Water-based anti-rust is a new type of decoration material. As you can see from the literal meaning, it is a material that does not react with rust, and it is also non-toxic and odorless, which greatly guarantees improve people's health. There may be many friends who don’t know much about it. Let me introduce its composition and categories below, so that we can increase our knowledge together.
Composition of water-based rust-resistant anti-rust coating
1. Selection of resin
Select according to the performance and compatibility of the resin, because alkyd resin is only suitable for ordinary It matches the topcoat made with solvents (gasoline, ethanol, etc.), while the shelf life of phenolic resin is short, making it inconvenient to produce and apply. Therefore, the film-forming substances currently widely used in water-based rust-resistant coatings mainly include epoxy resin, polyurethane resin, acrylic resin and styrene-acrylic emulsion.
2. Selection of pigments
Studies have shown that rust on the surface of steel is generally composed of two layers of rust. The looser one on the outside is fibrous rust, the inner one is denser and is magnetic rust. If the magnet rust continues to lose electrons, it will become the outer layer of fibrous rust. Therefore, to prevent corrosion from continuing, it is only necessary to prevent the gain and loss of electrons, or reduce the potential difference of metal corrosion. Adding reactive pigments to coatings can improve the anti-corrosion properties of coatings. Commonly used anti-rust pigments include phosphate, ZnO, talc, barium sulfate, etc. Since phosphate base resins have a wide selection range and many varieties, phosphate anti-rust pigments are used the most and have the best anti-rust effect. The main purpose is to use the strong reducing properties of these pigments to reduce the potential of rust and reduce it to an alkali iron structure that is more stable than the steel base material.
3 Selection of conversion agent
The main function of the conversion agent is to react with rust, enhance the conversion rate of rust in the coating, and convert the rust with positive surface potential of the steel into complex It inhibits rust from further corroding the steel foundation, thus improving the anti-corrosion ability. Traditional coatings that use red lead systems and chromium-containing systems as conversion agents are highly toxic and are no longer suitable for the development needs of today's society due to environmental considerations. Currently, most commonly used conversion agents use tannin-phosphoric acid. Tannin-phosphate rust converting agent has the advantages of low toxicity and regenerable tannins. In the presence of phosphoric acid, tannic acid easily reacts with Fe3 on the steel surface and in the rust layer to form a stable complex. Tridecylhydroxyphenol tannin derivatives can complex with iron at multiple points to form a protective film with a network structure, which is firmly adsorbed on the surface of steel. The effect of tannic acid-phosphate rust converting agent depends on the type of tannic acid, tannic acid concentration, phosphoric acid concentration, steel rust conditions, reaction time between rust and converting agent, the influence of other additives and the method of use.
Classification and anti-corrosion mechanism of water-based rust-bearing anti-rust coatings
Water-based rust-bearing anti-rust paints can be divided into: stable type, transformation type, penetrating type and functional type.
1. Stable water-based rust-resistant anti-rust coating
The anti-rust principle of stable water-based anti-rust coating is to utilize the reactive groups of the base resin itself in the paint and the A solid-phase reaction occurs between the added active anti-rust pigment and the rust layer. This reaction generates a stable polyacid complex in the coating, thereby stabilizing the rust and making the rust layer become one of the filler components of the coating. one. At present, the typical active anti-rust pigments used in stable rust-bearing anti-rust coatings are chromates, phosphates, ferrites, etc. The hydrolysis of active pigments can produce acid ions, which can react with the active rust acid in the rust layer to form complexes, which stabilize the rust, deactivate the rust, and prevent the steel from continuing to corrode. Depending on the amount of anti-rust pigment added, water-based rust-resistant anti-rust coatings suitable for a wide range of rust conditions on steel surfaces and with a wide range of applications can be prepared.
2. Transformation water-based rust-proof paint
Transformation water-based rust-proof paint can also be called reactive rust-proof paint. The paint contains a kind of material that can react with rust. A conversion agent for chemical reactions. This substance can convert rust in corrosion products into complexes or chelates that have a certain protective effect on the substrate. Common ones include phosphoric acid, potassium ferrocyanide, salicylic acid, etc.
The conversion-type water-based rust-resistant anti-rust coating contains organic acids, inorganic acids and other conversion agents, which react quickly with rust. Therefore, it can be applied to steel surfaces with a rust layer thickness of (40~100μm), and is suitable for A steel surface with a uniform rust layer and no old coating film and residual oxide scale. The disadvantage of this coating is that it is difficult to accurately determine the relationship between the thickness and uniformity of the rust layer and the amount of conversion liquid. If the conversion liquid is insufficient, the rust cannot be completely converted; if the conversion liquid is used too much, the residual acid will affect the anti-corrosion performance.
3. Penetrating water-based rust-proof anti-rust coating
Penetrating water-based rust-proof anti-rust paint itself does not react with rust, but by selecting a resin with strong permeability As the base resin of the paint, and with the help of penetrants and polar solvents, the paint has good permeability in the rust layer, thereby surrounding the loose rust and separating it from the base material. It effectively isolates the protected substrate and the corrosion product (rust) from the external corrosive medium, making the rust inactive. At the same time, it enhances the adhesion between the rust layer, coating and steel plate, thereby preventing the rust with a positive potential from further An electrochemical reaction occurs with steel with a relatively negative potential to generate new rust. The disadvantages of this coating are its high cost and difficulty in large-scale promotion, so it is rarely used.
4. Functional water-based rust-resistant anti-rust coating
Functional water-based rust-resistant anti-rust coating combines the same characteristics of stable, conversion and penetrating coatings. At the same time, the base resin is improved so that the base material can react with water, which can neutralize the remaining moisture in the rust layer, effectively remove the moisture in the rust layer, and enhance the anti-corrosion performance. Some functional water-based rust-proof coatings have the function of oil-based coating, and they still have strong anti-corrosion properties when the surface of the substrate is not completely deoiled. Mainly based on the fact that oil molecules are basically alkanes, the principle of miscibility is used to emulsify the oil molecules with the base materials and additives in the paint, thereby peeling off the oil molecules from the base material and integrating them into the paint as additives. Plasticizers are present.
The above is an introduction to the composition and classification of water-based rust-resistant anti-rust coatings. From the article, you can know that it is composed of resin, color and conversion agent, and its categories are mainly divided into four categories, namely stable type , transformation type, penetration type and functional type. The basic information about each type is also introduced in detail in this article. You can go to the above to learn more. I hope it will be of reference value to you.