Abstract: A plastic article such as key tops of a key board needs wear resistant printing. This is attained in a styrene-based resin body suitable for such an article including key tops, by a process for permeation printing, comprising the steps of printing an article with an ink comprising a medium having a solubility parameter of 8.5 to 11.5 (cal/cc).sup.1/2 and then covering the printed surface of the article to permeate the ink into the article. Further, a system suitable for permeation printing a plastic article is provided which comprises a transfer-type printing device and a body heating and covering device, the body heating and covering device comprising a covering body which is heated and covers the printed surface of the plastic article to cause ink to permeate into the plastic article.