Powder coating is a new type of solvent free 100% solid powder coating. It has two major categories: thermoplastic powder coatings and thermosetting powder coatings.
The coating is made of resin, pigments, fillers, curing agents and other additives in a certain proportion, and then prepared by the process of thermal extrusion and smashing and sieving. They are stored at room temperature, stable, electrostatic spray or fluidized bed dipping, reheating, baking, melting and solidification, so that a smooth and permanent coating can be formed to achieve the purpose of decoration and anticorrosion.
The leveling of coatings is the smoothness of coatings. There should be no irregular shape of orange peel, brush marks, corrugation and shrinkage holes. Usually, the method of direct observation by eyes is the parallel judgement of the sample and the standard sample to evaluate the quality of the film leveling.It differs from each person.Wavelength scanning method in automotive applications for surface characterization film has a semi quantitative effect, the long wavelength (10 ~ 0.6 mm) and HF (0.6-0.1mm) scan measurements in 0 ~ 100, the lower the value, show that the film surface is smooth, leveling.
The factors that affect the leveling of powder coating mainly include five aspects:
1. The melt viscosity of powder coating
For thermosetting powder coatings, in the melting process, with the crosslinking curing reaction, the higher the temperature is, the faster the curing reaction is, the faster the viscosity of the system rises, the shorter the flow time and the leveling is restricted. Therefore, when we choose a resin, we should try to choose low viscosity, reflecting slower activity resin, so that the coating will have enough time to leveling.
2. leveling additives
Add proper levelling agent in powder coating formulations, such as L88 of YINCAI TECHNOLOGY.After the powder coating melt, these additives can rapidly reduce the surface tension of coating, promote rapid flow before curing membrane, eliminate or reduce the peel brush mark, corrugated surface defects such as shrinkage.
3.the selection of pigment
Before matching,we should not only match the hue of each colour,but also consider the oil absorption of various pigments and adding amount.The oil absorption of inorganic pigments is much smaller than organic pigment,so if the colour we can do by inorganic pigment,try to avoid using organic pigments.The total proportion of various pigments according to customer requirements to adjust cover. Even if the amount of pigments with low oil absorption is too much, it can cause the difference of flow.
4.selection of filler
As everyone knows, filling material in powder coatings can not only reduce the cost, but also can improve the properties of powder coating, especially the wear resistance.
5. baking technology and production equipment
Powder coating baking has a heating process, have very important influence on the heating rate of coating leveling speed; under different heating rate, the trend of dynamic viscosity changes with temperature are basically the same, which began when the viscosity decreased with increasing temperature, and reaches the minimum value, then the viscosity decreases with the increase of temperature larger, this is due to the crosslinking reaction. More importantly, the faster the heating rate is, the smaller the minimum viscosity is, and the higher the corresponding temperature is, the better the curing of the coating and the better the leveling of the coating.
In addition, the production process is also concerned with the structure of extruder screw, the angle of mixing section, the setting of temperature and the speed of screw, and the particle size of mill.