Anti-corrosion coating, generally divided into conventional anti-corrosion coating and heavy anti-corrosion coating, is an essential coating in paint coatings. Conventional anticorrosive coating is used to prevent corrosion of metals and protect the service life of non-ferrous metals under general conditions; Heavy-duty anti-corrosion coating refers to a kind of anti-corrosion coating that can be applied in relatively harsh corrosive environment and has a longer protection period than conventional anti-corrosion coating.

With the development of social economy, important buildings, such as television towers, bridges, commercial buildings, as well as offshore platforms, port machinery and petrochemical industries, have increasingly high requirements for high durability coatings. From traditional alkyd, chlorinated rubber and other coatings to zinc-rich, epoxy, aliphatic polyurethane, fluorocarbon, polysiloxane and other anti-corrosion coating products.

In addition to the zinc-rich coating and epoxy coating used as the primer, which have long-term anti-rust performance, the high durability coating for outdoor use is more important to consider its excellent weather resistance, color and light retention requirements, improve its decorative performance and protective durability for structural facilities and equipment, reduce the number of maintenance and coating, save energy, labor and costs, etc, Reflect long-term economic utility. At present, the commonly used outdoor high durability coatings include polyurethane finish, fluorocarbon finish, polysiloxane coating, etc. The classification will be introduced below.

1. Polyurethane finish

Polyurethane topcoat for outdoor high durability mainly refers to NCO/OH two-component polyurethane coating, that is, polyisocyanate prepolymer as component A or component A; The topcoat coating is prepared with hydroxy-containing polymer compounds, such as hydroxy-containing polyacrylic resin, polyester resin, alkyd resin and organosilicon resin, as component B or component B. Among them, the acrylic polyurethane topcoat prepared by hydroxyl-containing acrylic resin and aliphatic polyisocyanate prepolymer is the most important topcoat in anti-corrosion coating. This kind of product also has a name of acrylic polyurethane topcoat. This is due to the slight dissolution between the coatings when the topcoat coating is applied before it completely reaches the curing state, which contributes to the bonding strength between the coatings.

Adding mica iron oxide, aluminum powder and other pigments to the finish coat can effectively enhance the anti-corrosion performance and appearance texture of the finish coat. This is a special requirement of some steel structures in recent years, with a silvery metal texture. For example, the theme pavilion of the 2010 Shanghai World Expo and the Shenzhen Bay Stadium. The polyurethane aluminum powder finish on the external surface of the storage tank in the petrochemical industry has better anti-corrosion and reflective heat effect.

The volume solid content of traditional polyurethane finish coating is 40% - 50%, which makes its VOC as high as 400g/L. The volume solid content of high solid polyurethane finish reached more than 60%, and VOC decreased to about 320g/L.

Waterborne polyurethane is mainly used to build the finish coat in the water-based system, and is used together with water-based inorganic zinc silicate and water-based epoxy coating. The technology and performance of waterborne two-component polyurethane coating can now meet the requirements of heavy corrosion protection. It can minimize the use of solvents under low temperature drying conditions (room temperature~80 ℃), and make contributions to reducing VOC volatilization in the overall industrial environment.

2. Fluorocarbon finish

FEVE ambient temperature curing fluorocarbon coating, using aliphatic isocyanate as curing agent, crosslinks and forms film at ambient temperature. The normal-temperature curing fluorocarbon paint, due to its better weather resistance in bridges, stadiums, airports, stations, commercial buildings, radar, marine engineering and other aspects, has increasingly begun to replace the traditional acrylic polyurethane application in recent years.

Infrastructure has always been the main market for the application of fluorocarbon finish, the most typical of which are the National Stadium "Bird's Nest", the Hangzhou Bay Sea-crossing Bridge, the Three Gorges Dam, and so on.

In marine engineering, polysiloxane has always been used in European and American countries, but fluorocarbon coatings have also been used in some projects in China, such as offshore wind power facilities.

In addition to the technical requirements of HG/T3792 cross-linked fluororesin coating, other industries, especially railway bridge TB/T1527, highway bridge JT/T722, and oil tank GB50393, SH/T3022 and other national and industrial standards, have specific technical requirements for fluorocarbon finish paint.

The petrochemical industry is under the corrosive environment of C4-C5. The corrosion resistance of steel structure has higher requirements than that of general infrastructure. Although polyurethane topcoat is its main application product due to its economy. However, fluorocarbon finish is obviously more suitable for humid and hot areas, high ultraviolet areas and applications.

3. Polysiloxane coating

The main difference between polysiloxane coating and polyurethane coating or fluorocarbon coating is that the volume solids can be as high as 70% or even 90%. This makes the high weatherability coating in the anticorrosive finish really meet the technical requirements of high solid content and low VOC.

The most important landmark projects of polysiloxane coating application in China in recent years are Guangzhou New TV Tower, Beijing T3 Terminal, Chongqing Chaotianmen Bridge, etc.

Use organic? Inorganic mixing technology enables two materials to form a polymer that shares a chemical bond, which is the main chemical reaction of polysiloxane. Through the mixing technology, the polysiloxane coating organically combines the best characteristics of organic matter (such as easy processing, flexibility, flexibility, gloss and curing at room temperature) and the best characteristics of inorganic matter (inertia, hardness, adhesion, chemical resistance, high temperature resistance, weather resistance, UV resistance and wear resistance). Common varieties include aliphatic epoxy modified polysiloxane and acrylic modified polysiloxane coatings.

The product technical standard of polysiloxane coating was drafted at the end of 2013, especially in the technical regulations involving the content of silicon and oxygen bonds similar to fluorocarbon coating, as well as the restrictions on harmful components, cycle test, etc. Before that, the basic requirements were specified in JT/T722-2008 Technical Requirements for Anticorrosive Coatings for Highway and Bridge Steel Structures.

The outdoor high durability coating represented by aliphatic polyurethane coating, fluorocarbon coating and polysiloxane coating, combined with metal thermal spraying, zinc-rich paint and epoxy coating, can meet the application under C5I and C5M corrosive environment specified in ISO12944. Its excellent and super high weather resistance and color and light retention performance make the overall coating performance reach 15-20 years or longer service life.

Under the new environmental protection situation and social development needs, high durability coatings are also making new progress in environmental protection, especially in the harmonious coexistence with human and nature. Lead-free and chrome-free, high solid content and low VOC are its latest technological development footnotes.

4. SUNSHOW Chemical contributes to the high durability anti-corrosion coating

As a leading manufacturer of polymer weathering additives, SUNSHOW Chemical is committed to solving the aging problem of materials. From the technical point of view, whether inert fluorocarbon or organic-inorganic hybrid siloxane coating is used, the most fundamental solution to solve coating aging is to reduce the generation and accumulation of free radicals during aging. The new chemical light stabilizer can fundamentally solve the aging phenomenon of coatings and further extend the service life of anti-corrosion coatings. New chemical ultraviolet absorbers (such as plastron ® 5530. Plasticizing ® 5516. Plasticizing ® 531) When the short-wave ultraviolet rays reach the coating surface, they can absorb the ultraviolet rays before the coating, convert the ultraviolet light energy into heat energy and release it, while the structure of the ultraviolet absorber itself will not change, and play the role of protecting the anti-corrosion coating. For a small amount of ultraviolet rays that penetrate the coating surface and enter the coating and destroy the coating to produce free radicals, the new chemical hindered amine light stabilizer (such as plastostatin ® 5513. Plasticizing ® 5529) can stop the generation of active free radicals and inhibit the process of self-accelerated aging. In addition, in order to completely protect the anticorrosive coating and prolong the service life of the anticorrosive coating, SUNSHOW Chemical has launched a series of new products, such as plastron, which are compounded with ultraviolet absorbers and hindered amine light stabilizers ® 205. Plasticizing ® 51。

At present, many products of SUNSHOW Chemical have been promoted in various anti-corrosion coatings at home and abroad, and many customers at home and abroad have responded well to SUNSHOW Chemical products.

This article is excerpted from the Proceedings of the 2014 Fluorosilicone Coating Industry Annual Conference