Tiny Capsules for Electronic Paper Displays
MIT's 1999 patent on a special ink made of tiny capsules that can change color when an electric field is applied, forming the basis for early e-readers.
Original patent title: “Microencapsulated electrophoretic display”
MIT's 1999 patent on a special ink made of tiny capsules that can change color when an electric field is applied, forming the basis for early e-readers. Granted to Massachusetts Institute of Technology in 1999 with 49 claims and 508 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent describes a material for electronic displays, like early e-readers. It's an 'electrophoretic material' made of a carrier liquid holding many tiny capsules, called microcapsules. Inside each microcapsule are particles that can move when an electric field is applied. Some particles are designed to reflect light better, making them appear bright. Others might be colored or even emit light. The key is that these particles can be moved to show different colors or patterns, and importantly, they stay that way even after the electric field is turned off. This 'bistability' is what makes it work like paper, holding an image without constant power. For example, imagine a microcapsule with black particles and white reflective particles. Applying a field can push the white particles to the front, making the capsule look white, or push the black particles forward, making it look black.
The gap
What does this patent NOT cover?
- Materials that require continuous power to maintain their displayed image.
- Displays where the particles do not have differential responsiveness to an electric field.
- Microcapsules that do not contain multiple phases or particles with contrasting visual properties.
- Materials where the visual appearance does not persist after the electric field is removed.
- Displays that rely solely on light emission without reflective elements for their appearance.
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
Key facts
What made this novel
The innovation lies in encapsulating the moving charged particles within tiny spheres and controlling their movement with an electric field, while also ensuring the image remains visible even when the field is off. This created a stable, low-power display that mimics the appearance of ink on paper.
The Patent Drawing
Schematic visualization of the patent's claim structure. Hand-drawn diagrams in progress for each landmark patent.
Where you've seen this
Real-world examples
Early Amazon Kindle devices
E-readers from other manufacturers
Electronic shelf labels
Some smart cards
Digital signage requiring low power
Why it matters
The bigger picture
This patent is foundational for the development of electronic paper (e-paper) technology. It describes the core microencapsulated electrophoretic display (EPD) technology that enabled the first generation of e-readers and other bistable displays. The ability to hold an image without power consumption was a significant leap for portable electronic devices.
Filed
March 18, 1997
Granted
October 5, 1999
Market context
Who's building on this
Companies in this space
E Ink Corporation, a spin-off from MIT that commercialized this technology, remains a dominant player in the e-paper market. Many companies producing e-readers and other bistable display devices utilize or licenselicensePermission from the patent owner to make, use, or sell the invention — usually in exchange for payment. Doesn't transfer ownership.Read more → this foundational technology.
Market impact
This patent directly led to the creation of the e-reader market, offering a reading experience far superior to backlit LCD screens for extended use. It enabled a new category of portable devices focused on reading and information display with minimal power draw, impacting the publishing and electronics industries significantly.
Claim 1 — Plain English
What this patent covers
This patent describes a material for electronic displays, like early e-readers. It's an 'electrophoretic material' made of a carrier liquid holding many tiny capsules, called microcapsules. Inside each microcapsule are particles that can move when an electric field is applied. Some particles are designed to reflect light better, making them appear bright. Others might be colored or even emit light. The key is that these particles can be moved to show different colors or patterns, and importantly, they stay that way even after the electric field is turned off. This 'bistability' is what makes it work like paper, holding an image without constant power. For example, imagine a microcapsule with black particles and white reflective particles. Applying a field can push the white particles to the front, making the capsule look white, or push the black particles forward, making it look black.
The clever bit
The innovation lies in encapsulating the moving charged particles within tiny spheres and controlling their movement with an electric field, while also ensuring the image remains visible even when the field is off. This created a stable, low-power display that mimics the appearance of ink on paper.
What it does not cover
- Materials that require continuous power to maintain their displayed image.
- Displays where the particles do not have differential responsiveness to an electric field.
- Microcapsules that do not contain multiple phases or particles with contrasting visual properties.
- Materials where the visual appearance does not persist after the electric field is removed.
- Displays that rely solely on light emission without reflective elements for their appearance.
Patent timeline
Application submitted to the patent office
Application published, typically 18 months after filing
Patent officially issued
Patent enters public domain
This patent is in the public domain
See the Freedom to Build guide — what is free to use, what is not, and how to cite this patent.
PatentBrief Score
Impact Score
High impact
Citation count
40/40
Highly cited
Claim breadth
20/20
Very broad protection
Recency
0/20
Older than 20 years
Assignee scale
20/20
Major company or institution
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
Heuristic Value Estimate
What this patent might be worth
$135K – $432K
Midpoint $270K · expired or expiring · industry ×1.5
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Claim text not yet imported for this patent
The original legal language
Original claims
49 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Comiskey, B., Albert, J., & Jacobson, J. (1999). Tiny Capsules for Electronic Paper Displays (U.S. Patent No. 5,961,804). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/5961804/e-ink-electronic-paper-display
Auto-generated from the patent record. Double-check author order and the issue date against the official USPTO document before submitting.
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Common Questions
Frequently Asked Questions
What does Tiny Capsules for Electronic Paper Displays cover?
MIT's 1999 patent on a special ink made of tiny capsules that can change color when an electric field is applied, forming the basis for early e-readers.
Who owns patent US 5961804?
Massachusetts Institute of Technology owns this patent, granted in 1999.
When does this patent expire?
This patent has expired and is now in the public domain — anyone can use the invention freely.
What is patent US 5961804 cited by?
This patent has been cited by 508 later patents that build on its ideas.
What problem does this patent solve?
This patent is foundational for the development of electronic paper (e-paper) technology. It describes the core microencapsulated electrophoretic display (EPD) technology that enabled the first generation of e-readers and other bistable displays. The ability to hold an image without power consumption was a significant leap for portable electronic devices.
What does this patent NOT cover?
Materials that require continuous power to maintain their displayed image.
Same assignee
More from Massachusetts Institute of Technology
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