Continuous inkjet (CIJ) technology is the market-leading method for adding variable information such as date and lot codes to a wide range of packaging, even though other types of printers such as piezo, thermal inkjet and laser have been taking some of that market share over the years.
If you go into any packaging operation, you’ll probably see one or more of these machines on the packaging lines.
While a CIJ printer looks simple, it is a complex device that requires extensive chemistry and physics to ensure a good-quality print on every package.
Let’s take a look at these coding systems – you can use the links below to jump to any area that interests you:
The Advantages of CIJ Printers
The First CIJ Printer
The first modern CIJ printer was patented by AB Dick Company (now Videojet) in 1969, but the original concept goes back much further.
The origin of continuous inkjet technology can be traced back to a machine called a siphon recorder, which William Thomson, the First Baron Kelvin, patented in 1867.
Lord Kelvin’s invention was designed to allow a written copy of telegraph messages to be produced and delivered to the recipient.
The system fed a moving length of paper tape under a printhead onto which a stream of ink was directed. The ink stream moved through an electrical coil and was energized, causing it to deflect and build an image corresponding to the dots and dashes in the message.
This is a similar concept to modern CIJ coders.
I wrote about this device here: Syphon Recorder
The image of the Syphon Recorder is from Wikipedia Commons
Challenges With CIJ Printers
How Does a CIJ Printer Work?
The printer basically generates a high-pressure stream of ink that is separated into individual droplets inside the printhead.
Each drop is either recirculated around the system or is deflected onto the material to be printed, making up a small part of the image.
The Ink and Fluidics System
CIJ Inks
CIJ inks typically consist of some or all of the following:
- Dyes or pigments for color
- Solvents (e.g., MEK, ethanol, or acetone) for quick drying
- Dispersing agents (for pigmented inks)
- Wetting agents to control surface tension
- Humectants to prevent dryness
- Penetration enhancers
- Polymer binders to aid adherence to substrates
The most notable properties of CIJ inks include:
- Low Viscosity: CIJ inks have a low viscosity, allowing them to flow smoothly through the printhead and easily disperse into droplets
- Fast Drying: These inks are designed to dry rapidly, often in less than one second, which is crucial for high-speed production lines
- Substrate Versatility: CIJ inks can adhere to a wide range of materials, including paper, plastics, metals, glass, and textiles
CIJ inks are specifically formulated to react to electrical charges, which is crucial for their functionality in continuous inkjet printing systems
The additive or makeup fluid usually consists of solvents, which help reduce the viscosity of the ink as the solvent in the circulating ink evaporates and ensures proper flow through the printer system.
Common solvents include alcohol (e.g., methanol, ethanol, propanol, and butanol) and Ketones (e.g., acetone, methyl ethyl ketone (MEK), and methyl isobutyl ketone).
These solvents may be used alone or in combination to achieve the desired properties and each type of CIJ ink usually has its own recipe of additive fluid.
CIJ Fluidic (Ink) System
Different CIJ OEMS implement the fluidics of a CIJ printer differently, but all versions have similar components.
Several filters are used to ensure there are no foreign particles in the ink that could cause blockages in the nozzle.
The tank for the additive fluid.
A pump to control the flow of the fluids.
It’s important to keep track of the ink viscosity so that when it reaches a pre-set level, the system add makeup fluid to the ink tank to reduce viscosity the working level. Keeping control of the viscosity is essential for consistent print quality.
In the Citronix example, the viscosity is measured using a viscometer close to the ink tank. Another method other CIJ printers use is measuring the ink stream’s velocity in the printhead.
While the ink is filled from bottles with the Citronix printer (the black cover on the top is for ink and the yellow one is for the additive fluid), others such as the Videojet printer shown here use a cartridge system for ink and additive.
The Videojet (along with some other brands) also uses a central service core unit, where all the ink system components and filters can be replaced as a single part.
The Printhead
The CIJ printhead is where the stream of ink is broken into individual droplets and directed onto the packaging material to create the required printed image.
The ink is pumped under pressure to the printhead, where a piezoelectric element in the nozzle oscillates, causing the ink stream to break into tiny droplets. These droplets are small, typically about 50-80 microns in diameter.
The CIJ printer runs continuously (hence the name continuous inkjet), and unless a drop of ink is charged as part of the print process, it is collected in the gutter and recycled through the system.
Charging Process
As the droplets break away from the continuous ink stream, they pass through charging electrodes that impart a variable negative electrostatic charge to the droplets intended for printing.
Deflection System
The charged droplets then pass between two deflection plates charged with about 7,000 volts, creating a strong electric field. This field deflects the charged droplets, controlling their trajectory toward the printing surface.
The charge on each drop determines how far it is deflected and its position in the final printed image.
Electronics and Interface
The electronics in Continuous Inkjet (CIJ) printers play a crucial role in controlling and coordinating various functions essential for high-speed, precise, and reliable printing.
Droplet Formation & Control:
The electronics in continuous inkjet (CIJ) printers are essential for precisely controlling the ink droplets that form printed images or text. They drive the piezoelectric transducer responsible for breaking the continuous ink stream into uniform droplets, with frequency regulation ensuring consistent droplet size and spacing. By controlling the charge electrodes, the electronics impart specific electrical charges to each droplet and modulate these charges to direct the droplets accurately onto the substrate.
The electronics also apply precise voltages to deflection plates to create an electrostatic field, allowing charged droplets to be deflected proportionally to their charge—this is how characters or images are formed. They also receive feedback from viscosity and temperature sensors within the ink system, adjusting heaters, coolers, and solvent additions to maintain optimal ink properties. Additionally, by regulating pumps and valves and utilizing pressure sensors for real-time feedback, the electronics maintain the correct ink pressure necessary for stable jet formation.
User Interface and System Control:
The electronics in a CIJ printer also manage user interactions and operational control through input processing and display output.
They interpret user commands to edit messages, select fonts, and adjust settings while controlling screens or touch panels to present system status and configuration options.
Underlying software operations run continuously on embedded processors to coordinate all printer functions seamlessly. In addition, the electronics integrate a network of sensors, monitoring ink levels and viscosity, nozzle performance, and droplet formation quality in real-time. If a problem arises—such as a clogged nozzle or low ink—the system can automatically initiate cleaning cycles or alert the operator to prevent downtime.
Beyond user and system feedback, the electronics ensure that printing stays in sync with the movement of products on a production line by processing signals from encoders and adjusting droplet release timing accordingly. They also provide robust safety and fault detection, shutting down components and notifying operators if a serious issue is detected.
Finally, communication interfaces like Ethernet or USB enable data exchange with external systems for remote diagnostics, updates, and broader integration into Industry 4.0 and other automated production environments.
CIJ printers are often included in integrated coding and labeling solutions, such as those provided by Videojet and Markem-Imaje. This allows the printer to be managed remotely and data being automatically sent for product runs – without the need for human intervention and reducing the chance of errors.
The printer electronics also manages power for the various printer functions, such as pumps, the drop management and the high voltages for the drop deflectors.
The electronics in CIJ printers are integral to the precise control of ink droplet generation, charging, and deflection, as well as maintaining optimal ink properties and coordinating the overall operation of the printer. They enable high-speed printing with accurate placement of ink droplets, ensuring quality print results suitable for various packaging and industrial applications.
The Advantages of CIJ Printers
Compatible With a Wide Range of Substrates
CIJ printers can print on a huge variety of materials, including glass, plastics, metal, paper, and wood, making them suitable for use in many industries.
High-Speed Printing
Suitable for fast-moving production lines, delivering clear and precise codes even at high speeds. CIJ printers are often seen on the fastest beverage canning lines and other high-volume packaging applications.
Non-Contact Printing
CIJ printers ensure accurate printing on uneven, curved, or textured surfaces without physical contact. Because the ink droplets leave the printhead at high speed, so they have a longer throw distance (the distance between the printhead and the item to be marked) than other inkjet printers.
Wide Range of Inks
Offers a variety of inks (e.g., quick-drying, food-safe, UV-visible, solvent-resistant) to suit diverse applications.
Over the years, inks have been developed with properties that enable them to operate in a huge number of packaging scenarios.
Some of the new develops in CIJ inks include MEK-free fluids as well as soft pigment inks that are easier to handle than traditional hard pigmants.
Continuous Operation
Designed for long-running, 24/7 operations with minimal downtime for maintenance.
CIJ printers are at their best when running continuously, so many users keep them running all the time to keep the ink circulating—even if the packaging line is not in operation.
Flexible Print Capabilities
Capable of printing variable data such as dates, batch codes, barcodes, and logos.
Small Character Printing
Ideal for detailed, small-font requirements, often needed for expiration dates or serial numbers. CIJ OEM has developed specialist printheads that create a smaller ink drop, making them well-suited for small font sizes.
Easy Integration
CIJ manufacturers are skilled at producing systems that integrate seamlessly into existing production lines with compact and flexible design options.
Cost-Effective for High-Volume Applications
Offers low cost per print for large-scale production runs, making it economical over time.
Quick Drying and Durable Marks
Prints dry almost instantly and produce durable, smudge-resistant codes that can withstand handling and storage.
Remote Operation and Monitoring
Many modern CIJ printers feature connectivity options for remote monitoring and adjustments via software. They can also interface with ERP systems and other enterprise software to manage print formats and data.
Environmentally Adaptable
Operates effectively in various environmental conditions, including dusty, humid, or cold settings; models are available with up to IP65 environmental protection.
Challenges With CIJ Printers
Complex Maintenance Requirements
Regular cleaning and maintenance are necessary to prevent clogging and ensure consistent performance.
Filter units need to be changed periodically (sometimes as part of a unified ink system core), and the printhead is often cleaned with solvents, especially to remove any ink that has dried on the deflector plates.
Older model CIJ printers might need to be cleaned before start-up. However, more modern systems often include flushing procedures to remove ink from the system before shutting down, making startup easier.
Ink containing heavy pigments can be difficult to handle on many CIJ models.
Ongoing Consumables Cost
Even when not actively printing, CIJ printers consume ink and additive fluids due to evaporation. These fluids, along with cleaning materials, add to the printer’s total operating cost.
Environmental Considerations
Solvent-based inks, additive fluids and cleaning materials can pose environmental concerns. Since they are treated as hazardous materials, they require proper handling and disposal.
Solvents used in CIJ printers can release fumes requiring ventilation or adherence to workplace safety regulations.
Manufacturers of CIJ inks have been developing MEK-free inks in recent years that can help address this issue.
Training and Expertise Needed
Because many variables are involved in CIJ printers, operators may require training to handle the equipment, especially when adjusting settings and troubleshooting.
In addition, many companies using these printers purchase a service plan from the manufacturer to ensure they always function correctly.
One important setup feature is that the stream of ink droplets needs to be carefully set to ensure the drops cleanly enter the gutter and don’t cause a mess that needs to be cleaned up.
Printer OEMs have worked hard to help with this, and some new models don’t need to be adjusted in this area.
Limited Print Resolution
While CIJ printers excel at speed, their resolution may not match other technologies like thermal inkjet (TIJ) for high-detail printing. This means that CIJ printers are not the best solution for printing high-resolution barcodes, such as the new GS1 Digital Link QR Codes.
Not Ideal for Low-Volume Production
Because CIJ printers work at their best when running continuously, they might not be suited to low-volume operations, where the printer might need to be idle for some time between production runs.
Final Thoughts
Several well-proven technologies could be considered when it comes to adding variable information such as date and lot codes and barcodes to packaging.
For anyone needing to print relatively simple codes, such as rwo or three lines of text, CIJ printers can be an excellent choice—especially for lines that are running most of the time.
If you are looking to introduce in-line coding of your products, whether for a new application or perhaps upgrading to handle the new 2D barcodes, be sure to choose a vendor that will fully audit your application and help you find the best solution for your particular needs.
You can also contact me at david@packagingnews.net with questions.
