Problems in drying and curing of coatings

1 Curing: the curing and drying control of the coating is important to achieve the best performance of the coating In many cases, it is experience, visual inspection and testing to carry out curing control Generally, we should pay attention to the curing of inorganic zinc silicate coating and other two-component coating using curing agent (1) inorganic zinc silicate coating needs moisture to help cure If the relative humidity is less than 60%, curing will become very slow In order to achieve rapid curing, high relative humidity and temperature are required Enough relative humidity can be added within a few hours after construction The fastest and best curing effect is to use hot steam MEK reagent (methyl ethyl ketone) can be used to test the curing state Dip the white cotton cloth with MEK reagent and wipe the coating surface If there is only a little color change or no color change, the coating has been cured Because inorganic zinc silicate coating is solvent resistant after curing See ASTM d4752-87 for this method (2) two component coating For example, epoxy coating, polyurethane coating and polyester coating, curing depends on temperature The coating surface can be wiped with solvent or stronger solvent of the coating to detect whether it has achieved good curing If the film has cured, the coating surface will not be affected 2 Wrinkling: film wrinkling usually occurs in oily paint, alkyd paint and phenolic paint For example, the surface of linseed oil expands due to oxygen absorption from the air, causing wrinkles on the surface of the unoxidized coating body In order to speed up the drying process, driers are usually added to these coatings Some are used to accelerate surface curing, others are used to evenly dry from the bottom to the surface If the coating contains excessive surface driers, wrinkling may occur in the thicker part of the coating Cobalt salts are commonly used as surface driers Zinc and lead compounds are used as driers The effect of temperature on wrinkling is quite large For the coating without wrinkling at room temperature, with the increase of temperature during baking, the surface curing is far faster than the curing of the body, and serious wrinkling will occur When the coating is applied under cold temperature, or under the sun's irradiation in hot days, the rapid drying of the coating and the moisture of the primer will cause wrinkling