Paper Properties: Surface Strength
Paper surface strength is a technical index to evaluate the binding force between paper surface fibers, fillers and rubber materials.
Paper with high surface strength is not easy to fluff during the printing process. The method of measuring the surface strength is to measure it with an IGT instrument (printing suitability Tester). The surface strength is determined by the critical speed of napping, and the unit is cm/s.
Paper strength has a great influence on printing. There are many technical indicators to express paper strength, such as breaking length, bursting resistance, folding resistance, tearing degree, friction resistance, etc., and printing workers are most concerned about surface strength. Low surface strength of paper will cause powder drop, lint loss, fuzzing, paper peeling, plate paste and other phenomena, which will directly affect printing speed and quality of printed products.
Lint refers to the phenomenon that the fibers on the surface of uncoated paper are pulled off individually. These sticky fibers adhere to the surface of the printing plate or blanket, and the next few printed sheets will be defective. In severe hair loss, the paper hairs will move against the direction of ink transmission, mix with ink, and then fill in the gaps between dots or lines on the printing plate to cause paste. A slight paste will affect the printing quality, and a serious one will cause the printing plate to be scrapped.
Peeling paper refers to the fact that the surface of the paper is peeled off in pieces due to the poor surface strength of the paper during the printing process. The peeling phenomenon mostly occurs during the printing process of coated paper. The peeled-off fragments stick to the printing plate or blanket and are not removed in time. After several impressions, the fragments are firmly stuck to the printing plate or blanket. The part of the debris is higher than other parts of the printing plate or blanket, and the debris is equivalent to a solid letterpress that will print a large ink dot, and around it is a white ring that cannot be printed with ink, which is the so-called annular white spot.
In order to overcome the printing quality problems caused by insufficient paper surface strength, measures such as reducing the viscosity of the ink (using a detackifier), reducing the thickness of the ink layer, slowing down the printing speed, and reducing the printing pressure can be taken, but this will reduce the printing quality. and production efficiency. The surface strength of paper is closely related to the quality of papermaking materials and papermaking machines, so the price of paper with high surface strength is very high.
