Introduction to the types and functions of coating materials

The whiteness should be high, especially in the coatings with high requirements for the color of the coating film, the whiteness is generally required to be above 90%;

Easy to disperse, which not only helps to reduce the energy consumption and time of grinding and dispersing in the production of coatings, but more importantly, it is conducive to the performance of the coatings.
Etc.
) have a direct impact;

Only low oil absorption and low oil absorption value can increase the critical pigment volume concentration (CPVC) of the coating, save resin base material, and meet the requirements of modern high-solid coatings that meet environmental protection requirements.
Dispersed filler slurry can be matched with pigments (especially titanium dioxide) whose oil absorption value is decreasing day by day.
The oil absorption value of non-metallic mineral fillers commonly used in coatings is shown in Table 1;

There should be a certain particle size and a narrow particle size distribution, and the sieve residue should be as low as possible.
Nowadays, coatings require fillers to have micronized or even ultra-fine particle sizes in many applications, so that it can take advantage of its spatial separation in the coating.
It can make the pigment particles in the coating evenly distributed, so as to maximize the potential of pigments for covering (such as titanium dioxide), coloring (such as color pigments) and anti-rust (such as anti-rust pigments), and play a part of replacing pigments.
effect;

It can make the coating have good rheological properties (fluidity, leveling, suspension, thickening, etc.
), so that the coating does not precipitate during storage, facilitates construction and film formation, and forms a smooth and flat coating film;

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 to a certain extent and not chemically react with the above components;

It has a suitable specific surface area, because it affects the viscosity, rheology, dispersion stability, sedimentation and oil absorption of the coating;

It has a definite particle shape and crystal morphology, so that the coating has a definite refractive index and other optical properties and guarantees the proper function of the filler in the coating.

Types of fillers commonly used in coatings

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

Calcium carbonate

Calcium carbonate is the most important filler (extender pigment) for coatings.

Classification of calcium carbonate for coatings

According to the characteristics of calcium carbonate for coatings, it is mainly divided into 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 activated calcium carbonate; heavy calcium carbonate (natural product) is divided into heavy calcium carbonate, heavy fine calcium carbonate, and heavy calcium carbonate.
Active calcium carbonate.

Precipitating calcium carbonate according to the crystalline form changes the process and controls the crystallization to obtain cubic crystals, needle crystals, spindle crystals, chain crystals and other fine calcium carbonate crystals.

Classification by crystal particle size Precipitated calcium carbonate can be divided into: fine calcium carbonate (average particle size 44～60um); medium calcium carbonate (average particle size 15～44um); fine calcium carbonate (average particle size 1～15um) ); Superfine calcium carbonate (0.
1～1um); Superfine calcium carbonate (<0.
1um).

Heavy calcium carbonate products are classified into single fly powder (200 mesh fineness), double fly powder (325 mesh fineness) and Sifei powder (400 mesh fineness) according to the powder fineness.
Calcium carbonate (1250 mesh fineness).

Application of calcium carbonate in coatings

Calcium carbonate is an important filler in paint production.
Calcium carbonate acts as a leveling effect for the framework 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 primers, it forms hydrogen bonds with metal surfaces to increase the adhesion of the paint film, and can absorb hydrogen ions to prevent the corrosion tendency of metal to form micro-batteries.
In addition, calcium carbonate has good weatherability, abrasion resistance, low electrolyte content, pH stabilization effect, and can improve corrosion resistance and paint rheology.
Coarse calcium carbonate is limited to putty, filling compound, metal primer and other products, which require high pigment content, fluidity and rough surface; medium calcium carbonate is used in architectural coatings and indoor matt or semi-finished products.
On light paint; fine-grained calcium carbonate is mainly precipitated calcium carbonate, which is used in printing inks.

Heavy calcium can be used in various internal and external coatings, and is most suitable for water-based coatings.
Due to poor acid resistance, it hinders its application in external coatings.
In general coatings, the amount of heavy calcium added is 10% to 35%, and the content in various relief coatings is as high as 50%.

The heavy calcium used in the coatings industry is mainly used to replace titanium dioxide (usually 10% to 20%, 30% in large quantities) and color pigments, in addition to increasing the amount, to replace light calcium and precipitated barium sulfate, to prevent corrosion and Partially replace anti-rust pigments.

When heavy calcium is used in interior architectural paint, it can be used alone or in combination with talc.
Compared with talcum powder, calcium carbonate can reduce the pulverization rate, improve the color retention of light-colored 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.
Light calcium can be used where the greatest matting effect is required.
It is more common to mix light calcium and heavy calcium in semi-gloss, dull paint and matt latex paint.

talcum powder

Talcum powder is a general-purpose filler in solvent-based coatings.
Due to the advent of finer-grained talcum powder, it has entered the water-based system.
It is currently used in various primers, intermediate coatings, road marking paints, industrial coatings and architectural coatings for internal and external use.
Due to the soft texture and low abrasiveness of talc, it has good suspension and dispersibility, so the proportion of talc filler consumed in my country's coating industry is relatively large.

The talc with flaky structure has excellent paintability, fluidity and smoothness of the coating film, water resistance and impermeability of enamel beads.
It is mainly used for primer and intermediate coatings.
Fibrous talc has higher oil absorption and good rheology, which can improve many properties of the coating, such as preventing sedimentation during storage and sagging during painting, and improving construction performance.

There are many grades of talc powder used in the coating industry, such as ordinary talc powder (-325 mesh), fine talc powder (-20um and -10um), ultra-fine talc powder (-5um), chemically pretreated talc Powder, etc.
, are suitable for various specific uses and purposes.

Coarse-grained talcum powder is used in some paint films that require roughness, such as the middle layer of interior wall primer and spot paint; ultra-fine talcum powder is used to control the gloss, consistency and sag of semi-gloss enamel; fine grade In addition to improving the performance of the coating film, and ultra-fine talc powder also has space separation ability, which can partially replace TiO2 and other pigments; chemically pretreated talc can also replace TiO2 pigments.

One disadvantage of talc powder is its high oil absorption.
Therefore, when low oil absorption is required, it must be combined with fillers and barite powder with low oil absorption.
In addition, the abrasion resistance of talc is not high.
When high abrasion resistance is required, other fillers should be added to make up for it.
Talc powder containing other non-metallic minerals is not suitable for external coatings that require high weather resistance because impurity minerals are easily reacted with acids (such as acid rain).
The whiteness of industrial talc powder decreases due to the colored impurities.
Therefore, talc powder is generally not used as a filler in occasions that require high filler brightness.
Talc has matting properties, so it is generally not used in high gloss coatings.

Kaolin

Kaolin is one of the fillers widely used in foreign coatings industry.
The U.
S.
has the largest consumption, which is about 300,000 tons per year in recent years, of which calcined kaolin is more than 100,000 tons per year.

Commonly used kaolin for coatings includes ultra-fine kaolin, calcined kaolin, activated kaolin (surface modified) and so on.
Kaolin can be used in various coatings, but mainly water-based architectural coatings, especially internal latex paints.
Because kaolin has good hiding power in water-based coatings, it can partially replace titanium dioxide pigments.
Ultra-fine kaolin can partially replace titanium dioxide, about 10% of the amount of titanium dioxide, which can reduce the cost of the paint, but has little effect on the gloss, hiding power and storage stability of the paint.
The refractive index of calcined kaolin was increased from 1.
56 to 1.
62, which made up for the original lack of hiding power and whiteness.
In addition, calcined kaolin can improve the opacity of the coating and the firmness of the coating film, and it is more resistant to washing and pulverization than uncalcined clay.
Calcined kaolin has been used to replace part of titanium dioxide in highway marking paint, powder coating, and building exterior latex paint.
Ultrafine kaolin and calcined kaolin can replace 15%-20% of titanium dioxide in exterior wall coatings.
Some kaolin exhibits poor suspending properties in solvent-thinned paints, but calcined kaolin treated with surface modification can overcome these shortcomings.

Silica

Porous powdered quartz (main component SiO2)

Porous silt quartz belongs to a kind of 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.
3m2/g), and the shape and structure are similar to a spherical shape without edges.
From the electron microscope image, the surface is all nanometer-scale mesopores, with an average pore diameter of about 8.
8nm (nanometers).

The surface of porous powdered quartz 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 cohesiveness of the product.
On the other hand, due to the presence of hydroxyl, it is easier to treat the surface of the coupling agent to increase its cross-linking and reinforcing effects, and increasing the physical and mechanical properties of the product can also increase the tensile strength of the coating film.

Porous powdered quartz contains ZrO2, zirconium dioxide has stable properties and high hardness.
In addition, the porous structure of porous powdered quartz makes the coating have better hardness performance and impact resistance.

Porous powdered quartz is a kind of silica system, and its safety is recognized.
It has been widely used in powder coatings, architectural exterior wall coatings, thick brushed coatings, fireproof coatings, waterproof coatings, environmentally friendly coatings, anticorrosive coatings, etc.
, and it is cheap Porous powdered quartz can reduce the cost of powder coatings, and at the same time replace barium sulfate to reduce the content of soluble barium in the product, meeting environmental protection requirements.

Natural porous powder quartz mainly plays an increasing and semi-reinforcing role in coatings.
It can be used in various coatings and architectural coatings, especially primers and intermediate coatings.
Fine-grained crystalline SiO2 can replace up to high in epoxy and polyphenol powder coatings.
50% TiO2.

Natural porous powder quartz has a variety of different particle shapes and structural characteristics due to its porous and high-porosity structure, plus excellent oil absorption (19-25g/100g), irregular structure and oil absorption The combination of it produces very good matting effect, high thickening ability and good pigment suspension.
It is used as a matting agent in coatings.
It is mainly used in flat emulsion paints and varnishes, primers and certain concrete coatings.
It is also used as a filler in coatings to increase the hiding power of opaque pigments.

White carbon black (or light silica) can prevent pigment precipitation due to its large specific surface area and good thermal stability.
It is especially used in latex paint to adjust the effective viscosity of the paint, improve the sag of the paint film and have a matting effect.
The paint film has good heat resistance stability.

Fumed silica is a multifunctional extender pigment and a rheology control agent for coatings with excellent performance.
In liquid coatings, its rheological control functions include: thickening, thixotropy, anti-sagging, and covering the edges; in solid powder coating systems, it promotes the free flow of powder and prevents agglomeration and fluidization.

Barium sulfate

There are two types of barium sulfate used as extender pigments in paints: natural and synthetic.
The natural product is called barite powder, and the synthetic product is called precipitated barium sulfate.

The appearance of barium sulfate is a dense white powder.
It is an inert substance with a density of 4.
5g/cm3.
It is the heaviest among extender pigments and has stable chemical properties.
It is almost insoluble in water, ethanol and acid.
It is soluble in hot sulfuric acid and is alkali-resistant.
Light fast.
The less impurity content is glassy luster, and the cleavage surface is pearly luster.
The oil absorption of barite powder is extremely low (6g/100g).
Precipitated barium sulfate has superior color and fine particles.

Barite powder filler is mainly used in industrial primers and automotive intermediate coatings that require high film strength, high filling power and high chemical inertness, and also used in topcoats that require higher gloss.
In latex paint, due to the high refractive index of barite (1.
637), the fine barite powder can have the function of translucent white pigment and can replace part of the titanium dioxide in the paint.

Wollastonite

The main component of wollastonite is calcium metasilicate (CaSiO3), which has a needle-like structure, good brightness, refractive index (1.
62) and relatively low oil absorption (20～26g/100g).

Wollastonite can be used as an extender pigment in coatings and replace part of white pigments, which can cover and increase the cost of paint.
Make the white paint maintain a long-lasting bright hue.

Wollastonite with needle-like structure (length-to-diameter ratio is 10:1-20:1) can act as a flattening agent in coatings, improve the mechanical strength of the coating film, and sometimes replace harmful asbestos in reinforced coatings.
Generally, finer-grained (such as 325 mesh) and fine-grained (10um) wollastonite powder are used in coatings, because they are beneficial to the hiding power of the coating.
It can be used for oil-based architectural coatings, sound-absorbing (sound insulation) coatings, road marking paints, polyvinyl acetate latex paints, etc.
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

Muscovite is mainly used in coatings, but phlogopite can also be used in a small amount.
It mainly uses its high-diameter-thickness ratio sheet structure, good heat resistance, weather resistance, transparency, chemical resistance, UV shielding and other properties to be used as fillers in anti-corrosion coatings and functional coatings.
It is mainly used in some special oil-based and water-based coatings in coating formulations, and the addition amount ranges from about 20% for industrial coatings to about 40% for embossed architectural coatings.

An important application field of wet milled mica powder is to be used as a carrier material for titanium pearlescent pigments.
Industries such as coatings, inks, and plastics all require mica-titanium pearlescent pigments of different specifications.

graphite

Natural graphite can be used in steel structure maintenance coatings because of its flake structure and good hiding rate; its good electrical conductivity and black color enable it to be used in electronic computer electrical 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.
Because of its good light resistance, it can be used in automotive paints as an effect pigment.
(Source: Global Coatings Network) (For more information, please log in: Global Coatings Network http:// )