Advice on storage of Paper and Board

The most common reason for complaints of paper and board is a consequence of the humidity of the air.

To avoid this and to create the best environment possible for paper and board follow the advice below.

The impact of moisture on cellulose fibre

The cellulose fibre that exist in paper and board is influenced by the moisture in the air of its surroundings.

If for example the surrounding air is more dry than the board then the board will evaporate moisture, which makes the fibres shrink and you end up with a sheet that swell in the middle, so called “curl”.

If on the other hand the air is more moist than the board then the fibres will take on the moisture which causes the fibres to swell and you end up with a ”wavy” sheet.

The fibres will be more affected cross direction than along the grain. If the fibres either swell or shrink, then it is not possible to condition them back to their original dimension.

Recommended Moisture and Temperature

Paper and board gets the least affected at a relative humidity of 45-55%. (Relative humidity= a measurement of the water content in % of the maximum moisture at a certain temperature).

If there is low relative humidity then the following things can happen to the material:

Changes of the dimension where the edges will shrink and the sheet will swell up in the middle, it can become static which has an impact on the run ability, the material can become brittle which can cause it to crack and there is an increased risk for dust.

If on the other hand the surrounding relative moisture is too high then it can cause the sheets to swell in the edges and that makes the sheets wavy and not flat.

If they are going to be printed the time for drying will be longer.

Instructions for Storage and Conditioning

The environment where the paper and board will be used needs to be controlled by climate control. A device for controlling the climate will compensate for the fluctuations of moisture and temperature. Relative humidity should be around 50-55%, temperature should be around 19-23˚C .

When the paper or the board arrives it is important that the wrapping of the material is unopened and that the material gets conditioned to the same temperature and moist that is in the surrounding environment where it will be used. Below you can see approximate time for how long this takes.

10˚C difference – 10 Hours

20˚C difference – 30 Hours

30˚C difference – 55 Hours

40˚C difference – 70 Hours

The material should never be stored on the floor but always on a pallet, don´t place it close to a radiator or air conditioning device.

If you have any further questions, please contact jill.andersson@swtpaper.se