The operational limits of the inventions are confined to the limits set by the numerical ranges. The numerical range signifies the limit to which the invention is covered. These include ranges associated with physical parameters such as temperature, pressure, and also chemical parameters including chemical compositions. How to claim numerical ranges? Are there restrictions in claiming numerical range beyond the restrictions imposed by the prior art?
The US patent law mandates that the numerical range must comply with the written description requirement. In an interesting case, the US court withheld an application based on the written description requirement for defining a specific example of 36% when the complete specification disclosed a range between 25% to 60% .1 However, when the claim was amended to include a range, closer to the lower limit of a specific example “between 35% and 60%”, the court allowed the patent, which was in compliance with the written description requirement after the amendment. An ideal example to highlight this would be an Indian application, 673/DELNP/2004, on the composition of an excipient in a formulation, which disclosed the ranges for the degree of methyl and hydroxy substitution in hydroxypropyl methyl celluloses, closer to either the lower (15% to about 35%) or the upper limit (2% to about 15%) (shown below) and adhered to the norms set by the written description requirement.
If the narrow ranges are covered by reference to a specific example, how to cover broader ranges and still comply with the written description requirement? In such cases, the complete specification must carry different sets of numerical range along with specific examples to map and cover portions for intermittent ranges. This can be best understood with 82/DELNP/2010, application on the composition of Azeotropic mixture of HFO-1234 /propane, which maps broader range from 0 to 100 and still captures either a lower or upper limit for this broader range.
Another interesting case law on numerical ranges is Eiselstein V. Frank (1995), wherein the use of “about” in describing the alloy with a Nickel content of “45% to 50%” failed to cover an alloy within a range from “50% to about 60%”.2 The use of “about” sets the limit of approximation and does not stretch beyond the limit proposed. In the above example, 82/DELNP/2010, “zero to about 50%”, “zero to about 40%” , “5 wt% to about 45 wt%”, sets the numerical range limit to the number defined by “about”. And use of “preferably” or “preferred” is common in disclosing the numerical ranges, which either explains the sweet spot of the invention or suggested range to carry out the invention. The following example from the Indian application, 262/DELNP/2005, discloses a composition of an active ingredient in a preferred range. But care must be exercised in practice, it does not exclude the broader range covered.
In essence, the numerical ranges has to be used in the claim with clear distinction from the prior art and adhere to the standards set by the written description requirement. And most importantly, the ranges claimed must match the ranges covered in the embodiment.