The mechanism of anti-skinning agents are used to prevent coating crust related to the paint drying. It is related to polymerization process of paint and the effect of drier. If the paint film radical polymerization and accelerate action can be controlled, the effect of anti-skinning can be achieved. But such control must be based on need and cannot affect the paint dry rate, nor affect the performance and quality of paint.
During the storage of air-drying oxidative drying film coating, because of the surface in contact with air and solvent evaporation, it will take oxidative polymerization on the surface and form gel, this is commonly called paint skinning. Such film is insoluble, so it must be filtered out before paint construction. In order to prevent the occurrence of this phenomenon, anti-skinning agents is often used.
There are three categories of anti-skinning agents currently: phenols, thiols and oxime compounds, among which oxime compounds with minimal side-effects. methyl ethyl ketoxime has the best comprehensive performance in oxime compounds.
The add amount of general anti-skinning agents in terms of total amount of paint for 0.1~0.3%, add amount of varnish should be controlled around 0.25%. Color paint depends on the pigment, for example, dry strong resistance carbon black pigments should be appropriate to reduce the adding amount; dry strong pigment red lead should increase dosage. By the way, resin types also has great influence on add amount, low degree of unsaturation resin should increase the amount.
Dosage and storage temperature of driers is critical. When drier dosage is large, anti skinning agent amount shall be increased accordingly, otherwise it will reduce the effect of anti-skinning agents. It may add less anti-skinning agent in Winter, as low temperature may slow the crust; on the contrary, high temperature may quick the crust, it may add more anti-skinning agents in Summar. Long storage time need more anti-skinning agents, short storage time can be less. All in all, addition of anti-skinning agent depends on the composition. OKCHEM has more chemicals raw materials for paint and coatings manufacturing, including anti skinning agents. Hope this can be helpful!