Resin is the main film forming material of powder coating powder, and it is the main component that determines the properties of powder coating powder and film performance.
Resin variety selection is good or bad, determine the quality of powder coating powder product, powder coating powder with resin properties and properties to determine the composition and use of powder coating powder formula, such as the choice of thermoplastic resin, then in the formula does not need curing agent, resin in a certain baking temperature and time conditions, Melt leveling becomes a film with certain physical and mechanical properties and mechanical strength, and this change is reversible. The choice is thermosetting resin, so it must be with curing agent supporting, resin and curing agent in a certain baking temperature and time conditions of chemical curing reaction, become a film with certain physical and mechanical properties and mechanical strength, this change is irreversible.
In addition, the choice is epoxy resin in thermosetting resin, so this powder coating powder can only be used in anti-corrosion and indoor products, can not be used outdoors; if the choice is polyester resin, then this powder coating powder can be used indoors and outdoors. The variety of resin determines the use of powder coating powder.
The resin used in general powder coating powder should have the following conditions.
(1) the melting temperature and decomposition temperature of the resin powder coating powder is generally powder coated to the coating above, and then must be heated baking, so that the resin in the powder coating powder melting flat film, or melting flat curing cross-linking film.
If the melting temperature of the resin and decomposition temperature is very close, once the baking temperature control is too high, it is easy to make the resin in the coating decomposition, it is difficult to get a good appearance and performance of the film.
Resin melt temperature and decomposition temperature, therefore, the temperature difference between the larger, such as epoxy resin, polyester resin, polyurethane resin, acrylic resin and thermosetting resin, and quite a number of thermoplastic resin can meet the conditions, but there are a small number of thermoplastic resin, such as PVC resin between the melting temperature and decomposition temperature of the temperature difference is small, The precision of controlling the baking temperature in the coating process should be high.
Because of the difficulty of controlling the temperature in the coating, the development of PVC powder in China is very slow, with little production and narrow application.
(2) the melting viscosity of the resin powder coating powder is adsorbed to the coating powder by electrostatic attraction, and then the powder coating powder melting leveling on the surface of the workpiece under the condition of heating and baking.
Because there is surface tension between the powder particles of molten powder coating, the coating film of resin with high melting viscosity is not easy to level; for the melting viscosity of the lower resin powder, coating powder is easy to level, so as to get a flat and uniform film.
Therefore, the lower the melting viscosity of the resin, the better, considering the melting leveling of the powder coating powder.
Generally, the melting viscosity of resins is closely related to the molecular weight and structure of resins, especially the molecular weight.
If the molecular weight of the resin is small, the corresponding melting viscosity of the resin is low, but if the molecular weight of the resin is too small, the melting temperature and glass temperature of the resin will appear too low, so that the storage stability of the powder coating powder and some properties of the film is reduced.
Therefore, under the premise of satisfying the properties of powder coating powder and coating film, low melting viscosity of resin is better.
Because the general thermosetting powder coating powder resin with small molecular weight, low melting viscosity under baking curing conditions; and thermoplastic powder coating powder resin with large molecular weight, melting viscosity is relatively high, so the thermosetting powder coating powder than thermoplastic powder coating powder film leveling.
In addition, it also requires that when the heating temperature is higher than the melting temperature of the resin, the melting viscosity of the resin decreases rapidly, which is conducive to the coating powder at low temperature, is conducive to the leveling of the coating film.
(3) the stability of the resin in powder coating spray from the powder coating powder to be recycled, if the stability of the powder coating powder is not good, in the process of recycling or in contact with air, moisture for a long time, influenced by environmental temperature, physical will happen (such as moisture absorption or dry powder for liquidity variation) or chemical changes to change the quality of the powder coating powder, Cause the recovery of powder coating powder can not be used, so that the powder coating powder can not reach the purpose of spray can be recycled, lost the advantages of powder coating powder.
The stability of resin is the key factor to determine the stability of powder coating powder. If the stability of resin is not good, it will bring some influence and problems to the storage stability and use stability of powder coating powder.
Therefore, the stability of powder coating powder resin must be better, to ensure the use of powder coating powder stability.
(4) mechanical pulverization of resin in the manufacturing process of powder coating powder, general resin and other components of the coating together to melt extrusion mixing, and then cooling, crushing and fine grinding to achieve the required particle size of powder coating powder.
This requires that the resin easily be mechanically crushed at room temperature.
All resins for thermosetting powder coatings and some resins for thermoplastic powder coatings can meet this condition; and part of the thermoplastic powder coating resin is relatively tough at room temperature, can not be mechanically crushed at room temperature, must be crushed under low temperature freezing conditions to meet the requirements.
This freezing pulverization process will increase the manufacturing cost of powder coating powder and bring some difficulties in popularization and application.
In order to avoid the difficulty of mechanical crushing of thermoplastic resins, a considerable amount of thermoplastic resins are chemically produced in powder form.
(5) Adhesion of resin to coated (workpiece) The adhesion of powder coating powder to coated (workpiece) mainly depends on the adhesion of resin to coat.
If the adhesion of the resin to the coating is good, then no primer is needed; if the adhesion of the resin to the coat is not good, then a primer must be applied to ensure adhesion to the coat.
Because thermosetting powder coating powder resin with polar groups, the adhesion to metal and other substrates is good; however, most thermoplastic powder coating powder resin with no polar group or polar group polarity is very small, weak adhesion to the coated, adhesion is not good, need to use the resin with polar group modification or primer to meet the adhesion requirements.
(6) The electrical properties of resin in powder coating powder coating method, electrostatic powder spraying is the most important coating method.
The electric performance of powder coating powder is mainly determined by the resin in powder coating powder composition. The electrostatic performance of resin is of great significance to the electrostatic spraying efficiency of powder coating powder.