The Secret Prior Art Trap: A Case Study on Conflicting Applications in China

In patent prosecution, the concept of a "conflicting application" or “secret prior art” plays a critical role in determining the patentability of an invention. This article explores the framework for assessing conflicting applications under Chinese patent law, with a comparative perspective on the approaches adopted in the United States.

Case Background: The Image Encoding Dispute

The subject of the appeal was a patent application for an image encoding technology, filed on June 5, 2019. The applicant had not claimed any priority. The CNIPA Examiner had issued a Final Rejection, asserting that the application lacked novelty in light of two prior PCT international applications:

1. D1-WO​ (WO2020207498A1): Claiming a single priority date of April 12, 2019.
2. D2-WO​ (WO2020227393A1): Claiming three priority dates, the earliest being May 9, 2019.

The applicant appealed this decision, leading to a thorough review by the Re-examination Board (the Board). The Board demonstrated how to verify the “four elements” utilizing this case.¹

Question 1: what is qualified as a valid publication to be considered a conflicting application?

Under Chinese patent law, a PCT application only acquires the status of a potential conflicting application after it has entered the Chinese national phase and has been published by the CNIPA. Chinese examiners should not use PCT publications as prior art directly, but instead should cite their Chinese counterparts. In this case, both of the PCT applications had corresponding CN national applications, allowing them to meet the “territory” elements (filed before CNIPA). In this case, the Board continued its review by replacing the PCT publications with their corresponding Chinese national phase publications: D1-CN​ and D2-CN.

Question 2: how can priority affect a conflicting application

The other elements were then reviewed for both D1-CN and D2-CN.

D1-CN: The subject application’s filing date (June 5, 2019) fell between D1-CN’s priority date (April 12, 2019) and its filing date (April 13, 2020). This makes priority verification essential.

D1-CN contained:

• technical matter present in its priority document, which was entitled to the early priority date of April 12, 2019, and
• new, unsupported matter, which was assigned the later filing date of April 13, 2020.

Only the content entitled to the April 12, 2019 date satisfied the "time" element for a conflicting application (filed before, published after) and disclosed identical technical solutions to those in the application in question, thereby meeting the “content” element. Consequently, D1-CN was deemed a valid conflicting application for novelty for those specific embodiments.

D2-CN: presented a more complex scenario with three priority dates. Only the earliest (May 9, 2019) was before the subject application’s filing date.

• For the content that was supported by the first priority, the "time" element was met. However, upon comparison, this content did not disclose the same invention as the subject application and therefore failed the "content" element.
• The remainder of D2-CN relied on later priority dates (after June 5, 2019), and thus immediately failed the "time" element. Therefore, there was no need to review the content element.

Consequently, D2-CN did NOT qualify as a conflicting application.​ The rejection based on this document was overturned.

Epilogue

The examiners in charge of this case followed up by writing an article, further suggesting that a potential conflicting application should be verified based on the following sequence: Territory → Time (with Priority Verification) → Content.​

1. Territory: confirm if it is a national-phase publication (the CN publication), not the WO or other publications.
2. Time (with Priority Verification): each technical embodiment must be traced back to its supporting priority document.
3. Content: only the content that meets the “time” element and is identical to the technical solution in the application in question can be used as a conflicting application.

EIP thoughts:

Conflicting application prior art is not unique to China. The United States has a similar concept, often referred to as "secret prior art," primarily under 35 U.S.C. § 102(a)(2)².

To facilitate understanding, we provide a comparison table below.

Unlike the U.S., where a secret prior art reference can be used to challenge both novelty and non-obviousness, China's approach is narrower. A conflicting application in China serves as a novelty-only bar. Its effectiveness is strictly limited to technical solutions fully supported by a valid priority claim and only after the PCT application has entered the Chinese national phase. Successfully navigating this requires meticulous priority verification and a focus on precise claim differentiation, as obviousness-type arguments are inapplicable.

Understanding these differences is essential for managing global patent portfolios and developing effective prosecution strategies in each key jurisdiction. Feel free to contact us at [email protected] if you have further questions.

This article is for general informational purposes only and should not be considered legal advice or a legal opinion on a specific set of facts.

1. In China, a conflicting application is a patent application that:
   - Was for the same invention
   - Was filed by any applicant​ (including the applicant itself under certain conditions)
   - Was filed before the China National Intellectual Property Administration (CNIPA).
   - Was filed before​ and published on or after​ the filing date (or priority date) of the subject application.
   This is normally understood as “four elements” for conflicting applications.
   Examination Guideline, Part Two, Chapter III, Section 2.2
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2. A United States patent or a WIPO-published application designating the US ) will be considered prior art against a later-filed application if it:
   - Was filed by another​ (not the same inventor),
   - Was effectively filed​ before the later application's effective filing date, and
   - Was granted or published​ on or after the later application's effective filing date.
   35 USC 102(a)(2)
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3. Before Oct. 1, 2009, only applicants filed by others were considered as conflicting applications.
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