The wire enters the curing zone after passing through the evaporation zone, where the main chemical reaction of the paint occurs in the curing zone, that is, the cross-linking and curing of the paint base. For example, polyester paint is a paint film in which a linear structure of resin is cross-linked into a network structure. The curing reaction is very important, and it is directly related to many properties of the enameled wire. If the curing is not enough, it will affect the flexibility, solvent resistance, scratch resistance, softening and breakdown of the enameled wire. Sometimes, although all the properties were good at that time, the stability of the paint film was poor, and after a period of storage, the performance data decreased or even failed. If cured excessively, the paint film becomes brittle, and the flexibility and thermal shock decrease. Most enameled wires can be judged by the color of the paint film to determine the degree of curing, but because the enameled wire is baked many times, it is not comprehensive to judge only from the appearance. When the internal curing is not enough and the external curing is sufficient, the color of the enameled wire is very good, but the peelability is very poor, and the heat aging test is carried out, and the paint film sleeve or large peeling may be carried out. Conversely, when the internal curing is good but the external curing is insufficient, the color of the enameled wire is also good, but the scratch resistance is poor.
In the curing reaction, the high density of the solvent gas or the humidity in the gas mostly affects the conjunctival reaction, which reduces the strength of the paint film of the enameled wire and affects the scratch resistance.
Proper curing of the paint film depends mainly on the baking temperature and baking time. Under the same conditions, the higher the baking temperature, the greater the degree of curing; under the same baking temperature, the longer the baking time, the greater the degree of curing. Baking time is also the line speed.
When the furnace temperature is too high, the crosslinked polymer chain segments, especially the branched side chains, will be broken and cracked to produce low molecular weight polymers with lower molecular weight, which will form e-liquid (old gum) after condensation. If the low molecular substances are not well ventilated in the process of escaping, it is possible to form old glue in the furnace mouth and chimney and produce old glue particles on the line, which will affect the quality of the product. The amount of old glue reflects the degree of cracking of the polymer to a certain extent. If most of the binder resin cracks, the mechanical properties, electrical properties and thermal properties of the paint film will be significantly reduced.
Different types of enameled wires have different requirements for the curing procedure of the paint film. Most enameled wires are fully baked every time they are painted to make the paint film well cured. However, the polyimide enameled wire is completely different. If the paint is fully cured during baking, the paint films of each paint will be delaminated and cannot form a solid whole, and the strength of the paint film will be very poor. , the scratch resistance is unqualified. This is due to the fact that the polyimide paint film is fully cured into an infusible substance after baking, coupled with its poor adhesion, resulting in the phenomenon of delamination of the paint film. During the scratch resistance test, the paint film will be layer scratches. Therefore, when the polyimide is baked, the paint film is basically cured but not sufficient, and there is still a small amount of base ends in some molecules of the paint film that have not reacted. The film is fully cured to form a relatively firm whole.