Against the backdrop of rapid socio-economic development, people's daily quality of life and standards are constantly improving, and the development of artificial intelligence is also accelerating. Replacing traditional manual operations with artificial intelligence is the trend of scientific development today, and more and more new technologies are widely used in the field of coatings.

The fineness of the coating, also known as the grinding fineness, is a measure of the dispersion of the coating and filler, and has a significant impact on the film quality, coating color, film gloss, durability and storage stability of the coating. For color paint with good dispersion and fine particles, there is less space between the pigment particles, resulting in a uniform color, good gloss and smooth surface of the paint film. Additionally, the pigment is less likely to agglomerate or precipitate during storage. At present, the commonly used method for determining fineness is ISO 1524:2013, but the uneven force and speed used during manual operation can lead to significant differences in test results. The fineness is in the micrometer range, and the observation of the fineness results requires strong professional skills and a wealth of practical experience from the operator. In addition, the rapid solidification of the coating and the short observation time can lead to significant human error. By improving traditional technology, using a newly invented automated program control operation mode and a mechanized automatic operation device for automatic fineness measurement, the speed and force of operation are ensured to be uniform, which can largely eliminate the influence of manual operation and greatly improve the authenticity of test results. The coating is automatically scraped onto the fineness plate, and the fineness is captured in real time by a camera and analyzed by professional software. The fineness value is directly displayed on the touch screen to ensure the repeatability, accuracy and fairness of the measurement results, avoiding human error and greatly improving production efficiency and cost savings. 

This article compares the fineness values of different coatings measured by automatic fineness measuring instruments and traditional manual measurement methods, identifies the differences and advantages and disadvantages of the two measurement methods, and analyzes and evaluates the feasibility and practicality of measuring fineness using the two methods. Using an automatic fineness meter and manual methods to measure the fineness of white latex paint, by controlling other variables to be the same, and individually changing factors such as light source type, reading time, reading angle, scraping angle and scraping speed, analyze the impact of these factors on the measured fineness value, and find the optimal testing range for factors that affect the measured fineness value of the coating. 

Experiment

Raw Materials and Instruments 

Main Raw Material

• Red emulsion paint: fineness 43 μm, Guangzhou Nippon Paint Co., Ltd; 
• Water-based pigment: fineness 25 μm, Guangdong Kedi New Materials Co., Ltd; 
• Polyurethane paint: fineness 23 μm, Guangdong Keshun Waterproof Technology Co., Ltd; 
• White latex paint: fineness of 40 μm, Akzo Nobel Swire Paints (Guangzhou) Co., Ltd; 
• Alkyd paint: fineness 51 μm, Guangdong Meitushi Chemical Co., Ltd; 
• Paint ① and Paint ②: Guangdong Kedi New Materials Co., Ltd 

Instruments

• The fineness grind gauge is crafted from quenched steel, measuring 175 mm in length, 65 mm in width and 23 mm in thickness. The groove depths are set at 100 μm, 50 μm and 25 μm, respectively. The scraper is a standard, single-edged steel blade, measuring 90 mm in length, 40 mm in width and 6 mm in thickness.

Fineness grind gauge. Image courtesy of BEVS Industrial.  

• The automatic fineness measuring instrument is controlled by a touch screen and fully automated by a computer program. All steps comply with ISO 1524:2013. The basic module of the automatic fineness measuring instrument includes:
  • Industrial high-definition camera
  • Industrial computer
  • Report output
  • Dynamic scraping system
  • Process control system
  • Power supply
  • Lighting system

Experimental Methods

Manual Measurement

Traditional manual operation steps are carried out according to ISO 1524:2013. 

Instrument Measurement

Turn on the instrument, set the sample name, sample number, operator and information storage location on the touch screen display. Place the cleaned and dried fineness grind gauge into the designated position in the instrument, install the scraper, take a small amount of sample and place it at the starting position of the deep end of the groove. Close the instrument door and click the "Start Measurement" button to initiate the measurement. The instrument will automatically measure and analyze, generate a test report, save the results and display them on the screen. The measurement is conducted in a constant temperature and humidity laboratory with a temperature of (23 ± 2) ℃ and a relative humidity of (50 ± 5)%.Automated particle analyzer. Image courtesy of BEVS Industrial. 

Results and Discussion

The Influence of Different Detection Light Sources on Fineness 

Under the same conditions, first, an automatic fineness measuring instrument was used to scrape the white latex paint on a fineness plate. Then, both the automatic fineness measuring instrument and traditional manual scraping method were used to measure the fineness. Six different standard light sources, including D65 (international standard artificial sunlight), TL84 (European, Japanese, and Chinese store light sources), CWF (American cold white store light source), F (reference light source for color comparison of household hotel lights), UV (ultraviolet light source), and U30 (American warm white store light source) were selected to measure the fineness of the latex paint. The test results are shown in Table 1.

TABLE 1 | Effect of different light source on fineness.

From Table 1, it is evident that, under the same conditions, testing samples under different light sources may yield varying results. Additionally, even when measuring under the same light source, there exists a certain disparity between the test results obtained using automatic fineness measuring instruments and traditional manual measurements. This discrepancy is likely attributable to human error. Among the standard light sources utilized in experimental testing, the result obtained using light source D65 for automatic fineness measurement is closest to the true fineness of latex paint. However, the fineness value cannot be accurately read under UV (ultraviolet light source). Therefore, among the tested light sources, D65 standard light source proves to be the most suitable. It is advisable to conduct readings under a light source that facilitates easy observation of the sample condition on the fineness plate, as failure to do so may lead to inaccurate test results. When performing manual readings, it is crucial to consider the operator's mental state and operational experience, as these factors may also contribute to inaccurate results.

The Influence of Reading Time on Fineness

Using white latex paint for testing, under the same conditions, when using an automatic fineness measuring instrument, the instrument is set to run immediately after scraping for high-definition photo analysis. For manual measurement, readings are taken immediately after scraping, and records are made at 1, 3, 5, 8, 12 and 15 seconds after scraping. The results are shown in Table 2.

TABLE 2 | Effect of reading time on fineness.

From Table 2, it can be seen that there is not much difference in the fineness measured by the instrument at times 1 s, 3 s and 5 s. However, the fineness measured at 8 s, 12 s, and 15 s is significantly higher. When other conditions are the same, the reading time is longer and the fineness value is higher, mainly because the particles become more obvious with the increase of curing time. The reason why manual measurement has a higher fineness value than instrument measurement is because the instrument measurement has already set a time for high-definition photography and then computer analysis, which takes less time and is more efficient. Manual reading is done after the experimental design time, and it takes a certain amount of time for the operator to read the value. In fact, manual reading takes longer than instrument measurement. Therefore, the operator should complete the reading within 5 seconds when measuring, and the observation must be fast and accurate to better ensure the accuracy of the measurement.

The Influence of Different Reading Angles on Fineness

Under the same other conditions, using an adjustable-angle high-definition camera in the instrument, the position of the fineness grind gauge is fixed, and the angle between the camera and the surface of the gauge is changed. The manual reading angle is obtained by changing the angle between the gauge and the operator's line of sight while keeping the operator's line of sight fixed. The fineness results of the latex paint are measured at angles of 10°, 20°, 30°, 60° and 90°, as shown in Table 3.

TABLE 3 | Effects of different reading angle on fineness.

From Table 3, it can be seen that under the same conditions, within a certain range of reading angles, different reading angles result in different fineness. This is mainly due to the reflection and refraction at some angles, which makes it difficult to see the particles on the fineness grind gauge clearly, resulting in smaller results. The results of manual measurement and instrument measurement are also different when reading at the same angle. It is difficult to control the angle during short-term observation when reading manually, which has a significant impact on the measurement results. According to the analysis of the result data, the suitable reading angle range is 10°~30°.

The Influence of Different Scraping Speeds on Fineness

Under the same conditions, the latex paint was scraped using different scraping speeds set by the instrument. Due to the difficulty in controlling the speed during manual scraping, the manual scraping speed was a rough speed. Tests were conducted at speeds of 20, 50, 80, 110 and 140 mm/s. The results are shown in Table 4.

TABLE 4 | Effect of different scraping speed on fineness.

From Table 4, it can be seen that under the same conditions, both manual scraping and instrument scraping have a certain impact on the fineness in terms of speed. If the scraping speed is too fast, it is often completed within 1 second or even 0.5 seconds. In such a short time, the paint does not completely wet the grooves, often resulting in orange peel, shrinkage or leakage, causing failure. If the scraping speed is too slow, it will also cause the paint to dry and affect the reading results. The result data analysis shows that the suitable scraping speed range is 110-140 mm/s.

The Influence of Different Scraping Angles on Fineness

Keeping other conditions constant, the angle between the scraper and the gauge was changed to scrape the latex paint. The scraping angles were tested at 30°, 60°, 90°, 120° and 150°, and the paint fineness results are shown in Table 5.

TABLE 5 | Effect of different scraper angle on fineness.

The results from Table 5 indicate that in both manual and auto scraping, when the scraping angle is less than 90°, the measured results are larger than the true value (40 μm). When the scraping angle is greater than 90°, the measured results are smaller than the true value, mainly due to the structure of the scraper. When the scraping angle is less than 90°, the thickness of the scraped film is larger, and when the scraping angle is greater than 90°, it is smaller. The scraper tilts backwards, resulting in a smaller fineness value; The scraper is tilted forward, and the measured fineness value is too high, so the scraper should be kept at 90° as much as possible for scraping and coating. The results of auto scraping and manual scraping are quite different, and it is difficult to control the scraping angle smoothly during manual scraping, which can also cause measurement errors.

Comparative Analysis of Auto and Manual Measurement of Fineness

Select 5 types of coating samples and have experienced fineness testing experimenters use the same equipment and standard testing methods to test different test samples in the same laboratory at short intervals. The instrument and manual measurements are carried out in accordance with ISO standard. The results obtained under the conditions of using a suitable D65 light source, reading angle of 15°~30°, reading time within 3 seconds, scraping completed within 2 seconds, and scraping angle of 90° are shown in Table 6.

TABLE 6 | Comparison of auto and manual measurement.

Note: GRR refers to the repeatability and reproducibility of measuring tools. GRR determination method: GRR ≤ 5% indicates good repeatability of the testing equipment; GRR ≤ 10% indicates that the testing equipment is acceptable; 10%

From the analysis in Table 6, it can be concluded that the results measured by the automatic fineness measuring instrument are significantly more accurate, with better repeatability and reproducibility than manual measurements. Additionally, the automatic fineness measuring instrument has faster measurement speed and higher efficiency. Based on the analysis of the above experimental results, it can be concluded that the type of light source, reading time, reading angle, scraping angle and scraping speed all have a certain impact on traditional manual fineness testing, resulting in large errors in experimental results. However, automatic fineness measuring instruments can greatly reduce the influence of these factors.

Conclusion

The most important step in measuring fineness of a coating is to accurately determine the particles displayed on the fineness gauge. However, the testing is affected by the performance of the instrument, as well as the viscosity, color and solvent volatility of the coating, and human errors such as the type of light source, reading time, reading angle, scraping angle, scraping speed, etc. In the actual process of detecting fineness, operators are easily affected by the above factors or their own state. They need to make strict judgments and analyses on various types of situations, which requires the operator's excellent skills to ensure the accuracy and effectiveness of the final measurement results. Otherwise, it will cause unstable detection results. Automatic fineness measuring instruments can avoid many manual operations and better control these factors, thereby reducing measurement errors and improving measurement accuracy. The rich measurement experience of traditional staff is an important factor that cannot be ignored in the measurement results. Therefore, staff must undergo strict on-the-job training and have rich practical experience before they can independently engage in the calibration of scraper fineness meters. The automatic fineness measuring instrument only requires personnel to be familiar with the various functions of the instrument and know how to operate and maintain the instrument. It offers simple operation, fast operation, and a low threshold for operators. Moreover, the automatic fineness measuring instrument is fully automated, which takes less time and improves detection efficiency.