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High-temperature baked coatings
A film that looks smooth at application can still change once it has been baked, so the leveling agent has to stand up to the heat too.
Some baked coatings show changed leveling, reduced surface slip or an unsatisfactory recoat condition after high-temperature curing. Ordinary leveling additives may be affected by the system at higher temperatures, so high-temperature coating needs to consider not only leveling performance but also the additive's heat resistance, compatibility and later recoat condition.
1
Introduction
In industrial baking finishes and metal coatings, the film normally has to be cured with heat.
As the baking temperature rises, solvent evaporation, resin flow and surface tension inside the film all change. In some high-temperature curing systems, a film that looks fairly smooth during application may show a different surface after baking.
Besides the resin and the curing system, the heat resistance of the leveling agent itself can be brought into the formulation review. An ordinary leveling agent mainly deals with spreading and surface smoothness during application; in a higher-temperature system, its stability during baking also needs attention.
2
Why high-temperature systems ask more of a leveling agent
A leveling agent usually changes the interfacial state of the coating surface, helping the film form a fairly uniform surface during application and curing.
During high-temperature baking, however, the system temperature rises markedly, and the interactions among resin, solvent and additives change with it. If the additive is not sufficiently compatible with the system, the surface state may change; if its heat resistance does not match the actual baking conditions, the final film appearance may also be affected.
For this reason, when choosing a leveling agent for a baked coating, it is not enough to look at leveling right after application. The surface after baking also has to be observed.
3
Where DH-4310 can be adjusted
DH-4310 is a polyester-modified polydimethylsiloxane silicone additive. Data show it can be used within a 230 °C range without thermal decomposition, which suits coating systems with heat-resistance requirements. In practice, three directions deserve attention.
Leveling performance
Improves the spreading of the coating on the substrate so that the film surface is more uniform.
Substrate wetting
For substrates that are hard to wet, compare the spreading and coverage of the film before and after adding the additive.
Subsequent coating
Some industrial products are recoated, so besides improving the current film, the state of the following coat should be observed through recoat testing.
4
What else to watch in high-temperature baked coatings
For a high-temperature curing system, panels with and without DH-4310 can be baked under identical conditions and compared. Besides surface flatness, watch slip, gloss, scratch resistance and anti-blocking. If the product is recoated later, add a recoat test.
The benefit is that the additive's behavior during application, during baking and in later coating can be observed together instead of through a single item.
DH-4310 has good compatibility with many coating systems, but actual use still requires small-scale trials according to resin type, baking temperature and application process.
5
How to think about the dosage
The reference dosage of DH-4310 is 0.5%-1.0% of the total formulation. In use, different ratios can be compared, for example starting from a lower ratio and increasing step by step.
The tests should focus on leveling, wetting, gloss, slip and recoat condition. If the surface performance changes little as the dosage rises, there is no need to raise the ratio further.
The baking temperature and time directly affect the final film, so the dosage should also be judged together with the actual process.
Frequently Asked Questions
Why does a high-temperature baked coating need a different leveling agent?
During baking the temperature rises markedly and the interactions among resin, solvent and additive change. If compatibility is insufficient, or heat resistance does not match the baking conditions, the final film appearance may be affected.
What is DH-4310?
It is a polyester-modified polydimethylsiloxane silicone additive. Data show it can be used within a 230 °C range without thermal decomposition.
What should be compared when testing it?
Put panels with and without DH-4310 through the same baking conditions and compare flatness, slip, gloss, scratch resistance and anti-blocking, plus a recoat test if the product is recoated.
What is the reference dosage?
0.5%-1.0% of the total formulation. Start from a lower ratio and increase gradually; if the surface performance no longer changes noticeably, there is no need to raise it further.
Summary
A leveling problem in a baked coating is not only about whether the film looks flat at application; the film after heat curing also has to be observed. For systems baked at higher temperatures, the additive's heat resistance, compatibility, substrate wetting and recoat condition are all worth testing.
DH-4310 is a polyester-modified polydimethylsiloxane leveling additive, usable in a 230 °C range according to the data, with a reference dosage of 0.5%-1.0%. In practice, run a gradient test according to the resin system, baking temperature and substrate, then fix the dosage from the film appearance and later performance.
