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Extension pigments Introduction In the past, insufficient attention was paid to the understanding of extension pigments, and only general research was conducted on them. In fact, it plays an important role in most paints. Since there are many types of extender pigments and their properties vary greatly, most formulas cannot apply their properties very accurately and effectively, so it is necessary to reposition and apply extender pigments more accurately to improve the product. White pigments are minerals with a low refractive index. They vary in particle size and shape, and exhibit very little hiding power in high-gloss and semi-gloss paints, but they have the performance of "high matt covering" (air pigment interface), reducing the cost of paint. They are also used to control gloss, streaks, suspension, viscosity, etc. The main types of extender pigments are carbonates, silicates, sulfates and oxides. Extender pigments are supplied in particle sizes ranging from 0.01 to 44μm in different shapes including spherical, needle-like, fibrous and flake-like. The shape of the particles affects the accumulation of pigments, the softness of the paint film, crack compensation, etc. The particle size and particle size distribution affect the hiding power, viscosity, porosity of the paint film, the demand for base materials and surfactants, gloss, fineness, etc. Whether the extender pigment reacts with the base material is related to salt water spray, foaming, corrosion resistance and cracking resistance. The best way to obtain comparable performance by substituting one extender pigment for another has been studied and reported. Research has found that when one extender pigment is substituted for another in equal weight or volume, significantly different paint properties are produced, e.g.: Thickness, durability, permeability, scrubbing properties, stain resistance, paint resistance, etc. Extender pigments are made by grinding the ore or splitting the stone into shape, or by a process of chemical precipitation and refining and size grading if necessary. Their size separation uses wet or dry sieving, flotation, centrifugal separation and other means. The source and processing of raw materials will affect the performance of the pigment. calcium carbonate or old powder: This extender pigment is widely used in indoor or outdoor paints to control gloss, mold growth, thicken and reduce costs. It is widely used in both natural and synthetic (precipitation) types, and its particle size range is extremely wide, from 0.05 to over 44 μm. Natural calcium carbonate is used in larger amounts because it is cheaper and performs in some ways as well as or better than synthetic calcium carbonate. The coarse grade limit is used for putties, pore-filling compounds, metal primers and other products that require high pigment content, flowability and rough surfaces. These levels have low matting effect. Medium particle size calcium carbonate is used in architectural coatings and interior matte or semi-gloss paints. Fine particle grades of calcium carbonate, mainly precipitated calcium carbonate, are used in printing inks. In formulations, two levels of products are often used to obtain the balance of required properties. Sources of natural calcium carbonate extender pigments are limestone and marble, with most grades containing 95-99% calcium carbonate. Some grades are graded by crushing and airflow. The finer grades are obtained by wet grinding and sedimentation or centrifugal classification. Different grades have great differences in particle shape, average particle size, particle size distribution and purity. Natural calcium carbonate extender pigments are also widely used in interior architectural paints, either alone or in combination with talc powder. Compared with talc, calcium carbonate can reduce the chalking rate, improve the color retention of light-colored paints and increase mildew resistance. Applications require specific particle sizes. Fine particles have a tendency to crack. Larger particles solve this problem. They have low binder requirements and low reactivity. These extender pigments are also used in exterior latex paints to improve color retention. Calcium carbonate acts as a buffer in water-based paint systems. Because this extender pigment is alkaline, it cannot be used with alkali-sensitive colored pigments such as Tillandsia and Chrome Green, nor can it collide with soluble iron or copper salts to cause contamination. Calcium carbonate cannot be used in acid-catalyzed curing melamine polyester systems because it neutralizes the catalyst. As a grade, precipitated or synthetic calcium carbonate pigment content ranges from 98% to over 99% and has a small particle size and narrow particle size distribution range, high oil absorption and brightness compared to natural calcium carbonate. The particle size of the better grades can vary from 0.03 to 8μm, which has entered the colloidal range. It has been reported that the optimal particle size for interior latex paints and paper coatings is 0.2 μm. Precipitated calcium carbonate is used where maximum matting effect is required. Certain grades have surfaces treated with rosin or fatty acids. These grades are easier to extrude and allow use in gloss products without significant loss of gloss. In some formulations, it reduces penetration into porous surfaces, thereby increasing sealing action and reducing topcoat penetration. talcum powder: Talcum powder has different crystal shapes depending on the part of the rock used, resulting in changes in physical properties. Generally, talc is a mixture of various types. The performance of paints using a specific talc product is determined by the type or type of mixture, the average particle size and the particle size distribution. Since most talc is mainly in fibrous or flaky form. This is the basis for general grading. Fibrous talc is generally considered to have the best outdoor durability and pigment suspension, but has some disadvantages in flow and smoothness. Flake talcum powder has excellent brushability, fluidity and smoothness of the coating film, and non-penetration of enamel. It also increases the "lubricity" of coatings and printing inks. The less granular form of talc has the best adhesion and sanding properties, suggesting its use in sandable sealers and surfacers. Talc is produced in many grades, each designed with a specific use and purpose. Particle sizes range from coarser for lower oil absorption to "ultra-fine" for high oil absorption, with scraper fineness as high as 7. There are also surface treatment grade talc powder with low oil absorption and scraper fineness of 6-7, which is used in glossy enamels. Talcum powder has a variety of desirable properties. Whether used in oil-based paint or water-based paint, its dry film has high brightness and good color. Talcum powder wetting and dispersing is very easy. In all liquid paints, such as organic solvents, alkyds and water-based ones, the stirring speed often does not need to exceed medium speed. It also suspends very well and helps suspend other pigments. The coarser grades are used in certain paint films that require roughness, such as interior primers, midcoats, and striped paints. Smooth grade (approximately scraper fineness 4) is generally used in architectural paints and also as general-purpose extender pigments. Ultra-fine talcum powder with a scraper fineness of 5-7 is used to control the gloss, consistency and sagging of semi-gloss enamels. Talcum powder is also widely used in joint cement, crack filler and caulking agent. These special needs products are available in coarse or fine grades as required. Talcum powder is widely used in various industrial paint varieties, especially primers and intermediate coats. Steel structure primers use fibrous talc as all or part of the extender pigment, which improves settling, film strength and recoating adaptability. Talc is advantageously used in many industrial quick-bake primer and vehicle topcoat formulations. Flake silicates including soapstone are used in intermediate coatings on metals where they tend to improve sandability and water resistance. This is because the flake lengthens the path for moisture to pass through the paint film, thereby increasing moisture resistance. clay: Clay (kaolin) is an extender pigment and its main component is aluminum silicate. At first, clay was mainly used in the paper industry, and now it is widely used. In recent years, clay has been used as an extender pigment in the coating industry. Simple air drying and air flow classification products are upgraded through water washing, strict particle size control, calcination and surface treatment. Calcination is the most significant of these improved methods, so this method has also entered large-scale production. Most of the clay particles are lamellar and hexagonal in shape, so after layering, particles with a large width-to-thickness ratio can be obtained. The layering method is similar to sand grinding. The clay can be pressure-cooked with caustic soda solution to increase its porosity, oil absorption, pH and brightness, and its density is smaller than that of calcined clay. It (including calcined clay, etc.) is called a "structural" pigment, which can improve hiding power, tinting strength and extinction in paints. For example, when used in indoor flat latex paint, it can replace part of titanium dioxide without affecting the quality. The widely used grades have a fineness of about 10 μm. All grades have varying degrees of hydrophilicity and are almost chemically neutral. The oil absorption range ranges from 25-44μm for non-calcined grade to 48-58μm for calcined grade. Different levels of brightness variation, reflection coefficient from 80-92%. Clay pigment increases the toughness of the paint film due to its flaky nature. Easier to powder than talc when used in architectural coatings. Improves sandability when used as an intermediate coat on metal. Calcined clay can be used in interior paints and produces a smooth paint film. The finest grade is used in colored semi-gloss and glossy paints to reduce floating and blooming phenomena. Some clay pigments show poor suspension in solvent-diluted paints, but surface-treated calcined grade clay can overcome these shortcomings. Since clay pigments are hydrophilic, they are also good extender pigments for water-based paints. They have good suspension properties, are easy to disperse and have good brushing and leveling properties. They are generally used together with other extender pigments. Barite and precipitated barium sulfate: Barium sulfate extender pigment comes in two forms: Barite and Precipitated Barium Sulfate, Recently developed, ground and bleached barite has several color and fineness improving properties. Precipitated barium sulfate has superior color and fine particles, but it is not widely used in the paint industry because barite meets the requirements and has a low cost. Barite is mainly used in interlayer coatings, including automotive primers. Due to their low oil absorption and dense granular or nodular structure, they provide good hole filling, thick film and enamel paint anti-penetration properties. This is necessary in most glossy finishes. Barite's chemical inertness makes it useful in several chemical-resistant coatings and in highly acidic conditions. In recent years, with the development of nanoscale materials, nanoscale barium sulfate is also commercially available in extender pigments. For example, Cimbar's Barifine nanoscale powder has a very large specific surface area, so surface properties have become its main properties. This ultra-fine product promotes pigment dispersion, improves gloss and clarity, and improves aluminum powder dispersion, providing UV stability and thixotropy. Silica: There are three unique and different types of silica manufacturing methods: ①as raw silica ； ②diatomite ； ③Synthetic silica. ①Quartz type or crystalline silica has a limited range of use, is difficult to disperse, and has poor suspension properties. If it is ground with a three-roller or ball mill, it will discolor badly. It is mainly used as a filling agent for wood. Its outstanding properties are low oil absorption and small shrinkage, inertness to the base material and good rough surface. ②Diatomaceous earth, or amorphous silica, is widely used in high-gloss paints and has a porous, brittle structure that comes in a variety of geometric shapes. Diatomaceous earth contains silica ranging from 83-95%. Most products are white, but some are light gray, light pink or light yellow. They also have high apparent specific gravity and very high oil absorption. The combination of irregular structure and high oil absorption produces very good matting effects, high thickening capacity and good pigment suspension. Diatomaceous earth is widely used in flat interior wall paints. Due to its porosity and brittleness, it reduces stain removal and scrubbing properties. It is also used in outdoor flat architectural paints and has excellent durability. Its usage ratio is limited by properties such as consistency, brushability and fluidity. Dispersion should be done by high-speed mixing or adding to the ball mill shortly before grinding is completed, otherwise, the brittle particles will be broken, * * Reduce matting ability and suspension performance. Since significant particle reduction is not feasible in coating manufacturing, it is important to carefully select the grade of diatomaceous earth by scraper fineness after mixing. ③Synthetic silica, also amorphous silica, is produced by synthesis and has a high matting effect and is used in varnishes and enamels to reduce gloss. Mica: Mica is composed of a group of certain minerals with different compositions and different physical properties. Muscovite type, composed of K2O·3Al2O3·6SiO2·2H2O, is a commonly used extender pigment. Mica is a large, flaky crystal with a book-like structure. Mica pigments are created by layering the mica with compressed air and using wet or dry grinding methods. Most widely used grades are wet milled, ranging from larger particles, approximately 325 mesh, to grades with an average particle size of only 5-10 μm. The flake-like structure of mica gives the paint unique properties. It enhances the mechanical strength of the paint film and increases the penetration of water and moisture into the substrate through the paint film. It is also used in small amounts in oil-based architectural paints to prevent cracking. Can also be used in latex architectural paints. The proportion of mica in paint is usually very low, accounting for about 5% of the total pigment. In exterior paints, mica creates a harsh shine by reflecting sunlight. calcium silicate: Calcium silicate is made of wollastonite and has a needle-like structure, good brightness and relatively low oil absorption. It is suitable for oil-based architectural paints, matte and semi-gloss indoor oil-based paints and latex paints, with a pH of approximately 9.9, providing a buffering effect and keeping latex paints alkaline.