First, the effect of coating ambient temperature and temperature on the film thickness
The powder spray amount is 170-200 g/min; the voltage is 70 KV, and the distance between the spray gun and the object to be coated is 20 cm. When the temperature is between 20 and 30 ° C and the humidity is between 60 and 80%, the coating efficiency of the powder coating is good, and the coating film is thick.
Second, the flatness of the film
In powder coatings, the thicker the film thickness, the more flat the surface. The main factors affecting the flatness of the powder coating film are the particle size and its distribution, the melt viscosity, the dispersion state of the pigment and the curing agent, and the like. For a resin having a high melt viscosity, if a flat coating film having a coating film thickness of 40 μm is to be obtained, the maximum particle size of the powder particle size is about 60 μm.
Third, the distribution of film thickness
In electrostatic powder coating, the unevenness of the thickness of the coating film is about twice that of the solvent coating due to the unevenness of the sprayed powder. It is necessary to correctly grasp the effective spray pattern of the coating equipment and control the indirect time of spraying. To prevent unevenness in spraying. When the area of the coated object is larger than the spray pattern of the coating equipment, it is preferable to use a reciprocating spray gun structure. When the parallel long strokes are arranged, the central portion of the object to be coated is thinner, and the line is arranged in a short stroke in series, and the film at the center of the object to be coated is thicker.
Fourth, coating efficiency
The main factors affecting the coating efficiency of powder coatings are the charging method of the coating equipment, the particle size distribution of the powder, the temperature and humidity of the coating environment. For this purpose, suitable powder coatings range from 10 to 80 μm. Relationship between coating efficiency and particle diameter The relationship between the particle diameter and the coating efficiency is as follows: coating efficiency of particle diameter: particle diameter (μm) of 150 or more is 35.0, and 150 to 100 is 35 to 60. Coating efficiency (%) 100 to 74 is 60 to 70, and 74 to 20 is 70 to 90. Therefore, the electrostatic force increases with the decrease in particle diameter with respect to the weight of the particles, and the particle size is 36 to 100 μm, and the powder of 150 to 400 can be used. The particles are completely attached to the cold coated object, and the larger particles are 74 to 177 μmc, 80 to 200 mesh. After the particles are sprayed, the powder may fall from the object to be coated. The epoxy resin has a particle size of 20 to 100 μm, and the equilibrium particle diameter distribution standard rope is preferably 10-80 μm, and the finest lower limit is 10 μm or less and 10% or less, and 60 μm or less particles are 60% or less, preferably 20 to 50 μm. The particle size distribution is easy to fly due to the fine powder of 20 μm or less, and the paint loss is also large.
Five, coated particles
It is caused by the incorporation of gelatinization, poorly soluble particles and impurities in the powder coating. The fine particles in the powder coating are likely to accumulate in the head of the spray gun or in the pipe to change the direction of the air flow. When it is deposited to a certain extent, it is sprayed in a coagulated state and adheres to the object to be coated, and does not melt when baked. And into a particle having a diameter of about 0.5-3 mm, adhered to the wall of the dusting chamber and the rubber in the recycling equipment: in the process of manufacturing the powder coating, agglomerates are formed due to the pigment: some of the resin is solidified during the melt mixing process to produce a gel Particles, which form particles on the coating film. In the electrostatic spraying construction, the environmental dust problem should also be paid enough attention. Dust comes from the air, the operator’s work tape bag recycles the fibers on the equipment and the peeling material on the baking equipment, etc., which also causes contamination of the coating film and particles on it during the electrostatic powder spraying process.