Pre-coated coil coatings must not only meet the production process requirements of pre-coated coils, but also meet the requirements for the processing and use of coils.
预涂卷材涂装采用连续辊涂生产工艺,其主要特点是基板行进速度快、涂料采用辊涂涂覆方式、涂膜短时髙温烘烤、出炉后迅速降温。预涂卷材涂料需要要满足这些涂装工艺的要求。第一,预涂卷材涂料的施工黏度有一定要求,为了满足辊涂施工要求、保证一定的涂膜厚度和流平性,溶剂型卷材涂料一般的施工黏度为50~100s(涂-4杯,25℃)。由于卷材涂料施工黏度较髙,为了保证足够的流平性,避免出现缩孔等涂膜缺陷,一般涂料中的流平剂用量较高。第二,预涂卷材涂料不能有明显的触变性(剪切稀释性)。辊涂施工时,基板与各辊子的运转速度不同(带料辊、涂覆辊和调节辊都有不同的转速),它们之间所带的涂料会受到一定的剪切力,在这种情况下,涂料应仍保持原来的黏度,不能因触变而发生黏度下降,否则如果涂料黏度因受剪切作用而明显降低,会使辊子上附着不住所要求的涂料量,影响涂覆效果。第三,涂膜固化一般采用髙温短时烘烤固化,烘烤温度一般在50~400℃烘烤时间20~60s,基板峰值温度(PMT,可用示温纸或测温枪在线测得)一般为204249℃;此外,涂覆后湿膜的闪干时间短,一般只有几秒到几十秒,所以预涂卷材中高沸点溶剂用量要比一般涂料高,否则会造成起泡、针孔和流平不好等缺陷。通常选用较高沸点的醇醚类、酮类和高沸点芳烃类、酯类溶剂等。第四,为了满足涂装要求,预涂卷材涂料要有定的固化性能,固化速率太快,容易产生起泡、针孔、流平差等表面缺陷;固化速率不够,涂膜不能完全固化,影响涂膜的物化性能,不能满足加工和使用要求Precoated coil coating products are generally divided into three categories according to their application, namely: primer, topcoat and backcoat. The pre-coated coil is a multi-coat system. Generally, the front of the substrate is coated with a primer and a top coat, and the back is coated with a back coat, and sometimes a primer is also coated . There are different performance requirements for primers, topcoats and backcoats. The main performance requirements of primers , topcoats and backcoats for precoated coils are listed in Figure 3-5-7 .
