What chemical changes have occurred in the use of thermoset powder coatings

's difference between thermoset powder coating and thermoplastic powder coating is that thermoset powder coatings will not be thermally cured again after heating and curing, and thermoplastic powder coatings will not be softened again if heated and plasticized again, so why will thermoset powder coatings not be thermally softened again after heating? The crux of the problem is that thermoset powder coatings react when heated, turning small molecules that were linear into a mesh three-dimensional macromolecule structureSo what chemical changes occur in thermoset powder coatings when they are heated? The following is a further explanation of the different resin systems(i) The epoxy polyester systemthe main film-forming substances of the system are epoxy resin and polyester resin with argon base, the curing reaction is indicated as follows
thethe.upload?gif?/powder/uploadFile/200497181517505.gif.gif./upload)essentially occurred is an esterification reaction, but also can be seen that the system's resistance to alkaline is limitedKnowing the mechanism of the reaction, it is possible to change the curing reaction speed of the resin by adding some promoters(2) Polyester resin system1.TGIC systemthe system of the "upload"/powder/uploadFile/2004971815555393.gif.gif.gif./upload)TGIC's high degree of ability determines the high cross-linking density of the system, that is, a TGIC molecule can react with multiple COOH, forming a stereomesh structure2.PrimidXL552 (hydroxylkylamide)the content of the "upload"gif/powder/uploadFile/20049718161633970.gif.gif./upload) because it is not too thick due to small molecular water released at the time of curing, and also increasethe spouts (Benzoin, etc.)(iii) epoxy resin system because of the epoxy powder coating curing agent is many, here only to double cyanamide as an example to explain the reaction activity of the double cyanamide is very low, generally need 200 degrees C / 30min conditions to cure completely, so the general use of curing promoter, so that it can be in 180 degrees C / 15 to 20min conditions to complete curing (4) the filmed substance serotonin polyurethane system is hydroxy polyester and closed isocyanate Their reactions are indicated as follows
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due to the removal of low molecular closure agents in the reaction, it is necessary to increase the amount of defoaming agent (rest fragrance) appropriately, and it is not easy to make too thick a coating film because acrylic powder coatings are used less in china, the introduction of them is not one of them