Corrosion and weather resistance of inorganic pigments
Paintwork materials must have high corrosion and weather resistance, because they are widely used in different climatic zones and are used to create coatings on a variety of objects: machinery, all kinds of equipment, buildings, etc. Paint and lacquer coatings must be highly resistant to sunlight, humidity, high and low temperatures, etc.
Pigment, like all constituents of paintwork material must be heat and light resistant, because it affects the weather resistance of the final coating (in most cases it has the main corrosion protection function).
All pigments by their effect on anticorrosive properties of the paintwork material can be divided into: neutral, inhibitor and stimulator. Stimulant pigments will only intensify the corrosion process if the integrity of the paintwork is compromised, neutral pigments will have no effect, while corrosion inhibitors will protect the surface.
All corrosion processes are divided into two types: electrochemical and chemical corrosion.
Organic pigments are less common in the paint industry than their inorganic counterparts. This is explained by the fact that organic pigments are somewhat inferior to inorganic ones in their characteristics. Pigments of organic origin have a very high intensity. Enamels and paints based on them attract with their richness, brightness and deep color. But the resistance of organic pigments to corrosion, hiding power, resistance to light and atmospheric corrosion leave much to be desired. In addition, these substances used in the paint industry are sensitive to chemicals.
Organic pigments can have a wide variety of colors, from light yellow tones to black. But the predominant colors are green, red and blue. There are very few inorganic substances that color paints and enamels in bright colors, or they are quite expensive and not readily available. Thanks to bright organic pigments, a wider range of colors is available on the paint market. In chemical terms, organic pigments are almost indistinguishable from organic dyes, but most dyes can be dissolved in many liquids. Pigments are insoluble at the same time.
The main property of an organic pigment is its color. Unlike dyes, they are used in the form of powders consisting of very fine particles. And the color of this powder is very much influenced by the shape of the primary particles, their structure and size, in principle, the dependence of the color on these properties, as in the inorganic pigments.
In the paint industry, organic pigments can be used to impart color to synthetic enamels, water-emulsion oil compositions and adhesive-based paints.
Sometimes organic substances are preferred. For example, iron oxide red pigments have little saturation and brightness and are often replaced with organic ones. Lead crowns (yellow) are known to be toxic and are not suitable for the production of interior paintwork materials, so they are replaced by safer materials. Very often organic pigments are additives to inorganic pigments. This is necessary to increase the saturation and brightness of paints.
By technical classification organic pigments are divided into two groups: pigment varnishes and pigments themselves. Pigment varnishes are subdivided into: derived from basic, mordant and acid dyes.
Classify substances of this type and by chemical structure. The commonness of chromomorphic systems is taken into account. Arylmethane, azo compounds, phthalocyanine, anthraquinone, polycyclic, nitroso- and nitro compounds are known.
In the paint industry the following compounds are widely used: anthraquinone, phthalocyanine, azo pigments and pigmented varnishes.