Paper warpage
The paper delay is the areal shrinkage (also shrinkage or paper input ) or stretching (also swelling or paper output ) of a sheet or sheet of paper . On the trimmed sheet, the shrinking and swelling during the moisture balance is expressed as plates or waves .
The paper warpage is due to the organic composition of the paper and to the fact that its physical and chemical properties change with fluctuations in humidity . At a certain humidity and temperature , depending on the nature of the fiber , paper absorbs a fixed amount of water from the air. Over time, light also changes the chemical composition and thus the water absorption characteristics of the paper.
In the general use of the finished product ( books , newspapers , photo paper ), the paper warpage does not play an essential role. It is important, however, when the paper is being processed or has to contain dimensionally accurate representations as a character carrier or is exposed to unsuitable, extreme environmental influences . Then the paper distortion is often the cause of processing and storage difficulties. In the case of dimensionally accurate representations (e.g. cartography documents ), the paper distortion can render the representation unusable.
The paper distortion that has occurred can be calculated if exactly known reference distances are attached at the time the drawing is created (if possible in the direction of the longitudinal and transverse expansion of the sheet), e.g. B. Scale bars or grid crosses . By measuring these distances and calculating them, you get a factor that indicates the longitudinal and transverse warpage of the paper. The paper distortion should also be noted when scanning , where it can be corrected digitally on the scan.
For less precise representations, the paper distortion can be estimated, provided that the direction and type of fiber are known. The ratio of the longitudinal and transverse swelling of the fibers is approx. 1: 3.
In order to avoid paper warping, paper for dimensionally stable character carriers is processed together with other materials. It is common to combine plastic or metal foils with papers, e.g. B. with laminated drawing board , laminated film material , paper-coated glass , polymer film , etc.