Quality control and testing of matting agent

Quality control and testing of matting agent

Zhou Miao CAI Ming (Wuhan Yincai Technology Co., LTD.) 

Foreword 

As a critical additive in powder coatings, the quality of matting agents directly determines the performance and quality of end products. Therefore, implementing rigorous quality control and comprehensive testing for these agents is essential. For instance, in premium powder coatings, matting agents must achieve exceptional fineness and uniformity to ensure the coating maintains the required level of subtlety and gloss. Given that different application scenarios demand distinct quality standards, targeted quality control measures should be implemented throughout both production and application processes.

I. Detection items of matting agent

1.1 Melting Point Testing: The melting point serves as a critical indicator of a matting agent's thermal stability. Precise measurement of this temperature allows evaluation of the product's performance across varying thermal conditions, ensuring reliable operation during processing and application. For instance, temperature-sensitive matting agents with excessively low melting points may melt prematurely in high-temperature environments, compromising their effectiveness. Our testing employs an automated method using a capillary sample placed in a heating block. Through preset programming and optical sensor detection, the system automatically monitors temperature changes, effectively eliminating human observation errors while automatically recording initial and complete melting temperatures (as specified in GB/T 617-2006).

1.2 Viscosity Testing: Viscosity serves as a critical parameter for evaluating the flow-ability of matting agents. Proper viscosity ensures uniform dispersion within the coating matrix, preventing sedimentation or stratification that would compromise product quality stability. Excessive viscosity may hinder even distribution, while insufficient viscosity could lead to sagging during storage and transportation. The cone plate viscometer employs a flat plate and a conical rotor with linear taper angles (0.5°-4°). The device operates through rotational motion where the conical rotor applies controlled stress at predetermined speeds, while the measuring component detects torque generated. The sample is precisely positioned in the narrow space between the plates, ensuring consistent shear rate application throughout the measurement process (GB/T9751.1-2008)

1.3 Particle Size Inspection: The particle size significantly impacts the matting efficiency of the additive and the surface characteristics of the paint film. Larger particles generally provide higher matting performance, though they may cause surface roughness that affects tactile feel and visual appearance. Conversely, smaller particles enhance the film's transparency and fineness, though this may correspondingly reduce matting efficiency.

To meet the requirements of various application scenarios, precise control of the particle size distribution of matting agents is essential. Common particle size measurement methods include laser diffraction, electron microscopy, and sedimentation techniques. We employ laser diffraction, which operates on the principle that particle clusters scatter light beams. The scattering angle of light is inversely proportional to particle size: larger particles have smaller scattering angles while smaller ones exhibit larger scattering angles. By analyzing the distribution of scattered light intensity across different angles, we can calculate the particle size distribution. Regardless of the detection method used, core parameters such as D10, D50, and D90 are typically employed to characterize particle size distribution (GB/T19077-2016).

1.4 TG Testing: Our company employs DSC (Differential Scanning Calorimetry) instruments for analysis. This method enables the determination of thermodynamic properties such as enthalpy changes and glass transition temperatures in matting agents. The data provides critical insights into structural transformations and thermal stability under varying temperature conditions, serving as a vital reference for formulation design and production process optimization.

The instrument uses a complex control system to ensure that the sample and reference are heated at the same rate during the test, monitors and records in real time the heat flow difference required to maintain the temperature consistency between them, and uses this heat flow difference as the vertical coordinate,

Temperature or time is taken as the horizontal coordinate, and a DSC curve is finally obtained. When the amorphous polymer changes from glassy state to high elastic state, a baseline step will appear in the DSC curve, and the corresponding midpoint temperature is TG(GB/T19466.2-2004).

1.5. Gelation Time Testing: The gelation time assessment of a matting agent serves as a critical quality control measure. Rather than directly evaluating the matting agent itself, this test primarily assesses its compatibility and reactivity with specific resin systems. Essentially, a longer gelation time indicates slower reactivity between the matting agent and resin system, suggesting better storage stability. Conversely, a shorter gelation time suggests faster reactivity, which may indicate potential storage issues.

1.6 Repeated extrusion: repeated extrusion is an effective method to quickly judge the storage stability of the matting powder. If the gloss increase amplitude and appearance change are small after repeated extrusion 2 or 3 times, it indicates good storage stability; otherwise, it indicates poor storage stability.

1.7 High and low dosage: When the amount of matting agent is high, sometimes there is no difference, but when the amount is low, the difference or quality instability can be shown, so it is necessary to do high and low dosage test. Yincai Company outdoor matting agent classic model L2018, 3% dosage shows gloss 30%, improved model L2018C, 3% dosage shows gloss 12%, the result shows the effectiveness is improved significantly.

1.8 Smoke: There are two kinds of smoke. One is that the matting agent itself emits smoke, which is easy to detect. The other is that the matting agent is used in powder and reacts with other components of the powder to produce smoke, which is easy to ignore and needs to be tested. Yincai’s L2018W outdoor matting agent and L2035W indoor semi-chemical matting agent are both low smoke matting agent.

1.9 Storage Stability: As a critical performance indicator ensuring long-term reliability, storage stability directly impacts gloss control, dispersion characteristics, and primary coating quality in paint/powder systems. Our accelerated testing is conducted in constant temperature and humidity chambers maintained at 50-60% relative humidity and 40℃,45℃, or 50℃ temperatures, in accordance with industry standards GB/T21782.8-2008.

II. Testing items of the plate made with the matting agent

2.1 Appearance aspects

Gloss Testing: The gloss measurement of a matting agent application is the most critical step in evaluating its performance, directly quantifying both the matting efficiency and stability of the effect. As a highly standardized process, it requires strict adherence to established protocols to ensure comparability of results. Typically, professional gloss meters are employed to measure at a 60-degree angle, with multiple measurement points selected on the sample. The average number is calculated to obtain the gloss data. Reference standards GB/T9754-2007。

Surface Leveling Assessment: This evaluates the surface smoothness of boards produced with a matting agent. Superior surface leveling enhances product aesthetics and reduces surface defects. The quality is assessed by examining the board's flatness and checking for orange peel-like shrinkage holes. Typically, shrinkage holes indicate poor compatibility between the matting agent and resin system, resulting in uneven surface tension. These holes manifest as orange peel patterns caused by ineffective dispersion of the matting agent, which forms micro-agglomerates that impair flow-ability.

Fineness detection: reflects the smoothness of the board surface. A fine surface can improve the texture and touch of the product, enhancing the market competitiveness of the product. It can usually be measured by touch or with the help of professional instruments.

Brightness and Clarity Measurement: This evaluates a surface's light reflection capability, including clarity and luminosity. High-brightness surfaces better showcase product aesthetics while enhancing visual impact. We conduct measurements using a brightness meter by selecting multiple points on the sample and calculating the average value.

2.2 Mechanical properties

Impact testing: Evaluates the structural integrity of a plate when subjected to impact. Using a pendulum impact tester, the pendulum is released at a specified height to strike the plate surface, with damage patterns being observed and documented. The testing criteria may reference GB/T20624.2-2006, by simulating the impact situation in actual use, generally speaking, the higher the impact strength, the less likely the product is to break during use.

Bending Testing: This evaluates a plate's deformation resistance during bending. The process involves gradually increasing bending force until the plate fractures or reaches predetermined deformation limits. Refer to standards like GB/T6742-2007. Superior bending performance ensures products remain resistant to breakage or deformation under external forces, thereby enhancing reliability and stability.

Bond Strength Testing: To evaluate the adhesion between coating layers and substrate surfaces, our company employs two methods: the Circle Drawing Method and the Grid Marking Method. The Circle Drawing Method utilizes an automated testing instrument that systematically creates progressively deeper circular grooves across the paint film surface. These grooves, starting from the thinnest layer and gradually increasing in depth until penetrating to the substrate, are observed for paint peeling patterns to assess bonding integrity with reference to GB/T1720-2020 for the grid method and GB/T9286-2021 for the grid method.

Hardness Testing: This evaluation measures surface hardness to assess scratch resistance. Using the pencil hardness method which is quick and intuitive, we employ an automated testing device. A pencil of known hardness is applied at a 45° angle to the paint film surface, identifying the maximum grade that prevents scratches. The test follows the GB/T6739-2022 standard. Yincai's G600 model demonstrates excellent surface hardness performance.

Wear Resistance Testing: Evaluates the wear resistance of panels. Using a paint film abrasion tester, the surface is subjected to friction under specified loads through grinding wheels, recording weight loss or surface changes. The test can be conducted according to GB/T 1768 standards. Products with superior wear resistance can maintain longer service life during use, reducing performance degradation and visual damage caused by wear. Yincai's G600-3 demonstrates exceptional wear resistance – when used at 20% higher dosage, wear reduction reaches 93%, achieving near-zero abrasion.

2.3 Other performance tests

Salt Spray Resistance Testing: This method simulates marine or high-salinity environments to evaluate the corrosion resistance of panels. Products demonstrating excellent salt spray resistance maintain superior performance and quality even in harsh conditions. The testing is typically conducted according to the GB/T1771-2007 standard.

Aging resistance testing: evaluates surface durability by simulating natural aging conditions including light exposure, temperature fluctuations, and humidity. Products demonstrating superior aging resistance maintain extended service life with stable performance. Standard testing follows GB/T 1865-2009 specifications. Yincai's G570 Acrylic Matting Resin and G600-1 Acrylic Matting Resin exhibit exceptional weather resistance.

Water Boiling Resistance Test: Evaluates performance changes in boards under high-temperature boiling conditions, including visual appearance and structural integrity. Products demonstrating excellent water boiling resistance maintain optimal functionality in humid or hot environments. The test is typically conducted according to GB/T 1733-93 standards. Yincai's Outdoor Matting Agent 2018N exhibits superior water boiling resistance.

III. CONCLUSIONS

Quality control and testing protocols for matting agents are critical to ensuring product quality and performance. By rigorously controlling parameters such as melting point, viscosity, particle size, DSC analysis, as well as post-manufacturing evaluations including surface characteristics, mechanical properties, and other performance metrics, manufacturers can effectively enhance product quality and stability to meet diverse application requirements. Moving forward, continuous research into matting agent quality control and testing technologies will drive the healthy development of the matting agent industry.