Established
Founded as "Toyo Sōdō Kōgyō" in Yamaguchi Prefecture's Tōno District (now Shunan City) by Tokusaburo Iwase, aiming for a "modern great ideal factory" in the soda industry. The ideal factory Iwase envisioned involved operating both ammonia process soda and electrolytic soda along with cement. By utilizing by-products from the soda production process as cement raw materials and using the waste heat from cement firing to generate steam required for soda production, this model simultaneously achieved competitive soda production and zero emissions.
The main gate at the time of establishment (now East Gate) and the main building (now Soda Production Department Office).
Establishment of Toyo Saida Industrial Co., Ltd.
Start of production of soda (soda ash, caustic soda) by the ammonia method.
Start of bromine production.
Start of production of ammonium chloride and hydrochloric acid in the chlor-alkali business.
Start of cement production in the chlor-alkali business.
Opening of the New York branch office, our company's first overseas location. Closed in 1979.
Start of production of ethylene dichloride (EDC) in the functional products business.
Start of production of vinyl chloride monomer (VCM) in the chlor-alkali business.
Start of production of low-density polyethylene (LDPE) and ethylene vinyl acetate copolymer (EVA) in the petrochemical business.
Start of production of synthetic zeolite at the Toyama plant (now Tosoh Zeolam) in the petrochemical business.
At that time, our company had developed with only one site in the Nanyo area, but to leap to a nationwide integrated chemical company and trace raw materials back to ethylene, we decided to expand to Yokkaichi. It was established as a wholly-owned subsidiary responsible for operating the Yokkaichi plant. In 1975, along with the merger of our company and Tekkōsha, Yokkaichi Higashi Sō also merged.
Start of production of ethylene amine in the functional products business.
Establishment of Yokkaichi East Saida. At the time, our company had developed only one site in the Nanyo area, but in order to become a nationwide comprehensive chemical company and trace back to the raw material of ethylene, we decided to expand to Yokkaichi. It was established as a wholly-owned subsidiary of our company responsible for operating the Yokkaichi plant. In 1975, Yokkaichi East Saida merged along with our company and Tekkōsha.
Start of production of electrolytic soda, vinyl chloride monomer, hydrochloric acid, and sodium hypochlorite.
PVC resin production started (currently Daioh PVC Co., Ltd. Yokkaichi plant)
Start of low-density polyethylene production.
High-speed liquid chromatography production started
Merged with Tekkōsha. Tekkōsha was established in 1925 with the purpose of producing ferroalloys. It built many factories mainly in the Tōhoku region, and also operated mines and its own power generation. It diversified into metal electrolytes, acetylene organic chemistry, and fertilizer businesses, and was a pioneer in the carbide process for producing vinyl chloride. Several businesses inherited from Tekkōsha remain important to our company today.
Merged with Kasumi Combinate (1972)
IJPC (Iran-Japan Petrochemical) established in October 1989; joint venture dissolved
Petroleum resin production started: C9 petroleum resin (Petco®) and C5-C9 petroleum resin (PetroTack®)
Paste PVC production started (Luron Paste®)
Zirconia powder production started
Chlorosulfonated polyethylene (TOSO-CSM®) production started
Linear low-density polyethylene production started
Sodium hypochlorite production started
High silica zeolite production started
Renamed to Tōsō Co., Ltd.
Dissolution of joint venture.
Shin Daikyoha Petrochemical was established in 1968 as an ethylene center company in the newly developed Kasumi Compound in Yokkaichi City, Mie Prefecture, as a joint venture among seven companies including Daikyo Oil, our company, and Tekkōsha. During the process, our company became the leading shareholder and, recognizing that strengthening and expanding the petrochemical business was essential to survive the harsh industry competition, merged. Our company became a comprehensive chemical company with an integrated petrochemical division. As a result, our Yokkaichi plant and Shin Daikyoha Petrochemical's Yokkaichi plant were merged into the "Yokkaichi Office", and the Nanyo plant became the "Nanyo Office".
Merged with Shin Daikyoha Petrochemical. Our company became the leading shareholder, merging to strengthen and expand the petrochemical business. The Shikokuchō plant and Shin Daikyoha Petrochemical's Shikokuchō plant were integrated into the "Shikokuchō Office", and the Nanyo plant became the "Nanyo Office".
Built a 1 million ton vinyl chain system. Decided to construct a new plant for PVC monomer. Increased production capacity, expanded the in-house power plant, and carried out bottleneck removal work at the ethylene plant. In 1999, the combined annual capacity of the Nanyo and Shikokuchō offices reached 1.034 million tons of PVC monomer and 1.026 million tons of electrolytic soda (including Tōhoku Tōsō Chemical), becoming the largest scale in Japan.
Japan Polyurethane Industry was established in 1960 with the purpose of producing polyurethane raw materials. Our company invested in 1963, and with the aim of expanding the vinyl isocyanate chain, it became a wholly-owned subsidiary in 2006 and merged in 2014.
Merged with Nippon Polyurethane Industry. Nippon Polyurethane Industry was established in 1960 to commercialize polyurethane raw material production. Our company invested in 1963, and to expand vinyl isocyanate chain, it became a wholly-owned subsidiary in 2006 and merged in 2014.
Functional product business: Developed conductive polymer (SELFTRON®)
Tosho, in collaboration with Chuo Bussan, developed the non-backbone polyethylene "Petrosen CZ11" for foam with high heat resistance. It is the first domestic non-backbone polyethylene with high heat resistance, and it has been selected as a material for the foam layer of Chuo Bussan's air-conditioning insulation pipes. Conventional cross-linked polyethylene foams were difficult to remelt, and many of the waste pieces were discarded.
Tosho has decided to acquire all shares (50%) of Nanyo Chemical, which is owned by Asahi Kasei, and make it a wholly‑owned subsidiary. By securing a stable supply of HDI monomers, Tosho aims to stabilize the HDI‑derived product business and ensure stable procurement for the new plant that began commercial operation at the end of September 2026.
Tosoh developed the fully automated chemiluminescent enzyme immunoassay system AIA-CL600 and began domestic sales on October 8, 2026. The AIA-CL series includes a mid-sized model that complements existing large, semi-large, and small models, enabling flexible proposals tailored to measurement purposes and installation environments. The company also indicates its policy to continue meeting diverse needs in clinical settings.
Tosoh Corporation has published its 2026 integrated report, TOSOH REPORT, and sustainability report on its website to enhance corporate value and help realize a sustainable society. The reports clearly explain the company's contributions to solving social issues and the value of its businesses. An explanatory video is also available on the company's official YouTube channel.
Tosoh Corporation will exhibit at BioJapan 2026 at Pacifico Yokohama from October 7 to 9, 2026. Its booth will feature life science products including cell culture equipment, magnetic particles for biomolecule purification and reagents for extracellular vesicle purification. Free advance registration is required.
Tosoh will revise prices for chloroprene rubber (CR). Effective with shipments from September 24, 2026, all Skyprene grades will increase by at least ¥110/kg for carboxyl-modified chip grades and at least ¥60/kg for other grades. The revision is necessary because increases in raw material prices and fixed costs have exceeded the limits of the company’s own efforts to absorb them.
Tosoh will raise prices for chlorosulfonated polyethylene (CSM) by at least ¥40/kg from current levels, effective with shipments from September 24, 2026. The measure responds to higher fixed and logistics costs amid inflation and is intended to ensure business continuity and stable supply.
Tosoh Corporation donated ¥15 million through the Japanese Red Cross Society to support people affected by the 2026 Kumamoto earthquake. The company hopes the affected areas will recover and rebuild quickly.
Stakeholders in the chemical industry, including Tosoh, are visualizing the movement of hazardous materials logistics on a national scale and working towards stabilizing transportation.
The chemical industry, including Tosoh, has formulated guidelines that introduce the first industry-wide data interconnection platform and standardize logistics data to address transportation capacity shortages.