At times, ambitious sign makers want to purchase a ValueJet printer and run it from the back of a bread truck as a mobile print shop. This is not a new idea, but it is a really bad idea for two reasons. The first is environmental, the second physical.

Environmental Challenges

Mutoh ValueJet and PrismJET printers have a specific operating range of temperature and humidity. Both are important to achieving good print quality ambient temperature: The recommended temperature range is 68 – 89°F. If run within this range, the printer works well, the media works well, and all is right with the world.

So what happens if you mess up?

If the ambient temperature is too low, the ink will lose its viscosity. Piezo print heads have extremely small nozzles through which the ink must be jetted. If the ink is too cold, it will thicken and will not flow through the nozzles. The result is poor print quality. If the ambient temperature is too high, the media will be too hot. In ecosolvent printers, the media has to be warmed before the ink hits it for optimal ink absorption. If the media is too hot, it will absorb too much heat and begin to ripple on the platen. This affects the distance between the head and the media and distorts the colors.

Relative Humidity

The recommended relative humidity range is 40 – 60%. Relative humidity affects both ink and media, but primarily the media. Again, the idea is for the media to absorb the ink. When an ink drop hits the surface, it spreads slightly. This is called “dot gain” and is part of the process of covering the media and getting a balance of rich color and crisp detail. If the relative humidity is too high, the media will already be oversaturated with moisture from the atmosphere. The result is excessive dot gain, which can result in dark banding and loss of crisp detail. If the humidity is too low, there may be insufficient dot gain, resulting in washed-out color and possible banding caused by the ink simply not covering the media. (Speaking of which, if your printer is indoors, but you store media in an area that’s not temperature controlled, make sure you bring the media indoors and give it a chance to warm up or cool off before you start printing.)

Physical Challenges

The operation of a modern digital printer requires a very precise harmony of movement between the print head and the media. This is dependent on correct head alignment and step adjustment. Running a printer in a moving vehicle, or even driving around with it in the back of a truck, is a pretty good way to knock it out of alignment.
As Brian Phipps from Mutoh puts it, “The constant jarring of the equipment could cause head alignment issues and a host of other issues.”

Unless you have an exceptionally nice truck like, say, a Nextel Cup or NHRA car trailer, you should think twice about setting up a mobile large format print shop.