Bertram Capital is buying Rowmark LLC for an undisclosed amount. Findlay, Ohio-based Rowmark manufactures engineered plastic sheets used for engravings and signs.

Bertram Capital, headquartered in San Mateo, Calif., invests in middle-market companies in the business services, consumer, health care, industrial and technology sectors.

The firm typically invests between $25 million and $100 million in each deal. Bertram has about $850 million in committed capital under management. The firm’s portfolio companies include Paula’s Choise, Spireon and Webex. Rowmark is the company’s third acquisition in the plastics industry.

Piper Jaffray acted as financial adviser to Bertram on the deal.