Electret Filter Media Patents: Who Leads, Where the Gaps Are 2026
- Filing is concentrated hard at the top: the leading assignee alone accounts for 2,993 of 9,921 records, and the ranked leaders' top 5 combined hold 51.8% of all records in scope.
- The bulk of the claim space sits in imaging, not filtration: G03G (electrography & electrophotography) touches 78.1% of records, while B01D (separation processes) — the category most people assume dominates — sits at 9.8%.
- Filing has cooled from its 2023 peak of 150: the 2021→2024 span (the last complete filing years) shows a 21% decline, from 113 down to 89.
Filing growth compares 2021 (113 records) with 2024 (89) — a three-year span. 2024 is the most recent year we treat as complete: publication lags filing by roughly 18 months, so 2025 onwards are still filling in and any growth rate that ends there would understate the field. Top-5 share is the combined record count of the five largest assignees divided by all 9,921 records in scope (CR5), not by the ranked leaders only.
What this landscape covers
Electret charging of filter media is the process of imparting a durable electrostatic charge to nonwoven fibres so they trap particles more effectively without added pressure drop. The dataset in scope spans 2015 to 2026 and pulls together corona charging, charge decay, surface potential, charge additives, humidity effects, filtration efficiency and storage stability as they intersect with electret filter media claims. The search string is built to capture both the electrostatic-charging mechanics and the filter-performance metrics used to prove them out.
The 9,921 records in scope are not evenly split between filtration and imaging. A large share of the corpus traces back to xerographic and electrophotographic charging technology that predates modern respirator and HVAC filter media, and those older mechanisms still anchor much of the current claim language. Reading the field means separating the imaging-derived charging science from the filtration-specific applications built on top of it.
Filing trend and technology composition
Two views of the same 9,921 records: how filing activity has moved year over year, and which IPC subclasses carry the claim density.
Filing trend, 2017–2026
Filings ran from 80 in 2017 to a peak of 150 in 2023, then eased to 89 by 2024 — a 21% pullback from the 2021 level of 113. 2025 and 2026 figures are still filling in as publication lags filing by roughly 18 months, so the recent-year drop should not be read as the field cooling on its own.
Technology composition by IPC subclass
G03G (electrography & electrophotography) touches 78.1% of the 9,921 records, reflecting how much of the underlying charging science originated in photocopier and printer drum technology. B01D (separation processes), D04H (nonwovens & felts) and B03C (magnetic/electrostatic separation) — the subclasses closest to filter media itself — sit far lower, at 9.8%, 4.7% and 2.5% respectively. Records can carry more than one class, so these shares add up past 100%.
Shares are the percentage of the 9,921 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Electret Charging of Filter Media with Eureka
This page is one run against one query. Ask Eureka your own question about electret charging of filter media and every answer comes back with the patent numbers behind it.
Try EurekaThe most-cited patents in this space
US6119691A — Electret filter media
An electret filter media, and mask, made of a nonwoven web of thermoplastic microfibers of substantially the same composition, nonconductive, with an effective fiber diameter less than about 15 micrometers. The web carries sufficient unpolarized trapped charge to exhibit an initial filtration quality factor of at least 0.31 measured under the DOP Penetration and Pressure Drop Test.Filed by Minnesota Mining and Manufacturing Company (3M), granted 2000-09-19.
| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US5496507A | Method of charging electret filter media | 926 |
| 2 | US4588537A | Method for manufacturing an electret filter medium | 758 |
| 3 | US5908598A | Fibrous webs having enhanced electret properties | 690 |
| 4 | US5401446A | Method and apparatus for the electrostatic charging of a web or film | 632 |
| 5 | US4375718A | Method of making fibrous electrets | 598 |
| 6 | JP1986210363A | Electrophotographic sensitive body | 512 |
| 7 | JP1988149669A | Contact electric charging method | 419 |
| 8 | US6375886B1 | Method and apparatus for making a nonwoven fibrous electret web from free-fiber and polar liquid | 382 |
| 9 | US6406657B1 | Method and apparatus for making a fibrous electret web using a wetting liquid and an aqueous polar liquid | 358 |
| 10 | US5411576A | Oily mist resistant electret filter media and method for filtering | 356 |
Citation counts favour older filings simply because they have had longer to be cited — treat this as a signal of influence on the field, not of current commercial relevance.
Each row carries its publication number; clicking a row searches Eureka by that number.
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Four figures worth sitting with before deciding where to file.
Five assignees hold half the field
The top 5 ranked assignees combined account for 5,140 of the 9,921 records in scope — 51.8% of everything published. That is a dense thicket for anyone entering without a licence or a clearly differentiated charging mechanism.
Imaging classes dominate the corpus
G03G (electrography & electrophotography) appears in 78.1% of the 9,921 records, far ahead of B01D (separation processes) at 9.8%. Most of the charging science was proven out in copier and printer drums before it migrated to filter media.
Filing has pulled back from its 2023 peak
After peaking at 150 filings in 2023, activity for the last fully-settled year (2024) sits at 89 — down 21% from the 113 filed in 2021. Later years are still incomplete because of publication lag.
Japan is the largest receiving office
Japan leads with 3,532 records, ahead of the United States at 2,794 and the EPO at 1,662. WIPO/PCT filings sit far behind at 328, suggesting most applicants pursue direct national routes rather than a single international filing strategy.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to electret charging of filter media, with the prior art for and against each one.
Who holds the ground
A small group of assignees built the foundational charging patents from imaging technology; recent-year momentum has cooled across nearly all of them, which is where an opening for new entrants may sit.
A single assignee dominates the ranking
The leading assignee holds 2,993 of the 9,921 records in scope — well over a quarter of the entire field on its own, built from decades of electrophotographic charging work later extended to filter media claims.
Recent-year filing has gone quiet at the top
Several of the most active historical filers, including the leading assignee, show zero filings in the latest tracked year and a -100% year-over-year change. This likely reflects publication lag rather than withdrawal from the space, but it does mean the newest claim activity is not concentrated where the older portfolios sit.
Co-filing is rare and tightly clustered
Only 10 co-assignee pairs appear in the dataset, and the strongest pair — two related entities within the same corporate group — accounts for 162 shared records. Cross-company collaboration is not a meaningful feature of this field; most portfolios are built and held internally.
| Assignee | Recent year | YoY |
|---|---|---|
| Canon KK | 0 | -100% |
| Xerox Corporation | 0 | — |
| Ricoh Co., Ltd. | 0 | — |
| 3M Innovative Properties Company | 0 | -100% |
| Minolta Co., Ltd. | 0 | — |
| Konica Corporation | 0 | — |
| Mitsubishi Chemical Corporation | 0 | -100% |
| FUJIFILM Holdings Corporation | 0 | — |
Where to take this
The landscape points to where claim space is dense and where it has thinned — the next step is testing a specific filing idea against it.
Map a candidate claim against the dense classes
If a new charging mechanism touches G03G or the top assignees' existing claim families, expect heavy prior art. Run the specific claim language through a full-text search before committing R&D spend.
Explore in EurekaWatch the momentum shift, not just the leaderboard
The leading assignees show zero recent-year filings, which may open room for a differentiated entrant rather than an incremental improvement on their existing patents.
Track assignee activity in EurekaLook past citation counts for current relevance
The most-cited records are decades old; use them to understand foundational mechanics, then check what has been filed since 2021 in the specific sub-area you're targeting.
Search recent filings in EurekaCommon questions
Electret charging is the process of imparting a semi-permanent electrostatic charge to nonwoven fibres, usually via corona discharge, so the fibres attract and trap particles more efficiently without increasing airflow resistance. Patents in this space cover the charging apparatus, the additives that help the charge persist, and test methods for verifying filtration efficiency after exposure to humidity or storage. In this dataset the charging science traces back heavily to electrophotographic (copier/printer) technology, which explains why imaging-related IPC classes dominate the corpus even though the practical application is filtration.
Filing is concentrated at the top: a single assignee holds 2,993 of the 9,921 records in scope, and the five leading assignees combined account for 51.8% of all records. This concentration reflects decades of continuous filing by companies that originally developed charging mechanisms for imaging equipment and later extended those portfolios into filter media and mask applications. Newer entrants face a dense prior-art landscape if they file claims that overlap with these established charging mechanisms.
Because the corona-charging and electret science used in filter media was largely developed and patented first for photocopier and printer drums, the G03G (electrography & electrophotography) class touches 78.1% of the 9,921 records in this dataset. B01D (separation processes), the class most associated with filtration itself, appears in only 9.8% of records. Anyone searching this space using only filtration-specific keywords risks missing the foundational charging patents that sit in the imaging classes.
Filing peaked in 2023 at 150 records and had declined to 89 by 2024, a 21% drop from the 113 filed in 2021. However, publication typically lags actual filing by around 18 months, so the 2025 and 2026 figures in this dataset are still incomplete and should not be read as evidence of a slowdown. The 2021-2024 window is the most reliable recent comparison available.
US6119691A, held by Minnesota Mining and Manufacturing Company (3M) and granted in 2000, claims a nonwoven electret filter media made of nonconductive thermoplastic microfibers under 15 micrometers in diameter, carrying enough unpolarized trapped charge to hit a specific filtration quality factor threshold under a defined DOP test. Designs that use similarly sized nonconductive thermoplastic microfibers relying on unpolarized trapped charge to meet that same performance benchmark sit closest to this claim. Alternatives that use conductive fibres, polarized charge mechanisms, or different fibre diameter ranges are more likely to sit outside its scope, though a full claim chart is needed to confirm freedom to operate.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.