The man received third-degree burns to his hands, wrists,superficial burns to his face and burns in his throat, lungs and stomach due to inhaling the steam.
The worker may not regain full function in his hands.
A WorkSafe investigation found Juken failed to provide the appropriate controls to ensure the press was prevented from starting up while work was being carried out inside of the machine.
It was also found to have failed to provide information, training and instructions to protect workers using the machine from associated risks.
Simon Humphries, head of specialist interventions at WorkSafe, said the company had fallen below adequate safety standards despite 20 earlier convictions.
"This company should have learnt from its previous history, but instead another worker has suffered from life-changing injuries," Humphries said.
"If you have dangerous areas in your workplace from which workers should be excluded, now is the time to put systems in place to ensure they cannot be put in harm's way," he said.
"Ensure that the area is clearly labelled as dangerous, that access is restricted and that your workers are advised on appropriate procedures when access is required."
Breaching minimum work health and safety standards could result in a fine of up to $1.5 million.
Juken said it was "extremely concerned" that the accident occurred and that it had taken "a significant toll on the injured worker and his family and on the staff who looked after him until emergency services arrived".
"This accident was avoidable and we acknowledge that JNL failed as an employer to have the appropriate safety measures in place to prevent this. We have apologised to him and his family that this occurred," the company said.
"We have supported the recovery and rehabilitation of our staff member who was injured and he remains in his role."
Juken said it cooperated with the WorkSafe investigation and had introduced additional safety measures "to prevent this type of accident occurring in the future".
Improving health and safety at the Triboard Mill in Kaitaia was a major part of the refurbishment plan announced for the mill last year, the company said.
Juken was convicted under sections 36(1)(a), 48(1) and (2)(c) of the 2015 Health and Safety at Work Act.