EP4680944A1

EP4680944A1 - Ultraviolet and infrared quantitative image analysis for evaluating coating performance

Info

Publication number: EP4680944A1
Application number: EP24715416.4A
Authority: EP
Inventors: Michael Q. Tran; Matthew Nicholas BENEDICT
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2023-03-14
Filing date: 2024-03-12
Publication date: 2026-01-21
Also published as: JP2026512252A; CN120677377A; WO2024192008A1; KR20250156174A

Abstract

A method for identifying and quantifying defects in a coated substrate, comprises: a) providing a system for acquiring and analyzing images; b) loading a coated substrate on a holder, wherein the coated substrate comprises a coating formed on a surface of a substrate; c) illuminating the coated substrate with a lighting 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, wherein 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 the defects on the coated substrate and/or a generated image identifying and/or quantifying the amount of the defects in the coated substrate, wherein the defects are migration/secretion or extraction defects caused by the movement or separation of components within the coating.

Description

ULTRAVIOLET AND INFRARED QUANTITATIVE IMAGE ANALYSIS

FOR EVALUATING COATING PERFORMANCE

FIELD OF THE INVENTION

This invention relates generally to quantitative image analysis for evaluating the performance of a coated substrate using ultraviolet and/or infrared imaging.

BACKGROUND

The appearance of a coated substrate 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 abnormalities, surface or texture differences, or other visible deviations. For example, the smoothness or leveling of a coated substrate may appear as a surface defect caused by shadows or variations in appearance. Resistance to defects caused by, for example, water, corrosion, dirt, grease, and efflorescence may appear as variations in the color of 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.

Such defects in coated substrates are typically observed or measured by human observation. Due to the difficulty in assessing many of the defects in coated substrates, the measurement of defects is often difficult to quantify accurately and/or reproducibly. Most measurements of defects are highly subjective and are typically measured on a simple arbitrary 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 generally results in a rough estimate. For defects related to migration/secretion or extraction of components, human observation and quantification is even more difficult as those defects may be extraordinarily difficult to see with the naked eye and/or require specific lighting and observation conditions to be observed/differentiated. 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.

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.

There is a need for a process that can more accurately and reproducibly detect defects in coated substrates to identify and quantify defects.

SUMMARY OF THE INVENTION

The invention relates to a method for identifying and quantifying defects in 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, wherein the imaging system is configured to acquire images in the infrared spectrum or the ultraviolet spectrum; ii) a lighting system comprising at least one light source for illuminating the coated substrate, wherein the lighting system is configured to emit light in the infrared spectrum or the ultraviolet spectrum; iii) a holder for holding the coated substrate in a position to be illuminated by the at least one light source; iv) an analysis unit configured to transform the one or more images and quantitatively analyze the one or more transformed images for defects in the coated substrate, 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; 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, contrast, wavelet transformation, morphological transformation, 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 f) providing an output, wherein the output comprises a value identifying an amount or percentage of the defects on the coated substrate and/or a generated 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 the movement or separation of components within the coating.

BRIEF DESCRIPTION OF THE FIGURES

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

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.

Figure 3 is an infrared image of a coated substrate used in a surfactant leaching test according to an embodiment of the present invention.

Figure 4 is a visible light image of a coated substrate used in a surfactant leaching test according to an embodiment of the present invention.

DETAILED DESCRIPTION

The inventors have found a process for reproducibly and accurately identifying and quantifying defects in coated substrates. More surprisingly, the inventors have found that infrared and ultraviolet imaging of coated substrates allows for reproducible and accurate identification and quantification of defects relating to migration/secretion or extraction of components within a coated substrate.

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.

Preferably, the coated substrate comprises a coating selected from 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 a metal, plastic, wood, glass, composite, fiberglass, paper, fabric, leather, or other substrate. For testing, it is preferred that the substrate has a flat or planar surface.

Defects in or on the coated substrate may be caused by a variety of issues. Examples of defects include, but are not limited to, color defects, surface or texture defects, and segregation/secretion or extraction defects.

Color defects may include stains from dirt, household stains (e.g., wine, pencil, lipstick, crayons, ink, markers, etc.), adhesion defects in which the coating does not adhere adequately to the substrate, hiding defects in which the coating allows the underlying substrate or sublayers to show through, grease resistance which evaluates the penetration of oil through the coating, early rain resistance in which a coating is tested for its ability to resist rain washout shortly after the coating is applied and cured, and efflorescence resistance in which the coatings ability to resist formation of efflorescence and alkali burnout is tested.

Texture or surface defects may be indicated by smoothness or leveling issues in which the coating may have an irregular or imperfect surface. Other texture or surface issues may include, for example, cracking or flaking.

Migration/secretion or extraction occurs when a component separates from other components or travels through the coating. Segregation/secretion and/or extraction may occur as a result of materials contacting the coating or incompatibilities of components within the coating. For example, surfactant leaching may occur when water-soluble materials leach to the surface of the coating when it is contacted with water. Other examples include the migration of binders or additives when influenced by time, temperature, or environmental conditions. While migration/secretion or extraction may lead to visible defects, oftentimes such defects are not easily visible. However, the present inventors have surprisingly found that migration/secretion or extraction defects may be identified and analyzed using the infrared or ultraviolet spectra. The species that migrate/secrete or may be extracted may have different properties that are observable in the infrared or ultraviolet spectra. For example, when analyzing for surfactant leaching, the inventors have found that the migrating components have a different thermal conductivity than the remaining components, making those defects readily identifiable in the infrared spectrum.

To analyze the coated substrate, a system for analyzing and quantifying defects is provided. A schematic drawing of a system for analyzing and quantifying defects 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.

Imaging system 10 is configured to acquire one or more images of the coated substrate 35. For detecting migration/secretion or extraction, the imaging system 10 is configured to acquire images in the visible, infrared spectrum, the ultraviolet spectrum, or combination thereof. Preferably, the imaging system 10 is configured to acquire images in the infrared spectrum. The imaging system 10 may comprise, for example, a camera, a thermal imaging system, or an image sensor. The imaging system 10 may further comprise a filter 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 being used to cause a specific component to fluoresce, a filter may be used to selectively transmit the fluoresced wavelength. Similarly, when using the infrared spectrum, filters may be used to block visible wavelengths and allow transmission of infrared wavelengths.

The lighting system 20 comprises at least one light source for illuminating the coated substrate 35. For detecting migration/secretion or extraction defects, the lighting system 20 may be configured to emit radiation in the infrared and/or ultraviolet spectra. The at least one light source may comprise a single light source or a plurality of light sources. When a single light source is used, the light source may comprise a ring light or a diffuser to provide uniform illumination to the coated substrate 35. When a plurality of light sources are used, the light sources may be arranged to provide uniform lighting. The plurality of light sources may also be controlled individually or within a predetermined group to control the lighting of the coated substrate 35. 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 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.

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.

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 by moving base 103, or the angle of the holder with respect to a fixed position may be adjusted.

Preferably, at least one of a 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. 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.

The system 100 further comprises an analysis unit 40 configured to transform 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 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.

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, 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 defects 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 the quantity /percentage of defects and/or an image or data set identifying the location, size, and/or number/percentage of defects. 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 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.

The method of identifying and quantifying defects in 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 defects on the coated substrate based on the at least one transformed image, and providing the output.

To identify and quantify defects based on migration/secretion and/or extraction of one or more components in the coating of the coated substrate, illuminating the coated substrate with the lighting system comprises illuminating the coated substrate with radiation in the infrared spectrum, the ultraviolet spectrum or both. The images acquired by the imaging system comprise infrared and/or ultraviolet images. Migration/secretion or extraction can be determined by the transformed images, which show different regions based on the migrated/secreted or extracted components different absorbance or reflectance of wavelengths in the infrared or ultraviolet spectra.

Example

To test for surfactant leaching, paint was applied to a substrate and dried in a constant temperature and humidity room for 4 hours. While the coated substrates were laid horizontally on a bench top, three separate areas of the paint were insulted with water. After a certain period of time, the coated substrates were hung vertically to allow the water to run off.

The samples were allowed to dry and the coated substrates were then analyzed.

The coated substrate was placed on a holder in a system for analyzing the coating. A light source emitting infrared light was used to illuminate the surface of the coated substrate and an infrared image was acquired using a camera, as shown in FIG. 3. A visible light image was also acquired as shown in FIG. 4. As can be seen by comparing FIGS. 3 and 4, no trails were visible in the visible light image, but clear trails were visible in the infrared image. The acquired infrared image was analyzed using a computer that applied a contrast detection algorithm to maximize the contrast within the image. The algorithm further calculated the total contrast in the area demonstrating surfactant leaching and provided a value quantifying the amount of leaching present on the surface of the coated substrate.

For comparison, the same sample was studied by human observation to estimate the amount of leaching. The amount of defects was given a rating on a 1 to 5 scale.

Claims

WHAT IS CLAIMED IS:

1. A method for identifying and quantifying defects in 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, wherein the imaging system is configured to acquire images in the infrared spectrum, the ultraviolet spectrum, or a combination thereof; ii) a lighting system comprising at least one light source for illuminating the coated substrate, wherein the lighting 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 analysis unit configured to transform the one or more images and quantitatively analyze the one or more transformed images for defects in the coated substrate, 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; 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, 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 f) providing an output, wherein the output comprises a value identifying an amount or percentage of the defects on the coated substrate and/or a generated 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 the movement or separation of components within the coating.

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

5. 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.

6. 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 the holder, 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.

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

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

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

10. The method according to claim 9, wherein the migration/secretion or extraction defects in the coated substrate comprises leaching of surfactants in the paint.