Talk about the technical application of water-based rust-turned-rust coating (I)

In order to slow corrosion, the most effective, simple and economical way is to paint anti-corrosion coatings on steel surfaces. In order to obtain excellent corrosion resistance, rust on the substrate must be removed before painting. Because rust is a loose, porous, constantly producing (expanding) substance, if not all in the cast iron surface painting will lead to poor corrosion protection of the paint film, so the surface treatment of cast iron is essential for anti-corrosion coatings
But in practical application will also encounter some can not completely remove rust or simply can not remove rust scenes, such as large building facades, bridges, complex structure of equipment, gas cabinets and other steel structures in the maintenance process, due to construction conditions, can not be used sand blasting or blasting pills and other methods of rust removal, but only with manual or power tools rust removal, the result will inevitably remain rust and a variety of corrosive residues, even if the use of expensive, high-performance anti-rust paint is difficult to play a role. There are also restrictions by construction conditions, such as climate, humidity and other external factors, so that conventional anti-corrosion, anti-rust coatings simply can not be used.
the rust removal process takes up a longer process throughout the coating process. Rusty paint in addition to rusty steel surface can be directly constructed, and can play the role of general primer and so on, but also has a good brushing, easy to construct, can be directly on the zinc or galvanized layer of the characteristics of construction. It can save manpower, working hours, equipment and funds, and help to improve the labor productivity of coating operations. Therefore, it is particularly necessary to develop a coating that requires a relatively wide range of requirements. Chemical anti-rust coatings are usually divided into general chemical anti-rust coatings, pre-coated primers and rust-striped coatings three categories. General chemical anti-rust paint according to the use of chemical rust-proof pigments, usually divided into five categories, namely red Dan rust-proof primer, zinc yellow rust-proof primer, phosphate-chromate anti-rust primer, boric acid anti-rust primer and organic acid anti-rust primer.
1. Stable rust coating
This type of stable rust action principle is mainly the use of active rust-proof pigments, rust-stabilizing agent in the coating of the slow hydrolyzing resulting in the distribution of anions and lively rust to form insoluble complex polyic acid complex, in order to achieve the purpose of stable rust. Commonly used active rust-proof pigments and rust stabilizers are phosphate, ferric acid (thorium, palladium, calcium, magnesium) salt, chromic acid (zinc, vanadium, calcium) salt, organic nitrogen base (e.g. diphenyl chromate, chromate, etc.). In rusty coatings, due to differences in raw materials and ratios, there are also differences in the stabilizing effect of rust. As a result, a wide variety of multi-performance products can be produced for use on steel surfaces with varying degrees of rust to meet different requirements. According to the different raw materials used, the representative varieties of stable rust coatings are nitrogen-containing organic alkali, R-damine acetone and other stable rust coatings as stabilizers. Stable rust coating does not contain organic, inorganic acid and other conversion agents, the role of rust is small, so that the rate of rust stability is slow, only suitable for the rust layer thin (generally less than 50 m, better within 30 m) steel surface use. Because it does not contain acids and other conversion agents, the steel surface conditions for coating are widely treated and widely applicable. In the rust is not uniform, residual solid oxidation skin or old coated steel surface can be coated, rust-free steel surface also has a good anti-rust effect.
2. Permeable rust coatings
these coatings are used to separate and surround the rust by the wetting and permeation of loose rust by the paint material. It contains neither stable rust nor conversion agent, and has little chemical effect on rust, so it is mainly suitable for steel surface construction with longer rust and less chemical pollution, especially for some riveting or bolting parts of steel structure. Zinc phosphate and zinc chromate hydrolyzed to produce insoluble mixed polychloride complexes with rust reactions, thus stabilizing the rust, while it can also react with organic ammonia (e.g. chromate, chromate diphenyls, etc.) to form more insoluble complex polyacid complexes; Medium to add the appropriate amount of zinc oxide, its hydrolyzed zinc hydroxide energy and acidic rust reaction to form a stable structure similar to trioxide iron, in the iron-red strip rust coating with alumina instead of 70% to 80% iron-red, because alumina is a stable sharpstone structure, so it has a good protective effect on steel. All these methods can effectively improve the rust-proof performance of solvent-based stable rust coatings.
Above these 2 types of rust coating because can not convert rust, so can only play the role of closed rust, if the rust remaining moisture or paint film on the water vapor and oxygen barrier performance is not ideal, this will not be able to ensure that the paint film has long-lasting protection characteristics.
3. Transformed rust coating
also known as reaction-type rust coating, in addition to containing the composition of the general coating, but also contains a chemical reaction with rust to make harmful rust into harmless or has a certain protective effect of the compound or chelate. This substance, which reacts with rust, is called a converter (e.g. phosphoric acid, potassium iron cyanide or tantacit acid, salyan acid, etc.). Conversion rust coating because it contains machine, inorganic acid and other conversion agents, the role of rust is fast, can be in the rust layer thick (40 to 100 m) of steel surface construction, suitable for corrosion is more uniform and no residual oxidizing skin and flaky thick rust of steel surface. The old coating film should be removed when repairing the re-painting. However, due to the relationship between rust layer thickness and uniformity and the quantity of conversion fluid is difficult to determine accurately, the amount of conversion fluid is insufficient, the conversion of rust is incomplete, the amount of excess residual acid, will affect the anti-corrosion performance.
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