Mineral Fillers Used in Paint

Mineral fillers, according to DIN 55943 (EN-Colouring materials—terms and definitions) standard, are defined as powdery substances that are practically insoluble in the medium in which they are applied, and are used to increase volume, obtain or enhance certain technical properties and/or modify optical properties. Filler materials are essentially natural minerals. They are obtained from the processing of natural raw materials, separation processes and grinding (micronization). Table 1 provides a general classification of filler materials used in paints. Industrial minerals used as fillers, besides being economical, provide important contributions to paint quality and performance through their physical and physicochemical properties. Particularly in Western Europe, calcium carbonate at 80-90 percent (calcite, chalk, limestone powders, dolomite, precipitated calcium carbonate and surface-coated carbonates) is used as mineral filler. Calcites (CaCO3) are predominantly used, having high whiteness and an average particle size of 2-5 μm. Following these, talc, kaolin (including calcined kaolin), silica (SiO2), barite (BaSO4) and mica are preferred in order. General properties of some mineral filler materials are shown in Table 2. Through careful selection of special types of filler materials in specific paints, it is possible to improve the properties of the paint or dry paint film. In matte and semi-matte paints, to prevent the formation of resin or oil layers on the paint surface that cause gloss, it is necessary to increase pigment concentration. In paints with high pigment concentration, effective opacity is achieved by adding filler material in place of some of the opaque pigments. Filler materials are less expensive than opaque pigments. Generally, filler materials do not directly affect the hiding power of paint. Table 3 provides oil absorption rates for some filler minerals.

Calcium Carbonate:

Calcite; with chemical formula CaCO3, is a mineral that forms the building stone of limestone with crystal grain size between 1 mm-10 cm. According to the Mohs hardness scale, its hardness is 3 and its specific gravity at 20°C is 2.7 g/cm3. Pure specimens contain 56% CaO, 44% CO2 in their composition and, depending on the rocks and minerals with which it is found, also contain small amounts of Mg, Fe, Mn, Zn, Sr, Cu, Pb, Co, Ba, Cr and As. Micronized calcite; is successfully used as a functional reinforcing material that enhances physical and chemical properties of the final product in many areas of the paint sector.

Talc:

Talc is one of the softest minerals found in nature. It can easily be scratched with a fingernail and has a hardness of 1. Talc is a hydrated silicate composed of magnesium, silica and oxygen. Its chemical formula is Mg3Si4O10(OH)2. Theoretically it contains 63.5% SiO2, 31.7% MgO and 4.8% H2O. The density of talc ranges from 2.6–2.8 g/cm3. Talc has poor heat and electrical conductivity but is fire-resistant. When heated at high temperatures it hardens, solidifies, and is not decomposed by acids.

Kaolin:

Kaolinite, an important clay mineral, is one of the industrial raw materials preferred for many diverse purposes in various sectors due to its superior physical, chemical, rheological and electrokinetic properties.

Quartz:

Quartz sand consists of quartz (SiO2) particles less than 2 mm, formed as a result of the decomposition of granite-type rocks. Parameters that determine application areas are the amounts of SIO2, Fe2O3, AI2O3, MgO, CaO, Co, Cr, As, P2O5 and physical properties suited to the requirements of industries.

Mica:

A ferric hydroxide with formula FeO(OH), it is found in needle-shaped or tabular crystals. Mica is the name given to a leafy silicate group that can be very easily split. Mica is generally found densely within feldspar. It is a transparent, industrial raw material that can be split into thin layers. These layers, which can be as thin as paper, are hard and highly resistant to very high temperatures. Barite: Barite is generally white in color; however, yellow, brown, pink, light green, light blue, grey and black colored varieties are also found. Barite has a hardness of 2.5-3.5, and its specific gravity ranges between 4.3-4.6. Its melting point is 1580°C. Its chemical composition is BaSO4, containing 65.70% BaO and 34.30% SO3. The barium content is 58.8%.

2. Properties of Mineral Fillers

Mineral fillers are applied for volume increase (filling) purposes to reduce the cost of the final product. The applicability of the filler material is generally determined by the following properties: • Chemical composition, • Particle shape and size distribution (PSD), • Density, • Specific surface area (SSA), • Brightness and yellowness, • Abrasiveness, • pH value, • Wettability/dispersibility, • Oil absorption. Particle Size: The size spectrum is characterized numerically by mean particle size (d50). Surface Area: Mineral fillers are classified according to their BET (Brunauer-Emmett-Teller) surface areas as follows: Low active <10 m²/g Semi-active 10-50 m²/g Active 50-100 m²/g Very active >100 m²/g Abrasiveness: Abrasiveness properties are generally dependent on their hardness and particle size. High degree of abrasiveness is an undesirable condition since it causes wear in machinery. Additionally, contamination occurs between the material and worn parts. This causes surface defects in the film. The abrasiveness of a mineral decreases with particle size. pH: Knowing the pH value, i.e., whether it is acidic or alkaline, is particularly important for paint manufacturers in predicting its behavior in formulation. Completely dispersed material gives uniform particle distribution in the medium it enters. With grinding, the surface activities of mineral fillers increase. Since their surfaces are also coated with hydroxyl groups, ground filler materials are generally hydrophilic (water-loving). The final dispersion should remain stable for long periods and no flocculation should occur. 3. Contribution of Mineral Fillers to Paint The properties that fillers bring to paint are as follows: • Better film formation, • Increased resistance to environmental effects, • Creating a support for the actual pigment, • Preventing rapid settling, • Reducing moisture transfer rate. In summary; in addition to the properties mentioned above, they reduce paint cost since they are less expensive than actual pigments. Associate Professor Öner Yusuf Toraman - Department of Mining Engineering / Niğde University

References

[1]Paints, Coatings and Solvents, Edited by Dieter Stoye, VCH Publishers, Inc., NY (USA), 1993.

[2]Industrial Minerals and Their Uses - A Handbook and Formulary, Peter A. Ciullo, Noyes Publ., 1996.

[3]S.Koltka, E.Sabah, Paint Sector and Synthetic (Precipitated) Calcium Carbonate (PCC), 8th International Industrial Raw Materials Symposium, Proceedings, pp.47-56, 29-30 November 2012, Istanbul.

[4]N.Şahin, 1978. Turkey's Calcite Potential and Preparation of Calcite as an Industrial Raw Material, Thesis, Hacettepe University, Ankara.

[5]S.Temur, 2001. Industrial Raw Materials, Çizgi Kitabevi, 3rd Edition, Konya. [6]M.Ayan, 1978. Ankara University Faculty of Science Department of Geological Engineering – Ankara.

[7]http://somamyo.cbu.edu.tr/docs/dergi/sayi4/4sayi2,pdf

[8]M.S.Eygi, G.Ateşok, 2010. Adsorption Mechanism of Anionic Polyelectrolytes on Kaolin, ITU Journal/Engineering Volume:9, Issue:3, 75-86.

[9]http://tr.wikipedia.org/wiki/Mika.

[10]http://www,maden.org.tr/resimler/ekler/2515f80224756b7_ek,pdf?tipi=5&turu=R&sube=0

[11]İ.Kurşun, B.İpekoğlu, 1995. An Overview of Turkey's Quartz Sand Potential, Industrial Raw Materials

Symposium, Izmir, Turkey.

[12]Ö.Y.Toraman, 2014. Mineral Filler Materials Used in Paints and Plastics, Boyatürk, April/May 2014, pp.34-36.

[13]MEGEP, Project for Strengthening the Vocational Education and Training System, Chemical Technologies, Additives, Ankara, 2009.

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