Which mineral fillers are suitable for powder coatings?

Powder coatings are powder coatings composed of solid resins, pigments, fillers and additives.

1.

In powder coatings, commonly used fillers include precipitated barium sulfate, barite powder, light calcium carbonate, heavy calcium carbonate, kaolin, talc, bentonite, precipitated silica, mica powder, quartz powder, silica powder, etc.

(1) Precipitated barium sulfate can enhance the leveling and gloss retention of powder coatings, and has good compatibility with other pigments.

(2) The quality of barite powder mainly depends on the grade of the ore and the fineness of the particles.

(3) Talc powder has a certain degree of thixotropy, which has a greater impact on the melt fluidity of powder coatings, and is often used in texture powders.

(4) Mica powder particles are scaly, excellent in heat resistance, acid and alkali resistance, and have an impact on the melt fluidity of powder coatings.

(5) Calcium carbonate is also one of the commonly used fillers, and is recognized by the market due to its wide resources and low prices.

(6) Inexpensive porous powdered quartz can reduce the cost of powder coatings, and at the same time replace barium sulfate to reduce the content of soluble barium in the product to meet environmental protection requirements.

Generally speaking, fillers for powder coatings are generally inorganic, and mainly have the following requirements:

• Density, the higher the density, the lower the coverage of the powder coating.
  

• Dispersion performance, generally the dispersibility of large particles is better than that of small particles.
  

• The particle size distribution and the particle size of the filler are very important.
  If the particle size of some filler particles and the thickness of the coating are large, the cured coating film will look very uneven and rather rough.
  

• Chemical properties, all fillers must be chemically inert to avoid reaction with certain components of the powder formulation such as pigments.
  

• Purity, the color of the filler should be as white as possible, some light-colored filler varieties can be accepted for use, but should be as stable as possible between batches.
  

• The smell should be as small as possible.
  

• The moisture content should not exceed 0.
  5% to avoid interference with the curing reaction and affect the dry powder fluidity of the powder coating.
  

2.
The selection principle of fillers for powder coatings

In powder coating formulations, although the role of fillers is not as important as resins, curing agents and pigments, they are also an indispensable part of most formulations.
When designing powder coating formulations, the following aspects should be considered in the selection of filler varieties and dosages.

(1) According to the application of powder coating:

For outdoor powder coatings, you should choose fillers with good weather resistance, good chemical stability, and not easy to pulverize; for indoor powder coatings, the requirements are not so strict, but the powder coatings used for anti-corrosion should be acid-resistant, alkali-resistant and salt-resistant.
And good fillers such as water resistance.

(2) According to the performance requirements of powder coatings:

• When the coating film has good leveling properties, fillers with small oil absorption and good dispersibility should be selected.
  It is best to use fillers that have been treated with surface treatment agents such as coupling agents and fatty acids or ultra-fine fillers, which is conducive to the dispersion of fillers.
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• In order to reduce the volume concentration of the filler in the formula, use precipitated barium sulfate with a higher density and good dispersion;

• In order to reduce the density of powder coatings, light calcium carbonate with a lower density is used;

• In order to improve the hardness of the coating film, use kaolin with high hardness;

• For general powder coatings that require matting, matting fillers, such as barite powder, can be used.
  The problem that should be noted here is that in the powder coating system with matting agent, the matting filler does not play a supplementary role for matting, and the gloss of the coating film is higher than that of powder coatings formulated with ordinary fillers;

• For sand grain powder coatings, bentonite can be used as a compound;

• In order to improve the electrical insulation performance, use quartz powder or mica powder;

• In lead-free powder coatings, calcium carbonate can be used.