when patent lapse?

A patent can lapse, or expire, for several reasons, including:

1. Failure to pay maintenance fees: Many countries require patent holders to pay maintenance fees to keep their patents in force. If the fees are not paid, the patent can lapse.
2. End of the patent term: The duration of a patent varies by country, but in most cases, a patent expires 20 years from the filing date of the patent application.
3. Abandonment: If the patent holder fails to take certain actions, such as responding to a patent office communication or paying a maintenance fee, the patent may be deemed abandoned and will lapse.
4. Invalidity: If a patent is found to be invalid or unenforceable, it may be deemed to have never existed and will lapse.

Once a patent has lapsed, the invention is no longer protected by the patent system, and anyone can make, use, sell, or import the invention without the need for permission or a license from the patent owner. It is important to note, however, that if the invention is protected by other forms of intellectual property, such as trademarks or copyrights, those protections may still be in force even after the patent has lapsed.