Packaging Corporation of America (PCA) has reported a decline in the third quarter 2011 earnings of 55% as higher costs and weaker sales mix and prices offset volume improvement, while tax credits also boosted the bottom line a year earlier.

The paper container board maker’s profit was $42m in the periord compared to $62m a year ago, while the net income was $122m in the first nine months of 2011 compared to $113m in 2010.

The firm’s net sales increased by 4.4% to $671m compared to the third quarter of 2010, and year-to-date net sales increased by 8.7% to $2bn compared to 2010.

According to PCA, shipments of corrugated products increased by 6.6%, including 1.4% from acquisitions and outside sales of containerboard were equal to last year’s third quarter.

During the quarter, containerboard production was 650,000t, up 4,000t over the same period last year and the inventories at the end of September were 22,000t below 2010 year-end levels.

PCA CEO Mark Kowlzan said the corrugated products demand remained good throughout the quarter and the company’s mills and box plants ran well, setting quarterly records for production and sales.