The fillers main function in coatings :
1. Improve the mechanical strength of the coating and the coating film;
2. Filling effect, increase solid content, reduce the amount of resin and solvent, and reduce cost;
3. Give the coating good fluidity, construction performance, and increase the thickness of the coating film;
4. Provide partial cover, weather resistance, anti-ultraviolet effect, and extend the service life of the film;
5. Special functionality, such as UV shielding, heat resistance, and minimal toxicity;
6. Improve the performance of other additives, such as thickeners, rheological agents, antistatic agents, UV stabilizers, etc.
Calcium carbonate, barite powder, quartz powder, talc powder, kaolin, mica powder, wollastonite, dolomite, etc. These fillers have different compositions and chemical properties, but all have common characteristics. These characteristics are used as coatings. Required for packing:
1. White or light color, the whiteness requirement is generally above 90%;
2. The particle size is small, the particle size distribution is narrow, easy to disperse, and the coating can be completely and uniformly covered;
3. To have low oil absorption, the low oil absorption value can increase the critical pigment volume concentration of the coating, save the resin substrate, and meet the requirements of modern high solids coatings.
4. It can make the coating have good rheology (flowability, leveling, suspension, thickening, etc.), so that the coating does not precipitate during storage, and it is easy to form a film to form a smooth and smooth coating film;
5. Good compatibility with other components of the coating film and no chemical reaction with other components;
6. Appropriate specific surface area, particle shape and crystal morphology. It directly affects the viscosity, dispersion stability, refractive index and other properties of the coating.
Using different fillers will tend to have different effects. There are three words describing the most used fillers: calcium carbonate reinforcement, talc toughening, and barium sulfate glazing.
1. Calcium Carbonate
Calcium carbonate is the most commonly used filler for coatings, and it is also widely used in the plastics industry and the paper industry. Calcium carbonate has good weather resistance, high strength, low price (the lowest coating filler), wear resistance, can improve the corrosion resistance of the coating and the rheology of the coating, reduce the chalking rate, improve the color retention, and improve the anti-pollution Performance, the disadvantage is easy to hoarfrost.
2. Talcum Powder
Talc powder is also called hydrous magnesium silicate, which is directly pulverized from talc. It has good lipophilicity, is easy to disperse in solvent-based coatings and does not form agglomerated precipitates. It is the main filler for solvent-based coatings, but it is easy to cause agglomerated precipitation in water-based coatings, so it is used in smaller amounts because it is very Strong oil absorption, not commonly used in powder coatings. The talc powder is basically fibrous or flake-shaped, and the fiber has good weather resistance, but the fluidity in the coating is poor, and the flatness of the coating film is also insufficient; the flaky talc powder can improve the leveling property of the coating, the flatness of the coating film and the gloss retention. Its chemical properties are extremely stable and can withstand high temperatures of 900 degrees. Its disadvantage is that it is easy to be powdered and should be used in an appropriate amount.
3. Barium Sulfate
Appearance is a dense white powder with a density of 4.5g/cm3. The polished barite powder is widely used in industrial primers, especially automotive primers. It is also used in topcoats that require higher gloss. Fine barite powder is in Partial replacement of titanium dioxide in latex paints. It has low oil absorption, high density, good filling performance, good gloss and good gloss retention, high chemical inertness, acid resistance, alkali resistance and light resistance. It has very high corrosion environment. Great value. The precipitated barium sulfate relative to barite powder has smaller particle size, higher price and easy sedimentation, and is an important filler for high-gloss semi-gloss powder coatings.
4. Mica Powder
Mica powder is a non-metallic mineral containing many components, 49% of which is SiO2 and 30% of which is Al2O3. The layered structure is a complex silicon oxide composed of two layers of silicon oxide tetrahedron sandwiching an aluminum oxide octahedron. Floor. Generally used for coatings is muscovite, which has good elasticity and toughness. The addition of a small amount of mica powder in the oil paint can prevent cracks, and the latex paint on the wall also has the functions of crack prevention and improved scrubbing performance. Another important application area of wet-milled mica powder is as a carrier material for titanium pearlescent pigments.
5. Kaolin
Also known as Baiyun, Guanyin, and clay, named after Gaoling Village, Jingdezhen, Jiangxi. It is divided into washed kaolin and calcined kaolin. It is in the form of flakes or tubes. It has good hiding property and good suspension. The cost of washed kaolin is low and it has the effect of improving the film feel. Calcined kaolin has high cost, but high whiteness and small particle size. It is widely used in exterior wall coatings. In powder coatings and high-grade exterior wall coatings, ultrafine calcined kaolin can be used instead of 15%-20% titanium dioxide.
6. Calcium sulfate
It exists in two basic forms: anhydrite and gypsum (gypsum powder). The most widely used paint is anhydrous gypsum, which can be calcined by gypsum. Anhydrous gypsum has bright color and good dispersibility, and can be used in some light paints and other coatings with special requirements.
7. Bentonite
The volume of bentonite can be increased to 5-6 times of the original volume after absorption, and the charged particles can be released in the aqueous solvent to cause electrostatic repulsion between the particles of the coating, so that there is significant thickening and suspension, which has become a low-end Thickening and suspending agents commonly used in exterior wall coatings have a large number of applications in low-grade architectural coatings and powder architectural coatings.
8. Silicon Dioxide
There are many varieties of silica for coatings, and the performance varies widely. There are two common types: fumed silica (ie, silica) and quartz powder.
Silica is an extremely pure amorphous silica with a blue-phase or white loose powder. It is chemically stable and insoluble in all solvents except hydrofluoric acid and strong base. The role in the coating is: 1. The liquid coating has a thickening effect in a stable state; 2. Thixotropy, so that the thick coating film does not appear to sag; 3. Prevent the pigment from sinking, dispersing, powder The coating is also used to prevent agglomeration; 4. Improve the water resistance and heat resistance of the coating film.
Quartz powder has high density, high hardness and chemical resistance. In functional architectural coatings, quartz powder is the main filler for wear-resistant floor coatings and acid-resistant coatings, and also the main filler for high-end wall putty. Natural porous powder quartz is also used as a matting powder for liquid coatings. Its comprehensive performance is good, and the oil absorption is low. However, the disadvantages such as difficulty in dispersion and easy agglomeration of the bottom cause its use to be quite limited.
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