Porous polyethylene filter membrane with asymmetric pore structure, and related filters and methods

This patent covers a method of making a porous high-density polyethylene (HDPE) film with an asymmetric pore structure for use as a liquid filtration membrane. In plain terms, claim 1 describes extruding a heated polymer solution "consisting essentially of" HDPE polymer and solvent at a defined extrusion temperature to form a sheet, then cooling that extruded film to set the porous structure. The key claimed limitation is the dual-solvent system: the solvent must contain a strong solvent (in which the polyethylene is soluble at the extrusion temperature) and a weak solvent (in which it is less soluble). This solvent contrast drives phase separation that produces a single-layer film with two opposed sides, pores running through the full thickness, and — the distinguishing feature — an asymmetric pore structure across that thickness. Dependent claim 2 narrows the polymer loading to 15–35 weight percent. The abstract frames the end use as filtering liquid chemicals to remove unwanted material, situating this squarely in process-fluid microfiltration.

The patent is assigned to Entegris Inc, a major supplier of filtration and materials-handling products to the semiconductor and microelectronics industries, with named inventors Cheng, Patel, Woo, and Proeung. It was granted in 2025, so it is a freshly issued patent with claims now fixed. The family is 13 members across 7 countries, indicating deliberate, moderately broad international prosecution consistent with a global supplier protecting a product line in its key manufacturing and customer regions rather than a one-jurisdiction filing. Its forward-citation count is 0, which is expected and uninformative for a patent granted this year — citation accumulation lags issuance by years, so the zero reflects recency, not lack of significance.

Where this patent stands: This reads as a focused refinement within Entegris's established membrane portfolio rather than a foundational filing. The asymmetric-pore HDPE concept is not new to the field (USF Filtration's 2000-era asymmetric microfiltration patents predate it), so the inventive weight sits in the specific dual-solvent (strong/weak) phase-separation route to a single-layer asymmetric HDPE film. Entegris already holds related membrane IP in this result set (US-8758887-B2, a multilayer porous membrane), so this 2025 grant extends and modernizes a product-aligned family aimed at high-purity liquid filtration for microelectronics. It is best characterized as strategic, product-underpinning IP — the kind of process-specific patent that protects a commercial membrane line — rather than an anchor reference others will widely cite.

The surrounding space is tightly clustered around membrane separation and is dominated by Separation & Filtration (B01D), which appears at 71.3× the corpus baseline — by far the strongest concentration signal here and clear evidence that the nearest art is a dense, mature niche. Two secondary clusters distinguish the two main commercial drivers of this technology: Water Treatment (C02F) at 30.2× and Layered Materials (B32B) at 11.7×, the latter reflecting the multilayer-membrane and battery-separator subfield. By citation impact the leading names are USF Filtration & Separations Group Inc (appearing twice, with 232 and 58 citations), Refined Technology Company (339 citations), Koch Membrane Systems Inc, and Sumitomo Electric Fine Polymer Inc (3 patents). Notably, Toray's battery-separator entities (Toray Tonen / Toray Battery Separator Film) appear on at least 5 of the nearest patents but do not lead the citation chart — a sign that polyethylene microporous-membrane manufacturing is heavily worked by Toray as a portfolio play even though individual filings are lightly cited.

The closest related patents:

• US-6045899-A — Highly asymmetric, hydrophilic, microfiltration membranes having large pore diameters (USF Filtration & Separations Group · 232 citations · 14-member family). The most-cited near reference and the anchor for the asymmetric-pore microfiltration concept that the subject patent applies specifically to HDPE.
• US-8758887-B2 — Multilayer porous membrane and process (Entegris Inc · 7 citations · 18-member family). The subject patent's own family sibling — Entegris's prior membrane process work, showing the 2025 grant extends an existing internal program from multilayer to single-layer asymmetric HDPE.
• US-8323547-B2 — Microporous polyethylene film manufactured according to liquid-liquid phase separation (SK Innovation Co Ltd · 0 citations · 12-member family). Directly on point: a liquid-liquid phase-separation route to porous polyethylene, the same mechanistic family as the subject's strong/weak-solvent approach, though aimed at a different end use.
• US-8465565-B2 — Polyethylene membrane and method of its production (Lydall Solutech BV · 12 citations · 16-member family). Another HDPE-membrane process filing in the same materials class, relevant to the polymer-and-solvent processing limitations of claim 1.

The field's leadership is commercial, not academic — the top assignees are filtration and materials companies (USF, Koch, Sumitomo, Donaldson, DuPont, Baxter), so the practical concern here is competitive positioning among established membrane suppliers rather than university licensing. Filing activity in this result set runs continuously from 2000 through 2025 with a cluster around 2