The move means the group will be vying with Bezier to be the biggest PoS printer in the country.
"We like the business. They share our approach to service and it fits with our strategy of selling more than just print," said St Ives chairman Miles Emley.
Kent-based Displaycraft, St Ives' existing PoS business, has sales of circa 8m and is part of its recently rebranded St Ives Print & Display division, which includes the multimedia packaging operations.
SP has litho, screen and digital printing facilities at its sites in Redditch and Birmingham. It made a pre-exceptional profit of 4.3m in the year to 31 March.
Clients include Halfords, Pizza Hut, Adams, Boots, Arcadia and Thomas Cook. It works for brands including Cadbury, Levi's, Harley Davidson, Bacardi and Jaguar.
The firm was the subject of an 18m MBO five years ago.
St Ives is paying an initial 33m for SP, the bulk of it in cash, and will pay up to 3.92m more if the firm hits certain profitability targets next year.
Story by Jo Francis