Natural Resources Wales (NRW) is investigating what happened at the Albany Molecular Research Inc site in Greenfield.
Lara Cubley, regulatory officer at NRW, said the spill was contained within a building.
She added action would be taken if the site's environmental permit had been breached.
The man taken to hospital at Ysbyty Glan Clwyd was kept in overnight as a precaution.
It is not known what chemical was involved.
A man has been treated in hospital after a chemical spill at a factory in Flintshire.