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Performance requirements, types and functions of fillers for coatings
Source: | Author:kesikeen | Published time: 273 days ago | 262 Views | Share:
Fillers (extenders) in coatings, usually white or slightly colored, with a refractive index of less than 1.7. It has the basic physical and chemical properties of paint pigments, but because the refractive index is similar to that of film-forming substances, it is transparent in paint and does not have the tinting strength and covering ability of color pigments. It is an indispensable pigment in paint.

Fillers (extenders) in coatings, usually white or slightly colored, with a refractive index of less than 1.7. It has the basic physical and chemical properties of paint pigments, but because the refractive index is similar to that of film-forming substances, it is transparent in paint and does not have the tinting strength and covering ability of color pigments. It is an indispensable pigment in paint. 

Since most of the fillers come from natural ore processed products, they have good chemical stability, wear resistance, water resistance, etc., and are cheap, and play a skeleton role in coatings. By filling to increase the thickness of the coating film, improve the mechanical properties of the coating film, and can play the role of durability, anti-corrosion, heat insulation, extinction and so on.

On the other hand, it is used as a way to reduce the cost of paint manufacturing. Using its cheap and far lower price than color pigments, on the premise of satisfying the covering power of the paint film, it is appropriate to add extender pigments to supplement the color pigments in the paint. some volume.

Main role and function

1. Play the role of skeleton and filling in the paint, increase the thickness of the paint film, and make the paint film plump and firm;

2. Adjust the rheological properties of coatings, such as thickening, anti-settling, etc.;

3. Improve the mechanical strength of the paint film, such as improving wear resistance and durability (such as: silicon powder);

4. Adjust the optical properties of the coating and change the appearance of the coating film, such as extinction, etc.;

5. The chemical reaction of the film-forming substances makes it a whole, so that the coating film can effectively block the penetration of light, improve its water resistance and weather resistance, and prolong the service life of the coating film;

6. As the volume filling in the coating, reduce the amount of resin and reduce the production cost;

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

Performance requirements

Different types and grades of coatings have different technical requirements for fillers, but the general requirements for fillers for coatings are as follows.

1. High whiteness, especially in coatings with high requirements on the color of the coating film, the whiteness is generally required to be above 93%.

2. 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, and the performance of the coating film (gloss, color, durability, etc.) have a direct impact.

3. To have low oil absorption, low oil absorption value can increase the critical pigment volume concentration (CPVC) of the coating, save the resin base material, can meet the requirements of modern high-solid coatings that meet environmental protection requirements, and can prepare higher content The pre-dispersed filler paste can be matched with the pigments (especially titanium dioxide and whitening powder) whose oil absorption value is decreasing day by day. The oil absorption value of non-metallic mineral fillers commonly used in coatings.

4. There should be a definite particle size and a narrow particle size distribution, and the sieve residue should be as low as possible. Now coatings require fillers to have a fine or even ultra-fine particle size in many application fields, so as to give full play to its space in the coating. The space separation effect makes the pigment particles in the coating film evenly distributed, so as to maximize the potential of pigment covering (such as titanium dioxide, whitening powder), coloring (such as color pigments) and rust prevention (such as anti-rust pigments) , play a role in partial replacement of pigments.

5. It can make the coating have good rheology (fluidity, leveling, suspension, thickening, etc.), so that the coating does not precipitate during storage, which is convenient for construction to form a film and form a smooth and smooth coating film.

6. 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 it should not react chemically with the above components.

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 form, so that the coating has a definite refractive index and other optical properties and ensures the due function of the filler in the coating.

The role of fillers in coatings

1. Calcium carbonate

There are two types of calcium carbonate, natural and synthetic (precipitation method), and the particle size range is very wide, 0.05-44 μm can be applied. Natural calcium carbonate is used in large quantities and is quite suitable in some applications because of its low price.

The coarser grades are limited to use in putty, caulking, primers for metals and other high-pigment products that require flow and rough surfaces. Coarse particle size calcium carbonate has very low extinction ability. Medium particle size varieties are mainly used in interior flat and semi-gloss coatings and housing coatings. The fine-grained varieties are mostly produced by the precipitation method and are used in printing inks. Usually two particle sizes of calcium carbonate are used in combination to achieve a balance of properties.

Natural calcium carbonate fillers are also widely used in outdoor housing coatings, either alone or in combination with talc. Compared with talc, natural calcium carbonate can reduce the pulverization rate, improve color retention, and improve anti-fouling performance.

2. Organic bentonite

Organobentonite is an inorganic mineral/organic ammonium compound, which uses bentonite as raw material and utilizes the lamellar structure of montmorillonite in bentonite and its ability to swell and disperse into colloidal clay in water or organic solvents. Made with technical insertion of organic covering agents. Organobentonite can form gel in various organic solvents, oils and liquid resins, and has good thickening, thixotropy, suspension stability, high temperature stability, lubricity, film-forming, water resistance and chemical stability , has important application value in the coating industry.

3. Talc

The main component of talc is magnesium silicate containing water, and the molecular formula is Mg3[Si4O10](OH)2. Talc belongs to the monoclinic system. Crystals are pseudo-hexagonal or rhombic flakes, occasionally. Usually into dense massive, leaf-like, radial, fibrous aggregates. It is colorless, transparent or white, but appears light green, light yellow, light brown or even light red due to a small amount of impurities; the cleavage surface is pearly.

Talc has excellent physical and chemical properties such as lubricity, fire resistance, acid resistance, insulation, high melting point, chemical inactivity, good covering power, softness, good gloss, and strong adsorption. So it has the tendency to easily split into scales and special lubricity.

Talc powder has good suspension and easy dispersibility, and low corrosiveness. In coatings, talc powder can act as a filler as a skeleton, which can reduce the manufacturing cost and improve the hardness of the paint film of the coating. It also has the characteristics of improving the stability of product shape, increasing tensile strength, shear strength and pressure strength, reducing deformation, elongation rate, thermal expansion coefficient, high whiteness, and uniform particle size dispersion. The talc powder with flaky particle structure can make the coating film have high water resistance and enamel impermeability. Weatherability of coatings.

Talc powder is mainly used in primers and intermediate coatings, and talc powder is preferred for many products and flash-bake primers and paints for transportation vehicles. The primer for steel structure can use talc powder in whole or in part to improve the precipitation of the coating, the mechanical strength of the coating film and the recoatability.

4. Wollastonite powder

The chemical formula of wollastonite is CaSiO3, and the theoretical chemical composition is: CaO48.25%, SiO251.75%. Pure wollastonite is rare in nature. During its formation, Ca is sometimes partially replaced by Fe, Mn, Ti, Sr and other ions to form an isomorphic body, and is mixed with a small amount of Al and a small amount of K and Na.

In the coating industry, wollastonite powder is used as a filler for paints and coatings, which can improve the physical and chemical properties of products, durable weather resistance, reduce the gloss of paints, enhance the expansion ability of coatings, reduce cracks, and can also reduce oil absorption and enhance Corrosion resistance. Wollastonite has bright color and high reflectivity, and is suitable for producing high-quality white paint and clear and transparent colored paint. Acicular wollastonite powder has good flatness, high color coverage and uniform distribution, and has the characteristics of anti-ultraviolet. It is widely used in interior wall coatings, exterior wall coatings, special coatings and latex paints. The particle size is ultra-fine, the whiteness and PH value are higher, the paint color and coatability are better, and the paint is alkaline and can be used as an anti-corrosion coating for metal equipment such as steel.

5. Ash calcium powder

Ash calcium powder is an air-hardening cementitious material, which can be used in architectural coatings to improve the water resistance and scrub resistance of coatings. Because lime-calcium powder can endow coatings with excellent properties at a lower cost, in recent years, people have applied lime-calcium powder to synthetic resin emulsion coatings according to the new requirements of national standards, so that the coatings can meet GB requirements at a lower cost. /T 9756-2001 and GB 18582-2001 requirements, and the state of the paint in the container, the leveling and the feel of the coating film are all good. Therefore, under the new requirements, ash calcium powder still has application value. However, the possibility of yellowing of the coating film still exists when the lime-calcium powder coating is applied to the old coating film, so the effect of the lime-calcium powder should not be exaggerated, but it can only be used for medium and low-grade interior wall coatings.

6. Mica powder

Mica powder is a kind of non-metallic mineral, which contains a variety of components, mainly including SiO2, the content is generally about 49%, and the content of Al2O3 is about 30%. Mica powder has good elasticity and toughness. Insulation, high temperature resistance, acid and alkali resistance, corrosion resistance, strong adhesion and other characteristics, is an excellent additive.

The application of mica powder in coatings is mainly reflected in the following aspects:

1) Barrier effect: The flake fillers form a substantially parallel orientation in the paint film, and the penetration of water and other corrosive substances into the paint film is strongly blocked. 50 times, preferably more than 70 times), the penetration time of water and other corrosive substances through the paint film is generally extended by 3 times. Since the sericite powder filler is much cheaper than the special resin, it has very high technical value and economic value. The use of high-quality sericite powder is an important means to improve the quality and performance of anti-corrosion coatings and exterior wall coatings. During the coating process, the sericite wafers lie down under the action of surface tension before the paint film is cured, and automatically form a structure that is parallel to each other and to the surface of the paint film. In such a layer-by-layer arrangement, its orientation is just perpendicular to the direction in which the corrosive substances penetrate the paint film, and the barrier effect is most fully exerted.

2) Improve the physical and mechanical properties of the paint film: The use of sericite powder can improve a series of physical and mechanical properties of the paint film. The key is the morphological characteristics of the filler, that is, the diameter-thickness ratio of the flaky filler and the aspect ratio of the fibrous filler. The granular filler is like the sand in the concrete, which plays a reinforcing role in the reinforcement.

3) Improve the anti-wear performance of the paint film: the hardness of the resin itself is limited, and the strength of many fillers is not high (such as talc). On the contrary, sericite is one of the components of granite, which is very hard and mechanically strong. Therefore, adding sericite powder as a filler in the coating can significantly improve its anti-wear performance. Car coatings, road coatings, mechanical anti-corrosion coatings, and wall coatings mostly use sericite powder.

4) Insulation performance: sericite has extremely high resistance and is the most excellent insulating material in itself. It forms a compound with silicone resin or silicone boron resin, and when it encounters high temperature, it is converted into a ceramic substance with good mechanical strength and insulating properties. , still maintain the original insulation state. Very important for mines, tunnels, special buildings, special facilities, etc.

5) Flame retardant: sericite powder is a valuable flame retardant filler. If combined with organic halogen flame retardant, flame retardant and fire retardant coatings can be obtained.

6) Anti-ultraviolet and infrared performance: sericite has excellent performance of shielding ultraviolet and infrared rays. Therefore, adding wet sericite powder to outdoor coatings can greatly improve the UV resistance of the paint film and delay the aging of the paint film. Its infrared shielding properties are used to formulate thermal insulation and thermal insulation materials (such as coatings).

7) Thermal radiation and high temperature coating: sericite has good infrared radiation ability, such as cooperating with iron oxide, it can cause excellent thermal radiation effect.

8) Sound insulation and shock absorption: sericite can significantly change a series of physical moduli of the material, forming or changing the viscoelasticity of the material. These materials efficiently absorb vibrational energy and attenuate shock and sound waves. In addition, shock waves and sound waves are repeatedly reflected between the mica wafers, which also reduces their energy. Sericite powder is also used to formulate sound-deadening, sound-insulating, and shock-absorbing coatings.

7. Calcined kaolin

Calcined kaolin has the characteristics of high whiteness, strong covering power, bright gloss, fine particle size, fast adsorption speed, excellent acid and alkali resistance, moderate oil absorption, stable physical and chemical properties, etc. It is a new type of plastic additive, non-toxic and tasteless. It is an environmentally friendly functional filler, which can directly reduce product cost by replacing part of titanium dioxide and all lithopone. Properties: plasticity, adhesion, dispersion, insulation, sintering, flame retardancy, fire resistance, adsorption, weather resistance, chemical stability.

8. Silica

The appearance of silica (silica) is white ultrafine powder, non-toxic, tasteless and odorless; silica (silica) has strong hygroscopicity, good electrical and thermal insulation properties, and can be heated under heating conditions. Does not decompose, except for hydrofluoric acid, insoluble in common acid, alkali and salt solutions.

Silica (white carbon black) is a multi-purpose chemical material, mainly used as a reinforcing agent for silicone rubber; silica (white carbon black) has strict particle size distribution, and has good matting properties and Thickening performance, used in paint, putty, as thickener, thixotropic agent, as anti-sticking agent in thin films and powdery materials, etc. It can partially or completely replace expensive fumed silica.

Untreated fumed silica (silica) is a general-purpose product of fumed silica, which can be used in coatings and inks to perform the following important functions. In liquid, rheological control, anti-settling; in powder, free flow, preventing caking and fluidization.

9. Barium sulfate (barite powder)

Barium sulfate (barite powder) is an environmentally friendly material with strong chemical inertness, good stability, acid and alkali resistance, moderate hardness, high specific gravity, high whiteness, and can absorb harmful rays. It is widely used in various coatings, medium and high-grade inks, Pharmaceutical synthetic chemicals, rubber, paper, ceramics, cosmetics and other fields.

Refined barium sulfate is widely used in various coatings (water-based, oil-based and powder coatings), inks, papermaking, engineering plastics, high-grade electrical insulating plastics, rubber products, etc. Barium sulfate can be used as a white paint, and can also be used as a filler for rubber and paper making, which can increase its weight and smoothness. Precipitated barium sulfate is used as filler, brightener and weighting agent in rubber, plastic, paper, paint, ink, coating and other industries.

10. Silicon powder

Silica micropowder is a non-toxic, odorless, non-polluting inorganic non-metallic material. , jet mill), flotation, pickling purification, high-purity water treatment and other multi-channel processing of micropowder. Because silicon micropowder has excellent properties such as good temperature resistance, acid and alkali corrosion resistance, high insulation, low expansion, stable chemical properties, and high hardness, it is widely used in chemical industry, electronics, integrated circuits (IC), electrical appliances, plastics, coatings , advanced paint, rubber, national defense and other fields. In the paint and paint industry, silicon micropowder has the characteristics of fine particle size, high hardness, good suspension and dispersibility, low oil absorption, and high resistivity. Corrosion resistance, wear resistance, insulation and high temperature resistance.