Outside of the US, foreign patent offices will often use your own prior patent filings against you. Avoid this trap by planning carefully.
Both US and foreign patent laws are based on various legal fictions. One legal fiction is that an invention is instantly created in a fully formed state. Another legal fiction is that even if a particular improvement to the invention was not actually obvious to the real inventor, still an examiner or judge may reject this improvement as being obvious to an imaginary “person of ordinary skill in the art”. Patent law just doesn’t cope with hindsight well.
In practice, we all know that real inventions often come into life slowly, usually after much trial and error. Complex inventions may take years to fully develop. The inventor is thus faced with a dilemma – file fast so as to be the first person to file, or keep working on the invention, file a better patent application, but possibly lose to someone who filed sooner?
US patent laws recognize this problem, and allow an inventor file as many patent applications as needed, even over a period of years, and gradually accumulate a “stack” of patent applications. This stack of patent applications captures both the time of earliest invention, as well as a later time-optimized form of the invention. Intuitively this system seems fair. Wouldn’t it be unfair to use an inventor’s own earlier work against the inventor?
Doesn’t this basic rule of fairness apply everywhere? Unfortunately it does not. The harsh reality is that outside of the US, other countries typically use an inventor’s own earlier patent applications against them.
This assumption of basic fairness often traps inventors and startups. Here the only way to avoid the trap is to recognize that this problem exists, and take steps to mitigate problems.
As a good rule of thumb for international patents, assume that there is at most a 12 month window after a first (US) patent application has been filed in which to make further improvements. Plan accordingly. If you have thought up improvements to your invention, it is far better to submit these improvements as an updated PCT patent application before the 12 month anniversary of the first patent application.
After 12 months, you can’t claim the priority date of your first US filing. Someone else can jump ahead of you and claim credit. Even worse, 18 months after filing (when usually your first US patent application will be published) your first US patent application can then be used against your later filed improvement.
It is very irritating to have an international examiner claim that your improved invention is obvious against your own earlier filed application. Even more irritating when you know that in reality the improvement was totally not obvious. Perhaps the improvement may have taken you a year or more of hard work! Too bad — to the foreign examiner, your improvement is obvious.
The lesson here is: if you have made improvements, file them as an updated international patent within 12 months of the filing date of your first invention (or in an emergency, at least before your first patent application is published — usually 18 months after first filing).