Mineral Filler Selection for Powder Coatings

Mineral Filler Selection for Top Coat Paints A top coat is a transparent or semi-transparent coating applied over an underlying base coat or primer layer as a sealing and protective finish. Top coat paint is a colored final coat used for decorative or protective coating. It is applied to an underlying primer coat, base coat paint, or another coating not designed as a final touch. When selecting a top coat paint, it is important that it is compatible with the paint or coating to which it will be applied, or there may be a chemical reaction between the two that could break down the base coat and jeopardize the paint job. Top coat paint can be applied over a wide variety of surfaces. Top coat painting applications can be performed on diverse surfaces such as concrete, plasterboard, plaster, iron, and steel. It can also be used on furniture. Top coat applications can be performed after proper priming operations are completed. A top coat is a coating layer that is in direct contact with the environment. Fillers affect the fundamental properties of top coats: 1. Abrasion resistance, 2. Barrier properties, 3. Chemical resistance, 4. Gloss and matte effect, 5. Interlayer adhesion, 6. Mechanical strength, 7. PVC, 8. UV resistance.

1. Abrasion Resistance

A coating's resistance to mechanical damage such as abrasion or scratching can be improved by using filler materials with high Mohs hardness, see equipment wear. Hard fillers such as quartz and feldspar increase coatings' resistance to mechanical wear such as abrasion and scratching.

2. Barrier Properties

A top coat's barrier properties can be improved by using filler materials with flat particle shapes.

3. Resistance to Chemical Effects

A top coat's chemical resistance is affected by the chemical composition of the fillers used and may decrease when fillers with insufficient chemical fastness are used.

4. Gloss and Matte Effect

Filler materials with high oil absorption values and high specific surface areas will effectively reduce the gloss of the coating.

5. Interlayer Adhesion

Interlayer adhesion refers to the adhesion of the top coat to the primer. Specialty filler materials with flat particle shapes can improve interlayer adhesion.

6. Mechanical Strength

Filler particles with a flat-platelet particle shape can improve the mechanical strength of a top coating, since these particles enhance film cohesion.

7. Pigment Volume Concentration (PVC)

The density of the filler property affects the top coat's PVC; a high-density filler material will have a low effect on a system's PVC.

8. UV Resistance

The effect of solid particles such as fillers on a top coat's UV resistance depends on the chemical composition of the particles. Most fillers are not sensitive to UV radiation in sunlight. In general, the UV resistance of top coats will therefore not be affected by the choice of fillers used in the system. An exception is mica, which can absorb UV radiation and thus improve a top coat's UV resistance.

Conclusion

In top coat paints, barrier properties, especially abrasion resistance, chemical resistance, gloss and matte effect, interlayer adhesion, mechanical strength, pigment volume concentration, and UV resistance are important. Feldspar and quartz stand out in terms of abrasion resistance, while talc and mica are notable as barrier property fillers. Mica is also effective in terms of mechanical strength and UV resistance.   Sources 1. Jochum Beetsma, https://coatings.specialchem.com/selection-guide/fillers-selection-for-paints-coatings (28 September 2022) 2. Ö.Y. Toraman, Mineral Fillers Used in Paints, BoyaTürk, June-July 2016, pp. 2-4. 3. Ö.Y. Toraman, Mineral Fillers Used in Paints and Plastics, BoyaTürk, April-May 2014, pp. 34-36. 4. Ö.Y. Toraman, Mineral Filler Selection in Paints, Turkcoat, April-May 2023, pp. 14-18. 5. Ö.Y. Toraman, Mineral Filler Selection for Primer Paints, Turkcoat, June-July 2023, pp. 14-18. 6. https://www.kbs-coatings.com/20210811-top-coat-paint.html (29 September 2022) 7. https://www.kayalarboya.com.tr/blog/icerik/sonkatboyauygulamasi (24 May 2023)   Prof. Dr. Öner Yusuf Toraman Niğde Ömer Halisdemir University Department of Mining Engineering