CHESAPEAKE <CSK> SEEKS TO SELL UNIT Chesapeake Corp said it has retained Salomon Inc <SB> to help it sell Plainwell Paper Co Inc, a maker of premium coated and uncoated printing papers and technical specialty papers with a capacity of 85,000 short tons a year. The company said it has decided to sell Plainwell in ordfer to focus on the production of kraft and tissue products, containers and treated wood products.