Next we come to the mechanism of coating resin
To obtain a better coating film, the narrower the molecular weight distribution of the unsaturated polyester resin, the better. Too wide a relative molecular mass distribution means that there is a resin with a relative molecular mass that is too small or too large to blend well with the other components of the paint. When baked under such conditions at high temperatures, the If the meltability is not good, the surface tension of the coating will not reach equilibrium. The force between the particles will produce a repulsive or contractive movement, and the melt flow time is limited. There can be no sufficient leveling time between them. With the curing of the coating, defects such as shrinkage holes and orange peel will appear on the surface of the coating film.
Therefore, resins with low melt viscosity, long gel time for powder coatings, and high fluidity at the melt level should be selected; but in terms of physical and mechanical properties of the coating film, the mechanical properties of short leveling time and long crosslinking and curing time are better. People should take into account. In addition, polyester powder products are easy to agglomerate during storage, and are prone to sag, orange peel, pinholes and other phenomena during spraying. This is due to the unsuitable glass transition temperature (Tg) of unsaturated polyester resin.
The production practice test shows that the Tg of unsaturated polyester resin is controlled within the range of 50 to 65 degrees Celsius, which can ensure the plump coating and good leveling, and can also store the powder coating under 40 degrees Celsius for four to six degrees. It does not agglomerate for a month and has a certain stability.