US 6213587

US Patent 6,213,587 — Search Results Summary

Caveat on sources

My direct USPTO-database query returned no results from the tool, and I found no CAFC 2026 docket in which U.S. Patent 6,213,587 is itself the patent-in-suit or the challenged patent. The 2026 CAFC Slingshot Printing LLC v. Canon U.S.A., Inc. appeals identified in my searches concern other Slingshot-owned patents (e.g., 7,195,341; 7,290,864; 7,484,823; 7,594,708). In one of those PTAB/CAFC matters, a reference identified as "Whitman" (which may be this patent, whose inventor is Charles S. Whitman) was cited as prior art against a different Slingshot patent — not as the patent being litigated. The bibliographic data below is drawn from the Google Patents record (authoritative text supplied in the request) and corroborating secondary sources; the assignment chain and litigation flags on that record are machine-generated and should be treated as non-authoritative.

Bibliographic data

• Patent number: US6213587B1
• Title: Ink jet printhead having improved reliability
• Inventor: Charles S. Whitman (Lexington, KY, US)
• Original assignee: Lexmark International Inc.
• Later assignees (recorded): Funai Electric Co., Ltd. (2013-05-14) → Slingshot Printing LLC (2019-03-29); Google Patents lists "Current Assignee" as Slingshot Printing LLC
• Application: US 09/356,573
• Filing date: July 19, 1999
• Issue date: April 10, 2001
• Status: Expired – Lifetime (anticipated expiration July 19, 2019, i.e., 20 years from filing)
• Examiner / firm (per freepatentsonline): Juanita Dionne Jackson; Goldberg Segalla LLP
• Classification: Class 347/47; also classified under B41J2/14, B41J2/14016, B41J2/14032, B41J2/1404, B41J2/14088, B41J2/14112, B41J2/14129, B41J2002/14387, B41J2202/03

Abstract

"The present invention relates to an inkjet printhead with improved reliability. The printhead comprises a transducer, a chamber, and a plate. At least a portion of the transducer is arranged within the chamber, and the plate is provided with at least one aperture capable of cooperating with the chamber to allow ink to be ejected therefrom. The plate has a thickness of less than 62 microns and the transducer can be selectively energized with a power density less than 2.159 GW/m² to cause droplets of the ink to be ejected. In one embodiment, the plate is separated from the transducer by a distance of less than 28 microns."

Technical essence (plain language)

The invention improves the lifetime/reliability of thermal inkjet printheads (whose failure mode is typically heater-resistor burnout) by simultaneously reducing three parameters relative to Lexmark's nominal production values: (1) the nozzle plate thickness (nominal ~62 microns), (2) the power density at which the heater resistors are fired (nominal ~2.159 GW/m²), and (3) preferably the barrier height / nozzle-plate-to-heater separation (nominal ~28–30 microns). The specification's empirical model shows that combining a thinner plate (down to ~40–51 microns, with practical limits near 35 microns) with lower firing power density (e.g., ~0.7–1.5 GW/m², practical floor ~0.7 GW/m²) multiplies predicted median-time-to-failure (MTTF). Ink chemistry also matters: phosphate-containing color inks favor smaller heater areas (< ~2,800 µm², e.g., ~1,850 µm²), while mono inks and non-phosphate multi-color inks favor larger heater areas (> ~1,900 µm², e.g., ~2,900 µm²).

Independent claims in plain language (34 claims total; independents are 1, 29, 31, and 33)

• Claim 1 (apparatus — printhead): An inkjet printhead having (a) a transducer at least partially inside an ink chamber, and (b) a plate with at least one aperture that works with the chamber to eject ink — where the plate is thinner than 62 microns and the transducer can be selectively energized at a power density below 2.159 GW/m² to eject ink droplets.

• Claim 29 (apparatus — multi-nozzle printhead): The same core idea scaled to an array: multiple transducers, each at least partly in its own respective chamber, under a plate having multiple apertures, each aperture cooperating with a respective chamber — where the plate is thinner than 62 microns and each transducer can be energized at a power density below 2.159 GW/m².

• Claim 31 (system — printer): An inkjet printer combining (a) a printhead with a transducer in a chamber and a plate having at least one aperture of thickness less than 62 microns, and (b) a power source capable of selectively energizing the transducer at a power density below 2.159 GW/m² to eject ink from the chamber.

• Claim 33 (method — improving printhead life): A method of increasing the life of an inkjet printhead having a transducer that heats an ink droplet, comprising: (a) arranging at least part of the transducer inside a chamber; (b) providing a plate with at least one aperture cooperating with the chamber, the plate being thinner than 62 microns; and (c) selectively energizing the transducer at a power density below 2.159 GW/m² to eject ink droplets. (Claim 34 adds the optional step of separating the plate from the transducer by less than 28 microns.)

Notable limitations in the data

• I could not confirm any CAFC 2026 docket number specifically for patent 6,213,587; the 2026 CAFC Slingshot v. Canon line concerns other patents in the same family/portfolio. Google Patents does show district-court litigation flags for this patent (Texas Western District Court cases 6:19-cv-00549, 6:19-cv-00363, 1:20-cv-00185), but I did not verify their current status or whether 6,213,587 was an asserted patent in them.
• Because the patent has expired (lapsed after July 19, 2019), any enforcement would be limited to pre-expiration conduct.
• If you need a definitive answer on whether 6,213,587 appears in any USPTO PAIR/assignment record or CAFC docket for 2026, that would require a direct query of the USPTO Patent Center/assignment database and the CAFC docket system, which were not reachable in this session.

Based on my searches, US Patent 6,213,587 ("Ink jet printhead having improved reliability," Whitman; assigned Lexmark → Funai → Slingshot Printing LLC) has been asserted in a series of patent-infringement litigations brought by Slingshot Printing LLC. Below is what I could confirm, followed by items I could not fully verify.

Confirmed district-court litigation involving the '587 patent

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

• Plaintiff: Slingshot Printing LLC
• Defendant: HP Inc.
• Court/Jurisdiction: U.S. District Court, Western District of Texas, Waco Division (Judge Alan D. Albright)
• Case No.: 6:19-cv-00549-ADA
• Filing date: September 20, 2019 (complaint; docket no. 1)
• Patents: The complaint asserts ten patents including 6,213,587 (plus 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/procedural history: Transferred to the Austin Division (by order dated Feb. 19, 2020), where it proceeded as 1:20-cv-00187-ADA. HP also filed inter partes reviews on related Slingshot patents (e.g., IPR2020-01659), and at least one of those IPRs was terminated on March 29, 2021 following a joint request to terminate (settlement-related). I did not obtain a definitive final judgment/termination order for the district-court case itself.
• 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) ; PTAB exhibit (PTACTS) showing transfer to 1:20-CV-187-ADA on 2/19/2020 with the '587 patent listed.

2. Slingshot Printing LLC v. HP Inc. — No. 6:19-cv-00363-ADA (W.D. Tex., Waco Div.)

• Plaintiff: Slingshot Printing LLC
• Defendant: HP Inc.
• Court/Jurisdiction: U.S. District Court, Western District of Texas, Waco Division
• Case No.: 6:19-cv-00363-ADA (per the litigation metadata on the patent's Google Patents page)
• Filing date: ~June 11, 2019 (the successor Austin docket, 1:20-cv-00184-ADA, shows an "initial civil docket" date of 06/11/2019)
• Status: The Unified Patents docket for the successor Austin case (1:20-cv-00184-ADA, Slingshot v. HP Inc.) shows a "Final Civil Docket" date of 04/01/2021, indicating termination around that time. I could not confirm the exact disposition (settlement vs. judgment) from the search results.
• Caveat: My identification of 6:19-cv-00363 as the Waco predecessor of 1:20-cv-00184 is an inference from the Google Patents litigation list and the matching filing date/parties on the Unified Patents docket; I could not pull the original Waco docket directly in this session.
• Sources: https://portal.unifiedpatents.com/litigation/Texas%20Western%20District%20Court/case/1:20-cv-00184 ; Google Patents litigation metadata for US6213587.

Litigation listed for the '587 patent but not fully verified

3. Case No. 1:20-cv-00185 (W.D. Tex.)

• The Google Patents page for the '587 patent lists a third U.S. district-court matter: 1:20-cv-00185 in the Western District of Texas (per Unified Patents litigation data embedded on the patent page). I was unable, within my search limits, to confirm the parties, exact filing date, or status of this case. Do not rely on this as confirmed without further docket verification.

Related proceedings to be aware of (not confirmed to name the '587 patent directly)

• Slingshot Printing LLC v. Canon U.S.A., Inc., Fed. Cir. No. 24-2127 (opinion dated July 21, 2026): CAFC appeal of a PTAB IPR decision involving a Slingshot printhead patent (references prior art "Imanaka/Hamafuku/Whitman," indicating a Whitman printhead patent in the same family), but the reported decision concerns a different patent number and I cannot confirm the '587 patent was the one at issue. https://law.justia.com/cases/federal/appellate-courts/cafc/24-2127/24-2127-2026-07-21.html
• Various HP- and Canon-initiated IPRs against Slingshot printhead patents (e.g., IPR2020-01084/01085/01086/01090 and IPR2020-01659) cite the '587-family litigation; those IPRs generally target other patents in the portfolio (e.g., 7,014,299; 7,195,341), not necessarily the '587 patent itself.

Bottom line

The '587 patent has been asserted in at least two confirmed W.D. Tex. actions by Slingshot Printing LLC against HP Inc. (6:19-cv-00549-ADA, filed 9/20/2019, transferred to 1:20-cv-00187-ADA; and 6:19-cv-00363-ADA, filed ~6/11/2019, transferred to 1:20-cv-00184-ADA), with the latter terminating around April 2021. A third listed case (1:20-cv-00185) and the precise final outcomes (settlement vs. judgment) could not be verified in this session. For the most current status, check PACER/Unified Patents directly for each case number.

Proceedings overview

Zero AIA trial proceedings (IPR/PGR/CBM) are on file for US 6,213,587. The USPTO Open Data Portal block in this prompt is authoritative: it lists no AIA trials for the patent, and independent web searching likewise surfaced no petition, institution decision, Final Written Decision, settlement, or Federal Circuit appeal directed at the '587 patent itself. The patent expired by operation of law on 2019-07-19 (20 years from the 1999-07-19 filing date; status on record: "Expired - Lifetime"). Bottom line for a defendant: there is no PTAB estoppel of any kind binding on any would-be challenger, and — more importantly — the patent is expired, so any assertion can only reach damages for alleged pre-2019-07-19 conduct; no injunction or post-expiration royalty is available.

Because the count is zero, the per-proceeding template below has no entries. What follows instead flags the closely-adjacent PTAB and litigation activity that frequently gets mistaken for a "challenge to the '587," and the strategic read from that adjacency.

Direct proceedings against US 6,213,587

None. No IPR, PGR, or CBM petition has been filed against the '587 patent, no institution decision exists, no Final Written Decision exists, and no party has been estopped under 35 U.S.C. § 315(e) with respect to this patent. I could not find any proceeding number to report, and I have not invented one.

Adjacent activity that is not a trial on the '587 (be careful not to conflate)

• HP Inc. v. Slingshot Printing LLC, IPR2020-01084, -01085, -01086, -01090 — HP filed a cluster of IPRs against Slingshot's inkjet patents after Slingshot sued HP in the Western District of Texas (e.g., Case 6:19-cv-00549, filed 2019-09-20; and the ADA complaint, No. 1:20-cv-00187, which asserts the '587 among ten patents). Public records confirm IPR2020-01086 is directed to U.S. Patent 7,014,299 (DocketAlarm: "Inter Partes Review of U.S. Pat. 7014299"), not the '587. None of the four HP IPRs has been shown to challenge the '587.
• Canon U.S.A., Inc. / Canon Inc. v. Slingshot Printing LLC, IPR2022-01541 (U.S. Patent 7,152,951) — Canon's petition and expert declaration cite the '587 (Whitman) as prior art against later Slingshot patents. The Board found claims 1–4, 6, 7, 9, 10, 20–22, and 24 unpatentable over Hamafuku + Imanaka + Whitman, and claim 5 over that combination plus Cleland. Slingshot appealed to the Federal Circuit (Slingshot Printing LLC v. Canon U.S.A., Inc., No. 24-2127), and the Federal Circuit affirmed on 2026-07-21 (nonprecedential; see Justia/CAFC). This is a validity loss for a different Slingshot patent and only shows the '587 being used against Slingshot as art — it does not touch the '587's own claims.
• Related CAFC activity, July 2026 — Law360 reported (2026-07-16) that the Federal Circuit upheld PTAB decisions invalidating claims in three other Slingshot patents (chips/temperature sensors in inkjet printheads) challenged by Canon. Again, these concern sibling patents, not the '587.

No proceeding number, panel, FWD, or settlement exists to report for the '587 because no trial was ever instituted on it.

Strategic summary

Claim-level status of US 6,213,587: All 34 claims (claims 1–34) remain exactly as issued — none canceled, none amended, none even challenged at the PTAB. Independent claims 1, 29, 31, and 33 (printhead, multi-transducer printhead, printer, and method claims) are entirely untested in AIA trials, as are all dependent claims. Because the ODP lists no proceeding, there is also no claim-construction ruling, no § 112 analysis, and no § 102/§ 103 merits decision by the Board on this patent. The only "narrowing" event in the file history is the terminal expiration on 2019-07-19.

Estoppel landscape: § 315(e)(2) estoppel is a non-factor here — estoppel attaches to a petitioner and its privies from a completed IPR, and there has been no IPR on the '587. No defendant or potential petitioner is estopped from raising any ground of unpatentability against this patent in district court. For a defendant currently facing assertion, every available prior-art ground under § 102 and § 103 — including art applied against sibling Slingshot patents (e.g., the Whitman-citing Canon combinations) and any art that a diligent search would surface — remains fully available. Note the important asymmetry: the '587 (Whitman) is strong enough prior art to have helped Canon invalidate other Slingshot patents, which cuts against its own inventiveness being robust.

Pattern signals: There is no serial IPR petitioner against this patent, and no defensive-aggregator IPR (e.g., Unified Patents) in the chain — the only defensive-aggregator footprint in the file is Unified Patents' litigation data appearing on the Google Patents page. The patent owner chain is: Lexmark (original) → Funai Electric (2013) → Slingshot Printing LLC (2019). Slingshot has litigated aggressively (three Texas WD cases on the family per the Unified Patents litigation data: 6:19-cv-00363, 6:19-cv-00549, 1:20-cv-00185) and has appealed PTAB losses on sibling patents to the Federal Circuit (e.g., No. 24-2127, affirmed 2026-07-21). The notable absence of any IPR on the '587 is best explained by timing and expiration, not by strength: the '587 died on 2019-07-19, and most of Slingshot's enforcement began around that date — a petitioner filing in 2020+ would gain no injunction relief and only narrow pre-expiration damages exposure, gutting the economic rationale for an IPR.

Recommended next steps

• Lead with expiration. The single most powerful defensive fact is that US 6,213,587 expired on 2019-07-19 (status: "Expired - Lifetime"). Any demand letter or complaint that seeks ongoing royalties or an injunction against current products has no statutory basis; relief is capped at proven damages for infringing acts before 2019-07-19 (subject to the 35 U.S.C. § 286 six-year look-back and laches-type defenses).
• Because there is no FWD to cite, there is no PTAB disposition to link. If the other side points you to "Slingshot lost at the PTAB" as leverage, correct the record: the PTAB/CAFC losses (e.g., IPR2022-01541; CAFC No. 24-2127, affirmed 2026-07-21) were against other Slingshot patents (7,152,951 and siblings) — and in those very cases the '587 (Whitman) was the prior art used to invalidate them. That is a powerful impeachment exhibit for your own validity defenses, not a strike against the '587.
• No PTAB deadlines apply — there are no active proceedings, no institution-decision deadline, no oral-hearing date, and no FWD due date. If you are sued on the '587, your validity attack belongs in district court under the clear-and-convincing standard (not the PTAB's preponderance standard), and you face no § 315(e) estoppel and no § 315(b) one-year bar because no IPR was ever filed.
• If you want the '587 invalidated as a matter of record (e.g., to clear a co-pending infringement case on a sibling patent or for defensive publication value), note that the PTAB generally will not institute AIA review of an expired patent absent a live controversy over pre-expiration damages; the practical forum is the district court. Confirm the litigation posture in the Texas WD cases (6:19-cv-00363, 6:19-cv-00549, 1:20-cv-00185) before assuming any exposure remains.

Caveat on sourcing: The "no proceedings" finding rests on the USPTO ODP data supplied in this prompt plus the web searches performed today. The ODP ingest can lag, and my searches did not exhaustively page through every PTAB petition database; if you need absolute certainty before a filing deadline, run a direct PTAB E2E search (e.g., https://ptab.uspto.gov and the PTAB API) for patent number 6,213,587 and confirm the expiration/term dates in USPTO Patent Center.

Key sources consulted: Google Patents US6213587B1 (litigation/assignment/status data, https://patents.google.com/patent/US6213587/en); DocketAlarm PTAB docket for IPR2020-01086 (7,014,299) and Canon IPR2022-01541 exhibits (https://www.docketalarm.com/cases/PTAB/IPR2020-01086/; https://www.docketalarm.com/cases/PTAB/IPR2022-01541/); Justia CAFC — Slingshot Printing LLC v. Canon U.S.A., Inc., No. 24-2127, decided 2026-07-21 (https://law.justia.com/cases/federal/appellate-courts/cafc/24-2127/24-2127-2026-07-21.html); The Recycler report on Slingshot v. HP (June 2019) listing the '587 among patents-in-suit.

I'll research the recorded assignment chain for US 6213587, starting with the USPTO assignment records and cross-referencing public data.

The RPX article confirms the Lexmark → Funai → Slingshot Printing chain. Now let me find the specific reel/frame records and litigation details.

I have litigation context. Now I need the specific USPTO reel/frame records and correspondent details for each assignment.

I hit the tool-call limit before I could pull the reel/frame-level USPTO records, so I want to be transparent up front: the assignment dates and parties below come from Google Patents' legal-event feed and secondary sources (RPX, Unified Patents, court dockets) that I could verify; I could not retrieve the reel/frame numbers or correspondent-of-record entries from the USPTO Assignment Center in this session, and I will not fabricate them. Each entry flags exactly what is verified and what still needs a USPTO Assignment Center pull.

Inventors

• Charles S. Whitman — sole named inventor. Employer at filing: Lexmark International, Inc. (Lexington, KY). The prosecution correspondence address of record was Lexmark's Intellectual Property Law Department, 740 West New Circle Road, Lexington, KY (visible in related PTACTS records for sibling Lexmark patents). No unusual pattern: single inventor, no evidence of mass departure before the 2013 portfolio divestiture (which happened 14 years post-filing, driven by corporate strategy rather than inventor churn).

Original assignee

• Lexmark International, Inc. — named assignee on the issued patent (original assignment recorded at filing, 1999-07-19). Lexmark was a major inkjet printer/printhead OEM and shipped products embodying the claimed reliability improvements (thin nozzle plate + reduced drive-power regime for thermal inkjet heads). Primary line of business: printing hardware, ink, and imaging supplies. Current status: operating, but out of inkjet — Lexmark sold its entire inkjet technology/patent portfolio (~1,500 US and foreign assets) to Funai Electric Co., Ltd. in 2013 for roughly $100M (per RPX), and Lexmark itself was taken private in 2016 by an Apex Technology/PAG-led consortium. No bankruptcy.

Assignment timeline

Three recorded ownership events exist (two post-issuance). No reel/frame numbers are given because I could not verify them this session — search the USPTO Assignment Center (patent number 6213587) to confirm reel/frame and correspondent for each entry below.

• 1999-07-19 (executed and recorded contemporaneously with filing — Google Patents legal event; reel/frame not verified this session)

  • Conveyance: Assignment of Assignors' Interest (original)
  • Assignor: Charles S. Whitman (inventor)
  • Assignee: Lexmark International, Inc.
  • Correspondent: Lexmark International, Inc. Intellectual Property Law Department, 740 West New Circle Road, Lexington, KY (prosecution address of record; the recorded-assignment correspondent is not separately verified)
  • Context: Standard employment-era invention assignment into the operating company.

• 2013-05-14 (recorded — Google Patents legal event "Assigned to FUNAI ELECTRIC CO., LTD"; reel/frame not verified this session)

  • Conveyance: Assignment (portfolio-wide; reported ~1,500 US + foreign assets)
  • Assignor: Lexmark International, Inc. and Lexmark International Technology, S.A.
  • Assignee: Funai Electric Co., Ltd.
  • Correspondent: Not verified this session. (For sibling Lexmark patents later held by Funai, the USPTO power-of-attorney record switched to Amster, Rothstein & Ebenstein LLP, New York, filed 2014-07-10 — that is a POA record, not the assignment correspondent.)
  • Context: $100M arm's-length divestiture of Lexmark's inkjet business to Funai — an operating-company portfolio sale, not a bankruptcy fire-sale (Lexmark was solvent).

• 2019-03-29 (recorded — Google Patents legal event "Assigned to SLINGSHOT PRINTING LLC"; reel/frame not verified this session)

  • Conveyance: Assignment
  • Assignor: Funai Electric Co., Ltd.
  • Assignee: Slingshot Printing LLC (Delaware LLC; address per court filings: 8455 Colesville Road, Suite 830, Silver Spring, MD 20910)
  • Correspondent: Not verified this session. Note: FreePatentsOnline's current agent-of-record snapshot lists Goldberg Segalla LLP (New York, NY) for this patent; that is a secondary-source snapshot I could not independently confirm against the Assignment Center record. Litigation counsel for Slingshot in the W.D. Tex. suits is Daignault Iyer LLP (Ronald M. Daignault, Chandran B. Iyer, Richard Juang) with Raymond W. Mort III as local counsel.
  • Context: Transfer of 100+ Funai-held former-Lexmark US assets to a newly formed licensing LLC, immediately followed by NPE assertion against HP and Canon.

Timeline diagram

timeline
    title Ownership of US 6213587
    1999 : Filed by Lexmark
         : Patent issued
    2013 : Portfolio sold to Funai Electric
    2019 : Transferred to Slingshot Printing
         : Slingshot sues HP in W D Tex

NPE / troll-pattern signals

1. Shell-entity transfer — Present. Funai (an operating consumer-electronics/printer company) transferred this patent to Slingshot Printing LLC, a Delaware LLC formed to hold and assert patents, with no products in commerce. Its pleaded address (8455 Colesville Road, Suite 830, Silver Spring, MD) is a registered/serviced-office address, and RPX contemporaneously characterized Slingshot as a "recently formed NPE" (RPX insight, June 12, 2019). Transfer recorded 2019-03-29 (Google Patents legal event). This is more than naming inference — RPX and the subsequent litigation pattern supply the conduct evidence.

2. Known asserter in the chain — Present. Slingshot Printing LLC appears on RPX's NPE coverage and in Unified Patents' litigation directory. This patent was asserted in at least three W.D. Tex. cases flagged on the Google Patents family record: 6:19-cv-00549, 6:19-cv-00363, and 1:20-cv-00185 (all Slingshot Printing LLC v. HP Inc. / related), plus sibling cases 1:20-cv-00184 and 1:20-cv-00187 and a Canon matter. US 6,213,587 is expressly listed among the patents-in-suit in the Slingshot v. HP complaints (e.g., The Recycler, June 2019; complaint exhibit in IPR2020-01086).

3. Repeat correspondent across the chain — Unclear. I could not verify the correspondent of record on the 2013 and 2019 assignment recordings this session, so I cannot make the recurrence finding the prompt asks for. What is verifiable: the same litigation team (Daignault Iyer LLP attorneys Daignault, Iyer, Juang, Siem, Charkow) appears across the multiple Slingshot v. HP cases — but that is litigation counsel, not the assignment correspondent. Recommend pulling the reel/frame records at the USPTO Assignment Center to test recurrence (e.g., whether Goldberg Segalla or another single firm filed both Funai-era and Slingshot-era recordings).

4. Cascading transfers — Not present. Only two post-issuance transfers, six years apart (2013, 2019), through a clean operating-company chain (Lexmark → Funai → Slingshot). No chained-LLC ladder within 24 months.

5. Pre-litigation transfer — Present. Funai → Slingshot recorded 2019-03-29; the first Slingshot infringement complaints against HP were filed June 11, 2019 (The Recycler; RPX article dated June 12, 2019). That is roughly 10–11 weeks — well inside the 6-month window — indicating the transfer was arranged to enable assertion.

6. Bankruptcy fire-sale — Not present. Lexmark was solvent; the 2013 Funai transfer was a negotiated ~$100M divestiture of the inkjet line. Lexmark's later 2016 take-private was not a bankruptcy.

7. Privateering — Present (strongly indicated). RPX reported that "assignment records suggest that Funai might hold an economic interest in Slingshot's litigation" (RPX, June 12, 2019). Consistent with that, the W.D. Tex. court granted HP's motion to compel production of "any agreements between Slingshot Printing LLC (and any affiliates) and Funai Electric Co., Ltd. (and any affiliates)" (Docket, 6:19-cv-00549 et seq.). The pattern — Funai transfers patents to a shell, which sues HP (a direct competitor in printers/consumables) — is textbook privateering, with Funai plausibly funding/backstopping the suits.

8. Defensive aggregator (anti-NPE) — Not present. The chain terminates at Slingshot Printing LLC, an asserting NPE; no RPX/AST/LOT/Unified/OIN acquisition.

Verdict

NPE — high confidence.

The record shows an operating company (Funai) transferring this former-Lexmark patent to a newly formed, product-less Delaware LLC (Slingshot Printing LLC) in March 2019, followed within ~11 weeks by multiple W.D. Tex. infringement suits against HP (June 2019) — the exact shape of a transfer-to-asserter. RPX identifies Slingshot as an NPE and reports assignment records suggesting Funai retained an economic interest in the litigation, which is a privateering signal. The only gap is reel/frame-level confirmation of the assignment recordings and their correspondents, which I could not retrieve in this session; the parties, dates, litigation, and NPE characterization are corroborated by Google Patents legal events, RPX, Unified Patents, and court dockets.

Verify the underlying recordings at the USPTO Assignment Center: https://assignmentcenter.uspto.gov/ (search patent number 6213587).

I'll verify the key cited references individually, focusing on the closest ones, and confirm the front-page citation list.

I have the authoritative front-page list of 29 U.S. patent references cited on US 6,213,587 (confirmed against the patent PDF, freepatentsonline, and the PTAB IPR2022-01541 exhibit). Let me verify a few of the most substantive references (the HP "Keefe" architecture patents and the Canon references) before finalizing.

Prior-Art Analysis — U.S. Patent 6,213,587 B1 ("Ink jet printhead having improved reliability")

Scope note on what I verified

I confirmed the exact front-page "References Cited" list from the issued patent image (29 U.S. patents) via freepatentsonline's mirror of the patent, cross-checked against the Google Patents record and the PTAB exhibit copy of the patent (IPR2022-01541, Ex. 1005). I searched the USPTO-linked databases but, as before, they were not directly reachable; the freepatentsonline front-page list matches the patent PDF and is treated as ground truth for the citation set. All 29 references below are those printed on the face of US 6,213,587 B1. None of the references is US 6,213,587 itself (i.e., no self-citation), and none of the numbers has been "corrected."

Governing law framing (pre-AIA § 102)

US 6,213,587 was filed July 19, 1999 and issued April 10, 2001, so it is governed by pre-AIA 35 U.S.C. § 102. A cited reference "potentially anticipates" a claim only if the single reference discloses every claim limitation, arranged as in the claim (pre-AIA § 102(a)/(b)/(e)). The two limitations that dominate the independent claims (1, 29, 31, 33) are the plate thickness of less than 62 microns and the power density of less than 2.159 GW/m²; dependent claims add plate-to-transducer separation (< 28 µm, 8–27 µm, ~24 µm), heater areas (< 2,800 / > 1,900 / ~2,900 µm²), and ink chemistry (mono; non-phosphate multi-color; phosphate-containing).

Key honest caveat: Based on the public records available to me, no single cited reference appears to expressly disclose both of the two numerical limitations (a sub-62-micron plate and firing at power density < 2.159 GW/m²). The figure 2.159 GW/m² is an unusually precise value tied to Lexmark's nominal firing condition, and I found no cited reference that quantifies firing power density in those terms. Accordingly, in the per-reference notes below, "potentially anticipates" is used to mean "the reference discloses the structural claim elements and is the type of single reference that could form the basis of a § 102 rejection if the numeric plate-thickness/power-density limitations were shown to be present or inherent." For the numerical combination, the cited art is realistically § 103 combination material, not clean § 102 material — consistent with the fact that the examiner allowed the claims over this exact citation set.

One procedural flag: reference US 6,045,214 issued April 4, 2000 — after the July 19, 1999 filing of 6,213,587 — but because its underlying application (08/827,241) was filed March 28, 1997, it is available as § 102(e) prior art against 6,213,587. All other 28 references issued before July 19, 1999 and are classic § 102(a)/(b) art.

Group A — Closest prior art (thermal inkjet printhead architecture: heater-in-chamber + barrier + orifice/nozzle plate, with dimensions)

These disclose the basic structure recited in claim elements 1(a)/(b), 29(a)/(b), 31(a), and the apparatus steps of claim 33, and several quantify barrier/chamber dimensions. They are the references an anticipation case would have to build on for the structural side of the claims.

1. US 6,045,214 A (Murthy, Komplin, Powers; Lexmark) — "Ink jet printer nozzle plate having improved flow feature design and method of making nozzle plates"

• Filed: Mar. 28, 1997 (US 08/827,241) | Issued: Apr. 4, 2000 | Class 347/47
• Description: Polymeric (e.g., polyimide) nozzle plates in which firing chambers, ink supply channels, nozzle holes, and debris-trapping projections are ablated into the plate itself; discloses nozzle-plate thicknesses of about 15–200 microns, preferably 25–125 microns — ranges that overlap and extend below 62 microns — and heater substrates underlying the plate.
• Claims potentially anticipated: Element-level support for claim 1(b) and the "plate … thickness of less than 62 microns" limitation (its disclosed ranges include sub-62-micron plates); claim 7–9 (sub-60 / 35–55 / ~40-micron thickness) to the extent the disclosed ranges are shown to cover those values. Does not disclose the < 2.159 GW/m² power-density limitation, so not a complete § 102 anticipation of claims 1, 29, 31, or 33.

2. US 5,563,642 A (Keefe, Ho, Courian, Steinfield, Childers, et al.; Hewlett-Packard) — "Inkjet printhead architecture for high speed ink firing chamber refill"

• Filed: Apr. 2, 1992 (continuation-in-part chain; parent US 5,278,584) | Issued: Oct. 8, 1996 | Class 347/84
• Description: Substrate with ink firing elements in individual firing chambers; barrier layer defining channels and separate inlet passages for refill; nozzle member with orifices overlying the chambers. Discloses a barrier-layer thickness of approximately 19–32 microns — i.e., a chamber-height/separation range that overlaps the claimed "less than 28 microns" and "about 8 to about 27 microns" (claims 2–3).
• Claims potentially anticipated: Structure of claims 1, 29, 31, 33 elements; the barrier/separation dimension of claims 2–3. No teaching of < 62-micron plate thickness or < 2.159 GW/m² power density found.

3. US 5,648,805 A (Keefe et al.; Hewlett-Packard) — "Inkjet printhead architecture for high speed and high resolution printing"

• Filed: Apr. 2, 1992 (CIP filed Oct. 6, 1994) | Issued: Jul. 15, 1997 | Class 347/65
• Description: Barrier layer containing ink channels and firing chambers between a rectangular substrate (two spaced arrays of ink ejection elements) and a nozzle member with an array of orifices; each orifice associated with a firing chamber and ejection element; firing frequencies up to 12 kHz; ≥ 600 dpi.
• Claims potentially anticipated: Elements of claims 1, 29 (plurality of transducers/chambers/apertures), 31, 33. Same numeric-limitation gap as above.

4. US 5,604,519 A (Keefe et al.; Hewlett-Packard) — "Inkjet printhead architecture for high frequency operation"

• Filed: Apr. 2, 1992 (CIP filed Oct. 6, 1994) | Issued: Feb. 18, 1997 | Class 347/13
• Description: Firing chambers with firing elements, separate per-chamber inlet passages for high-frequency refill, "primitive" firing groups (one element fired at a time), firing signals > 8–12 kHz, and on-substrate drive circuitry.
• Claims potentially anticipated: The "selectively energized … to cause droplets … ejected" and power-source aspects of claims 31/33 at a functional level (energizing firing elements), and claim 29's array structure. No power-density numeric.

5. US 5,638,101 A (Keefe et al.; Hewlett-Packard) — "High density nozzle array for inkjet printhead"

• Filed: Apr. 2, 1992 | Issued: Jun. 10, 1997 | Class 347/65
• Description: Densely packed nozzle arrays/orifice plates with associated firing chambers and heating elements for high resolution.
• Claims potentially anticipated: Claim 29's plurality-of-apertures arrangement and claims 1/31/33 structure. Numeric limitations not shown.

6. US 5,619,236 A (Keefe et al.; Hewlett-Packard) — "Self-cooling printhead structure for inkjet printer with high density high frequency firing chambers"

• Filed: Apr. 2, 1992 | Issued: Apr. 8, 1997 | Class 347/84
• Description: High-density, high-frequency firing-chamber architecture with thermal-management (self-cooling) structure.
• Claims potentially anticipated: Structural elements of claims 1, 29, 31, 33; no power-density/plate-thickness numerics.

7. US 5,594,481 A (Keefe et al.; Hewlett-Packard) — "Ink channel structure for inkjet printhead"

• Filed: Apr. 2, 1992 | Issued: Jan. 14, 1997 | Class 347/65
• Description: Barrier-layer ink channel structure feeding firing chambers in an inkjet printhead.
• Claims potentially anticipated: Chamber/channel/plate structure of claims 1, 29, 31, 33. Numeric limitations not shown.

8. US 5,719,605 A (Anderson, Cook, Cramer; Lexmark) — "Large array heater chips for thermal ink jet printheads"

• Filed: Nov. 20, 1996 | Issued: Feb. 17, 1998 | Class 347/59
• Description: Lexmark's "megachip" — a unitary multi-cell silicon heater chip with multiple banks of heater elements; a layer forming a plurality of ink chambers and at least one overlying nozzle plate with nozzles, each nozzle overlying a chamber containing a heater element; TAB interconnect.
• Claims potentially anticipated: Nearly all structural elements of claim 29 (plurality of transducers, each in a respective chamber, plate with a plurality of apertures) and claims 31/33. Does not address plate thickness < 62 µm or power density < 2.159 GW/m².

9. US 5,182,577 A (Ishinaga et al.; Canon) — "Ink jet recording head having an improved substance arrangement device"

• Filed: Jan. 25, 1990 | Issued: Jan. 26, 1993 | Class 347/58
• Description: Roof-shooter-type inkjet head: substrate with heat-generating elements, liquid paths/chambers formed by a grooved member, and an orifice/plate arrangement.
• Claims potentially anticipated: Structural elements of claims 1, 29, 31, 33. Numeric limitations not shown.

10. US 5,481,287 A (Tachihara; Canon) — "Liquid jet recording head having a plurality of heating elements and liquid jet recording apparatus having the same"

• Filed: Dec. 25, 1986 | Issued: Jan. 2, 1996 | Class 347/62
• Description: Recording head with plural heating elements and liquid paths, addressing heater reliability/life considerations.
• Claims potentially anticipated: Plurality elements of claim 29; heater-in-chamber structure of claim 1/31/33.

11. US 4,638,337 A (Torpey et al.; Xerox) — "Thermal ink jet printhead"

• Filed: Aug. 2, 1985 | Issued: Jan. 20, 1987 | Class 347/65
• Description: Early Xerox thermal inkjet printhead construction with heater elements, barrier-defined channels/chambers, and an orifice plate.
• Claims potentially anticipated: Basic structure of claims 1, 29, 31, 33. No sub-62-micron plate thickness / sub-2.159 GW/m² power-density disclosure found.

12. US 4,870,433 A (Campbell et al.; IBM) — "Thermal drop-on-demand ink jet print head"

• Filed: Jul. 28, 1988 | Issued: Sep. 26, 1989 | Class 347/62
• Description: IBM thermal drop-on-demand head architecture (heater, ink channels, orifice plate).
• Claims potentially anticipated: Structural elements of claims 1/29/31/33 only.

Group B — Heater/resistor composition and life-reliability art (relevant to the transducer/life objective of the claims)

13. US 4,931,813 A (Pan et al.; Hewlett-Packard) — "Ink jet head incorporating a thick unpassivated TaAl resistor"

• Filed: Sep. 21, 1987 | Issued: Jun. 5, 1990 | Class 347/62
• Description: TaAl thin-film resistor design without passivation for inkjet heads — directly relevant to the heater-resistor "transducer" and to the patent's TaAl heater discussion.
• Claims potentially anticipated: The "transducer" limitation of claims 1/29/31/33 at the level of a TaAl heater; nothing on plate thickness or power density.

14. US 4,947,193 A (Deshpande; Xerox) — "Thermal ink jet printhead with improved heating elements"

• Filed: May 1, 1989 | Issued: Aug. 7, 1990 | Class 347/62
• Description: Improved heating-element design/layout in a thermal inkjet printhead.
• Claims potentially anticipated: Transducer/heater elements of claims 1/29/31/33.

15. US 4,951,063 A (Hawkins et al.; Xerox) — "Heating elements for thermal ink jet devices"

• Filed: May 22, 1989 | Issued: Aug. 21, 1990 | Class 347/62
• Description: Heating-element geometry/material for thermal inkjet devices.
• Claims potentially anticipated: Transducer/heater element limitation only.

16. US 5,066,963 A (Kimura et al.; Canon) — "Ink jet head having heat-generating resistor comprised of a complex compound"

• Filed: Apr. 18, 1989 | Issued: Nov. 19, 1991 | Class 347/62
• Description: Heat-generating resistor formed of a complex compound for an inkjet head.
• Claims potentially anticipated: Heater-resistor composition limitation only.

17. US 5,530,467 A (Ishigami et al.; Toshiba) — "Sputtering target, film resistor and thermal printer head"

• Filed: Feb. 1, 1990 | Issued: Jun. 25, 1996 | Class 347/204
• Description: Film-resistor materials/sputtering targets for thermal heads.
• Claims potentially anticipated: Heater-resistor material limitation only.

18. US 5,745,147 A (Johnson et al.; Eastman Kodak) — "Resistance-stable thermal print heads"

• Filed: Jul. 13, 1995 | Issued: Apr. 28, 1998 | Class 347/200
• Description: Designs aimed at resistor resistance stability / lifetime — the same reliability objective as 6,213,587, though in a thermal print-head (non-inkjet) context.
• Claims potentially anticipated: Background for the transducer-life objective; no chamber/plate/power-density combination.

Group C — Nozzle plate, orifice formation, and cartridge-level art

19. US 5,389,954 A (Inaba et al.; Canon) — "Laser process apparatus for forming holes in a workpiece"

• Filed: Nov. 21, 1990 | Issued: Feb. 14, 1995 | Class 347/258
• Description: Laser ablation apparatus for forming nozzle holes — a manufacturing reference.
• Claims potentially anticipated: None of the claimed apparatus/method features directly (manufacturing tool, not a printhead).

20. US 5,148,185 A (Abe et al.; Seiko Epson) — "Ink jet recording apparatus for ejecting droplets of ink through promotion of capillary action"

• Filed: Jun. 10, 1986 | Issued: Sep. 15, 1992 | Class 347/65
• Description: Inkjet head in which capillary action promotes droplet ejection; heater and nozzle arrangement.
• Claims potentially anticipated: Structural elements of claims 1/29/31/33 only.

21. US 4,914,562 A (Abe et al.; Seiko Epson) — "Thermal jet recording apparatus"

• Filed: Jun. 10, 1986 | Issued: Apr. 3, 1990 | Class 347/63
• Description: Companion Epson thermal-jet recording apparatus.
• Claims potentially anticipated: Structural elements only.

22. US 5,818,478 A (Gibson; Lexmark) — "Ink jet nozzle placement correction"

• Filed: Aug. 2, 1996 | Issued: Oct. 6, 1998 | Class 347/45
• Description: Correction of nozzle placement relative to heater position (alignment).
• Claims potentially anticipated: None directly (alignment method; no chamber/plate-thickness/power-density disclosure).

23. US 5,661,510 A (Brandon et al.; Lexmark) — "Ink-jet cartridge venting"

• Filed: Nov. 22, 1994 | Issued: Aug. 26, 1997 | Class 347/87
• Description: Cartridge venting (pressure regulation).
• Claims potentially anticipated: None of the core claim limitations.

24. US 5,751,324 A (Brandon et al.; Lexmark) — "Ink jet cartridge body with vented die cavity"

• Filed: Mar. 14, 1996 | Issued: May 12, 1998 | Class 347/87
• Description: Cartridge body with vented die cavity.
• Claims potentially anticipated: None of the core claim limitations.

Group D — Thermal (non-inkjet) print-head art (cumulative background; relevant to heater structure only)

25. US 4,296,309 A (Shinmi et al.; Canon) — "Thermal head"

• Filed: May 19, 1977 | Issued: Oct. 20, 1981 | Class 347/204
• Description: Early Canon thermal head with heat-generating resistors and protective layers — bubble-jet lineage.
• Claims potentially anticipated: Heater/resistor structure only.

26. US 4,672,392 A (Higeta et al.; Hitachi) — "Thermal head for thermal printer"

• Filed: Nov. 12, 1984 | Issued: Jun. 9, 1987 | Class 347/202
• Description: Thermal print head for a thermal printer.
• Claims potentially anticipated: Heater structure only.

27. US 4,907,015 A (Kaneko et al.; Hitachi) — "Thermal printing head"

• Filed: Aug. 26, 1987 | Issued: Mar. 6, 1990 | Class 347/204
• Description: Thermal printing head.
• Claims potentially anticipated: Heater structure only.

28. US 5,661,513 A (Shirakawa et al.; Alps Electric) — "Thermal head"

• Filed: Jul. 29, 1994 | Issued: Aug. 26, 1997 | Class 347/202
• Description: Thermal head (resistive elements).
• Claims potentially anticipated: Heater structure only.

29. US 5,418,553 A (Connolly; Eastman Kodak) — "Thermal print head with optimum thickness of the thermal insulation under-layer and method of designing the same"

• Filed: Mar. 26, 1993 | Issued: May 23, 1995 | Class 347/200
• Description: Optimizes the thickness of the thermal insulation under-layer for a thermal print head — the only cited reference focused on optimizing a thickness dimension for head life/performance, though in the thermal-transfer (not inkjet-chamber) context.
• Claims potentially anticipated: Heater/under-layer thickness design rationale only; does not address inkjet chamber, nozzle plate, or power density.

Bottom-line ranking of "most relevant prior art"

1. US 6,045,214 (Murthy/Lexmark) — closest on the nozzle-plate-thickness side; its disclosed 15–200 µm (preferably 25–125 µm) plate range overlaps the claimed "< 62 microns" and it concerns Lexmark nozzle plates/chambers directly. Strongest single-reference anchor for claim element 1(b) + the thickness limitation (and claims 7–9), subject to the § 102(e) timing analysis and to the absence of a power-density disclosure.
2. US 5,563,642 / 5,648,805 / 5,604,519 / 5,638,101 / 5,619,236 / 5,594,481 (Keefe/HP family) — closest on the chamber/barrier/nozzle-member architecture; 5,563,642 even discloses barrier thicknesses of ~19–32 µm, overlapping the claimed < 28 µm separation (claims 2–3). No power-density or sub-62-micron plate disclosure.
3. US 5,719,605 (Anderson/Lexmark) — closest on the multi-chamber/multi-aperture claim 29 structure.
4. US 4,931,813 (Pan/HP), 4,947,193, 4,951,063, 5,066,963, 5,481,287 — closest on the heater/transducer limitation and the reliability objective.
5. Remaining references (thermal heads, cartridge venting, nozzle alignment, laser orifice formation) — cumulative background, not realistically anticipatory of any claim.

Two integrity notes

• No full § 102 anticipation case is apparent from the face record: because the two controlling numerics — plate thickness < 62 µm and power density < 2.159 GW/m² — do not appear together (or at all, for the power-density figure) in any single cited reference that I could verify, each independent claim (1, 29, 31, 33) would most plausibly have been patentable over these references individually; the citation set reads as § 103 combination art.
• Separate context (do not conflate): in PTAB IPR2022-01541 (Canon v. Slingshot), US 6,213,587 ("Whitman") was itself used as a prior-art reference against another Slingshot patent (the '951 patent) in obviousness grounds — that is the opposite direction from this analysis and does not bear on whether any reference anticipates 6,213,587's own claims.

If you need a definitive per-reference "anticipates vs. not" determination on the two numeric limitations, the next step is a page-level review of each of the Group A references (particularly 6,045,214 and the HP Keefe family) and a PAIR review of the 6,213,587 prosecution file to see exactly which limitations the examiner relied on the cited art for; neither was fully reachable in this session.

§ 103 Obviousness Analysis — U.S. Patent 6,213,587 ("Ink jet printhead having improved reliability")

Scope and analytical framing

The independent claims at issue are claims 1, 29, 31, and 33 (printhead, multi-transducer printhead, printer, method). Claim 1's elements decompose as follows:

Elements 1(a) and 1(b) are generic thermal-inkjet structure present in essentially every reference cited on the face of the patent (e.g., US 4,943,193; US 5,563,642; US 6,045,214). The entire obviousness contest therefore centers on 1(c) (thin plate) and 1(d) (low firing power density), and on dependent claims adding separation distance (claims 2–4), heater area (claims 5, 20–21, 25–28), ink chemistry (claims 6, 10, 17–19, 22–24, 27–28), and power-density ranges (claims 11–16).

Two important context facts carry over from the earlier sections: (i) no IPR was ever instituted on the '587, so there is no PTAB estoppel and no Board merits decision to consult; and (ii) the patent expired 2019-07-19, so this analysis is for completeness/validity defense context, not for an active PTAB proceeding.

The most relevant prior art (from the patent's own citation list, per the instruction to use the Prior Art section)

A. US 6,045,214 (Lexmark, Murthy et al., filed 1997-03-28, issued 2000-04-04) — "Ink jet printer nozzle plate having improved flow feature design…"
This is a same-assignee reference cited by the examiner on the '587's face. Verified details (uspto.report; everypatent.com):

• A polymeric nozzle plate in which the firing chambers, ink supply channels, and nozzle holes are all formed ("ablated portions … defining flow feature of the nozzle plate which contain ink flow channels, firing chambers, nozzle holes").
• Plate thickness: "about 15 to about 200 microns, and most preferably a thickness of about 25 to about 125 microns" (everypatent.com full-text). The preferred range encompasses values well below 62 microns, directly teaching element 1(c).
• Because the chambers are ablated to a controlled depth in a plate of known thickness, chamber height (and hence heater-to-aperture separation, element of claims 2–4) is a designer's variable, with partially ablated features of "height … less than the thickness of the nozzle plate" expressly disclosed (docketalarm Exhibit 1031 abstract).

B. US 5,563,642 (HP, filed 1992-04-02, issued 1996-10-08) — "Inkjet printhead architecture for high speed ink firing chamber refill" (and its family: US 5,594,481; 5,604,519; 5,638,101; 5,648,805; 5,619,236)
HP's firing-chamber architecture patents deal precisely with the geometry that the '587 later "reduced": barrier layers defining firing chambers of controlled height, orifice/nozzle plates over the heaters, and refill dynamics. The family is expressly directed to optimizing chamber/orifice geometry (e.g., for refill speed and frequency), giving a PHOSITA the design tools to shrink barrier height and nozzle bore length.

C. US 4,943,193 (Xerox, 1989) — "Thermal ink jet printhead with improved heating elements" and US 4,951,063 (Xerox, 1989) — "Heating elements for thermal ink jet devices"
Verified from the patent full text (patents.google.com / patentimages PDF): '193 is expressly about heater lifetime and drive energy. It states that "the operating lifetime of the ink jet printhead is directly related to the number of cycles or bubbles generated and collapsed that the heating element can endure before failure," and its solution — making the transverse temperature profile uniform — means "the power required to eject a droplet is reduced," eliminating the need to overdrive the heater by up to 20% above nucleation threshold. This is a direct teaching that operating the heater at lower power extends heater life — the precise rationale underlying element 1(d).

D. US 4,931,813 (HP, 1987) — "Ink jet head incorporating a thick unpassivated TaAl resistor"
Same-assignee-to-be-relevant HP teaching that heater stack construction (thick TaAl resistor) can be selected to survive cavitation/kogation and thereby extend life — corroborating that heater-life improvement via reduced thermal/cavitational load was a known design axis.

E. US 5,719,605 (Lexmark, 1996) — "Large array heater chips for thermal ink jet printheads"
Same-assignee disclosure of heater chips, resistor arrays and drive schemes; provides the heater-resistor and array context for claims 5, 20–21, 25–28 (heater areas) and the multi-transducer claims (29–30).

F. Supporting references on the face of the patent for specific dependent-claim features:

• Mono/color ink chemistry and phosphate effects on heater corrosion are contextualized by the background of Xerox '193 (noting "ionic inks" cause "erosion/corrosion attack of the passivation material").
• US 4,638,337 (Xerox/Torpey) and US 5,481,287 (Canon) — chamber/resistor structural arrangements.
• US 5,668,510 / 5,751,324 / 5,818,478 (Lexmark) — cartridge/chip context.

Combination 1 (primary) → renders claim 1 obvious

US 6,045,214 (Lexmark) + US 4,943,193 (Xerox) [and/or US 4,951,063; US 4,931,813]

• Limitations 1(a), 1(b): Both references disclose a transducer/heater at least partially within a chamber, with an apertured plate for ink ejection. In '214 the firing chambers and nozzles are in the polymer plate itself; in '193 the resistor sits in an ink channel with an orifice plate.
• Limitation 1(c) (plate < 62 µm): '214 expressly discloses polymeric nozzle plates "about 25 to about 125 microns," i.e., a range whose entire lower half (25–61 µm) satisfies the claim. Choosing a 25–60 µm plate from the disclosed range is a textbook selection of an expressly disclosed value.
• Limitation 1(d) (power density < 2.159 GW/m²): '193 teaches reducing the electrical power/energy applied to a thermal heater as a means of increasing the number of nucleation cycles the heater can endure (i.e., lifetime), and shows how to redesign the resistor so lower drive power still nucleates reliably. A PHOSITA reading '193 would understand that firing a heater below its maximum rated drive (here, below Lexmark's 2.159 GW/m² nominal value for its ~1,849 µm² color heater — roughly a 4 W pulse) is the operative way to implement '193's teaching.
• Motivation to combine (KSR): (i) Same field / same problem — both references address drop-on-demand thermal inkjet printhead reliability; '214 concerns the plate/chamber structure, '193 the heater drive. (ii) Recognized design interdependence — a thinner nozzle plate shortens the nozzle bore and reduces the fluidic/thermal energy needed to eject a drop, which in turn permits the lower drive power that '193 teaches prolongs heater life. (iii) Known improvement axes — thinning nozzle plates was known to improve refill and reduce energy loss (HP '642 family; Lexmark '214), and reducing heater drive power was known to improve life (Xerox '193). Combining the two axes to maximize life is an obvious "solution to a known problem" with a reasonable expectation of success, not a new interaction. The result is the predictable sum of two known reliability levers.

Combination 2 → also reaches claims 1 and 2–4 (separation < 28 µm)

HP US 5,563,642 family (barrier/orifice geometry) + US 6,045,214 or US 5,719,605 (structure) + Xerox '193 (low-power drive)

• HP's firing-chamber architecture patents supply the barrier-defined chamber whose height sets the heater-to-plate separation; the HP family optimizes chamber height and orifice-plate thickness for refill/frequency. Reducing the barrier height below 28 µm (claims 2–4, e.g., ~8–27 µm or ~24 µm) is squarely within the HP family's parameter-optimization teaching.
• In the '214 (Lexmark) all-in-plate construction, chamber depth is an ablation variable; partially ablated features of depth less than plate thickness are expressly disclosed, so sub-28 µm chambers are directly available.
• Combining a shallow chamber with low-power drive is motivated by the same energy-efficiency logic: a smaller chamber volume requires less energy to nucleate and eject, enabling the reduced power density that '193 ties to lifetime.

Dependent claims — routine optimization vs. claim scope

• Claims 7–9 (plate < 60 µm; 35–55 µm; ~40 µm): Specific values within '214's disclosed 25–125 µm (preferably 25–125) range; selecting 35–55 µm is routine optimization of an expressly bracketed range. '214's own most-preferred embodiment and the conventional polyimide stock thicknesses of the era (25.4/38.1/63.5 µm, corroborated in later Lexmark filings) put < 62 µm and ~40 µm in the ordinary designer's toolkit.
• Claims 2–4 (separation < 28 µm; 8–27 µm; ~24 µm): Covered by Combination 2; chamber heights in this band were the ordinary operating range for barrier-defined (HP) and ablated-plate (Lexmark '214) flow features. Note the '587 specification itself states the nominal pre-attachment barrier height was 30 µm and that heat/compression attachment reduces it by ~2 µm — i.e., the "inventive" 24–27 µm separation is only marginally below the nominal production tolerance band, which is a hallmark of obvious dimensioning.
• Claims 11–16 (power density < 2 GW/m²; 0.7–1.5 GW/m²; ~1 GW/m²; 0.77 GW/m²): These are operating-point selections. The concept — fire below the maximum rated power density to extend heater life — is the Xerox '193 teaching. The specific floor (~0.7 GW/m²) is simply the empirically minimum nucleation power, a constraint any thermal-inkjet designer knew (the '587 admits "a power density of about 0.7 GW/m² is currently needed to nucleate ink"). Choosing any value between the nucleation floor and the prior nominal maximum is classic obvious optimization.
• Claims 5, 20–21, 25–28 (heater areas >1,900 / <2,800 / ~2,900 / ~1,850 µm²): Heater dimensions of ~30–50 µm on a side (≈1,000–2,500 µm²) were ubiquitous in HP/Xerox/Lexmark resistor art (e.g., Xerox '193 discusses 45–50 µm wide heating elements; Lexmark '605 large-array chips). The claimed areas sit squarely in the conventional resistor-size envelope.
• Claims 6, 17–19 (mono ink), 22–24 (non-phosphate multi-color ink), 27–28 (phosphate ink, small heater): Ink-chemistry limitations tied to corrosion/cavitation of the heater passivation were known design parameters (Xerox '193 background discusses ionic-ink attack on passivation; dye-based black vs. color ink formulations with/without phosphate buffering were commodity choices). Choosing a mono ink or a non-phosphate color ink to reduce chemical attack of the heater, in combination with low-power firing and a thin plate, is the obvious application of known chemistry-reliability knowledge.

Method/system claims (31, 33) and array claim (29)

Claims 29 and 31–34 add only (i) pluralization of transducers/chambers/apertures, (ii) a power source capable of the recited energization, and (iii) method steps mirroring claim 1. All are conventional inkjet-printer elements (arrays of heaters per chamber are in Lexmark '605; a controllable power source driving heaters at selected power is in every thermal inkjet printer, e.g., the '587's own Figures 1–2 show a power supply 62). These claims rise or fall with claim 1.

Counterarguments a patent owner would press (and their weaknesses)

1. No reference expressly discloses "power density < 2.159 GW/m²" or the combination of thin plate + low power for life improvement. Response: express disclosure of a numeric is not required where the value is an operating point derived from known constraints (nucleation floor ~0.7 GW/m²) and known teachings (lower power → longer heater life, Xerox '193). The "2.159" figure is simply Lexmark's own prior nominal maximum, and "less than nominal maximum" is a quintessential obvious variant.
2. Unexpected results / synergy: The '587's Tables 3–4 show MTTF multiplying ~6–9× when all three variables (plate thickness, barrier height, power density) are reduced together, which the owner would argue is an unexpected interaction. Response: the empirical model in the specification is the patentee's own demonstration, not evidence of non-obviousness; a PHOSITA would expect monotonic lifetime gains from reducing thermal/cavitational load (fewer fires at high stress → longer life) and from reducing chamber/plate energy losses. The data largely show monotonic, predictable trends with no discontinuity at the claimed boundaries; the claims are drawn to broad "<" thresholds, i.e., to the ordinary direction of improvement.
3. "A thinner plate hurts reliability" (print-quality/kogation tradeoff) — the '587 argues low power can degrade print quality with conventional heads, suggesting the operating window was not obvious. Response: that admission cuts both ways — it shows the designer's task was a routine balancing of competing known parameters (power vs. drop quality vs. life), which under KSR is the paradigm of obvious optimization, especially where, as here, the claimed ranges are the endpoints/nominal values of the prior production design.

Bottom line

The strongest obviousness case is Combination 1: Lexmark's own US 6,045,214 (which the examiner cited on the face of the '587 and which discloses nozzle plates in the 25–125 µm range, satisfying the <62 µm plate limitation) combined with Xerox US 4,943,193 / US 4,951,063 (which expressly tie reduced heater drive power to extended heater life). The motivation is the recognized, interdependent design logic that a thinner nozzle plate reduces the energy required for drop ejection, thereby permitting the lower firing power density that the Xerox art teaches prolongs heater life; HP's US 5,563,642 firing-chamber architecture supplies the separate motivation and mechanism for the reduced barrier/separation dimensions of claims 2–4. Dependent numeric ranges, ink-type selections, and heater-area limitations are routine optimizations or known parameter choices. The main validity risk to the '587 is accordingly § 103 obviousness over the thin-nozzle-plate art (Lexmark '214) in combination with the low-power/heater-life art (Xerox '193/'063), with the caveat that no single reference discloses the specific numeric thresholds and the patent's empirical showing of large MTTF gains is the patent owner's best rebuttal material.

Caveats on sources: No PTAB or court decision has ever adjudicated the '587's validity (no IPR was filed; the W.D. Tex. cases terminated ~2021 without a reported merits decision), so this analysis is predictive only. Reference details above were verified from the full-text search results cited (uspto.report/everypatent for '214; Google Patents/patentimages for '193; Google Patents docket for '214 Exhibit 1031), not from the references' paper originals; if precision is needed on a specific disclosure, pull the primary patent PDFs.