It has turnover of around E23m a year and earnings of E3.7m. The company employs 480 people.
In a letter to shareholders, Ardagh Glass said it expected to acquire the remaining shares in HSU over the next few months on similar terms.
Ardagh earlier this year said it significantly narrowed its operating losses in 2003 and will shortly be changing its name to South Wharf.
The firm posted retained trading losses for 2003 of E1.02m compared to a loss of E2.89m last year, while the profit retained for the period was E1.9m compared to a loss of E11.73m.