Company history

Tosoh began as a defection. Iwase Tokusaburo was managing director of Tokuyama Soda, an established maker on the Inland Sea coast, when he judged that the explosive growth of rayon and staple fibre would demand more caustic soda and soda ash than his own employer could supply. Rather than argue for it there, he left and built it himself: in February 1935 he founded Toyo Soda Manufacturing at Tonda, Yamaguchi (today Shunan), on the promise of an “ideal ammonia-soda plant,” and started mass production of soda ash in May 1936.

Chlor-alkali is the textbook process industry — it eats salt, electricity and limestone, and it rewards concentration. Toyo Soda put everything on one site, Nanyo, where the sea, the salt fields and coal-fired power all met. Capital went from ¥3m to ¥10m in 1937; soda-ash capacity, planned at 200 tonnes a day, reached 560 by the end of 1938. In 1942, at the navy’s request, the company added Japan’s first bromine plant working directly from seawater, for anti-knock feedstock. Wartime controls left no room to open plants elsewhere — and that constraint, by forcing every yen back into Nanyo, is part of why the site grew so fast.

In August 1946 the occupation authorities designated both the ammonia-process and the electrolytic soda plants as reparations. The company’s flagship line sat idle for four years — restart was permitted only in January 1950, and the designation itself was not lifted until April 1952. What kept Toyo Soda alive in the gap was the electrolytic plant it was still allowed to run, and a scramble to find products for the idled equipment: chlorosulfonic acid in 1947, then a widening range of chlorine- and bromine-based chemicals. In October 1953 it went further outside its trade, completing a cement plant inside the Nanyo grounds with Onoda Cement, and rode the post-war construction boom with it. Losing the core business is what taught the company to build next to it.

When the third president died suddenly in 1954, Ninomiya Yoshimoto took over and ran a decade of head-office-led rationalisation and continuous capital spending: sales of roughly $15.8M (¥6bn) in FY1954 more than doubled to about $37.8M (¥14bn) by FY1963. Around the soda core he added phosphoric acid (1962), a joint venture with America’s Stauffer Chemical (1965), and — from an in-house column for liquid chromatography — an entry into scientific instruments. These small, adjacent moves are the distant seed of what the company would later call its “third pillar.”

The larger step was petrochemicals. With the Shunan complex forming in 1964, Toyo Soda set up a joint EDC venture with its old rival Tokuyama Soda, began making vinyl chloride monomer by its own oxychlorination process in May 1966, and added low-density polyethylene the same year and ethyleneamines in 1967 — all inside the Nanyo fence. Meshing the electrolysis plant with petrochemical units on one site meant the chlorine that comes off caustic-soda production never had to be sold to anyone else. It was elegant, and it was cramped: land, water and ethylene supply at Nanyo had a hard ceiling, and clearing it would require a second home.

In 1969 the company broke the rule it had lived by for thirty-four years and committed to a plant outside Nanyo, joining an expansion around Daikyowa Petrochemical in the Yokkaichi complex on Ise Bay. VCM and mercury-cell electrolysis came on stream in 1971, high-pressure polyethylene in 1972, PVC polymer in 1973: in barely three years a one-plant company had a second base of equal weight. Overseas production started in parallel — electrolytic manganese dioxide in Greece (1973), PVC polymer in Indonesia (1975), ethyleneamines in the Netherlands (1978) — which is where the unusually export-heavy shape of today’s portfolio comes from.

The reach became national in April 1975 with the absorption of Tekkosha, a Tohoku ferroalloy maker that had itself diversified into manganese dioxide and PVC. Five plants — Yamagata, Toyama, Hyuga, Sakata, Ishinomaki — arrived at once, giving seven in total, and a Tokyo research centre opened the same month. It remains the largest single acquisition in the company’s history. Through the oil shocks that followed, the answer was structural: converting boilers from heavy oil to coal, with a coal-fired unit at Nanyo in 1982.

Under Yamaguchi Toshiaki, president from 1984, the company set out to stop being read as a soda maker. In October 1987 it adopted a corporate identity programme and changed its name from Toyo Soda Manufacturing to Tosoh; in 1988 it bought Varian’s sputtering-target business in North America and entered semiconductor materials. Then, in October 1990, it merged with Shin-Daikyowa Petrochemical — the ethylene centre at Yokkaichi — and its downstream affiliate Yokkaichi Polymer, taking the olefin chain into the parent company. Consolidated sales jumped to about $2.3B (¥330bn). Twenty-one years after the decision to go to Yokkaichi, and fifty-five after founding, Tosoh was being named alongside Sumitomo Chemical, Mitsubishi Kasei and Mitsui Toatsu — running ethylene, vinyl and caustic soda on two coasts at once.

The integrated chain was used hard. Through the late 1990s Tosoh concentrated investment on the vinyl side, and by June 1999 both caustic soda and vinyl chloride monomer had reached a combined one million tonnes a year across Nanyo and Yokkaichi — the scale that made it the largest domestic player in soda and PVC. April 2008 completed the next stage: 400,000 tonnes a year of MDI and 1,000 MW of captive generation, so that power and caustic soda at the top and vinyl and urethane at the bottom ran as one operation.

Five months later, Lehman Brothers failed. In the year ended March 2009 Tosoh posted its first consolidated operating loss — $196.5M (¥20bn) in the red, with a net loss of $244.8M (¥25bn) — and the basic-materials segment alone accounted for $169.4M (¥18bn) of the operating shortfall. The chain built to capture every step of the value also concentrated every step of the risk: a process industry that adds capacity at the top of demand is crushed by fixed costs at the bottom, and the gap between completing the investment and reporting the loss was half a year.

The pattern was not new. Two decades earlier, riding the bubble, the company had gone for aggressive ethylene expansion, been caught by the Gulf crisis and the turn in prices, withdrawn from ten businesses to cut weight, and then restarted investment narrowly in PVC — expansion, retreat and re-focus inside two or three years. What survived from that swing was the habit of backing the strong line rather than spreading thin, and it is the same habit that carried the 2008 bill.

In October 2014 Tosoh absorbed Nippon Polyurethane Industry, bringing chlorine-based products (PVC) and isocyanates (MDI) under one roof and completing the vinyl–isocyanate chain: from the electricity that splits salt, through caustic soda and chlorine, to MDI as the final derivative, all inside its own process. Sales of intermediate chlorine and hydrogen chloride to outsiders fell close to zero. The design point was to absorb the swings of a commodity business with steadier, higher-value urethane demand downstream — and it worked in the accounts: chlor-alkali operating profit recovered from FY15 onward, reaching $593.8M (¥67bn) in the year to March 2018 and $633.1M (¥70bn) in the year to March 2022.

Meanwhile the businesses seeded decades earlier came of age. Specialty materials — high-silica zeolites, zirconia, quartz glass, instruments, bioscience — closed on the core through the 2010s, and by FY21–FY22 were earning between $331.1M (¥44bn) and $398.1M (¥52bn) a year in operating profit. Engineering (water treatment, plants for the electronics industry) grew faster still: in FY24 it turned $1.1B (¥169bn) of sales into $221.8M (¥34bn) of operating profit, the highest margin in the group. That year the segment ranking read specialty $254.8M (¥39bn), engineering $221.8M (¥34bn), chlor-alkali $62.7M (¥10bn) — the company known as a soda maker no longer earning its living from soda.

The pendulum has since swung back. The mid-term plan begun in FY2025 replaces the old commodity/specialty split with two segments, chain and advanced, and directs between $1.5B (¥220bn) and $1.7B (¥250bn) of investment over three years into the chain — chlor-alkali and petrochemicals — on the reasoning that tilting too far toward the newer specialty businesses would leave the founding assets un-renewed. The target is $1.1B (¥170bn) of operating profit by 2030. Tosoh’s answer to the question of what to keep has been consistent for ninety years: keep it, and grind it down on cost.