EP4680945A1

EP4680945A1 - Quantitative image analysis system for evaluating coating performance

Info

Publication number: EP4680945A1
Application number: EP24717500.3A
Authority: EP
Inventors: Kevin J. Henderson; Jonathan P. Derocher; Michael W. LINSEN; Maxwell INGRAM; Mathias WEEKS; Michael Q. Tran
Original assignee: Dow Global Technologies LLC; Rohm and Haas Co
Current assignee: Dow Global Technologies LLC; Rohm and Haas Co
Priority date: 2023-03-14
Filing date: 2024-03-12
Publication date: 2026-01-21
Also published as: CN120731360A; WO2024192005A1; JP2026509404A; KR20250154596A

Abstract

A system (100) for quantifiable analysis of a coated substrate (35), comprises: an imaging system (10) for acquiring one or more images of the coated substrate, wherein the imaging system is configured to acquire images for a plurality of channels, wherein each of the plurality of channels comprises a predetermined range of wavelengths; a lighting system (20) comprising at least one light source for illuminating the coated substrate; a holder (30) for holding the coated substrate in a position to be illuminated by the at least one light source; and an analysis unit (40) configured to transform the one or more images and quantitatively analyze. the one or more transformed images for defects in the coated substrate, wherein the coated substrate comprises a coating formed on a surface of a substrate.

Description

QUANTITATIVE IMAGE ANALYSIS SYSTEM FOR EVALUATING

COATING PERFORMANCE

FIELD OF THE INVENTION

This invention relates generally to quantitative image analysis system for evaluating performance of a coated substrate.

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 a human. Due to the difficulty of 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 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 extration of components, human observation and quantification is even more difficult as those defects may be extraordinarily difficult to see with the naked eye. 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 system 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 system for quantifiable analysis of a coated substrate, comprising: an imaging system for acquiring one or more images of the coated substrate, wherein the imaging system is configured to acquire images for a plurality of channels, wherein each of the plurality of channels comprises a predetermined range of wavelengths; a lighting system comprising at least one light source for illuminating the coated substrate; a holder for holding the coated substrate in a position to be illuminated by the at least one light source; 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, wherein the coated substrate comprises a coating formed on a surface of a substrate.

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 image from an efflorescence test analyzed by an image analysis system according to an embodiment of the present invention.

Figure 4 is an image from an early rain resistance test analyzed by an image analysis system according to an embodiment of the present invention.

Figure 5 is an image from an adhesion test analyzed by an image analysis system according to an embodiment of the present invention.

Figure 6 is an image from an applied hiding test analyzed by an image analysis system according to an embodiment of the present invention.

Figure 7 is an image from a stain resistance test analyzed by an image analysis system according to an embodiment of the present invention.

Figure 8 is an infrared image of a coated substrate used in a surfactant leaching test according to an embodiment of the present invention.

Figure 9 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 and system for reproducibly and accurately identifying and quantifying defects in coated substrates.

As used herein, the term “coated substrate’- refers to a substrate comprising a coating on 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 m, 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 coatings (including, for example, acrylic coatings, vinylacrylic 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 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 migration/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 and/or extraction occurs when a component separates from other components or travels through the coating. Migration/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 and/or extraction may lead to visible defects, oftentimes such defects are not easily visible. However, the present inventors have surprisingly found that migration/secretion and/or extraction defects may be identified and analyzed using the infrared and/or ultraviolet spectra. The species that migrate/secrete or may be extracted may have different properties that are observable in the infrared and/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. The imaging system 10 is configured to acquire images for a plurality of channels, wherein each of the plurality of channels comprises a predetermined range of wavelengths. For example, each of the channels may consist of wavelengths associated with a single color of light in the visible spectrum (e.g., red = 620 to 780 nm, orange = 585 to 620 nm, etc.). Alternatively, each channel may consist of a predetermined range of wavelengths (e.g., channel 1 = 400 to 500 nm, channel 2 = 500 to 600 nm, etc.). In yet another example, one channel may comprise the visible light spectrum and a second channel may comprise either the ultraviolet spectrum or infrared spectrum. In another example, one channel may comprise wavelengths in the near-infrared range (800 to 1000 nm) and a second channel may comprise wavelengths longer infrared wavelengths (e.g., 1000 to 1500 nm). Preferably, the imaging system is configured to acquire images in at least one channel comprising wavelengths in the visible light spectrum and at least one channel comprising wavelengths in the infrared spectrum, the ultraviolet spectrum, or both. More preferably, the imaging system is configured to acquire images in at least one channel comprising wavelengths in the visible light spectrum and at least one channel comprising wavelengths in the infrared spectrum. In embodiments where the system is used for detecting migration/secretion and/or extraction defects, the imaging system 10 is configured to acquire images in the infrared spectrum, the ultraviolet spectrum, or both.

In embodiments where the defect being analyzed is a color-based defect, the imaging system may be configured to acquire images in channels most relevant to the color of the defect. For example, when analyzing a coated substrate for early rain resistance testing, a substrate may be provided with a blue primer and coated with a white paint. When exposed to water, defects will expose the underlying blue primer. The imaging system 10 may then be configured to acquire at least one image in a channel comprising blue wavelengths. A second channel may be used as a control.

The imaging system 10 may comprise, for example, a camera, a thermal imaging system, an ultraviolet 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, such as, for example, at least one channel of a predetermined wavelength. For example, when the imaging system 10 is configured to detect in the ultraviolet spectrum, a filter may be used to block channels of 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 and the imaging system may be configured to acquire an image in a channel comprising 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. The lighting system 20 may be configured to emit radiation in the visible light spectrum, the infrared spectrum, the ultraviolet spectrum, and combinations thereof. Preferably, the lighting system is configured to emit radiation in wavelengths associated with at least one of the plurality of channels used by the imaging system 10. For example, when detecting migration and/or segregation defects, the lighting system 20 may be configured to emit radiation in the infrared and/or ultraviolet spectra and the imaging system may be configured to acquire images in the same wavelengths. 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 using 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. 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 quantity/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 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.

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 and/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 and/or ultraviolet spectra.

Examples

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.

All or a subset of the acquired images were then transformed using an image analysis algorithm t. The image analysis algorithm identified and quantified the defects in the coated surface.

Efflorescence Test (Prophetic Example)

To test the efflorescence resistance of a primer, a coated substrate will be prepared by coating the substrate with a primer and a topcoat. The bottom of the coated substrate will be contacted with an alkaline liquid to determine whether the primer can block the penetration of the alkaline liquid.

The sample will be analyzed by human observation and by the inventive system. A representative image to be analyzed is shown in FIG. 3, where the light areas are expected to show corroded areas, i.e., areas in which the coating fails to block migration of the alkaline solution, and the dark areas are expected to show uncorroded areas, i.e., areas in which the coating is effective. Human observation will be performed by estimating the areas in which color change can be observed. Analysis by the inventive system is expected to be quantifiable and reproducible.

Early Rain Resistance Test (Prophetic Example)

To test water resistance of wet paint cured for 20 minutes, a substrate having a blue primer applied will be coated with a topcoat of white paint. The topcoat will be cured for 20 minutes after which water will be applied to the top of the coated substrate for a predetermined period of time. As the water washes over the coated substrate, portions of the white topcoat are expected to fall off, revealing the blue primer underneath. An image of a coated substrate following similar water resistance testing is shown in FIG. 4.

The sample will then analyzed by human and by the inventive system. The human observation to estimate the amount or percentage of blue showing through the white topcoat. The sample will also be analyzed by the inventive system, which is expected to provide a reproducible and quantifiable result.

Adhesion Test

A paint sample was applied to a substrate and cured. A crosshatch tool was used to scribe a set of lines. Tape was applied and pulled from the crosshatched area. The adhesive power of the paint was quantified by a human tester who counted the number grids in which the paint remained in the crosshatched area. An image (FIG. 5) of the sample was also analyzed by the inventive system using frequency space to locate areas and quantify the percentage of remaining paint. The inventive system was also able to quantify adhesion of a clear coat based on the light profile used. The clear coat was difficult to observe for the human tester accurately and reproducibly.

Applied Hiding Test

A paint sample was applied at a natural spread rate on a Leneta chart, i.e., a chart with a combination of black and white areas. After the paint dried, the coated chart was analyzed by a human tester, who provided a rating on a 1 to 5 scale based on how much of the underlying black areas could be observed. An image (FIG. 6) of the same sample was analyzed using the inventive system, which used a wavelet transform to locate areas and quantify the hiding rate by constructing a linear regression between pixel intensity and the manual rating. The analysis by the inventive system was more quantitative and reproducible compared to the human observations.

Stain Resistance Test

A stain resistance test was performed by first applying the selected stain on the painted substrate. Possible stain types included: household stain such as pencil, wine, crayon, coffee, narrow and wide marker stains, and dirt. The sample was then washed or scrubbed using a sponge for a defined number of cycles. The color change before and after washing was then used to quantify a paint’ s ability to resist stain. An image of a painted substrate stained with various materials, including marker, pencil and crayon, is shown in FIG. 7.

Surfactant Leaching Test

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. 8. A visible light image was also acquired as shown in FIG. 9. As can be seen by comparing FIGS. 8 and 9, 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 system for quantifiable analysis of a coated substrate, comprising: an imaging system for acquiring one or more images of the coated substrate, wherein the imaging system is configured to acquire images for a plurality of channels, wherein each of the plurality of channels comprises a predetermined range of wavelengths; a lighting system comprising at least one light source for illuminating the coated substrate; a holder for holding the coated substrate in a position to be illuminated by the at least one light source; 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, wherein the coated substrate comprises a coating formed on a surface of a substrate.

2. The system according to claim 1 , wherein the plurality of channels comprise channels in at least two spectra selected from the visible light spectrum, the infrared spectrum, and the ultraviolet spectrum.

3. The system according to claim 2, wherein the imaging system is configured to acquire at least one visible light image in a channel in the visible light spectrum and at least one infrared image in a channel in the infrared spectrum.

4. The system according to claim 3, wherein the analysis unit is configured to transform the at least one visible light image and the at least one infrared image, and the analysis unit is further configured to compare defects in the at least one visible light image and the at least one infrared image to quantitatively analyze the defects in the coated substrate.

5. The system according to claim 4, wherein comparing defects in the at least one visible light image and the at least one infrared image comprises identifying a maximum amount of defects detected in the at least one visible light image and the at least one infrared image.

6. The system according to 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.

7. The system 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.

8. The system according to any one of the preceding claims, wherein the at least one light source comprises a plurality of light sources.

9. The system according to any one of claims 1 to 7, wherein the at least one light source comprises a ring light or a diffuse light source.

10. The system according to any one of the preceding claims, wherein the at least one light source emits light in at least one spectrum selected from the visible light spectrum, the infrared spectrum, the ultraviolet spectrum, and combinations thereof.

11. The system 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 light of a wavelength in one of the plurality of channels or preferentially blocks light of a wavelength in one of the plurality of channels.

12. The system according to any one of the preceding claims, wherein transforming the one or more images comprises applying at least one transformation selected from image thresholding, wavelet transformation, morphological transformation, color detection, pattern detection, clustering, and combinations thereof.

13. The system according to any one of the preceding claims, further comprising a graphical user interface (GUI) for displaying the one or more transformed images and for displaying a quantification of the defects in the coated substrate.

14. The system according to claim 13, wherein the GUI is configured to select one or more of the plurality of channels for acquiring the one or more images and to select the type of defect to be analyzed by the analysis unit.

15. The system according to any one of the preceding claims, wherein the coating comprises paint.