Development and types of zinc-rich primers
Early zinc-rich primers were invented by Australian Victov Night ingale in the 1930s and were prepared by adding zinc powder to water glass.
This primer then required drying to cure.
This is an inorganic zinc-rich paint.
In the early fifties, the United States improved on this and developed a successful post-curing inorganic zinc-rich paint.
Its basic formula is still water glass with a large number of zinc powder. The coating obtained from it does not need to dry, but spray phosphoric acid solution or magnesium chloride solution and get dry.
Therefore, our country in the sixties widely promote this coating, railroad bolted beams of the bolted plate at the antirust anti-skid coating, is the use of this inorganic zinc-rich paint, in addition to its excellent corrosion resistance, but also to maintain its coefficient of friction in the 0.45 or more.
At the end of the seventies, the international development of alcohol-soluble self-curing inorganic zinc-rich paint. The base material is ethyl orthosilicate in a small amount of hydrochloric acid catalyzed by hydrolysis polycondensation obtained from the poly silicic acid acetic acid.
General polymerization degree to n = 4 ~ 10, too high easy to glue, too low is not easy to film.
It is characterized by fast drying, good adaptability to construction, is currently widely used inorganic zinc-rich paint.
At about the same time, epoxy zinc-rich primer was developed. Its base material is epoxy/polyamide, there are also epoxy/amine additives.
This zinc-rich primer is characterized by the surface treatment requirements of the substrate is not as harsh as the inorganic zinc-rich paint, and good adhesion with the substrate, the paint film is flexible and easy to match with the topcoat.
Some people think that the cured epoxy resin conductivity is poor, will hinder the electrochemical protection of zinc powder, in fact, due to the large content of zinc powder, many zinc powder particles in the coating film is not completely wrapped by the resin, and still be able to contact with the steel substrate and play its cathodic protection, due to the above advantages, it has been widely used.
The Zhegao Bridge on the Huainan Railway Duplicate Line is a steel plate bridge deck with orthogonal anisotropic plates, which is coated with epoxy zinc-rich primer, and has been free of any corrosion for eight years now.
In the last 20 years, environmental protection is more and more attention by countries which correspondingly developed a water-soluble self-curing inorganic zinc-rich primer, its base material for lithium silicate, potassium silicate, etc., modulus of 5 or more.
Paint film can be self-curing, no need to spray phosphoric acid or magnesium chloride solution.
Its corrosion resistance is slightly inferior to the water-soluble post-curing inorganic zinc-rich primer, in the water structure on the application of promising.
To summarize, in the following table lists the classification of zinc-rich primer and its brief performance.
Durability of zinc-rich primers
As mentioned earlier, the protective role of zinc-rich primers is to protect steel at the expense of itself, so the durability of zinc-rich primers, or the protection of the “life” in the end how?
Zinc-rich primer coating steel exposed to corrosive environments, zinc slowly corrosion products that are deposited in the voids between the zinc powder particles and the surface of the steel plate, so that the paint film has the function of isolation of the environment, at the same time due to the corrosion products of the cover, making the paint film and steel substrate interface, to maintain a slightly alkaline, so that the steel and zinc powder Department of the Department of the maintenance of difficult to corrode the state, and therefore reduce the rate of depletion of zinc, and of course improve the zinc rich The durability of zinc-rich paint film is improved.
