A method for identifying defects in optical thin films and its application

Abstract

This invention relates to the field of optical thin films, and more particularly to a method for identifying defects in optical thin films and its application. The method for identifying defects in optical thin films includes the following steps: S1: Identifying and confirming the defect area, determining the location of reflected light rays; S2: Applying colored dye to both surfaces of the thin film; S3: Observing the changes in reflected light rays on both surfaces of the thin film after dye application, and comparing to confirm the surface where the defect is located. The optical thin film defect identification method provided in this application can simply and effectively identify the surface where defects are located in optical thin films. The method is simple, efficient, and has low time and labor costs, reducing the inspection costs for enterprises.

Description

Technical Field

[0001] This invention relates to the field of optical thin films, and more particularly to a method for identifying defects in optical thin films and its application. Background Technology

[0002] The excellent light transmittance of optical films places high demands on the film surface. During the production of optical-grade films, the film is pulled to its winding stage by a drag system. When the film passes over a drag system with attached foreign objects or surface damage, the stress from the foreign object and the speed of dragging, or when the foreign object comes into contact with the film, can cause extremely minor damage to the surface of the optical-grade film. The finished product exhibits bright lines of varying lengths or with fixed spacing along the longitudinal direction. The product surface is extremely bright under reflected light, creating a stark contrast with the reflected light from the optical film surface. This defect is known in the industry as scratches. It severely affects the appearance quality of the product and reduces the yield.

[0003] In the production of optical thin films, the drying area typically involves the movement of 400-600 guide rollers. Foreign objects may be present between the film and the rollers, causing regular, millimeter- or micrometer-sized scratches due to friction during rotation. Furthermore, excessive rotational resistance of the guide rollers can lead to displacement between them and the film, and the hardness of the rollers can scratch the film surface. These scratches are highly random and difficult to detect. Current defect handling methods require first checking for nearby objects in the film's running area to determine if scratches are caused by foreign objects contacting the film. Then, all guide rollers driving the film, both passive and active rollers, must be inspected. If any guide roller bearings are found to be malfunctioning or stopped, they need to be lubricated or replaced. If no bearing abnormalities are found, all guide roller bearings need to be lubricated – a large-scale process that is quite challenging. Alternatively, increasing the drag tension can give the film greater capacity to drive the unpowered guide rollers, preventing wear caused by excessive speed differences. However, this method is prone to longitudinal tension line wrinkles, making it counterproductive.

[0004] In the methods for identifying and confirming defects, CN103630547B provides a defect detection method for optical thin films with periodic structures. This method involves capturing the original image on the optical thin film, then capturing sub-images and comparison images, calculating the average grayscale value of the processed image, and analyzing the grayscale value to determine whether there are defects. This method is not only complex and cumbersome to operate, but also cannot effectively determine the surface of the thin film where the defect is located during actual operation, thus hindering the accurate identification and judgment of defects.

[0005] Therefore, in order to solve the above problems, this application provides a method for identifying defects in optical thin films. Summary of the Invention

[0006] To address the aforementioned problems, the first aspect of this invention provides a method for identifying defects in optical thin films, comprising the following steps: S1: identifying and confirming the defect area and determining the location of the reflected light; S2: wetting the two surfaces of the thin film with colored dye; S3: observing the changes in the reflected light on the two surfaces of the thin film after wetting with colored dye and comparing to confirm the surface where the defect is located.

[0007] As a preferred embodiment, step S1 includes a static defect identification method and a dynamic defect identification method.

[0008] As a preferred embodiment, the static defect identification method is as follows: When the film is in a static state, it is irradiated by a light source to form a light spot on the surface of the film. The light spot moves with the width of the film as the horizontal coordinate. The light source and the film form a certain irradiation angle. An observation point is set up, and the observation point forms a reflection angle with the irradiation direction of the light source and ensures that the observation point is above the light source. Then, the changes in the light spot are observed laterally at the observation point. If there is a scratch, it will appear as a thin bright line (reflected line) in the light spot, which is different from the brightness of the reflected light of the light spot.

[0009] As a preferred embodiment, the light spot is a circular shadowless light spot; the diameter of the circular shadowless light spot is 50-200mm.

[0010] As a preferred embodiment, the illumination angle between the light source and the thin film in the static defect identification method is 30-60°; the reflection angle between the observation point and the illumination direction of the light source in the static defect identification method is 30-60°.

[0011] As a preferred embodiment, the dynamic defect identification method is as follows: when the guide roller is dragging the film, it is also illuminated by a light source to form a light spot on the surface of the film. The light source moves parallel to the film surface, and the light source and the film form a certain illumination angle. An observation point is set, and the observation point forms a reflection angle with the illumination direction of the light source and ensures that the observation point is below the light source. Then, the changes in the light spot are observed laterally at the observation point. If there is a scratch, it will appear as a thin bright line (reflective line) in the light spot, which is different from the brightness of the light spot reflection.

[0012] As a preferred embodiment, the illumination angle between the light source and the thin film in the dynamic defect identification method is 30-60°; the reflection angle between the observation point and the illumination direction of the light source in the dynamic defect identification method is 30-60°.

[0013] As a preferred embodiment, step S2 involves coating and wetting the two surfaces of the film with an adhesive colored dye, ensuring that the coating and wetting area completely covers the reflective areas in step S1.

[0014] As a preferred embodiment, step S3 is as follows: observe the changes in reflected light at observation points on different film surfaces by applying and impregnating colored dye through diffuse reflection, and then compare and determine the surface where the defect is located.

[0015] As a preferred embodiment, in this application, when the colored dye is immersed into the film surface where the defect is located, the colored dye will change the reflective surface of the scratch at the defect site, forming diffuse reflection of light. At this time, when observed at the observation point on the film surface where the defect is located, the reflected light disappears, while at the same position on the film surface without defects, the reflected light observed at that observation point will be dim or disappear.

[0016] As a preferred embodiment, in this application, when the colored dye is immersed in the same position as the defect on the undefective film surface, the reflected light disappears at the observation point on the undefective film surface due to the diffuse reflection of light, while the reflected light can still be clearly observed at the observation point on the film surface where the defect is located.

[0017] Therefore, this application can determine the exact surface of the film where the defect is located by observing the results of wetting different film surfaces with the two colored dyes mentioned above. This is mainly because, through the ingenious design of the observation points on both sides of the optical film, after determining the specific location of the defect, the presence of the reflected light from the "marker" can be observed through the diffuse reflection of light caused by the colored dye on the optical film. Due to the influence of the defect, when the colored dye wets different optical film surfaces, the presence of the defect causes differences in the diffuse reflection of light, and this difference can directly lead to the appearance of the reflected light. Therefore, through continuous observation and comparison, the surface where the defect is located can be directly determined, and the guide roller can be cleaned or repaired according to the defect location, which is at least 50% more efficient than previous methods.

[0018] A second aspect of the present invention provides an application of the above-mentioned optical thin film defect identification method, including the application of the optical thin film defect identification method in the optical thin film preparation process.

[0019] Beneficial effects:

[0020] 1. The optical thin film defect identification method provided in this application can easily and effectively identify the surface where defects are located in optical thin films. The method is simple and efficient, with low time and labor costs, reducing the inspection costs for enterprises.

[0021] 2. The optical thin film defect identification method provided in this application is different from the existing optical thin film defect identification methods that cannot quickly and accurately identify the surface where the defect is located. It can directly determine the surface where the defect is located by cleverly utilizing the diffuse reflection phenomenon of light on different thin film surfaces.

[0022] 3. The optical film defect identification method provided in this application can quickly identify defects on the surface of the optical film in practical applications, thereby directly eliminating half of the potentially problematic equipment locations during the cleaning and repair of guide rollers, thus improving guide roller repair efficiency by at least 50%.

[0023] 4. The optical thin film defect identification method provided in this application, through the ingenious design of observation points on both sides of the optical thin film, after determining the specific location of the defect, observes the presence of the reflected light of the "marker" by the diffuse reflection of light caused by the colored dye on the optical thin film. Because of the influence of the defect, when the colored dye wets different optical thin film surfaces, the presence of the defect causes the diffuse reflection of light to be different, and this difference can directly lead to the imaging of the reflected light. Therefore, through continuous observation and comparison, the surface where the defect is located can be directly determined.

[0024] 5. The optical thin film defect identification method provided in this application can pinpoint the specific location of the damaged surface of the thin film offline by scratching the transverse position of the thin film and segmenting the longitudinal position, and finally by using a dip-coating identification method. At the same time, a scratch observation method is used on the thin film, with the thin film path segmented as the observation unit, to observe and locate the defect segment by segment, saving time and improving work efficiency. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the observation point and the position of the light source in the dynamic defect identification method.

[0026] Figure 2 This is a schematic diagram of the observation point and the position of the light source in a static defect identification method.

[0027] Figure 3 This is a schematic diagram showing the diffuse reflection effect of light on the film surface where the defect is located after being coated and impregnated with colored dye.

[0028] Figure 4 This is a schematic diagram showing the diffuse reflection effect of light on a flawless thin film surface after it has been coated and impregnated with colored dye.

[0029] In the picture:

[0030] 1-Optical thin film, 2-Light source, 3-Observation point, 4-Defect, 5-Film surface where the defect is located, 6-Film surface without defects. Detailed Implementation

[0031] Example 1

[0032] Example 1 provides a method for identifying defects in optical thin films, comprising the following steps: S1: identifying and confirming the defect area and determining the location of the reflected light; S2: wetting the two surfaces of the thin film with colored dye; S3: observing the change in the reflected light on the two surfaces of the thin film after wetting with colored dye and comparing to confirm the surface where the defect is located.

[0033] The example uses a TAC film, which runs through the guide shaft of the drying oven.

[0034] Step S1 employs a static defect identification method: When the optical film 1 is stationary, it is illuminated by a light source 2, forming a light spot on the surface of the optical film 1. The light spot moves with the width of the optical film 1 as the horizontal coordinate. The light source 2 and the optical film 1 form a certain illumination angle. An observation point 3 is set up, and the observation point 3 forms a reflection angle with the illumination direction of the light source 2, ensuring that the observation point 3 is above the light source 2. Then, the changes in the light spot are observed laterally at the observation point 3. If there is a scratch, it will appear as a thin bright line (reflected line) in the light spot, which is brighter than the reflected light of the light spot.

[0035] The spot is a circular, shadowless light spot with a diameter of 100 mm.

[0036] In the static defect identification method, the illumination angle formed by the light source 2 and the optical thin film 1 is 40°; in the static defect identification method, the reflection angle formed by the observation point 3 and the illumination direction of the light source 2 is 40°.

[0037] At the determined reflective light position, the same light source 2 and observation point 3 are respectively set on both sides of the optical film 1.

[0038] Step S2 involves applying an adhesive colored dye to both surfaces of the optical film 1, ensuring the application completely covers the reflective areas from step S1. The colored dye is Blue 755, manufactured by BASF.

[0039] Step S3 is as follows: By observing the changes in reflected light at observation point 3 on the surface of different optical thin films 1 through the diffuse reflection of light after applying and impregnating colored dye, the surface where the defect 4 is located can be compared and judged.

[0040] like Figures 2-4 As shown, when colored dye is immersed into the film surface 5 where the defect is located, the colored dye will change the reflective surface of the scratch, forming diffuse reflection of light. In this way, the observation point 3 of the film surface 5 where the defect is located will not see the scratch under the light spot of the light source 2, and will lose the reflective light. However, under the light spot of the light source 2 on the film surface 6 without defects, the observation point 3 will find that the reflective light of the scratch is dim.

[0041] When a colored dye is applied to the flawed area (i.e., the scratched area) of the unblemished film surface 6, the unblemished film surface 6 will experience diffuse reflection of light due to the colored dye, and the observation point 3 of the unblemished film surface 6 will lose its reflected light. However, the reflected light from the scratch can still be seen at the observation point 3 of the flawed film surface 5 under the light spot of the light source 2. Therefore, the surface where the flaw 4 is located is confirmed.

[0042] Results: The scratch on the TAC film was determined by lateral measurement of the film width. The scratch was located 300mm from the right edge and was observed to be a continuous straight scratch.

[0043] Example 2

[0044] The specific implementation method of this embodiment is the same as that of embodiment 1, except that: Figure 1 As shown; Step S1 adopts a dynamic defect identification method: When the optical film 1 is driven by the guide roller, it is irradiated by the light source 2, forming a light spot on the surface of the optical film 1. The light spot moves with the width of the film as the horizontal axis. The light source 2 and the optical film 1 form a certain irradiation angle. An observation point 3 is set. The observation point 3 forms a reflection angle with the irradiation direction of the light source 2 and ensures that the observation point 3 is below the light source 2. Then, the changes in the light spot are observed laterally at the observation point 3. If there is a scratch, it will appear as a thin strip of bright line (reflective line) in the light spot, which is brighter than the brightness of the light spot reflection.

[0045] The spot is a circular, shadowless light spot with a diameter of 100 mm.

[0046] In the static defect identification method, the illumination angle formed by the light source 2 and the optical thin film 1 is 40°; in the static defect identification method, the reflection angle formed by the observation point 3 and the illumination direction of the light source 2 is 40°.

[0047] Results: The scratches on the film were located 460 mm from the left edge, and the scratch spacing was 314 mm, showing a periodicity.

[0048] Example 3

[0049] The specific implementation method of this embodiment is the same as that of embodiment 1, except that: the TAC film runs through the guide rollers of the drying box, and scratches and defects are detected at the finished product winding position by online monitoring.

[0050] Results: The scratches on the film were irregular, short, and widely distributed laterally, ranging from 500 to 600 mm from the left side of the film.

[0051] Comparative Example 1

[0052] Comparative example: Scratches appeared on the finished TAC film winding. Through online scratch observation, the scratches were observed to be regular and straight with a length of 25mm. The location identification method described in this application was not used, so it was impossible to determine the location of the scratch in the drying box. It was necessary to adjust or check each box in sections to find the location area. It was impossible to determine which side of the film the scratch was on, so all guide rollers needed to be treated.

[0053] Performance Evaluation

[0054] The technical solutions of the embodiments and comparative examples are recorded, including the scratch and defect area, the number of guide rollers checked, the location of scratch and defect, and the improved processing efficiency compared with previous processing methods during the identification process.

[0055] Table 1

[0056]

[0057]

Claims

1. A method for identifying defects in optical thin films, characterized in that: The steps include the following: S1: Identification and confirmation of the defective area, and determination of the location of the reflective rays; S2: Colored dye impregnation on both surfaces of the film; S3: Observe the changes in reflected light on both surfaces of the film after colored dye impregnation, and compare to confirm the surface where the defect is located.

2. The optical thin film defect identification method according to claim 1, characterized in that: Step S1 includes a static defect identification method and a dynamic defect identification method.

3. The optical thin film defect identification method according to claim 2, characterized in that: The static defect identification method is as follows: When the film is in a static state, it is irradiated by a light source to form a light spot on the surface of the film. The light spot moves with the width of the film as the horizontal axis. The light source and the film form a certain irradiation angle. An observation point is set up. The observation point forms a reflection angle with the irradiation direction of the light source and ensures that the observation point is above the light source. Then, the changes in the light spot are observed laterally at the observation point. If there is a scratch, it will appear as a thin bright line in the light spot, which is different from the reflective brightness of the light spot.

4. The optical thin film defect identification method according to claim 3, characterized in that: The light spot is a circular shadowless light spot; the diameter of the circular shadowless light spot is 50-200mm.

5. The optical thin film defect identification method according to claim 4, characterized in that: In the static defect identification method, the illumination angle between the light source and the thin film is 30-60°; in the static defect identification method, the reflection angle between the observation point and the direction of light source illumination is 30-60°.

6. The optical thin film defect identification method according to claim 5, characterized in that: The dynamic defect identification method is as follows: when the guide roller is dragging the film, it is also illuminated by a light source to form a light spot on the surface of the film. The light source moves parallel to the surface of the film and forms a certain illumination angle with the film. An observation point is set up, and the observation point forms a reflection angle with the direction of the light source and ensures that the observation point is below the light source. Then, the changes in the light spot are observed laterally at the observation point. If there is a scratch, it will appear as a thin bright line in the light spot, which is different from the brightness of the light spot reflection.

7. The optical thin film defect identification method according to claim 6, characterized in that: In the dynamic defect identification method, the illumination angle between the light source and the thin film is 30-60°; in the dynamic defect identification method, the reflection angle between the observation point and the illumination direction of the light source is 30-60°.

8. The optical thin film defect identification method according to claim 7, characterized in that: Step S2 involves applying an adhesive colored dye to both surfaces of the film, ensuring that the application area completely covers the reflective areas from step S1.

9. The optical thin film defect identification method according to claim 8, characterized in that: The S3 step is as follows: observe the changes in reflected light at observation points on different film surfaces by applying and impregnating colored dye through the diffuse reflection of light, and then compare and determine the surface where the defect is located.

10. An application of the optical thin film defect identification method according to any one of claims 1 to 9, characterized in that: This includes the application of this optical thin film defect identification method in the optical thin film fabrication process.

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