Quantitative image analysis system for evaluating coating performance

Abstract

A method for quantifying surface features on a coated substrate, comprising: a) providing a system for acquiring and analyzing images; b) loading a coated substrate on the holder, wherein the coated substrate comprises a coating formed on a surface of a substrate; c) illuminating the coated substrate with a lighting system, wherein illuminating the coated substrate comprising illuminating the coated substrate at an angle of incidence of 15 to 85 relative to a plane parallel to a surface of the coated substrate to generate shadows of any surface features 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 features on the coated substrate based on the at least one transformed image; and f) providing an output, wherein the output comprises a value identifying at least metric selected from an amount or percentage of the surface features on the coated substrate, a size of the surface features on the coated substrate, a standard deviation of the size of the surface features on the coated substrate, and / or a generated image illustrating the amount or percentage of the surface features on the coated substrate.

Description

[0001] QUANTITATIVE IMAGE ANALYSIS SYSTEM FOR EVALUATING COATING

[0002] PERFORMANCE

[0003] FIELD OF THE INVENTION

[0004] This invention relates generally to processes for quantitatively analyzing images for coating performance.

[0005] BACKGROUND

[0006] The appearance of a coated substrate is one of the most important performance evaluation metrics used by consumers and researchers. Defects or features in coated substrates can manifest themselves in many different ways, including color abnormalities, surface or texture differences, or other visible deviations. For example, the irregularity in smoothness or leveling of a coated substrate may appear as a surface defect caused by shadows or variations in appearance. The irregularity in appearance of a coating can result from several issues, including, for example, recesses in the coating (e.g., fisheyes, craters, dewetting), orange peel, pinholes, and application properties (e.g., paint spattering or brush taps testing).

[0007] Such defects or features in coated substrates are typically observed or measured by a human. Due to the difficulty of assessing many of the defects or features in coated substrates, the measurement of defects or features is often difficult to quantify accurately and / or reproducibly. Most measurements of defects or features are highly subjective and are typically measured on a simple scale, such as a numerical scale of 1 to 5, where the human observer assigns a value based on their interpretation of the surface of the coated substrate. Variations in the values assigned by one observer and the next are common, and quantification of the defects or features generally results in a rough estimate. Due to the subjective nature of the measurements, observations are typically normalized within each study. Therefore, data acquired by human observation from one study cannot be reliably combined with data from another study.

[0008] Attempts have been made to automate the defect detection process. U.S. Patent Application Publication No. US 2022 / 0082508 discloses a method for providing a coating composition-related prediction program which includes providing a database of qualitative and / or quantitative characterizations of coating surfaces and training a machine learning model to develop a composition-quality-prediction program for predicting the properties of a coating surface to be produced. However, the database of qualitative and / or quantitative characterizations are generated by manually identifying and labeling digital images, where the qualitative and / or quantitative characterization of the image is based on a scale with values assigned by a human observer. Therefore, the database is compiled with data based on human observations.

[0009] There is a need for a process that can more accurately and reproducibly detect surface features on coated substrates to identify and quantify surface features.

[0010] SUMMARY OF THE INVENTION

[0011] The invention relates to a method for quantifying surface features on a coated substrate, comprising: a) providing a system for acquiring and analyzing images, 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 holder for holding the coated substrate in a position to be illuminated 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 for features on the coated substrate, wherein the features are selected from recesses in the coated substrate, orange peel, pinholes, and application properties , b) loading a coated substrate on the holder, wherein the coated substrate comprises a coating formed on a surface of a substrate; c) illuminating the coated substrate with the lighting system, wherein illuminating the coated substrate comprises 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 to generate shadows of any features on the surface of the coated substrate; d) acquiring at least one image of the coated substrate with the imaging system; e) transforming the at least one image of the coated substrate with the analysis unit, wherein transforming the at least one image of the coated substrate comprises processing the at least one image of the coated substrate with an algorithm selected from the group consisting of image thresholding, wavelet transformation, morphological transformation, blob detection, circularity filtering, color detection, pattern detection, clustering, and combinations thereof, to provide at least one transformed image and quantifying the surface features on the coated substrate based on the at least one transformed image; and f) providing an output, wherein the output comprises a value identifying at least metric selected from an amount or percentage of the features on the coated substrate, a size of the features on the coated substrate, a standard deviation of the size of the features on the coated substrate, and / or a generated image illustrating the amount or percentage of the surface features on the coated substrate.

[0012] BRIEF DESCRIPTION OF THE FIGURES

[0013] Figure 1 is a schematic drawing of a system for acquiring and analyzing images according to an embodiment of the present invention.

[0014] Figure 2 is a schematic drawing of the position of a light source with respect to a coated substrate according to an embodiment of the invention.

[0015] Figure 3 is an image of paint spatters captured on a black vinyl chart.

[0016] Figures 4 and 5 show a sequence of images in a spattering resistance analysis including an unprocessed image (FIG. 4) and an image showing the results of the image analysis in which identified spatters are identified according to an embodiment of the invention (FIG. 5).

[0017] Figures 6 and 7 show a sequence of images in a brush tap analysis including an unprocessed image (FIG. 6) and an image showing the results of the image analysis in which surface features caused by brush taps are identified according to an embodiment of the invention (FIG. 7).

[0018] DETAILED DESCRIPTION

[0019] The inventors have found a process for reproducibly and accurately identifying and quantifying features in coated substrates.

[0020] As used herein, the term “coated substrate” refers to a substrate comprising a coating on a surface thereof, such as, for example, a paint coating on a metal or paper substrate. The coating preferably has a thickness of less than 500 pm, more preferably less than 300 pm, and even more preferably less than 200 pm, and a thickness preferably greater than 50 nm, more preferably greater than 100 nm, and even more preferably greater than 250 nm. Multilayer coatings may have a greater thickness. The coated substrate may also comprise multiple layers, including for example, a primer or base coat.

[0021] As used herein, the terms “surface feature” and “feature” refer to abnormalities in the surface of a coated substrate. A feature may comprise a defect resulting from the formulation of the coating, or the feature may comprise an application property in the surface caused by a user / applicator or the manner in which the coating is applied. For example, paint spatter is a surface feature which may be caused, for example, when paint is ejected from the roller or the substrate during application. In the detection of paint spatters, the coated substrate may be a substrate that is adjacent to a surface being coated to determine the spattering resistance of the coating formulation. For example, the coated substrate for a spattering resistance test may comprise a substrate placed immediately below a substrate on which the coating formulation is applied to collect any spatters that are ejected during coating.

[0022] Surface features in or on the coated substrate may be caused by a variety of issues. Examples of surface features include, but are not limited to, recesses in the coating (e.g., fisheyes, craters, dewetting), orange peel, pinholes, and application properties, which may be caused by applicator or the application process (e.g., paint spattering or brush taps testing). As used herein, a “crater” refers to a round to ovoid recess in the coating that does not extend to the substrate or underlying layer; a “fisheye” refers to a round or ovoid recess that extends to the substrate; and “dewetting” refers to a recess, not necessarily round or ovoid, that extends to the substrate and is greater than 3 mm. As used herein, “orange peel” refers to a bumpy surface resembling the surface of an orange peel. As used herein, “pinholes” refer to pinpricks to small craters caused by entrained air, solvent popping, or telegraphed defects in a basecoat. Application properties include spattering, which is caused by coating ejected during application, and brush taps, which may include bubbles or grits generated by tapping (e.g., a brush or roller) on the painted surface.

[0023] Preferably, the coated substrate comprises a coating selected from polyurethane coatings, epoxy coatings, acrylic coatings (including, for example, acrylic coatings, vinyl-acrylic coatings, and styrene-acrylic coatings), alkyd coatings, and zinc-rich coatings. More preferably, the coated substrate comprises a paint. The substrate may comprise a metal, plastic, wood, glass, composite, fiberglass, paper, fabric, leather, or other substrates. For testing, it is preferred that the substrate has a flat or planar surface.

[0024] To analyze the coated substrate, a system for analyzing and quantifying surface features is provided. A schematic drawing of a system for analyzing and quantifying surface features 100 is shown in FIG. 1. The system 100 comprises an imaging system 10, a lighting system 20, a holder 30 for holding a coated substrate 35, and an analysis unit 40.

[0025] Imaging system 10 is configured to acquire one or more images of the coated substrate 35. The imaging system 10 may comprise, for example, a camera, an image sensor, or an optical tactile sensor. The imaging system 10 may further comprise a filter for preferentially or selectively transmitting or blocking predetermined wavelengths of light, such as, for example, at least one channel of a predetermined wavelength. An optical tactile sensor is a device which comprises a tactile sensor in the form of a soft elastomer having a contact surface that directly measures vertical and lateral distortion of a surface (i.e., surface features on the coated substrate 35) is contacted by the contact surface of the soft elastomer of the optical tactile sensor. A camera or image sensor is used in conjunction with the optical tactile sensor to acquire an image of the side of the soft elastomer opposite the contact surface. The contact surface of the optical tactile sensor may be coated to improve the imaging of the coated substrate.

[0026] The lighting system 20 comprises a light source for illuminating the coated substrate 35 or the optical tactile sensor. The lighting system 20 is preferably configured to emit radiation in the visible light spectrum. The light source preferably comprises a single light source so that surface features are visible as shadows when illuminated. Preferably, the light source is a point light source or a directional light source. Preferably, the lighting system 20 is configured to allow for adjustments to the intensity of the light, the angle of incidence on the coated substrate 35 or optical tactile substrate, or wavelength of light emitted. To reduce potential influence by outside lighting, the system 100 may be covered or enclosed (not shown) such that only light from the lighting system 20 is used to acquire the images.

[0027] The lighting system 20 is configured to illuminate the coated substrate or optical tactile sensor at an angle of incidence, a as shown in FIG. 2, of 15° to 85°, and preferably from 20° to 70°.

[0028] The substrate holder 30 is used to hold the coated substrate 35 for imaging by the imaging system 10. The holder 30 is configured to hold the coated substrate in a position to be illuminated by the lighting system 20 as it is imaged. The holder 30 may be configured to hold a single coated substrate 35 or a plurality of coated substrates. The holder 30 may be stationary or adapted to allow samples to be automatically loaded / unloaded.

[0029] Preferably, at least one of the imaging system 10 and the holder 30 is adjustable so that the position of the coated substrate 35 can be changed relative to the imaging system 10. For example, as shown in FIG. 1, the imaging system 10 may be mounted on an arm 101 attached to a vertical support 102. The arm 101 may be configured to be adjustable such that the distance between the imaging system 10 and the holder 30 can be selected. Alternatively, the arm 101 may be moveable between more than one position. In another alternative, the holder 30 may be adjustable to raise or lower the holder 30 using base 103, or the angle of the holder with respect to a fixed position may be adjusted.

[0030] 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 height or angle adjustable relative to the holder 30 to change the angle of incidence, a, of the light 25 as shown in FIG. 2. For example, the lighting system 20 may be adjustable to allow for a shallower or steeper angle of incidence on the coated substrate 35 to control the size of the shadows generated. For example, a coated substrate with small surface features may be illuminated at a greater angle of incidence to increase the size of the shadows, whereas a coated substrate with larger surface features may be illuminated at a smaller angle of incidence to decrease the size of the shadows. By controlling the angle of incidence, the size of the shadows can be controlled to minimize the amount of overlap between adjacent surface features.

[0031] Additionally, the lighting system 20 may be adjustable to allow for rotation of the lighting system 20 around the coated substrate 35 such that the angle of incidence, a, is the same, but the light is directed on the coated substrate 35 from a different angle, e.g., from the side rather than the front of the coated substrate 35. By allowing for different lighting angles, multiple images may be acquired to identify surface features that may be otherwise unaccounted for in a single image. For example, a small surface feature aligned with a larger surface feature and the source of light may fall within the shadow of the larger surface feature. By rotating the light source relative to the coated substrate 35, multiple images may be acquired and compared by the analysis unit 40, described below, to identify all of the surface features on the coated substrate. Additionally, acquiring multiple images at different angles may allow for more accurate quantification of features. For example, a wide but narrow surface feature may generate a large shadow at one angle, but a small shadow at another angle. Acquisition and analysis of multiple images therefore allows for more accurate analysis of surface features. Such analysis would be very difficult for a human observer attempting to make a similar analysis.

[0032] The system 100 further comprises 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 surface features in or on the coating of the coated substrate 35. The analysis unit 40 may comprise, for example, a computer, workstation, notebook computer, tablet computer, or smartphone. The analysis unit 40 may comprise an application or program adapted to transform and analyze the images from the imaging system 10. Information obtained and / or generated by the system 100 may be stored locally within the analysis unit 40, a server, cloud storage, or media storage device.

[0033] The analysis unit 40 is preferably configured to transform acquired images by processing the acquired images with an algorithm selected from image thresholding, wavelet transformation, morphological transformation, blob detection, circularity filtering, color detection, pattern detection, contrast detection, clustering, and combinations therefore. The transformed images may then be analyzed by the analysis unit 40 to identify and / or quantify surface features in or on the coating of the coated substrate 35 and to provide an output of the analysis. Preferably, the output comprises a value signifying at least one metric selected from the quantity / percentage of surface features, a size of the features on the coated substrate, a standard deviation of the size of the features on the coated substrate, and / or an image or data set identifying the location, size and / or quantity / percentage of features.

[0034] Preferably, the analysis unit 40 comprises or is connected to a display comprising 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 quantifying the amount, percentage, size or size deviation of surface features present in the coated substrate 35. Alternatively, the GUI may display a transformed image identifying the location, size, and / or quantity / percentage of surface features.

[0035] The method of identifying and quantifying surface features in or on a coated substrate according to the present invention comprises providing the system for acquiring and analyzing images, loading a substrate on the holder, illuminating the coated substrate with the lighting system, acquiring at least one image of the coated substrate with the imaging system, transforming the at least one image of the coated substrate with the analysis unit to provide at least one transformed image and identifying and quantifying surface features in or on the coated substrate based on the at least one transformed image, and providing the output.

[0036] Examples

[0037] A system having a similar arrangement as shown in FIG. 1 was prepared using a 5 MP camera as the imaging system, an 8 channel multi-spectrum light ring as the lighting system, and a customizable sample holder to hold a coated substrate for imaging and analysis. The 8 channel multi- spectrum light ring was configured to emit in channels consisting of ultraviolet, blue, green, yellow, red, far red, infrared, and white light. The camera was configured to have the ability to acquire images in each of the channels emitted by the lighting system.

[0038] All or a subset of the acquired images were then transformed using an image analysis algorithm. The image analysis algorithm identified and quantified the surface features in or on the coated surface.

[0039] Spatter Resistance

[0040] Paint spatters are tiny droplets of liquid paint that can be ejected from the roller / substrate while coatings are applied on substrates during roller application. The liquid droplets can land on adjacent surfaces or areas not meant to be painted. Coatings with good spatter resistance will reduce the work associated with preparing the surface and cleaning up after painting as well as help painters to get the work done more efficiently.

[0041] The spatter resistance was evaluated by taping two vinyl charts to the bottom of a 4 ft by 4 ft primed drywall panel and applying a coating of paint to the dry wall panel with a 7 in long, 3 / 8 in nap woven roller. The paint spatters would be captured by vinyl charts. A representative image of a vinyl chart with paint spatters is shown in FIG. 3, which represented a commercial interior flat paint with poor spatter resistance. A selected area of vinyl chart from another coating is shown in FIG. 4, which included both paint spatters captured during roller application and an artifact that is not from paint spatter.

[0042] The coated substrate shown in FIG. 4 was analyzed by the image analysis system according to the present invention. The captured image was transformed into a matrix to perform image thresholding to remove background noise. A blob detection algorithm was then applied to identify individual spatter droplets. The algorithm identified and located blobs or connected pixels to capture the spatter. The algorithm was further refined based on fundamental physics of spatter droplet generation to take into account undesired experimental artifacts, such as, for examples, liquid paints left on the test panel caused by accidental touching of the panel with the roller. As shown in FIG. 5, the non-circular shape located in the upper right corner was not included in the blob detection.

[0043] The image analysis system of the present invention identified paint spatter droplets that were not obvious to the naked eye.

[0044] The spatter resistance of 73 paints were evaluated using the image analysis system and compared with a manual rating by human. The human tester provided a score based on the observations on a scale of 1 to 5, with 5 being best in spatter resistance. Positive correlation was observed between the image analysis system of the present invention and the human test method, but the image analysis system was able to capture differences better than the human test method.

[0045] Brush Tap

[0046] Brush tap is a test method used to evaluate foaming issue in applied coating which could occur during paint application. A coated substrate was prepared by applying a paint with a brush to a Lenata opacity chart. Right after the application of the paint, the paint brush was used to tap on the paint before there was total film formation. The air trapped inside the paint film could create bubbles or bubbles that burst and turned into visible surface features if the coating did not fully level and flow before drying. An unprocessed image of the coated substrate is shown in FIG. 6.

[0047] The coated substrate shown in FIG. 6 was analyzed by the image analysis system according to the present invention. The captured image was transformed into a matrix to perform image thresholding to remove background noise. To extract the bubble features without picking too much noise, a Hough circle transform was used to identify the bubbles. This algorithm helps avoid misidentifying other surface features that may appear that are not circular in shape. The processed image identifying the brush tap surface features is shown in FIG. 7.

Claims

WHAT IS CLAIMED IS:

1. A method for quantifying surface features on a coated substrate, comprising: a) providing a system for acquiring and analyzing images, 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 holder for holding the coated substrate in a position to be illuminated 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 for surface features on the coated substrate, wherein the surface features are selected from recesses in the coated substrate, orange peel, pinholes, and application properties; b) loading a coated substrate on the holder, wherein the coated substrate comprises a coating formed on a surface of a substrate; c) illuminating the coated substrate with the lighting system, wherein illuminating the coated substrate comprising illuminating the coated substrate at an angle of incidence of 15° to 85° relative to a plane parallel to a surface of the coated substrate to generate shadows of any surface features on the coated substrate; d) acquiring at least one image of the coated substrate with the imaging system; e) transforming the at least one image of the coated substrate with the analysis unit, wherein transforming the at least one image of the coated substrate comprises processing the at least one image of the coated substrate with an algorithm selected from the group consisting of image thresholding, wavelet transformation, morphological transformation, blob detection,circularity filtering, color detection, pattern detection, clustering, and combinations thereof, to provide at least one transformed image and quantifying the surface features on the coated substrate based on the at least one transformed image; and f) providing an output, wherein the output comprises a value identifying at least metric selected from an amount or percentage of the surface features on the coated substrate, a size of the surface features on the coated substrate, a standard deviation of the size of the surface features on the coated substrate, and / or a generated image illustrating the amount or percentage of the surface features on the coated substrate.

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

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

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 vary at least one parameter selected from an angle between the lighting system and the holder, a distance between the lighting system and theholder, and a relative position between the lighting system and the holder, and acquiring at least one image of the coated substrate with the imaging system comprises adjusting a relative position between the lighting system and the holder to acquire at least two images of the coated substrate at different positions.

5. The method according to claim 4, wherein the step of illuminating the coated substrate comprises illuminating the coated substrate at multiple angles and acquiring at least one image of the coated substrate comprises acquiring at least one image at each of the multiple angles.

6. The method according to claim 5, wherein the multiple 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 according to any one of the preceding claims, wherein the imaging system comprises at least one of camera, an image sensor, and an optical tactile sensor.

8. The method according to any one of the preceding claims, wherein the surface features on the coated substrate are selected paint spatters and brush taps.

9. The method according to any one of the preceding claims, 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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