Quantitative image analysis system for evaluating surface-based coating performance

Abstract

The present disclosure provides a method for quantifying surface defects on a coated substrate, the method comprising: a) providing a system for acquiring and analyzing images; b) loading the coated substrate on a holder, wherein the coated substrate comprises a coating layer formed on a surface of the substrate; c) irradiating the coated substrate with an illumination system, where irradiating the coated substrate comprises irradiating the coated substrate at an angle of incidence of 15 DEG to 85 DEG relative to a plane parallel to a surface of the coated substrate to create a shadow of any defect on the surface of the coated substrate; d) acquiring at least one image of the coated substrate with an imaging system; e) transforming the at least one image of the coated substrate with an analysis unit to provide at least one transformed image, and quantifying the surface defects on the coated substrate based on the at least one transformed image; and f) providing an output, wherein the output comprises values identifying the amount or percentage of the defects on the coated substrate and / or a generated image showing the amount or percentage of the surface defects on the coated substrate.

Description

Technical Field

[0001] The present invention generally relates to a method for quantitatively analyzing images to determine surface-based defects on a coated substrate. Background Technology

[0002] The appearance of coated substrates is one of the most important performance evaluation metrics used by consumers and researchers. Defects in coated substrates can manifest themselves in many different ways, including color anomalies, surface or texture differences, or other visible deviations. For example, the smoothness or leveling of a coated substrate may appear as surface defects caused by shading or changes in appearance. Resistance to defects caused by, for example, water, corrosion, dirt, grease, and weathering can manifest as color variations in the coated substrate. Other defects in coated substrates may be more difficult to observe visually, such as the migration / secretion or extraction of components within the coated substrate.

[0003] Such defects in coated substrates are typically observed or measured by humans. Because many defects in coated substrates are difficult to assess, defect measurements often struggle to be accurately and / or reproducibly quantified. Most defect measurements are highly subjective and are usually measured on simple scales, such as numerical scales of 1 to 5, where human observers assign values ​​based on their interpretation of the surface of the coated substrate. Variation in values ​​assigned by one observer over the next is common, and quantification of defects often results in coarse estimates. Due to the subjective nature of the measurements, observations are typically normalized in each study. Therefore, data obtained from one study through human observation cannot be reliably combined with data from another study.

[0004] Attempts have been made to automate the defect detection process. US Patent Application Publication No. 2022 / 0082508 discloses a method for providing a composition-related prediction procedure, which includes providing a database of qualitative and / or quantitative characterizations of the coating surface, and training a machine learning model to develop a composition quality prediction procedure for predicting the properties of the coating surface to be produced. However, the database of qualitative and / or quantitative characterizations is generated by manually identifying and labeling digital images, where the qualitative and / or quantitative characterizations of the images are based on scales with values ​​assigned by human observers. Therefore, the database is compiled using data based on human observation.

[0005] There is a need for a method that can more accurately and reproducibly detect defects in coated substrates in order to identify and quantify defects. Summary of the Invention

[0006] This invention relates to a method for quantitatively measuring surface defects on a coated substrate, the method comprising:

[0007] a) Provide a system for acquiring and analyzing images, the system including

[0008] i) An imaging system for acquiring one or more images of the coated substrate;

[0009] ii) A lighting system comprising a light source for illuminating the coated substrate;

[0010] iii) A holder for holding the coated substrate in place where it will be irradiated by the light source;

[0011] iv) An analysis unit configured to transform the one or more images and quantitatively analyze the one or more transformed images to determine defects on the coated substrate.

[0012] b) Loading a coated substrate onto the holder, wherein the coated substrate includes a coating formed on the surface of the substrate;

[0013] c) Illuminate the coated substrate with the lighting system, wherein illuminating the coated substrate includes illuminating the coated substrate at an angle of incidence of 15° to 85° relative to a plane parallel to the surface of the coated substrate, so as to generate a shadow of any defects on the surface of the coated substrate.

[0014] d) Use the imaging system to acquire at least one image of the coated substrate;

[0015] e) Transforming the at least one image of the coated substrate using the analysis unit, wherein transforming the at least one image of the coated substrate includes processing the at least one image of the coated substrate using an algorithm selected from the group consisting of image thresholding, wavelet transform, morphological transform, color detection, pattern detection, clustering, and combinations thereof, to provide at least one transformed image, and quantifying these surface defects on the coated substrate based on the at least one transformed image; and

[0016] f) Provide output, wherein the output includes values ​​identifying the amount or percentage of defects on the coated substrate and / or a generated image showing the amount or percentage of surface defects on the coated substrate. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a system for acquiring and analyzing images according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram showing the position of the light source relative to the coated substrate according to an embodiment of the present invention.

[0019] Figure 3 It is a transformed color image from a rollout charted, analyzed by an image analysis system according to an embodiment of the present invention, for smoothness testing.

[0020] Figure 4 It is a transformed texture image from a roll-up chart for smoothness testing, analyzed by an image analysis system according to an embodiment of the present invention.

[0021] Figure 5 It is a black and white image generated by an image analysis system according to an embodiment of the present invention, which is generated by white light irradiation from the top of a sample from a leveling test method.

[0022] Figure 6 It is a transformed texture image from a leveling test method, analyzed by an image analysis system according to an embodiment of the present invention. Detailed Implementation

[0023] The inventors have discovered a method for reproducibly and accurately identifying and quantifying defects in coated substrates.

[0024] As used herein, the term "coated substrate" refers to a substrate whose surface includes a coating, such as a paint coating on a metal or paper substrate, for example. The coating preferably has a thickness of less than 500 μm, more preferably less than 300 μm, and even more preferably less than 200 μm, and preferably greater than 50 nm, more preferably greater than 100 nm, and even more preferably greater than 250 nm. Multilayer coatings can have even greater thicknesses. The coated substrate may also comprise multiple layers, including, for example, an undercoat or base coating.

[0025] Preferably, the coated substrate includes coatings selected from polyurethane coatings, epoxy coatings, acrylic coatings (including, for example, acrylic coatings, vinyl-acrylic coatings, and styrene-acrylic coatings), alkyd resin coatings, and zinc-rich coatings. More preferably, the coated substrate comprises paint. The substrate may include metal, plastic, wood, glass, composites, fiberglass, paper, fabric, leather, or other materials. For testing purposes, it is preferred that the substrate has a flat or planar surface.

[0026] Defects in or on coated substrates can be caused by a variety of issues. Examples of defects include, but are not limited to, color defects, surface or texture defects, and migration / secretion or extraction defects.

[0027] Color defects can include stains from dirt, household stains (e.g., wine, pen, lipstick, crayon, ink, markings, etc.), adhesion defects where the coating does not adhere sufficiently to the substrate, hidden defects where the coating allows the underlying substrate or sublayer to be exposed, grease resistance to assess the permeability of oil through the coating, early rain resistance to test the coating's ability to resist rain erosion shortly after application and curing, and weathering resistance to test the coating's ability to resist weathering formation and efflorescence.

[0028] Texture or surface defects can be indicated by smoothness or leveling issues, in which the coating may have an irregular or imperfect surface. Other texture or surface problems may include, for example, cracking or peeling.

[0029] Migration / secretion and / or extraction can occur when components separate from other components or travel through a coating. Migration / secretion and / or extraction can occur due to material contact with the coating or component incompatibility within the coating. For example, surfactant leaching can occur when a water-soluble material leaches to the surface of the coating when the coating comes into contact with water. Other examples include the migration of adhesives or additives when affected by time, temperature, or environmental conditions. While migration / secretion and / or extraction can result in visible defects, these defects are often not easily observed. However, the inventors have surprisingly discovered that migration / secretion and / or extraction defects can be identified and analyzed using infrared or ultraviolet spectroscopy. Migrating / secreting or extractable substances can have different properties that can be observed in infrared or ultraviolet spectroscopy. For example, when analyzing surfactant leaching, the inventors have found that migrating components have different thermal conductivities than the remaining components, making those defects easily identifiable in infrared spectroscopy.

[0030] To analyze coated substrates, a system for analyzing and quantifying defects is provided. Figure 1 The diagram shows a schematic of a system 100 for analyzing and quantifying defects. The system 100 includes an imaging system 10, an illumination system 20, a holder 30 for holding a coated substrate 35, and an analysis unit 40.

[0031] Imaging system 10 is configured to acquire one or more images of a coated substrate 35. Imaging system 10 may include, for example, a camera or an image sensor. Imaging system 10 may further include filters for preferentially or selectively transmitting or blocking light of a predetermined wavelength, such as at least one channel of a predetermined wavelength.

[0032] The lighting system 20 includes a light source for illuminating the coated substrate 35. The lighting system 20 is preferably configured to emit radiation in the visible spectrum. The light source preferably comprises a single source, such that surface defects are visible as shadows when illuminated. Preferably, the light source is a point source or a directional source. Preferably, the lighting system 20 is configured to allow adjustment of the light intensity, the angle of incidence on the coated substrate 35, or the wavelength of the emitted light. To reduce the potential influence of external lighting, the system 100 may be covered or enclosed (not shown) so that only light from the lighting system 20 is used to acquire images.

[0033] The lighting system 20 is configured to be at an angle of 15° to 85°, preferably 20° to 70°. Figure 2 The incident angle α shown irradiates the coated substrate.

[0034] The substrate holder 30 is used to hold a coated substrate 35 for imaging by the imaging system 10. The holder 30 is configured to hold the coated substrate in a position illuminated by the illumination system 20 when it is being imaged. The holder 30 may be configured to hold a single coated substrate 35 or multiple coated substrates. The holder 30 may be stationary or adapted to allow automated loading / unloading of samples.

[0035] Preferably, at least one of the imaging system 10 and the holder 30 is adjustable, such that the position of the coated substrate 35 can be changed relative to the imaging system 10. For example, as Figure 1 As shown, the imaging system 10 can be mounted on an arm 101 attached to a vertical support 102. The arm 101 can be configured to be adjustable, allowing selection of the distance between the imaging system 10 and the holder 30. Alternatively, the arm 101 can be movable between more than one position. In another alternative, the holder 30 can be adjustable to raise or lower the holder 30 using the base 103, or the angle of the holder relative to a fixed position can be adjusted.

[0036] Preferably, at least one of the lighting system 20 and the holder 30 is adjustable relative to each other, such that the position of the coated substrate 35 can be changed relative to the lighting system 20. For example, the lighting system 20 may be adjustable in height or angle relative to the holder 30 to change the position of the coated substrate 35. Figure 2The incident angle α of the light 25 is shown. For example, the lighting system 20 can be adjustable to allow for shallower or steeper incident angles on the coated substrate 35 in order to control the size of the generated shadow. For example, a coated substrate with small surface defects can be illuminated at a larger incident angle to increase the size of the shadow, while a coated substrate with larger surface defects can be illuminated at a smaller incident angle to decrease the size of the shadow. By controlling the incident angle, the size of the shadow can be controlled to minimize the amount of overlap between adjacent surface defects.

[0037] Additionally, the lighting system 20 can be adjustable to allow it to rotate around the coated substrate 35, such that the incident angle α is the same, but the light is directed onto the coated substrate 35 from different angles, for example, from the side of the coated substrate 35 instead of the front. By allowing different lighting angles, multiple images can be acquired to identify defects that might otherwise be overlooked in a single image. For example, a small surface defect aligned with a larger surface defect and the light source may fall into the shadow of the larger surface defect. By rotating the light source relative to the coated substrate 35, multiple images can be acquired and compared by the analysis unit 40, as described below, to identify all surface defects on the coated substrate. Furthermore, acquiring multiple images at different angles allows for more accurate quantification of defects. For example, a wide but narrow defect may produce a large shadow at one angle but a small shadow at another. Therefore, the acquisition and analysis of multiple images allows for more accurate analysis of surface defects. Such analysis would be very difficult for a human observer attempting a similar analysis.

[0038] The system 100 further includes an analysis unit 40 configured to transform images acquired by the imaging system 10. The analysis unit 40 further quantitatively analyzes the transformed images to identify and / or quantify the amount or percentage of defects in or on the coating of the coated substrate 35. The analysis unit 40 may include, for example, a computer, workstation, laptop, tablet, or smartphone. The analysis unit 40 may include applications or programs suitable for transforming and analyzing images from the imaging system 10. Information acquired and / or generated by the system 100 may be stored locally in the analysis unit 40, a server, a cloud storage device, or a media storage device.

[0039] The analysis unit 40 is preferably configured to transform the acquired image by processing it with algorithms selected from: image thresholding, wavelet transform, morphological transform, color detection, pattern detection, contrast detection, clustering, and combinations thereof. The transformed image can then be analyzed by the analysis unit 40 to identify and / or quantify defects in or on the coating of the coated substrate 35, and to provide analytical output. Preferably, the output includes a value representing the number / percentage of symbolized defects, and / or an image or dataset identifying the location, size, and / or number / percentage of defects.

[0040] Preferably, the analysis unit 40 includes or is connected to a display including a graphical user interface (GUI). The GUI is preferably configured to display the output of the analysis unit 40. For example, the GUI may display a value indicating the amount or percentage of defects present in the coated substrate 35. Alternatively, the GUI may display a transformed image identifying the location, size, and / or number / percentage of defects.

[0041] The method for identifying and quantifying defects in a coated substrate according to the present invention includes: providing a system for acquiring and analyzing images; loading the substrate onto a holder; illuminating the coated substrate with an illumination system; acquiring at least one image of the coated substrate with an imaging system; transforming the at least one image of the coated substrate with an analysis unit to provide at least one transformed image; identifying and quantifying defects on the coated substrate based on the at least one transformed image; and providing an output.

[0042] To identify and quantify defects based on the migration / secretion and / or extraction of one or more components in a coating of a coated substrate, the coated substrate is illuminated with an illumination system, including radiation with infrared, ultraviolet, or both. Images acquired by an imaging system include infrared and / or ultraviolet images. Migration / secretion and / or extraction can be determined by a transformed image that displays different regions based on the different absorbance or reflectance of the migrated / secreted or extracted components at different wavelengths in the infrared or ultraviolet spectra.

[0043] Example

[0044] Using a 5MP camera as the imaging system, an 8-channel multispectral halo as the illumination system, and a customizable sample holder to hold the coated substrate for imaging and analysis, a method was developed to fabricate samples with properties such as... Figure 1 A similar system arrangement is shown. An 8-channel multispectral light ring is configured to emit light in channels consisting of ultraviolet, blue, green, yellow, red, far-infrared, infrared, and white light. A camera is configured to acquire an image in each of the channels emitted by the illumination system.

[0045] Then, an image analysis algorithm is used to transform all or a subset of the acquired images. This image analysis algorithm identifies and quantifies defects in the coated surface.

[0046] Smoothness test

[0047] A coated substrate is prepared by applying a paint coating to a substrate using a roller. The coated substrate is tested by human testers and an image analysis system according to the invention. For human testers, smoothness is estimated based on observations of roller pattern, surface uniformity, and surface roughness. Human testers provide subjective scores on a scale of 1 to 5 based on their observations.

[0048] The coated substrate was also analyzed using the method of the present invention. Images were acquired using the system described above. For one test, from Figure 3 The color image is reconstructed from the images obtained from each of the optical channels. In another test, the texture image is reconstructed from four images illuminated by white light from the top, left, right, and bottom of the sample, respectively. Figure 4 As shown. In two tests, the acquired images were processed and transformed by applying wavelet transform to locate defects and quantify smoothness by constructing a linear regression between pixel variances. The image analysis method of this invention provides quantifiable and reproducible values ​​for the amount of surface defects.

[0049] Leveling test

[0050] A coated substrate is prepared by applying paint at a set spreading rate using a threaded steel bar to simulate brushstrokes, creating a coating with parallel ridges and valleys. The coated substrate is analyzed by human testers and the method according to the invention. Based on the test method of ASTM D 4062, human testers observe the coated substrate to determine the extent to which the applied coating flows to form a uniform film with a smooth surface. Ratings are provided on a scale of 1 to 10.

[0051] The coated substrate is then analyzed using the method according to the invention. For one test, a black and white image is generated by illuminating the image with white light from the top of the sample, such as... Figure 5 As shown. In another test, texture images were reconstructed from four images illuminated by white light from the top, left, right, and bottom of the sample, respectively, as shown. Figure 6 As shown. In both tests, the acquired images were analyzed using algorithms that included edge detection for detecting defective regions and wavelet transform for providing quantifiable leveling scores.

Claims

1. A method for quantitatively measuring surface defects on a coated substrate, the method comprising: a) Provide a system for acquiring and analyzing images, the system comprising i) An imaging system for acquiring one or more images of the coated substrate; ii) A lighting system comprising a light source for illuminating the coated substrate; iii) A retainer for holding the coated substrate in a position to be irradiated by the light source; iv) An analysis unit configured to transform the one or more images and quantitatively analyze the one or more transformed images to determine defects on the coated substrate. b) Loading a coated substrate onto the retainer, wherein the coated substrate includes a coating formed on the surface of the substrate; c) Illuminating the coated substrate with the lighting system, wherein illuminating the coated substrate includes illuminating the coated substrate at an incident angle of 15° to 85° relative to a plane parallel to the surface of the coated substrate, so as to generate shadows of any defects on the surface of the coated substrate. d) Acquire at least one image of the coated substrate using the imaging system; e) Transform the at least one image of the coated substrate using the analysis unit, wherein transforming the at least one image of the coated substrate includes processing the at least one image of the coated substrate with an algorithm selected from the group consisting of image thresholding, wavelet transform, morphological transform, color detection, pattern detection, clustering, and combinations thereof, to provide at least one transformed image, and to quantify the surface defects on the coated substrate based on the at least one transformed image; as well as f) Provide output, wherein the output includes values ​​identifying the amount or percentage of the defects on the coated substrate and / or a generated image showing the amount or percentage of the surface defects on the coated substrate.

2. The method according to claim 1, wherein the light source is selected from point light sources and directional light sources.

3. The method according to any one of the preceding claims, wherein at least one of the imaging system and the holder is adjustable to change at least one parameter selected from the angle between the imaging system and the holder, the distance between the imaging system and the holder, and the relative position between the imaging system and the holder, and acquiring at least one image of the coated substrate with the imaging system includes adjusting the relative position between the imaging system and the holder to acquire at least two images of the coated substrate at different locations.

4. The method according to any one of the preceding claims, wherein at least one of the lighting system and the holder is adjustable to change at least one parameter selected from the angle between the lighting system and the holder, the distance between the lighting system and the holder, and the relative position between the lighting system and the holder, and acquiring at least one image of the coated substrate with the imaging system includes adjusting the relative position between the lighting system and the holder to acquire at least two images of the coated substrate at different locations.

5. The method of claim 4, wherein the step of irradiating the coated substrate includes irradiating the coated substrate at multiple angles, and acquiring at least one image of the coated substrate includes acquiring at least one image at each of the multiple angles.

6. The method of claim 5, wherein the plurality of angles are different angles of incidence between 15° and 85° relative to a plane parallel to the surface of the coated substrate.

7. The method of claim 5, wherein the plurality of angles are different angles formed by rotating the holder relative to the light source, wherein the holder rotates in a plane parallel to the surface of the coated substrate.

8. The method according to any one of the preceding claims, wherein the surface defects in the coated substrate are selected from smoothness defects and leveling defects.

9. The method according to any one of the preceding claims, the method further comprising displaying the output on a graphical user interface (GUI).

10. The method according to any one of the preceding claims, wherein the coating comprises paint.

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