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Summary of application characteristics of mineral fillers in coatings

Release time:

2024-01-29 09:38

 

Summary of application characteristics of mineral fillers in coatings

 

1. Overview

Coating is a kind of liquid state or can be liquefied solid powder state or thick slurry state, can be evenly coated and can be firmly attached to the surface of the coated object, and the coated object to play a decorative role, protection and special role, or a combination of several functions of the film-forming material.

Coating products in addition to paint, but also includes the use of a variety of synthetic resin, emulsion, etc. as the main raw material production of solvent-based coatings, latex-type coatings, water-soluble coatings, powder coatings.

Inorganic fillers in coatings, also known as body pigments, are sometimes called pigment extenders, which can be divided into non-functional fillers and functional fillers. The former mainly plays an incremental role to reduce the cost of raw materials for coatings; the latter, in addition to having an incremental role, also has the function of improving certain properties of coatings or coating films, such as controlling rheology, improving adhesion, controlling gloss, improving hiding power, preventing corrosion and optimizing pigment product concentration.

2. 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) in the coating from the skeleton, filling role, increase the film thickness, so that the film plump solid;

2) Adjust 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) 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 coating can effectively block the penetration of light, improve its water resistance and weather resistance, and extend the service life of the coating;

6) As a filler in the coating, reduce the amount of resin and reduce production costs;

7) the chemical properties of the coating plays an auxiliary role, such as enhancing rust, moisture resistance, flame retardancy, etc.

8) Different coating varieties and grades have different technical requirements for fillers, but the general requirements for fillers for coatings are as follows.

9) whiteness should be high, especially in the coating film color requirements are very high, whiteness is generally required in more than 90%.

10) Easy to disperse, which is not only conducive to reducing the energy consumption and time of grinding and dispersing in the production of coatings, but more importantly, it is conducive to the performance of coatings, because the dispersion of fillers and pigments is good or bad. It has a direct impact on the performance of the coating film (gloss, color, durability, etc.).

11) It is necessary to have lower oil absorption and low oil absorption value to improve the critical pigment volume concentration (CPVC) of the coating, save the resin base material, adapt to the requirements of modern high-solid coatings that meet the requirements of environmental protection, prepare a higher content of pre-dispersed filler slurry, and match the pigments (especially titanium dioxide) with decreasing oil absorption value.

12) There should be a definite particle size and narrow particle size distribution, and the sieve residue should be as low as possible. Now the coating requires that the filler has a fine or even ultra-fine particle size in many application fields, so that it can play its space in the coating. The role of separation, so that the pigment particles in the coating are evenly distributed, so as 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.

13) can make the coating has good rheological properties (fluidity, leveling, suspension, thickening, etc.), so that the coating does not precipitate during storage, which is convenient for the construction of film formation and forms a smooth and flat coating film.

14) It should have good compatibility with the base material, pigments and other additives in the coating, but it should also 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) 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.

3. Types of fillers commonly used in coatings

The fillers commonly used in coatings are calcium carbonate (heavy calcium, light calcium), barite powder (barium sulfate), talcum powder, kaolin (porcelain land), porous powder quartz (silica), white carbon black, precipitated barium sulfate, mica powder, wollastonite, bentonite, etc.

 
Calcium carbonate
 

Calcium carbonate is the most important filler for coating (body pigment)

Classification of calcium carbonate for coatings

According to the characteristics of calcium carbonate for coating according to the characteristics of the main points of light calcium carbonate and heavy calcium carbonate. Light calcium carbonate and heavy calcium carbonate. Light calcium carbonate (precipitated calcium carbonate) is divided into ordinary precipitated calcium carbonate, fine calcium carbonate, superfine calcium carbonate and active calcium carbonate; heavy calcium carbonate (natural product) is divided into heavy calcium carbonate, heavy fine calcium carbonate and heavy active calcium carbonate.

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 the fineness of the powder. Ultrafine calcium carbonate (fineness grade 1250 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, which require high pigment content, fluidity and coarse surface. Medium grade calcium carbonate is used in architectural coatings and indoor matted or semi-gloss paint. Fine grade calcium carbonate is mainly precipitated calcium carbonate, which is used in printing ink.

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.

 

 

Talcum powder

 

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

 

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.

 

 

Silica

 

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

 

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

 

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.

 

 

Mica powder

 

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.

 

 

Graphite

 

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.

 

 

aluminum hydroxide

 

In the category of inorganic flame retardant additives, aluminum hydroxide is the largest and most widely used, it is not only good flame retardant performance, but also can prevent smoke, do not produce dripping, do not produce toxic gases, therefore, access to a wider range of applications, the use is also increasing year by year. Scope of use: thermosetting plastics, thermoplastics, synthetic rubber, coatings and building materials and other industries.

Aluminum hydroxide as an inorganic flame retardant, although it has excellent flame retardant effect, but its filling amount has a certain high standard, such a high filling amount is bound to affect the compatibility and mechanical properties of polymer and inorganic filler, resulting in the performance of flame retardant products are seriously affected. In view of the above reasons, more and more individuals or research institutions on the surface modification of aluminum hydroxide (we call it activation), activated aluminum hydroxide produced. The molecular formula of active aluminum hydroxide is AL(OH)3 or AL2O3 · 3H2O, with a molecular weight of 78, white powder, mainly containing aluminum hydroxide, coupling agent, etc.

The use of high-quality raw materials by ultrafine airflow grinding classification, coupling agent surface activation of aluminum hydroxide-activated aluminum hydroxide in essence to solve the defects of traditional aluminum hydroxide. Activated aluminum hydroxide as an additive halogen-free smoke suppressant, flame retardant, which is characterized by large addition amount, good flame retardant effect, low cost, good improvement of the arc resistance of the material, enhanced impact strength and bending strength. 2. Its surface area is increased, the fluidity is increased, the particle size distribution is uniform, the stability is good, and the corrosive gas is not produced. Good dispersion in the resin, the amount of more, less prone to bending white phenomenon. Used in plastic, not volatile, not exudation, can be retained in the plastic for a long time. It has good compatibility with many other substances.

Application range of activated aluminum hydroxide

 

The application range of activated aluminum hydroxide in the production of products has been greatly expanded, especially in recent years, the application of activated aluminum hydroxide in wire and cable has made a substantial breakthrough. The application of aluminum hydroxide in wire and cable as flame retardant filler improves the electrical performance of wire and cable more efficiently, increases the flame retardant ability of wire and cable, and achieves low pollution. Another active aluminum hydroxide used in insulation materials, flame retardant hose, tape, wind cloth, electrical materials, etc.

 

 

 

 

 

 

 

Summary, coatings, pigments, materials, calcium carbonate, fillers, used, talcum powder, action,

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