Patent Litigation: Defenses

By Attorney

When a patent owner sues for infringement, there are a number of defenses available to the defendant, the most common of which is that the defendant’s invention doesn’t infringe -- that is, the two inventions are not substantially similar and the invention accused of infringing does not "read" on the claims of the patent. (The claims are statements included in a patent application that describe or "recite" the structure of an invention in precise and exact terms; they are considered the boundaries of the patent.) In addition to arguing that infringement has not occurred, a defendant may also raise the following defenses:

Patent Invalidity

A lawsuit for patent infringement almost always becomes two separate battles — one in which the plaintiff claims damage from infringement, and the other in which the defendant attempts to terminate the patent rights by proving the patent is invalid. For example, the Polaroid company sued Kodak for infringement of ten instant photography patents. The court determined that Kodak infringed seven Polaroid patents but that the other three Polaroid patents were invalid. To prove that a patent is invalid, the defendant must attack the patent on the basis of lack of novelty or nonobviousness — that is, show prior art (pre-existing inventions and publications) that anticipates or renders the patent’s claims obvious or prove that sales or disclosure of the patented invention occurred more than one year prior to filing the patent application.

Inequitable Conduct

If the defendant can prove that a patent owner intentionally misled a patent examiner or should have known that withheld information was material (important) to the examination process, the issued patent will be declared invalid.

Exhaustion (First Sale Doctrine)

Once a patented item is sold, rights to that item are exhausted and it is not an infringement to resell it. This defense does not apply if the defendant purchased and resold an infringing invention, one that was initially sold without authorization from the patent owner.

Repair Doctrine

It is not an infringement to repair a patented device and replace worn out unpatented components. This defense does not apply if the defendant completely rebuilt an invention or repaired an infringing invention.

File Wrapper Estoppel

If, during the patent application process, the inventor admits limitations to the invention or disclaims certain rights, those admissions or disclaimers will become part of the file wrapper (collective patent documents at the USPTO) and the patent owner cannot later sue for infringement over any rights that were disclaimed in the file wrapper. This defense is known as file wrapper estoppel (or prosecution history estoppel). Estoppel means that a party is prevented from contradicting a former statement or action.

Patent Misuse

A patent owner who has misused a patent cannot sue you for infringement. Common examples of misuse are violations of the antitrust laws, or unethical business practices. For example, if a patent owner conspired to fix the price of the patented item, this would violate antitrust laws.

Waiting Too Long to File the Lawsuit

There is no time limit (or statute of limitations) for filing a patent infringement lawsuit, but monetary damages can be recovered only for infringements committed during the six years prior to the filing of the lawsuit. Despite the fact that there is no law setting a time limit, courts will not permit a patent owner to sue you for infringement if the owner has waited an unreasonable amount of time to file the lawsuit (a principle known as “laches”). Generally, courts consider anything over a six-year period an unreasonable delay in filing the suit, unless the patent owner can provide some excuse for the delay.

Portions of this article are derived from Patent, Copyright & Trademark: An Intellectual Property Desk Reference by Richard Stim.