What is Continuous Ink Jet Printing?

Continuous Inkjet Printing: An Enduring Technology Powering High-Speed Industrial Marking

Inkjet printing has come a long way since its origins in the 19th century, evolving from experimental beginnings into one of today‘s most ubiquitous and versatile digital printing technologies. Of the two main inkjet techniques, continuous inkjet (CIJ) printing stands out for its ability to print extremely fast on all kinds of surfaces while using inexpensive inks. First patented in the 1960s, CIJ powers most industrial coding and marking applications thanks to its reliability, simplicity, and efficiency.

A Look Back at Inkjet‘s Humble Beginnings

Inkjet printing traces its early development to a series of crucial discoveries in the 1800s. In 1833, Felix Savant became the first to observe that liquid forced through a narrow aperture would break up into uniform droplets of consistent size. This discovery laid important groundwork, but another few decades passed before the next leap came courtesy of Lord Rayleigh, an English physicist who derived the mathematical relationship governing the breakup of liquid jets:

d = (6Qf(v))^(1/3)

Where d is the droplet diameter, Q is the liquid flow rate, f(v) is a constant related to the fluid‘s viscosity v and surface tension. This equation precisely predicts the uniform droplet size resulting from any jet of liquid based on its physical properties. Building on this progress, the first patented inkjet device arrived in 1867. Dubbed the "plume pen," William A. Burt‘s device applied ink droplets to paper but lacked reliability. Practical inkjet would have to wait until the 1940s, when commercial devices finally reached the market.

Arguably the biggest breakthrough came when Richard Sweet of Stanford University figured out that applying an electric charge to ink drops lets them be precisely steered by electric fields onto paper. This enabled accurate and consistent inkjet printing through an electrically controlled, continuous jet of ink that could be turned on and off. Originally described in 1965, Sweet‘s "continuous inkjet" (CIJ) printing method would go on to become the dominant approach used in high-volume industrial printing applications.

How CIJ Printing Works

CIJ might sound high-tech, but its underlying mechanism is elegantly simple. As its name suggests, CIJ printing relies on an uninterrupted, continuous jet of ink that issues forth from the printhead.

The printhead contains a reservoir holding ink, with a pump to push ink through a tiny nozzle aperture, usually 50 to 80 microns across. Due to hydraulic pressure of around 0.5 to 70 psi and surface tension in the range of 28-73 dyn/cm, the emerging liquid forms a consistent stream that immediately breaks up into tiny uniform droplets about 1.5 to 2.5 times wider than the nozzle diameter.

Sweet‘s key breakthrough discovery was that by applying an oscillating electric charge to the emerging ink jet using a charging electrode, the stream of droplets could each be imparted with controlled electric charge levels between 0-100 mV or more. A charge amplifier boosts the control signals from circuitry that determines the charging waveform. The stream then passes through high voltage deflection plates with a field strength over 7500 V, which alters droplet trajectory depending on charge.

[[ Image showing charged drops being deflected between a pair of charged deflection plates here ]]

Finally, a gutter assembly recycles unused droplets back into the reservoir while the desired printed drops impact the substrate. Sophisticated electronics running proprietary algorithms precisely coordinate the entire process by calculating charge levels and distributions required to build up images dot by dot at astonishing speed.

So in summary, CIJ printing relies on:

1. Producing a continuous stream of uniform ink droplets
2. Charging droplets electrically to different levels
3. Deflecting them by different amounts using electric fields
4. Recycling/reusing droplets not needed for printing

A typical CIJ printer fires up to 64,000 ultra-precise drops per second through a microscopic nozzle onto a moving substrate below. It builds up printed text, images, barcodes and graphics dot by dot without ever contacting the material being imprinted.

What Sets CIJ Apart? Speed, Simplicity and Adaptability

Continuous inkjet offers enticing advantages stemming from intrinsic aspects of its technology that explain its standing as the leading industrial printing method. Three major benefits make it better suited than alternative printing techniques:

High Speed
Owing to the constant droplet generation from an uninterrupted pressurized stream, CIJ printheads achieve extremely high flow rates measured in litres per hour. This enables blazing fast print speeds far surpassing other inkjet methods. Even printing complex graphics or DataMatrix barcodes, speeds can exceed 984 feet (300 meters) per minute. Such rapid throughput keeps pace with the fastest product assembly lines.

Simplicity and Reliability
With no complex mechanical components, CIJ hardware tends to be extremely tolerant of harsh industrial environments and heavy duty operation. In contrast, the printhead nozzle of drop-on-demand inkjet printers faces constant clogging risks since they only fire droplets intermittently as needed per print job. CIJ‘s constant ink flow precludes nozzle clog issues, allowing reliable 24/7 operation for months before routine cleaning or filter changes are needed. As an example, the Xaar 5601 printhead common in high-end CIJ printers permits over a year of continual operation.

Adaptability
While desktop inkjets rely on specially coated paper, CIJ inks strongly adhere to nearly any material thanks to flexible ink chemistry. From plastics, glass and metals to cardboard, wood and ceramic glazes, CIJ handles them all. Print quality stays superb regardless of surface texture, shape, orientation or speed – an impossible feat for contact based pad printers. Further augmenting flexibility, CIJ printheads mount on highly configurable bracket assemblies, enabling adaptation for oddly shaped products. This adaptability suits CIJ perfectly to coding and marking tasks.

Vital Role of CIJ Printers in Package Coding and Product Marking

Continuous inkjet‘s virtues make it perfectly suited for printing variable content like expiration dates, tracking codes, serial numbers and regulatory information on all kinds of consumer products and packaging. By imprinting such dynamic data directly on materials or finished goods, CIJ facilitates inventory control, authentication, safety compliance and supply chain tracking.

Food and Beverages

Date codes, ingredients lists, allergen info, tracking codes and more get imprinted right onto bottles, cans, bags, cartons and wrappers at filling or packaging stages. CIJ adheres despite condensation and abrasion from shipping, outperforming labels. A survey by packaging manufacturer Accraply found that across hundreds of converters, 89% used CIJ printers for secondary coding needs as of 2015, with 48% planning to increase future CIJ usage.

Pharmaceuticals and Medical Devices

Beyond mandatory expiration dates, CIJ imprints serialized codes or batch numbers to verify authenticity, prevent diversion of drug shipments and enable item-level tracking through complex global supply chains. According to a MarketsAndMarkets analysis, the pharmaceutical packaging and serialisation market is projected to reach $104.9 billion by 2026, with CIJ playing a major role in serialisation efforts.

Electronics and Automotive
From warning symbols to object markers, date stamps and serial numbers, CIJ indelibly marks precise permanent codes onto components as small as 01005 chip capacitors to aid inventory control and part lifetime tracking. During PCB assembly alone, over 12 million products per month get marked by CIJ. The automotive industry also relies heavily on CIJ to indelibly mark parts for identification and tracing.

"Continuous inkjet remains unmatched for precision marking during high speed electronics fabrication processes," says Dr. Mike Willis, Chief Scientific Officer at Cerulean, an industrial printing startup. "Whether micro-scale circuits or automotive powertrain components, CIJ imprints variable codes permanently onto everything from metals and plastics to glass."

According to industry surveys, 99% of automotive OEMs now utilize permanent product marking techniques as part of quality control. The vast majority – over 80% by some estimates – rely on continuous inkjet for fast flexible marking.

Cosmetics and Personal Care

CIJ effortlessly prints ingredients, logos, barcodes and other dynamic markings onto incredibly diverse materials like plastics, laminated foils and woven fabrics at production line conveyor belt speeds over 1000 feet/minute. This allows last minute customization and regionalization of product packaging.

To quantify growth among CIJ adopters, coding and marking specialist Danaher surveyed consumer packaged goods manufacturers and found a 12.6% year-over-year increase in CIJ printer usage in 2021 alone. Of respondents, 67% reported coding an increasing percentage of products using CIJ compared to older techniques like hot stamp or roller coders.

….And Many More

Pipes, wires, tools, toys, appliances, furniture – virtually every manufactured product benefits from CIJ marking for inventory control or surface personalization. The technology prints onto literal eggs and bananas in the peel without harming the consumable contents inside!

Recent Innovations Expand CIJ‘s Capabilities

Continuous inkjet technology continues rapidly improving in reliability, print quality and application range. For example, adding specialized UV curing modules after the print station instantly solidifies UV-sensitive inks by bombarding them with high intensity ultraviolet light. This greatly expands the number of inks and printable materials.

Alternatively, some cutting-edge CIJ systems apply a protective nano-layer coating on top of printed output using an integrated micro-deposition module. This nanoscale polymer or OTHER_ORGANIC_COMPOUNDS film just microns thick shields printed codes from wearing off over time – greatly extending code lifetime compared to bare ink.

On the hardware front, sophisticated self-maintenance features like automated printhead alignment, self cleaning cycles and nozzle failure detection all reduce overall maintenance while eliminating downtime and manual intervention. Modern controllers embed Linux-based operating systems and connectivity enabling remote code updates or control via cloud interfaces.

Upgraded electronics leverage faster processors and custom ASICs to enhance printed output quality through techniques like greyscale printing by modulating drop volumes. This expands printable colors and effects using traditional inks. Anti-piracy features have also emerged, like subsurface laser engraving markers embedded below a product‘s surface, only revealed after CIJ overprinting physically alters the surface layer.

The Future of CIJ Technology

Over 50 years since its debut, continuous inkjet remains unmatched for the majority of industrial printing applications thanks to intrinsic advantages rooted in its straightforward yet ingenious operating principle. While digital drop-on-demand inkjets now dominate the consumer desktop printing market, they can‘t rival CIJ‘s lean efficiency that effortlessly handles the toughest marking jobs.

With ever-growing production volumes and substrate variety in modern manufacturing, CIJ will likely continue dominating coding and marking applications for the foreseeable future even as the underlying technology evolves. Experts predict the industrial coding and marking equipment market to grow over 6% CAGR annually, reaching $7.57 billion by 2028 as more manufacturers switch to CIJ.

As an enduring pillar of industrial printing technology, CIJ‘s next 50 years seem assured thanks to continual technical ingenuity by industry engineers finding ways to exploit this unique printing process. Whether incremental tweaks or paradigm shifts, CIJ technology forms an essential backbone of manufacturing infrastructure across every industry.