IP Law Daily, PATENT—W.D. Wis.: Packaging manufacturer did not infringe convertible shipping box patents, (Nov 9, 2026)

By Ravindra Kumar Singh, B.L.

The accused pizza packaging lacked the continuous tear line required by the asserted patents, and its alternative tearing mechanism did not establish infringement under the doctrine of equivalents.

A federal district court in Wisconsin has ruled that packaging manufacturer Pratt Industries, Inc. and its affiliates did not infringe two patents covering shipping boxes that convert into retail-ready display cases. Granting summary judgment to Pratt, the court held that its corrugated cardboard packaging for frozen pizzas lacked the “single tear line” required by every asserted patent claim. Instead, the accused packaging incorporated two perforated tear lines separated by a cut-out handhold, which did not satisfy the patents’ requirement of a continuous physical tearing mechanism. The court also rejected patent owner Delkor Systems, Inc.’s infringement allegations under the doctrine of equivalents and directed entry of judgment for Pratt, ending the litigation (Delkor Systems, Inc. v. Pratt Industries, Inc., No. 3:25-cv-00306-jdp (W.D. Wis. Nov. 6, 2026)).

Convertible packaging patents. Delkor, a Minnesota-based packaging equipment manufacturer, owns U.S. Patent Nos. 9,555,919 (the ’919 patent) and 10,421,580 (the ’580 patent), both entitled “Convertible Package Assembly and Display System.” The ’580 patent is a continuation of the ’919 patent. The inventions describe a flat sheet of packaging material that can be folded into a shipping box and subsequently converted into a retail display by removing its upper portion along a tear line. According to the patents, the design reduces material requirements, facilitates machine assembly, and produces a more attractive retail display.

Delkor accused Pratt Industries and two affiliated companies of infringing claim 1 of the ’919 patent and claims 5 and 7 of the ’580 patent through their manufacture and sale of corrugated packaging for frozen pizzas. Both parties sought summary judgment on infringement, agreeing that the accused product’s structure and operation were undisputed. Pratt did not challenge patent validity. Consequently, the dispute centered on interpreting the patent claims and determining whether the accused packaging satisfied their limitations.

Continuous tear line requirement. The asserted claims required a package formed from a single piece of material containing a “single tear line” along which the upper portion could be separated from the lower portion. Pratt argued that this limitation required a physically continuous line extending through the packaging blank. Delkor maintained that a tear line could include different physical features, including a cut-out handhold, as long as they formed one connected removal path.

Applying the claim construction principles established in Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005), the court examined the ordinary meaning of the disputed language alongside the patents’ common specification. It found that a tear line necessarily involved material capable of being physically torn. A cut-out handhold could not qualify because the material within the opening had already been removed.

The specification also repeatedly described the claimed tear line as continuous. Although it permitted multiple sections forming one tear line, those sections remained physically connected across the packaging blank. The court therefore rejected Delkor’s argument that a continuous tearing motion alone satisfied the limitation.

Incorporated patent. Delkor additionally relied on an earlier patent issued to Leftwich and others, incorporated by reference into its patents, which disclosed a packaging assembly containing a cut-out aperture along a line of weakness.

The court acknowledged that incorporated patent disclosures could inform claim construction but emphasized their limitations. Citing Finjan LLC v. ESET, LLC, 51 F.4th 1377 (Fed. Cir. 2022), it explained that incorporation by reference does not transform the incorporated invention into the invention claimed by the host patent.

Unlike Delkor’s patents, the Leftwich patent did not describe its line of weakness as continuous. Accordingly, the earlier disclosure could not override the asserted patents' express language. Because Pratt’s packaging contained a handhold separating two perforated lines, it lacked the required single continuous tear line.

Doctrine of equivalents. Delkor alternatively argued that Pratt’s packaging performed substantially the same function in substantially the same way to achieve the same result. Its packaging expert testified that users could remove the upper portion of both boxes in a single tearing motion.

However, the expert acknowledged that Pratt’s handhold made separation easier because part of the material was already removed. The court considered this distinction significant because ease of conversion was among the claimed invention’s principal advantages. Under Akzo Nobel Coatings, Inc. v. Dow Chemical Co., 811 F.3d 1334 (Fed. Cir. 2016), equivalence requires particularized evidence addressing the disputed limitation. The court concluded that no reasonable jury could find equivalence given the acknowledged functional difference.

Thus, the court granted Pratt’s motion for summary judgment of noninfringement and denied Delkor’s competing motion. Because the absence of a single continuous tear line disposed of every asserted claim, the court declined to address the parties’ remaining arguments concerning the requirement for fifteen polygonal sections.

The Case is No. 3:25-cv-00306-jdp.

Judge: Peterson, J.

Attorneys: Qiushi Yang (Stafford Rosenbaum LLP) for Delkor Systems, Inc. Elijah Byrnes Van Camp (DeWitt LLP) for Pratt Industries, Inc.

Companies: Delkor Systems, Inc.; Pratt Industries, Inc.

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