The following article appears in the journal JOM, 48 (6) (1996), p. 67. JOM is a publication of The Minerals, Metals & Materials Society

Double Patenting—One Patent per Invention

Patent claims recite the scope of protection provided by a patent. The Patent Statute precludes the issuance of two commonly owned patents containing claims for the identical invention. This is referred to as "same invention double patenting." Court decisions have created a second type of double patenting. When a claim of one patent is an obvious variation of a claim of another and both patents are owned by the same person or company or subject to an obligation of assignment to the same person or company, the second patent is invalid because of "obviousness-type double patenting," unless curative action is taken.

The first type of double patenting precludes the issuance of two patents for the same invention and has its origin in Section 101 of the Patent Statute, which states that an inventor may obtain a patent for any of the recited categories of inventions. This language has been interpreted to be an absolute bar to the issuance of a second patent for the identical invention. In determining whether a second patent is for the identical invention of a first patent, one determines whether there are patent claims that "cross-read." This means that if a claim in the first patent is identical to a claim of the second patent, no practice would infringe one claim without infringing the other. If such is the case, the second patent to issue is invalid on the basis of same invention double patenting.

The issue of double patenting may be raised after before patents have issued. It could be raised during the pendency of both applications or after one patent has been issued. The Patent and Trademark Office Examiner could issue a provisional double patenting rejection of one or more claims in a patent application. An applicant responding to such a rejection could avoid the same by modifying the claims so that the claims do not cover the identical invention.

In the obviousness-type double patenting, a first patent or application has at least one claim which, though not identical to any claim of the second patent or application, is an obvious variation and would not be patentable were one citable as prior art against the other. In this situation, there is no effort to patent the identical invention in two separate patents. The potential harm is that by having claims that are obvious variations of each other in two separate patents, the expiration of the first patent results in an improper extension of the patent rights due to the unexpired second patent. The obviousness-type double patenting objection may be overcome by filing a "terminal disclaimer." This is a written statement by the owner stating that the owner has disclaimed the period of the second issued patent that would extend beyond the expiration of the first patent. This terminal disclaimer avoids the double patenting objection only so long as the patents are commonly owned.

Double patenting applies even if the inventor or inventors named in each patent or application are not identical, so long as there is common ownership. If, however, two patent applications owned by different parties claimed the identical invention, the applications might become involved in an interference proceeding. In an interference, the Patent and Trademark Office requires proof of which inventive entity completed its invention first and would grant the claims to that party. Under certain circumstances, there can be an interference between an issued patent and a pending application.

For other situations where different parties own the patents or applications which claim obvious, but not identical, inventions, their relative effective dates as prior art against one another would be considered. The one with the later effective date would be rejected or invalid based on prior art considerations rather than double patenting.

One exception to the double patenting rejection involves the Patent and Trademark Office's right to enter a "restriction requirement" in a patent application where two or more independent and distinct inventions are claimed in a patent application. When this occurs, an applicant is required to elect to pursue a single group of claims directed toward a single invention. The claims that are not elected can be pursued by a divisional application, which involves filing certain documents with the Patent and Trademark Office, paying an additional filing fee, and requesting that the Patent and Trademark Office open a new file for a separate application (which, while being accorded the benefit of the filing date of the first application, will be prosecuted separately). In the event that the second application becomes a patent, it cannot be invalidated on the basis of any alleged double patenting as the only reason there would be more than one patent is that the Patent and Trademark Office ruled that there was more than one invention disclosed and claimed in the original application.

The Patent Statute states that a patent issuing on either the original application or a divisional application cannot be employed as a reference against the other. This has been interpreted as precluding raising a double patenting objection. If, however, the applicant had voluntarily filed two applications that matured into two patents and the later issued patent were to be challenged based on double patenting, the defense of the Patent and Trademark Office restriction requirement would not be available. It is, therefore, desirable to include as much closely related subject matter in one application as one can rather than voluntarily fragmenting the disclosure into a plurality of applications. Also, in some instances, a restriction requirement might not be entered by the Patent and Trademark Office against a single application, in which case one patent would issue. In others, if the restriction requirement were entered and the parent patent issued and one or more additional patents issued from one or more divisional applications, none of these would be in jeopardy of invalidation based upon double patenting.

It will be appreciated, therefore, that in situations where commonly owned separate applications are voluntarily filed, one must be careful that no claim of one application or patent recites the same invention as another. To the extent to which an obviousness-type double patenting relationship exists between one or more claims of one application or patent and one or more claims of another application or patent, this defect can be cured by a terminal disclaimer.