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Home > Nanotechnology Columns > Magda Carvalho PhD, JD > Obviousness: On carbon nanotubes

Magda Carvalho
Patent Attorney
Patent Law at M. Carvalho

Carbon nanotube inventions have succeeded as innovative and hundreds of patents have been awarded. But as claimed inventions accumulate, issues of patentability relating to obviousness inevitably arise. Specifically, methods that produced end-derivatized single-wall carbon nanotubes could not successfully stand up to 35 U.S.C. § 103 rejection at the Board of Patent Appeals and Interferences (BPAI).

November 1st, 2008

Obviousness: On carbon nanotubes

This column discusses ex parte Colbert et. al. (September 30, 2008), which was a case before the BPAI over a rejection based on obviousness.(1) The invention related to a method for producing end-derivatized single-wall nanotubes. The invention combined known elements by known methods and as such it was vulnerable to an obviousness attack. In this scenario, one way to rebut a prima facie case of obviousness is to make a showing of unexpected results achieved by the invention. Most important, the results must be accompanied by evidential facts/data and not mere arguments (hypotheses or conclusions). Colbert presented "evidence," but nonetheless the claims were held invalid as being obvious. Colbert's evidence had no effect because it did not specifically address the matters affecting the determination of obviousness. The case emphasizes the importance of submission of test data showing unexpected/surprising results to rebut a prima facie case of obviousness.

What are carbon nanotubes?

Carbon nanotubes are hollow cylinders (tubes) made of carbon atoms of about 1-3 nanometers (1 nm = 1 billionth of a meter) in diameter, and hundreds to thousands of nanometers long. Sometimes the tubes have a single wall — called single-wall carbon nanotubes— or have multiple walls — called multi-wall carbon nanotubes. The single-wall nanotubes have a diameter in the range of 1.1-1.3 nm, the walls are bent and contain characteristic defects. Multi-wall carbon nanotubes are structures that consist of several concentric tubes of carbon, nested inside each other like Russian dolls, and are strong and resistant to damage. Whereas the multiwall nanotubes are tens of nanometers across, the typical diameter of a single-wall nanotube is just one or two nanometers. Some carbon nanotubes can be extremely efficient conductors of electricity and heat; depending on their configuration, some act as semi-conductors. Single-wall carbon nanotubes are excellent conductors and exhibit electrical properties that are not shared by the multi-walled carbon nanotubes. Since the carbon nanotubes are composed entirely of carbon, they are extremely light.


As discussed earlier in the June column (Obviousness: KSR rationale applied to nanotechnology. ) an unsettling question for the nanotech industry is how the Supreme Court's decision in KSR v. Teleflex will impact their patents.(2) The ruling has also an effect on how the U.S. Patent Trademark Office handles applications as several patent application rejections have cited the KSR ruling. Examiners now have room to maneuver with respect to the application of reasons to combine prior art elements as they can now look for inferences (interconnected teachings of several references), a need in the art (marketplace demands), or even common sense (artisan's knowledge).

The Supreme Court's KSR decision focused on combination claims; inventions created by combining known elements. Obviousness is a question of law based upon factual inquiries of (i) determining the scope and content of the prior art, (ii) ascertaining the differences between the claimed invention and the prior art, and (iii) resolving the level of ordinary skill in the art. The rebuttal of a prima facie case of obviousness is by way of an affidavit or declaration that includes objective evidence of non-obviousness, called secondary considerations. Secondary considerations include copying, long felt but unsolved need, failure of others, commercial success, unexpected results created by the claimed invention, licenses showing industry respect for the invention and skepticism of skilled artisans before the invention. Facts established by rebuttal evidence must be evaluated with facts on which the conclusion of prima facie obviousness was reached.(3)

Ex parte Colbert et. al. (September 30, 2008).

The invention included claim coverage for a method of producing carbon nanotubes derivatized at their ends. The nanotube's caps could be removed at one or both ends by short exposure to oxidizing conditions and the resulting chemical structures could then be derivatized using known reactions. The inventors claimed that the novelty was on making end-derivatized single wall carbon nanotubes, which was distinct from the prior art that produced end-derivatized multi-wall nanotubes. The patent Examiner took a different view, concluding that the invention was obvious. On appeal, the BPAI affirmed obviousness.

The Examiner found the invention obvious in view of two references, Hiura and Iijima. The method for mass production of nanotubes was disclosed by Iijima ("the synthesis of abundant single-shell [carbon nano]tubes"). The end-derivatization method was disclosed in Hiura where it was a "liquid-phase oxidation" reaction that produced end-derivatized carbon nanotubes, specifically multi-wall nanotubes. The method provided for a higher selectivity regarding the quality of nanotubes than the conventional "gas-phase oxidation" reaction. In addition, the prior art did not teach away. Indeed, Hiura suggested that his method would work on all types of carbon nanotubes including single-wall nanotubes. Thus, an artisan could have combined the teaching of both references to obtain what the invention claimed — end-derivatized single-wall nanotubes. The BPAI affirmed obviousness.

On appeal, Colbert (Appellants) made several arguments why an artisan would not be led to combine the prior art references to produce end-derivatized single wall carbon nanotubes by Hiura's method. The BPAI found that all arguments failed to rebut the prima facie case of obviousness. The first argument was devoid of evidence. Appellants explained that single-wall and multi-wall nanotubes were different species and that such difference led to unexpected results. By definition, single wall carbon nanotubes are molecules of carbon, not able to support defects in growth, are more susceptible to chemical destruction and are difficult to separate because they "rope" together. Whereas the multiwalled nanotubes are assemblies of carbon, composed of multiple layers arranged in a scrolled fashion, can withstand wall defects, are resistant to chemical destruction and are readily separable since they do not "rope." Appellants alleged that the chemistry that can be done with each species was unpredictable and/or there was a lack of expectation of success to produce end-derivatized single wall nanotubes by Hiura's method. The BPAI found Appellants' conclusion unsupported. The argument lacked evidence (test data) showing that the distinctive chemistry of single-wall nanotubes rendered the results unexpected.(4) The BPAI reasoned that Hiura disclosed "producing end-derivatized carbon nanotubes" without limitation on their wall type and suggested his process would produce all known nantotubes including "single-wall" nanotubes. Thus, an artisan would expect to produce single-wall nanotubes in Hiura's method.(5) Appellants mistake was not to show test data of unexpected results.

In the second argument the evidence did not substantiate the argument's position. Appellants contended that Hiura's chemical protocol would be expected to fail as to the single-wall nanotubes. As proof of it, Appellants showed Hiura's Fig. 3, depicting the wall of a multiwalled nanotube bearing carbon-carbon bonds breakage after chemical treatment. So, it followed that a method that damaged multi-wall nanotubes, which were strong and more resistant to chemical damage, would destroy the not so robust single-wall nanotubes. Accordingly, Hiura's teaching when combined with that of Iijima would not have suggested a reasonable likelihood of success as applied to the single-wall nanotubes. The BPAI found otherwise. The BPAI found that Fig. 3 represented uncapped nanotubes after oxidation treatment; as a result the nanotubes were only shortened and not destroyed. The Board concluded that Fig. 3 merely suggested that single-wall nanotubes would also get shorter, but not necessarily destroyed. The Board observed that in Hiura's process the problem of chemical destruction of the nanotubes was minimized. Hiura's process solved the erosion problem seen in the conventional methods ("gas-phase" or "steam"). In addition, the method provided for a high degree of purification and uncapping and the reaction was "controllable." Consequently, production of high quality end-derivatized single-wall nanotubes would be practicable. Furthermore, Appellants own invention did not show to be free of similar carbon-carbon bond breakage.

The third argument was an exercise in inferences. The Appellants attempted to show that it could be inferred in the art that Hiura's "liquid-phase oxidation" method destroyed single-wall nanotubes. Appellants argued that Dujardin reference, published after Appellant's filling date, warned that "gas-phase oxidation" method destroyed single-shell nanotubes "before anything else." Appellants alleged that in Durjadin, the phrase "gas-phase oxidation" included Hiura's "liquid-phase oxidation" because it meant all "oxidation" reactions since Dujardin cited Hiura as describing "opening and purifying multi-walled carbon nanotubes" with "oxidants…" The BPAI disagreed. The BPAI noted that the contextual place of citations matters. Dujardin cited Hiura after a statement on the difficulty in purifying single-wall nanotubes as compared to multiwalled nanotubes and this was what Hiura stood for. The BPAI reasoned that Dujardin's statement "[i]t was believed that purification of single-shell nanotubes based on preferential oxidation and/or separation using surfactants was much more difficult that of [multi-shell] nanotubes," referred to the difficulty of purifying single-wall nanotubes by Hiura's method which could be due to low yields of this type of nanotubes and not necessarily to their destruction. The BPAI agreed that Dujardin related the prior art "gas-phase oxidation" to the destruction of single-wall nanotubes but that "gas-phase oxidation" method was distinct from Hiura's method. Hiura disclosed a "liquid-phase oxidation" reaction which was milder, more selective, and more controllable than the conventional harsh "gas-phase" reaction mentioned in Dujardin. Thus, an artisan could not have read Dujardin to include Hiura's "liquid-phase oxidation" method.

What was the flaw with the Appellants arguments?

Arguments must be evidence-based. Attorney's arguments do not translate into evidence. Here, Hiura's did not relate to "single-wall" nanotubes but it did not exclude them and, indeed Hiura suggested that the method would work for the single-wall nanotubes. Thus, as the BPAI pointed out the evidence had to show or suggest that end-derivatized single-wall nanotubes could not be expected to be produced in Hiura's method. To rebut a prima facie showing, the BPAI was looking for evidence of (i) unexpected results regarding end-derivatization of single-wall nanotubes; (ii) that the prior art did not suggest a reasonable likelihood of success when using single-wall nanotubes; (iii) that the chemical reactivity of single-wall nanotubes was unpredictable; (iv) that when comparing properties between the two types of nanotubes it demonstrated unexpected results; (v) that an artisan would have understood that single-wall nanotubes would be destroyed by Hiura's method; and/or (vi) that Appellants own method was free from the carbon-carbon bond breakage of Hiura's method.

(1) Ex Parte Colbert et. al, No. 2008-3765 (Bd. Pat. App. & Int. September 30, 2008).
(2) KSR Int'l Co v. Teleflex Inc., 127 S.Ct. 1727 (2007).
(3) For a discussion on obviousness see Irah H. Donner, Patent Prosecution: Practice &
Procedure Before the U.S. Patent Office (ed. 2004).
(4) In re Preda, 401F.2d 825,826 (CCPA 1968) "[I]n considering the disclosure of a reference, it is proper to take into account not only specific teachings of the reference but also the inferences what one skilled in the art would reasonably be expected to draw therefrom."
(5) In re Pearson, 494 F.2d 1399, 1405 (CCPA1974) "Attorney's argument in a brief cannot take the place of evidence."

Please send your comments to Magda Carvalho at

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