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    Home > Coatings News > Paints and Coatings Market > How to solve the problem of "flash rust" of water-based coatings? Method please see here.

    How to solve the problem of "flash rust" of water-based coatings? Method please see here.

    • Last Update: 2020-10-16
    • Source: Internet
    • Author: User
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    It is generally believed that metal substrates, water and oxygen are the three factors that produce flash rust. Water-based coatings are applied directly to the metal substrate, which is often referred to as "flash rust" due to the high volatile latent heat of the water (2257.2 KJ/KG, 0.1Mpa), the water stays on the metal substrate for a longer period of time and the metal substrate begins to rust. The phenomenon of "flash rust" usually occurs at this time before the coating film is dried and cured, and is generally considered to be an electrochemical phenomenon, caused by the dissolution and precipitation of iron compounds related to

    . Since the water-based coating itself is a conductor, the charge migration channel is formed for different areas where there is a difference in the likeness, and corrosion is produced under the joint action of water and oxygen, resulting in brown or black rust on the surface of the coating film.
    if the paint curing process, low temperature, high humidity (ESPECIALLY severe when RH is greater than 85 percent) slow dry conditions, will directly bring "flash rust" problems. The substrate of the coating is an iron substrate with unstable pre-treatment unclean quality and is also prone to "flash rust", especially the newly treated steel surface is most prone to flash rust. Or the lower the pH of the coating system, the easier it is to flash rust. The degree of difficulty in producing flash rust on a metal substrate is: cast iron >carbon steel> degree zinc plate (grinding) > makou iron (grinding) > iron plate or wire> aluminum alloy.
    According to the conditions produced by "flash rust", the problem of preventing "flash rust" can be started from the following aspects:
    1, accelerated drying: high temperature, low humidity is conducive to preventing flash rust; The easier it is to produce flash rust, because the thickness of the paint film causes a sharp decline in the rate of moisture evaporation; 3, avoid metal substrate pollution, try to use the substrate that is not easy to flash rust; 4, the pH value of the coating: the higher the pH value, the less likely it is to produce flash rust Ph adjustment to 9.5 or so is more appropriate; 5, resin system: phenyl propylene, pure propylene emulsion and other self-drying system is most likely to produce flash rust, while water-soluble acrylic, polyester resin system is not easy to produce flash rust; 6, the use of anti-flash rust agent can effectively prevent flash rust production; 7, zinc phosphate and aluminum phosphate and other corrosion-resistant pigments, at the same time, also have a corrosion inhibition effect.
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