The owner of the Cooper River paper mill continues to grow.

Helped by a big recent acquisition and rising prices for its products, KapStone Paper and Packaging Corp. is reporting record third-quarter results. Sales jumped 74 percent to $539 million and net income soared 144 percent to $44 million.

The company’s stock was up more than 11 percent this morning, to $50.74.

“The third quarter was an exceptional quarter for KapStone,” CEO Roger W. Stone said in a written statement.

The period included the $1.08 billion acquisition of Longview Fibre Paper and Packaging Inc.

Like KapStone, the Washington-based company makes containerboard and corrugated containers, as well as specialty papers, mostly at mills spread over a few Western states.

The newly acquired business added $54 million in operating earnings and $198 million in revenue since the deal closed in July, Stone said.

Northbrook, Ill.-based KapStone also said sales of paper increased 55 percent to 662,000 tons while the average selling price was $57 a ton higher than the third quarter of 2012.

“Our integration of Longview continues on plan,” Stone said. “We have now identified $18 million of synergies that should benefit KapStone by the end of 2015. However, more significant than the synergies identified thus far are the substantial benefits from operating efficiencies and capital programs in progress. Looking ahead, we believe we are well-positioned to improve our profitability by benefiting from full quarters of Longview results, strong performance from our legacy operations and robust cash flows.”

KapStone acquired its North Charleston paper mill and a Summerville-based lumber and chip mill business from MeadWestvaco Corp. in July 2008.