In order to properly reject a claim limitations that excludes something (sometimes called negative limitations), an examiner must show that the prior art teaches the exclusion. The Federal Circuit has explained this as silence is not disclosure, and the PTAB generally follows this guidance. But, the PTAB will also liberally interpret disclosure to find exclusion of a feature in ways that might be unexpected to those without substantial experience in prosecution. Today we review an example.

The case is appeal 2022002616, serial number 15/899,143 to 3M. The invention relates to flat fold filtering face piece respirators. Claim 16 on appeal is reproduced below:

16. A flat fold filtering face piece respirator that comprises:
a harness; and
a mask body that lacks a nose foam and that comprises:
a filtering structure that contains a cover web and a filtration layer that contains electrically-charged microfibers, the filtering structure being folded over upon itself in a nose region of the mask body to create an overlapped portion that is present when the respirator is in an open condition and a folded condition, wherein the overlapped portion comprises a width (W) that is 1 centimeter or more wide and that extends across the upper perimeter of the mask body in a generally straight line when the respirator is in the folded condition, the folded filtering structure having a deflection greater than 0.8 mm and having a recoverability of at least 50% when tested under the Deflection and Recoverability Test, wherein the folded filtering structure has a thickness (T) of about 1 mm to about 5 mm; and a nose clip disposed in the nose region on the overlapped portion of the filtration layer such that the nose clip is disposed on an outer surface of the mask body or beneath the cover web.

As seen from claim 16, there is an express negative limitation: a mask body that lacks a nose foam.

The examiner rejected the claim based on a combination of three, or alternatively, four references. As part of those combinations, one of the references (Bostock) relied on in both rejections taught the use of a nose foam when using a nose clip. 3M argued that Bostock was therefore deficient, because the disclosure relied upon by the examiner expressly included a nose foam. The PTAB, however, pointed out that Bostock referred to the feature as “optional” and thus expressly taught an option without nose foam (citations omitted):

As cited by the Examiner, Bostock discloses respirators having nose clips configured in many different arrangements, including nose clips located on the outer surface of a mask. Bostock also expressly states that a nose foam is optional. Nothing in Bostock limits its teachings to the express embodiments or examples disclosed, and nothing in Bostock requires a nose foam when a nose clip is included. Thus, we agree with the Examiner that Bostock teaches a nose clip located on the outer surface of a mask and optional nose foam and that the combined teachings of the cited references satisfy claim 16.

So, while it is true that silence is not disclosure, teachings that a features is optional will likely be used by the Office as an express teaching of the lack of that feature. Read the specification carefully and avoid relying only on the drawings for your arguments that the prior art teaches including a feature proscribed by the claims.