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The non-uniform uptake of water or atmospheric moisture on two sides causes the side with greater moisture content to expand; thus curling towards the drier side. Curling is common for papers that are only coated on one side. Curling can be corrected by equalizing the uptake of atmospheric moisture of both sides. For single side coated paper, increasing coating hydrophilicity can minimize or prevent curling.
Dot gain is the increase of the applied ink drop's diameter (ink droplet spreading). One possibility is to reduce the paper surface porosity, another possibility is to increase a little bit the hydrophobicity of the paper (adding wax-based performance additives) or to increase the ink viscosity.
There are different kinds of mottling but nearly all have the same source: non-uniform liquid uptake. In order to prevent this we are using different wax-based performance additives in order to uniform the liquid uptake.