Development and Coating of Powder Crack Coating

Thermosetting powder crackle paint not only has many advantages of thermosetting powder coatings, but also forms beautiful crackle patterns after application, which are natural, elegant, and rustic, and can be adjusted according to the shape of the work and the size of the cracks. This type of powder coating can be widely used in the painting of toys, crafts, and architectural doors and windows. Powder crackle paint utilizes changes in the melting viscosity, surface tension, and curing speed of the powder coating during baking to cause shrinkage on the coating surface, resulting in a crackle effect. The typical methods to create cracks include increasing the amount of filler or reducing the amount of base material, generally choosing fillers with high oil absorption to hinder the normal flow of resin during film formation; this prevents the resin from fully enveloping or just perfectly covering the pigment and filler particles, leaving no excess resin to fill the gaps between the pigment and filler particles, thus forming a three-dimensional structure with the pigment and filler as the framework, and exposing the color of the primer at the cracks.

Precautions for powder crack coating construction

(1) During the powder coating process, it is important to ensure that the powder coating on the surface of the metal workpiece is applied evenly, with a uniform and suitable thickness. If it is too thick, it may cause unclear crack boundaries; if too thin, issues such as exposure of the substrate and pinholes may occur.

(2) It is recommended to spray in sequence from high to low. First coat the secondary surfaces, followed by the primary surfaces, and it is best to complete the spray in one go. Some hard-to-reach areas may require local touch-ups, which can make the existing cracks disappear.

(3) To achieve the best spraying effect, before construction, the materials should be screened through a sieve that is slightly larger, and the powder supply system in the fluidized bed should adjust various process parameters such as powder air pressure, atomization air pressure, the distance between the nozzle and the workpiece, and the movement speed of the spray gun for optimal results.

(4) When using powder crackle coatings, it is important to prevent contamination by other types of coatings. If conditions permit, it is best to have two sets of equipment for separate use.

(5) When using electrostatic spraying, the thermal spraying of the workpiece produces better texturing effects than cold spraying. This is because, during thermal spraying, the powder coating melts quickly upon contact with the workpiece, and the coating immediately starts to convect (if containing metallic pigments, the pigments will float), allowing enough time to rotate to the best reflective angle. In contrast, cold spraying takes a longer time for the workpiece's heat capacity to raise the temperature from room temperature to curing temperature, which means that for an extended period, the resin remains at high viscosity, hindering the formation of texture due to internal resistance. If the gelation time of the coating is short, it will gradually gel during the heating process, and when it reaches the curing temperature, the coating will have already formed a gel, making the formation of texture impossible.

Common problems with powder crackle coating

(1) Running: Powder coating with cracks is caused by the coating film being too thick during spraying; another reason may be that the heating rate is too slow, leading to an excessively long gelation time for the powder coating. The solution is to control the film thickness and speed up the heating rate. Of course, it is also possible that the melting viscosity of the powder coating itself is too low, causing running.

(2) Uneven cracking: If the spray gun's movement speed is uneven during the spraying process, the thickness of the coating film will be inconsistent, thus it is essential to strictly control the manual process during spraying to achieve uniform and beautiful cracks.

(3) Exposing the substrate and pinholes: Poor surface preparation of the workpiece leads to the surface adhering to substances with surface tension (such as oil or spots), or the compressed air contains oil or water. The solution is to strictly control the quality of the workpiece before spraying. Of course, severe substrate exposure may occur when spraying this powder coating too thinly.

(4) Others: Such as when the impact strength and adhesion of the coating film are poor, the curing temperature is too low, the time is too short, the coating is too thick, or the phosphating film is poor or too thick, or insufficient pretreatment, etc.

Conclusion

The production process of crackle powder coating is simple, with stable quality performance and excellent decorative properties, and it has been widely used for painting general metal surfaces. Due to its uniqueness, crackle powder coatings are suitable for various systems, and with the further development of powder coatings, research into crackle powder coatings has become very valuable. The application of crackle powder coatings is straightforward, easily creating patterns that are evenly distributed, making it an ideal high-decorative powder coating. I firmly believe that crackle powder coatings, with their novel decorative effects and reasonable pricing, will be favored by a wide range of users.