低温涂敷型环氧粉末涂层玻璃化转变温度异常问题研究

摘要

In recent years,a series of low application temperature fusion bonded epoxy (LAT-FBE) powder which can be applied below 190 ℃ has been developed in order to solve the new challenges of 3-layer PE(3LPE) anticorrosion for high grade steel pipe.Although the conversion degree of some LAT-FBE coatings can meet the requirements of 99％,the difference in the glass transition temperature between two successive thermal analysis scans (△Tg)is significantly over-2 ℃,which can be defined as "△Tg negative over value".The two indicators evaluating the curing degree of LAT-FBE coating are contrary,and it seriously influences the quality evaluation of LAT-FBE coating.Experimental research based on theoretically analysis for △Tg negative over value is made in this paper.The results show that the direct cause of △Tg negative over value is abnormally increase of Tg3.The root cause is the unstable state of LAT-FBE molecular structure,and the molecular chains lack flexibility,the coating shows great internal stress.%为解决高钢级钢管对三层结构聚乙烯(3LPE)防腐工艺提出的新要求,粉末涂料企业针对性地开发了一系列涂敷温度低于190℃的低温涂敷型环氧粉末(LAT-FBE).若干型号的LAT-FBE涂层存在固化转化率大于99％,但玻璃化转变温度差值(△Tg)却明显小于-2℃的现象,即“△Tg负向超差”问题.评价涂层固化度的2个指标发生冲突,严重影响LAT-FBE涂层合格与否的准确判定.在理论分析的基础上,对△Tg负向超差问题进行了实验研究.结果表明:导致△Tg负向超差的直接原因是涂层Tg3异常升高,其根本原因是LAT-FBE涂层的分子结构处于不稳定状态,分子链段柔性较低,涂层存在较大的内应力.