So there is a process x that is well known and has an expired patent. The original patent does not specify what materials exactly can this process be used on. Basically,

(whatever) -> x -> (anything else)

There is an active patent (US123) for the transformation of materials (1) into (2) that specifies a process that looks like:

(1) -> a -> x -> b -> c -> (2).

This is a first instance where x is used on (1).

QUESTION: Can you register a patent that describes a process like this:

(1) -> x -> y -> z -> (2),

while US123 is still active?

Sorry for the somewhat confusing language, I tried to make this as broad as possible so that this question can be referred to by other people

  • You might edit your question so that the title question is not a different question than the body asks. – George White Jun 6 '19 at 4:10

QUESTION: Can you register a patent that describes a process like this: (1) -> x -> y -> z -> (2), while US123 is still active?

First, The active or expiry status of the prior patent doesn't impact the the grant of your patent claims though, it affects the practice of you invention if your process infringe any one of claims of prior patent.

As for your question can the process be patented? Yes, the new process developed by you could be patented as long as it is not obvious or anticipated by the prior art.


The simple answer is that a patent protects what its claims specify. You have to carefully read and understand the claims. To infringe, you must implement each and every step of at least one claim. Parsing claims can be tricky, so it is best to consult with a patent attorney. Since you are asking about an issued patent, you could identify it in your question and we might be able to help interpret its claims.

  • Actually, in process patents you can also infringe the patent by providing an essential component for the process or using the result of the process. This varies greatly by jurisdiction, but it does have practical relevance in at least some bigger countries – DonQuiKong Jun 9 '19 at 8:33
  • @DonQuiKong I’d like to understand this further. Is the a link you could provide that explains your comment? – Eric Shain Jun 9 '19 at 14:41
  • Google “indirect patent infringement“, that should lead you there. It's a risk for example if you have a patent on coding and decoding a certain movie format and I sell decoders. (For example there is case law from the German courts on “mpeg“, but I don't know if it's available in English). – DonQuiKong Jun 9 '19 at 22:19

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