How Canon's Bubble Jet Printers Make Ink Droplets
Canon's 1988 patent on bubble jet printing uses a tiny heater to instantly vaporize ink, creating a bubble that pushes out a droplet of ink from the printer head.
Original patent title: “Bubble jet recording method and apparatus in which a heating element generates bubbles in a liquid flow path to project droplets”
Canon's 1988 patent on bubble jet printing uses a tiny heater to instantly vaporize ink, creating a bubble that pushes out a droplet of ink from the printer head. Granted to Canon Inc in 1988 with 11 claims and 1,806 forward citations, and it is now in the public domain.
Coverage
What does this patent actually cover?
This patent describes how bubble jet printers work. Imagine a tiny tube, called a liquid flow path, with ink inside. At one end is an opening, the orifice, where ink droplets come out. Near this opening, but not too close, is a heating element. When the printer needs to make a dot, it sends a signal to this heater. The heater instantly gets super hot, boiling the ink right next to it. This creates a bubble. The bubble expands and pushes the ink in front of it out of the orifice, forming a droplet. Once the bubble pops, the heater cools down, and more ink flows in to fill the path, ready for the next droplet. The key is heating the ink *really* fast and only in a small spot, so it's a violent bubble, not just gentle simmering.
The gap
What does this patent NOT cover?
- Printing methods that use continuous streams of ink droplets.
- Printing methods that rely on mechanical pressure or vibration to eject ink.
- Printing methods where the heating element heats the entire ink chamber uniformly.
- Printing methods that do not involve the formation and collapse of a vapor bubble in the ink.
- Inkjet printers that use piezoelectric crystals to eject ink.
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 the precise control of heat. Instead of just warming the ink, the patent claimsclaimsThe numbered statements at the end of a patent that legally define what the inventor owns.Read more → a method to heat it so rapidly and locally that it causes a 'change of state' – essentially, a tiny, explosive bubble. This bubble generation is far more efficient for ejecting droplets than slower heating methods.
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
Canon Bubble Jet printers (e.g., BJ series)
HP thermal inkjet printers
Epson thermal inkjet printers
Most consumer-grade inkjet printers
Why it matters
The bigger picture
This patent is foundational for bubble jet (also known as thermal inkjet) printing technology. It enabled Canon to develop its highly successful line of inkjet printers, which brought affordable color printing to homes and offices worldwide. This technology is still a dominant force in the consumer inkjet printer market.
Filed
February 6, 1986
Granted
February 2, 1988
Market context
Who's building on this
Companies in this space
Canon Inc. remains a primary developer and user of this technology. Other major printer manufacturers like HP and Epson also employ similar thermal inkjet principles, though they may have developed their own patented variations or improvements on the core concept.
Market impact
This patent helped establish thermal inkjet as a leading technology for consumer printers, directly competing with and eventually surpassing early dot matrix and other inkjet technologies in many markets. It fueled the growth of the home and small office printing market by enabling lower-cost, higher-quality color printing.
Claim 1 — Plain English
What this patent covers
This patent describes how bubble jet printers work. Imagine a tiny tube, called a liquid flow path, with ink inside. At one end is an opening, the orifice, where ink droplets come out. Near this opening, but not too close, is a heating element. When the printer needs to make a dot, it sends a signal to this heater. The heater instantly gets super hot, boiling the ink right next to it. This creates a bubble. The bubble expands and pushes the ink in front of it out of the orifice, forming a droplet. Once the bubble pops, the heater cools down, and more ink flows in to fill the path, ready for the next droplet. The key is heating the ink *really* fast and only in a small spot, so it's a violent bubble, not just gentle simmering.
The clever bit
The innovation lies in the precise control of heat. Instead of just warming the ink, the patent claims a method to heat it so rapidly and locally that it causes a 'change of state' – essentially, a tiny, explosive bubble. This bubble generation is far more efficient for ejecting droplets than slower heating methods.
What it does not cover
- Printing methods that use continuous streams of ink droplets.
- Printing methods that rely on mechanical pressure or vibration to eject ink.
- Printing methods where the heating element heats the entire ink chamber uniformly.
- Printing methods that do not involve the formation and collapse of a vapor bubble in the ink.
- Inkjet printers that use piezoelectric crystals to eject ink.
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
Strong
Citation count
40/40
Highly cited
Claim breadth
7/20
Moderate scope
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
$41K – $130K
Midpoint $81K · expired or expiring · industry ×0.9
Heuristic only — blends forward/backward citation counts, claim scope, time remaining, litigation history, and CPC-derived industry baseline. Real valuations need a professional appraisal.
Patent Claims
0 independent claims · 1 dependent
Claims are the legal boundaries of the patent. An independent claim stands alone. A dependent claim adds limitations to its parent, narrowing — but not broadening — the scope.
The original legal language
Original claims
11 claims as filed with the patent office.
Concepts involved
Citations
Patent lineage
Cite this patent
Ohno, S., Sato, Y., Endo, I., Nakagiri, T., & Saito, S. (1988). How Canon's Bubble Jet Printers Make Ink Droplets (U.S. Patent No. 4,723,129). U.S. Patent and Trademark Office. https://patentbrief.org/patent/us/4723129/inkjet-bubble-jet-printing
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 How Canon's Bubble Jet Printers Make Ink Droplets cover?
Canon's 1988 patent on bubble jet printing uses a tiny heater to instantly vaporize ink, creating a bubble that pushes out a droplet of ink from the printer head.
Who owns patent US 4723129?
Canon Inc owns this patent, granted in 1988.
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 4723129 cited by?
This patent has been cited by 1806 later patents that build on its ideas.
What problem does this patent solve?
This patent is foundational for bubble jet (also known as thermal inkjet) printing technology. It enabled Canon to develop its highly successful line of inkjet printers, which brought affordable color printing to homes and offices worldwide. This technology is still a dominant force in the consumer inkjet printer market.
What does this patent NOT cover?
Printing methods that use continuous streams of ink droplets.
Same assignee
More from Canon Inc
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