FRANKFURT (Reuters) - Swiss packaging maker SIG Combibloc is preparing an autumn stock market listing in Zurich that could value it at about 4.5 billion euros ($5.5 billion), three people close to the matter said.

FILE PHOTO - The logo of SIG Combibloc Group, manufacturer of carton packaging and filling machines for beverages and food, is seen at a plant in the town of Neuhausen, Switzerland June 15, 2016. REUTERS /Arnd Wiegmann

Its private equity owner Onex ONEX.TO has hired Rothschild ROTH.PA as an IPO adviser, and other investment banks have also been contacted regarding their interest in helping organize a potential deal, the sources said.

A spokesman said SIG did not comment on speculation about its capital market plans. Rothschild declined to comment, while Onex was not immediately available for comment.

SIG makes cartons for beverages and food and competes with larger rival Tetra Pak, a unit of Tetra Laval. It is expected to post earnings before interest, tax, depreciation and amortization of about 450 million euros this year.

A listing may value the company at 9-10 times that, including debt, in line with other peers including Bery BERY.N, Ball BLL.N, Silgan SLGN.O, Bemis BMS.N or Polyone POL.N, the sources said.

Onex bought SIG in 2015 from New Zealand billionaire Graeme Hart in a deal valued at 3.75 billion euros ($4.62 billion) that left the Canadian private equity company and SIG’s management as 100 percent owners.

In an increasingly crowded European equity raising market, Switzerland is seeing a flurry of stock market listings, including medical devices maker Medartis and sensor maker Sensirion announced this week.

Rothschild is also working on the Zurich IPO of cargo handler Swissport and, on an as yet unspecified exchange, the listing of logistics firm Ceva, sources have said.

SIG had been listed in Switzerland before as part of the Schweizerische Industrie Gesellschaft (SIG) conglomerate that made everything from juice cartons and passenger trains and military weapons. Its businesses were gradually sold off as the company trimmed its focus to packaging.

At the time of Onex’s purchase in 2015, the firm had seven production facilities across Europe, South America and Asia Pacific. It currently employs than 5,000 people at about 40 locations around the world.

($1 = 0.8116 euros)