When preparing a disclosure of the steps of a new chemical process, method of manufacturing a new compound, or any invention that requires the reporting of physical or chemical parameters such as temperature, composition, molecular weight, etc., careful attention should be given to the reported ranges of those values. As an inventor, you should give thought to the extent that the ranges can be stretched. How broad of a range will conceivably work? In what range could a competitor financially compete with the new product or method, even if the range is broader than the optimal range and would require additional costs? What range of values would be very commercially competitive with the new product or method? Answering these questions will ensure that the description of the invention as filed with the Patent Office is broad enough to support any amendments that slightly narrow the claims and will also provide the broadest possible protection against your competitors.
A recent patent infringement suit filed by Viskase Corporation illustrates the importance of numerical ranges and how they can affect the rights granted under a patent.
Viskase had six patents related to heat-shrinkable, multilayer thermoplastic compositions having outer layers constructed of biaxially stretched sheets of "very low density polyethylene" (VLDPE) copolymers. Four of the patents described the outer layers of VLDPE as having specific limitations. In particular, Viskase claimed outer layers of VLDPE having a "density below about 0.91 g/cm^sup 3^."
American National Can Company (ANC) marketed a similar thermoplastic composition. ANC's heat-shrinkable films were constructed of linear ethylene copolymer having a density of 0.912 g/cm^sup 3^.
In determining whether ANC's product infringed upon Viskase's patent, the first task of the court was to determine the meaning of the phrase "below about 0.91 g/cm^sup 3^." The court reasoned that any number that would round up or round down to 0.91 was included in the range of "about 0.91." So, any linear ethylene copolymer, heat-shrinkable film having a density between 0.905 and 0.914 g/cm^sup 3^ would infringe upon Viskase's patent. Since ANC's film fell inside of this range, the court concluded that the film infringed the patent.
ANC disagreed with the court's conclusion and appealed the decision. On appeal, ANC argued that the written description of the invention and the prosecution history, as well as conventional descriptions of the densities of various classes of polyethylenes, make clear the phrase should not have been given broader meaning than "below about 0.910 g/cm^sup 3^,11 in other words, between 0.9095 and 0.9104 g/cm^sup 3^. In support of its argument, ANC pointed out that during the prosecution of the patents Viskase used three significant figures, 0.910 g/cm^sup 3^, to describe the density of the VLDPE layer.
Viskase distinguished its invention from a cited prior art reference that described a multi-layer, heat-shrinkable composition using a linear low density polyethylene copolymer having a density range of "0.910 to 0.940 g/cm^sup 3^." It distinguished its product by stating that the Viskase product has a density below about 0.910 g/cm3, which is not within the claimed range of the prior art reference.
Additionally, ANC argued that 0.91 g/cm^sup 3^ is a generally accepted dividing line between "very low" and "low" density polyethylenes, and that a density range of the breadth adopted by the lower court would take "very low density" into the range of "low density."
The appellate court agreed with ANC's contentions based upon Viskase's own argument to the Patent Examiner. Despite evidence that conventional descriptions of polyethylene densities did not establish a dividing line between VLDPE and LDPE precisely at 0.910 g/cm^sup 3^, the appellate court concluded that Viskase itself set the boundary at 0.910 g/cm^sup 3^ for its patents and that films having a density of 0.912 g/cm^sup 3^ did not fall within the range encompassed by Viskase's claims.
This example not only shows the importance of the attention that must be given to disclosed numerical ranges, but also illustrates how approximations can add breadth to a claimed invention. Claimed numerical ranges or limitations will be read literally when words like "about" or "approximately" are not used. But potentially infringing products or methods will not escape infringement simply because they come near to, but outside, the claimed numerical limit when words of approximation appear in the claims. Also, it should be kept in mind that the written description of the invention should use the same words of approximation. This will ensure that the claims are supported by the written description and that issues similar to those faced by Viskase won't affect you.
[Author Affiliation]
comments and questions regarding these developments should be directed to CEP's Washington office: (202) 962-8690: Fax: (202) 962-8699; e-mail: dc@aiche.org;http://www.aiche.org.
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