Not many print professionals truly understand the influence of paper moisture on various print jobs. High levels of moisture affect printing uptime and output quality. If you want to know how to distinguish “bad” or “good” moisture you should measure it.
The measurement of moisture content is on a scale of relative humidity (referred to as RH). Most papers are designed to have a relative humidity of 45-55% in a 72°F environment, and the manufacturers produce paper to an absolute moisture content between 4.0 and 6.0%. This means that water makes up 4 to 6% of the paper’s total weight.
The thing is, once the paper is unpacked, it can either absorb or release moisture. Paper will consistently try to reach equilibrium with the moisture in the air, so it will pick up moisture from its environment, and will release moisture into the environment.
For example, paper exposed to a 50% RH environment will accumulate moisture content of up to 7% in just four hours.
When dealing with papers for digital printing, take precautions to ensure optimum performance:
- Locate the press in a controlled temperature and humidity environment of 65-75°F and 40-50% RH.
- Store the paper in the original wrapper. The ream wrappers are designed as moisture barriers.
- To eliminate temperature differences between the paper and the environment, acclimate the paper in its wrapper at print room conditions for 24 hours before printing.
- Understand the importance of purchasing and using paper with the right moisture content for your purpose.
- Maintain stable moisture content through good paper handling within recommended guidelines.
To learn more about good paper handling practices, check out this article – Measuring Paper Moisture.