Invalidity dossier
US 5844720
Prism sheet
Current assignee: Goyo Paper Working Co Ltd
Added 9/23/2026, 7:49:59 PM
Active provider: DeepSeek · deepseek-flash
Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
US 5,844,720 — "Prism Sheet" (Overview)
Title: Prism Sheet
Patent number: US 5,844,720
Assignee/current assignee: Goyo Paper Working Co., Ltd.
Inventors: Shuzo Ohara; Takumi Kosugi; Osamu Kawaguchi; Tetsuro Taen; Kenji Kawashima; Yu Tsuyama
Priority date: 1995-09-08 · Filing date: 1995-11-15 · Grant/publication date: 1998-12-01
Status as listed: Expired – Lifetime (anticipated expiration 2015-11-15)
Source: https://patents.google.com/patent/US5844720/en
Purpose
The patent concerns a prism sheet for liquid-crystal display devices (LCD TVs, computers, word processors) whose display is uniform and high in brightness, free of interference fringes, and less prone to damage.
Plain-language scope
The sheet has, on one side, lens units made of substantially triangular prisms with nearly parallel longitudinal axes, and a roughened surface on the other side. As stated in the definitions, when the roughened surface is treated as the 100 baseline for characteristic values, the prism surface is not less than 50 in glossiness, not more than 70 in internal reflective ability, and not more than 70 in friction coefficient when the plane including the prism peaks is rubbed by the roughened surface. The description states the prism vertical angle is preferably 70°–110° and the distance between adjacent prism units is 10–1,000 µm (preferably 10–500 µm, most preferably 10–100 µm), with prism height determined by that interval and the vertical angle.
The excerpt notes a tension the invention addresses: a lens sheet with sharp vertical angles tends to suffer damaged prism peaks during handling, causing visible scratch of light, so minimizing such damage is described as essential. FIG. 1 is identified as a perspective view of the sheet; FIG. 2 as a perspective view of the sheet used in a backlight.
What the excerpt does not establish
The supplied text is explicitly excerpted ("[Excerpt only; consult the source for omitted text.]"). It does not provide the full claims, the complete description (e.g., the truncated "the thic…" passage), examples or measurement methods, referenced figures/images, or the full prior-art discussion. No litigation, ownership-transfer, validity, or prior-art conclusions are drawn here.
Generated 10/1/2026, 9:41:46 PM
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Litigation summary
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Proceedings on file (0)
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PTAB challenges
AIA trial proceedings at the USPTO Patent Trial and Appeal Board — IPR, PGR, and CBM. Petitioners, judge panels, claim-level invalidation outcomes from Final Written Decisions, and Federal Circuit appeals. The single most important defensive datapoint after litigation history.
Assignment history
Inventors, original assignee, and the chain of ownership recorded with the USPTO — including the correspondent attorney who recorded each assignment, since shell-LLC chains often share one repeat-player attorney even when the entity names look unrelated. Surfaces NPE / patent-troll patterns: shell-entity transfers, known asserters in the chain, repeat correspondent fingerprints, pre-litigation assignments, and bankruptcy fire-sales.
Prior art
Earlier patents, publications, and products that may anticipate or render the claims unpatentable.
Obviousness
Combinations of prior art that suggest the claimed invention would have been obvious under 35 U.S.C. § 103.
Extensions
Patent term adjustments, term extensions, continuations, divisionals, family members, and expiration dates.
Derivative works
Defensive disclosure: derivative variations of each claim designed to render future incremental improvements obvious or non-novel.