Printhead Selection: Why Temperature Isn’t Everything

Operating temperature matters because it affects how a fluid behaves. In general, heating a fluid reduces its viscosity, which can make it easier to jet. For phase-change materials that are solid at room temperature, including certain waxes and hot-melt inks, heat is also required to melt the material before jetting can begin. 

There are therefore applications in which a very high operating temperature is indispensable. If a material has a high melting point, the printhead and wider fluid system must be able to reach and consistently maintain a suitable temperature throughout production.

But temperature is not always the application requirement in itself, sometimes it is the means used to bring a fluid into a printhead’s accepted viscosity range.

If a printhead can reliably jet fluids at higher viscosities, it may be possible to achieve the desired result without heating the fluid to the same extreme. Xaar’s Ultra High Viscosity Technology, for example, is designed to jet fluids at around 100cP under jetting conditions, compared with the much narrower viscosity range associated with conventional inkjet.

With this in mind, the question is not ‘what is the highest temperature available?’, it’s ‘what does this particular fluid and application need to perform successfully?’

A printhead does not operate in isolation. It forms part of a larger system incorporating fluid supply, electronics, temperature control, software, motion and material handling, as well as cleaning and maintenance processes.

Specifying a higher operating temperature can consequently affect more than just the printhead. Fluid must be heated and maintained at the correct temperature as it travels through the system, electronics may require additional protection or cooling, and the system must manage temperature changes during start-up, shutdown and production, while preventing unwanted solidification or changes in viscosity.

While a higher operating temperature may be absolutely necessary for an application, it does come with certain complexities, including system design complications, raised energy consumption, increased maintenance demands and cooling and heat-management requirements.

It is therefore critical that extreme temperature is only specified when there is genuine need. If a fluid can be jetted successfully at a lower temperature, specifying the highest available figure could add complexity without creating equivalent production value.

Ultimately, the objective should be to identify the temperature that enables stable, repeatable production, not simply the maximum temperature that can be reached.

When it comes to printhead performance, multiple factors must be considered. Drop size, firing frequency, resolution and fluid interaction can be just as influential as temperature in determining the final result.

For example, whilst a printhead designed to eject comparatively large drops may be well suited to applications requiring significant material deposition, the same printhead may be less appropriate where fine features, precise edge definition or tightly controlled surface coverage are required.

This means that specification must involve a level of feature prioritisation relevant to the application. A printhead might offer the highest operating temperature in its category, but does it also deliver the drop size, resolution and frequency required?

Xaar’s high-viscosity technology illustrates how fluid capability can contribute to print performance as well as material compatibility. Benefits include reduced spreading, improved edge definition and the ability to use fluids with increased pigment or particle loading. 

When balancing performance considerations, aspects such as print quality and temperature must be assessed together against the actual product requirement to ensure the central needs of the application are met.

Datasheets provide a valuable basis for comparing technologies, but they cannot reproduce every interaction between a printhead, fluid, waveform, substrate and production environment.

It’s also important to consider that the maximum capability figures stated on a specification sheet may not be intended to be achieved simultaneously. Maximum temperature, frequency, speed and material laydown should not automatically be treated as one combined operating point. 

A robust selection process should therefore move beyond test-condition figures and investigate how the printhead is likely to perform under conditions that reflect the proposed application.

Questions to consider include:

• At what temperature will the chosen fluid actually be jetted?

• What is its viscosity at that temperature?

• Can the system maintain that temperature consistently throughout the fluid path?

• What print quality is achieved at the required line speed?

   

• How quickly and reliably can the system start from cold?

• How stable is jetting during an extended production run?

If possible, testing with representative fluids, waveforms, substrates and production conditions provides a much stronger basis for decision-making than comparing isolated maximum values.

Printhead specification is all about finding the right balance of capabilities to meet the specific requirements of the application in question.

For one application, temperature may be the non-negotiable factor because of the material’s melting point. For another, the priority may be fine detail, higher jetting frequency, greater fluid viscosity, faster start-up, simpler maintenance or lower energy use.

The strategic approach to printhead selection is to start with the desired production outcome and work backwards:

• Define the material and its behaviour

• Establish the required print or deposition quality

• Determine the necessary speed and productivity

• Identify a practical jetting window

• Evaluate the implications for the complete system

   

• Test the proposed combination under representative conditions

• Compare the lifetime cost and operational risk

This produces a specification shaped by the application, rather than by whichever number appears most impressive on paper.

Industrial inkjet systems succeed when their component technologies work together.

Maximum operating temperature can be an important capability, but it should be considered alongside fluid viscosity, drop size, frequency, print quality, system complexity, reliability, maintenance and total cost of ownership.

By looking beyond a single headline figure, OEMs and manufacturers can select a printhead that meets the real needs of the application and delivers dependable value in production.

For more information on printhead specification.