Mitchell will hand over the reins of the Huntingdon-based document business process outsourcer (DBPO) to Donnelley's Bob Nelson (pictured left), who has been in the UK since January working with Mitchell on the transition.

"I'm leaving happy, in the sense that the business is going from strength to strength," said Mitchell, who founded the firm with 5m of venture capital backing 10 years ago.

He added that it was "pretty much the case" that he knew he would leave the business at some point after he sold it, "but I wanted to leave in an agreeable fashion and organised in such a way that we had a proper hand-over".

Mitchell, who personally netted 33m from the sale, said he was now looking for other opportunities for private equity-backed deals, but had no fixed idea about the size or type of business he was looking for. "I'll know it when I see it," he said.

Nelson previously headed up sales at RR Donnelley's Texas-based Integrated Print Communications and Global Solutions division. He said he first heard about Astron when the company started looking into buying it and "loved the model". "I knew [the DBPO model] was coming to the US and volunteered to take a deeper look," he said.

Nelson added that DBPO, which he described as "the A to Z of getting into the customer's processes", was "core" to Donnelley's strategy: "Our last two major acquisitions [Astron and US-based Office Tiger] have been in this space."

Pure print managers or print manufacturers had been "battered", Nelson said, and the key to Astron's success was that it had long since gone beyond print management to offer other services, such as transactional print, fulfilment and call centres. "If all you're doing is sending bills out, you'll ultimately be commoditised," Nelson said.

He confirmed that Astron had a "huge pipeline" and was on the verge of announcing some big deals.