A few weeks ago I worked on an assignment with a paper supplier who starting offering digital printing on their custom papers. When I walked through the door of their production facility I felt as though I walked into a wall of heat and humidity. It was about 90 degrees and 90% humidity.
The great surprise was that they knew that temperature and humidity affected their paper so they kept them in temperature controlled rooms, but they must not have realized the issues that heat and humidity created in digital print production. This reminded me of the first time I learned the effects of temperature and humidity on paper. I was sitting in a classroom at GATF (Graphic Arts Technical Foundation) in the orientation class as a new staff person.
Working for GATF was a great experience because it was all about education. When I was hired I was the youngest consultant on staff compared to people who had 20 or 30 years of experience almost all in the pressroom. I was brought on as the “digital guy.” Most of the courses at GATF were team taught so I would talk about “digital stuff” and sit in during the other presentations. This is where I learned about the color, scanning, offset printing and paper.
It was during these presentations that I learned about the role that paper plays in both offset and digital printing. Like any newbie I had no idea that moisture in paper was important in print production. I was fascinated by the discussion of how paper absorbs moisture from the air like a sponge and it is called moisture content. I remember the questions we were asked in class. Why do we have wavy paper in the summer? Why do we have static in the winter? Why do we fight curl year-round?
Best Printing is at Comfortable Conditions
Of course now I know all about the issues of humidity and moisture content. The moisture content of a print shop is measured as relative humidity and it affects the amount of moisture in paper. Typical paper is produced to an absolute moisture content between 4.0 and 6.0%, meaning 4 to 6% of the paper’s total weight is made up of water. But once unpacked the paper can either absorb or dissipate moisture. In the best conditions the paper is designed to be stable in a 45-55% relative humidity (RH) at 72°F environment.
The key is making sure you purchase and use the right paper for the right use and maintain stable conditions which are close to those recommended. Different printing processes work best with certain amounts of moisture. In digital printing the moisture content can affect the toner adhesion, paper jams and the fuser roller temperature. In offset it can affect the interaction between the ink and the press, the paper and the press, and the ink and paper. Inkjet is affected by many of the same issues but is even more susceptible to dot gain or ink spreading, drying delays and ink show through.
On this assignment the focus was inkjet printing. There is a tremendous amount of new product development with inkjet papers because of the focus on inkjet presses. But in general inkjet paper is optimized for ink absorbency, color development, water resistance, light resistance, gas resistance, and run ability. The problem was that printing at 90 degrees and 90% humidity is troublesome for most digital printing processes.
Have you run into any issues when the temperature and humidity is too high in the summer or too low in the winter?