Concentrations of Acid Specified to Avoid Prior Art Precluded Use of Doctrine of Equivalents

Case: Biagro v. Grow More, Inc. , No. 04-1414 (Fed Cir. 9/13/05)

The One Sentence Summary: There was no infringement, either literal or under the doctrine of equivalents, where accused fertilizer did not contain "phosphorous-containing acid" when that limitation was added during reexamination to avoid prior art so that prosecution history estoppel applied.


What They Were Fighting About: Plaintiff Biagro sued Grow More for patent infringement on fertilizer patent claims. The claims included a limitation stating "wherein said phosphorous-containing acid or salt thereof is present in an amount of about 30 to about 40 weight percent." This limitation was added during reexamination to avoid prior art. The district court construed this limitation to require the presence of phosphorous acid in an aggregate amount of 30-40 percent. Grow More's accused product was made from phosphorous acid, but contained no acid in the final product. The district court held on summary judgment that Grow More did not infringe literally or under the doctrine of equivalents. The Federal Circuit panel affirmed.

Federal Circuit Holdings:

• The district court properly construed the term "amount of phosphorous containing acid" as requiring phosphorous acid rather than its chemical equivalent. There was no support in the specification for including the chemical equivalent, and only one reference in the prosecution history where the examiner had referred to an equivalent.
• Extrinsic evidence of the use of chemical equivalent amounts in labeling of fertilizers was not relevant because it was not connected to the patent or the claim language.
• The trial court properly interpreted the term "at least one phosphorous-containing acid or salt thereof . . . wherein said phosphorous-containing acid or salt thereof is present in an amount of about 30 to about 40 weight percent" to require that the aggregate amoount of the acids or salts be 30-40 percent. This interpretation was correct when the prosecution history made clear that it was the total concentration of acids or salts that was important.
• Under the proper claim interpretation, there was no literal infringement.
• By narrowing its claim in reexamination to add the concentration of acid to avoid prior art, the patentee presumptively surrendered the equivalents as to the amount of acid.
• Surrender of equivalents could not be avoided on the grounds that the purpose of the amendment was tangential. Here, the concentration was added as a limitation because of prior art at another concentration - thus, it was not tangential.
• The fact that the top portion of the concentration range added in the limitation was unnecessary to distinguish the prior art did not render the amendment tangential for purposes of avoiding Festo surrender of equivalents through prosecution history estoppel.