Briefly describe the use skills of aluminum paste
As a metal pigment, aluminum paste can produce special effects that are different from other ordinary pigments. It is different from other ordinary pigments in the formulation of coatings, coating production methods, and construction methods during use.
1. Arrangement and orientation of aluminum sheet:
The best effect is achieved when the flake pigment is oriented parallel to the surface of the coating film. Poor parallel orientation can cause "turbidity" or diffuse reflection. The orientation of flake pigments is related to the formulation and construction conditions. The volatilization of the solvent causes the shrinkage of the wet coating film, and finally presses the aluminum pigment into a horizontally oriented position. The stronger this effect, the better the arrangement effect. Therefore, the more fast-evaporating strong solvent in the coating formulation, the greater the solid content during construction. Low, the better the effect, but it is necessary to ensure that the coating film just sprayed is just slightly moist and smooth. The higher the solvent content in the coating, the stronger this effect. This explains the orientation phenomenon of flake pigments. Therefore, the optical properties of low solids coatings are better than high solids coatings. The volatilization of the solvent will cause a strong vortex inside the wet film, but if the solvent volatilizes too slowly, a so-called Bernard vortex will be formed, which will cause the aluminum sheets to roll up and down with the Bernard vortex, flowing randomly and arranging chaotically, as a result The coating film is black and white, with large spots. Obstruct the parallel orientation of aluminum pigments. Resins can be used to promote the rapid volatilization of solvents (such as butyl cellulose CAB), and some additives are also used. They can fix flake pigments. There are reports in the literature that wax dispersions can have a "spacing effect", and surfactants also have a similar function. But the function should be tested before use.
2. Pigment dispersion:
The aluminum paste contains a certain amount of slow volatile mineral oil, additives, etc. to ensure its good storage stability and dispersibility. Therefore, the storage of the aluminum paste requires a good airtight, otherwise it will cause air drying and oxidation for a long time in contact with the air. Lead to poor dispersion, paint film particles, black and coarse. Under normal circumstances, the intact airtight packaging can be stored for more than one year. In order to achieve satisfactory special effects, the metallic pigment must be completely dispersed in the coating system, and the coating should be in a uniform state without fine particles. Aluminum flakes are easy to bend and break. If high-speed stirring or other continuous and intensive processing are carried out during the paint production process, its geometric structure is easily destroyed, resulting in coarse particles, dark colors, reduced coverage, and metal migration. Therefore, high-shear dispersing means should not be used. Suggestion: adopt the pre-dispersion method; first select an appropriate solvent or a mixture of several solvents, add the solvent to the aluminum paste at a ratio of 1:1 or 1:2, and stir slowly until uniform (about 10-20min). Add wetting or dispersing agent to the system. In general production, the aluminum paste is soaked in a solvent for a few hours before stirring.
3. Choice of solvent:
The choice of solvent is mainly determined by the paint material determined by the formula. Non-leafing aluminum pastes can be widely used in polar and non-polar solvents, such as aliphatic or aromatic hydrocarbons, esters (such as butyl acetate), ketones (such as methyl ethyl ketone, methyl isobutyl ketone), alcohols (such as Ethanol), ether alcohols, of which esters have the best effect. Moisture will react with aluminum to generate hydrogen and cause a sounding effect. Therefore, the moisture in the coating should be strictly controlled below 0.15%. It is recommended to use a dehydrating agent to remove excessive moisture in the coating solvent or thinner. Chlorine-containing solvents (halogenated hydrocarbons...) are not suitable for any aluminum paste pigments. Chlorinated solvents will release HCI and chemically react with the fine aluminum pigments.
4. Resin system:
Many commonly used paint base materials such as oily varnish base materials, acrylate, alkyd, epoxy, polyurethane.