Court Clarifies the Burden of Proof for Common General Knowledge and Admissibility of Supplementary Experimental Data
Date: 16 April 2025
【Volume 151】
During the examination of inventive steps in patent application practice, if a citation does not directly disclose a certain technical feature in the claims, it is common for examiners to negate the inventive step on the grounds that "such a technical feature is already well known in the field". However, in patent invalidation proceedings, the burden of proof on the invalidation requester or the Intellectual Property Office (IPO) is higher when establishing the existence of "common general knowledge". Moreover, if a patentee seeks to rely on supplementary experimental data to demonstrate that the invention produces an unexpected effect compared to the prior art, thereby establishing an inventive step, the question of how to strengthen the admissibility and probative value of the supplementary experimental data has long been a subject of interest within the field. Recently, the Intellectual Property and Commercial Court (IP Court) provided a detailed analysis of these two issues in a patent invalidation case concerning an invention related to biodegradable materials (2023 Xing Zhuan Su Zi No. 16 Administrative Judgment of the Intellectual Property and Commercial Court), making it a noteworthy reference.
Case Fact
The plaintiff in this case is the patentee of Taiwan invention patent No. I682882, titled "Biodegradable Composition" (hereinafter referred to as the '882 patent). The invalidation requester challenged the '882 patent, arguing that it lacked an inventive step. After examination, the IPO issued a decision invalidating all claims of the '882 patent. Dissatisfied with the decision, the plaintiff filed an administrative appeal with the Ministry of Economic Affairs, but the appeal was dismissed. The plaintiff then initiated an administrative litigation before the IP Court. However, the IP Court upheld the IPO's original decision and dismissed the plaintiff's case.
Major Technical Features of '882 Patent
The '882 patent discloses a biodegradable composition comprising:
- 5~90 wt% polylactic acid (PLA);
- 5~80 wt% plant fibers; and
- 5~70 wt% polybutylene succinate-grafted-maleic anhydride (PBS-g-MA).
Supporting Evidence for Invalidation and Primary Disputed Issues
The invalidation requester submitted three pieces of evidence to claim that the '882 patent lacks an inventive step. The primary evidence, Exhibit 2 (CN102002223A), discloses a fully biodegradable polylactic acid (PLA) composite material containing the components listed in the table below.
Preferably, the flexibilizer is PBS-g-PLA, wherein using a PBS-grafted-PLA copolymer as the flexibilizer enhances the compatibility between PBS and PLA while also improving the toughness and heat resistance of the composite material.
Accordingly, Exhibit 2 does not specifically disclose the technical feature of "using MA as the grafting monomer for the PBS-grafted copolymer" as claimed in the '882 patent. This raises the question: does Exhibit 2 sufficiently demonstrate that the '882 patent lacks an inventive step?
Opinions of the IPO and the IP Court
1. The IPO has submitted supporting evidence to demonstrate that the distinguishing technical feature, using maleic anhydride (MA) as the grafting monomer for the PBS-grafted copolymer, is common general knowledge. Exhibit 2 is sufficient to claim that the '882 patent lacks an inventive step.
Exhibit 2 discloses that the composite material contains components such as PLA and plant fibers, and addresses technical problems such as improving compatibility between components and enhancing the toughness and heat resistance of the composite material. During the examination, the IPO provided multiple prior art and journal references to demonstrate that "using a backbone for miscibility with one component of a blend, and a graft end for reaction with another component to form a graft copolymer, thereby improving the compatibility between components of the blend" is a well-known knowledge in the technical field to which the '882 patent pertains. Therefore, in order to promote the compatibility between PLA and plant fibers contained in the composite material, a person ordinarily skilled in the art would be motivated to use PBS as the backbone and MA as the grafting monomer to form a PBS-g-MA copolymer (i.e., PBS-g-MA) in the composite material disclosed in Exhibit 2, based on such common general knowledge. PBS can substantially mix with PLA, as documented in CN104629281A, which was provided by the IPO as evidence of common general knowledge. This patent reference states that "a solubilizer using PBS as the graft backbone is also applicable to PLA composite materials." Furthermore, MA is known to react with hydroxyl groups on plant fibers. Therefore, the '882 patent was a simple modification of the technical content disclosed in Exhibit 2. Exhibit 2 demonstrates that the '882 patent lacks an inventive step.
2. The court deemed that the patentee failed to demonstrate that the '882 patent produces an unexpected effect
The patentee argued that the technical means in Exhibit 2 would significantly disrupt the orientation of polymer chains, resulting in reduced polymer crystallinity. The patentee then presented comparisons of heat distortion temperature as evidence to assert that the technical effects of the '882 patent could not have been expected by a person ordinarily skilled in the art based on Exhibit 2. However, the court pointed out that the heat distortion temperature testing methods adopted in Exhibit 2 and the '882 patent differed significantly, questioning whether directly comparing the data obtained from both methods is technically meaningful. Furthermore, heat distortion temperature is influenced by numerous factors, including polymer type and molecular weight, plant fiber type, composition ratio of each component, processing conditions, etc. Thus, polymer crystallinity cannot be conclusively determined solely based on variations in heat distortion temperature. Moreover, both the examples of the '882 patent and the supplementary examples only compared the results based on the presence or absence of compatibilizers. The patentee failed to demonstrate that the use of specific compatibilizers, such as PBS-g-MA, in the '882 patent produces unexpected effects compared to the prior art, or results in a significant enhancement of an efficacy or a new performance.
The patentee additionally submitted supplementary experimental data and microscopic images of the product in an attempt to prove that the '882 patent has better mechanical properties. However, the court found that such data were neither obtained from a third-party testing agency nor presented as complete test reports. These data lacked information such as specific preparation steps, testing methods and conditions, thereby raising doubts about their credibility.
Wisdom Analysis and Suggested Strategies
1. A person who asserts the existence of specific common general knowledge bears the burden of proof for its existence
In patent application practice, even if a citation does not directly disclose a certain technical feature in the claims, it is common for examiners to negate the inventive step of an invention by reasoning that "such technical feature is already well-known technique in the field". However, in patent litigation, a higher burden of proof applies for "common general knowledge". When there is a dispute between parties regarding the existence of "common general knowledge", the party asserting its existence bears the burden of proof. Proving whether "common general knowledge" exists in the technical field is an objective matter that can be determined with concrete evidence, rather than a mere subjective judgment made by those in the technical field1.
In this case, the main reason why the plaintiff (patentee) lost the lawsuit was that prior art had already disclosed composite materials containing components such as PLA and plant fibers. Moreover, the prior art provided relevant teachings and suggestions such as improving compatibility among components and enhancing toughness and heat resistance. The IPO further submitted multiple patent and journal references to demonstrate that the distinguishing technical feature of the '882 patent compared to prior art was already considered "common general knowledge" in the field. Accordingly, the court concluded that the '882 patent was only a simple modification of prior art combined with common general knowledge at the time of filing, resulting in the particularly evident obviousness of the '882 patent.
2. Suggested Strategies for Supplementary Experimental Data
Although the patentee intended to use supplementary experimental data to prove that the invention of the '882 patent provided unexpected effects compared to prior art, the supplementary data lacked test reports recognized by third-party institutions and did not clearly describe the experimental conditions and methods, making it difficult to serve as persuasive evidence. Furthermore, these data also failed to demonstrate that the '882 patent can achieve superior effects due to the use of "specific compatibilizers".
It is recommended that, when facing challenges regarding patent validity, patentees should consider the correlation between prior art, experimental data, and their assertions. Supplementary experimental data should include detailed information on preparation steps, experimental methods and conditions, and should be accompanied by declarations, affidavits, or other statements from the experimenters to ensure the evidence’s admissibility. Only then can the supplementary experimental data potentially be accepted by the court. It should be noted that the court’s acceptance of supplementary data does not equate to supporting the patentee’s assertions. The patentee must design experiments that clearly demonstrate the significant differences and technical effects of the claimed invention compared to prior art, thereby enhancing both the admissibility and probative value of the supplementary experimental data.
[1] 2011 Xing Zhuan Su Zi No. 71 Administrative Judgment of the Intellectual Property Court
