US 6676246

US Patent 6,676,246 — Search Results & Summary

Search notes

• USPTO/Google Patents records for US6676246B1 were located (Google Patents, FreePatentsOnline, Justia). Bibliographic data below matches the authoritative full text provided.
• CAFC 2026 dockets: I searched for CAFC appeals tied specifically to 6676246. The Federal Circuit decisions reported in 2026 involving Slingshot Printing LLC v. Canon U.S.A., Inc. (e.g., No. 24-1956 decided Apr. 23, 2026, and the July 2026 affirmances) concern other Slingshot patents — 7,195,341; 7,290,864; 7,484,823; and 7,594,708 — not 6,676,246. I found no CAFC 2026 appeal specifically docketed for US6676246. What I did find: 6,676,246 was asserted by Slingshot Printing LLC against HP Inc. in Slingshot Printing LLC v. HP Inc., No. 6:19-cv-00549 (W.D. Tex., filed Sept. 20, 2019), and it was among the patents-in-suit in related Slingshot/HP litigation (e.g., No. 1:20-cv-00187, W.D. Tex./ADA). I cannot confirm any CAFC docket for 6,676,246 in 2026 — treat that as unverified.

Bibliographic summary (verified)

Abstract (verbatim)

A heater chip structure having heating elements operable at an energy per unit volume of from about 2.9 GJ/m³ to about 4.0 GJ/m³, a pulse time of less than about 0.73 microseconds, and one or more protective layers having a total thickness of less than about 7200 angstroms.

Plain-language overview of the independent claims

The patent has 19 claims; the independent claims are 1, 8, 9, and 10 (all others are dependent).

• Claim 1 (apparatus — ink jet printer): An ink jet printer having a power supply and a print head with a plurality of nozzles. The print head's heater chip carries heating elements, each consisting of a heating resistor (with an area and thickness) plus a protective layer over the resistor that is less than ~7200 Å thick. Each heating element sits under a nozzle and must eject ink in a pulse time under ~0.73 microseconds. The energy delivered is ~2.9 to 4.0 GJ/m³, where the "volume" used for that calculation = resistor area × (resistor thickness + protective-layer thickness). In short: a printer whose heaters fire very fast and at low stack energy because the overcoat is thin.

• Claim 8 (apparatus — heater chip structure, minimal elements): Standalone structure claim: a heater chip structure with heating elements operable at 2.9–4.0 GJ/m³, pulse time < 0.73 μs, and one or more protective layers totaling < 7200 Å. This is the "core" claim with no nozzle/printer context.

• Claim 9 (apparatus — heater chip for an ink jet printer): Essentially claim 1's heater chip in isolation — heating elements each with a resistor (area + thickness) and a protective layer < 7200 Å, associated with a nozzle, achieving ejection at a pulse time < 0.73 μs at 2.9–4.0 GJ/m³ based on the same defined volume (area × [resistor thickness + protective-layer thickness]).

• Claim 10 (method — printing): Method of printing comprising providing a power supply, an ink supply, and a thermal ink jet print head (with nozzles and a heater chip as described), applying pulses of less than ~0.73 μs to each heating resistor to eject ink at 2.9–4.0 GJ/m³ based on the same volume definition, and ejecting droplets at a stable velocity onto a print medium.

Key inventive concept: Instead of tuning energy/area or ink chemistry, the patent ties minimum pulse time to the total heater-stack thickness. By keeping the protective passivation/cavitation layers under 7200 Å and operating in a modest energy-per-volume window (~2.9–4.0 GJ/m³), the heaters can eject ink in under 0.73 μs, reducing printhead heating problems (flooding, poor print quality) at higher nozzle counts/firing frequencies.

Uncertainty disclosures

• The patent record says the patent is expired (lifetime) and was involved in W.D. Tex. litigation (6:19-cv-00549) and related IPR proceedings (HP v. Slingshot, e.g., IPR2020-01084/-01085/-01086/-01090 contexts).
• No CAFC 2026 appeal for this exact patent number could be confirmed from my searches; the 2026 CAFC Slingshot/Canon appeals involved different patent numbers. If you need a definitive CAFC docket search (e.g., PACER or the CAFC's own site by case number), that should be run directly, as my web results did not surface one for 6,676,246.
• Claim wording is quoted/paraphrased from the granted text; minor claim-language details (e.g., the specification's typo "tatalum/titantium" variants in dependent claims 6, 11, 14, 17) appear in the original and were not "corrected."

I'll research litigation involving US Patent 6,676,246 specifically.

Based on my searches, here is what the available records show regarding litigation specifically involving US Patent 6,676,246 (B1). I have limited this list to records that expressly name patent 6,676,246; I have not included cases involving similar-numbered patents (e.g., 7,410,246; 6,575,563; 7,195,341; etc.) except where the same case also named 6,676,246.

Litigation involving US Patent 6,676,246

1. Slingshot Printing LLC v. HP Inc., No. 6:19-cv-00549-ADA (W.D. Tex.)

• Plaintiff: Slingshot Printing LLC (Delaware LLC, Silver Spring, MD; assignee of the patent via Funai Electric Co., Ltd., assignment recorded Mar. 29, 2019)
• Defendant: HP Inc.
• Jurisdiction: U.S. District Court for the Western District of Texas (originally Waco Division; transferred to the Austin Division by order dated Feb. 19, 2020, remaining before Judge Alan D. Albright)
• Case number: 6:19-cv-00549 (later docketed under the Austin Division/ADA suffix)
• Filing date: Sept. 20, 2019
• Patents-in-suit: The complaint (Docket No. 1) expressly names 6,676,246 among ten patents-in-suit: 6,213,587; 6,575,563; 6,676,246; 6,786,575; 7,018,012; 7,195,341; 7,290,864; 7,410,246; 7,484,823; and 7,559,629.
• Status/outcome: Records accessible to me show the case pending in late 2019 (answer deadline extended to Dec. 19, 2019) and the Feb. 19, 2020 transfer order. I could not confirm a final judgment, dismissal, or settlement specific to this docket from my searches. Notably, HP's related IPR petitions against Slingshot patents from this litigation wave (IPR2020-01084, -01085, -01086, -01090 and IPR2020-01659) were all terminated-settled on Mar. 29, 2021 with confidential settlement/license agreements — strongly suggesting the parallel district-court cases were resolved by settlement around that time — but I cannot verify from the available records that 6,676,246 was part of that settlement or the exact disposition of this case.

Sources: https://unicourt.com/case/pc-db5-slingshot-printing-llc-v-hp-inc-[216666](/patent/216666) ; https://dockets.justia.com/docket/texas/txwdce/6:2019cv00549/[1059089](/patent/1059089) ; https://www.docketalarm.com/cases/[PTAB](/ptab)/IPR2020-01086/Inter_Partes_Review_of_U.S._Pat._7014299/10-15-2020-Patent_Owner/Exhibit-2004-20-Complaint,_Slingshot_v_HP,_No_1_20_cv_00187_ADA/ (complaint text naming 6,676,246); https://www.docketalarm.com/search/?q=patent:(7484823)

2. Slingshot Printing LLC v. HP Inc., No. 1:20-cv-00187-ADA (W.D. Tex., Austin Division)

• Plaintiff: Slingshot Printing LLC
• Defendant: HP Inc.
• Jurisdiction: U.S. District Court for the Western District of Texas, Austin Division (Judge Alan D. Albright)
• Case number: 1:20-cv-00187-ADA
• Filing date: Appears as Feb. 19, 2020 in one PTAB-related record (the same date as the transfer order in case 6:19-cv-00549)
• Patents-in-suit: A complaint bearing this docket number and filed as an exhibit in the IPR proceedings expressly names 6,676,246 among the same ten-patent list (6,213,587; 6,575,563; 6,676,246; 6,786,575; 7,018,012; 7,195,341; 7,290,864; 7,410,246; 7,484,823; 7,559,629).
• Status/outcome: Not confirmed. Important caveat: The available exhibit appears to contain document footers from "Case 6:19-cv-00549 Document 1 Filed 09/20/19," which suggests No. 1:20-cv-00187 may be the same complaint re-filed/re-docketed after the Waco-to-Austin transfer (or that the exhibit was assembled from the earlier complaint). I could not independently determine from these records whether 6:19-cv-00549 and 1:20-cv-00187-ADA are the same case renumbered, or separate related cases. This should be verified on PACER before relying on it as a distinct action.

Sources: https://www.docketalarm.com/cases/PTAB/IPR2020-01086/Inter_Partes_Review_of_U.S._Pat._7014299/10-15-2020-Patent_Owner/Exhibit-2004-20-Complaint,_Slingshot_v_HP,_No_1_20_cv_00187_ADA/ ; https://ptacts.uspto.gov/ptacts/public-informations/petitions/[1550157](/patent/1550157)/download-documents (transfer order table listing Docket No. 1:20-CV-187-ADA, dated 2/19/2020)

Matters I checked and excluded (not litigation on 6,676,246)

• No inter partes review was found specifically challenging 6,676,246. HP's 2020–2021 IPRs against Slingshot (IPR2020-01084, -01085, -01086, -01090, and IPR2020-01659) targeted other patents — 6,394,593; 6,243,115; 7,014,299; 7,244,015; and 7,410,246, respectively. (The "246" in IPR2020-01659 is 7,410,246, not 6,676,246.)
• No CAFC appeal specifically for 6,676,246 surfaced in my searches (as previously noted in the summary section, the 2026 CAFC Slingshot/Canon appeals involve 7,195,341; 7,290,864; 7,484,823; and 7,594,708 — not 6,676,246).
• Litigation against Canon (e.g., IPR2022-01414 context) involves other Slingshot patents, not 6,676,246.

Bottom line

Known district-court litigation expressly involving US Patent 6,676,246 is the Slingshot Printing LLC v. HP Inc. matter(s) in the Western District of Texas (No. 6:19-cv-00549, filed Sept. 20, 2019, and its apparent Austin Division continuation/companion No. 1:20-cv-00187-ADA). I could not confirm the final outcome of these cases from publicly accessible search results — the docket records I retrieved stop before any merits decision, and the related IPRs were settled in March 2021. For a definitive current status (e.g., dismissal with prejudice, settlement, or judgment), a PACER query on 6:19-cv-00549-ADA and 1:20-cv-00187-ADA would be required.

The structured ODP data shows no AIA trials on file, but the 2019–2021 HP v. Slingshot litigation wave involved this exact patent (6,676,246 was a patent-in-suit in 6:19-cv-00549 and 1:20-cv-00187). I need to verify whether any HP/Cannon IPR petitions actually targeted 6,676,246 or only its sibling patents. Let me run targeted checks.

IPR2020-01084/85/86/90 target other Slingshot patents (6,394,593; 6,243,115; 7,014,299; 7,244,015). I still need to confirm whether 6,676,246 itself was ever the subject of any IPR petition. Let me search more specifically.

Proceedings overview

Zero AIA trial proceedings — no IPR, PGR, or CBM — have ever been filed against US 6,676,246. The USPTO Open Data Portal (ODP) structure in this record reports no AIA trial activity for the patent, and web searches confirm that every HP Inc. v. Slingshot Printing LLC IPR from the 2020 wave (IPR2020-01084, -01085, -01086, -01090, -01659) and every Canon v. Slingshot IPR was directed to sibling patents, not 6,676,246. The defensive posture is therefore the mirror image of a "hardened" patent: all 19 claims of 6,676,246 are entirely untested at the PTAB — none canceled, none sustained, no estoppel running against anyone — but the patent expired 2022-12-27, so a defendant's exposure is limited to pre-expiration conduct and validity can be fought in district court on any ground, free of § 315(e)(2) estoppel.

There are no proceedings to itemize at claim level for this patent. Rather than invent entries, the sections below (a) document the absence, (b) map the closely-related proceedings on the same Slingshot heater-chip portfolio so you can see the pattern this patent escaped, and (c) give the strategic read.

Adjacent proceedings (context only — none involves 6,676,246)

These are the proceedings that a superficial search will surface. Do not confuse them with challenges to 6,676,246 — each names a different patent number.

IPR2020-01084 / -01085 / -01086 / -01090 — HP Inc. v. Slingshot Printing LLC (settled, terminated 2021-03-29)

• Type: Inter Partes Review
• Filed: 2020-06-15
• Patents actually challenged: 6,394,593 (IPR2020-01084); 6,243,115 (IPR2020-01085); 7,014,299 (IPR2020-01086); 7,244,015 (IPR2020-01090)
• Status: Terminated-Settled (each); institution decisions issued 2021-01-14; joint motions to terminate and confidential settlement/license agreements (e.g., Ex. 1017, "Confidential Slingshot-HP Settlement License and Release Agreement") filed 2021-03-16; termination decisions 2021-03-29.
• Relevance to 6,676,246: None directly. These petitions arose from the same Slingshot v. HP W.D. Tex. wave (e.g., 1:20-cv-00184-ADA et seq.) in which 6,676,246 was asserted in 1:20-cv-00187-ADA, but HP never petitioned against 6,676,246 itself. The March 2021 global settlement of the HP-Slingshot dispute (evidenced by these terminations) is the likely reason this patent and others in the wave never reached a PTAB merits decision.

IPR2020-01659 — HP Inc. v. Slingshot Printing LLC (settled, terminated 2021-03-29)

• Type: Inter Partes Review
• Filed: 2020-09-20
• Patent actually challenged: 7,410,246 ("Heater chip configuration for an inkjet printhead and printer") — note the similar "heater chip" subject matter to 6,676,246; not the same patent number.
• Status: Terminated-Settled; panel of APJs Garth Baer, John Hamann, Stacy Margolies; terminated 2021-03-29 before any Final Written Decision.
• Relevance to 6,676,246: Illustrates that HP's IPR campaign against the Slingshot heater-chip portfolio settled before merits decisions — which is why 6,676,246, even if it had been petitioned, likely would also have ended in settlement rather than a FWD.

Canon IPRs (2022–2026) — Canon U.S.A., Inc. / Canon Inc. v. Slingshot Printing LLC

• Type: Inter Partes Review
• Patents actually challenged: 7,195,341; 7,290,864; 7,484,823; 7,594,708 — none is 6,676,246.
• Status: Final Written Decisions found challenged claims unpatentable as obvious; the CAFC affirmed in Slingshot Printing LLC v. Canon U.S.A., Inc., No. 24-1956 (Fed. Cir. 2026-04-23) and companion appeals affirmed 2026-07 (see IPWatchdog, 2026-07-16). These are the 2026 CAFC dispositions referenced in earlier sections of this analysis — they concern 7,195,341, 7,290,864, 7,484,823 and 7,594,708, not 6,676,246.
• Relevance to 6,676,246: Shows the broader Slingshot portfolio is vulnerable on obviousness grounds in front of the Board and the CAFC — but no one has yet brought that fight to 6,676,246.

Strategic summary

Claim-by-claim status of 6,676,246: every claim is UNTESTED at the PTAB. Independent claims 1, 8, 9, and 10 and dependent claims 2–7 and 11–19 stand exactly as granted on 2004-01-13. No FWD has ever addressed them, no claim has been canceled, and none has been "sustained" in the IPR sense because no petition was ever instituted. That cuts both ways: the patent has no PTAB scar tissue, but it also has no PTAB validation, and the Canon results against the parallel heater-chip portfolio (7,290,864, 7,484,823, 7,594,708, 7,195,341 — all invalidated as obvious and affirmed) signal that these Lexmark-origin thermal-inkjet claims are far from bulletproof.

Estoppel landscape — this is the cleanest part of the picture. Because no IPR was ever instituted on 6,676,246, § 315(e)(2) estoppel binds nobody. A defendant facing assertion today can raise any prior-art ground — § 102, § 103, § 112, on-sale/public-use bars, printed publications — in district court without stepping around any PTAB record. There is no petitioner, no privy, and no previously-raised-or-reasonably-could-have-raised ground to work around. The § 315(b) one-year bar is likewise a non-issue for any defendant who was never served with a complaint more than a year before filing its own petition — though for a patent that expired 2022-12-27, the practical remedy calculus (no injunction, damages only for the pre-expiration period, if the statute permits recovery at all for the expired window) makes a district-court § 282(b) defense the more efficient path than a new IPR.

Pattern signals. (1) The same patent owner — Slingshot Printing LLC, the Funai/Lexmark successor — has faced two aggressive petitioner waves: HP in 2020 (five IPRs on siblings, all settled and terminated 2021-03-29 after a global license/settlement) and Canon in 2022+ (four patents invalidated, CAFC-affirmed in 2026). (2) 6,676,246 was asserted against HP in W.D. Tex. (Slingshot Printing LLC v. HP Inc., No. 6:19-cv-00549, filed 2019-09-20, and No. 1:20-cv-00187-ADA) yet HP chose not to petition IPR against it — possibly because the parties' 2021 settlement mooted the need, or because the patent's expiration (2022-12-27) limited the value of a challenge. (3) No defensive aggregator (e.g., Unified Patents) appears in any proceeding record for this patent number.

Recommended next steps

1. Verify the "no activity" finding yourself before relying on it. Run the patent number in PTAB E2E/PTACTS (https://ptab.uspto.gov and https://ptacts.uspto.gov) and the USPTO ODP AIA-trial API. The ODP block in this record shows no proceedings, and my searches of Docket Alarm, IPverse, PTACTS, and secondary sources found no petition naming 6,676,246 — but ODP ingests lag, and a petition filed in the last ~60 days (e.g., 2026) may not yet appear. Given the Canon/Slingshot 2026 CAFC activity, a late-stage petition against this patent would not be shocking; check before you rely on absence.

2. Anchor your defense in the expiration, not in IPR history. The patent's adjusted expiration is 2022-12-27 and its legal status is "Expired – Lifetime." There is no active proceeding and no FWD to cite. If you are defending a demand letter, your first line is: no injunctive relief is available; damages (if any) are confined to acts before 2022-12-27; and validity is fully contestable under 35 U.S.C. § 282(b) with no § 315(e)(2) estoppel.

3. If you want a PTAB data point, borrow from the Canon playbook. The Canon IPRs and the 2026 CAFC affirmances (e.g., No. 24-1956, decided 2026-04-23; companion affirmances reported 2026-07-16) show the Board and Federal Circuit finding closely related Slingshot heater-chip claims obvious over combinations of thermal-inkjet prior art. The same art and argument templates (e.g., motivation-to-combine analysis, use of patent-figure disclosures) are available to you in a district court § 282(b) defense against 6,676,246 — with no estoppel constraint.

4. Confirm the HP litigation disposition. The 6:19-cv-00549 and 1:20-cv-00187-ADA cases involving 6,676,246 appear to have been resolved in the March 2021 HP-Slingshot global settlement (per the confidential settlement agreements filed in the HP IPRs and the 2021-03-29 termination decisions). If you are facing a new assertion, confirm current ownership (Slingshot Printing LLC per the 2019-03-29 assignment) and whether any license from that settlement covers your customer or supply chain.

Bottom line: there are no IPR/PGR/CBM proceedings on 6,676,246 — none pending, none decided, none settled. That absence is a double-edged signal: this patent has never survived (or failed) a PTAB challenge, so a defendant is free to attack validity on any ground in district court, but should expect the patent owner to defend it vigorously given the patent survived the HP wave untouched while its siblings were either settled or invalidated.

I'll research the full assignment record for US 6676246, starting with the USPTO assignment database and cross-referencing legal-event records.

Let me search for more specific assignment record details and the correspondent attorneys.

The litigation and ownership context is emerging. Now let me find the specific assignment record details including correspondents of record.

Based on the research completed, here is the reconstructed ownership record. Note upfront: reel/frame numbers, parties, and dates below come from the USPTO-derived legal-event feed on Google Patents (which indexes the same underlying records as the USPTO Assignment Center). The correspondent-of-record field is not exposed in that feed, and I was unable to complete a direct Assignment Center query within my available search steps — that specific field is flagged below rather than guessed.

Inventors

• Frank Edward Anderson — Lexmark employee at filing. Named assignor on the Nov. 19, 2002 assignment to Lexmark International, Inc. (reel 013523/0690). He appears as inventor on numerous subsequent Lexmark micro-fluid ejection patents (e.g., later low-ejection-energy filings in 2004–2006), consistent with a career Lexmark/inkjet-engineer profile.
• Robert Wilson Cornell — Lexmark employee at filing. Co-assignor on the same Nov. 19, 2002 assignment to Lexmark.

Pattern note: Both inventors executed the assignment to Lexmark the day before the application was filed (assignment effective 2002-11-19; application filed 2002-11-20) — a routine employee-assignment timing. I have no data indicating either inventor departed Lexmark within 12 months of filing, so no fire-sale precursor signal is present.

Original assignee

Lexmark International, Inc. (Kentucky) — the entity named on the issued patent and the assignee of the inventors' rights.

• Line of business / product embodiment: Lexmark was a major operating thermal-inkjet printer OEM at filing; the '246 heater-chip construction (thin protective stack, <0.73 µs pulse time, 2.9–4.0 GJ/m³) is directed at the thermal inkjet printheads Lexmark designed and shipped in its own printers and cartridges. Yes — Lexmark shipped products embodying the claimed subject matter.
• Current status: Inkjet technology and assets (including this patent) were sold to Funai Electric Co., Ltd. in 2013 for ~$100M (announced April 2013; assignment recorded May 2013). Lexmark itself was acquired by a Chinese consortium (Apex Technology/Ninestar) and taken private in 2016. It remained an operating (laser-focused) company as of my last verifiable data; I could not verify 2026 operating status from the searches completed.

Assignment timeline

Three recorded assignments appear in the USPTO-derived legal-event record. No security agreements, mergers, releases, or name changes are recorded for this patent.

• 2002-11-19 (executed) / recorded 2002-11-20 — Reel 013523/0690

  • Conveyance: Assignment of Assignors' Interest
  • Assignor: Frank Edward Anderson; Robert Wilson Cornell
  • Assignee: Lexmark International, Inc.
  • Correspondent: Not available in the Google/UPSTO-derived feed — verify in Assignment Center directly.
  • Context: Standard employee/inventor assignment to the employer at filing. Same-day execution relative to the filing date (Nov. 20, 2002).

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

  • Conveyance: Assignment
  • Assignor: Lexmark International, Inc.; Lexmark International Technology, S.A.
  • Assignee: Funai Electric Co., Ltd. (Japan)
  • Correspondent: Not available in the Google/UPSTO-derived feed — verify in Assignment Center directly.
  • Context: The ~$100M sale of Lexmark's inkjet business, patents, and the former Lexmark ink-cartridge plant (Philippines) to Japanese OEM Funai — an arm's-length operating-company divestiture, not a bankruptcy or fire-sale (Lexmark was solvent and exiting inkjet).

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

  • Conveyance: Assignment
  • Assignor: Funai Electric Co., Ltd.
  • Assignee: Slingshot Printing LLC (Delaware LLC; USPTO record lists Maryland address — 8455 Colesville Road, Suite 830, Silver Spring, MD 20910 per the later complaint)
  • Correspondent: Not available in the Google/UPSTO-derived feed — verify in Assignment Center directly. (Related observation: Slingshot's litigation counsel — Raymond W. Mort III, Chandran B. Iyer, Jason S. Charkow, Ronald M. Daignault, Michael A. Siem — recurs across Slingshot's HP and Canon suits; this indicates a single repeat-player assertion program, but it is not the recorded-assignment correspondent tell.)
  • Context: Bulk transfer of 100+ former Lexmark US patent assets from Funai to a newly formed NPE, per RPX Insight (June 12, 2019: "New NPE Begins Litigating Former Lexmark Patents Among More Than 100 Received from Funai").

Additional non-assignment legal events (for completeness): Certificate of correction 2004-06-08; maintenance fees paid 2007 (4th year), 2011 (8th year), 2015 (12th year); patent expired-lifetime with adjusted expiration Dec. 27, 2022.

Timeline diagram

timeline
    title Ownership of US 6676246
    2002 : Filed by Lexmark
         : Inventors assign to Lexmark
    2004 : Patent issued
    2013 : Assigned to Funai Electric
    2019 : Assigned to Slingshot Printing
         : First suit filed vs HP

NPE / troll-pattern signals

1. Shell-entity transfer — Present. Reel 048745/0551 (recorded 2019-03-29) moved the patent from Funai Electric (an operating OEM that manufactured inkjet hardware) to Slingshot Printing LLC, a Delaware LLC with its principal place at 8455 Colesville Road, Suite 830, Silver Spring, MD 20910 — an office-suite address with no manufacturing operation. RPX Insight independently characterized Slingshot as a "recently formed NPE" that received "more than 100 US assets from Funai." Slingshot ships no products.

2. Known asserter in the chain — Present. Slingshot Printing LLC is identified as an NPE by RPX (insight.rpxcorp.com, June 12, 2019) and is a repeat high-frequency plaintiff: it sued HP Inc. (W.D. Tex. No. 6:19-cv-00549, filed Sept. 20, 2019, naming US 6,676,246 among ten patents-in-suit; and No. 1:20-cv-00187) and later Canon. This patent does not appear on the Acacia/Marathon/IV/Wi-LAN/Mosaid list, but Slingshot's RPX-listed NPE status satisfies the signal.

3. Repeat correspondent across the chain — Unclear / not verifiable from available sources. The correspondent-of-record field is not visible in the USPTO-derived feed I could access, and I could not complete a direct Assignment Center query. This is the single largest evidentiary gap in this analysis. The recurring litigation counsel noted above is suggestive of a coordinated program but is not the recorded-assignment correspondent tell, so I do not count it as a finding.

4. Cascading transfers — Not present. The chain is only three links spanning 17 years (2002 Lexmark → 2013 Funai → 2019 Slingshot). No chained-LLC cascade within 24 months. The 2019 link is a single bulk transfer, not a series.

5. Pre-litigation transfer — Present. Reel 048745/0551 was recorded 2019-03-29; the first infringement suit naming this patent (6:19-cv-00549, W.D. Tex.) was filed 2019-09-20 — approximately 5.8 months later, inside the 6-month window. The transfer put clean standing in the hands of the asserting entity immediately before suit.

6. Bankruptcy fire-sale — Not present. Neither Lexmark (2013 divestiture) nor Funai (2019 transfer) was in bankruptcy at the relevant time; the Lexmark→Funai sale was a negotiated ~$100M operating divestiture of a solvent company's inkjet line.

7. Privateering — Present (reported). RPX Insight stated that "assignment records suggest that Funai might hold an economic interest in Slingshot's litigation," and HP later moved to draw Funai into the W.D. Tex. dispute (reported by Actionable Intelligence: "HP Seeks to Drag Funai into Slingshot Printing Patent Dispute"). An operating OEM (Funai) transferring patents to an NPE that sues a competitor (HP) — with indicia Funai retained an economic stake — is the classic privateering configuration. I weight this as reported evidence rather than independently verified.

8. Defensive aggregator (anti-NPE) — Not present. The chain terminates at Slingshot Printing LLC, an assertion entity. No RPX, AST, LOT Network, Unified Patents, or OIN involvement.

Verdict

NPE — high confidence

The patent moved from an operating company (Funai, reel 030416/0001) to a licensing-only Delaware LLC with no products (Slingshot Printing, reel 048745/0551, recorded 2019-03-29) that is independently tracked as an NPE by RPX, and Slingshot filed its first infringement suit naming this patent ~5.8 months later (W.D. Tex. 6:19-cv-00549, filed 2019-09-20). RPX's report that Funai may retain an economic interest in Slingshot's litigation adds a privateering overlay. The only weak point is the unverified correspondent-of-record field (signal 3), which does not change the outcome given two independently strong signals.

Verification link: USPTO Assignment Center — https://assignmentcenter.uspto.gov/ (search Patent No. 6676246; confirm reel/frame entries 013523/0690, 030416/0001, and 048745/0551 and retrieve the correspondent-of-record names for each, which are not reproduced in the Google Patents legal-event feed).

I have reached the tool-call limit, so I will now answer directly from the authoritative full-text record provided plus the search results already retrieved above.

USPTO search confirmation — US 6,676,246

I searched for the literal patent number 6676246 and confirmed the USPTO-record bibliographic data via Google Patents/FreePatentsOnline/Justia mirrors of the USPTO record (the authoritative full text supplied in this session):

• Patent No.: US 6,676,246 B1 — Heater construction for minimum pulse time
• Application: US 10/300,536, filed Nov. 20, 2002; granted Jan. 13, 2004
• Inventors: Frank Edward Anderson; Robert Wilson Cornell (assignee at issue: Lexmark International, Inc.)
• Status: Expired – Lifetime (adjusted expiration Dec. 27, 2022)

No results for similar numbers were substituted. The record's own "Citations" lists were used as the authoritative source for the prior-art inventory below.

Anticipation framework used here

Because the application was filed Nov. 20, 2002, pre-AIA 35 U.S.C. § 102 governs. For each cited reference I therefore assessed three routes, as applicable:

• § 102(a) – known/used in the U.S. or patented/described in a printed publication before the invention date;
• § 102(b) – patented or described in a printed publication more than one year before Nov. 20, 2002 (i.e., before Nov. 20, 2001);
• § 102(e) – a U.S. patent (or published application) by another whose application was filed before Nov. 20, 2002.

Anticipation requires a single reference disclosing every limitation of the claim, expressly or inherently. The independent claims at issue are:

• Claim 8 (broadest): a heater chip structure with heating elements operable at (i) energy per unit volume of ~2.9–4.0 GJ/m³, (ii) pulse time < ~0.73 μs, and (iii) protective layer(s) totaling < ~7200 Å.
• Claims 1, 9 (printer / heater chip): add nozzle association, the defined volume = resistor area × (resistor thickness + protective-layer thickness), and the electrical-power-supply context.
• Claim 10 (method): adds applying pulses < 0.73 μs at 2.9–4.0 GJ/m³ and ejecting at "stable velocity."
• Dependent claims add resistor thickness 500–1500 Å (claims 2, 3, 13, 16, 19), area 300–1100 μm² (claims 3, 13, 16, 19), protective thickness 1000–7200 Å (claim 4), multi-layer overcoat (claim 5), and specific material lists (claims 6, 7, 11, 12, 14, 15, 17, 18).

Bottom line up front: No single cited reference discloses the full combination of all three numerical limitations (thin stack < 7200 Å and pulse < 0.73 μs and 2.9–4.0 GJ/m³ on the claimed volume metric). The two references the examiner flagged (*) — US 6,142,612 and US 6,491,377 — are the closest, but each still appears to miss at least one core numeric limitation. The realistic anticipation case is weak; the better validity attack on these facts would be § 103 obviousness combinations.

Cited references and § 102 analysis

Google's record lists "Citations (23)" and, in expanded form, "Patent Citations (26)." Deduplicating family members (EP0490668A2/B1; EP1078757A2/A3; US6227640B1/US20010008411A1) yields the unique references below. Data (dates, inventors, assignees, titles) are taken from the patent's own citation lists unless noted.

A. Closest references (partial-disclosure candidates)

1. US 6,491,377 B1 — "High print quality printhead" (Hewlett-Packard)

• Filed Aug. 30, 1999 (priority, US 09/386,015); published Dec. 10, 2002. Cited by examiner (*).
• Description: A high-density thermal inkjet printhead (≥ 6 heater resistors/mm²; each resistor ≥ 70 Ω) whose "overlaying passivation thermal barrier characteristic [is] adjusted to enable ejection of an ink drop of less than 6.5 ng with an energy impulse equal to or less than 1.4 μJ." Dependent claim 5 caps the passivation layer at < 5000 Å — i.e., squarely within the "< 7200 Å" window of claims 1, 8, 9, 10.
• § 102 analysis: Qualifies as prior art under § 102(e) (US application filed 1999 by HP, "another," before Nov. 20, 2002). It expressly meets the protective-layer < 7200 Å limitation. It does not expressly disclose a pulse time < 0.73 μs or the 2.9–4.0 GJ/m³ energy-per-volume metric as defined in the claims (energy is expressed per-drop in μJ, and drop volume, not heater-stack volume, is used). Without inherency evidence, it does not anticipate claims 1, 8, 9, or 10; it is the single strongest § 103 building block. Potentially relevant to dependent claims 4–6, 11–14, 17 if the energy/pulse gaps could be supplied in an inherency argument — which I cannot confirm on this record.

2. US 6,142,612 A — "Controlled layer of tantalum for thermal ink jet printer" (Lexmark; inv. Charles S. Whitman)

• Filed Nov. 6, 1998; published Nov. 7, 2000. Cited by examiner (*).
• Description: Optimizes the sputtered tantalum cavitation/protective layer thickness (optimum ~9,000 Å over SiC) on a Si₃N₄/SiC/Ta stack so printhead life improves without increasing current-pulse width; explains that thicker overcoats otherwise force longer pulse widths and lower power density, degrading print quality.
• § 102 analysis: § 102(b) statutory-bar art (published > 1 year pre-filing). It is highly relevant to the specification's pulse-time/stack-thickness teaching but teaches a protective stack with Ta alone ~9,000 Å — i.e., a total protective thickness above the claimed < 7200 Å ceiling. It therefore affirmatively does not satisfy that limitation and does not anticipate claims 1, 8, 9, or 10. Also relevant to dependent claims 6/11/14/17 (Ta, SiC, SiN materials) but on its thickness teaching it runs contrary.

3. US 6,331,049 B1 — "Printhead having varied thickness passivation layer and method of making same" (Hewlett-Packard)

• Filed Mar. 12, 1999; published Dec. 18, 2001.
• Description: A printhead whose passivation layer is made thin over the ink-expulsion (heater) element to reduce turn-on energy (TOE) and thicker over circuitry; expressly teaches TOE ∝ passivation thickness.
• § 102 analysis: § 102(b) art. Satisfies the concept of a thin overcoat over the resistor but does not, on the available record, state the claimed numerical trio (< 7200 Å total, < 0.73 μs, 2.9–4.0 GJ/m³). Not anticipatory of claims 1, 8, 9, or 10; good § 103 combination material with US 6,491,377 / US 6,139,131.

4. US 6,139,131 A — "High drop generator density printhead" (Hewlett-Packard; Prasad et al.)

• Filed Aug. 30, 1999; published Oct. 31, 2000.
• Description: 432-drop-generator, 1200-dpi-class printhead with matrix addressing and defined firing intervals; expressly defines pulse time t_PW = 1.4 μs ± 0.1 with dead time for cooling.
• § 102 analysis: § 102(b)/§ 102(e) art. Discloses pulse-time engineering for dense printheads, but its exemplified pulse time (1.4 μs) is outside the claimed "< 0.73 μs" window, and it does not disclose the 2.9–4.0 GJ/m³ energy-per-volume metric or the < 7200 Å stack. It does not anticipate; it is strong § 103 background (and in fact illustrates the "conventional" longer-pulse regime the '246 patent seeks to leave).

5. US 6,139,131's companion — US 6,491,377 (see item 1) and US 6,139,131 are the two HP filings most often paired with US 6,337,609/6,491,377 family art.

B. Drive/pulse-energy control art (secondary relevance; none anticipates the structure claims)

6. US 5,726,690 A — "Control of ink drop volume in thermal inkjet printheads by varying the pulse width of the firing pulses" (HP; Bohorquez et al.)

• Filed May 1, 1991; published Mar. 10, 1998. § 102(b) art.
• Description: Varies drop volume by varying firing-pulse width (demonstrated ~1.5–3.5 μs range); teaches shorter pulse widths give improved ejection dynamics and that turn-on energy shifts ~0.5 μJ/μs with pulse width.
• § 102 analysis: Discloses the pulse-width-tuning concept but in a longer (≥ ~1.5 μs) regime and with no stack-thickness or energy-density limits. Not anticipatory of claims 1, 8, 9, 10.

7. US 5,682,185 A — "Energy measurement scheme for an ink jet printer" (HP; Wade et al.)

• Filed Oct. 29, 1993; published Oct. 28, 1997. § 102(b) art.
• Description: Measuring/controlling energy delivered to thermal inkjet heaters.
• § 102 analysis: No disclosure of the claimed thin-stack/pulse/energy-volume combination. Not anticipatory.

8. US 6,244,682 B1 — "Method and apparatus for establishing ink-jet printhead operating energy from an optical determination of turn-on energy" (HP; Walker et al.)

• Filed Jan. 25, 1999; published Jun. 12, 2001. § 102(b) art.
• Description: Determines turn-on energy optically to set operating energy.
• § 102 analysis: Energy-setting method only; no stack-thickness/pulse limitations. Not anticipatory.

9. US 6,227,640 B1 — "Variable drop mass inkjet drop generator" (HP; Maze et al.) (also published as US 2001/0008411 A1)

• Priority Mar. 23, 1994; published May 8, 2001. § 102(b) art.
• Description: Drop generator producing variable drop masses.
• § 102 analysis: No relevant stack/pulse/energy-density disclosure. Not anticipatory.

10. US 6,318,845 B1 — "Ink-jet printing apparatus and method for varying energy for ink ejection for high and low ejection duties" (Canon)

• Filed Jul. 10, 1998; published Nov. 20, 2001. § 102(b) art.
• Description: Varies ejection energy with print duty.
• § 102 analysis: Duty-based energy control; not anticipatory.

11. US 5,742,307 A — "Method for electrical tailoring drop ejector thresholds of thermal ink jet heater elements" (Xerox; Watrobski et al.)

• Filed Dec. 19, 1994; published Apr. 21, 1998. § 102(b) art.
• Description: Electrically trimming individual heater thresholds.
• § 102 analysis: Trimming method; not anticipatory.

C. Heater-stack / protective-layer construction art

12. US 4,719,478 A — "Heat generating resistor, recording head using such resistor and drive method therefor" (Canon; Tachihara et al.)

• Filed Sep. 27, 1985; published Jan. 12, 1988. § 102(b) art.
• Description: Early bubble-jet heat-generating resistor with protective layers and drive method.
• § 102 analysis: Remote; does not meet the claimed ranges. Not anticipatory.

13. US 4,936,952 A — "Method for manufacturing a liquid jet recording head" (Canon; Komuro)

• Filed Mar. 5, 1986; published Jun. 26, 1990. § 102(b) art.
• Description: Manufacturing method for liquid-jet heads with protective layers.
• § 102 analysis: Process art; no claimed combination. Not anticipatory.

14. US 4,968,992 A — "Method for manufacturing a liquid jet recording head having a protective layer formed by etching" (Canon; Komuro)

• Filed Mar. 4, 1986; published Nov. 6, 1990. § 102(b) art.
• Description: Etch-formed protective layer in a liquid jet head.
• § 102 analysis: Process art; not anticipatory.

15. US 5,580,468 A — "Method of fabricating head for recording apparatus" (Canon; Fujikawa et al.)

• Filed Jul. 11, 1991; published Dec. 3, 1996. § 102(b) art.
• Description: Fabrication of a recording head.
• § 102 analysis: Fabrication method; no claimed operating ranges. Not anticipatory.

16. US 6,315,853 B1 — "Method for manufacturing an ink jet recording head" (Canon; Kubota et al.)

• Filed Oct. 13, 1995; published Nov. 13, 2001. § 102(b) art.
• Description: Manufacturing an ink jet recording head.
• § 102 analysis: Process art; not anticipatory.

17. US 6,042,221 A — "Ink-jet recording head and ink-jet recording apparatus" (Canon; Komuro)

• Filed Jun. 30, 1995; published Mar. 28, 2000. § 102(b) art.
• Description: Ink-jet head/printhead structure with heater and protective layers.
• § 102 analysis: General structure; no disclosed combination of all three claimed parameters. Not anticipatory.

18. US 5,831,648 A — "Ink jet recording head" (Hitachi Koki; Mitani et al.)

• Filed May 29, 1992; published Nov. 3, 1998. § 102(b) art.
• Description: Ink jet recording head.
• § 102 analysis: General; not anticipatory.

19. US 4,595,823 A — "Thermal printing head with an anti-abrasion layer and method of fabricating the same" (Fujitsu; Sorimachi et al.)

• Filed Mar. 17, 1983; published Jun. 17, 1986. § 102(b) art.
• Description: Thermal printhead with an anti-abrasion (protective) layer — earliest protective-layer art on the face of the patent.
• § 102 analysis: Remote field/era; no claimed ranges. Not anticipatory.

20. US 5,387,460 A — "Thermal printing ink medium" (Fuji Xerox; Hirakata et al.)

• Filed Oct. 17, 1991; published Feb. 7, 1995. § 102(b) art.
• Description: Ink medium for thermal printing.
• § 102 analysis: Ink/medium art, not heater structure. Not anticipatory.

D. Foreign references

21. EP 0 490 668 A2/B1 — "Ink jet recording" (Canon)

• Filed Dec. 12, 1990; published Jun. 17, 1992 (A2); B1 1996. § 102(b) art.
• Description: Ink jet recording head/apparatus with heaters and overcoat layers.
• § 102 analysis: General; no claimed combination. Not anticipatory.

22. JP 06-320729 A (JPH06320729A) — "Ink jet recording head, and method and device for inspecting same" (Canon)

• Filed May 11, 1993; published Nov. 22, 1994. § 102(b) art.
• Description: Ink jet head and inspection method/device.
• § 102 analysis: Inspection-related; not anticipatory.

23. EP 1 078 757 A2/A3 — "Liquid discharge head, driving method therefor, and cartridge, and image forming apparatus" (Canon)

• Filed Aug. 24, 1999; published Feb. 28, 2001 (A2); A3 2001. § 102(b) art.
• Description: Liquid discharge head with driving method.
• § 102 analysis: Driving-method disclosure; no claimed stack/energy combination demonstrated. Not anticipatory.

E. Anomalous entry

24. US 6,412,290 B1 — "Cryogenic refrigerating device" (Aisin Seiki)

• Filed Oct. 19, 1999; published Jul. 2, 2002.
• Description: A cryogenic refrigeration device — unrelated to inkjet art. This appears to be a data-aggregation artifact in the Google record rather than substantive prior art.
• § 102 analysis: Not anticipatory of any claim; should be disregarded unless confirmed against the actual USPTO Notice of References Cited (which I could not independently verify in this session).

Most relevant prior art — prioritized

Caveats and uncertainty disclosures

• I verified the record mirrors (Google Patents / FreePatentsOnline / Justia) but could not pull the USPTO's actual "Notice of References Cited" (PTO/SB/08) or the examiner's search history before the tool limit. The two *-marked references (US 6,142,612; US 6,491,377) are the only ones the Google record flags as examiner-cited.
• My § 102 conclusions are "potential anticipation" assessments only. On the disclosed text, no cited reference appears to anticipate any independent claim, because the three quantitative limitations (protective stack < 7200 Å and pulse time < 0.73 μs and 2.9–4.0 GJ/m³ on the claim-defined volume) are not all present in any single document. A rigorous anticipation position would require inherency evidence or full-text confirmations beyond what I retrieved.
• The dependent claims most exposed if a § 103 (not § 102) case were mounted using US 6,491,377 + US 6,331,049 would be claims 4–6, 11–14, and 17 (thin overcoat + material lists); the material-list claims (6, 7, 11, 12, 14, 15, 17, 18) recite conventional TaAl/TaN/SiN/SiC/DLC/Ta materials that individually appear throughout the cited art.
• Patent-number and identifier spellings above are literal (including the specification's own "tatalum"/"titantium" typos in claims 6, 11, 14, 17, which I did not alter).

§ 103 Obviousness Analysis — US 6,676,246 ("Heater construction for minimum pulse time")

Statutory framework. Application filed Nov. 20, 2002; issued Jan. 13, 2004. Pre-AIA 35 U.S.C. § 103 applies. All grounds below assume an invention date no earlier than the filing date (no priority or conception evidence in the record) and rely on references that qualify as prior art under pre-AIA § 102(a), (b), or (e) as noted for each.

One correction to the earlier Prior Art section (flagged per operating rules). That section classified US 6,331,049 as "§ 102(b) art." That is incorrect: US 6,331,049 published Dec. 18, 2001, which is less than one year before the Nov. 20, 2002 filing date (the § 102(b) bar date was Nov. 20, 2001). US 6,331,049 nonetheless qualifies as prior art under § 102(a) (published before the invention date) and § 102(e) (US application filed Mar. 12, 1999, by Hewlett-Packard, another, before the '246 invention date). This does not change the analysis but corrects the statutory hook. Similarly, US 6,491,377 published Dec. 10, 2002 — after the '246 filing date — so it is prior art only via § 102(e) (HP application filed Aug. 30, 1999), not § 102(a)/(b). All other references used below are § 102(b) art as dated in the Prior Art section.

I. The claim scope to be attacked

Independent claims: 1, 8, 9, 10. Dependent: 2–7, 11–19.

• Claim 8 (broadest): a heater chip structure having heating elements "operable at an energy per unit volume of from about 2.9 GJ/m³ to about 4.0 GJ/m³," "a pulse time of less than about 0.73 microseconds," and "one or more protective layers having a total thickness of less than about 7200 angstroms." Note what claim 8 does not require: no nozzle, no ink, no resistor area/thickness, no defined volume metric, no power supply, no "stable velocity." Two of the three limitations are purely functional ("operable at …," "a pulse time of …").
• Claims 1 and 9: add a power-supply context (claim 1) and, materially: each heating element = resistor (area, thickness) + overlying protective layer < 7200 Å; the element has a "volume … determined by the area of the heater resistor multiplied by the sum of the thickness of the heater resistor and the thickness of the protective layer"; ink is ejected through an associated nozzle in a pulse time < 0.73 μs; and the energy delivered per that defined volume is 2.9–4.0 GJ/m³.
• Claim 10 (method): the same structure, plus applying pulses < 0.73 μs at 2.9–4.0 GJ/m³ and ejecting droplets "at a stable velocity."
• Dependent claims: resistor thickness 500–1500 Å (2, 3, 13, 16, 19); resistor area 300–1100 μm² (3, 13, 16, 19); protective layer 1000–7200 Å (4); multi-layer overcoat (5); conventional overcoat material lists — SiN, SiC, Ta, TiW, DLC, Si-DLC, TaB, TiN, Ti, WSi (6, 11, 14, 17); conventional resistor material lists — TaAl, TaN, TaAl:N, Ta+TaAl (7, 12, 15, 18).

II. The person of ordinary skill in the art (PHOSITA)

A design or process engineer with (i) a bachelor's degree in electrical engineering, materials science, or chemical engineering and 2–5 years of experience developing thermal inkjet printheads; (ii) working knowledge of thin-film resistor and passivation/cavitation layer deposition (materials, thicknesses, stress, adhesion); (iii) familiarity with heater drive electronics, turn-on energy (TOE), pulse-width control, and firing-frequency/nozzle-density tradeoffs; and (iv) access to the standard thermal-inkjet literature (e.g., the HP, Canon, Lexmark patent corpus and the Lloyd & Taub chapter in Output Hardcopy Devices). This is a mature, crowded field by 2002 — as the '246 specification's own background and the sheer density of the cited art (26 listed references, largely HP/Canon/Lexmark thermal-inkjet heater patents spanning 1983–2002) confirm.

III. The claimed "invention" as the specification frames it — and the admissions that help the challenger

The specification discloses no new material, no new device architecture, and no new drive scheme. Its entire contribution is a parameter window:

"it has been discovered that the required pulse time for satisfactory operation of an ink jet heater is generally a function of the heater stack thickness and is generally independent of the heater area and ink composition" … "relatively low pulse times and improved printer performance may be achieved by constructing the heater chip to limit the thickness of the protective layers and applying only relatively low power to the resistors." (Detailed Description; emphasis added)

Three points matter for § 103:

1. The patentee concedes the governing physical relationship (stack thickness → pulse time) and disclaims any dependence on area or ink. That relationship is precisely what the closest prior art already teaches (see § IV below). The claims merely package the consequence of a thin stack as functional limitations.
2. All materials are conventional and the specification says so — "the invention is not limited to any particular material or combination of materials in the protective layer"; the passivation/cavitation materials are the industry-standard SiN/SiC/Si-DLC/DLC/Ta set; resistor materials are the industry-standard TaAl/TaN family.
3. No criticality data. The specification contains no comparative examples, no data showing that 0.73 μs or 7200 Å or 2.9–4.0 GJ/m³ are critical boundaries, and no showing of unexpected results. The values are stated as design windows. That is the classic profile of a claim vulnerable under KSR as an obvious optimization of result-effective variables.

IV. The closest prior art (from the record's cited references, confirmed against the underlying patents)

Primary reference — US 6,491,377 B1 ("High print quality printhead," HP; examiner-cited; § 102(e), app. filed Aug. 30, 1999)

Confirmed from the patent itself:

• Claim 1: a printhead with heater resistors at a density ≥ 6 resistors/mm², each ≥ 70 Ω, "having an overlaying passivation thermal barrier characteristic adjusted to enable ejection of an ink drop of less than 6.5 ng with an energy impulse equal to or less than 1.4 μJ."
• Claim 5: "the passivation layer has a thickness of less than 5000 Å."

This single patent discloses a high-nozzle-density, high-frequency-class printhead with (i) a protective (passivation) layer under the claimed 7200 Å ceiling (indeed under 5000 Å) and (ii) expressly low-energy operation (≤ 1.4 μJ), targeting the same problem the '246 patent says it solves — high nozzle density requiring short address times and low energy to avoid printhead heating artifacts.

Secondary reference — US 6,142,612 A ("Controlled layer of tantalum for thermal ink jet printer," Lexmark/Whitman; examiner-cited; § 102(b)/(e), filed Nov. 6, 1998)

A Lexmark patent (same corporate origin as the '246) addressing the exact variable the '246 patent claims to have discovered. It optimizes the sputtered tantalum cavitation-layer thickness over a Si₃N₄/SiC/Ta stack and, per the Prior Art section, "explains that thicker overcoats otherwise force longer pulse widths and lower power density, degrading print quality." In other words, the art's own language teaches the stack-thickness ↔ pulse-width relationship on which the '246 claims rest. Its specific Ta optimum (~9000 Å) lies above the '246's 7200 Å total ceiling, which a patent owner will call "teaching away" (see § VIII), but its explicit framing of overcoat thickness as the pulse-width control variable is the intellectual bridge to the '246 claims.

Tertiary reference — US 6,331,049 B1 ("Printhead having varied thickness passivation layer," HP; § 102(a)/(e), filed Mar. 12, 1999)

Confirmed from the patent: the passivation layer is made "relatively thin over the ink expulsion element to reduce the energy required to expel ink" and thick over circuitry; "TOE is related to passivation layer thickness in that the thicker the passivation layer, the more energy required"; a reduction "from 0.75 microns to 0.38 microns achieves a TOE reduction of approximately 22%," with thicknesses "reduced below 0.38 microns, for example, to 0.2 microns or below" (2000 Å). This is an express teaching that thinning the passivation over the heater element alone — while keeping it thick elsewhere — cuts TOE, and it quantifies the relationship. A 0.2 μm passivation over a ~0.1 μm resistor yields a sub-7200 Å (indeed ~3000 Å) heater stack.

Context references for pulse-time / firing-frequency engineering

• US 6,139,131 A (HP, § 102(b)/(e), filed Aug. 30, 1999): high-drop-generator-density printhead (432 generators; 1200-dpi-class) with matrix addressing and explicitly engineered firing intervals; defines pulse time t_PW = 1.4 μs ± 0.1 with dead time for thermal recovery — i.e., it treats pulse width as the design variable for increasing nozzle count and firing frequency, the very context of the '246 background.
• US 5,726,690 A (HP, § 102(b)): drop-volume control by varying firing-pulse width; teaches that shorter pulse widths improve ejection dynamics and that TOE shifts with pulse width (~0.5 μJ/μs) — i.e., pulse width and energy are linked, controllable variables.
• US 6,244,682 B1 / 6,227,640 B1 (HP): operating-energy selection (turn-on energy) and variable-drop-mass generators — showing energy is set to the minimum reliable value, per TOE methodology.
• US 4,719,478; 4,936,952; 4,968,992; 5,580,468; 6,042,221; 6,315,853 (Canon); 5,831,648 (Hitachi Koki); EP 0 490 668; EP 1 078 757; JP 06-320729: general heater-resistor + protective-layer construction and driving methods using the same conventional SiN/SiC/Ta stacks and TaAl-family resistors.

V. Proposed § 103 combinations and claim mapping

Ground 1 (strongest): US 6,491,377 + US 6,142,612 (+ US 6,331,049, + US 6,139,131 as needed) → claims 1, 8, 9, 10

Ground 2: US 6,331,049 + US 6,491,377 (+ US 6,142,612) → claims 1, 8, 9, 10

Same mapping, with 6,331,049 as the primary: it is the reference that most directly teaches the spatially selective thinning of the passivation layer over the heater element to reduce expulsion energy, expressly acknowledging (and solving) the countervailing reliability problems of thin passivation by keeping the layer thick over circuitry. Combining 6,331,049's thin-over-heater architecture with 6,491,377's high-density, high-resistance, low-energy heater design and with 6,142,612's pulse-width/overcoat-thickness teaching yields the same claimed structure and operating window.

Ground 3 (against claim 8 in particular): 6,491,377 or 6,331,049 "alone + PHOSITA knowledge"

Claim 8's minimal elements — a thin-stack (< 7200 Å) heater chip operable at low energy density and sub-0.73 μs pulses — track 6,491,377 (or 6,331,049) plus the admitted stack-thickness/pulse-time relationship. A challenger can argue claim 8 is obvious over 6,491,377 in view of the PHOSITA's routine practice of setting pulse width to the minimum reliable value for the stack (TOE methodology per 6,244,682/5,726,690), with the < 0.73 μs and 2.9–4.0 GJ/m³ figures being nothing more than the measured operating point of the disclosed thin-stack device.

VI. Motivation to combine — KSR analysis

Same field, same problem, complementary teachings. All principal references are thermal inkjet printhead patents addressing heater/passivation stack design, energy, and firing density. KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007), requires no explicit "suggestion"; the combination is of known elements with predictable results, driven by a recognized design need:

1. The problem was known and shared. The '246 background describes it: as nozzle count and firing frequency rise, "the time available to address all nozzle hole positions … decreases," and thick insulating protective layers "increase the amount of energy that must be applied … [and] correspondingly … the pulse time." That is not a novel problem statement — it is the same problem 6,142,612 (thick overcoats → longer pulses, lower power density → degraded quality), 6,331,049 (passivation thickness ↑ ⇒ TOE ↑), 6,491,377 (dense, low-energy, thin-passivation design), and 6,139,131 (dense-array pulse-time engineering) each address.
2. The combination is of complementary, non-competing solutions. 6,331,049 and 6,491,377 push toward thin passivation for low energy; 6,142,612 explains why thickness is the pulse-width lever (even though its own lifetime-optimized Ta choice is thick). A PHOSITA seeking short pulses at high frequency reads the thin-stack references and 6,142,612's mechanism together and arrives at: thin protective stack (< 7200 Å, indeed ~2000–5000 Å), low pulse energy, sub-microsecond pulse width. That is precisely the claimed combination.
3. The results were predictable. The patentee's own admission that pulse time is a function of stack thickness (independent of area and ink) means the claimed pulse-time result follows mechanistically from the thin-stack structures already in 6,491,377/6,331,049. There is no new physics, no new material, and no new circuit in the '246 patent.
4. Portfolio context is probative. The PTAB and the Federal Circuit have now repeatedly held closely related Slingshot (ex-Lexmark) thermal-inkjet chip claims unpatentable as obvious over combinations of ordinary thermal-inkjet patents — e.g., Slingshot Printing LLC v. Canon U.S.A., Inc., No. 24-1956 (Fed. Cir. Apr. 23, 2026) (claims of 7,195,341 obvious over Torgerson US 6,412,917 + Bruce US 7,240,997); the July 16, 2026 affirmances (7,290,864 obvious over US 7,722,144/7,278,703/6,582,062; 7,484,823 and 7,594,708 obvious over "Benjamin" + "Giere'673," including US 7,384,113/6,612,673). Those are different claims (substrate layout, bondpad routing, temperature sensing), but they confirm the Board's and CAFC's treatment of this exact patent family's incremental, parameter/layout-driven claims in a mature field. Nothing about 6,676,246's claim scope — which is more functional and less structural than those — places it on stronger ground. (Sources: https://www.cafc.uscourts.gov/opinions-orders/24-1956.OPINION.4-23-2026_2681303.pdf; https://ipwatchdog.com/2026/07/16/cafc-affirms-two-ptab-obviousness-rulings-in-canon-printhead-patent-disputes/.)

VII. Dependent claims

• Resistor thickness 500–1500 Å and area 300–1100 μm² (claims 2, 3, 13, 16, 19): conventional thin-film resistor dimensions. TaAl-family resistors of ~1000 Å and heaters of ~10⁻¹¹–10⁻⁹ m² are pervasive in the cited Lexmark/HP/Canon stack art (6,142,612; 6,331,049; 6,042,221) and are implicit in 6,491,377's resistor-density and drop-size disclosures. A PHOSITA choosing dimensions for a 6.5-ng drop generator would land in these ranges as a matter of routine scaling.
• Protective layer 1000–7200 Å (claim 4): directly overlaps 6,491,377 claim 5 (< 5000 Å) and 6,331,049's 2000–3800 Å thin regions; ranges that merely overlap or bracket disclosed values are classically obvious.
• Multi-layer overcoat (claim 5): 6,142,612's Si₃N₄/SiC/Ta stack and 6,331,049's passivation + protection/cavitation layer 124 are multi-layer.
• Material-list claims (6, 11, 14, 17 — SiN, SiC, Ta, TiW, DLC, Si-DLC, TaB, TiN, Ti, WSi; and 7, 12, 15, 18 — TaAl, TaN, TaAl:N, Ta+TaAl): every listed material was a known passivation/cavitation or resistor material in the art (SiN/SiC/Ta appear in 6,142,612 and 6,331,049; DLC/Si-DLC in the '246's own disclosure as alternatives; TaAl/TaN throughout the Canon/Lexmark art). The claims recite "one or more materials selected from the group" — i.e., picking any one conventional material from a closed list of known-function materials, with no unexpected property shown, is obvious (cf. In re Applied Materials, 692 F.2d 1289 (Fed. Cir. 1982) — selecting from a finite list of known alternatives with predictable results).

VIII. The honest counter-analysis — where the § 103 case is weakest (and what a patent owner would say)

1. The < 0.73 μs number is below every exemplified pulse width in the closest art. 6,139,131 operates at 1.4 μs ± 0.1; 5,726,690 demonstrates ~1.5–3.5 μs. No cited reference demonstrates stable-velocity ejection at sub-0.73 μs. The challenger's best answer is mechanistic (thin-stack thermal time constant ~0.2–0.5 μs) plus the admitted stack-thickness/pulse-time relationship — but if the patent owner can produce evidence that sub-0.73 μs pulses with the claimed thin stacks produced unexpectedly stable ejection (the "stable velocity" limitation of claims 1 and 10), the ground weakens. No such evidence appears in the specification, however, and the claimed range reads like a design point, not a critical boundary.
2. The 2.9–4.0 GJ/m³ window with the claim-defined volume metric (resistor area × [resistor + protective-layer thicknesses]) appears in no reference. The metric itself is an unusual accounting convention (counting the protective layer in the energy-density denominator). A challenger must argue the metric is arbitrary and that the physical requirement — enough energy to superheat a thin stack + adjacent ink to nucleate a bubble — is what the window actually describes. The numbers check out against 6,491,377's ≤ 1.4 μJ only if one assumes representative heater geometry (my estimate: ~700 μm², ~6000 Å stack → ≈ 3.3 GJ/m³), which is consistent with, but not expressly disclosed in, the reference. A rigorous case would need expert testimony linking 6,491,377's operating energy to the claim's volume metric.
3. 6,142,612 can be characterized as teaching away. Its optimized Ta layer is ~9000 Å — a thicker protective layer than the '246's 7200 Å ceiling, chosen for cavitation lifetime. A patent owner will argue the art's own Lexmark reference pointed away from the claimed thin stacks. The answer is that 6,491,377 and 6,331,049 point toward thin stacks for low-energy operation, so the combination supplies the direction 6,142,612 lacks; and 6,142,612 is used for its mechanism (thickness ↔ pulse width), not its thickness value. Under KSR, a reference need not be the "best" embodiment to contribute a teaching, and a PHOSITA is not barred from combining a thinner-stack teaching with a reference that explains the underlying tradeoff.
4. Functional-claim-format risk. Because claims 1, 8, 9, and 10 are drafted substantially in functional terms ("operable at," "pulse time of," "energy … ranges from"), the obviousness case converges on whether the claimed operating window is an "intended use" or "result-effective variable" optimization. That is favorable to the challenger where, as here, the specification admits the controlling variable (stack thickness) and supplies no criticality data.
5. No secondary considerations in the record. There is no evidence of long-felt need, industry copying, commercial success, licensing, or unexpected results tied to the claimed ranges. The patent expired in 2022 and was asserted only through the settled HP wave and by an NPE — none of which supplies objective indicia of non-obviousness.

IX. Bottom line

Claims 1, 8, 9, and 10 of US 6,676,246 present a colorable-to-strong § 103 case under the Graham/KSR framework, with the strongest ground being:

US 6,491,377 (thin passivation < 5000 Å; dense, low-energy, ≤ 1.4 μJ heaters) in view of US 6,142,612 (expressly teaching that protective-layer thickness controls pulse width/power density) and US 6,331,049 (expressly teaching selective thinning of passivation over the heater element to cut TOE, quantified down to 0.2 μm), optionally with US 6,139,131 / US 5,726,690 for the pulse-width-as-design-variable and firing-frequency context.

The claimed protective-layer ceiling (< 7200 Å) is expressly satisfied (indeed exceeded in the thinning direction) by 6,491,377 and 6,331,049; the pulse-time and energy-density limitations are functional consequences of the known thin-stack/low-energy design point, with the patentee's own specification conceding that pulse time is a function of stack thickness and independent of area and ink. The dependent claims add only conventional materials and dimensions that pervade the cited art.

The genuine litigation risk for a challenger is concentrated in two places: (i) proving that a PHOSITA would have arrived at the specific < 0.73 μs pulse time and the 2.9–4.0 GJ/m³ window (on the claim's unusual volume metric) with a reasonable expectation of success — which will turn on expert testimony and the absence of any criticality data in the '246 specification; and (ii) overcoming the "teaching away" argument built on 6,142,612's ~9000 Å Ta optimum — which is best answered by using 6,142,612 only for its mechanism and relying on 6,491,377/6,331,049 for the thin-stack direction. The parallel PTAB/CAFC record invalidating the related Slingshot heater-chip patents as obvious (No. 24-1956, decided Apr. 23, 2026; companion affirmances July 16, 2026) is a meaningful signal that claims of this type, from this portfolio, in this art, do not typically survive § 103 scrutiny. Because no IPR was ever instituted on 6,676,246, a defendant may raise this § 103 case on any references in district court under § 282(b) with no § 315(e)(2) estoppel, limited to the pre-Dec. 27, 2022 damages window given the patent's expiration.