Three Stages in The Curing Process of Powder Coatings

第一阶段：结聚（1min-3min  40-60℃）

The first stage: coalescence (1 min-3 min, 40-60 C)

粉末在烘烤过程中，随着温度的升高，粉末涂料颗粒表面开始熔融，继而熔融的周界相互聚集。

During the curing process, with the increase of temperature, the surface of powder coatings particles began to melt, and then the melted periphery aggregated with each other.

第二阶段：熔融铺展及流平（3-7min 80-100℃）

The second stage: melt spreading and leveling (3-7 min, 80-100 C)

流平阶段，在这个阶段，由于流平剂本身具有很低的软化点，所以，当粉末涂料中加入流平剂以后，整个体系的软化点降低。流平剂快速迁移至熔融体系的表面，形成一层表面张力局部均一的分子层。

In leveling stage, because of the low softening point of leveling agent itself, the softening point of the whole system decreases when leveling agent is added to powder coatings. The leveling agent migrates rapidly to the surface of the melt system, forming a molecular layer with locally uniform surface tension.

铺展阶段，整个粉末涂料体系变为熔融态，此时流平剂已经迁移至熔融涂料的表层，所以它对粉末内部树脂和填料颜料之间的润湿效果不明显，所以需要加入另外一种软化点较高，不易快速迁移至表层的丙烯酸酯类聚合物来降低熔融涂料内部与底材、颜填料间的表面张力，从而促进熔融体系对底材的铺展和对颜填料的浸润。这种助剂即增光剂（又名光亮剂、湿润促进剂）。

During the spreading stage, the whole powder coating system becomes melting state, and the leveling agent has migrated to the surface of the melting coating. Therefore, the wetting effect between the resin and filler pigments in the powder is not obvious, so another kind of acrylate polymer with higher softening point is needed, which is not easy to migrate to the surface quickly. The surface tension between the low melting coating and the base material, pigments and fillers promotes the spreading of the melting system to the base material and the infiltration of pigments and fillers. This additive is a brightener (also known as brightener, wetting promoter).

在此过程中，随着温度升高，粉末涂料粘度急剧降低，即流平和浸润的推动力远大于由粘度产生的阻碍，所以此过程是浸润和流平的主要阶段。由于增光剂和流平剂的共同作用，熔融涂料内部的表面张力降低，所以树脂更易浸润颜填料，并且加速熔融流体内部存在的水分等挥发性物质从表面溢出（加入安息香可以加速气泡破裂溢出[9]），溢出后的气泡会在表面张力作用下，变成平整的表面。

In this process, with the increase of temperature, the viscosity of powder coatings decreases sharply, that is, the driving force of leveling and wetting is much greater than the hindrance caused by viscosity, so this process is the main stage of wetting and leveling. The surface tension of the melt coating decreases due to the combined action of brightener and leveling agent, so the resin is easier to infiltrate the pigments and fillers, and the volatile substances such as water in the melt fluid are accelerated to overflow from the surface (adding benzoin can accelerate bubble bursting and overflow [9]). The overflowed bubbles will act as surface tension. When used, it becomes a flat surface.

第三阶段：固化（7min-15min  130-200℃）

The third stage: Curing (7min-15min 130-200 C)

粉末在高温下开始固化，体系粘度开始逐渐变大，在表面张力不变的情况下，流动阻力迅速变大，故此时粉末基本不会发生流平。

When the powder solidifies at high temperature, the viscosity of the system increases gradually. When the surface tension remains unchanged, the flow resistance increases rapidly, so the powder will not leveling at this time.

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