With the ever changing weather in the UK the storage of paper is more important than you think. Fibres in paper store humidity and moisture and could affect printing quality and cause digital press jamming.

Paper is hygroscopic; meaning it picks up moisture from its environment and it will release moisture into the environment to try to reach equilibrium with the moisture in the air. Other hygroscopic substances include cellulose fibres (such as cotton and paper), sugar, caramel, honey, glycerol, ethanol, methanol, diesel fuel, sulphuric acid, methamphetamine, many fertilizer chemicals, and many salts including table salt.

Moisture content is important in inkjet, laser, and offset printing, so the importance of purchasing and using paper with the right moisture content is paramount. You should try and maintain stable moisture content with your paper handling to try to work within the recommended specifications.

The newer printing technologies such as high speed laser and inkjet have had a changeable affect on printing and the effect of moisture content on the paper transport, toner adherence, and quality because of the absorption of inkjet inks and inkjet papers.

How is Moisture Content Measured?

Moisture content 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 (this is not unusual of many manmade sundries). But once unpacked, the paper can either absorb or dissipate moisture. Most papers are designed to be stable in a 45-55% relative humidity at 22°C environment.

A complete lack of moisture would result in the paper become dust as water is obviously vital to the stability of the material. 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.

Storing and Handling Paper

• Store the paper in a room where the temperature and humidity are controlled. If that is not possible, leave the paper in the room that it will be printed in for 24 hours.
• Keep the paper shrink wrapped and away from outside walls.
• Before you remove the wrap, make sure that the paper is the same temperature as the surrounding air.
• Keep your production space between 45 – 55% RH, temperatures constant and near comfortable conditions.
• Watch outside doors for moisture loss/gain, especially from loading docks and consider installing a second barrier such as plastic or forced air between the docks and production areas.
• Acclimate the paper after printing to allow moisture return (offset, laser) or “outgas” (inkjet)

Following the guidelines and advice of the Paper and Ink manufacturers can save you money and effort.