Curing of polyurethane powder coatings

2021-12-03   Pageview:624

The curing temperature of polyurethane powder coatings must generally be higher than the temperature at which containment is eliminated (approximately 170ºC). During curing, part of the sealer is released from the coating as a gas. A prerequisite for obtaining good process coatability is that crosslinking should take place in the appropriate range (175-200ºC, 8-30 minutes).














JN-25 type and JN-50 type, JN type is a new type of anti-corrosion pigment based on aluminum tripolyphosphate derived from the APW series. It is suitable for the requirements of medium and low-grade paint for anti-corrosion pigments. The price is relatively low. Can further reduce the cost of paint. It has good substitution performance for red lead and other toxic anti-rust pigments, and its use and performance are basically the same as APW.

In addition to zinc phosphate series and aluminum phosphate series, phosphates also include magnesium phosphate, calcium phosphate, and silicophosphate series, which are mainly products of foreign companies.
Borate pigments are more soluble than conventional phosphate pigments and have a higher pH. Therefore, there are storage stability problems in some latex systems and carboxyl-containing ethylene polymers. However, in many resins, especially alkyd resins, the corrosion inhibition effect is very good. The corrosion inhibition mechanism of borate pigments is generally Said to be attributed to the alkalinity of its water extract. It buffers the coating/metal interface so that the pH value there is greater than 9. Under this condition, iron is passivated, and borate ions can also passivate the anode.

The Halox electrochemical test of the latex primer containing calcium borosilicate ptfe powder production composite pigment shows that the protection mechanism is basically an anodic polarization, which is cathodic to a certain extent. These test data also show that if the concentration of the corrosion inhibitor or the thickness of the coating film is high enough to maintain the concentration of borate ions on the interface at a high level, it can also play a protective role in the weak chloride environment, in order to reduce the penetration of chloride ions. It is important to maintain a relatively low PVC/CPVC ratio, so as to have a favorable boric acid/chloride ion ratio. In the environment of chloride ion, the effective grading effect of calcium borosilicate pigment is effective against chlorine by the corrosion inhibitor at the coating interface. The ratio of ions is related. Only when the added amount of the specific corrosion inhibitor pigment is exceeded, an effective corrosion protection effect can be produced. The effective level is determined by the thickness of the coating film.


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