In patent practice, there is a type of claims that often trouble applicants/patentees/inventors and patent attorneys alike — the method claims. Such claims protect a series of operational steps, and while they can directly embody the core inventive concept, they often face difficulties in obtaining evidence(s) and enforcing rights in infringement litigation. In contrast, if a method invention can be converted to a product claim, particularly by defining the product using such as parameter features, it may often achieve stronger protection.

Among the top ten reexamination and invalidation cases of 2023 in China, two cases — one involving "Polyurethane Polishing Pad"(ZL201410448504.X) and the other "Poly(arylene ether) Copolymer" (ZL200680046261.0) — both featured parameter limitations, providing an excellent lens for observation. This article will discuss the value of parameter limitations in patent drafting in light of these two cases.

I. The "Three Hurdles" in Enforcing Method Patents

Let us first consider why method patents are difficult to enforce. In practice, there are three main approaches to obtaining evidence(s) of infringement of a method patent.

The first is investigative evidence collection, where lawyers or investigators obtain complete evidence of the infringing method that meets the "three requirements" for evidence — authenticity, legality, and relevance. This entails obtaining notarized photographs, videos, or technical manuals, drawings, and other evidence(s) from legitimate sources. While this sounds comprehensive, in practice, the alleged infringer often guards the production process as a core trade secret, making it inaccessible to outsiders, rendering this approach largely impractical.

The second approach is "preliminary evidence plus evidence preservation." This involves first obtaining preliminary leads such as photographs, videos, or witness statements that have not been notarized, and then applying for evidence preservation after filing the case with the court. The challenge, however, lies in the fact that evidence preservation inherently relies on surprise; if the opposing party receives advance notice, thekey equipment parameters may already have been "adjusted."

The third approach is the shifting of the burden of proof. The patentee provides preliminary evidence(s) demonstrating the likelihood of infringement, and the court orders the defendant to provide its method for manufacturing the product. This approach carries the greatest risk for the patentee — if the court deems the preliminary evidence(s) insufficient, the burden of proof will not be shifted; even if it does, the defendant has various avenues for maneuverability.

It is evident that the path to enforcing method patents is fraught with obstacles. So, is there a better alternative?

II. Parameter Limitations: "Embedding" the Method in the Product

The answer is yes — converting a method invention to a product claim, particularly by defining the product using such as parameter features.

So-called parameter features define a product through its physical properties, chemical composition, or structural parameters, such as viscosity, hardness, molecular weight, number of functional groups, and the like. When a product can only be manufactured using a specific method, protecting the product may indirectly protects the method.

Let us examine how parameter limitations were applied in the specific cases.

In the "Polyurethane Polishing Pad" case, the independent claims not only limited the formulation components but also defined three physical performance parameters: a tangent delta Δ of 0.04-0.10, a Young's modulus of 140-240 MPa or 180-240MPa, and a Shore D hardness of 44-56 or 46-54. These parameters collectively characterize the performance features of the polishing pad, such that even if someone replaces some of the formulation components (while still falling within the scope of the formulation components recited in the independent claims) or adjusts the process steps, infringement may still be found as long as the final product falls within these parameter ranges.

In the "Poly(arylene ether) Copolymer" case, the independent claims, in addition to limiting the product as an oxidative copolymerization product comprising monohydric phenol and dihydric phenol monomers, employed four parameters to define the polymer: an average number of hydroxyl groups per molecule of 1.8-2 or 1.85-1.95, an intrinsic viscosity of 0.04-0.15 or 0.04-0.09 dL/g, a proportion of copolymer chains containing dihydric phenol ends of 10-70 or 35-70 mol%, a proportion of biphenol units of 0.5-1.5 wt%, and the like. This combination of parameters precisely defines the structural characteristics of a product obtainable only through the specific polymerization method.

What these two cases share is this: the parameters were not arbitrarily selected but were closely linked to the manufacturing method. In other words, it is highly probable that only the patented method yields a product satisfying these parameters; thus, the presence of such a product essentially allows for an inference that the patented method was used, shifting the burden of proof to the defendant.

III. Three Major Benefits of Parameter Limitations

Drawing from the above cases, the advantages of claim limitations using parameters can be summarized in three points:

First, evidence collection is easier. Products are publicly sold, allowing the patentee to directly purchase the accused infringing product for testing and obtain parameter data. This is far simpler and more lawful than infiltrating a factory to capture production processes. Compared to method-based evidence collection, parameter-based evidence collection may not require applying for evidence preservation, worrying about the destruction of evidence, or grappling with the legality of surreptitiously recorded videos. The product itself can serve as the most powerful piece of evidences.

Second, the burden of proof may shift. Pursuant to Article 66 of the Patent Law, for a method for manufacturing a new product, the burden of proof is reversed — the plaintiff needs only prove that the defendant has produced an identical product, and the defendant must then prove that its manufacturing method is different. Parameter limitations precisely serve to clearly define the scope of what constitutes an "identical product".

Third, the scope of protection is more robust. As demonstrated in the "Poly(arylene ether) Copolymer" case, a carefully designed set of parameters can form a "coordinated combination".Even if individual parameters may have been disclosed in the prior art, the overall combination of parameters may still possess novelty and inventiveness.

IV. Four Key Points for Drafting Parameter-Limited Claims

Of course, parameter-limited claims are not a panacea, and there are four key points to bear in mind when drafting them:

First, the correlation between the parameters and the method. It is essential to ensure that only the patented method can yield a product within the claimed parameter ranges; otherwise, the parameters become "illusory" and fail to provide substantial protection for the intended method.

Second, the synergistic effect of parameters. Individual parameters may not readily distinguish from the prior art, but a combination of multiple parameters often creates a stronger limiting effect. Mathematical relationships or correlations between parameters can form a more robust technical barrier. For example, parameter combinations can be defined through ratios, products, functional relationships, etc. Of course, for unconventional parameters, it is necessary to provide clear definitions and experimental verification in the specification to satisfy the requirements of sufficient disclosure and support, while avoiding the inclusion of prior art within the scope of protection. In the "Poly(arylene ether) Copolymer" case, the synergistic effect of the four parameters was ultimately recognized as conferring inventiveness.

Third, the supporting role of the specification. The parameters recited in the claims should not be arbitrarily introduced; the specification must sufficiently demonstrate the relationship between the parameters and the performance through examples and comparative examples. In the review of both cases, the collegial panels focused on whether the experimental data in the specification adequately supported the parameter features.

Fourth, the detectability of the parameters. The parameters in the claims must be capable of being measured and verified using available technical means; otherwise, the patentee may face an inability to provide evidence during infringement comparison. Choosing parameters defined by industry-standard, standardized testing methods can significantly reduce subsequent enforcement costs. Of course, protection is not unavailable for parameters defined by non-standard, specific testing methods; however, such specific testing methods require the specification to fully disclose the relevant testing equipment and methodology details to enable reproducible implementation and comparison.

V. Conclusion

The essence of patent protection lies in the exclusive right to a technical solution, not in the documentation of a laborious process. Although method claims can directly embody the inventive concept, from an enforcement perspective, method inventions should be converted to product claims wherever possible, for instance, by employing parameter features to construct a protective web of product claims.

In the two cases discussed above, the original patentees were respectively Rohm and Haas Electronic Materials CMP Holdings, Inc./Dow Global Technologies Inc. (now merged into DuPont Electronic Materials Holding, Inc./DDP Specialty Electronic Materials US LLC) and General Electric Company (now SABIC Global Technologies B.V.) — both multinational chemical industry giants. Their patent strategizing offers valuable lessons for us. Product claims constructed with parameter features can not only withstand invalidation challenges to a certain extent but also place the patentee in a favorable position in infringement litigation.

It is hoped that this article may provide some inspiration for inventors and patent drafters: when drafting a method invention, it is worthwhile to consider — can this method be captured using a product claim? If so, what parameters could be used to define it? Is there a computational relationship or synergistic effect among these parameters? Addressing these questions may well lay a solid foundation for the future enforcement of the patent.