I. Appearance Identification Method
The appearance identification method is the most basic and convenient way to judge the quality of powder coatings. It requires no professional equipment and can be initially screened using only sight and touch. It mainly includes three sub-dimensions: feel, volume, and storage time.
1.1 Feel
The core of feel judgment is to perceive the fineness and fluffiness of the powder by touch, which is directly related to the powder's spraying performance. During operation, take an appropriate amount of powder (about 5-10 grams) in the palm of your hand, gently rub it, and feel its texture: if the powder feels smooth and fine, and naturally disperses after releasing, without obvious lumps or rough particles, it indicates that the powder has high particle uniformity and good dispersibility, belonging to high-quality powder. This type of powder can pass smoothly through the spray gun nozzle during spraying, is less likely to clog the equipment, and has stronger adhesion to the workpiece surface. The amount of secondary powder fallout (i.e., powder that does not adhere to the workpiece after spraying and falls back for recycling) is small, which can effectively reduce raw material waste and lower usage costs. Conversely, if the powder feels rough to the touch, with a noticeable grainy or heavy feel, or even slightly lumpy, it indicates uneven particle size, possibly due to insufficient grinding or moisture absorption during storage, classifying it as inferior powder.
1.2 Volume
Volume assessment primarily relies on the bulk density of the powder coating, indirectly reflecting its filler content, and thus determining quality and cost. The main components of powder coatings include resin, pigments, and fillers. Resin is the core component determining coating performance and has a higher cost; fillers (such as calcium carbonate and talc) are mainly used to reduce costs, and excessive addition can affect the coating's adhesion, weather resistance, and other properties. High-quality powder coatings have a high resin content and low filler content, resulting in a low bulk density and a larger volume for the same weight. Conversely, inferior powders, in order to reduce costs, add a large amount of filler, leading to increased bulk density and a smaller volume for the same weight. In practical judgment, you can select packaging of the same specifications (such as a standard cardboard box) and compare the fullness of the packaging of different brands of powder: if the powder inside the box is more fluffy and the overall volume is larger, it indicates that the powder has less filler, higher resin content, and is of better quality; if the powder inside the box is compacted and the volume is significantly smaller, it indicates that there is too much filler and the quality is poor. Inferior powder, due to excessive filler, is prone to problems such as low powder coverage and easy cracking of the coating during spraying. Furthermore, the spraying area for the same weight is much smaller than that of high-quality powder, indirectly increasing usage costs. For example, 20 kg of powder may cover 120-140 square meters of workpiece with high-quality powder, while inferior powder may only cover 80-100 square meters, equivalent to an increase in usage cost of 30%-50% per square meter.
1.3 Storage Time
The length of storage time directly reflects the chemical stability of powder coatings. High-quality powders have good resistance to moisture absorption and clumping, and can be stored at room temperature for a long time without affecting their performance. Inferior powders, due to unreasonable formulations or poor raw material quality, have poor storage stability and are prone to performance degradation over time. Under normal circumstances, high-quality powder coatings can have a shelf life of up to 12 months in a room-temperature, dry, and ventilated storage environment. During this period, key properties such as leveling (i.e., the smoothness of the coating surface after baking) and color uniformity will not change significantly, and a high-quality coating can still be formed after spraying. Inferior powders typically have a shorter shelf life, some even less than 3 months: after 3 months of storage, the powder is prone to clumping, leveling deteriorates, and defects such as orange peel and pinholes may appear on the coating surface after spraying. If the storage time is too long, problems such as pigment precipitation and resin aging may also occur, leading to decreased coating adhesion and failure to meet usage requirements. Therefore, when purchasing powder coatings, in addition to paying attention to the production date, you can also judge the quality by comparing the state of different batches of powder: if powders of the same brand but different batches remain fluffy and fine under the same storage conditions, while later batches show lumps and roughness, it indicates that the powder of that brand has poor stability and may have potential quality problems.
II. Spraying Area Identification Method
Spraying area is a core indicator for measuring the cost-effectiveness of powder coatings and is directly related to the resin content in the powder. High-quality powders typically have a resin content controlled between 55% and 65%. This ratio ensures the coating's various properties (such as adhesion and weather resistance) while achieving high spraying efficiency. However, some unscrupulous manufacturers, in order to reduce costs, will lower the resin content to below 45% by adding large amounts of fillers to reduce raw material costs, but this will lead to a significant reduction in the spraying area. In actual testing, a "comparative testing method" can be used: select powders of the same color and weight from two brands (e.g., 1 kg each), and spray them under the same spraying equipment, process parameters (e.g., spraying voltage, air pressure, distance), and workpiece surface conditions. Count the area or number of workpieces that can be covered. If brand A powder can spray 6-7 standard workpieces (or cover approximately 6 square meters), while brand B powder can only spray 4-5 standard workpieces (or cover 4-5 square meters), it indicates that brand B powder has a low resin content and excessive filler, making it a substandard powder. For manufacturers, a smaller spraying area means higher usage costs. Based on the industry average of "6 square meters sprayed per kilogram of powder," if a certain powder can only spray 5 square meters per kilogram, it means that for every square meter less sprayed, the manufacturer needs to purchase an additional 0.2 kilograms of powder. Based on the average market price of powder coatings at 15-30 yuan/kg, for every square meter less sprayed, the cost per kilogram of powder increases by 3-6 yuan (0.2 kg × 15 yuan/kg = 3 yuan, 0.2 kg × 30 yuan/kg = 6 yuan). Long-term use of such inferior powders will significantly increase production costs and reduce product competitiveness.
III. Spraying Personnel Efficiency
The efficiency of spraying personnel is directly related to the powder application rate (i.e., the proportion of powder adhering to the workpiece surface). High-quality powders have excellent application performance, significantly reducing operational difficulty and improving work efficiency; inferior powders have a low application rate, increasing operational burden and slowing down production. High-quality powders, due to their uniform particle dispersion and good electrical properties (easily adsorbed onto the workpiece surface during electrostatic spraying), require only 1-3 sprays to completely cover the substrate (such as the base color of a metal workpiece), and the amount of secondary powder recovery (powder not adhering to the workpiece and requiring recovery) during the spraying process is small. Taking the painting of car wheel hubs as an example, skilled workers using high-quality powder can complete the painting of 1-2 hubs within 1 minute, with recycled powder accounting for only 10%-15% of the total usage. This not only reduces the workload of recycling equipment but also minimizes powder waste. Inferior powder, due to its poor particle charge properties and dispersion, has a low powder application rate, typically requiring 3-5 coats to cover the substrate. Some powders even detach from the workpiece surface after painting due to insufficient adhesion, leading to a significant increase in secondary recycled powder (potentially exceeding 30% of the total usage). This not only increases repetitive labor for painters (such as repeated touch-ups) but also prolongs the painting time for a single workpiece. For example, painting 10 workpieces with high-quality powder might only take 10 minutes, while using inferior powder might take 20-30 minutes, with the output within the same timeframe being only half that of high-quality powder, severely impacting production efficiency. Spraying operators can visually judge the quality of powder coatings through actual operation: if the powder adheres easily, covers the substrate quickly, and produces little recycled powder, it is high-quality powder; if the powder is difficult to adhere, requires repeated spraying, and produces a lot of recycled powder, it is low-quality powder.
IV. Adhesion and Aging Identification Method
Adhesion (i.e., the bonding strength between the coating and the workpiece substrate) and aging performance (i.e., the coating's ability to resist environmental factors during use) are the core performance indicators of powder coatings, directly determining the product's service life. High-quality powder excels in these two indicators, while low-quality powder exhibits obvious defects. A coating formed by high-quality powder coating has strong adhesion. After scoring the coating surface with a cross-hatching tool (an industry standard testing tool), peeling it off with tape shows no peeling. Simultaneously, the coating has good toughness; after bending the workpiece 180 degrees, the coating shows no cracking or peeling. In terms of aging performance, high-quality powder coatings can remain non-chalking and non-fading for several years (usually 3-5 years or more): for outdoor products (such as outdoor furniture and transportation facilities), even after long-term exposure to ultraviolet rays, wind, rain, and alternating high and low temperatures, the coating can still maintain good gloss and color uniformity; for indoor products (such as appliance casings and hardware accessories), even after long-term contact with moisture and friction, the coating is not easily peeled off or worn. Inferior powder coatings have poor adhesion; when tested with a cross-cutting knife, the coating easily peels off with the tape; the coating is brittle, and cracks will appear even with slight bending of the workpiece. Aging performance is also a major weakness: only 3 to 6 months after spraying, the coating will begin to show signs of chalking (powder will flake off when the coating surface is touched), and the color will gradually fade and yellow; if used in outdoor products, poor weather resistance will also cause the coating to wrinkle and peel, leading to rust on the substrate and significantly shortening the product's lifespan. In actual testing, in addition to routine tests such as cross-cut and bending, a "long-term observation method" can be used for judgment: place the sprayed sample outdoors or in a simulated harsh environment (such as a high-temperature and high-humidity chamber), and observe the coating condition regularly. If there is no significant change within 3 months, it is a high-quality powder; if chalking or fading occurs in a short period of time, it is an inferior powder.
V. High-Temperature Identification Method
The high-temperature identification method is mainly used to test the temperature and weather resistance of powder coatings, especially suitable for outdoor light-colored powders (such as white and light gray). If these powders have poor temperature resistance, they are prone to discoloration and loss of gloss after high-temperature baking or long-term sun exposure. The operation method is as follows: place the sprayed workpiece (or powder coating sample) in an oven, adjust the temperature to 220-230 degrees Celsius, keep it at that temperature for 10-15 minutes, remove it, cool it to room temperature, and observe the changes in the color and gloss of the coating. High-quality powder coatings, made with heat-resistant resins and pigments, exhibit minimal color change after high-temperature baking (e.g., white powder remains pure white without yellowing) and maintain essentially the same gloss (retaining its original luster without significant dulling). Even under prolonged high-temperature use, the coating maintains stable performance. Inferior powder coatings, using low-cost resins and pigments, have poor heat resistance. After high-temperature baking, their color changes significantly (e.g., white powder turns yellow, light gray powder darkens), and gloss decreases drastically, resulting in a "dulling" phenomenon (the coating surface loses its gloss and becomes matte). If such powders are used on workpieces requiring high-temperature baking (e.g., automotive parts, oven shells) or products exposed to prolonged outdoor sunlight, discoloration and loss of gloss are highly likely, affecting the product's appearance and performance. It is important to note that different types of powder coatings have different temperature resistance requirements (e.g., indoor and outdoor powder coatings have different temperature resistance standards). High-temperature testing requires adjusting the temperature and time according to the powder's intended use to ensure accurate test results.
VI. Environmental Identification Method
Environmental friendliness is a crucial factor in powder coating procurement. High-quality powder coatings use compliant raw materials, ensuring their environmental performance; inferior powder coatings may use recycled materials and harmful additives, posing a risk of exceeding environmental standards. High-quality powder coatings primarily use raw materials produced by reputable large manufacturers. Resins, pigments, and fillers all comply with national environmental standards (such as the EU RoHS Directive and China's GB 18581 standard), and are free of heavy metals (such as lead, cadmium, and mercury), volatile organic compounds (VOCs), and other harmful substances. During the production process, manufacturers conduct rigorous testing on raw materials, and finished products undergo third-party environmental testing (such as SGS testing), providing complete test reports to ensure product environmental compliance and prevent harm to operator health and the environment. Inferior powder coatings, in order to reduce costs, may use large amounts of recycled powder (i.e., recycled secondary powder that has undergone simple processing and reprocessing). This type of recycled powder may contain impurities, aged resin, and even harmful heavy metals; some manufacturers may also add pigments or additives that do not meet environmental standards, leading to products exceeding environmental limits. While these powders are inexpensive, they may release harmful substances during use, violating environmental regulations and potentially harming the respiratory system and skin of operators. Long-term use may also lead to environmental pollution. To determine the environmental friendliness of powder, the following methods can be used: First, check if the manufacturer provides a third-party environmental testing report (such as an SGS report), clearly stating that heavy metals, VOCs, and other indicators meet standards. Second, observe the powder's odor; high-quality powder has no obvious odor, while inferior powder may have an irritating smell due to the presence of harmful additives. Third, choose brands with a good market reputation and proper production qualifications, avoiding the purchase of unbranded, untested powders.
VII. Summary
The quality of powder coatings directly affects the spraying effect, product lifespan, and usage costs. The six identification methods mentioned above provide a comprehensive basis for judgment from different dimensions (appearance, efficiency, performance, and environmental protection). In actual procurement and use, it is recommended to use these methods comprehensively: first, conduct preliminary screening through visual identification methods (feel, volume, storage time); then, determine the cost-effectiveness through spraying area and work efficiency tests; and finally, verify long-term performance and compliance through adhesion, high-temperature, and environmental protection tests. It should be noted that a single method may have limitations (e.g., powders with good appearance may not necessarily have strong adhesion). Only through multi-dimensional verification can high-quality powders be accurately selected. For enterprises, while selecting high-quality powders may increase initial procurement costs, in the long run, it can reduce raw material waste, improve production efficiency, extend product life, ultimately reduce overall costs, and enhance product competitiveness. Therefore, mastering scientific methods for identifying powder coatings is of great significance for enterprises to control production quality and reduce operational risks.
