WAUKEGAN, Ill. (AP) _ Lawyers for a man sentenced to 80 years in prison for fatally poisoning his son in a botched effort to extort money from a baby formula manufacturer said they will continue to try to prove his innocence.

Ricky Irby Sr. was convicted of murder in May for the sulfuric acid poisoning of Quinten Irby. The boy was 3 months old when the poisoning occurred, but lingered for more than two years before dying in August 1986.

Irby was sentenced Friday by Lake County Circuit Judge Harry Hartel, who could have ordered Irby, 29, to death.

In explaining why he was sparing Irby, Hartel said Irby had no substantial criminal record before the child's death and was unlikely to commit another such crime.

Irby would be eligible for parole in 40 years, prosecutors said.

Irby's lawyers said they intend to appeal.

''We're very relieved that there's no death penalty,'' said Irby's attorney, Robert Will. ''It's going to make the appeal much less complicated. Now we can concentrate on the guilt or innocence in our appeal.''

The boy's mother, Sheila Smith, earlier this year pleaded guilty to the boy's murder in return for a 20- to 65-year prison sentence. Her sentencing was scheduled for July 19.

Ms. Smith, now 27, was said to have administered the poison to the boy after the couple contrived a scheme to accuse a formula manufacturer of selling tainted formula.

In 1987, Irby filed a lawsuit against Abbott Laboratories, maker of Quinten's baby formula. But the lawsuit was dropped a year later.

On Friday, prosecutors said they were pleased with the sentence.

Irby was responsible for ''the most horrible crime one could imagine,'' said assistant Lake County state's attorney Matt Chancey.

''He did not personally inflict the acid. But he is still morally and legally responsible, and he more likely was the instigator and leader of the plan,'' Chancey said. ''Obviously, we would have been happier had he received the death penalty. But we're pretty happy with 80 years.''