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The performance and quality of powder coatings are largely determined by the selection of raw materials. Powder coatings mainly consist of synthetic resins, curing agents, pigments, fillers, and additives. Choosing each raw material is like building with blocks – missing a piece or choosing the wrong one will affect the overall effect. Today, we'll cover the key points for selecting these raw materials, as well as storage and application safety precautions, to help you fully grasp the crucial aspects of controlling powder coating quality from the source.
Synthetic resins are like the "skeleton" of powder coatings. Their structure and properties directly determine the core performance of the coating and film, so resin selection must be strictly controlled. For thermosetting powder coatings, the primary requirement for the resin is that it "contains active functional groups" – just like the skeleton needs "connecting points" to react with other components during baking and film formation, forming a network-like "structure." This structure makes the coating film strong and durable, less prone to cracking and peeling. For example, epoxy powder coatings contain epoxy groups, and polyester powder coatings contain carboxyl groups, all to form a stable structure during curing. In addition, a sufficiently large temperature difference between the resin's melting temperature and decomposition temperature is crucial in actual construction. If the temperature difference is small, it's like cooking between the temperatures of boiling and burning an egg—it's difficult to control the heating temperature. Too low a temperature results in incomplete resin melting and poor coating leveling; too high a temperature causes resin decomposition, leading to bubbles and yellowing of the coating. For example, some inferior resins have a melting temperature of 120℃ but a decomposition temperature of only 150℃; slight miscontrol during baking can cause problems. High-quality resins, on the other hand, have a temperature difference of over 50℃, providing ample temperature adjustment space during construction and significantly reducing operational difficulty.
If the resin is the "skeleton," then the hardener is the "adhesive." It allows the resin's "connection points" to fully react and can significantly adjust the performance of the coating and film. It is an important means of resin modification, so the hardener must be "suitable." First, the curing agent must be in a solid state at room temperature, such as powder, granules, or flakes—this is to ensure better mixing with other solid raw materials and avoid "caking" or "separation" during production. If the curing agent is liquid, mixing it with solid resins and pigments is like "mixing water with sand," easily forming sticky lumps that affect subsequent crushing and sieving processes. More importantly, the curing agent must have "latency"—simply put, it "doesn't cause trouble normally, but only works when needed." During the production and storage of powder coatings, it cannot chemically react with resins or other components, nor can it agglomerate on its own; only when the temperature rises to the threshold for baking and curing will it be "awakened," reacting rapidly with the active functional groups of the resin to form a stable coating film. For example, commonly used blocked isocyanate curing agents can be stably stored at room temperature for more than 6 months. Once placed in an oven at 160°C or higher, they can quickly deseal and participate in the curing reaction, ensuring the storage stability of the coating without affecting the film-forming effect.
Although pigments and fillers are often mentioned together, they have different focuses, and their selection should consider both aesthetics and practicality. The main function of pigments is "color matching," determining the color and gloss of the coating film. When selecting pigments, "tinting strength" should be considered first—for example, even with the same red pigment, a high-quality azo red pigment can achieve a vibrant red with a small amount added; while a low-quality pigment may require a large amount but still result in a dull color. "Weather resistance" should also be considered. For outdoor powder coatings (such as billboards and outdoor furniture), the pigment must be able to resist ultraviolet radiation, otherwise it will fade and yellow quickly; indoor coatings have slightly lower requirements for weather resistance, but must ensure uniform color and avoid "spots." Fillers, on the other hand, are used to strengthen the coating film and reduce costs. Commonly used fillers include calcium carbonate, barium sulfate, and talc. When selecting fillers, attention should be paid to "particle size" and "dispersibility"—particles that are too coarse will result in a grainy texture on the coating surface, affecting the appearance; particles that are too fine are prone to moisture absorption and clumping, causing production problems. For example, in machine tool housing coatings requiring high hardness, ultrafine barium sulfate filler is chosen to improve film hardness while maintaining a smooth surface. In ordinary pipe anti-corrosion coatings, cost-effective calcium carbonate filler can meet basic strength requirements while reducing raw material costs. Furthermore, the amount of filler added should not be excessive, otherwise it will affect the reaction between the resin and curing agent, leading to decreased coating adhesion.
Although additives are added in small amounts to powder coatings (usually only 1%-5%), they are crucial, solving many detailed problems and improving coating quality. Common additives include leveling agents, defoamers, and scratch-resistant agents. For example, leveling agents allow molten coating to spread more evenly on the workpiece surface, avoiding "orange peel" texture; defoamers help air bubbles in the coating escape during baking, reducing pinholes; and scratch-resistant agents form a protective film on the coating surface, making furniture and appliance casings less prone to scratches. When selecting additives, the key is "compatibility"—for example, leveling agents must match the type of resin. Epoxy powder uses epoxy leveling agents, and polyester powder uses polyester leveling agents; otherwise, they will not only be ineffective but may also conflict with other components, leading to pinholes in the coating. Additionally, the purity of the additives is also crucial. Inferior additives may contain impurities, which can contaminate the coating and affect its appearance.
Selecting the right raw materials is only the first step; safe storage and application are equally important. Otherwise, even the best raw materials can be ruined.
The storage environment must be far from fire sources, avoid direct sunlight, and maintain good ventilation. The temperature should be controlled below 35℃. This is because the resins and curing agents in powder coatings are easily ignited by high temperatures or open flames. Direct sunlight can also cause the raw materials to age, affecting performance. For example, if coatings are stored in an open-air warehouse in summer, the temperature under direct sunlight may exceed 40℃, causing the curing agent to prematurely "awaken," resulting in the coating clumping and becoming unusable. Avoid storing powder coatings in locations susceptible to contamination from water, organic solvents, oil, and other materials. Water will cause the powder to absorb moisture and clump, while organic solvents and oils will react chemically with the raw materials, damaging the coating's composition. For example, storing powder coatings with paint or thinner will allow the solvents from the thinner to seep into the coating packaging, causing the coating to deteriorate.
During the painting work area, proper safety precautions must be in place, such as providing fire extinguishers, setting up warning signs, and strictly prohibiting smoking and the use of open flames. Because powder dust is generated during spraying, if the concentration reaches a certain level, it may cause an explosion upon contact with an open flame, so all sources of ignition must be eliminated on site. Equipment used in painting operations, such as powder spray guns and powder supply containers, must be properly grounded to eliminate static electricity. Powder coatings will acquire static electricity during spraying; if the equipment is not grounded, the accumulated static electricity may generate sparks, leading to safety accidents. For example, if the powder spray gun is not grounded, the charged powder sprayed may adhere to the equipment surface due to static electricity, forming dust accumulation over time, which may ignite upon contact with a spark.
Quality control of powder coatings begins at every stage of raw material selection—choosing the right synthetic resin as the "skeleton," finding the right curing agent, ensuring both aesthetics and practicality in pigments and fillers, providing detailed supplementary additives, and implementing standardized storage and application safety measures are all crucial to guaranteeing coating performance from the source and ultimately producing a smooth, strong, and durable film. For manufacturers, rigorous screening of each raw material and thorough incoming inspection are essential; for application companies, attention must be paid to storage environment and equipment grounding, and standardized operating procedures must be followed. Only in this way can quality problems caused by incorrect raw material selection or safety negligence be avoided, allowing powder coatings to fully realize their advantages, meeting both product appearance and performance requirements while ensuring safe production and application.
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