Yes, it is. Previously, I had focused on industrial inkjet challenges which require a change in ink formulation. In this article I’ll focus on the production environment, specifically temperature. The importance of which is often underestimated. I’ll share my experience by way of example.
Global Limited, a company I just made up, decided to install a digital printer on their production floor. They removed a screen press near a dock door in their packaging warehouse. Historically, screen printing their promotional products was the last step before packaging and shipping. The new inkjet press will allow customization, eliminate prepress, reduce labor, and shorten lead time significantly. On paper, this is the classic “no brainer”.
Installation went smoothly, as did operator training. It took time for Global Limited’s sales team to win over existing clients on the value of customization. A few months past. Work was slow and sporadic on the new digital line but growing steadily.
I received a phone call in May from the operations director asking if I could fly out for a visit…..ASAP. Sales had successfully primed the pump for the new digital line and a large consumer products company expects delivery of massive orders continuing through summer. A second customer signed a deal for a fulfillment program requiring significant output from the new inkjet printer. The deal would require the implementation of a second inkjet press later in the year. Global already decommissioned a staging area and pad printer in the neighboring warehouse for the new work.
“That sounds great, so what’s the problem?”, I ask, along with the usual questions in preparation for a site visit. The director explains with frustration, “Essentially, the down time is killing us…We can’t run more than 10 minutes before we have to stop. There is no pattern.” Some of the issues he was experiencing include, rapid deterioration of image quality, color shift through the day or week, drop out, excessive satellites, misting, banding, nozzle starvation….then nozzle plate flooding, short printhead life, and decreased ink shelf life.
Well, I love a challenge…
Global Limited has a massive plant just south of Fort Collins and I’m impressed with the size of their operation. The beauty of industrial inkjet is the barrier of entry is quite low. I have seen a husband and wife take out a second mortgage to finance a small digital flatbed to start a sign shop out of their garage! You can get into digital embellishment on any budget along with some ingenuity. However, Global’s plant was on a much larger scale housing a range a range of flexo, screen, pad printing operations, along with a fab shop, and paint booths for more complex projects.
It’s a chilly 44°F when I arrive at the plant and the shift lead takes me straight out to the digital line. He can see I am a little underdressed for the plant temperature and reassures me I will be complaining about the heat by noon!
Temperature
At the heart of every digital printer is the intimate relationship between the ink and printhead. The temperature of the ink is inversely related to the viscosity of the ink. Below is a plot of the temperature - viscosity sweep of an inkjet ink.
As you can see, as temperature drops, the viscosity increases. And vice versa. Printheads are into stable relationships without a lot of surprises or change….especially around viscosity. Without getting into ink delivery, waveform design, negative pressure, ink properties and its influence on jetting, let’s just say that holding ink temperature constant is critical for success in industrial inkjet.
Holding ink temperature constant is critical for success
The warehouse has no climate control. In spring and summer, the warehouse is cold in the mornings and progressively warmer all day. In fall and winter, employees wear layers, and there are space heaters located by the cubicles. We can also expect to see significant blasts of hot or cold air when dock doors are opened for trucks depending on time of year. Employees are used to it and their other print and converting operations behave just fine.
As we discuss the impact of unstable temperature and inkjet with the operations team, there is frustration as climate control in the warehouse would cost a fortune and isn’t feasible. I am also told that as part of the sales process, engineers from Global and the digital press manufacturer did run productivity runs and sustaining tests to ensure fit for use. I know the answer but ask anyway, “Where were all these tests run?”
Testing of a pallet of customer supplied material was coordinated with a distributor using a demonstration center asset. HVAC held temperature at 70°F 24 hours a day. Humidity was controlled by a commercial grade humidifying system aiming for 50% to minimize static. All windows were blocked. The printer’s power supply as well as compressed air were also tested for stability. Substrates and fluids for the press were also stored in climate control. Results were great!
Inkjet presses are typically designed to run in an environment with a temperature set to 70° Fahrenheit. I have yet to see a digital press which had color profiling or operating window validated in under varying environmental conditions. A digital press may have onboard heaters, fans, and exhaust but ultimately the printer is designed to operate in a stable environment similar to that of an office. If you are planning to operate a digital inkjet press in a manufacturing space without climate control, you have to test this…. exhaustively. That means waveform, negative pressure, waveform, voltages, even profiles for color gamut will need to be evaluated at plant temperatures you expect the inkjet press to experience. Otherwise, you cannot assume reliable long runs hitting print target specifications.
What can Global Limited do at this point?
Climate Control
The most reliable solution is to implement an HVAC system so that the environment for their digital press is constant. It will create an environment the printer was engineered and tuned for. This is typically the costliest solution and not what clients want to hear. Previously, at a midwestern corrugated plant, when I brought this up I was told, “Absolutely not, it will kill the whole business model!”
Isolation
Let’s move on to plan B then! With a massive plant and a digital press that is having a hard time due to fluctuating temperatures, we can erect a climate control structure around the press. You can also move the digital line to an area with climate control. I have seen several factories using industrial inkjet to produce building panels, ceramic tile, display graphics, and thermoforms literally built a room around their digital press. Typically, this would entail framing a room around the press, and hanging drywall. Although I did see a plant in Europe once literally but the press in what looked like a plastic bubble! But it works.
Press Modification
Its really not the whole press which suffers from varying temperature. The print zone is usually the most sensitive. Whether the print bars on a single pass or the carriage on a scanning system, this is the area where climate control is most critical. Press engineers could work on enclosing and conditioning the print zone. However, I would not expect you will be able to take delivery of a customized print zone from an inkjet press manufacturer quickly. The Glory1604 is one example of an inkjet press built with an enclosed cabin around the print zone to control both temperature and humidity to aid in both printing and drying.
In the end, Global Limited determined the fastest solution to implement was to build a small climate controlled room around the press and mount two mini splits spec’d to provide the necessary heat or conditioned air to hold the room at 70°F. The press did require exhaust and so the room air balancing wasn’t perfect but quality and reliability was greatly improved.
Temperature is an often overlooked variable when setting up a new industrial inkjet process. The reason being is that analog printing and manufacturing processes are much more flexible when it comes to environment and its assumed an inkjet printer will not require anything different. Over the course of 30 years in printing very seldom have I come across climate-controlled production floors beyond the front office and break room. As companies embrace industrial inkjet, investments in creating an optimum environment need to be addressed in early stages to avoid costly problems later.
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