CHICAGO — Private equity firm Mill Rock Capital has created a new platform, Mill Rock Packaging Partners LLC, to invest in growth oriented companies with advanced service and product capabilities in the specialty packaging industry. As part of the platform, Mill Rock has acquired Trojan Lithograph from Arbor Investments, a private equity firm focused on the food and beverage industry.

Founded in 1950 and headquartered in Renton, Wash., Trojan is a specialized designer and manufacturer of folding cartons and single-face laminate packaging for the food, beverage and consumer industries. Financial terms of the transaction were not disclosed.

Arbor has owned Trojan since 2014. Over the past six years, Arbor bolstered Trojan’s senior management and undertook sizable capital projects to expand capabilities, increase capacity and enhance efficiencies. Arbor helped Trojan prioritize the food and beverage industries and expanded the packager’s geographic reach to the broader Western United States.

“We’re proud of the transformational initiatives and wide-ranging operational enhancements we executed with this investment,” said Josh Schoenfelder, vice president of Arbor, which last fall recapitalized The Bakery Cos. “Now with enviable state-of-the-art operations, Trojan has emerged as the preeminent market leader of scale for high-end, graphic packaging solutions in the Pacific Northwest.”

Ian May, president of Trojan, will join other senior leadership in continuing in their operating roles with the transition in ownership.

“We enjoyed an outstanding partnership with Arbor,” Mr. May said. “Their steadfast strategic support, resources and capital investments were instrumental in driving our growth, and positioning us well to meet our evolving customer needs with highly differentiated, impactful, and eye-catching packaging.”