https://www.reuters.com/article/us-southkorea-japan-laborers-factbox/factbox-the-high-tech-materials-at-the-heart-of-a-japan-south-korea-row-idUSKCN1TX12I >Japan said it would tighten curbs on exports of high-tech materials used in smartphone displays and chips to South Korea amid a widening dispute over South Koreans who were forced to work for Japanese firms during World War Two.