Transitional phrases between the preamble and the body of a claim are an important consideration in claim drafting. But even when that phrase is selected to be strategically narrow, support for and interpretation of the transition phrases can sometimes produce unexpected outcomes. A recent case illustrates these issues: Appeal 2024-001691, Application 16/759,218.
But first a brief review of the longstanding practice and the three traditional transitional phrases that govern the relationship between the preamble and the body of a claim:
“comprising” - the most common and broadest transitional phrase, “comprising,” is open-ended. This allows the inclusion of additional, unrecited elements to still fall within the claim’s scope.
“consisting of” - this is a closed term. It excludes any element not specifically recited, except for unavoidable impurities or elements inherently part of the structure or process.
“consisting essentially of” - this phrase defines a scope that is partially open. It allows for unlisted ingredients or steps only if they do not materially affect the basic and novel characteristics of the claimed invention.
Understanding these distinctions is important not only for proper claim drafting but also for anticipating the impact of examiner rejections.
Turning now to the PTAB case cited above, the Dyson invention relates to a filter media. Claim 1 on appeal is reproduced below:
A filter media consisting essentially of: a hydrophobic membrane, and a hydrophilic protective scrim secured to an upstream facing surface of the hydrophobic membrane such that a portion of the surf ace of the hydrophobic membrane is exposed to dust through the hydrophilic protective scrim, wherein the hydrophobic membrane comprises fibres of a first polymer having a diameter less than 1 micron, the hydrophilic scrim comprises fibres of a second polymer, the first polymer has a contact angle greater than 90 degrees, and the second polymer has a contact angle less than 90 degrees.
The examiner had cited prior art with a “pre-filter” in addition to the recited elements of claim 1. Dyson thus argued that the transition phrase would exclude additional elements that materially affect the novel characteristics of the claim. Specifically, Dyson cited the MPEP 2131 to support its argument that the examiner erred. The examiner’s response seemed to agree that if the claim were limited by the preamble, the prior art might be excluded, but nevertheless maintained the rejection by arguing that under the Broadest Reasonable Interpretation, the claim should actually be interpreted as using the term “comprising” in the preamble.
As explained above, patent professionals know that there is a substantial difference in using the preamble “comprising” as compared with “consisting essentially of.” The PTAB first reviewed the specification and prosecution history, noting that the specification and original claims used “comprising” in the preamble, and that nowhere in the specification was there any support for the “consisting essentially of” preamble. From the decision (internal citations omitted):
Appellant argues that the transitional phrase “consisting essentially of” in claim 1 should be interpreted to exclude the pre-filter in Kawano. Appellant cites paragraph 21 of US Pub. 2020/0316532 A1 as support, but does not explain why this paragraph requires the recited filter media to exclude such a component. Paragraph 21 is silent as to a pre-filter and we decline to import a negative limitation into claim 1 based on such silence.
Under the broadest reasonable interpretation standard, we agree with the Examiner and construe the claim term “consisting essentially of” to mean “comprising” in light of the Specification. As such, claim 1 is open-ended and does not exclude the prior art pre-filter. The rejection of claim 1 is therefore affirmed.
Thus, despite there being no written description rejection, the PTAB appears to use the BRI rubric, and the generally heightened (as a practical matter) written description requirement for negative limitations, to rewrite the claim’s preamble back to the original language.
While the outcome here may be tied to the specific facts of this case, one might consider some approaches to provide alternative outcomes. For example, one might utilize boilerplate in a specification noting that while the claims originally might utilize comprising, the specification contemplates replacing that transition with “consisting of” or “consisting essentially of” in other embodiments. Of course this may have other unintended consequences as well.
While patent practitioners may think they know what transition terms mean, this case illustrates that even black letter law can bend to Patent Office interpretations based on the support, or lack thereof, in the specification.