Storage advice for paper and paperboard
The most common reason for complaints about paper and paperboard is due to the humidity of the air. To avoid this and to create the best possible environment for paper and paperboard, follow the advice below.
The effect of cellulose fiber on moisture
Cellulose fibers found in paper and paperboard are greatly affected by the humidity they are surrounded by. If, for example, the surrounding air is drier than the paperboard, the paperboard will emit moisture, this causes the fibers to narrow and you get a sheet that curves out in the middle. If, on the other hand, the air is more humid than the paperboard, then the fibers will absorb the moisture, which causes the fibers to swell and then the sheets become wavy. The fibers change more across the fiber direction than along. Once the fibers have swelled or narrowed, it is not possible to condition the material back to its original dimension.
Recommended humidity and temperature
Paper and paperboard are least affected at relative humidity between 45-55%. (Relative humidity = a measure of the water content of the air in % of the maximum humidity at a certain temperature). If the ambient moisture is too low, the following things can happen with the material: Dimensional changes where the edges contract and the sheet bulges out in the middle, it can become static which affects driveability, the material becomes brittle which means that it can crack and there is a greater risk of dusting.
If, on the other hand, the ambient relative humidity is too high then it can cause the sheet to swell at the edges which makes the sheets wavy and uneven, if it is to be printed it gives a longer drying time.
Storage and conditioning instructions
The environment in which the paper and paperboard will be used needs to be controlled by air conditioning. An air conditioning system will compensate for the changes in humidity and temperature that occur. Relative humidity should be between 50-55%, the temperature should be between 19-23˚C.
When the paper or paperboard arrives, it is of the utmost importance that the packaging is unbroken and that the material is conditioned to the same temperature and humidity that is present in the environment where it is to be used. Below you can see approximately 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, nor should it be placed near elements or air conditioning systems.