Ultraviolet and infrared quantitative image analysis for evaluating coating performance

Abstract

A method for identifying and quantifying defects in 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) illuminating the coated substrate with an illumination system; 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, where transforming the at least one image of the coated substrate comprises processing the at least one image to provide at least one transformed image, and identifying and quantifying defects on the coated substrate based on the at least one transformed image; and f) providing an output comprising a value identifying an amount of defects on the coated substrate, and / or a generated image identifying and / or quantifying an amount of defects in the coated substrate, where the defects are migration / secretion or extraction defects caused by movement or separation of components within the coating.

Description

Technical Field

[0001] The present invention generally relates to quantitative image analysis for evaluating the properties of coated substrates using ultraviolet imaging and / or infrared imaging. Background Art

[0002] The appearance of a coated substrate is one of the most important performance evaluation criteria used by consumers and researchers. Defects in a coated substrate 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 manifest as surface defects caused by shading or changes in appearance. Resistance to defects caused by, for example, water, corrosion, dirt, grease, and weathering may manifest as changes in the color of the coated substrate. Other defects in a coated substrate may be more difficult to visually observe, such as migration / secretion or extraction of components within the coated substrate.

[0003] Such defects in coated substrates are typically observed or measured through human observation. Due to the difficulty in assessing many defects in coated substrates, defect measurement is often difficult to quantify accurately and / or reproducibly. Most defect measurements are highly subjective and are typically measured on a simple, arbitrary scale, such as a numerical scale of 1 to 5, where a human observer assigns a value based on their interpretation of the coated substrate's surface. Variation in the values ​​assigned from one observer to the next is common, and defect quantification often results in rough estimates. Human observation and quantification are even more difficult for defects related to the migration / secretion or extraction of components, as these defects can be very difficult to see with the naked eye and / or require specific lighting and viewing conditions to observe / distinguish. Due to the subjective nature of the measurements, observations are typically normalized within each study. Consequently, data acquired through human observation from one study cannot be reliably combined with data from another.

[0004] 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, the method comprising 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 the coating surface to be produced. However, the database of qualitative and / or quantitative characterizations is generated by manually identifying and labeling digital images, wherein the qualitative and / or quantitative characterizations of the images are based on a scale having values ​​assigned by human observers. Therefore, the database is compiled using data based on human observations.

[0005] What is needed is a method for more accurately and reproducibly detecting defects in coated substrates for identification and quantification of the defects. Summary of the Invention

[0006] The present invention relates to a method for identifying and quantifying defects in a coated substrate, the method comprising:

[0007] a) providing a system for acquiring and analyzing images, the system comprising

[0008] i) an imaging system for acquiring one or more images of the coated substrate, wherein the imaging system is configured to acquire images in the infrared spectrum or the ultraviolet spectrum;

[0009] ii) an illumination system comprising at least one light source for illuminating the coated substrate, wherein the illumination system is configured to emit light in the infrared spectrum or the ultraviolet spectrum;

[0010] iii) a holder for holding the coated substrate in a position to be illuminated by the at least one 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 in the coated substrate,

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

[0013] c) irradiating the coated substrate with the lighting system;

[0014] d) acquiring at least one image of the coated substrate with the imaging system;

[0015] 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, contrast, wavelet transform, morphological transform, color detection, pattern detection, clustering, and combinations thereof to provide at least one transformed image, and identifying and quantifying defects on the coated substrate based on the at least one transformed image; and

[0016] f) providing an output, wherein the output comprises a value identifying the amount or percentage of the defects on the coated substrate and / or generating an image identifying and / or quantifying the amount or percentage of the defects in the coated substrate,

[0017] Wherein the defect is a migration / secretion or extraction defect caused by the movement or segregation of components within the coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of a system for acquiring and analyzing images according to an embodiment of the present invention.

[0019] Figure 2 is a schematic diagram of the position of a light source relative to a coated substrate according to an embodiment of the present invention.

[0020] Figure 3 is an infrared image of a coated substrate used for surfactant leaching testing according to an embodiment of the present invention.

[0021] Figure 4 is a visible light image of a coated substrate used for surfactant leaching testing according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present inventors have discovered a method for reproducibly and accurately identifying and quantifying defects in coated substrates. Even more surprisingly, the present inventors have discovered that infrared and ultraviolet imaging of coated substrates allows for reproducible and accurate identification and quantification of defects associated with the migration / secretion or extraction of components within the coated substrate.

[0023] As used herein, the term "coated substrate" refers to a substrate that includes a coating on its surface, such as, for example, a paint coating on a metal or paper substrate. 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 a thickness of greater than 50 nm, more preferably greater than 100 nm, and even more preferably greater than 250 nm. Multilayer coatings may have greater thicknesses. The coated substrate may also include multiple layers, including, for example, a primer or basecoat.

[0024] Preferably, the coated substrate comprises a coating selected from the group consisting of polyurethane coatings, epoxy coatings, acrylic and vinyl acrylic coatings, alkyd coatings, and zinc-rich coatings. More preferably, the coated substrate comprises a paint. The substrate may comprise metal, plastic, wood, glass, composites, fiberglass, paper, fabric, leather, or other substrates. For testing, it is preferred that the substrate have a flat or planar surface.

[0025] Defects in or on a coated substrate may be caused by a variety of problems. Examples of defects include, but are not limited to, color defects, surface or texture defects, and segregation / excretion or extraction defects.

[0026] Color defects may include stains from dirt, household stains (e.g., wine, pencil, lipstick, crayon, ink, marker, etc.), adhesion defects where the coating does not adhere adequately to the substrate, hidden defects where the coating allows the underlying substrate or sublayer to show through, grease resistance which assesses the penetration of oil through the coating, early rain resistance which tests the ability of the coating to resist rain washout shortly after the coating is applied and cured, and weathering resistance which tests the coating's ability to resist efflorescence formation and efflorescence.

[0027] Texture or surface defects can be indicated by smoothness or leveling problems where the coating may have an irregular or imperfect surface. Other texture or surface problems can include, for example, cracking or flaking.

[0028] Migration / secretion or extraction occurs when a component separates from other components or travels through a coating. Segregation / secretion and / or extraction may occur due to material contact with the coating or incompatibility of components within the coating. For example, surfactant leaching may occur when a water-soluble material leaches to the surface of the coating when the coating is in contact with water. Other examples include the migration of adhesives or additives when affected by time, temperature, or environmental conditions. Although migration / secretion or extraction may result in visible defects, such defects are generally not easily visible. However, the present inventors have surprisingly discovered that infrared or ultraviolet spectroscopy can be used to identify and analyze migration / secretion or extraction defects. The substances that migrate / secrete or can be extracted may have different properties that can be observed in the infrared or ultraviolet spectrum. For example, when analyzing surfactant leaching, the present inventors have found that the migrating component has a different thermal conductivity than the remaining components, making those defects easily identifiable in the infrared spectrum.

[0029] For analyzing coated substrates, a system for analyzing and quantifying defects is provided. Figure 1 A schematic diagram of a system 100 for analyzing and quantifying defects is shown in FIG. The system 100 comprises an imaging system 10 , an illumination system 20 , a holder 30 for holding a coated substrate 35 , and an analyzing unit 40 .

[0030] The imaging system 10 is configured to acquire one or more images of the coated substrate 35. To detect migration / secretion or extraction, the imaging system 10 is configured to acquire images in the visible spectrum, infrared spectrum, ultraviolet spectrum, or a combination thereof. Preferably, the imaging system 10 is configured to acquire images in the infrared spectrum. The imaging system 10 may include, for example, a camera, a thermal imaging system, or an image sensor. The imaging system 10 may also include filters for preferentially or selectively transmitting or blocking predetermined wavelengths of light. For example, when the imaging system 10 is configured to detect in the ultraviolet spectrum, a filter may be used to block all visible light. Alternatively, if ultraviolet light is used to cause a specific component to fluoresce, a filter may be used to selectively transmit the fluorescent wavelength. Similarly, when the infrared spectrum is used, a filter may be used to block visible wavelengths and allow transmission of infrared wavelengths.

[0031] The illumination system 20 includes at least one light source for illuminating the coated substrate 35. To detect migration / secretion or extraction defects, the illumination system 20 can be configured to emit radiation in the infrared spectrum and / or the ultraviolet spectrum. The at least one light source can include a single light source or multiple light sources. When a single light source is used, the light source can include a ring light or a diffuser to provide uniform illumination of the coated substrate 35. When multiple light sources are used, the light sources can be arranged to provide uniform illumination. The multiple light sources can also be controlled individually or in predetermined groups to control the illumination of the coated substrate 35. Preferably, the illumination system 20 is configured to allow adjustment of the intensity of the light, the angle of incidence on the coated substrate 35, or the wavelength of the emitted light. To reduce the potential impact of external illumination, the system 100 can be covered or encapsulated (not shown) so that only light from the illumination system 20 is used to acquire the image.

[0032] 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 to be illuminated by the illumination system 20 when it is imaged. The holder 30 can be configured to hold a single coated substrate 35 or a plurality of coated substrates. The holder 30 can be stationary or adapted to allow for automated loading / unloading of samples.

[0033] 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, Figure 1As 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 so that the distance between the imaging system 10 and the holder 30 can be selected. 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 by moving the base 103, or to adjust the angle of the holder relative to a fixed position.

[0034] Preferably, at least one of the lighting system 20 and the holder 30 is adjustable relative to each other so that the position of the coated substrate 35 can be changed relative to the lighting system 20. For example, the lighting system 20 can be height-adjustable or angle-adjustable relative to the holder 30 to change the position of the coated substrate 35. Figure 2 The incident angle α of the light 25 is shown. For example, the illumination system 20 can be adjustable to allow for shallower or steeper angles of incidence on the coated substrate 35. Additionally, the illumination system 20 can be adjustable to allow the illumination system 20 to be rotated about the coated substrate 35 so that the incident angle α is the same, but the light is directed onto the coated substrate 35 from a different angle, for example, from the side of the coated substrate 35 rather than the front.

[0035] The system 100 further includes an analysis unit 40 configured to transform the images acquired by the imaging system 10 into transformed images. 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, a workstation, a laptop, a tablet computer, or a smartphone. The analysis unit 40 may include an application or program suitable for transforming and analyzing images from the imaging system 10. The information obtained 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.

[0036] The analysis unit 40 is preferably configured to transform the acquired image by processing the acquired image using an algorithm selected from the group consisting of image thresholding, wavelet transforms, morphological transforms, 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 provide an analyzed output. Preferably, the output includes a symbolic value representing the number / percentage of defects and / or an image or dataset identifying the location, size, and / or number / percentage of defects.

[0037] Preferably, 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 analysis unit 40. For example, the GUI may display a value quantifying the amount of defects present in coated substrate 35. Alternatively, the GUI may display a transformed image identifying the location, size, and / or number / percentage of defects.

[0038] A 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 a substrate on 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; and identifying and quantifying defects on the coated substrate based on the at least one transformed image; and providing an output.

[0039] To identify and quantify defects based on migration / secretion and / or extraction of one or more components from a coating on a coated substrate, illuminating the coated substrate with an illumination system includes illuminating the coated substrate with radiation in the infrared spectrum, the ultraviolet spectrum, or both. The image captured by the imaging system includes an infrared image and / or an ultraviolet image. Migration / secretion or extraction can be determined by a transformed image that displays distinct regions based on different absorbances or reflectances of the migrating / secreting or extracting components at wavelengths in the infrared or ultraviolet spectrum.

[0040] Example

[0041] To test for surfactant leaching, paint was applied to a substrate and dried in a constant temperature and humidity chamber for 4 hours. While the coated substrate was placed horizontally on a workbench, three separate areas of the paint were impregnated with water. After a period of time, the coated substrate was hung vertically to allow the water to drain. The samples were allowed to dry before analyzing the coated substrate.

[0042] The coated substrate is placed on a holder in a system for analyzing the coating. A light source emitting infrared light is used to illuminate the surface of the coated substrate, and a camera is used to acquire an infrared image, such as Figure 3 As shown. We also obtained Figure 4 As shown in the visible light image. Figure 3 and Figure 4As can be seen, no traces are visible in the visible light image, but clear traces are visible in the infrared image. The acquired infrared image is analyzed using a computer that applies a contrast detection algorithm to maximize the contrast within the image. The algorithm further calculates the total contrast in areas showing surfactant leaching and provides a value that quantifies the amount of leaching present on the surface of the coated substrate.

[0043] For comparison, the same samples were studied by human observation to estimate the amount of leaching. The amount of defects was rated on a scale of 1 to 5.

Claims

1. A method for identifying and quantifying defects in a coated substrate, the method comprising: a) providing a system for acquiring and analyzing images, said system comprising i) an imaging system for acquiring one or more images of the coated substrate, wherein the imaging system is configured to acquire images in the infrared spectrum, the ultraviolet spectrum, or a combination thereof; ii) an illumination system comprising at least one light source for illuminating the coated substrate, wherein the illumination system is configured to emit light in the infrared spectrum, the ultraviolet spectrum, or a combination thereof; iii) a holder for holding the coated substrate in a position to be illuminated by the at least one light source; iv) an analyzing unit configured to transform the one or more images and quantitatively analyze the one or more transformed images to determine defects in the coated substrate, b) loading a coated substrate on the holder, wherein the coated substrate includes a coating formed on a surface of the substrate; c) illuminating the coated substrate with the lighting system; 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 transform, morphological transform, color detection, pattern detection, clustering, and combinations thereof to provide at least one transformed image, and identifying and quantifying defects on the coated substrate based on the at least one transformed image; as well as f) providing an output, wherein the output comprises a value identifying the amount or percentage of the defects on the coated substrate and / or generating an image identifying and / or quantifying the amount or percentage of the defects in the coated substrate, wherein the defects are migration / secretion or extraction defects caused by movement or separation of components within the coating. 2 . The method of claim 1 , wherein the imaging system is configured to acquire images in the infrared spectrum, and acquiring at least one image comprises acquiring at least one infrared image. 3 . The method of claim 1 , wherein the imaging system is configured to acquire images in the ultraviolet spectrum, and acquiring at least one image comprises acquiring at least one ultraviolet image.

4. The method of any one of the preceding claims, wherein at least one component within the coating differs from other components within the coating in infrared absorptivity or reflectivity or ultraviolet absorptivity or reflectivity.

5. The method of 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 group consisting of 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 the relative position between the imaging system and the holder to acquire at least two images of the coated substrate at different positions.

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

7. The method of any one of the preceding claims, wherein the imaging system further comprises at least one optical filter, wherein the at least one optical filter preferentially transmits or blocks light of predetermined wavelengths.

8. The method of any preceding claim, further comprising displaying the output on a graphical user interface (GUI).

9. A method according to any preceding claim, wherein the coating comprises paint.

10. The method of claim 9, wherein the migration / secretion or extraction defect in the coated substrate comprises leaching of a surfactant in the paint.

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