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The Technology Inside: Inkjet Print Heads

March 20, 2013

The drops of ink, when arranged algorithmically by the millions into patterns on media, can compose breathtaking photorealistic images, intricately detailed schematics and spectacular works of art.

In many ways, inkjet print heads are among the most innovative and visionary technologies of our time. For professionals and consumers alike, inkjet printing technologies have made producing full color high quality photographs, documents and fine art reproductions easier, cleaner and more affordable.

At the time, the invention of inkjet printing represented a significant departure from concepts behind most other forms of printmaking. Before the advent of inkjet print heads, most other printing methods required the application of ink directly onto paper with a printing plate or printing blanket that carried ink to make a physical impression on the surface of the paper. This need often meant that printing presses were large, messy and expensive.

As an alternative to conventional direct printing techniques, early developers of inkjet printing realized that near-microscopic drops of ink could be “sprayed” onto paper in a controlled manner to produce images on demand. The drops of ink are so small that are each one is almost invisible to the human eye, yet when arranged algorithmically by the millions into patterns on paper (or other media) these tiny drops of ink can compose breathtaking photorealistic images, intricately detailed schematics and spectacular works of art.

One of the characteristics of inkjet printing that makes the technology truly revolutionary is the elimination of direct contact between the print head and the surface of the media on which an image is being produced. By eliminating the need for direct contact between a printing plate and paper, the inventors of inkjet printing opened the doors to easier, cleaner and lower cost printing on a wider variety of paper and media types.

So what’s inside an inkjet print head and how does it work?

The anatomy of the modern inkjet print head is comprised of a tiny chamber where ink is fed and an even smaller nozzle out of which the ink is ejected by force, as needed, one drop at a time. This method, known as Drop-On-Demand (DOD), enables a high level of control over the rate and placement of ink drops to produce high quality and high-resolution images.

Today, there are two primary types of inkjet print head technologies in use: Piezo and Thermal. The main distinction between the two types is the method used to “force” drops of ink out the nozzle. Both technologies have unique strengths and advantages.

Piezo Inkjet Print Heads are often found in production printing and sign making devices. Piezo inkjet print heads force ink out the nozzle by pulsating a tiny membrane within the ink chamber. The pulsating movement of the membrane creates a pressure wave that pushes ink from the chamber and out the nozzle. The movement of the membrane is stimulated by piezoelectric material that can be made to flex and bend when exposed to an electric charge. Because electrical charges can be turned on and off, quickly flexing the piezoelectric material can be precisely controlled, like a switch, and thereby be used to control the rate of ink being ejected through a nozzle.

Among the strengths of the piezoelectric inkjet print heads is that the mechanism is compatible with a variety of ink formulations including aqueous (water), oil, eco-solvent and solvent based inks. This feature makes piezo inkjet print heads especially useful for certain production printing applications, such as signs and banners, because solvent based inks can be printed on low-cost vinyl which is popular for outdoor applications.

The disadvantages of piezo inkjet print heads include high acquisition and maintenance costs. Though piezo print heads are highly durable and long lasting, they are also expensive to manufacture and replace. Over time, the performance of all print heads tends to slowly deteriorate and will eventually need to be replaced. While the lifespan of a piezo print head is longer than a thermal print head, it is more problematic when it comes time to replace the piezo print head. Most thermal print heads are designed for easy-end user replacement whereas piezo print heads typically require a service technician. This increases the maintenance cost of piezo inkjet print heads and extends the downtime during which the printer is unusable. The cost of piezo inkjet print heads has therefore limited their appeal in many professional, office and home printing applications.

Another limitation of piezo inkjet technology is print speed. The most commonly found piezo inkjet print heads have just 720 nozzles. This means that to achieve higher resolution imaging, the print head must make multiple passes over the media and repeatedly ejecting ink onto the same area of media until the desired level of dots per inch can be achieved. This need for multiple print head passes results in slower overall print throughput speeds, but produces a high-resolution image.

By comparison, Thermal Inkjet Print Heads offer a number of advantages over piezo inkjet print heads. As the name suggests, thermal inkjet print heads use heat (rather than piezoelectric materials) to force ink from the chamber and out the nozzle. Conceptually similar to the way water bubbles when boiled, thermal inkjet print heads use heat to rapidly create a bubble of ink vapor within the print head chamber and forces ink to eject out through the nozzle. After ejecting ink, the chamber then cools quickly to allow more ink to refill the chamber and the process is repeated.

The use of a vapor bubble to force ink out the nozzle is ingenious because, unlike the membrane in a piezo print head, a thermal inkjet print head has no moving parts. This means that a thermal inkjet print head is less expensive to produce and is less likely to clog. The low cost and high-performance ratio of thermal inkjet print heads has been a key driver behind the popularity of the technology for professional, office and home use devices.

Over the years, Canon has invested heavily in thermal inkjet print head technology and is credited with the development of a specific type of thermal print head known as “bubble jet.” Using the same high precision technology used in making semi-conductors, Canon has perfected a technique of print head manufacturing known as Full-Photolithography Inkjet Nozzle Engineering (FINE). This patented Canon process enables the manufacturing of high density print heads with exceptional precision. Whereas typical thermal print heads have a maximum of only 600 nozzles, Canon produces print heads for imagePROGRAF printers with a total of 15,360 nozzles. This high density of nozzles means that Canon print heads are able to eject more drops of ink with each pass over the media to produce higher resolution images faster than other manufacturer’s thermal or piezo print heads. In addition to creating print heads with a higher density of nozzles, Canon has also positioned the heat source more directly over each nozzle. By optimizing the position of the heating element, Canon print heads are able to more precisely control the force of ink ejection and increase the accuracy of ink drop placement onto the media. The result is the ability to produce higher quality images with greater detail in less time.

The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.

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