are the two methods used to produce bonded metallic powder coating in current industries.
of the conventional plain powder, except that the pigments contain strip-shaped metallic flakes with special
surface treatment. All these ingredients (pigments, resins, additives, and fillers) are well-mixed, meltextruded, and then ground into powders, which are the final bonded product.
Apparently, metallic flakes and base particles have been well bonded with each other after the melting process, which makes this kind of bonded product with excellent operation stability. However, the mixing and shearing in the extruder at a high temperature are more likely to change the pigment particle size and ruin the metal
surface effect .
Therefore, the melt-extrusion method did not find wide application in the powder
coating industry for the main-stream sheet-shaped metallic pigments. In the thermal bonding method,
metallic flakes and coating powders are heated in a chamber by high-speed stirring until the
temperature precisely reaches the softening point (glass transition temperature) of the coating powder.
Then, the sticky surface of the base particles glue up the metallic flakes. This approach not only
solves the problems in the non-bonding and melt-extrusion methods, but also gives the product a shiny
and uniform final appearance. With this method, the temperature control of the blending process is
If it is under the softening temperature, there will be no bonding between metallic
flakes and base particles; and once it exceeds this point by a couple of degrees, particles of the powder
are easily bonded with each other (mis-bonding) and may even cause pre-curing. This requires bonding
machines that are competent for precisely controlling the inner temperature. Moreover, in industrial
applications, the temperature is generally set a little higher than the softening point to ensure wellbonding, which would increase the possibility of mis-bonding base particles and pre-curing of coating
Therefore, in order to ensure the quality of metallic powder coating, post-treatments
(such as grinding and sieving) are necessary. These issues make the bonding process complicated,
expensive, and low-efficient, which limits the application level and field of the metallic powder