This question already has an answer here:
Is US patent 3611966 still valid?
If yes, is there any provided expiration date?
If the patent application filing date was on or before June 8, 1995, the nominal expiration date is the longer of 17 years from the date of issue or 20 years from the earliest non-provisional priority claim. So it should have expired unless the owner renewed the patent. (I can't find the renewal date, but it was filed on June 4, 1969)