission axis of linearly polarized light having a specific vibration direction extracted from natural light (randomly polarized light), thereby changing the vibration direction of the incident linearly 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. In the polyvinyl alcohol polarizing film, there are used a film obtained by dyeing a polyvinyl alcohol film with iodine and a film obtained by dyeing a polyvinyl alcohol film with a dichroic dye.

The "absorption axis" refers to a direction of an axis of vibration absorbed by the polarizer, and generally refers to an angle in accordance with an extending direction of the polarizer.

The phrase "the 1 st polarizing plate and the 2 nd polarizing plate which are orthogonally arranged in 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 invention and its constituent elements and specific embodiments/aspects are explained below. In the present application, "to" is used in the sense of including numerical values described before and after the "to" as the lower limit value and the upper limit value.

[1] Structure of method for detecting defect of uneven alignment of phase difference film

The method for detecting an orientation unevenness defect in a retardation film of the present invention includes the above steps (1) to (5), and more preferably includes the step (6), the step (7), and the step (8) following the step (5).

First, a conventional visual evaluation method for the orientation unevenness defect will be briefly described.

Fig. 1 is a schematic diagram schematically showing a conventional visual evaluation method 10 for an alignment unevenness defect.

The evaluation of the alignment unevenness defect of the retardation film 1 refers to a method of qualitatively observing the alignment unevenness defect of the retardation film 1 by visual observation 5 by transmitting the irradiation light L emitted from the flat LED lighting 2 located at the lower part in the order of the 1 st polarizing plate 3, the retardation film 1, and the 2 nd polarizing plate 4. 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, and therefore the irradiation light L is not transmitted as it is and becomes a dark portion, but the evaluator slightly rotates the retardation film 1 from the absorption axis direction of the above polarizing plate (inclines in the arrow inclined direction 6 in the figure), and the irradiation light L is polarized along the slow axis direction of the retardation film and becomes a transmission light, and is observed as a dark region if there is an orientation unevenness defect under the visual observation 5.

Therefore, the method of evaluating the quality of the retardation film is a qualitative method of evaluating the quality of the retardation film, because the evaluation results are influenced by the skill of the operator in the method of handling the retardation film and the experience of the operator in the defect of the alignment unevenness.

The method for detecting defects of alignment unevenness of a retardation film of the present invention is a method for evaluating the above-mentioned defects by a fixed procedure using an optical evaluation device, and therefore, can provide a quantitative evaluation method for evaluating defects that are not personal.

The steps of the method for detecting an orientation unevenness defect of a retardation film of the present invention will be described in detail below.

When a film was provided between 2 polarizing plates (the 1 st polarizing plate and the 2 nd polarizing plate) in a crossed nicols state, light was not transmitted and nothing was observed even if the film was provided so that the orientation of the slow axis of the film was the same as the orientation of the absorption axis of the polarizing plate. When the film is slightly rotated with respect to the absorption axis of the polarizing plate, the polarization state of light passing through the film changes (the direction of polarization changes slightly) according to the slow axis of the retardation film, and therefore the light is allowed to pass through the 2 nd polarizing plate and reach the polarizing plate.

Since the current defect of alignment unevenness as an inspection object has a slight luminance change, when the polarizing plate or the retardation film is excessively rotated, light reaching a camera as an imaging device is excessively strong and cannot be observed. As a result of the examination, when any one of the 1 st polarizing plate and the 2 nd polarizing plate or the retardation film is rotated so that the retardation axis of the retardation film is in the 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 retardation unevenness can be most clearly observed, and therefore, the retardation unevenness is defined within the range.

In an actual operation, in the alignment defect detecting apparatus shown in fig. 5 described later, it is preferable that the absorption axis of the polarizing plate is inclined with respect to the slow axis of the retardation film by rotating the 1 st polarizing plate and the 2 nd polarizing plate without rotating the retardation film.

As an illumination device for irradiating inspection light, it is preferable that inspection light is transmitted through the 1 st polarizing plate, the retardation film, and the 2 nd polarizing plate in this order, and a sufficient area is required for photographing the inspection light, and the luminance is as uniform as possible.

The Light source of the illumination 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 surface light source (flat surface light source), preferably using flat LED lighting.

It is preferable to manage the light quantity of the inspection light in the inspection machine control software Lab VIEW (manufactured by National Instruments), measure the in-plane average luminance of a luminance calculation region (for example, a rectangular region of about 80mm × 60mm to 400mm × 300 mm) set in the Lab VIEW, and adjust the light quantity of the light source so that the luminance value converges in the range of 128 ± 10, thereby obtaining a sufficient luminance image for evaluation.

In addition, with regard to 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 dependence of the incident angle. If the dark portion of the connecting end portion is also included so that the in-plane average luminance is adjusted to 128 ± 10, the central portion becomes excessively bright and a critical unevenness cannot be detected, so that the luminance calculation region is preferably set to be narrower than the inspection region. For example, when the inspection area is 400mm in length × 300mm in width, the luminance calculation area is preferably 90mm in length × 80mm in width.

The imaging device is not particularly limited, and a CCD camera of a segment type or a line sensor type can be used. The segment type is used when the inspection area range of the retardation film can be covered by imaging within several times, and the line sensor type is used when a wider range than this is required, which is preferable in terms of imaging time and accuracy.

The camera as the photographing device can be, for example, model acA2500-14gm manufactured by BASLER corporation, and the lens can be model H6X8-1.0-II manufactured by APACECOM corporation.

The inspection area is determined by the angle of view of the 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, the sample can be measured regardless of the width by performing the examination a plurality of times.

For example, when the inspection region is 400mm in length and 300mm in width for a sample 450mm in length and 2500mm in width as a retardation film, the inspection may be performed by a plurality of times of photographing. The size in the longitudinal direction is fixed according to the examination region of the device. The width is a maximum width generally used as a retardation film.

The angle of view θ of the lens attached to the camera is calculated, in detail, based on the distance between the lens tip position of the image pickup device and the retardation film and the size in the longitudinal direction of the inspection area on the retardation film, but is preferably within 23 ° with respect to the longitudinal direction of the retardation film from the viewpoint of enabling evaluation of alignment unevenness defects with good work efficiency and in a quantitative manner.

Fig. 2 is a schematic diagram illustrating the angle of field θ of a lens attached to a camera used in an inspection.

Regarding the distance WD (the short term of the working distance, which means the distance from the front end of the lens to the position where the object is focused) between the front end of the lens 56 and the retardation film 51, for example, when WD is assumed to be 1150mm in the alignment unevenness defect inspection apparatus 50 according to the present invention, the angle of view θ of the lens is 22.14 ° when the length 51a of the retardation film is 450mm and the width 51b thereof is 375mm with respect to the conveyance direction 51c of the retardation film 51 in the photographing region of the camera. When the inspection area was 400mm long and 300mm long, θ was 19.73 °. Can be obtained by calculation.

The purpose of the general differentiation processing is to emphasize the edge portion of the captured luminance image. The differential processing is processing for extracting an edge of an image by differential filtering (a portion where brightness rapidly changes in the extracted image is referred to as edge extraction), but in the case of an image, the difference between pixel values (referred to as "difference" in the present invention) is taken to approximate the differential. In the differential processing, it is preferable to obtain and use a kernel when a matrix called a kernel (also called a matrix) is subjected to differential processing in a direction within a range of 35 ° to 55 ° and a kernel when the matrix is subjected to differential processing in a direction within a range of-55 ° to-35 ° in the study stage.

The edge refers to a portion divided into a bright and dark region in the image. When emphasizing an edge, it is desirable to perform processing in a direction orthogonal to a direction in which a boundary between light and dark 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 variation in this angle, and in order to cope with this, it is preferable to perform the orientation of the differentiation process within a range of 35 ° to 55 ° with respect to the retardation axis of the retardation film with a margin.

The software for differentiation is not limited, and it is preferable to use analysis software NI vision (National Instruments).

And (5): and binarizing the edge-emphasized luminance image by using predetermined binarization software and a threshold value to obtain bright pixels each having a threshold value or more and dark pixels each having a threshold value or less, and detecting orientation unevenness from the bright pixels or the dark pixels.

In the photographed image, the alignment unevenness defect is observed as a dark region. Therefore, it is desirable to leave a group of dark-looking elements in the image at the time of binarization, and therefore setting a threshold value is performed so as to leave only elements having a luminance lower than the threshold value.

In this case, 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 by the following method.

[a] The photographed luminance image was read into a personal computer using analysis software NI vision (National Instruments). The luminance image is preferably not artificially changed because it changes with the adjustment of the focus, contrast, and brightness.

[b] The definition setting of black and white is performed.

In the analysis software NI vision, when a Black Background is checked, the luminance value 0 is represented by Black and the luminance value 255 is represented by white. When not checked in Black Background, the luminance value 0 is represented by white and the luminance value 255 is represented by Black.

[c] Noise removal of images

Shading (shading) processing is performed. The shading processing is processing for removing noise by averaging luminance in an image.

[d] A band pass filter is applied.

For example, the band pass filter value is preferably 20 to 100. The setting value is dependent on the initial luminance image, and is preferably set to an optimum value.

[e] Binarization of the luminance image is performed.

The setting is performed by 8-bit, and a threshold value is set. The threshold value is preferably adjusted by the analysis software NI vision (National Instruments).

The threshold value varies depending on the contrast of the image, and is preferably set by the evaluator without being fixed.

If the threshold is decided, it becomes a black and white image. Binarization is performed using a predetermined threshold value to obtain dark pixels each having a threshold value or more and bright pixels each having a threshold value or less, and the alignment unevenness is detected from the bright pixels or the dark pixels.

Fig. 3 is a specific example of an image binarized by a predetermined threshold value.

Fig. 3A is a captured original luminance image, in which dark pixel portions that appear dark are candidates for uneven alignment defects. Fig. 3B shows a result of determining a threshold value so as to clearly leave a candidate for the uneven alignment defect and binarizing the pixel as a dark pixel.

The method for detecting an orientation unevenness defect of the present invention preferably further includes the following steps (6), (7) and (8).

And (6): and performing image processing for emphasizing a component in an oblique direction by performing dilation processing on the binarized luminance image in the oblique direction in a range of 70 ° to 120 ° with respect to the direction of differential (difference) processing of the retardation film.

Since a large amount of noise other than the orientation defect non-uniformity elements remains in the image immediately after binarization, the noise is easily reduced by performing dilation processing to emphasize the defective portion. Here, the "Dilation process" generally refers to a process of processing a binarized black-and-white image, and a process of replacing a pixel in the vicinity of a target pixel with white if 1 pixel is white is referred to as Dilation (scaling). The "contraction process" described later is a process of replacing a pixel having black in the periphery thereof by black as long as 1 pixel is referred to as contraction (Erosion).

In order to leave this alignment defect unevenness and remove noise, it is effective to perform processing along the direction in which the unevenness exists. When the direction of the differential processing is expressed with reference to the direction, the processing is performed in the direction orthogonal to the differential processing. The reason for this is that the direction of the differentiation processing is preferably performed in a direction orthogonal to the direction in which the unevenness exists. However, since the directions of the unevenness are also varied, in order to cope with the variation, it is preferable to perform the expansion process in an inclined direction within a range of 70 ° to 120 ° with respect to the direction of the differentiation (difference) process with a margin for the angle.

And (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 performed subsequent to the expansion processing is also processing for removing noise as much as possible, and similarly, the direction of the differentiation processing is performed in a direction orthogonal to the direction in which the unevenness exists, and therefore, it is preferable to perform the contraction processing in an oblique direction within a range of 70 ° to 120 ° with respect to the direction of the differentiation (difference) processing with a margin for the angle of the direction in which the unevenness exists.

The expansion process and the contraction process can be performed using the analysis software NI vision (National Instruments).

And (8): 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.

This step is also referred to as filtering processing or filtering, and the "filtering condition defined by the representative length of each pixel region" is a condition empirically required for detecting an alignment unevenness defect.

From the binarized luminance image, for example, filtering is performed to remove an element having a shape close to a perfect circle (filtering processing 1), an element having a short removal length (filtering processing 2), or an element having an area outside a predetermined range (filtering processing 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 filtering process 1, a value obtained by setting a hewood (Haywood) circular factor H: 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 is left. Further, the Hawood circularity factor H is 1 in the case of a perfect circle.

In the filtering process 2, it is preferable to remove a pixel region having a length equal to or less than a specific length from the long side having the non-uniform orientation.

In the filtering process 2, the expansion factor L is set as: when the quotient of the maximum Feret diameter of the pixel region divided by the short side (Feret) of the equivalent rectangle is obtained, it is preferable to detect the alignment unevenness defect by leaving only the pixel region in the range of 4. ltoreq. L.ltoreq.13.

The filtering software used for the filtering process is not limited, and may be implemented 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) photographing the phase difference film to obtain a brightness image,

(P2) a process of shading the luminance image (averaging the luminance in the image to remove noise),

(P3) the emphasis of the edge portion based on the differential (difference) processing of the luminance image,

(P4) binarization of the luminance image,

(P5) an emphasis process (expansion and contraction process) of the binarized image,

(P6) filtering process 1 to the binarized image (removing elements whose shape is close to a perfect circle),

(P7) filtering process 2 to the binarized image (removal of short-length elements),

(P8) filtering process 3 to the binarized image (removing elements whose area is outside the specified range),

(P9) detecting only the orientation unevenness defect from the binarized image by the filtering process.

[2] Apparatus for detecting defect of uneven orientation of retardation film

The device for detecting a defect in misorientation of a retardation film used in the method for detecting a defect in misorientation of a retardation film according to the present invention comprises: a 1 st polarizing plate and a2 nd polarizing plate orthogonally disposed in nicols with the retardation film interposed therebetween; a light source that irradiates inspection light to the retardation film via the 1 st polarizing plate; an imaging device for imaging the retardation film through the 2 nd polarizing plate to obtain a luminance image; and a defect detection unit that detects a defect from the luminance image, the defect detection unit including: an edge detection circuit that rotationally disposes the 1 st polarizing plate and the 2 nd polarizing plate or the retardation film so that a slow axis of the retardation film is in a range of-10 ° to 10 ° (excluding 0 °) with respect to an absorption axis of either the 1 st polarizing plate or the 2 nd polarizing plate disposed orthogonally to the nicol, and performs a differential (difference) process in a direction in a range of 35 ° to 55 ° or-55 ° to-35 ° with respect to the slow axis of the retardation film on the captured luminance image to emphasize an edge portion; and a binarization circuit for binarizing the luminance image after the edge detection by using a predetermined threshold value so that each pixel becomes a bright pixel equal to or more than the threshold value and a dark pixel lower than the threshold value.

The device 50 for detecting an orientation irregularity defect of a retardation film according to the present invention is a device for transmitting irradiation light L emitted from a flat LED illumination 52 positioned below in the order of a light shielding plate 53, a 1 st polarizing plate 54, a retardation film 51, a light shielding plate 53, and a2 nd polarizing plate 55, and photographing an orientation irregularity defect of the retardation film 51 by a camera 57 having a lens 56 attached thereto. At this time, the absorption axes of the 1 st polarizing plate 53 and the 2 nd polarizing plate 54 are arranged so as to be crossed nicols, and therefore the irradiation light L is not transmitted as it is and becomes a dark portion, but by slightly rotating (inclining) the retardation film 51 from the absorption axis direction of the polarizing plate, the irradiation light L is polarized in accordance with the direction of the slow phase axis of the retardation film 51, and the alignment unevenness is photographed as a dark region in the photographed image.

In the alignment defect detecting apparatus 50, it is preferable to include a mechanism (not shown) for rotating the retardation axis of the retardation film with respect to the retardation axis of the first polarizing plate 54 and the second polarizing plate 55 so that the absorption axis of the polarizing plates is in the range of-10 ° to 10 ° without rotating the retardation film 51.

The dimensions of each part are not particularly limited, and for example, a long sample cut to 450mm in the longitudinal direction and 2000mm in the width direction is used for 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 the inspection device having the configuration shown in fig. 2 is preferably mounted in order to inspect an area of 400mm in the longitudinal direction and 300mm in the width direction, for example, from the viewpoint of inspection efficiency.

The light source of the illumination 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 segment type or a line sensor type can be used. The segment type is used when a measurement target range of the retardation film can be covered by imaging within several times, and the line sensor type is used when a wider range than this is required, which is preferable in terms of imaging time and accuracy.

The specifications of the camera and the lens are as described above.

Preferably, the defect detecting section includes an image processing circuit that performs dilation processing on the binarized luminance image in an oblique direction within a range of 70 ° to 120 ° with respect to a direction of differentiation (difference) processing of the retardation film to emphasize a component in the oblique direction.

Further, it is preferable that the defect detecting unit includes an image processing circuit that performs a contraction process on the luminance image in the same direction after the expansion process is performed.

Preferably, the defect detection unit includes 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 contraction processing.

[ Defect detecting section ]

The respective configurations of the defect detecting unit 100 will be described.

As shown in fig. 6, the defect detection 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 each of these units is communicably connected to each other via a bus 106.

The control unit 101 includes: a CPU (Central Processing Unit) 101a that totally controls the operation of the defect detecting Unit 100; 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 in which a program and fixed data read and executed by the CPU 101a are stored; and so on. The program memory 101c is constituted by a ROM or the like.

The recording unit 102 stores and records data of various thresholds used in the image processing circuit and data of the irradiation conditions of the illumination device 52, in addition to image data after photographing and image processing.

The communication unit 103 includes a communication interface such as a network I/F, and transmits the measurement conditions input from the operation display unit 105 to the photographing adjustment apparatus 120 via a network such as an intranet. The communication unit 103 receives image data transmitted from the image capturing apparatus 130.

The data processing unit 104 performs image processing based on the luminance image data received by the communication unit 103 and photographed by the photographing 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 section 104 includes a shading processing circuit 104a, an edge detection circuit 104b for performing differentiation (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 retardation film to emphasize an edge portion (step (4)), a binarization circuit 104c for binarizing the luminance image after edge detection by a predetermined threshold value to make each pixel a bright pixel equal to or more than the threshold value and a dark pixel lower than the threshold value (step (5)), an image processing circuit 104d for performing expansion processing or contraction processing on the luminance image (steps (6) and (7)), and a filter circuit 104e for 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 contraction processing (step (8)).

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, an operation key group, and the like (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 data processing apparatus 100 may also include an external output device 150 communicably connected to the data processing apparatus 100. The external output device 150 may be a general PC (Personal Computer), an image forming apparatus, or the like. The external output device 150 may function as an operation display unit instead of the operation display unit 105 of the data processing apparatus 100.

Examples

The present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "part(s)" or "%" are used, and unless otherwise specified, "part(s) by mass" or "% by mass" is meant.

[ example 1]

< preparation of retardation film for evaluation >

The retardation film 101 for evaluation was produced by the following method.

(preparation of Fine particle Dispersion dilution)

After 10 parts by mass of AEROSIL R812 (manufactured by AEROSIL CORPORATION, Japan, having a primary average particle diameter of 7nm and an apparent specific gravity of 50g/L) and 90 parts by mass of ethanol were stirred and mixed in a dissolver for 30 minutes, they were dispersed by using a high-pressure emulsifier (Manton Gorlin) as a high-pressure disperser to prepare a fine particle dispersion.

88 parts by mass of methylene chloride was added to the fine particle dispersion obtained with stirring, and the mixture was stirred and mixed in a dissolver for 30 minutes to dilute the mixture. The obtained solution was filtered through a polypropylene funnel filter TCW-PPS-1N manufactured by ADVANTEC Toyo corporation to obtain a fine particle dispersion diluted solution.

(preparation of inline (in-line) additive solution)

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 further stirring for 30 minutes, 6 parts by mass of cellulose acetate propionate (CAP: degree of substitution with acetyl group 2.00, degree of substitution with propionate 0.60, weight-average molecular weight 27 ten thousand) was added while stirring, and further stirring for 60 minutes. The obtained solution was filtered through Finemet NF manufactured by Nippon Seikagaku corporation to obtain an inline additive solution. The filter material used was a material with a nominal filtration accuracy of 20 μm.

(preparation of coating Material)

The following ingredients were put into a closed vessel and completely dissolved while heating and stirring. The obtained solution was filtered at a temperature of 50 ℃ using a filter equipped with a leaf disc type filtration apparatus to obtain a main dope. The filter material used was a material with a nominal filtration accuracy of 20 μm.

< composition of Main coating >

100 parts by mass of the main dope 1 and 2.5 parts by mass of the inline additive solution were thoroughly mixed by an inline Mixer (a Dongli static type inline Mixer Hi-Mixer, SWJ) to obtain a dope.

(film-making Process)

The obtained dope was uniformly cast on a stainless steel band support by using a band casting apparatus under conditions that the temperature of the dope solution was 35 ℃ and the width was 1950mm and the final film thickness was 40 μm. On the stainless steel belt support, the organic solvent in the obtained coating film was evaporated until the residual solvent amount became 100 mass% to form a web (web), and then the web was peeled off from the stainless steel belt support. The obtained web was further preliminarily dried at 110 ℃ for 5 minutes so that the amount of the residual solvent became 10 mass%, and then the web was stretched by a tenter at 160 ℃ by 1.4 times with respect to the original width in the TD direction, giving a predetermined retardation described below. The elongation rate was 300%/min.

After stretching by a tenter, relaxation was performed at 130 ℃ for 1 minute, and drying was terminated while conveying the film through a drying zone by a large number of rolls. The drying temperature was 130 ℃ and the conveying tension was 100N/m. The obtained film was cut in 2000mm width, and both ends of the film were subjected to knurling with a width of 10mm and a height of 5 μm, 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 101 for evaluation having a length of 4000m and a dry film thickness of 40 μm.

As a result of measurement by the above measurement method, the retardation of the retardation film 101 is Ro: 50nm and Rt: 120 nm.

< evaluation of defects due to orientation unevenness >

The alignment unevenness defect evaluation apparatus shown in fig. 5 was used to detect and evaluate the alignment unevenness defect of the retardation film produced as described above through the following steps (1) to (8).

The retardation film for evaluation was cut into a long sample having a length direction of 450mm and a width direction of 2000 mm. The distance between the front end position of the lens of the imaging device and the retardation film is set to 1150mm, and the angle of view theta of the lens calculated from the distance and the size of the inspection area on the retardation film in the longitudinal direction is set to 20 DEG, whereby imaging was performed a plurality of times in the inspection area of 400mm in the longitudinal direction and 300mm in the width direction.

Step (1): and a step of disposing the phase difference film between the 1 st polarizing plate and the 2 nd polarizing plate disposed in a crossed nicols manner, and rotatably disposing the 1 st polarizing plate and the 2 nd polarizing plate so that a retardation axis of the phase difference film is-7 DEG with respect to an absorption axis of a polarizer of the 1 st polarizing plate.

In the angles shown in table I, counterclockwise is a negative value, and clockwise is a positive value.

Step (2): and irradiating the retardation film with inspection light from a flat LED via the 1 st polarizing plate.

And (3): and a step of obtaining a luminance image by photographing the retardation film through the 2 nd polarizing plate by a photographing device (camera).

And (4): and obtaining a luminance image with an edge portion emphasized by differentiating (differentiating) the captured luminance image in a direction of 40 ° with respect to a slow axis of the phase difference film.

And (5): and binarizing the edge-emphasized luminance image by using a predetermined threshold value to obtain a bright pixel in which each pixel is equal to or more than the threshold value and a dark pixel which is lower than the threshold value, and detecting the orientation unevenness from the bright pixel or the dark pixel.

And (6): and performing image processing for emphasizing a component in a direction inclined at 90 ° with respect to the direction of differential (difference) processing of the retardation film by performing expansion processing on the binarized luminance image.

(Filter 1)

Set as the Hawood circular 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 H ≦ 5 of 1.5 is left.

(Filter 2)

After setting to the stretch factor L: when the quotient of the maximum Ferrett diameter of the pixel region divided by the short side (Ferrett) of the equivalent rectangle, only the pixel region in the range of 4. ltoreq. L.ltoreq.13 is left.

[ examples 2 to 8]

In the evaluation conditions of example 1, the same evaluation was performed with the device conditions θ, θ f, and θ p (each representing 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 changed, and examples 2 to 8 were obtained.

Here, θ represents the angle of view of a lens attached to a camera, θ f represents the angle formed by the retardation axis of the retardation film and the absorption axis of the polarizing plate, and θ p represents the angle formed by the absorption axes of 2 polarizing plates.

[ comparative examples 1 to 3]

Using the alignment unevenness defect evaluation apparatus of fig. 1, 3 persons having an evaluation experience of 1 year or more (visual 1), an evaluation experience of half a year or more and less than 1 year (visual 2), and an evaluation experience of less than half a year (visual 3) were evaluated as evaluators to perform the evaluations of comparative examples 1 to 3.

Comparative example 4

Evaluation was performed according to examples described in paragraphs [0113] to [0122] of Japanese patent application laid-open No. 11-30591.

Comparative example 5

Evaluation was carried out according to example 1 described in paragraphs [0098] to [0099] of Japanese patent application laid-open No. 2013-50393.

Evaluation

(1) Multiplicity of the flowers

The complexity was judged from the time taken for evaluation of 1 sample.

Very good: less than 1 minute

Good: 1 minute or more and less than 5 minutes

And (delta): 5 minutes or more and less than 10 minutes

X: 10 minutes or more

The evaluation methods are considered to be less complicated and superior in the case of good properties to good properties.

(2) Detection accuracy

The detection accuracy was rated by the degree of coincidence between the results of quality evaluation performed after the display device was assembled using the inspected retardation film (customer-side evaluation results) and the quality evaluation results in the film state (evaluation results in the company).

Very good: the evaluation results of 9-10 samples are consistent

Good: the evaluation results of 6-8 samples are consistent

And (delta): the evaluation results of 3-5 samples are consistent

X: the evaluation results of 0-2 samples are consistent

The detection accuracy is required to be not less than Δ, and preferably good to excellent.

Table I shows the above evaluation methods and evaluation results.

[ Table 1]

As is clear from the evaluation results in table I, the use of the method and apparatus for detecting an orientation unevenness defect of a retardation film according to the present invention improves the complexity and detection accuracy of the evaluation of an orientation unevenness defect of a retardation film relative to the visual evaluation.

Therefore, according to the present invention, it is possible to provide a method and an apparatus for detecting an orientation unevenness defect of a retardation film, the method and the apparatus being as follows: by detecting and evaluating the defect of the orientation unevenness of the retardation film based on the quantitative evaluation of the optical system, the evaluation is not personal, and the evaluation reproducibility can be improved more easily.

Industrial applicability

The method and apparatus for detecting an orientation unevenness defect of a retardation film according to the present invention can detect and evaluate an orientation unevenness defect of a retardation film by quantitative evaluation using an optical system, and the evaluation is not personal and is suitable for evaluating an orientation unevenness defect of a retardation film more easily.

Description of the symbols

1 phase difference film

2 Flat LED Lighting

3 st polarizing plate

4 nd 2 nd polarizing plate

5 visual examination

6 direction of inclination

L irradiation light

Theta angle of view

10 conventional visual evaluation method for defects of uneven alignment

50 orientation unevenness defect detection device

51 phase difference film

51a is long

51b width long

52 flat panel LED lighting

53 shading plate

54 th polarizing plate

55 nd 2 nd polarizing plate

56 lens

57 Camera

100 defect detecting part

101 control unit

101a CPU

101b RAM

101c program memory

102 recording part

103 communication unit

104 data processing part

104a shading processing circuit

104b edge detection circuit

104c binarization circuit

104d image processing circuit

104e filter circuit

105 operation display part

120 photographic adjusting device

130 photographic device

150 external output device

Claims

2. The method for detecting an orientation unevenness defect of a retardation film according to claim 1, further comprising:

and (6) performing image processing for emphasizing a component in an oblique direction by performing dilation processing on the binarized luminance image in the oblique direction in a range of 70 ° to 120 ° with respect to the direction of differential (difference) processing of the retardation film.

3. The method for detecting an orientation unevenness defect of a retardation film according to claim 2, further comprising:

and (7) performing a contraction process on the luminance image in the same direction after the expansion process is performed.

4. The method for detecting an orientation unevenness defect of a retardation film according to claim 3, further comprising:

and (8) 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 orientation unevenness defect component in the direction.

5. The method of detecting defects of alignment unevenness of a retardation film according to any one of claims 1 to 4,

the field angle theta of the lens calculated according to the distance between the lens front end position of the photographing device and the phase difference film and the size of the length direction of the inspection area on the phase difference film is within 23 DEG relative to the length direction of the phase difference film.

6. An apparatus for detecting uneven alignment of a retardation film, which is used in the method for detecting uneven alignment defects of a retardation film according to any one of claims 1 to 5, the apparatus comprising:

a defect detecting section for detecting a defect from the luminance image,

the defect detection unit includes:

7. The apparatus for detecting defects in misorientation of a retardation film according to claim 6,

the defect detection unit includes an image processing circuit that performs expansion processing on the binarized luminance image in an oblique direction within a range of 70 ° to 120 ° with respect to a direction of differentiation (difference) processing of the retardation film, and emphasizes a component in the oblique direction.

8. The apparatus for detecting defects in misorientation of a retardation film according to claim 7,

the defect detecting unit includes an image processing circuit that performs a contraction process on the luminance image in the same direction after the expansion process is performed.

9. The apparatus for detecting defects in misorientation of a retardation film according to claim 6,

the defect detection unit includes a filter circuit that extracts, as an orientation unevenness defect component in the direction, a portion that satisfies a filter condition defined by a representative length of each pixel region from the luminance image after the contraction processing.

10. The apparatus for detecting defects in misorientation of a retardation film according to any one of claims 6 to 9,