What’s in a Range? When Innovation Overlaps with Prior Art

August 2020

By: Rackham H. Karlsson 

Technological progress is often incremental. However, even incremental improvements to a machine or process can make the difference between commercial success or failure. Are these commercially valuable advancements patentable? In particular, what happens when an invention’s key innovation involves numerical values or ranges (e.g., temperatures, ratios of materials, etc.) that overlap with a range described in the prior art? It turns out that it is sometimes possible to get a patent on such an invention, but only if fairly demanding legal criteria are satisfied.

In patent law, the term “overlapping range” refers to an overlap between what is claimed as an invention and what is described in the prior art.  Where the ranges of a claimed invention overlap the ranges in the prior art, even by only a small amount, there is a presumption that the claimed invention is obvious and therefore unpatentable. For example, in one recent case before the Federal Circuit, claims to a chemical process operating in a range of temperatures below room temperature, from 10-18 degrees Celsius, were found to be obvious over a prior art process operating at room temperature, in a range from 18-25 degrees Celsius. The overlap in the ranges at 18 degrees Celsius rendered the patent invalid.

It is not necessary for an overlapping range to be found in a single prior art reference in order to invalidate a patent. In a case concerning weight lifting plates, the patent owner had claims to a weight plate with three handles (i.e., openings in the body of the plate that allow for easier handling when loading the plate onto a barbell). These claims were found to be invalid based on a combination of prior art references, which described weights having one handle, two handles, and four handles. Collectively, the references described a range of prior art that rendered the claims to three-handle plates obvious.

In some cases, it is not even necessary for an invention to strictly overlap with the range described in the prior art if the difference is merely in degree. For example, where a patent applicant sought a patent on a tennis racket handle with a certain ratio of materials, the claims were found to be unpatentable even though the ratio did not overlap with the ratios described in the prior art. Because the performance features of the materials used were well known in the field, the court considered the claimed ratio to be merely an obvious product of experimentation, rather than a patentable innovation. Where the general conditions of a patent claim are disclosed in the prior art, the courts do not consider it to be inventive to discover the optimum or workable ranges through routine experimentation.

Still, while overlapping ranges create a presumption of obviousness, patent owners can overcome that presumption with evidence that their claims embody some unique feature or inventive concept beyond a mere numerical difference in value or range. For example, the Supreme Court case Minerals Separation, Ltd., et al. v. Hyde, 242 U.S. 261 (1916) dealt with a process for separating ore from gangue. It was well known in the prior art to use oil in such processes, and the primary difference between the claimed invention and the prior art was in optimizing the amount of oil used. Even so, the Supreme Court found these claims to be patentable, because the relatively “minute” amount of oil used combined with air bubbles to yield an “unexpected result,” a frothy suspension that carried the ore to the surface. This unexpected result was different from anything found in prior processes that also used oil, and therefore elevated the invention to patentability.

Mineral Separation teaches that any inventor considering claims involving a range of temperatures, weights, times, or ratios of ingredients, chemicals, or components, must carefully consider the inventive significance of the range. An invention is unlikely to be patentable if the improvement over the prior art is merely a matter of degree. However, if the particular value or range used in the invention is critical in achieving the intended result – not simply doing so more effectively than before – then that criticality may breathe life into the patent claim. Ideally, the invention would use that value or range differently than in the prior art (as in the Minerals Separation case, where the oil combined with air bubbles to create a frothy suspension). In addition, it is worth considering whether there are any differences in the process used to obtain the claimed value or range (e.g., by cooling a room to below room temperature, if the prior art always operates at room temperature).

In short, in the presence of an overlapping range, showing that the claimed range is critical to producing a useful, unexpected result that is not described in the prior art can help overcome an obviousness rejection or challenge. Meanwhile, in those cases where filing a patent application does not seem to be a good value proposition, it is worth considering other ways of protecting the intellectual property.