The parties and the patents

The proceedings are Duke Manufacturing Co. v. Marmon Foodservice Technologies, Inc., IPR2026-00479 (U.S. Patent 10,841,981), IPR2026-00480 (U.S. Patent 10,492,641) and IPR2026-00481 (U.S. Patent 9,980,322), each accorded a September 30, 2026 filing date, and IPR2026-00482 (U.S. Patent 11,771,264), IPR2026-00483 (U.S. Patent 10,512,363) and IPR2026-00484 (U.S. Patent 9,976,750), each accorded an October 2, 2026 filing date. Each patent is titled Multi-Zone Food Holding Bin. The petitions say the '981 patent claims priority to the '641 and '322 patents, and that the '264 patent claims priority to the '363 and '750 patents and to U.S. Patent 10,852,002.

Duke names itself as the real party in interest. In mandatory notices filed October 21, 2026, Marmon identifies itself as the sole owner of each patent. USPTO assignment records show each patent assigned to Prince Castle LLC and a merger and change of name to Marmon Foodservice Technologies, Inc. recorded January 26, 2021 (reel 55107, frame 0614).

What the claims cover

Claim 1 of the '322 patent covers a multi-zone food holding bin with a front-opening food holding compartment whose bottom is a continuous, planar aluminum surface extending to the front face of the chassis, and two adjacent food holding zones in that compartment. Each zone has an independently controllable radiant heating element at the top and an independently controllable conductive heating element at the bottom, and a food holding tray rests on the planar surface. Claim 1 of the '264 patent covers a method of maintaining different temperatures in a bin with two food holding compartments of two zones each, by independently operating a top and a bottom heating element in each of the four zones to four temperature setpoints that are independent of each other.

The grounds

Every ground is obviousness under 35 U.S.C. 103. Each petition presents two sets of grounds. The first set builds on what the petitions call the IRHS Documents: an operators manual, a specifications sheet, a service manual, and Duke website pages for Duke's Infrared Heatsink holding units. The petitions say those documents were publicly accessible before the patents' April 2016 priority dates, including that the manual shipped with more than 360 units in 2014. The second set starts from U.S. Publication 2010/0288748 (Fortmann'748). Secondary references include Hartfelder, Shei'099, Shei'821, Shei'155, Veltrop, Poole, Jones, McMillan, Vaseloff, Reese, Fortmann'967, Fortmann'197, Merco, Stanger, Loy, and Prince Castle, which the petitions describe as a Marmon website. Each petition is supported by a technical expert's declaration.

The petitions challenge claims 1 to 29 and 31 to 66 of the 66-claim '981 patent, claims 1 to 24 and 26 to 34 of the 34-claim '641 patent, all 10 claims of the '322 patent, all 20 claims of the '264 patent, claims 1 to 26 and 28 to 37 of the 37-claim '363 patent, and all 10 claims of the '750 patent.

The Missouri case and the earlier petition

Duke's petitions and Marmon's mandatory notices identify Marmon Foodservice Technologies, Inc. v. Duke Manufacturing Co., No. 4:25-cv-01491, pending in the Eastern District of Missouri, as a related matter for each patent. Marmon filed that case on October 3, 2025. Its complaint asserts nine patents: the six patents here, U.S. Patent 10,852,002, and U.S. Design Patents D1,020,455 and D1,064,814. On September 3, 2026, District Judge Zachary M. Bluestone dismissed without prejudice Marmon's induced, contributory, and willful infringement claims and denied Duke's motion to dismiss the design patent counts. Marmon filed an amended complaint on September 18, 2026; it is not on the public docket.

Duke's petition against the '002 patent, IPR2026-00406, was accorded a July 2, 2026 filing date. Marmon filed a discretionary denial brief there on September 8, 2026, arguing that Duke's decision to challenge one patent while leaving eight asserted patents untouched meant the proceeding could not simplify the Missouri case, and filed a preliminary response on October 6, 2026.

Each new petition states that Duke was not served with a complaint alleging infringement of the challenged patent more than one year before the petition was filed. Under 35 U.S.C. 315(b), an inter partes review may not be instituted if the petition is filed more than one year after the petitioner, a real party in interest, or a privy of the petitioner is served with a complaint alleging infringement of the patent.

What to watch next

The Board's notices according filing dates are dated October 9, 2026, except in IPR2026-00482, where the notice is dated October 13, 2026. Under 37 CFR 42.107(b), Marmon may file a preliminary response in each proceeding within three months of its notice. Under the USPTO's interim Director discretionary process, a discretionary denial brief from Marmon is due within two months of the notice, and the notices give Duke three months from the notice to oppose. Watch for those filings, the institution decisions in the six proceedings, and the decision on institution in IPR2026-00406.