Refresher: Partial priority
The two most important facts when establishing the effective date of a claim:
Priority may only be granted for the same invention - Art.87(1) EPC
Multiple priorities may be claimed - Art.88(2) EPC
Partial priority can occur in two situations, one of them is covered in G 2/98 (explicitly named alternatives), the other one in G 1/15 (generic “OR” claims with conceptual split).
1) Explicitly named alternatives in a claim - G 2/98
G 2/98, r.6.6: No multiple effective dates for an "AND" claim. For example, D1 discloses A, later D2 discloses A+B. A claim to A+B has no partial priority from D1.
r.6.7: Multiple effective dates are possible for an "OR" claim. For example, D1 discloses A, D2 discloses B as an alternative to A. A claim to "A or B" can get priority for A from D1 and for B from D2.
EPO Guidelines F-VI 1.5: "Subject-matter of a European application will be accorded the priority date of the earliest priority application which discloses it. If, for instance, the European application describes and claims two embodiments (A and B) of an invention, A being disclosed in a French application and B in a German application, both filed within the preceding 12 months, the priority dates of both the French and German applications may be claimed for the appropriate parts of the European application; embodiment A will have the French priority date and embodiment B the German priority date as effective dates. If embodiments A and B are claimed as alternatives in one claim, these alternatives will likewise have the different priority dates as effective dates."
FR: discloses embodiment A
DE: discloses embodiment B
EP (claiming priority from both FR and DE):
Option 1) claim 1: embodiment A –> effective date is filing date of FR
claim 2: embodiment B –> effective date is filing date of DE
Option 2) claim 1: embodiment A or B –> claim has two effective dates
"If, on the other hand, a European application is based on one previous application disclosing a feature C and a second previous application disclosing a feature D, neither disclosing the combination of C and D, a claim to that combination will be entitled only to the date of filing of the European application itself. In other words, it is not permitted to "mosaic" priority documents. An exception might arise where one priority document contains a reference to the other and explicitly states that features from the two documents can be combined in a particular manner."
A1: feature C
A2: feature D
EP (claiming priority from both A1 and A2): claim 1: features C and D –> no valid priority, effective date is filing date of EP
2) Generic “OR” claims - G 1/15
G 1/15 deals with situations where a subsequent application claiming priority from one or more previous applications itself comprises additional subject-matter not present in the priority document(s).
In the approach taken by G 1/15, the broader claim (generic “OR” claim) is de facto conceptually divided into two parts: the first part corresponds to the invention as disclosed in the priority document, while the second part is the remaining part of the subsequent broader claim. The first part enjoys the priority of the first application, whereas the second part does not enjoy this priority, but itself gives rise to a right to priority as laid down in Article 88(3) EPC.
EPO Guidelines F-VI 1.5: “According to G 1/15, entitlement to partial priority may not be refused for a claim encompassing alternative subject-matter by virtue of one or more generic expressions or otherwise (generic "OR" claim) provided that said alternative subject-matter has been disclosed for the first time, directly, or at least implicitly, unambiguously and in an enabling manner in the priority document.”
This often comes up in questions where the second application discloses a broader range than the priority application.
Example (using DeltaPatents Main exam question C7-16 as inspiration):
NL1: process having a heating step at a temperature of 100-150°C
(After filing of NL1, applicant realises that the process works in a broader temperature range.)
EP2 (claiming priority from NL1): claim: process having a heating step at a temperature of 70-250°C.
EP2 claim can be divided into the following conceptual parts:
1. 100-150°C –> entitled to priority, so effective date is filing date of NL1
2. 70-100°C and 150-250°C –> priority not valid, so effective date is filing date of EP2
So, a prior art disclosing 120°C, published after the filing date of NL1 but before the filing date of EP2 –> not novelty destroying (since prior art was published later than the effective date of the first conceptual part)
A prior art disclosing 200°C, published after the filing date of NL1 but before the filing date of EP2 –> novelty destroying (since prior art was published earlier than the effective date of the second conceptual part)