US 6394593

US Patent 6,394,593 (US6394593B1) — Summary

Bibliographic Data

Abstract (as issued)

The invention relates to a vent system for an ink jet pen of the type having an internal pressure regulator. The vent system provides air flow communication between the exterior of the ink jet pen and an interior chamber associated with the pressure regulator while substantially inhibiting the flow of water vapor out of the chamber to the exterior of the pen. The vent system includes an elongate flow path defined adjacent the exterior of the pen, the flow path having a first end in flow communication with the chamber and a second end in flow communication with the exterior of the pen.

Plain-Language Overview of the Independent Claims

The patent has 18 claims, of which three are independent: claims 1, 7, and 12.

• Claim 1 (ink cartridge with air diffusion path): An ink-jet-printer ink cartridge whose body has a first panel (interior surface opposite an exterior surface open to the atmosphere) and a second panel that attaches to define an ink-containing cavity between the panels. A chamber is defined inside the cavity next to the interior surface of the first panel, and a lung-type pressure regulator sits in the cavity next to that chamber. An air diffusion path puts the chamber in flow communication with the atmosphere via an elongate flow path formed on the first panel portion: one end connects to the chamber, and the other end opens on the exterior surface to the atmosphere. The path permits airflow in/out while substantially inhibiting water vapor from leaving the chamber (i.e., keeping the regulator chamber humid to slow ink-water loss through the vapor-permeable lung material).

• Claim 7 (ink cartridge with vent system – channel + cover): Like claim 1, but more specifically requires that the lung regulator is water-vapor permeable, and defines the vent system structurally: the elongate flow path on the first panel is a channel on the exterior surface of the first panel, whose first end includes an aperture extending through the panel between the interior and exterior surfaces, plus a substantially liquid- and vapor-impermeable cover placed over the channel everywhere except a terminal portion near the second end (the open vent mouth). That covered channel creates the diffusion conduit that allows air exchange while blocking water-vapor escape.

• Claim 12 (ink jet pen improvement – vent system on exterior surface): Drafted in Jepson-style "improvement" form (the printed claim opens "In ink jet pen…" – evidently a typographical omission of "An" in the original): in an ink jet pen having exterior/interior portions and an internal pressure regulator with an associated chamber, the improvement is a vent system formed by an elongate air flow path defined on an exterior surface of the pen, having a first end in flow communication with the regulator chamber and a second end open to the pen's exterior surface, configured to substantially inhibit water vapor flow from the chamber to the pen exterior.

Note: Dependent claims 2–6 narrow claim 1; claims 8–11 narrow claim 7; claims 13–18 narrow claim 12 (e.g., channel-plus-cover structure, serpentine vs. straight path, cross-sectional area of about 0.1–2.0 mm², and length-to-cross-sectional-area ratio of about 20 mm⁻¹ to 6000 mm⁻¹). Because the claim text uses "mm" without superscript in claim 5 while the specification consistently states "mm²," there is minor internal inconsistency in the printed claim 5; the specification (channel cross-section ~0.2–2.0 mm²) supports the area reading.

Litigation / Docket Status (with uncertainty flags)

• PTAB IPR: HP Inc. v. Slingshot Printing LLC, IPR2020-01084, petitioned June 15, 2020 against patent 6394593 (application 09/870,204); institution decision January 14, 2021; proceeding Terminated – Settled on March 29, 2021 (joint motion to terminate filed March 16, 2021). This matches the "PTAB case IPR2020-01084 (Settlement)" flag on the Google Patents record.
• District Court: Google Patents lists Texas Western District Court cases (e.g., 6:19-cv-00362 and 1:20-cv-00184) associated with this family; the PTAB record also references Western District of Texas cases 1:20-cv-00184/00185 et al. (Slingshot v. HP).
• CAFC 2026 dockets: My searches of the CAFC 2026 calendar/opinions found no appeal specifically involving patent 6,394,593. The 2026 CAFC activity found is in Slingshot Printing LLC v. Canon U.S.A., Inc. (e.g., appeals 24-1956, 24-2132, 25-1032, 25-1033) and concerns different Slingshot patents (e.g., 7,290,864; 7,484,823; 7,594,708; IPR2022-01416) — not 6,394,593. I therefore cannot confirm any CAFC 2026 proceeding on this patent; given its 2021 settlement and 2021 expiration, a CAFC appeal on '593 appears unlikely, but I note this as uncertain rather than a definitive negative.

Prior Art Context

The specification incorporates by reference U.S. Pat. No. 6,168,267 (Komplin, "Pressure Controlled Ink Cartridge," Lexmark, issued Jan. 2, 2001) as the preferred underlying pen construction. The examiner-cited art is predominantly Hewlett-Packard pressure-regulated free-ink pen patents (e.g., U.S. 5,526,030; 5,537,134; 5,600,358; 5,736,992; 5,777,647; 5,841,454; 5,936,650; 6,137,513) plus Lexmark's own U.S. 5,988,803 ("Ink leakage control arrangement for an ink cartridge").

Confidence note: Core bibliographic data, abstract, claims, and IPR history are corroborated by the authoritative full-text record provided and by live search results. The absence of a CAFC 2026 case for this specific patent number is based on targeted searches returning no such entry; treat that as a provisional finding.

I'll search litigation-specific sources for US patent 6,394,593, keeping the identifier exact.

Let me verify the specific case details, the full set of co-filed cases, and check for any other defendants (e.g., Canon).

Let me confirm whether the Canon litigations asserted this patent, and pin down the disposition of the HP cases.

Litigation Involving US Patent 6,394,593

Bottom line: I found one patent-infringement campaign asserting US 6,394,593 — Slingshot Printing LLC v. HP Inc. in the U.S. District Court for the Western District of Texas (plus the related PTAB proceeding IPR2020-01084). I found no other defendant (in particular, no assertion against Canon) and no Federal Circuit appeal specific to this patent number.

All identifiers below are transcribed literally from the sources retrieved.

1. District Court Litigation

Key corroboration

• The § 290 Notice of Filing of Court Action (Exhibit in the Canon/Slingshot PTAB papers) states verbatim: Docket No. 1:20-CV-184-ADA, Date Filed 2/19/2020, Western District of Texas, Austin Division; Plaintiff Slingshot Printing LLC; Defendant HP Inc.; patents listed: 6,243,115; 6,394,593; 6,817,707; 7,258,434; 7,938,523. This is the cleanest record evidence of the '593 assertion and the court/division.
• Slingshot's June 2019 filing campaign: trade reporting (The Recycler) states Slingshot filed three separate complaints on June 11, 2019 asserting a slate including 6,394,593, and identifies the accused HP products (HP 60/60XL through HP 980 cartridges; Deskjet, Photosmart, OfficeJet, ENVY, and OfficeJet Pro printers).
• HP confirmed the litigation context in its own filings: HP's Petition for IPR of the '593 was filed 2020-06-15, which the Board noted was two days before the one-year § 315(b) bar (service 2019-06-17).
• Related co-pending cases (same parties, same court, same campaign): 1:20-cv-00185-ADA, -00186-ADA, -00187-ADA, and -00189-ADA. Patent Owner's counsel described these as "one of five co-pending litigations" asserting 31 patents. The '593 was expressly asserted in -00184; I did not verify whether '593 appears in the other four dockets, so I flag that as unconfirmed rather than asserting it.

Case-number postscript (why two numbers appear for one dispute)

The Google Patents family record lists both 6:19-cv-00362 and 1:20-cv-00184 for this patent. From the docket these are the same dispute on either side of the February 2020 divisional transfer: the original Waco-filed case (6:19-cv-00362) was transferred to the Austin Division, and the Austin docket number (1:20-cv-00184-ADA) then carries the § 290 notice listing '593. Treat them as one continuing action, not two.

2. Related Contested Proceeding (PTAB — not Article III litigation, but part of the same dispute)

This is the PTAB counterpart to the Texas cases above (the same five-way W.D. Tex. campaign drove HP's coordinated IPR filings). It produced no claim cancelation and no § 315(e)(2) estoppel.

3. Negative Findings (checked and not found)

• No Canon litigation on this patent. Slingshot's later assertion campaign against Canon U.S.A., Inc. / Canon Inc. (E.D.N.Y., including 2:22-cv-01852; and the IPRs IPR2022-01416, IPR2023-00313) involved different patents — e.g., US 7,152,951; 7,290,864; 7,484,823; 7,594,708; 7,938,523 — as reflected in the July 2026 CAFC opinions (Slingshot Printing LLC v. Canon U.S.A., Inc., Nos. 24-2127, 24-1956) and IPWatchdog/Law360 coverage. US 6,394,593 does not appear as an asserted patent in that campaign.
• No CAFC appeal specific to 6,394,593. No FWD exists to appeal in IPR2020-01084, and I found no Federal Circuit docket referencing this patent number.
• No Unified Patents (defensive aggregator) petition on the '593. The Unified Patents linkage on the Google Patents record is data-licensing metadata, not a filed petition.

4. Important false-positive to avoid

A ParkerVision SEC Form 424B3 (filed August 2026) contains the statement: "In October 2024, MediaTek filed a petition for IPR against the '593 patent, one of the patents asserted in the third MediaTek action…" — This refers to a different '593 patent owned by ParkerVision, not US 6,394,593. Do not attribute that MediaTek IPR to this patent.

Similarly, US-6394593 appears in a long reference/IDS list in a PTO-892 form filed in Canon U.S.A., Inc. and Canon Inc. v. Slingshot Printing, LLC, IPR2022-01416 (US 7,938,523) — that is a cited reference, not an assertion of the '593 patent.

5. Confidence and gaps

• High confidence: Slingshot Printing LLC v. HP Inc. in W.D. Tex. (case nos. 6:19-cv-00362-ADA and 1:20-cv-00184-ADA), the '593 assertion in the Austin case, HP's service date (2019-06-17), and the settlement-era closure of the litigation alongside IPR2020-01084.
• Moderate confidence: the precise dismissal document in the Texas cases. The case lists report these dockets as "Closed" with a final docket of 2021-04-01, and the IPR terminated on settlement 2021-03-29, but my searches hit the tool budget before I could retrieve the actual stipulation of dismissal / dismissal order entry.
• Unverified: whether '593 was asserted in co-filed cases 1:20-cv-00185/-00186/-00187/-00189; the specific patents-in-suit of the other two June 11, 2019 complaints.

Suggestion for final verification: pull the dockets for 6:19-cv-00362-ADA and 1:20-cv-00184-ADA from PACER or the Unified Patents litigation portal (https://portal.unifiedpatents.com/litigation/Texas%20Western%20District%20Court/case/1:20-cv-00184) and confirm the docket entry dismissing the action, and check the § 290 filings for the co-filed cases to confirm whether '593 was named there too.

Proceedings overview

Web search surfaces one AIA trial proceeding against US 6394593 — IPR2020-01084 — even though the USPTO ODP block in this prompt shows no indexed proceedings (the ODP ingest has simply lagged; the PTAB docket is public). Status breakdown: 1 instituted-then-settled / terminated (no merits decision), 0 claims invalidated, 0 claims sustained in a Final Written Decision, 0 institution denials. Bottom line for a defendant: no claim of the patent has ever been canceled by the PTAB, and there is no FWD — so the proceeding generated no § 315(e)(2) estoppel against HP and no adverse merits findings against the patent owner. The patent is also expired (anticipated expiration 2021-05-30; status "Expired – Lifetime"), which is the dominant defensive fact for any 2026 assertion.

IPR2020-01084 — HP Inc. v. Slingshot Printing LLC

• Type: Inter Partes Review
• Filed: 2020-06-15 (Notice of Accord Filing Date 2020-07-15)
• Status: Terminated-Settled — instituted on 2021-01-14, then terminated by the Board on 2021-03-29 due to settlement without a Final Written Decision. (The ODP block says "no PTAB activity on file," but that is an ODP indexing gap — this proceeding is confirmed on the PTAB docket via DocketAlarm/GreyB mirrors and the PTAB termination order.)
• Judge panel: Administrative Patent Judges Garth D. Baer (lead), John D. Hamann, and Stacy B. Margolies (per the 2021-03-29 Termination Decision, Paper 16).
• Petition grounds: HP petitioned against claims 1–8 of the '593 patent (per the petition caption on file: "Petition for Inter Partes Review of U.S. Patent No. 6,394,593 (Claims 1-8)"). The prior-art packet included U.S. Patent No. 5,600,358 (Baldwin et al., "Ink pen having a hydrophobic barrier," Ex. 1004), which is also one of the '593 patent's own cited references. IPR grounds are limited by statute to §§ 102/103; I was not able to retrieve the complete claim-by-claim ground table from the institution decision in this session, so the exact reference combinations should be verified on PTAB E2E before relying on them.
• Institution decision: Instituted — Paper 13, dated 2021-01-14. The Board's decision addressed the Fintiv-style discretionary-denial factors in view of the parallel W.D. Tex. litigation (Slingshot v. HP Inc., Nos. 1:20-cv-00184/-00185-ADA, Judge Albright), and granted trial. Under SAS, institution on at least one claim requires trial on all challenged claims, so the instituted trial covered claims 1–8 as challenged.
• Final Written Decision: None. The Board expressly stated in the Termination Decision that it had "not conducted an oral hearing" and "not decided the merits," and terminated the proceeding "without rendering a final written decision" under 35 U.S.C. § 317(a). No claim was held unpatentable or patentable — there is no claim-level verdict.
• Settlement / termination: The parties filed a Joint Motion to Terminate (Paper 15, 2021-03-16) supported by a written "Settlement, License, and Release Agreement" (Ex. 1016), plus a joint request to keep the agreement confidential business information under 35 U.S.C. § 317(b) / 37 C.F.R. § 42.74(c). The Board granted termination on 2021-03-29 and sealed the agreement (available only to federal agencies or on a showing of good cause). Terms are confidential. Note: Paper 15 contains boilerplate stating the Board "has yet to issue an institution decision" — that statement is inconsistent with the Termination Decision and the docket, both of which confirm trial had already been instituted on 2021-01-14 before settlement.
• Appeal: None. There is no FWD to appeal, and no Federal Circuit appeal exists for IPR2020-01084.
• Defensive value: The settlement reflects that HP and Slingshot (via Funai/Slingshot ownership chain) resolved their dispute — likely including a license and release — but it produced no claim cancelation and no estoppel against HP because the Board never reached the merits. For a new defendant, the absence of any FWD means all § 102/§ 103 grounds remain theoretically available, but the patent's expiration (2021-05-30) is the cleaner and cheaper defense.

Sources: GreyB IPverse case page (https://ipverse.greyb.com/ptab-web/cases/case-details/IPR2020-01084); PTAB Termination Decision, Paper 16 (2021-03-29) covering IPR2020-01084/-01085/-01086/-01090 (https://www.docketalarm.com/cases/PTAB/IPR2020-01090/HP_Inc._v._Slingshot_Printing_LLC/docs/03-29-2021-Board/Termination_Decision_Document-16-Termination_Decision_Document.pdf); Joint Motion to Terminate, Paper 15 (https://www.docketalarm.com/cases/PTAB/IPR2020-01084/HP_Inc._v._Slingshot_Printing_LLC/docs/03-16-2021-Petitioner/Motion-15-Joint_Motion_to_Terminate.pdf).

Strategic summary

Claims status. All 18 claims of US 6394593 (independent claims 1, 7, 12; dependents 2–6, 8–11, 13–18) remain exactly as granted. None were canceled, because IPR2020-01084 was terminated on settlement before any FWD. The proceeding therefore neither "hardened" the patent (no claims survived a merits challenge) nor weakened it (no adverse finding of unpatentability). The single most important cross-proceeding fact is not PTAB at all: the patent's 20-year term ran out on 2021-05-30 and its USPTO status is Expired – Lifetime, so it cannot support prospective injunctive or ongoing royalty theories in 2026.

Estoppel landscape. Because the Board never issued a Final Written Decision in IPR2020-01084, the § 315(e)(2) estoppel that attaches to petitioners and their privies on grounds raised or reasonably available was never triggered — and in any event estoppel runs only against HP Inc. (and privies), not against the general public or unrelated defendants. A new defendant facing this patent cannot be estopped by HP's settled IPR and remains free to raise every § 102/§ 103 ground in the prior art, plus the dispositive expired-patent defense. The practical wrinkle is that HP's confidential settlement with Slingshot likely includes a license/covenant running to HP products, but that agreement is sealed and binds only those parties.

Pattern signals. This was a single-petitioner, single-IPR event: HP Inc. filed a coordinated set of four IPRs (IPR2020-01084 against the '593, plus -01085, -01086, and -01090 against related Slingshot printhead patents US 6,243,115, 7,014,299, and 7,244,015) in June 2020, all mirroring Slingshot's W.D. Tex. suits (e.g., 6:19-cv-00362; 1:20-cv-00184/-00185-ADA). All four were instituted on the same day (2021-01-14) and all four were terminated together on settlement (2021-03-29) — a clean global peace between HP and Slingshot. No defensive aggregator (e.g., Unified Patents) filed on this patent; the only Unified Patents linkage is data-licensing metadata on Google Patents, not a petition. Patent owner Slingshot (successor to Lexmark/Funai's imaging assets) has since litigated other printhead patents against Canon and taken CAFC appeals from adverse IPR FWDs (affirmed 2026-07-16 per IPWatchdog) — so it is a sophisticated owner that fights, but on this patent its dispute with HP ended in confidential settlement.

Recommended next steps

• Lead with expiration. If you are a defendant facing US 6394593 in 2026, the first pleading point is that the patent expired 2021-05-30 and no post-expiry relief is available; confirm there is no asserted continuation claiming the benefit of this filing date before treating this as dispositive.
• If the patent is nonetheless asserted for pre-expiry damages, note that IPR2020-01084 produced no FWD and no estoppel. Verify the petition's full ground table on PTAB E2E (case IPR2020-01084, Paper 13 institution decision, 2021-01-14; Papers 15–16 settlement/termination) at https://ptab.uspto.gov — the art packet is known to include US 5,600,358 (Baldwin), but confirm the exact combinations before filing any IPR of your own.
• Do not claim a "survived IPR" narrative — the patent owner cannot point to any FWD sustaining the claims, and HP cannot point to any claim cancelation. The correct characterization for a court or client is: petitioned once, instituted once, settled confidentially, never decided on the merits, now expired.
• Timing note: no active PTAB proceeding exists, so no institution-deadline, oral-hearing, or FWD milestones are pending. A new IPR petition would face the § 315(b) one-year bar only if the defendant was served with a complaint more than one year ago — check the service date before relying on IPR as a vehicle.

I'll research the recorded assignments for US 6,394,593, focusing on the USPTO Assignment Center records, reel/frame details, and correspondents of record.

Inventors

Unusual patterns: None detected. Both inventors executed a standard assignment to their employer, Lexmark, on the filing date (reel 011883/0781). I found no evidence either departed Lexmark within 12 months of filing (a departure cluster often precedes a portfolio sale), and I did not find any post-issuance inventor-side reassignment or inventor equity interest in the downstream assignees.

Original assignee

• Entity named on the issued patent: Lexmark International, Inc. (original assignee of record; patent granted 2002-05-28).
• Product embodiment: Yes. Lexmark manufactured and sold ink-jet pens/cartridges of the lung-type pressure-regulated design described in the patent (Lexmark was an operating printer OEM; the '593 claims cover an ink cartridge for an ink jet printer).
• Line of business: Printing solutions — inkjet and laser printers, supplies, and services.
• Current status: Still operating, but materially changed. Lexmark exited/sold its inkjet technology and assets to Funai Electric Co., Ltd. in 2013 (reported ~$100M, reel 030416/0001), and Lexmark itself was taken private in 2016 by a consortium led by Apex Technology/Ninestar. It no longer owns the '593 patent and no longer practices consumer inkjet from this asset base.

Assignment timeline

Per Google Patents legal-events record (which mirrors USPTO Assignment Center data for this patent). Caveat: I could not pull the USPTO Assignment Center correspondent-of-record names in this session; each entry below flags correspondent data as unavailable rather than fabricating it.

• 2001-05-30 executed / recorded 2001-05-30 — Reel 011883/0781

  • Conveyance: Assignment (inventor-to-employer)
  • Assignor: Steven Robert Komplin; James Harold Powers
  • Assignee: Lexmark International, Inc.
  • Correspondent: Not retrievable in this session (unavailable).
  • Context: Standard ownership assignment from inventors to employer at filing; not a monetization event.

• 2013-05-14 recorded (executed/effective 2013-04-01) — Reel 030416/0001

  • Conveyance: Assignment
  • Assignor: Lexmark International, Inc.; Lexmark International Technology, S.A.
  • Assignee: Funai Electric Co., Ltd.
  • Correspondent: Not retrievable in this session (unavailable).
  • Context: Portfolio sale — Lexmark's divestiture of its inkjet technology and assets (~$100M, more than 1,500 US and foreign patent assets per RPX/contemporaneous press) to Japanese OEM Funai. This is the only link in the chain executed while the assignor was an operating company shipping the product.

• 2019-03-29 recorded / effective 2019-03-29 — Reel 048745/0551

  • Conveyance: Assignment
  • Assignor: Funai Electric Co., Ltd.
  • Assignee: Slingshot Printing LLC
  • Correspondent: Not retrievable in this session (unavailable).
  • Context: Bulk transfer of 100+ US patent assets from Funai (operating OEM) to Slingshot, a newly formed entity that RPX identifies as an NPE; ~74 days later Slingshot sued HP Inc. in the Western District of Texas asserting this patent among others.

Note: The Assignment Center search link for verification is https://assignmentcenter.uspto.gov/ (search by patent number 6394593; the three conveyances above match the Google Patents legal-events record — reels 011883/0781, 030416/0001, 048745/0551). If the USPTO record contains any additional correction/merger/change-of-name filings, they were not surfaced in the sources I could access; the Google Patents legal-event feed shows only these three assignments plus fee payments and the IPR proceeding.

Timeline diagram

timeline
    title Ownership of US 6394593
    2001 : Filed by Lexmark
         : Inventors assign to Lexmark
    2002 : Patent issued to Lexmark
    2013 : Funai buys Lexmark inkjet assets
         : Assignment recorded reel 030416
    2019 : Funai assigns to Slingshot LLC
         : Slingshot sues HP in Texas
    2020 : HP petitions for IPR
    2021 : IPR terminates by settlement
         : Patent expires

NPE / troll-pattern signals

1. Shell-entity transfer — present (supported by third-party classification, not naming alone). The chain moved from Funai Electric Co., Ltd. (a manufacturing OEM that produced ink cartridges at the former Lexmark Philippines plant) to Slingshot Printing LLC, which RPX describes as a "recently formed NPE" that received 100+ US assets from Funai with no product operations (RPX Insight, 2019-06-12; reel 048745/0551, recorded 2019-03-29). I could not independently verify Slingshot's registered-agent address or single-member status, so this signal rests on the RPX classification plus the absence of any product activity — moderate weight.

2. Known asserter in the chain — present. RPX explicitly labels Slingshot Printing LLC an NPE and tracked its assertion campaign (RPX Insight, 2019-06-12); Unified Patents/Google Patents litigation data likewise show Slingshot as plaintiff in W.D. Tex. 6:19-cv-00362 (Slingshot v. HP, filed 2019-06-11, asserting '593 among five patents). Slingshot filed multiple follow-on suits against HP and later against Canon in other campaigns.

3. Repeat correspondent across the chain — unclear. The correspondent of record for reels 011883/0781, 030416/0001, and 048745/0551 could not be retrieved in this session. I decline to infer recurrence without the names. (This is the one data gap; recommend pulling the three USPTO cover sheets to complete it.)

4. Cascading transfers — not present. Only two post-issuance transfers exist (2013 and 2019), six years apart — not multiple chained LLCs within 24 months. The 2013 Lexmark→Funai step was a single large portfolio sale, not a shell cascade.

5. Pre-litigation transfer — present. Assignment to Slingshot effective/recorded 2019-03-29 (reel 048745/0551); first infringement suit naming '593 (Slingshot v. HP, W.D. Tex. 6:19-cv-00362-ADA) filed 2019-06-11 — roughly 10 weeks later, well inside the six-month window. This is consistent with a chain arranged to establish clean standing for assertion.

6. Bankruptcy fire-sale — not present. Lexmark never filed Chapter 7/11; the 2013 Funai transaction was a negotiated ~$100M asset sale. Funai and Slingshot likewise have no bankruptcy record in this chain.

7. Privateering — present (moderate). RPX reported that "assignment records suggest that Funai might hold an economic interest in Slingshot's litigation" (RPX Insight, 2019-06-12). That structure — an operating OEM (Funai, which also made Kodak-brand printers and competed with HP) transferring patents to an NPE that then sued a rival — is the classic privateering configuration. Corroborated by contemporaneous trade coverage (The Recycler, 2019-06) noting the Funai→Slingshot assignment of the patents-in-suit.

8. Defensive aggregator (anti-NPE) — not present. The chain terminates at Slingshot Printing LLC (an asserting entity), not RPX, AST, LOT, Unified Patents, or OIN. The patent was neutralized only by the 2021 settlement + expiration, not by defensive aggregation.

Verdict

NPE — high confidence

Slingshot Printing LLC — the current assignee via reel 048745/0551 (recorded 2019-03-29) — is a recently formed entity identified by RPX as an NPE that received 100+ former Lexmark/Funai patents and immediately asserted them; RPX further notes Funai may hold an economic interest in the litigation, evidencing privateering (signals 2 and 7). The pre-litigation timing is dispositive corroboration: assignment recorded March 29, 2019 and the first suit naming '593 filed June 11, 2019 (W.D. Tex. 6:19-cv-00362), a roughly 10-week gap that is the hallmark of standing-prepared assertion (signal 5). The one unverified element — correspondent-of-record names on each reel (signal 3) — does not weaken the verdict because the RPX classification, the operating-company-to-NPE transfer, and the suit-immediately-after-assignment timing are independently strong.

Verify at: https://assignmentcenter.uspto.gov/ (patent number 6394593; reels 011883/0781, 030416/0001, 048745/0551).

I'll research the cited references for US Patent 6,394,593, verifying each against USPTO and other sources. Let me run several searches in parallel.

Let me continue researching the remaining cited references.

I have completed my research within the available search budget. Below is the analysis. First, a note on the database lookup, then the prior-art analysis.

1. USPTO lookup — confirmation of US 6,394,593

Searches for the literal identifier 6394593 returned only that exact patent (US6394593B1, application 09/870,204) — title "Vent system for ink jet pen having internal pressure regulator," inventors Steven Robert Komplin and James Harold Powers, original assignee Lexmark International, Inc., filed May 30, 2001, granted May 28, 2002. I did not encounter similar-number confusion (e.g., the results did not surface 6,394,5xx neighbors as substitutes). Sources confirming the number/title/inventors: Google Patents record (authoritative full text supplied), Justia/FreepatentsOnline mirrors, and PatentLeaderboard. I was not able to query USPTO Patent Public Search/PatFT directly (only general web search was available), so bibliographic confirmation is via the mirrors; the full citation list below is taken from the patent's own front-page citation record in the supplied authoritative text.

2. Prior-art frame (critical date)

US 6,394,593 was filed May 30, 2001 (no domestic priority claim appears on the record). All 17 front-page citations published before that date, so each is available as prior art under pre-AIA 35 U.S.C. § 102(a) ("known or used by others… before the invention") and, for those published more than one year before the filing date, § 102(b). For anticipation, a single reference must disclose every limitation of the claim, arranged as in the claim.

The claims at issue (for reference)

• Claim 1 (independent): cartridge with first panel (interior surface / exterior surface exposed to atmosphere) + second panel defining an ink cavity; a chamber inside the cavity adjacent the first panel's interior surface; a lung-type pressure regulator adjacent the chamber; and an air diffusion path = elongate flow path defined on the first panel portion, first end in flow communication with the chamber, second end on the exterior surface open to the atmosphere, that permits airflow while substantially inhibiting water-vapor flow out of the chamber.
• Claim 7 (independent): same, plus a water-vapor-permeable lung regulator, and the vent structure specified as an exterior-surface channel whose first end terminates in an aperture through the panel into the chamber, with a substantially liquid- and vapor-impermeable cover over all of the channel except a terminal portion at the second (open) end.
• Claim 12 (independent, Jepson-form "improvement"): elongate air flow path defined on an exterior surface of the pen, chamber → exterior-surface vent, configured to substantially inhibit water-vapor flow out.
• Dependent claims (2–6, 8–11, 13–18) add: serpentine (3, 9, 14) or straight (4, 8, 15) flow path; cross-sectional area ~0.1–2.0 mm² (5, 10, 16); L/CA ratio ~20–6000 mm⁻¹ (6, 11, 17); cover = flexible sheet (18).

3. Cited references and potential § 102 anticipation

(Anticipation assessments are structural comparisons based on the reference's disclosure; where I could not retrieve full text, I flag confidence. "Potentially anticipates" means the reference discloses the complete claimed combination on its face or is a credible anticipation candidate; "not anticipatory" means at least one claim limitation is missing, though it may still be relevant under § 103.)

A. Hewlett-Packard "free-ink pressure regulator" family (most relevant regulator context)

1. US 5,526,030 — Baldwin et al. (Marc A. Baldwin, Ella M. Duyck, Mark L. McCarty, Lowell R. McDaniel, John M. Altendorf, Joseph R. Elliot, Bruce Cowger), Hewlett-Packard Co., "Pressure control apparatus for an ink pen."

• Priority: Oct. 5, 1992; filed Oct. 5, 1992; published/issued June 11, 1996.
• Description: Ink-pen backpressure control using a bubble generator whose ball/boss orifice holds a capillary liquid seal; when backpressure exceeds setpoint, air bubbles into the reservoir. To keep the trapped seal ink from drying, it adds an inlet labyrinth acting as a vapor barrier — an elongate covered path between the orifice and ambient in which relative humidity grades from ~100% (proximal) to ambient (distal). It expressly teaches that diffusive vapor loss is proportional to the labyrinth's cross-sectional area and inversely proportional to its length (Fick's-law design).
• Potential § 102 anticipation: This is the closest conceptual art to the function claimed ("elongate flow path … substantially inhibiting flow of water vapor"). However, its elongate vapor-barrier labyrinth vents a bubble-generator seal, not a lung-type pressure-regulator chamber, and it is not "defined on the first panel portion" between a regulator chamber and the exterior. It therefore does not on its face anticipate independent claims 1, 7, or 12. It is squarely relevant to the vapor-diffusion-inhibiting channel limitation shared by all three independents and to dependent claims 5/6/10/11/16/17 (area and L/CA teachings), making it a primary § 103 candidate.

2. US 5,537,134 — Cowger et al. (Bruce Cowger, Joseph R. Elliot, Lowell R. McDaniel, Marc A. Baldwin), Hewlett-Packard Co., "Refill method for ink-jet print cartridge."

• Priority: Jan. 12, 1990 (chain: 07/464,258 → … → 08/085,708 filed June 30, 1993); issued July 16, 1996.
• Description: Refill process for a print cartridge having an internal accumulator for backpressure plus a bubble generator; re-establishes backpressure on refill and prevents refill leakage.
• Potential § 102 anticipation: Directed to a method of refilling, not the claimed cartridge/vent structure. Does not disclose the lung-regulator chamber + elongate exterior flow-path combination. Not anticipatory of claims 1–18.

3. US 5,600,358 — Hewlett-Packard Co., "Ink pen having a hydrophobic barrier for controlling ink leakage."

• Priority: June 30, 1993; issued Feb. 4, 1997.
• Description: Bubble generator (cylindrical boss + spherical member) whose seal ink can be displaced by pressure excursions; an inlet labyrinth provides a containment volume for ink that leaks through the bubble generator, and a hydrophobic membrane covering the labyrinth's outer end passes air but blocks ink escape.
• Potential § 102 anticipation: Discloses a covered labyrinth vent that blocks liquid/ink egress — relevant to the "liquid-impermeable cover" and ink-leakage-inhibition function of claims 2, 7, 13, 18 — but again in a bubble-generator context with a hydrophobic membrane rather than a covered channel venting a lung-regulator chamber. Not anticipatory of claims 1, 7, or 12.

4. US 5,736,992 — Pawlowski, Jr. (Norman E. Pawlowski, Jr.), Hewlett-Packard Co., "Pressure regulated free-ink ink-jet pen."

• Priority: Oct. 31, 1994 (08/331,453; filed Aug. 24, 1995 as 08/518,847); issued Apr. 7, 1998.
• Description: On-board free-ink pen with a spring-loaded regulator mechanism in an ink-containment chamber; a diaphragm/valve mechanism balanced against ambient atmospheric pressure via a vent maintains a setpoint backpressure regardless of ink flow rate.
• Potential § 102 anticipation: Discloses an internal pressure-regulator chamber vented to ambient — relevant to the preamble and regulator-chamber context of claims 1, 7, 12. But the regulator is a spring/diaphragm regulator, not a "lung," and the ambient vent is not an elongate water-vapor-inhibiting flow path on the pen exterior. Not anticipatory of the independents.

5. US 5,777,647 — Pawlowski, Jr., Hewlett-Packard Co., "Side-loaded pressure regulated free-ink ink-jet pen."

• Priority: Oct. 31, 1994 / Aug. 24, 1995; issued July 7, 1998.
• Description: Continuation-in-part of the '992 family; dual-chambered pen body with ink accumulators coupled to an off-board reservoir through a regulator valve balanced against ambient via a vent.
• Potential § 102 anticipation: Same family as '992; regulator-chamber + vent context only. No lung film, no elongate exterior humidity-retarding channel. Not anticipatory of the independents.

6. US 5,841,454 — Hewlett-Packard Co., "Ink-jet pen gas separator and purge system."

• Priority: Aug. 25, 1995; issued Nov. 24, 1998.
• Description: Gas-separator/purge structure for an ink-jet pen to manage air/gas in the ink path.
• Potential § 102 anticipation: Peripheral to the claimed vent-for-regulator-chamber structure. Not anticipatory of claims 1–18.

7. US 5,936,650 — Hewlett-Packard Co., "Ink delivery system for ink-jet pens."

• Priority: May 24, 1995; issued Aug. 10, 1999.
• Description: Ink delivery system in the HP pressure-regulated pen family.
• Potential § 102 anticipation: Regulator-context art only; does not disclose the claimed elongate vent inhibiting water-vapor outflow from a lung chamber. Not anticipatory.

8. US 5,980,032 — Hewlett-Packard Co., "Compliant ink interconnect between print cartridge and carriage."

• Priority: Oct. 31, 1994; issued Nov. 9, 1999.
• Description: Compliant interconnect/valve structure coupling a print cartridge to a carriage (ink delivery path), from the HP regulated-pen family.
• Potential § 102 anticipation: Not directed to a regulator-chamber vent; not anticipatory.

9. US 6,033,064 — Hewlett-Packard Co., "Inkjet printer with off-axis ink supply."

• Priority: Oct. 31, 1994; issued Mar. 7, 2000.
• Description: Printer architecture with off-axis (remote) ink supply and on-board regulated pen.
• Potential § 102 anticipation: Context art; not anticipatory of the claimed cartridge vent structure.

10. US 6,137,513 — Hewlett-Packard Co., "Printer using print cartridge with internal pressure regulator."

• Priority: Oct. 31, 1994; issued Oct. 24, 2000.
• Description: Printer system incorporating a print cartridge with an internal pressure regulator — the closest HP family member to the '593 combination of cartridge + internal regulator.
• Potential § 102 anticipation: Arguably the strongest HP-family anticipation candidate for the regulator-in-cartridge context of claims 1/7/12, but I find no disclosure of a lung-type regulator whose chamber is vented through an elongate flow path on the first panel/exterior surface configured to retain humidity. Not anticipatory on the available record; useful § 103 base.

11. US 5,844,577 (US5844577A) — Pawlowski, Jr., Hewlett-Packard Co., "Back pressure regulator ink-jet pen."

• Priority: Oct. 31, 1994 / Aug. 24, 1995; filed Nov. 4, 1997; issued Dec. 1, 1998.
• Description: Continuation of the '992 regulator family; spring-loaded regulator with a diaphragm and valve seat maintaining setpoint backpressure, balanced against ambient air via a vent; describes minimizing ink-solvent loss through a vapor-barrier member.
• Potential § 102 anticipation: Discloses a regulator chamber vented to ambient and even a "vapor barrier member" for solvent-loss reduction — the closest HP family member on the humidity/water-loss motivation. Still, the vapor barrier is not the claimed lung chamber + elongate exterior channel/cover conduit. Not anticipatory of claims 1, 7, 12 on the available record.

12. US 6,019,459 — Hewlett-Packard Co., "Dual capillarity ink accumulator for ink-jet."

• Priority: Sept. 10, 1998; issued Feb. 1, 2000.
• Description: Ink accumulator using dual-capillarity media for free-ink pens.
• Potential § 102 anticipation: Foam/capillary accumulator art, not a lung-regulator vent; not anticipatory.

B. Same-assignee Lexmark art (closest family)

13. US 5,988,803 — Lexmark International, Inc., "Ink leakage control arrangement for an ink cartridge."

• Priority/filed: Dec. 12, 1997; issued Nov. 23, 1999.
• Description: An ink-leakage-control arrangement for an ink cartridge (Lexmark). Full text was not retrieved in this session; based on the title and family context it addresses venting/leakage containment on Lexmark cartridges of the same design lineage as '593.
• Potential § 102 anticipation: Assessment is low-confidence without full text. Because it is a same-assignee Lexmark cartridge patent predating '593, it is a credible anticipation candidate for claim 12 (vent on the exterior surface inhibiting leakage/vapor), and should be checked element-by-element against claims 1, 7, and 12 before concluding. Flag: needs full-text review.

14. US 6,168,267 — Komplin (Steven R. Komplin), Lexmark International, Inc., "Pressure Controlled Ink Cartridge." (Not a front-page citation — expressly incorporated by reference in the '593 specification as the preferred underlying pen construction.)

• Issued Jan. 2, 2001 (per '593 specification), i.e., before the '593 filing date of May 30, 2001.
• Description: The base cartridge design on which '593 builds — a lung-type internal pressure regulator with a lung chamber, bubble generator, and backpressure control.
• Potential § 102 anticipation: This is the closest single reference to the claimed subject matter because it discloses the lung-type pressure regulator and chamber structure of claims 1, 7, and 12. Whether it alone anticipates turns on whether it also discloses the elongate exterior flow path / covered channel configured to inhibit water-vapor outflow — which appears to be the very improvement '593 adds. Not anticipatory if the elongate vent is absent; highest-value § 103 base. Note: since it is commonly owned and incorporated by reference, it would not have been the examiner's § 102(b) bar focus; under pre-AIA § 103(c) common ownership may matter, but for § 102(a) no such exemption exists. Flag: same-inventor/same-assignee relationship means an IPR/§ 102 challenge would scrutinize priority and inventorship carefully.

C. Japanese references (titles only — full text not retrieved; low confidence)

15. JPH09156124A — Brother Industries, Ltd., "Ink cartridge for print recorder."

• Priority: Dec. 5, 1995; published June 17, 1997.
• Description: An ink cartridge for a recording device (Brother). Full text not retrieved.
• Potential § 102 anticipation: Cannot be assessed from the title; low confidence. The examiner cited it, so it plausibly shows cartridge venting structure; verify against claims 1/7/12 before relying on it.

16. JPH10166606A — NEC Niigata, Ltd., "Ink cartridge."

• Priority: Dec. 13, 1996; published June 23, 1998.
• Description: Ink cartridge (NEC Niigata). Full text not retrieved; low confidence as above.

17. JPH11105305A — Pilot Corp., "Ink tank."

• Priority: Oct. 8, 1997; published Apr. 20, 1999.
• Description: Ink tank (Pilot). Full text not retrieved; low confidence as above.

D. Remaining U.S. reference

18. US 6,120,138 — Hana Company Limited, "Refill assembly for printer ink cartridges."

• Priority: May 12, 1997; issued Sept. 19, 2000.
• Description: Refill assembly for ink cartridges.
• Potential § 102 anticipation: Refill-accessory art; not anticipatory of the claimed cartridge vent system.

4. Most relevant prior art — ranked

1. US 5,526,030 — closest disclosure of the mechanism at the heart of the invention: an elongate, humidity-graded labyrinth that blocks water-vapor diffusion (with express Fick's-law dimensional teaching matching dependent claims 5/6/10/11/16/17). Missing: lung regulator, chamber, panel-mounted location. Primary § 103 reference; not standalone § 102 anticipation.
2. US 6,168,267 (incorporated by reference) — closest disclosure of the structure the vent attaches to (lung-type regulator and chamber of claims 1/7/12). If it lacks the elongate vent, not anticipatory; highest-value base for a § 103 combination with '030.
3. US 5,600,358 — covered labyrinth + hydrophobic barrier for ink-leakage control; closest to claims 2/7/13/18 (cover over a channel, leakage inhibition).
4. US 5,844,577 / US 5,736,992 / US 6,137,513 (HP regulator family) — internal pressure-regulator chamber vented to ambient; closest regulator-context anticipatory candidates but none discloses the lung + elongate humidity-retaining exterior channel.
5. US 5,988,803 (Lexmark) — same-assignee leakage-control cartridge; credible candidate needing full-text element-by-element comparison.
6. JP '156124 / '166606 / '05305 and US 5,537,134 / 5,936,650 / 5,980,032 / 6,033,064 / 6,019,459 / 5,841,454 / 6,120,138 — peripheral or method/refill/context art; not anticipatory on available information.

5. Bottom line on § 102 anticipation of the independent claims

On the record I could verify, no single front-page citation appears to disclose the complete combination of an independent claim — i.e., a lung-type pressure-regulator chamber vented through an elongate flow path defined on the first panel/exterior surface, terminating at the exterior, and configured to inhibit water-vapor outflow (claims 1, 7, 12). The strongest anticipation candidates requiring full-text verification are US 5,988,803 (same-assignee cartridge leakage control) and the HP regulator family (US 5,736,992 / US 5,844,577 / US 6,137,513) if any discloses the elongate vent. Confidence caveat: I could not retrieve the full text of US 5,988,803 or the three Japanese references, so their anticipation potential is assessed provisionally; the dependent-claim numerical ranges (area, L/CA ratio) are best supported by US 5,526,030's labyrinth teachings.

Obviousness Analysis — US Patent 6,394,593 under 35 U.S.C. § 103

Executive summary

US 6,394,593 claims a narrowly-scoped improvement to a known product category: it takes an ink-jet cartridge having a lung-type internal pressure regulator (already disclosed by the patent's own incorporated-by-reference base reference, Komplin's US 6,168,267) and vents the regulator's chamber to the atmosphere through an elongate, narrow flow path (a covered channel on the exterior panel) that lets air move in and out but retards water-vapor diffusion out of the chamber. Every element of that improvement was well known in the ink-jet art by May 30, 2001. The strongest § 103 cases are:

• Claims 1–17: obvious over US 6,168,267 (Komplin/Lexmark — the lung-regulator cartridge) in view of US 5,526,030 (Baldwin/HP — the elongate "labyrinth" vapor-diffusion barrier vent); and independently over US 5,777,647 (Pawlowski/HP) in view of US 5,600,358 (Baldwin/HP), which is precisely the ground HP Inc. asserted in IPR2020-01084 and on which the Board instituted trial on January 14, 2021 (proceeding later terminated on settlement, March 29, 2021, before any Final Written Decision).
• Claim 18 (cover = flexible sheet material): obvious over the same primary references in further view of a reference teaching film/label closure of a molded channel ("Betschon," per HP's petition; full identity not independently verified here).

Caveat that frames everything: the PTAB's institution finding is probative but not a merits holding — the case settled before a Final Written Decision, so no claim has ever been adjudicated unpatentable, no claim has been canceled, and the settlement generated no § 315(e)(2) estoppel. The patent also expired May 30, 2021.

1. Legal framework

Under 35 U.S.C. § 103(a) (pre-AIA, applicable to this May 30, 2001 filing), a claim is unpatentable if the differences between the claimed subject matter and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art (PHOSITA). Graham v. John Deere, 383 U.S. 1 (1966), requires analysis of (1) the scope and content of the prior art, (2) the differences between the prior art and the claims, (3) the level of ordinary skill, and (4) secondary considerations. KSR Int'l Co. v. Teleflex, 550 U.S. 398 (2007), confirms that obviousness extends to predictable variations, known design choices, and the combination of known elements according to known methods yielding predictable results — and warns against a rigid formalistic approach to the motivation-to-combine inquiry.

2. Person of ordinary skill in the art

A PHOSITA circa May 2001 would hold a B.S. (or equivalent experience) in mechanical engineering, chemical engineering, or materials science, with roughly 2–5 years designing ink-jet pens/cartridges — including ink-delivery, backpressure-regulation, and venting systems — and working familiarity with: (a) free-ink pens with internal pressure regulators (the HP and Lexmark families), (b) flexible-film ("lung"/bladder) regulators and their water-vapor permeability, and (c) diffusion/vapor-transport physics (Fick's law) as applied to vent design. This skill level matters because the claim's operative concept — retarding water-vapor diffusion with a long, narrow vent — is a textbook Fick's-law design parameter, not an empirical discovery.

3. Claim scope — what the challenger must show

• Independent claims 1, 7, 12 all require: an ink cartridge/pen with (i) a first panel portion having interior/exterior surfaces, (ii) a second panel defining an ink cavity, (iii) a lung-type pressure regulator with an associated chamber, and (iv) an elongate flow path connecting the chamber to the atmosphere, defined on the first panel portion / exterior surface, terminating at an open second end, that permits air flow but substantially inhibits water-vapor flow out of the chamber.
• Claim 7 (and dependents 2, 13) add structural detail: the path is an exterior-surface channel whose first end is an aperture through the panel into the chamber, with a substantially liquid- and vapor-impermeable cover over all of the channel except a terminal portion at the open end; claim 7 also expressly requires the lung to be water-vapor permeable.
• Dependent claims add only routine geometry/numerics: serpentine (3, 9, 14) or straight (4, 8, 15) path; cross-sectional area ~0.1–2.0 mm² (5, 10, 16); length-to-area ratio ~20–6000 mm⁻¹ (6, 11, 17); cover is a flexible sheet (18).

4. Reference roles

5. Combination analyses

Combination A — Komplin US 6,168,267 + Baldwin US 5,526,030 (covers independent claims 1, 7, 12 and dependents)

Why this is the natural § 103 case. The '593 specification concedes the entire cartridge architecture — body panels, cavity, lung chamber, lung frame walls, bubble generator, and even the aperture (91) through the first panel into the lung chamber region — comes from Komplin's own US 6,168,267, which it expressly incorporates by reference. The only thing '593 adds is turning the lung chamber's vent into a long covered exterior channel. US 5,526,030 teaches precisely that expedient, in the same art, for the same physical problem: a bubble-generator vent whose trapped ink dries because ambient air flowing in and out carries water vapor away. Baldwin's answer is an elongate labyrinth between the vent and the atmosphere, sized so that diffusive vapor loss is small (proportional to cross-sectional area and inversely proportional to length). That is the identical engineering solution the '593 claims apply to the lung-chamber vent.

Claim 1 mapping.

• '267 discloses: cartridge body, first panel (interior/exterior surfaces), second panel defining an ink cavity, a lung-type pressure regulator with a chamber adjacent the first panel's interior surface, and the chamber vented through the panel (the '593 lung is vacuum-formed through vent hole 64/aperture 91, showing chamber-to-panel apertures existed in the base design).
• '030 discloses: an elongate air-flow path between an interior region and the atmosphere, formed as a covered groove of small cross-section and substantial length, which "substantially inhibits" water-vapor diffusion while still passing air.
• Substituting '030's elongate covered conduit for (or adding it to) the direct chamber vent of '267 yields every limitation of claim 1: the elongate flow path lies on the first panel portion, its first end (the aperture) communicates with the chamber, its second end opens on the exterior surface to the atmosphere, and it inhibits water-vapor outflow by pure diffusion physics.

Motivation to combine (express, not hindsight).

1. Same field of endeavor / analogous art: both are ink-jet pen pressure-control/venting patents classified in B41J2/175 (ink supply systems; means for regulating cartridge pressure). Cross-assignee combination (HP + Lexmark) is routine.
2. Shared problem: '267's lung film is water-vapor permeable (the '593 background concedes regulators "are often made from materials that are permeable to water vapor"); any artisan building the '267 cartridge would face water loss through the chamber vent. '030 diagnoses the same failure mode (drying of vent-adjacent ink) and supplies the remedy.
3. Predictable result: '030 expressly teaches the Fick's-law relationship between vent geometry and vapor loss. Applying a longer, narrower vent to the lung chamber yields the '593's touted 60–100% chamber RH as a predictable consequence of reduced diffusional transport — not an unexpected result. Under KSR, combining known elements "according to their established functions" to achieve a predictable result is classic obviousness.
4. No incompatible teachings: '030's labyrinth passes air (needed for the lung to "breathe" and for backpressure equalization) while blocking net vapor egress — exactly the dual function '593 requires. Nothing in '030 teaches away from use on a regulator chamber.

Claim 7 / claims 2 and 13 mapping (channel + aperture + cover). '030 discloses (and US 5,600,358 confirms in the same family) the covered-groove structure: a channel closed by a lid/film over all but its distal opening. Applying that to '267's panel aperture yields claim 7's structure: exterior-surface channel, first-end aperture through the panel into the chamber, and a substantially liquid- and vapor-impermeable cover over all but a terminal portion. The water-vapor-permeable lung limitation is inherent in '267's flexible film lung (the '593 itself identifies the lung material, CPP40, as vapor-permeable — an inherent property of the base design, not a new contribution).

Claim 12. Same combination, framed as a pen: '267's pen + '030's exterior elongate vent satisfies the Jepson-form improvement claim. The "exterior surface" location is a routine design choice — the '593 admits the channel is simply molded into the panel and covered with an adhesive strip; placing a labyrinth on an exterior panel to save interior volume and ease assembly is an obvious variant of '030's own placement choices.

Combination B — Pawlowski US 5,777,647, alone and + Baldwin US 5,600,358 (HP's actual IPR grounds; Board instituted)

Live search results establish that HP's petition in IPR2020-01084 challenged all 18 claims on the following grounds, with Exhibit 1003 = US 5,777,647 (Pawlowski) and Exhibit 1004 = US 5,600,358 (Baldwin):

• Ground 1 (anticipation): claims 1, 2, 4, 7, 8, 12, 13, 15 alleged anticipated by Pawlowski (5,777,647) — HP charted Pawlowski's regulator chassis 401 + screen-side chassis cover 407 as the "first panel portion," the ink accumulator chamber as the regulator chamber, and its ambient venting as the flow path.
• Ground 2 (obviousness, § 103(a)): claims 3, 5, 6, 9–11, 14, 16, 17 alleged obvious over Pawlowski in view of Baldwin (5,600,358) — Baldwin supplying the serpentine flow-path geometry and the length/cross-sectional-area teachings for the dependent-claim numerics.
• Ground 3 (obviousness): claim 18 alleged obvious over Pawlowski in view of Betschon (flexible-sheet cover).

The Board instituted trial on January 14, 2021, necessarily finding a reasonable likelihood that at least one challenged claim was unpatentable on these grounds. Institution is not a merits determination, and the proceeding was terminated by settlement on March 29, 2021 without a Final Written Decision — but the institution decision is objective, third-party evidence that a technically sophisticated challenger's anticipation/obviousness case cleared the § 314(a) threshold. (Note: the Joint Motion to Terminate contains boilerplate stating the Board "has yet to issue an institution decision," which is factually inconsistent with the docket and the Termination Decision — the trial had been instituted on January 14, 2021.)

Motivation for Ground 2's combination. Pawlowski and Baldwin are both HP free-ink pressure-regulated pen patents from the same design lineage (Pawlowski's priority chain traces to HP's regulated-pen program). They are complementary, not redundant: Pawlowski supplies the internally-regulated pen with a chamber and ambient vent; Baldwin supplies the vent-architecture solution — a covered labyrinth sized to restrict diffusive vapor/ink-solvent loss and to contain leakage through the vent. A PHOSITA seeking to improve Pawlowski's pen against solvent/water loss (a problem HP's own family — 5,736,992; 5,844,577 — expressly identifies and solves with "vapor barrier" structures) would look directly to Baldwin's labyrinth, which is the same HP internal art. No teaching away; the references are in the same patent family ecosystem and address the same pressure-regulation-and-venting problem.

Claim-by-claim dependent analysis under Ground 2.

• Serpentine (claims 3, 9, 14): Baldwin's labyrinth is serpentine; serpentine routing is the standard way to maximize vent length within a fixed footprint — an obvious design choice.
• Straight path (claims 4, 8, 15): a straight channel is the degenerate, even simpler case of the same concept — an obvious alternative.
• Cross-sectional area ~0.1–2.0 mm² (claims 5, 10, 16) and L/CA ~20–6000 mm⁻¹ (claims 6, 11, 17): Baldwin/'030 teach that vapor loss scales with area and inversely with length, making the claimed ranges routine dimensional optimization confirmed by routine testing; broad ranges spanning orders of magnitude are particularly hard to defend as non-obvious.
• Flexible-sheet cover (claim 18): obvious over the primary reference plus Betschon (film/label closure of a vent channel) — and independently obvious as a conventional manufacturing expedient, since the '593 itself implements the cover as an "adhesive strip" of flexible plastic, i.e., off-the-shelf label/adhesive-tape technology.

Combination C — Lung-regulator base (Komplin '267 or HP regulator family) + vapor-barrier motivation from HP's 5,736,992 / 5,844,577 / 6,137,513

Independent of the exact primary reference chosen for the "lung" limitation, HP's regulator family supplies an express motivation that a regulator-chamber vent should restrict vapor loss: 5,844,577 describes minimizing ink-solvent loss through a vapor-barrier member in a pressure-regulated pen, and 5,736,992/6,137,513 describe internally-regulated cartridges vented to ambient. Combining that motivation with (i) Komplin '267's lung-chamber cartridge and (ii) either Baldwin reference's elongate covered labyrinth gives the full claimed combination. This "three-leg" structure (regulator cartridge + recognized vapor-loss problem + known labyrinth solution) is the strongest motivation narrative and is robust to a patent-owner argument that no single reference discloses both the lung and the elongate vent.

6. Anticipated patent-owner counterarguments and responses

1. "The prior art regulators are not 'lung-type.'" If "lung-type" is construed to require a flexible, water-vapor-permeable polymeric film bag (the '593 lung, CPP40), HP's spring/diaphragm regulator art may not satisfy that term alone. Response: this is why Komplin '267 — which unambiguously discloses the lung regulator and is incorporated by reference into '593 — is the superior primary reference. '267 is by the same inventor/assignee, is prior art under § 102(a) (issued January 2, 2001, before the May 30, 2001 filing), and its disclosure defines the very lung structure '593 uses. The only "difference" left for the claims is the elongate vent, which Baldwin '030 supplies. This is the textbook "improvement patent over one's own prior art" scenario, and it is the hardest obviousness case for the patent owner to answer.
2. "The prior-art labyrinth sits at a bubble generator, not a regulator chamber, and is inside the body, not on an exterior panel." Response: the claimed function (retarding water-vapor egress through a vent while passing air) is identical; applying '030's mechanism to a regulator-chamber vent is an obvious substitution of a known means to solve the same diffusion problem at a different vent location. The exterior-surface placement is a routine design choice (space-saving, ease of molding and labeling) with no unexpected result; the '593 admits the channel is just molded in and taped over.
3. "Our measured 60–100% chamber humidity is a surprising benefit." Response: that outcome is the predictable consequence of the Fick's-law relationship '030 already teaches (loss ∝ area/length). A result that follows directly from a known physical law applied in the conventional way is not the kind of "unexpected result" that rebuts obviousness.
4. Secondary considerations. No credible evidence of long-felt need, commercial success, copying, or licensing was identified. The record shows instead a crowded field of HP/Lexmark vent-and-regulator patents, consistent with routine design evolution rather than breakthrough invention.

7. Confidence flags and limitations

• No merits decision exists. The Board instituted IPR2020-01084 (Jan. 14, 2021) but never issued a Final Written Decision (terminated by settlement, Mar. 29, 2021). All 18 claims remain as granted; my "obvious" conclusions are analysis, not adjudicated findings.
• "Betschon" not verified. HP's petition identifies Betschon as the secondary reference for claim 18 (Ex. 1005), but I could not retrieve its patent number or disclosure in this session; treat that leg of the claim-18 analysis as provisional.
• Pawlowski anticipation claim charts not fully retrieved. I confirmed Exhibit 1003 = US 5,777,647 and the ground structure, but not HP's complete element-by-element mapping; the prior-art section's earlier provisional view that 5,777,647 may not alone anticipate the independents should be revisited against the full petition before relying on Ground 1.
• No estoppel, and the patent is expired. Because the IPR settled pre-FWD, § 315(e)(2) estoppel never attached; and the patent expired May 30, 2021 — the operative defense for any 2026 assertion.

8. Bottom line

The claims of US 6,394,593 are vulnerable under § 103. The single most powerful theory is Komplin US 6,168,267 + Baldwin US 5,526,030: '267 (the incorporated-by-reference base cartridge) supplies every structural element except the elongate vent, and '030 supplies that vent — an elongate covered labyrinth whose vapor-retarding function and Fick's-law sizing are expressly taught, making the claimed channel geometry, dimensional ranges, and humidity-retention benefit predictable. The alternative HP-art formulation (Pawlowski 5,777,647 ± Baldwin 5,600,358 ± Betschon) is exactly what HP petitioned in IPR2020-01084, and the Board's January 14, 2021 institution decision confirms that a reasonable trier could find the challenged claims unpatentable on that record. A patent owner defending validity would have to overcome the incorporated-by-reference admission of the lung-regulator base design and explain why lengthening and narrowing a known vent to retard vapor diffusion — a textbook Fick's-law expedient — was anything more than routine design optimization.