Unjustified Patent Enforcement

This thesis analyses the legal consequences of subsequent patent invalidation
on infringement actions, contracts and warning letters.
Patent invalidation has a retroactive effect. The revoked patent should be
treated as has never exist while it was used against third parties. There is a
certain legal agreement that, if the patent is invalidated in the course of
pending trial, the case is dismissed. However, the consequences of a patent
invalidation on a final judgement differ among the surveyed jurisdictions.
When the patent has been used as a legal instrument to negotiate a license or
purchase a patent, in most cases, patent invalidation will not oblige the
licensor to repay the licensing fees for the time when the patent was in force.
However, does the licensor have the right to ask for post-invalidation
royalties. Different jurisdictions give different answers.
Moreover, the patentee has every right to give third parties notice of his
exclusive right. This might be done by warning letters. Sending warning letter
to a primary infringer may be a customary action before filing a law suit.
However, a conflict arises when the patentee sends warning letters to
secondary infringers. On the one hand, patent law does not distinguish
between primary and secondary infringers. On the other hand, sending
warning letter to secondary actors has less justification since secondary
infringer will not will to start a legal proceeding against the patentee. They
simply switch to alternatives. In such a case, the primary infringer’s
reputation and business might be destroyed.
After studying the legal solutions in the surveyed jurisdiction, I came to the
opinion that: to a certain extent the alleged infringer should be able to claim
back the damages he suffered due to an infringement action which was based
on defective patent. In case of a contracts, the licensor should lose his right in
claiming post-invalidation royalties. Warning letters against primary
infringers should not be actionable, while a no-fault liability should apply when the unjustified warning was sent to secondary infringers, and a per-se prohibition rule should apply for warning the public at large.

Available at SSRN