Prosecution History Estoppel


Prosecution History Estoppel

Although patent law is primarily controlled by federal legislation, there are a number of important equitable doctrines, including prosecution history estoppel, that are created by judges in order to ensure a balanced playing field for both inventors and their competitors.

Prosecution history estoppel acts as a limitation on the breadth of a patent, preventing inventors from claiming dominion over a space.

File Wrapper Estoppel

Prosecution history estoppel, sometimes known as “file-wrapper estoppel,” and “prosecution disclaimer,” is an important tenet of patent law. Because patent applications can be narrowed as part of the patent approval process, also known as patent prosecution, inventors often amend their original applications in order to have them approved. Thus, the actual claims in the granted patent may be much narrower than in the original application.

Prosecution history estoppel prevents patent owners from claiming rights over the claimed material that exists in the gap between the original application and the actual granted patent. Specifically, if an inventor amended the patent application to accommodate the requirements of patent law, the inventor cannot then turn around and claim that someone else is infringing a claim narrowed by that application.

This doctrine prevents an inventor from claiming that a patent protects more than what is in the actual grant, and echoes other principles of judicial estoppel that prevent a party from taking and benefiting from inconsistent positions in front of different administrative or judicial bodies.

In cases of literal infringement – where the defendant directly copied the patented invention, prosecution history estoppel does not typically play a role. However, it often appears in cases of indirect patent infringement, including in cases where the patent owner files an patent infringement action based on the doctrine of equivalents.

Prosecution history estoppel can also be invoked by the U.S. Patent Office after a patent is granted, if the patent holder requests that the Patent Office either reissue or reexamine the patent application to reinstate the broader claim that was narrowed through an amendment. A patent owner may not reclaim space that they relinquished during the patent prosecution process in order to receive the patent grant in the first place.

In addition to amendments that restrict or otherwise limit claims in the patent application, written or oral statements made to the Patent Office during the patent prosecution process regarding claim limitations can be invoked in a prosecution history estoppel claim. Similarly, statements made limiting the scope of the patent claims during American Invents Act trials, such as inter partes review and post grant review, can also be used in a prosecution history estoppel claim.

Because prosecution history estoppel can act as a bar to enforcement of otherwise valid patent rights, it is important that patents and their amendments be drafted carefully, with this potential limitation in mind. Inventors should carefully consider the ramifications of narrowing their original patent claims before committing to a more limited invention than originally proposed.

Prosecution History Estoppel and the Doctrine of Equivalents

Prosecution history estoppel and the doctrine of equivalents often come into play in the same cases. The doctrine of equivalents is a form of indirect infringement, where the defendant is manufacturing, selling, or otherwise distributing a product that is extremely similar but not an exact duplicate of a patented invention without the patent owner’s permission. This doctrine prohibits third parties from profiting off the invention of another by making or selling an item that, for all intents and purposes, copies a patented invention, except for superficial or minor differences.

The doctrine of equivalents applies when:

  • Two elements are interchangeable, and
  • A person with ordinary skill in the art would have known that the two elements were interchangeable at the time the infringement occurred.

The doctrine of equivalents allows patent holders to pursue indirect infringers who are not literally copying the invention protected by their patent. A plaintiff is successful only if each claim in the original patented invention can be found in the allegedly infringing item. This is because courts must balance the patent holder’s rights to a monopoly on the granted patent against the rights of others to occupy unprotected spaces surrounding the patent, following the principal that patent claims cannot encompass more than what is granted by the U.S. Patent Office.

In cases in which the patent holder claims indirect infringement under the doctrine of equivalents, the defendant may raise prosecution history estoppel as an affirmative defense to block the infringement claims. The burden falls on the defendant to prove each element is present when raising a prosecution history estoppel defense. Prosecution history estoppel is one of the key checks and balances in indirect infringement doctrine of equivalent cases.

Elements of Prosecution History Estoppel

In order to successfully raise prosecution history estoppel as an affirmative defense, a defendant must show:

  • The patent owner made a statement,
  • The defendant reasonably relied on this statement,
  • The defendant is now facing legal detriment, such as an infringement action, by its reliance on the patent owner’s statement, and
  • Justice requires enforcement of the patent owner’s original statement.

The prosecution history estoppel affirmative defense looks specifically at statements the patent owner made to the U.S. Patent Office during the patent application period regarding the scope of what is included and not included in the patent claims. Because the patent prosecution process is a back-and-forth conversation with the patent examiner, the patent owner may discuss intended limitations and put forth patent amendments.

Both patent amendments and statements to the Patent Office during the patent prosecution process have the potential to prevent claims of patent infringement under the doctrine of prosecution history estoppel. In cases of “argument-based estoppel,” where the defendant’s reliance on prosecution history estoppel stems from statements made directly to the Patent Office, rather than amendments made to the patent’s claims during the patent prosecution process, the defendant must show a clear and unmistakable surrender of subject matter.

Once the defendant has made its case that prosecution history estoppel applies, the burden of proof shifts back to the patent owner to refute the defendant’s claims and argue that amendments and communications with the Patent Office were not intended to limit the patent’s claims.

Amendments to a patent claim do not automatically prove that prosecution history estoppel prohibits a patent owner from succeeding in a patent infringement action. Instead, the court must look at the reasons why the patent holder amended the application. In cases of translation, for example, the purpose of an amendment would be to clarify the language used, not to limit the patent application in order to receive the patent grant.

In doctrine of equivalents indirect infringement cases, the plaintiff, arguing under the presumptive bar approach, must show:

  • The equivalent in the defendant’s allegedly infringing product was unforeseeable at the time the claim was drafted;
  • The limiting amendment did not surrender the particular equivalent in question; or
  • There was some reason why the patent owner could not have recited the equivalent in the claim.

The presumptive bar approach allows the patent owner a further opportunity to argue in favor of an expanded interpretation of the claims in its granted patent.

Drafting Patents to Avoid Prosecution History Estoppel

When drafting patents, it is important to think ahead to potential patent litigation because many patent lawsuits boil down to the content of the granted patent. However, the perfect patent application is extremely rare without further amendment. Patent amendments are par for the course. One estimate suggests that 85-90% of simple patents contain amendments, while virtually all complex inventions only receive grants after their patent applications are amended. Because of this reality, it is important to consider the reasons and ways patents are invented, and patent applicants should take care to limit potentially negative effects of narrowing statements and amendments in order ensure their patents are as broad as possible.

The patent prosecution process is similar to a conversation between the patent examiner and the inventor, the patent examiner will examine the patent and issue an office action objection to certain pieces of the patent application. The inventor then has the opportunity to respond to objections, arguing in favor of the patent as drafted, or to amend the patent to nullify the examiner’s objections.

There are a number of ways a patent can be amended. These can include:

  • Adding a mistakenly omitted name of a co-inventor,
  • Amending patent specifications to bring them into conformity with the Patent Act,
  • Amending the claims to combine a dependent claim with a main claim, to describe them more clearly, or to remove claims over unpatentable material, and
  • Amending the drawings to add further light on what part of the invention the proposed patent will protect.

When amending patent applications, inventors cannot add new matter into the disclosure of an invention. Requirements for patent amendments are listed in 35 CFR 1.121. Inventors may also face Restriction Requirements from the patent examiner as a prerequisite to receiving their patent grant, which may further narrow the scope of the patent’s claims.

Because patent amendments are extremely common, it is important to go into the patent prosecution process with the goal of minimizing amendments in mind. Some steps that can be taken to minimize amendments and the potential consequences stemming from them are:

  • Conducting a proper due diligence search of prior art before submission of the patent application to limit the chances of a conflict. Not every patent grant will be drafted using the same language to describe similar technology, so it is important to approach patent research using a broad net in order to catch as many potential conflicts as possibly early on in the process.
  • Paying careful attention to the language used in the patent application, including whether nouns are plural and how structure, function, and relationships are described in the patent application. Also consider what limitations you include as part of your claims, even when it comes down to what articles you use. “A” or “an” may inadvertently mean “one,” when you do not intend to write this limitation into your application. The patent application will not only be read by the examining attorney – it will become part of the public record, searchable as prior art, and potentially subject to interpretation by a jury that does not necessarily have a technical background. With this in mind, patents should be picked over with a fine-tuned comb before submission.
  • Paying equal, if not greater, attention to how eventual amendments are read. It can be tempting to think short-term when amending a patent to meet examiner requirements and have a patent get approved more quickly. However, patents are about the long game. Amendments should be treated with the same care as the original patent application in terms of editing and review before submission. Before submitting an amendment, an inventor should consider whether there are foreseeable ways to draft amendment language that would broaden the scope of the proposed patent claims.
  • Remembering that all parts of the prosecution history are subject to the public record and will play into opposing counsel’s arguments when raising prosecution history estoppel as an affirmative defense to an infringement claim. Be deliberate in communications with the patent examiner when discussing the intention behind a patent application as well as the language used. Disclaimers made to the patent examiner regarding the intended scope of protection can be used later by defendants in infringement actions to prevent the patent owner from obtaining relief. These communications include not only the initial approval process, but also those during ex parte reexamination, as well as during inter partes review and post grant review trials in front of the Patent Trial and Appeal Board.

Important Prosecution History Estoppel Cases

Prosecution history estoppel is an equitable defense, meaning that it is defined by the courts and not statutory language. There are a number of important court cases that have helped shape this doctrine.

Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.

Festo Corp. is an important 2002 Supreme Court case dealing with the relationship between the doctrine of prosecution history estoppel and the doctrine of equivalents. Festo owned several patents on a particular technology, but narrowed certain claims in order to comply with claim structure requirements under the Patent Act. Shoketsu began selling items that were similar to Festo’s products and used technology that had been listed as part of the original patent claim that was later amended. Festo later sued Shoketsu for patent infringement under the doctrine of equivalents.

The Supreme Court unanimously held that prosecution history estoppel does not automatically apply every time patent claims were amended. Instead, when this defense is raised, the court must examine the reasons behind the amendment to determine whether the patent owner intended to surrender patent claims. In situations in which the patent owner purposefully limited the patent to comply with the requirements of patent law, prosecution history estoppel can act as a bar to infringement claims. This is especially true when, as in the Festo case, there were foreseeable ways to broaden the claims at the time the amendment was made.

Advantek Marketing, Inc. v. Shanghai Walk-Long Tools Co.

Advantek Marketing is a 2018 case from the U.S. Court of Appeals for the Federal Circuit that applied the doctrine of prosecution history estoppel to a design patent infringement case. Advantek invoked the doctrine of equivalents in claiming that the defendant indirectly infringed its patent. Although Advantek’s prosecution history and patent amendments may have created limitations on what rights it had beyond the scope of the granted patent, the Court found that Shanghai’s design amounted to infringement, regardless of the limitations found in subsequent amendments. Thus, even in cases where amendments may create limitations, plaintiffs can still raise successful infringement claims based on the doctrine of equivalents.

UCB, Inc. v. Watson Laboratories, Inc.

UCB was a 2019 Federal Circuit case examining the relationship between a Restriction Requirement issued by the patent examiner and the applicability of prosecution history estoppel. There, although the patent examiner issued two Restriction Requirements before granting UCB’s patent application, UCB never made a narrowing amendment. As a result, prosecution history estoppel was not invoked. While Restriction Requirements issued prior to a patent grant may open the door for future prosecution history estoppel claims, UCB demonstrates that this will not always be the case, echoing further court cases that prosecution history estoppel should not automatically be applied in every situation. Instead, the doctrine requires careful understanding of both the patent claim’s substantive matter, and the procedural elements that led to changes between the original patent application and the eventual patent grant.

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