The number of workers poisoned by a toxic chemical at a Taiwanese factory in Jiangsu province has increased from 47 to 62, more than a month after angry employees attacked the company over management and pay disputes.

Workers from United Win Technology, which is owned by the Taiwan-based Wintek Corporation that produces iPad components for Apple, have suffered from muscular atrophy and damage to their nervous systems since August 2008 after they used n-hexane as a cleaning agent for touch panels produced at the Suzhou factory.

They complained they had not been given safety instructions, nor warned of the dangers of the chemical, and had worked in poorly ventilated rooms for long hours.

Among the 100 potential victims placed under medical supervision, 47 were confirmed as being poisoned by overexposure to the toxic chemical earlier last month. The figure has now risen to 62, according to company executives.

"There may be a latent period before symptoms of poisoning show up. That's why we are now finding more victims," James Chen, general manager of United Win, told China Daily yesterday.

Some of the previously confirmed patients had already recovered and left the hospital, but the company will launch a second round of medical checks next month, including those who have recovered, to ensure they have fully regained their health, he said.

"We also replaced the toxicant with alcohol last August as soon as we found it could cause chronic poisoning. In the future, any chemical used at the factory will have to pass a safety assessment," Chen added.

N-hexane is known to create extensive peripheral nervous system failure in humans. In severe cases, atrophy of the skeletal muscles is observed, along with a loss of coordination and problems of vision.

Liu Jie, spokesman for the Suzhou Industrial Park where the factory is located, confirmed that all victims have received treatment. "There are now 44 workers who are still hospitalized. A compensation plan will be worked out after they recover and receive work injury appraisal," he said.

Wintek is one of the world's leading producers of small- size mobile phone panels and touch panels. Its customers include Nokia and Apple.

Employees at its Suzhou unit had previously complained about being subjected to a poor working environment and disrespect for their rights.

Their discontent led to a mass protest on Jan 15 when more than 2,000 of them smashed vehicles and facilities at the factory.

The local government said workers had been provoked by rumors that the company planned to cancel a year-end bonus, which company executives later dismissed and promised to distribute before the Chinese Spring Festival.