Pigments and fillers should be used widely, such as in plastics, coatings, inks, etc.Among them, the application of the two in the coating is very much discussed. Here is a brief summary of the application of pigments and fillers in the coating.
The role of pigments and fillers
1. The role of pigments
Pigment is one of the indispensable components in the production of paint. In addition to providing color decoration for the coating, it can also provide more physical and chemical properties for the coating, such as covering, light resistance, weather resistance, temperature resistance, chemical resistance, gloss and mechanical strength. The use of functional pigments in coatings can give coatings special properties, such as special decorative effects (metallic texture, pearlescent luster, luminous, fluorescent, etc.), anti-corrosion, fire prevention, conductive, antistatic, temperature and other special functions.
2. The role of filler
The main role of fillers in coatings is twofold: one is to fill and reduce costs; the other is to change the physical and chemical properties of the coating or paint by adding fillers.Inorganic fillers in coatings are also called physicalPigments,Sometimes also calledPigmentsThe extender can be divided into non-functional filler and functional filler.The former mainlyIncrementfunction to reduceRaw material cost of coatings;The latter, in addition to having an incremental effect, also has an improved coating or coating film.Some performance functions, such as controlling rheology, improving adhesion, controlling gloss, improving hiding power, preventing corrosion and optimizing pigment product concentration.Coatings are the main users of inorganic fillersAt present, China's coating production is about 25 million tons/year, and the total consumption of filler is about 7 million tons/year.
Function and requirements of fillers in coatings
The filler (extender pigment) in the coating is usually white or slightly colored, and the refractive index is less than 1.7. It has the basic physical and chemical properties of pigments for coatings, but because the refractive index is similar to that of film-forming substances, it is transparent in coatings, and does not have the tinting power and hiding ability of coloring pigments. It is an indispensable pigment in coatings. Since the vast majority of fillers come from natural ore processing products, their chemical stability, wear resistance, water resistance and other characteristics are good, and the price is low, and they play a skeleton role in the coating.
By filling to increase the thickness of the film, improve the mechanical properties of the film, and can play a durable, anti-corrosion, heat insulation, extinction and so on. On the other hand, it is used as a way to reduce the manufacturing cost of coatings, using its low price, the price is far lower than the color pigment, under the premise of meeting the hiding power of the paint film, the appropriate addition of body pigments to supplement the volume of color pigments in the paint.
The use of fillers in coatings, cost reduction is not the only role. The main role and function of the filler is:
1. Play the role of skeleton and filling in the coating, increase the thickness of the paint film, and make the paint film plump and solid;
2. Adjust the rheological properties of the coating, such as thickening, anti-precipitation, etc;
Improve the mechanical strength of the paint film, such as improving wear resistance and durability;
4. Adjust the optical properties of the coating and change the appearance of the coating film, such as extinction;
5. The film-forming substance chemically reacts to make it into a whole, so that the film can effectively block the penetration of light, improve its water resistance and weather resistance, and extend the service life of the film;
6, as a filler in the coating, reduce the amount of resin, reduce production costs;
7, the chemical properties of the coating play an auxiliary role, such as enhanced anti-rust, anti-moisture, flame retardant, etc;
Different coating varieties and grades have different technical requirements for fillers, but the general requirements for fillers for coatings are as follows;
1, the whiteness should be high, especially in the coating film color requirements are very high, the whiteness is generally required to be more than 90%;
2, easy to disperse, which not only helps to reduce the energy consumption and time of grinding dispersion in coating production, more importantly, it is conducive to the performance of the coating, because the dispersion of fillers and pigments is good or bad, the film performance (gloss, color, durability, etc.) have a direct impact;
3, to have a lower oil absorption, oil absorption value is low in order to improve the critical pigment volume concentration (CPVC), save resin base material, in order to meet the requirements of environmental protection requirements of modern high solid coating, in order to prepare a higher content of pre dispersed filler slurry, in order to reduce the oil absorption value of the pigment (especially titanium dioxide) matching. The oil absorption value of commonly used non-metallic mineral fillers for coatings is shown in Table 1;
4, there should be a definite particle size and narrow particle size distribution, sieve residue should be as low as possible, now the coating requires filler in many applications with fine or even ultra-fine particle size, so as to play its role in the space in the coating, so that the pigment particles in the film are evenly distributed, in order to maximize the pigment cover (such as titanium dioxide), coloring (such as color pigments) and rust (such as anti-rust pigments) and other potential, play a part of the role of alternative pigments;
5. It can make the coating have good rheological properties (fluidity, leveling, suspension, thickening, etc.), so that the coating does not precipitate during storage, which is convenient for construction and film formation to form a smooth and flat coating film;
6. It should have good compatibility with the base material, pigment and other additives in the coating, but it should also be inert and not chemically react with the above ingredients;
7. It has a suitable specific surface area, because it affects the viscosity, rheology, dispersion stability, sedimentation and oil absorption of the coating;
8. It has a definite particle shape and crystal morphology, so that the coating has a definite refractive index and other optical properties and ensures that the filler should have the function in the coating.
Types of fillers commonly used in coatings
Fillers commonly used in coatings are calcium carbonate (heavy calcium, light calcium, nano calcium), barite powder (barium sulfate), talc powder, kaolin (porcelain land), porous powder quartz (silica), white carbon black, precipitated barium sulfate, mica powder, wollastonite, bentonite, etc.
Calcium carbonate is the most important filler for coatings (body pigment).
classification of calcium carbonate coatings:
According to the characteristics of calcium carbonate for coating, it is mainly divided into light calcium carbonate, nano calcium carbonate and heavy calcium carbonate.Light calcium carbonate (precipitated calcium carbonate) is divided into ordinary precipitated calcium carbonate, fine calcium carbonate, ultrafine calcium carbonate and active calcium carbonate;Heavy calcium carbonate (natural products) is divided into heavy calcium carbonate, heavy fine calcium carbonate, heavy active calcium carbonate, etc.; nano calcium carbonate has water-based nano calcium, coating special nano calcium, etc.
According to the crystal form classification of precipitated calcium carbonate to change the process and control the crystallization, you can get the cubic crystal system, needle crystal, spindle crystal, chain crystal and other fine calcium carbonate crystals.
According to the crystal particle size, precipitated calcium carbonate can be divided into: particulate calcium carbonate (average particle size 44 ~ 60um); Medium calcium carbonate (average particle size 15 ~ 44um); Fine calcium carbonate (average particle size 1 ~ 15um); Ultrafine calcium carbonate (0.1 ~ 1um); Ultrafine calcium carbonate (<0.1um).
Heavy calcium carbonate products are divided into single-fly powder (fineness grade 200 mesh), double-fly powder (fineness grade 325 mesh) and four-fly powder (fineness grade 400 mesh) according to powder fineness grade. Ultrafine calcium carbonate (fineness grade 1250-3000 mesh).
application of calcium carbonate in coatings:
Calcium carbonate is an important filler in coating production.Calcium carbonate plays the role of filling the skeleton and substrate (steel plate, wood) in the paint film, and enhances the deposition and permeability of the paint film.Especially used in metal anti-rust primer, it forms hydrogen bonds with the metal surface, increases its paint film adhesion, and can absorb hydrogen ions to prevent the corrosion tendency of metal to form microbatteries.In addition, calcium carbonate face to the weather is good, with wear resistance, low electrolyte content, pH stability effect, can improve corrosion resistance and coating rheology.Coarse grade calcium carbonate is limited to putty, hole filling compounds, metal primers and other products, they need high pigment content, fluidity and coarse surface;Medium grade calcium carbonate used in architectural coatings and interior matted or semi-gloss paint;Fine-grained calcium carbonate is mainly precipitated calcium carbonate and is used in printing inks.
Heavy calcium can be used in various internal and external coatings, and is most suitable for application in water-based coatings. Poor acid resistance hinders its application in external coatings. In general coatings, the addition of heavy calcium is 10% to 35%, and the content is as high as 50% in various relief coatings.
In addition to the use of heavy calcium in the paint industry, it is mainly used to partially replace titanium dioxide (generally 10% to 20%, and 30% when the amount is large) and color pigments, to replace light calcium and precipitated barium sulfate, to prevent corrosion and partially replace anti-rust pigments.
When heavy calcium is used for interior construction paint, it can be used alone or in combination with talcum powder. Compared with talcum powder, calcium carbonate can reduce the chalking rate, improve the color retention of light colored paint and increase the resistance to mold.
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, matte and matte latex paints. Nano-calcium is used in latex paint, water-based paint, automobile chassis paint, etc.
Talcum powder is a general-purpose filler in solvent-based coatings. Due to the advent of more fine-grained talc powder, it has entered the water-based system. At present, it is used in various primers, intermediate coatings, road marking paints, industrial coatings and internal and external architectural coatings. Because talcum powder has soft texture, low abrasiveness, good suspension and dispersion, the proportion of talcum powder filler consumed in China's coating industry is large.
The flake structure of talcum powder has excellent brushing, coating fluidity and smoothness, water resistance and enamel beads do not penetrate, mainly used for primer and intermediate coating. Fibrous talcum powder has higher oil absorption and good rheological properties, which can improve many properties of coatings, such as anti-sedimentation during storage and sagging during brushing, and improve construction performance.
There are many grades of talc powder for coating industry, such as ordinary particle size talc powder (-325 mesh), fine grade (-20um and-10um) talc powder, ultra-fine grade talc powder (-5um), chemical pretreatment of talc powder, etc., respectively, suitable for a variety of specific uses and purposes.
Coarse talc is used in some paint films that need roughness, such as interior wall primer intermediate layer and striped paint. Ultrafine talc is used to control the gloss, consistency and sagging of semi-gloss enamel. Fine and ultra-fine talc not only can improve the coating performance, but also has space separation ability, which can partially replace TiO2 and other pigments. Chemical pretreated talc can also replace TiO2 pigment.
One disadvantage of talcum powder is its high oil absorption, so it must be combined with low oil absorption fillers and barite powder where low oil absorption is required. In addition, the wear resistance of talc is not high, in the need for high wear resistance of the occasion, to add other fillers to make up. Talc powder containing other non-metallic minerals is not suitable for external coatings requiring high weather resistance due to the reaction of impurity minerals with acids (such as acid rain). Industrial talcum powder due to containing colored impurities and whiteness decreased, and thus the packing brightness requirements are very high occasions, generally do not use talcum powder as filler. Talc powder has matting properties, so it is generally not used in high gloss coatings.
Kaolin is one of the fillers widely used in foreign coating industry. The largest amount in the United States, about 300000 tons/year in recent years, of which calcined kaolin is more than 100000 tons/year.
The kaolin commonly used for coatings includes ultrafine kaolin, calcined kaolin, activated kaolin (surface modified), etc. Kaolin can be used in a variety of coatings, but mainly in water-based architectural coatings, especially within the latex paint, due to kaolin in water-based paint has a good hiding power, which can partially replace titanium dioxide pigment. Ultrafine kaolin can partially replace titanium dioxide, about 10% of the amount of titanium dioxide, which can reduce the cost of paint, but has little effect on the gloss, hiding power and storage stability of the paint. The refractive index of calcined kaolin is increased from the original 1.56 to 1.62, which makes up for the deficiency of the original covering power and whiteness. In addition, calcined kaolin can improve the opacity of the coating and the firmness of the coating, and has more scrub resistance and powder resistance than the uncalcined soil. Calcined kaolin instead of part of titanium dioxide in highway marking paint, powder coatings, building exterior latex paint has been a certain application. Ultrafine kaolin and calcined kaolin can replace 15% ~ 20% of titanium dioxide in exterior wall coatings. Certain kaolins exhibit poor suspensibility in solvent-diluted paints, but calcined kaolins treated with surface modification can overcome these disadvantages.
Porous powder quartz (main component SiO2)
Porous powder quartz belongs to a volcanic ash sedimentary rock. The natural particle size of the product is fine (about 0.5μm), the particle distribution is uniform, the specific surface area is large (8.3 m2/g), and the shape structure is similar to spherical without angular shape. From the electron microscope image, the surface is full of nano-scale mesopores, and the average pore diameter is about 8.8nm (nanometer).
Porous powder quartz surface contains a certain amount of hydroxyl (-OH)-silanol. As a polar functional group, it is used in powder coatings to help improve the adhesion and adhesion of the product. On the other hand, due to the presence of hydroxyl, more easily through the coupling agent surface treatment, increase its crosslinking, reinforcing effect, increase the physical and mechanical properties of the product can also improve the tensile strength of the film.
Porous powder quartz contains ZrO2, zirconium dioxide is stable in nature, high hardness, and the porous structure of porous powder quartz makes the coating have better hardness performance and impact resistance.
Porous powder quartz belongs to a kind of silica system, and its safety is recognized. It has been widely used in powder coatings, architectural exterior wall coatings, thick napping coatings, fireproof coatings, waterproof coatings, environmental protection coatings, anti-corrosion coatings, etc. Cheap porous powder quartz can reduce the cost of powder coatings and replace barium sulfate to reduce the content of soluble barium in products to meet environmental protection requirements.
Natural porous powder quartz mainly plays an incremental and semi-reinforcing role in coatings, and can be used in various coatings and architectural coatings, especially primers and intermediate coatings. Fine crystal SiO2 can replace up to 50% TiO2 in epoxy and polyphenol powder coatings.
Natural porous quartz powder because it is porous, high porosity structure, with a variety of different particle shapes and structural characteristics, coupled with excellent oil absorption (19~25g/100g), irregular structure and oil absorption The combination produces a very good matting effect, high thickening ability and good pigment suspension. It is used as a matting agent in coatings. Mainly used in flat latex paint and varnish, primer and some concrete coatings, it is also used as a filler to increase the hiding power of hiding pigments in coatings.
Silica (or light silica) due to the large specific surface area, good thermal stability can prevent pigment precipitation, especially in the use of latex paint, adjust the effective viscosity of the paint, improve the film sagging and matting effect, good heat stability of the paint film.
Fumed silica is a kind of multi-functional extender pigment, and it is also an excellent rheology control agent for coatings. In liquid coatings, its rheological control functions include: thickening, thixotropy, anti-flow hanging, and edge coverage; in solid powder coating systems, it enhances the free flow of powder and prevents agglomeration and fluidization.
Barium sulfate used as paint pigment has two kinds of natural and synthetic, natural products called barite powder, synthetic products called precipitated barium sulfate.
The appearance of barium sulfate is a dense white powder, which is an inert substance with a density of 4.5g/cm3. It is the heaviest in the body pigment and has stable chemical properties. It is almost insoluble in water, ethanol and acid. Less impurity content is glass luster, cleavage surface is pearl luster. The oil absorption of barite powder is very low (6g/100g). Precipitated barium sulfate has a superior color and fine particles.
Barite powder fillers are mainly used for industrial primers and automotive intermediate coatings that require high film strength, high filling force and high chemical inertness, and are also used in topcoats that require higher gloss. In latex paint, due to the high refractive index of barite (1.637), fine barite powder can have the function of translucent white pigment, can replace part of titanium dioxide in the coating.
Wollastonite is mainly composed of calcium metasilicate (CaSiO3), which has a needle-like structure, good brightness, refractive index (1.62) and relatively low oil absorption (20-26g/100g).
Wollastonite in the paint can be used as a body pigment and instead of part of the white pigment, cover, incremental role, reduce the cost of paint. Keep the white paint bright for a long time.
Needle-like structure of wollastonite (aspect ratio of 10:1~20:1), in the coating can play the role of flat agent, improve the mechanical strength of the coating film, sometimes in the reinforced coating instead of harmful asbestos. Generally, more fine grade (such as 325 mesh) and fine grade (10um) wollastonite powder are used in coatings, because it is beneficial to the hiding power of coatings. Can be used for oily architectural coatings, sound absorption (sound insulation) coatings, road marking paint, polyvinyl acetate latex paint, etc. The surface-treated wollastonite can be used in industrial alkyd, epoxy and other anti-corrosion coatings to improve the corrosion resistance of metal primers and partially replace active anti-rust pigments.
The main application of muscovite coatings, but also a small amount of application of phlogopite. The main use of its high diameter to thickness ratio of the sheet structure, good heat resistance, weather resistance, transparency, chemical resistance, UV shielding and other properties, in anti-corrosion coatings, functional coatings as a filler. It is mainly used in some special oil-based and water-based coatings in coating formulations, and its dosage ranges from about 20% of industrial coatings to about 40% of embossed architectural coatings.
An important application area of wet ground mica powder is used as a carrier raw material for titanium pearlescent pigments. Coatings, inks, plastics and other industries require different specifications of the series of mica titanium pearlescent pigments.
Natural graphite can be used in steel structure maintenance coatings because of its flake structure and good hiding rate. Its good conductivity and black color make it can be used in electronic computer electric shielding coatings, which can contain up to 75% graphite. Another use is anti-static floor coatings. It can be used in heat-resistant coatings, primers, sealing coatings and water-resistant coatings. Due to its good light resistance, it can be used in automobile paints as an effect pigment.
The market capacity of China's coatings is promising, and the strong demand in the downstream maintains the growth momentum of the coatings industry.Calcium carbonate is the most important filler for coating (body pigment), to create a domestic hundreds of billions of calcium powder market we work together!