Swiss specialty chemicals and biotechnology company Lonza Group Ltd. said Monday it will buy Arch Chemicals Inc., a maker of antibacterial products, for $1.2 billion in cash.

The deal values the Norwalk, Conn., company at $47.20 per share. Lonza plans to will start a tender offer for Arch Chemicals shares by Friday, and it expects to complete the acquisition later in 2011.

Lonza said it will have about $1.6 billion in annual revenue from sales of bacteria-killing products, making it one of the leaders in that market. Arch Chemicals reported $1.38 billion in revenue in 2010, and Lonza said $1.2 billion of that total came from sales of products used to kill harmful bacteria in water, in industrial applications, for wood protection, and for personal care. Lonza said the market for antibacterial products is growing steadily and is worth about $10 billion per year.

Shares of Arch Chemicals surged 11 percent Friday despite weak economic news, and the stock gained $4.23, or 10 percent, to $46.40 in premarket trading. Lonza said it is offering a premium of 36.7 percent to the stock's average closing price over the last 30 days.

Arch Chemicals has approximately 3,000 employees and 23 manufacturing and research sites.