Paper & humidity
Paper and humidity
The humidity of the environment can influence the 'runability' of paper in the printer. Fibres in the paper will swell or shrink when humidity in the climate around the paper changes. This influences paper stiffness and formation.
Humidity and temperature
When the relative humidity (RH) in the air around the paper is high, the paper fibres will take up moisture and swell. When the relative humidity is low, the air around the paper will extract moisture from the paper, so the fibres will shrink. This swelling or shrinking of fibres is also called deformation. The best relative humidity lies around 55% at 21 °c
Deformation and paper
Deformation mostly causes paper curl:
Waviness of the edges
The paper edges have become larger while the centre of the paper is still the same. This happens when paper is exposed to an environment with high relative humidity, or cold paper enters a warm place. The moisture condensates on the paper and the fibres in the edges of the paper swell.
Edges get shorter
The moisture close to the paper edge is extracted, so the edges shrink, while the centre of the paper remains the same. This is caused by air with a lower relative humidity than the paper.
Curl
Curl will appear if paper without a damp-proof wrapper is exposed for a longer time to dry air. This curl can also occur if the paper is quickly cooled down after facing a rapid temperature increase in the printer. In that case, on the complete surface of the paper moisture comes out of the paper.
Prevent
Deformed paper can get stuck in the printer and cause a paper jam. You can prevent this by opening the ream in an environment where both temperature and relative humidity are the same as where the paper is stored. As long as paper stays in the wrapper the relative humidity of the storage is not important. There will be no interference between the paper and the humidity in the surrounding air thanks to the damp-proof packaging. Once the ream will be opened, it is important to take care of the following timetable for acclimatisation of the paper:
Temperature differences between paper storage area and printer or copier location
| |
| 5°C/10°F | 8°C/15°F | 11°C/20°F | 13°C/25°F | 17°C/30°F | 22°C/40°F | 28°C/50°F |
| Number of Cartons | Acclimatisation times in hours (at least) |
| 1 | 4 | 8 | 11 | 14 | 17 | 24 | 34 |
| 5 | 5 | 9 | 12 | 15 | 18 | 25 | 35" |
| 10 | 8 | 14 | 18 | 22 | 27 | 38 | 51 |
| 20 | 11 | 16 | 23 | 28 | 35" | 48 | 67 |
| 40 | 14 | 19 | 26 | 32 | 38 | 54" | 75 |