Inkjet Printing — How a Hot Wire Discovered the Bubble Jet
Canon's 1977 bubble jet patent describes the thermal inkjet process — where a tiny heater vaporizes ink to form a bubble that ejects a droplet — discovered accidentally when a researcher touched a syringe of ink with a hot soldering iron.
Original patent title: “Bubble jet recording method and apparatus in which a heating element generates bubbles in a liquid flow path to project droplets”
What this patent covers
The actual claim
This patent describes a method of propelling ink droplets from a nozzle using thermal energy. A small resistive heater element (a few microns across) sits inside the ink channel just behind the nozzle opening. When a brief electrical pulse (a few microseconds) heats the element to over 300°C, the ink in contact with it vaporizes instantly, forming a rapidly expanding bubble. The bubble's expansion pushes ink out through the nozzle as a droplet. When the heater cools, the bubble collapses and fresh ink is drawn into the channel by capillary action. The cycle repeats thousands of times per second for each nozzle. By precisely controlling which nozzles fire and when, the print head creates patterns of ink droplets that form characters and images.
What this patent does NOT cover
The boundaries
- Piezoelectric inkjet (Epson's approach) — uses mechanical pressure from a piezo crystal rather than heat to eject droplets
- Laser printing — uses static electricity and toner powder, not liquid ink
- Continuous inkjet (CIJ) — a different approach where ink streams continuously and unwanted drops are deflected away
- UV-cured or solvent-based industrial inkjet — different ink chemistries for industrial printing
These exclusions are unique to PatentBrief — derived from the actual claim language, not patent-office boilerplate.
What made this novel
The bubble jet was discovered independently and simultaneously at Canon in Japan and Hewlett-Packard in the U.S. in 1979 — both teams had the same accident. At Canon, researcher Ichiro Endo accidentally touched a syringe full of ink with a hot soldering iron; the heat vaporized ink and shot a droplet out of the needle. At HP, a similar accident occurred in the same year. Both companies filed patents, and the result was a cross-licensing agreement. HP called it 'thermal inkjet'; Canon called it 'bubble jet' — same physics, different name. The technology reduced the cost of a printer by a factor of 10 compared to daisy-wheel and dot-matrix printers, ultimately making inkjet the dominant home printing technology for 30 years.
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
HP's ThinkJet (1984) was the first commercial thermal inkjet printer — it sold for $495 and used replaceable cartridges, establishing the 'razor and blades' business model of cheap printers with expensive ink
Canon's BJ-80 (1985) was the first bubble jet printer; Canon and HP's cross-licensing agreement allowed both companies to build on each other's patents
Modern inkjet print heads fire droplets at 18,000–30,000 per second per nozzle, with droplet volumes as small as 1 picoliter — enabling photographic-quality output from consumer printers
Why it matters
The bigger picture
Inkjet printing democratized color printing. Before it, color printing required professional offset presses or expensive laser systems. The bubble jet / thermal inkjet made it possible to print photographs at home for a few cents per page. HP's ink business became one of the most profitable in the company — selling ink at roughly $8,000 per liter for standard cartridges. The business model of cheap hardware and expensive consumables, pioneered by inkjet, has been applied to razors, coffee machines, and printers of all types.
Filed
February 6, 1986
Granted
February 2, 1988
Claim 1 — Plain English
What this patent covers
This patent describes a method of propelling ink droplets from a nozzle using thermal energy. A small resistive heater element (a few microns across) sits inside the ink channel just behind the nozzle opening. When a brief electrical pulse (a few microseconds) heats the element to over 300°C, the ink in contact with it vaporizes instantly, forming a rapidly expanding bubble. The bubble's expansion pushes ink out through the nozzle as a droplet. When the heater cools, the bubble collapses and fresh ink is drawn into the channel by capillary action. The cycle repeats thousands of times per second for each nozzle. By precisely controlling which nozzles fire and when, the print head creates patterns of ink droplets that form characters and images.
The clever bit
The bubble jet was discovered independently and simultaneously at Canon in Japan and Hewlett-Packard in the U.S. in 1979 — both teams had the same accident. At Canon, researcher Ichiro Endo accidentally touched a syringe full of ink with a hot soldering iron; the heat vaporized ink and shot a droplet out of the needle. At HP, a similar accident occurred in the same year. Both companies filed patents, and the result was a cross-licensing agreement. HP called it 'thermal inkjet'; Canon called it 'bubble jet' — same physics, different name. The technology reduced the cost of a printer by a factor of 10 compared to daisy-wheel and dot-matrix printers, ultimately making inkjet the dominant home printing technology for 30 years.
What it does not cover
- Piezoelectric inkjet (Epson's approach) — uses mechanical pressure from a piezo crystal rather than heat to eject droplets
- Laser printing — uses static electricity and toner powder, not liquid ink
- Continuous inkjet (CIJ) — a different approach where ink streams continuously and unwanted drops are deflected away
- UV-cured or solvent-based industrial inkjet — different ink chemistries for industrial printing
Patent Journey
From filing to expiry
Patent Filed
1986
Patent Granted
1988 · 2yr after filing
Highly Cited
1,806 patents cite this
Patent Expired
2006
PatentBrief Score
Impact Score
Moderate
Citation count
40/40
Highly cited
Claim breadth
7/20
Moderate scope
Recency
0/20
Older than 20 years
Assignee scale
0/20
Independent or smaller assignee
PatentBrief Impact Score — based on citation count, claim breadth, recency, and assignee scale. Not a legal assessment.
The original legal language
Original claims
11 claims as filed with the patent office.
Glossary
Key terms defined
- picoliter
- One trillionth of a liter — the unit used to measure inkjet droplet volume; modern print heads eject 1–3 picoliter droplets
- bubble jet
- Canon's name for thermal inkjet — the ink bubble formed by vaporization ejects the droplet
- thermal inkjet
- HP's name for the same technology — uses heat to vaporize ink and propel droplets
- capillary action
- The force that draws fresh ink into the nozzle channel after a droplet is ejected — no pump required
Citations
Patent lineage
Stay in the loop
Get a weekly digest of new patents.
One email per week. No spam. Unsubscribe anytime.
Keep exploring
Related patents you should know
US 12564871 · 2026
A Fixture for Cleaning Showerheads with Multiple Separate Chambers
This patent describes a cleaning device for showerheads that uses a fixture with three or more separate internal compartments and channels to direct cleaning fluid to the showerhead's upper surfaces.
ASM IP HOLDING BV
US 12324579 · 2025
Surgical Stapler Battery Health Check During Operation
This patent describes a powered surgical stapler that can detect if some of its rechargeable battery cells are damaged while it's actually firing staples, helping ensure the procedure finishes safely.
CILAG GMBH INT
US 12471982 · 2025
Surgical Tool That Combines Energy Treatment and Stapling
CILAG's patent details a surgical instrument that applies therapeutic energy to tissue, monitors its properties, then deploys staples, adapting the stapling based on the initial energy treatment and monitoring.
CILAG GMBH INT
US 11918209 · 2024
Real-Time Surgical Instrument Status on Live Video During Operations
This patent describes a surgical system that shows live video from inside the body and overlays important information about the surgical tool directly onto the screen, helping surgeons operate more precisely.
CILAG GMBH INT
US 8697359 · 2014
How to Use CRISPR-Cas9 to Edit Genes in Human Cells
This patent describes a method and system for precisely altering gene expression in eukaryotic cells, including human cells, using an engineered CRISPR-Cas9 system that targets and cleaves specific DNA sequences.
Massachusetts Institute of Technology
US 4683195 · 1987
How to Make Many Copies of a Specific DNA Segment
This patent describes the Polymerase Chain Reaction (PCR), a fundamental process for making millions of copies of a specific DNA or RNA segment from a tiny sample, enabling its detection.
Cetus Corp
Semantically similar
You might also find these interesting
US 2612994 · 1952
The Barcode — The Lines on Every Product in Every Store
US 4166152 · 1979 · Minnesota Mining and Manufacturing Co
The Post-it Note Adhesive — Invented as a Failure That Stuck Around
US 3541541 · 1970 · Stanford Research Institute
The Computer Mouse — Invented 30 Years Before Anyone Cared
US 2495429 · 1950 · Raytheon Manufacturing Co
The Microwave Oven — Invented When a Radar Engineer Melted a Chocolate Bar
Patent monitoring