In 1957, the Asahi Kasei Group and Mitsubishi Group became Japan’s earliest manufacturers of polystyrene, Asahi Kasei using technology licensed from Dow Chemical, and Mitsubishi using technology licensed from Monsanto. Domestic Japanese demand for polystyrene rose steadily due to rapid economic growth and increased adoption of polystyrene to replace other materials. This resulted in a healthy expansion of business for both companies. After peaking in 1990, however, domestic demand began declining markedly as electric appliance manufacturers increasingly shifted their production to overseas facilities. To cope with falling demand, the Asahi Kasei Group and Mitsubishi Group both restructured their polystyrene operations, including the closure of some of their production facilities.

In October 1998, Asahi Kasei and Mitsubishi Chemical established A&M Styrene combining their respective polystyrene businesses in order to achieve further cost reductions through production capacity cut-backs. After starting out as a marketing company, A&M Styrene became an integrated polystyrene company in October 1999 with the additional integration of the polystyrene production and R&D divisions of its two parent companies.

The polystyrene business of Idemitsu Petrochemical (now Idemitsu Kosan) began in 1968, with manufacture using in-house technology. The business grew steadily before domestic demand for polystyrene began declining in the 1990s, and Idemitsu also implemented measures to raise efficiency, including closure of some production facilities.

PS Japan was born in April 2003 through the combination of A&M Styrene and the polystyrene business of Idemitsu Petrochemical. The combination was based on an understanding among Asahi Kasei, Mitsubishi Chemical, and Idemitsu Petrochemical that this would enable further cost reductions and production capacity optimizations which were essential to strengthen the operational foundation and ensure the sustainability of the polystyrene business. PS Japan has been Japan’s leading polystyrene manufacturer ever since.

PS Japan has continued maintain its solid position as the leader of the Japanese polystyrene industry despite the severe business environment marked by sluggish domestic demand and competition from imported resin. In October 2009, Asahi Kasei and Idemitsu Kosan acquired all shares of PS Japan held by Mitsubishi Chemical, and PS Japan became a joint venture between the two companies.