Summary of functional and application properties of mineral fillers for coatings

1. Overview The coating is a liquid state or a liquefiable solid powder state or a thick slurry state, which can be uniformly coated and firmly adhered to the surface of the object to be coated, and plays a decorative and protective role on the object to be coated. And a special effect, or a combination of several kinds of film-forming substances.
In addition to paint, the coating products include solvent-based coatings, latex-based coatings, water-soluble coatings, and powder coatings produced by using various synthetic resins and emulsions as main raw materials.
Inorganic fillers in coatings, also known as body pigments, sometimes called pigment extenders, can be divided into non-functional fillers and functional fillers. The former mainly plays an incremental role in reducing the raw material cost of the coating; in addition to the incremental effect, the latter also has the function of improving certain properties of the coating or coating film, such as controlling rheology, improving adhesion, controlling gloss, and improving Covering power, preventing corrosion and optimizing pigment concentration.
Coatings are one of the main users of inorganic fillers. At present, the world's coating production is about 23 million tons / year, and the total consumption of fillers is about 6 million tons / year. China has become one of the world's largest paint producing countries. Currently, it produces about 3 million tons of paint per year, and consumes about 800,000 to 1 million tons of inorganic filler per year.

2, the function and requirements of the filler in the paint The filler (body pigment) in the paint, usually white or slightly colored, a class of pigment with a refractive index of less than 1.7. It has the basic physical and chemical properties of pigments for coatings, but because it has a refractive index similar to that of film-forming materials, it is transparent in coatings, does not have the tinting strength and hiding ability of coloring pigments, and is an indispensable pigment in coatings. . Since most of the fillers come from natural ore processing products, they are chemically stable, wear-resistant, and water-resistant, and are inexpensive, and play a skeleton role in the coating. By increasing the thickness of the coating film by filling, the mechanical properties of the coating film are improved, and the effects of durability, corrosion resistance, heat insulation, and matting can be achieved. On the other hand, it is used as a way to reduce the cost of manufacturing paints. It is cheaper and cheaper than pigments. Under the premise of satisfying the hiding power of paint film, appropriate addition of body pigments to supplement color pigments in paints should be Some volume.
The use of fillers in coatings is not the only way to reduce costs. The main functions and functions of the packing are:
1) The skeleton and filling effect in the coating, increase the thickness of the paint film, and make the paint film full and firm;
2) adjusting the rheological properties of the coating, such as thickening, anti-precipitation, etc.;
3) Improve the mechanical strength of the paint film, such as improving wear resistance and durability;
4) adjusting the optical properties of the coating and changing the appearance of the coating film, such as matting;
5) The film-forming substance undergoes a chemical reaction to make it a whole, so that the film can effectively block the penetration of light, improve its water resistance and weather resistance, and prolong the service life of the film;
6) As a filler in the coating, reduce the amount of resin and reduce the production cost;
7) It plays an auxiliary role in the chemical properties of the coating film, such as enhancing rust, moisture resistance and flame retardancy.
8) Different coating types and grades have different technical requirements for fillers, but the general requirements for fillers for coatings are as follows.
9) The whiteness should be high, especially in paints with high color requirements for coating film, the whiteness is generally required to be above 90%.
10) Easy to disperse, which not only helps to reduce the energy consumption and time of grinding dispersion during paint production, but more importantly, it is beneficial to the performance of the coating, because the dispersion of the filler and pigment is good, the film properties (gloss, color, Durability, etc.) has a direct impact.
11) To have lower oil absorption, low oil absorption value can increase the critical pigment volume concentration (CPVC) of the coating, and save the resin base material, in order to meet the requirements of modern high solids coating materials meeting environmental protection requirements, in order to prepare higher content. The pre-dispersed filler slurry can be matched with pigments with a decreasing oil absorption value (especially titanium dioxide). The oil absorption values ​​of commonly used non-metallic mineral fillers for coatings are shown in Table 1.1.

Table 1.1 Oil absorption values ​​of non-metallic mineral fillers commonly used in coatings/(g/100g)

12) There should be a certain particle size and a narrow particle size distribution, and the sieve residue should be as low as possible. Now the coating requires the filler to have a finer or even finer particle size in many applications, so that it can exert its space in the coating. The spacer layer acts to evenly distribute the pigment particles in the coating film, thereby maximizing the potential of pigment covering (such as titanium dioxide), coloring (such as color pigment) and rust prevention (such as rust-preventing pigment) to partially replace The role of pigments.
13) The coating can 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 flat coating film.
14) It should have good compatibility with the base materials, pigments and other additives in the coating, but at the same time it should be inert and not chemically react with the above ingredients.
15) It has a suitable specific surface area because it affects the viscosity, rheology, dispersion stability, sedimentation and oil absorption of the coating.
16) Having a defined particle shape and crystal morphology, the coating has a defined refractive index and other optical properties and ensures that the filler should function in the coating.

3. Commonly used filler types in coatings Commonly used fillers are calcium carbonate (heavy calcium, light calcium), barite powder (barium sulfate), talc, kaolin (porcelain land), porous powder quartz (silicon dioxide), White carbon black, precipitated barium sulfate, mica powder, wollastonite, bentonite, and the like.
1) Calcium carbonate Calcium carbonate is the most important filler for coatings (physical pigment)
Classification of calcium carbonate for coatings Classification by characteristics of coatings Calcium carbonate is mainly classified into light calcium carbonate and heavy calcium carbonate according to characteristics. Light calcium carbonate and heavy calcium carbonate. Light calcium carbonate (precipitated calcium carbonate) is divided into ordinary precipitated calcium carbonate, fine calcium carbonate, ultra-fine calcium carbonate, active calcium carbonate; heavy calcium carbonate (natural product) is divided into heavy calcium carbonate, heavy fine calcium carbonate, heavy Active calcium carbonate.
The precipitated calcium carbonate is classified according to the crystal form to change the process and control the crystallization, and a fine calcium carbonate crystal such as a cubic crystal system, a needle crystal, a spindle crystal or a chain crystal can be obtained.
According to the crystal particle size classification, precipitated calcium carbonate can be divided into: granular calcium carbonate (average particle size 44-60um); medium calcium carbonate (average particle size 15~44um); fine calcium carbonate (average particle size 1～15um) ); ultra-fine calcium carbonate (0.1 ~ 1um); ultra-fine calcium carbonate (<0.1um).
The heavy calcium carbonate product is divided into single fly powder (fine grain size 200 mesh), double fly powder (fine grain size 325 mesh) and four fly powder (fine grain size 400 mesh) according to the fineness of the powder; Calcium carbonate (fineness grade 1250 mesh).
Calcium Carbonate in Coatings Calcium carbonate is an important filler in the production of paints. Calcium carbonate acts as a filling agent for the skeleton and the substrate (steel plate, wood) in the paint film to enhance the deposition and permeability of the paint film. Especially used in metal anti-rust primers, it forms hydrogen bonds with the metal surface, increases the adhesion of the paint film, and absorbs hydrogen ions to prevent the metal from forming a corrosion tendency of the microbattery. In addition, calcium carbonate has good surface weatherability, wear resistance, low electrolyte content, pH stabilization effect, corrosion resistance and rheology of the coating. Crude grade calcium carbonate is limited to putty, hole-filling compounds, metal primers and other products that require high pigment content, fluidity and coarse surface; medium-grain calcium carbonate is used in architectural coatings and indoors for matt or half On varnish; fine-grained calcium carbonate is mainly precipitated calcium carbonate for printing inks.
Heavy calcium can be used in various interior and exterior coatings, and is most suitable for use in waterborne coatings. Due to poor acid resistance, it is hindered from its application in exterior coatings. In general coatings, the amount of heavy calcium added is 10% to 35%, and the content in various embossed coatings is as high as 50%.
The coating industry uses heavy calcium in addition to increments, mainly used to partially replace titanium dioxide (typically 10% to 20%, 30% in large quantities) and color pigments, replacing light calcium and precipitated barium sulfate, anti-corrosion and Partially replaces anti-rust pigments.
When heavy calcium is used in interior architectural paints, it can be used alone or in combination with talc. Compared with talc, calcium carbonate can reduce the rate of chalking, improve the color retention of light paints and increase the anti-fungal properties.
Compared with heavy calcium, light calcium has a small particle size and a narrow particle size distribution range, high oil absorption and brightness, and light calcium can be used where the maximum matting effect is required. Light calcium and heavy calcium are more commonly used in semi-gloss, matt paints and matt emulsion paints.

2) Talc Powder Talc powder is a general-purpose filler in solvent-based coatings. It has entered the aqueous system due to the introduction of finer-grain grade talc. It is currently used in a variety of primers, intermediate coatings, road marking paints, industrial coatings, and interior and exterior architectural coatings. Because talcum powder has soft texture and low abrasion, and has good suspension and dispersibility, it has a large proportion of talc filler in China's coating industry.
The talc powder of the sheet structure has excellent paintability, fluidity and smoothness of the coating film, water resistance and impermeability of the magnetic lacquer beads, and is mainly used for the primer and the intermediate paint. Fibrous talc powder has a higher oil absorption and good rheology, which can improve the performance of the coating, such as anti-storage, sedimentation and sag during painting, and improved construction performance.
There are many grades of talc for the coatings industry, such as talc powder (-325 mesh), fine grade (-20um and -10um) talc, ultrafine talc (-5um), chemically pretreated talc. Powder, etc., are applicable to various specific purposes and purposes.
The coarser grade talc is used in some rough film, such as the inner wall primer intermediate layer and the marking paint; the ultrafine grade talc powder is used to control the gloss, consistency and sag of the semi-photomagnetic paint; In addition to improving the film properties, ultrafine grade talc has a spatial separation capability, which can partially replace pigments such as TiO2; chemically pretreated talc powder can also replace TiO2 pigment.
One disadvantage of talc is that the oil absorption is high, so where low oil absorption is required, it must be combined with a low oil absorption filler and barite powder. In addition, the wear resistance of talc powder is not high, and in the case where high wear resistance is required, other fillers are added to make up. Talc powder containing other non-metallic minerals is not suitable for use in exterior coatings requiring high weatherability because the impurity minerals are easily reacted with acids such as acid rain. Industrial talcum powder has whiteness due to the inclusion of colored impurities, so talc powder is generally not used as a filler when the filling brightness is very high. Talc has a matting property, so it is generally not used in high gloss coatings.