Packaging Corporation of America announced that it has entered into a definitive agreement to acquire substantially all of the assets of TimBar Corporation, a large independent corrugated products producer, in a cash-free, debt-free transaction for a cash purchase price of $386 million.   Under the terms of the agreement, PCA will acquire five corrugated products plants, two fulfillment centers and four design centers located primarily in the eastern and southeastern US. The transaction is str...