Color variation on the surface of industrial aluminum profiles is also a common issue with powder coating. The color of powder coating sprayed on the surface of industrial aluminum profiles from the same batch or different batches varies. The main reasons for color variation are as follows.
The mixing time is not uniform.
② Improper selection of pigments can lead to difficulty in dispersing organic pigments, necessitating thorough mixing. Different types of titanium dioxide powders exhibit varying L values (whiteness) and can result in color differences. To prevent color variations during production, it is required to extrude a small amount of sheet material before mass production, crush it, and measure its L, a, and b values using a spray plate. The color difference range should be ∆E < 0.5, and uniform parameters are required for the process.
Coating particles: In the electrostatic powder coating process for industrial aluminum profiles, the most common issue is particles, which are generally caused by both coating defects and application defects. The sources of coating particles are as follows:.
① Gelled particles: The filler is not well dispersed or contains impurities. To avoid this phenomenon, measures can be taken from several aspects.
A. Raw material control
Inspection of resin: Dissolve 100g of resin in acetone or ethyl acetate and toluene (2:1), and observe for any insoluble impurities.
b. Filler inspection: Use a 200-mesh sieve. After sieving BaSO4 or TiO₂ in water, touch the top of the sieve with your hand. It is best if there is no rough grain feeling.
Process Control B: The premixing time should not be excessively long, and regular inspections should be conducted to check for residues in the dead spaces inside the premixer. The temperature of the extruder must be well controlled, neither too high nor too low, generally within the range of 100-110℃. After producing a certain batch, the extruder should be opened to remove the residues inside the extruder threads, as these residues are prone to gelation after prolonged heating, which can also be a cause of particle formation.
C. Equipment Control: Regularly check the pre-mixing cylinder and the screw threads of the extruder for any damage, and replace them promptly if damaged, as damaged screw threads can affect the mixing effect. Regularly check the inlet pipes of the crusher for rust and clean the filter screen of the filtered air system regularly.