Spraying starch to improve strength of containerboard produced from weak recycled furnish

Producers of recycled furnish–based testliner and corrugating-medium grades often struggle to reach required strength properties compared to producers of packaging grades produced from virgin fibers. Starch can be used on a size press to compensate for the lost fiber strength, weakened from recycling. However, conventional size-press technologies have limitations when large starch pickup amounts are targeted, or when speeds are relatively high in modern packaging board machines. Spray sizing overcomes many roadblocks, and sufficient strength improvements are achieved for recycled testliner and corrugated medium. Dongil Paper Manufacturing Co. Ltd. in South Korea is a pioneer in the use of spray technology, with three spray units already in production. The spray device provides a large window for starch application and gives an exceptional transfer rate to the web. Clean operation, no wearing parts, and ease of running are other advantages when operating a starch-spray device. The theoretical provisions for effective starch transfer to the web and control of starch penetration are described in this paper. The theories are supported by pilot trial results as well as production experience. Starch application with spray is a new and innovative approach for producing packaging board grades economically from a fully recycled fiber source.