In this work, the curing and hardness evolution of a two-component polyurethane (PU) coating in four different environments, three of which were solvent evaporation-suppressed conditions, were studied. In contrast to previous studies, the simultaneous use of Fourier-transform infrared spectroscopy, gravimetric analysis, and pendulum hardness allowed a transient mapping of the degree of isocyanate conversion, solids concentration, and coating hardness. Furthermore, to explore in more detail the coupling of the underlying mechanisms, the evolution in the average coating glass transition temperature was estimated by dynamic mechanical analysis, and the data was simulated using the so-called Kelley–Bueche equation. For the curing conditions investigated, the final coating hardness differed by a factor of two, with the lowest values obtained for the evaporation-suppressed conditions. Due to the isocyanate groups reaching full conversion for all four series, the reason for the lower hardness was attributed entirely to the plasticizing effect of residual solvent. Using a K_α value of 0.687 in the Kelley–Bueche equation, the coating glass transition temperature as a function of the PU volume fraction could be successfully simulated and was found to increase from about 282 K at a volume fraction of 0.79 to 319 K at one of 0.93. In addition, when the experimental temperature was lower than the coating glass transition temperature, a proportional increase in the pendulum hardness with the reciprocal loss factor was seen. The effects of catalyst concentration in the coating were also investigated, and this parameter was found to have a strong influence on both the surface conversion, the solids concentration, and the coating hardness. A too fast curing rate shortens the time to vitrification, after which the solvent evaporation rate becomes diffusion-controlled and very low, leading to higher residual solvent contents and significantly lower hardness values. The results obtained provide guidelines for how to optimize ventilation conditions during the curing of solvent-based, thermoset PU coatings.

在这项工作中，研究了两种组分的聚氨酯（PU）涂料在四种不同环境中的固化和硬度演变，其中三种环境是溶剂蒸发抑制条件。与以前的研究相比，同时使用傅里叶变换红外光谱，重量分析和摆锤硬度可以瞬时绘制异氰酸酯转化率，固体浓度和涂层硬度。此外，为了更详细地探讨潜在机理的耦合，通过动态力学分析来估算平均镀膜玻璃化转变温度的变化，并使用所谓的Kelley-Bueche方程对数据进行模拟。对于所研究的固化条件，最终涂层硬度相差两倍，在蒸发抑制条件下获得最低值。由于所有四个系列的异氰酸酯基团均达到完全转化，因此硬度较低的原因完全归因于残留溶剂的增塑作用。用一个ķ _α当Kelley–Bueche方程的数值为0.687时，可以成功地模拟作为PU体积分数的函数的镀膜玻璃化转变温度，发现它从0.79体积分数的约282 K增加到0.93之一的319K。另外，当实验温度低于镀膜玻璃化转变温度时，观察到摆锤硬度与倒数损失因子成比例地增加。还研究了涂层中催化剂浓度的影响，发现该参数对表面转化率，固体浓度和涂层硬度都有很大影响。太快的固化速度会缩短玻璃化时间，此后溶剂的蒸发速度会受到扩散控制，而且非常低，导致更高的残留溶剂含量和明显更低的硬度值。获得的结果为如何在溶剂型热固性PU涂料固化过程中优化通风条件提供了指导。