Next Wave Partners will remain the majority shareholders and KKR Credit is taking a substantial minority shareholding.
"The funding from KKR Credit will be used to refinance the company's capital structure and also finance the implementation of the company's growth strategy," Petainer said in a statement.
The transaction is expected to complete later in April 2016.
"The financial and operational strength of KKR Credit, alongside the continued support of Next Wave Partners, provides the business with a robust financial structure to continue and accelerate our growth strategy, both through market consolidation and the development of our new product pipeline," Petainer Chief Executive Nigel Pritchard said.