A judge in the Fox Valley has approved the sale of a paper mill to a liquidation firm. The Industrial Assets firm was ordered to look for a new buyer that would operate the Appleton Coated plant — and if a buyer’s not found in 90 days, it can sell its machinery and equipment. Industrial Assets is spending 21-and-a-half-million dollars to buy Appleton Coated, which has made paper for magazines and textbooks. It decided to sell the facility due to a declining demand for printable papers — and at least some of the plant’s 620 workers are hoping a new buyer could come forward and keep the facility running.