The patent application was filed on June 7, 1995 and issued on April 8, 1997.
US patents issuing from patent applications filed on or after June 8, 1995 have a term of 20 years from the earliest non-provisional patent application priority date. US patents issuing from patent applications filed prior to June 8, 1995 have a term equal to the greater of 17 years from issuance or 20 years from the earliest non-provisional patent application priority date.
In this case, since 17 years after issuance is greater, the patent expires on April 9, 2017.
The above reasoning is clear. However, the patent is a divisional of a continuation of a continuation-in-part of an abandoned application filed July 25, 1990:
Division of Ser. No. 254,136, Jun. 6, 1994, which is a continuation of Ser. No. 7,664, Jan. 22, 1993, abandoned, which is a continuation of PCT WO 92/02,307 filed Jul. 23, 1991, which is a continuation-in-part of Ser. No. 557,104, Jul. 25, 1990, abandoned.
Normally, this would affect the expiration date of the patent by using the earliest filing date. In this case, that would appear to be July 25, 1990, giving an expiration date of April 8, 2014.
The Legal Status are as follows:
Feb 20, 1996 AS Assignment Owner name: TRIMEX COMPANY, NORTH CAROLINA Effective date: 19930521 Jun 27, 2000 FPAY Fee payment Year of fee payment: 4 Sep 13, 2004 FPAY Fee payment Year of fee payment: 8 Sep 25, 2008 FPAY Fee payment Year of fee payment: 12
Do the expiration date rules for divisional patents and continuations not apply to patents filed prior to June 8, 1995?
Do abandoned or continuation-in-part normally have any additional effect on the calculation of an expiration date?