FRANKFURT (Reuters) - U.S. private equity investor KKR said on Wednesday its investment agreement with the main shareholders in German publisher Axel Springer, under which it is making an offer to buy out minorities, was valid for five years.

Asked by Reuters, a KKR spokesman said that this represented a minimum period, adding that the company’s engagements on average lasted between five and seven years.

Funds controlled by KKR earlier on Wednesday offered 63 euros a share to buy out minority shareholders, representing a 40% premium and putting an equity value of 6.8 billion euros ($7.7 billion) on the business.

The offer is being launched in concert with the company’s main shareholders, founder Axel Springer’s widow Friede and Chief Executive Officer Mathias Doepfner, who want to de-list the firm following its share price slide over the past year.