JP2015004674A - Method for discriminating defect of optical film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for accurately discriminating cluster defects among defects of an optical film. The present invention relates to a method for determining defects in an optical film. The method for determining defects in an optical film of the present invention includes a step (S1) of photographing a transferred optical film to acquire an image of the optical film, and detecting a foreign substance from the image, and any one of the foreign substances. When two or more foreign substances are present in a circle having a radius of 5 mm centered on the foreign substance, the detection condition is not strengthened by providing a step (S2) of determining the aggregate of the foreign substances including the foreign substance in the center as a cluster defect. The defective rate of the optical film can be reduced. [Selection diagram] Fig. 4

Description

  The present invention relates to a film defect detection method. More specifically, the present invention relates to a method for detecting cluster defects in an optical film.

  In recent years, various image display devices such as a liquid crystal display, an organic light emitting display, a field emission display (FED), and a plasma display panel (PDP) have been widely developed and used.

  On the other hand, since various defects occur in the manufacturing process before the image display device is put on the market, it undergoes many inspection processes. Among them, one of the most frequently used components in image display devices is various optical films such as polarizing films and retardation films. Therefore, defects in optical films are one of the main causes of image display device defects. It is. In detecting a defect in the optical film, first, it is determined whether or not it is a defect, and then an accurate determination is made. After that, when it is determined as a defect, the defect is repaired or discarded, and further the cause of the defect Removal is an important part in terms of production yield in the manufacturing process.

  In the production of optical films, a line process is usually used for mass production in industry. Therefore, the defect is detected by continuously photographing the optical film at a specific position on the line and determining the defect at the photographed portion.

  Conventionally, it has been important to detect various defects reliably for defect determination. In this regard, Korean Laid-Open Patent Publication No. 10-2010-0024753 discloses a method for discriminating a line-shaped foreign object by comparing a closed curve including the foreign object and the area of the foreign object.

  However, recently, as the cost of parts increases with the trend of increasing the size of optical films, more accurate defect determination methods are required. Therefore, there is still a need for a method that can accurately determine defects.

Korean Published Patent No. 10-2010-0024753

  An object of this invention is to provide the method of discriminating a cluster defect correctly among the defects of an optical film.

  1. Step (S1) of photographing the transferred optical film to obtain an image of the optical film, detecting foreign matter from the image, and placing the foreign matter in a circle having a radius of 5 mm around one of the foreign matters. If there are two or more, a step (S2) of determining an aggregate of the foreign matters including a central foreign matter as a cluster defect (S2).

2. In the item 1, the defect determination method for an optical film, wherein the radius is 4 mm, 3 mm, 2 mm, or 1 mm.

  3. In the item 1, the defect determination method for an optical film, wherein the foreign matter has a major axis length of 30 to 100 μm.

  4). In the item 1, the defect determination method for an optical film, wherein the foreign matter has a major axis length of 30 to 50 μm.

  5. In the item 1, the optical film defect determination method, wherein the photographing in the step (S1) is performed by a reflection optical system method, a transmission optical system method, or both methods.

  6). In the item 1, in the step (S2), when it is determined as the cluster defect, the method further includes a step of marking a corresponding portion of the optical film.

  The defect determination method of the optical film of the present invention is not a defect in a foreign substance in an individual unit, but when the foreign substance is concentrated in a predetermined area, a defective synergistic effect due to such concentration causes a defective product. Since it can be a cause, it is possible to reduce the defect rate of the optical film by providing a method for determining such a state (cluster defect) as a defect.

  The optical film defect discriminating method according to the present invention is not a method for enhancing the detection conditions of the detection device, but a method for judging the degree of foreign matter clustering, thereby enhancing the replacement or detection conditions of the detection device. Cluster defects can be detected.

FIG. 1 is a diagram showing a schematic structure of a reflection optical system inspection apparatus. FIG. 2 is a diagram showing a schematic structure of a transmission optical system inspection apparatus. FIG. 3 is a photograph actually taken of an example of a cluster defect. FIG. 4 is a diagram schematically showing an example of a cluster defect.

  In the present invention, a step (S1) of capturing an image of the optical film by capturing a transported optical film, detecting foreign matter from the image, and having a radius of 5 mm centering on one of the foreign matters. When there are two or more foreign substances in a circle, the step (S2) of determining the aggregate of the foreign substances including the central foreign substance as a cluster defect (S2), thereby reducing the defect rate of the optical film without strengthening the defect detection conditions. Can be reduced.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  First, the transferred optical film is photographed to obtain an image of the optical film (S1).

  In general, the optical film is manufactured by being transferred through a continuous process, for example, a roll-to-roll process. Therefore, in order to determine the defect of the optical film, the optical film is photographed on the upper part of the optical film transferred in a certain direction, and an image of the optical film is acquired. If there is a region where foreign matter exists in the acquired image, a step of selecting this and determining whether or not it is a defect is performed.

  For example, a reflection optical system, a transmission optical system, or both can be used as the method of the photographing apparatus used to detect defects in the optical film.

  The reflection optical system inspection apparatus means an apparatus that performs inspection with light reflected from an inspection object. Specifically, a light source is positioned on one side of the inspection film and irradiates the inspection film with light. The photographing apparatus is an apparatus that captures an inspection film on the same side as the light source with the inspection film as a reference (condenses light reflected by the inspection film) to acquire an inspection image.

  FIG. 1 (a: side view, b: plan view) schematically shows a film defect detection method using a reflection optical system inspection apparatus. Referring to FIG. 1, in the reflection optical system inspection apparatus, in the plan view shown in FIG. It is configured to be located in any direction. That is, the arrangement direction of the light source and the photographing device is located in a direction parallel to the inspection film transfer direction. Then, a defect is detected using an image captured at the position as an inspection image.

  The transmission optical system inspection device refers to a device that performs inspection with light transmitted through an inspection object. Specifically, a light source is disposed on one side of the inspection film and irradiates the inspection film with light. The photographing apparatus is an apparatus that captures an inspection film on the opposite side of the light source with the inspection film as a reference (condenses light transmitted through the inspection film) and acquires an inspection image.

  A film defect detection method using a transmission optical system inspection apparatus is schematically shown in FIG. Referring to FIG. 2, the transmission optical system inspection apparatus is configured such that the light source and the imaging device are positioned in the vertical direction with respect to the inspection film to be inspected. Then, a defect is detected using an image captured at the position as an inspection image.

  The transmission optical system inspection apparatus can be further added with the configuration depending on the specific type of optical film to be inspected. For example, when the optical film to be inspected is a polarizing film, another polarizing film perpendicular to the polarization direction of the polarizing film of the sample to be inspected can be disposed on the top of the film to be inspected. In this case, if the polarizing film to be inspected is a non-defective product, no light passes through the two polarizing films whose polarization directions are perpendicular to each other, so a black image is obtained, but there is a foreign object in the polarizing film to be inspected. Then, since the direction of polarization changes in that portion, light leakage eventually occurs, and an image having a bright portion (that is, a foreign matter portion) is obtained.

  Next, a foreign object is detected from the image, and when there are two or more foreign objects in a circle having a radius of 5 mm centering on any one of the foreign objects, the aggregate of the foreign objects including the central foreign object is determined as a cluster defect. (S2).

  In the present invention, the “foreign matter” is a portion that deviates from the average uniformity of the optical film, and is determined to be within the normal range according to the discrimination result (non-defective foreign matter) or a product defect. It is a portion that can be determined to be a “defect” that is a cause.

  Sorting the area where foreign matter exists from the acquired image is to set the average uniformity of the optical film, and then use the image processing software etc. Can be carried out.

  The types of foreign matter defined in the present invention can be classified into a brighter part (bright spot) and a darker part (dark spot) than the periphery in the captured image. Such a bright spot or dark spot includes not only an optical bright spot or dark spot found on an optical film but also a bright spot or dark spot caused by unevenness.

  As described above, the detected foreign matter can be classified into a non-defective foreign matter and a foreign matter that becomes a defect. A typical example of a non-defective foreign material is a case where the size is too small to cause a defect. Therefore, a foreign material having a predetermined size or less is not determined to be a defect according to a standard required for the optical film.

  On the other hand, if fine foreign matters that are non-defective foreign matters are in a cluster state, it may actually be recognized as defective when used in a product, which may be a problem. However, conventional optical film defect determination methods individually separate unit foreign substances and determine whether or not they are defective according to a predetermined standard. Therefore, fine foreign substances that are non-defective defects are in a cluster state. Even if this is the case, it could not be determined as a defect. An example in which such fine foreign substances form a cluster state is shown in FIG. As shown in FIG. 3, if the fine foreign matter is in a cluster state, it is recognized as defective when used in an actual product. However, in the conventional defect determination method for individual foreign matter, it is a defect. It was difficult to recognize.

  The present invention provides a method of discriminating a foreign object as a defect when a foreign substance is concentrated in a predetermined region to solve the above-described problems. Specifically, when two or more foreign objects detected from an image captured by the inspection imaging apparatus exist in a circle having a radius of 5 mm centering on any one foreign object, the set of the foreign objects including the central foreign object The body is determined to be a defect (hereinafter referred to as a cluster defect).

  The cluster area for determining whether or not the defect is a cluster defect is a circle having a radius of 5 mm with reference to the central foreign matter. When the radius exceeds 5 mm, there are almost no cases where it is recognized as a defect when actually used.

  On the other hand, depending on the specific application of the optical film to be manufactured, the radius of the cluster region can be further reduced. The smaller the radius of the cluster region, the less often it is determined that the defect is a cluster defect. Therefore, the cluster radius is further reduced if it is not required to be intact with respect to the optical film. For example, the radius of the cluster region may be 4 mm, 3 mm, 2 mm, or 1 mm, but is not limited thereto.

  In the present invention, the size of the unit foreign matter forming the cluster defect is not particularly limited. Preferably, it has a size greater than or equal to the size recognized as a foreign object in the image, and has a size of two or more in the cluster region. For example, the length of the major axis of the foreign material is 100 μm or less, and preferably 50 μm or less. In the present invention, the lower limit of the size of the foreign matter varies depending on the type of the photographing apparatus, and it can be detected no matter how fine the non-defective foreign matter is. For example, the thickness may be 30 μm. Accordingly, the size of the foreign matter according to the present invention may be, for example, 30 to 100 μm, preferably 30 to 50 μm, based on the long axis of the foreign matter, but is not limited thereto.

  A schematic illustration of the cluster defects is shown in FIG. Referring to FIG. 4, since the foreign substances 1, 2, and 3 exist inside a circle having a predetermined radius with the foreign substance 2 as the center, two or more foreign substances exist in the cluster region. Determined.

  In the present invention, when it is determined that the defect is a cluster defect in the step S2, the method may further include a step of marking a corresponding portion of the optical film.

  Marking can be performed in areas where the optical film is actually used, or in the remaining areas (areas that are not actually used) that are removed when processed into the final product.

  By marking the portion where the cluster defect has occurred, it can then be easily used to classify and remove the portion where the cluster defect has occurred.

  In addition, the marking can count the number of the markings, calculate the defect occurrence rate from it, and control the manufacturing process. It can also be used as an index to compare the image with the actual optical film. It can also be used to confirm whether or not the above determination is correctly performed.

  The defect determination method of the present invention can be applied to various optical films. Examples of such an optical film include a polarizing film and a retardation film, but are not limited thereto.

  As described above, according to the present invention, when foreign substances are concentrated in a predetermined area, the concentration can further cluster and cause defective products. Therefore, such a state (cluster defect) is determined as a defect. Provide a method. In addition, the defect determination method of the present invention is not a defect in a foreign substance in an individual unit, but in order to be able to detect a case where the foreign substance is concentrated in a predetermined region and causes a defect, the defect of the optical film The rate can be reduced.

  As described above, the present invention has been described with reference to the disclosed embodiments and drawings. However, the present invention is not limited thereto, and the present invention is provided by persons having ordinary knowledge in the technical field to which the present invention belongs. It goes without saying that various modifications and variations can be made within the scope of the technical idea and the equivalent scope of the following claims.

Claims (6)

Capturing an image of the optical film to obtain an image of the optical film (S1);
Detecting foreign matter from the image, and determining two or more foreign matters in a circle having a radius of 5 mm centering on any one of the foreign matters, and determining the set of foreign matters including the central foreign matter as a cluster defect (S2) An optical film defect discrimination method.   The defect determination method for an optical film according to claim 1, wherein the radius is 4 mm, 3 mm, 2 mm, or 1 mm.   The optical film defect determination method according to claim 1, wherein the foreign matter has a major axis length of 30 to 100 μm.   The defect determination method for an optical film according to claim 1, wherein the foreign matter has a major axis length of 30 to 50 μm.   5. The optical film defect determination method according to claim 1, wherein photographing in the step (S <b> 1) is performed by a reflection optical system method, a transmission optical system method, or both methods. 6.   The optical film defect determination method according to any one of claims 1 to 5, further comprising a step of marking a corresponding portion of the optical film when the cluster defect is determined in the step (S2).

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