The thickness, tightness, smoothness, dustiness, water content, pH of packaging paper printing paper and its influence on offset printing.
(1) Thickness. Refers to the thickness of the paper, the thickness of the paper should be uniform, otherwise it will cause obvious differences in the printing effect.
(2) Tightness. Tightness refers to the degree of looseness or tightness of the paper structure, also called specific gravity or volume. Tightness is closely related to ink absorption and smoothness. Generally, the ink absorption of paper decreases with the increase of tightness, so the paper with high tightness should use oxidized conjunctival drying ink.
(3) Smoothness. Smoothness refers to the smoothness and smoothness of the paper surface. The smoothness determines the closeness of the contact between the paper and the blanket. Obviously, the clarity of graphics printed on poorly smoothed paper will be affected.
(4) Degree of dust. Dustness refers to the presence of black and non-black spots on the surface of the paper that are different from the paper color. In offset printing, the restrictions on dust are mainly determined according to the requirements of the printed matter. For example, when printing portraits and maps, large dust and black dust spots are not allowed.
(5) Water content (degrees). Moisture content refers to the moisture content of a certain weight of paper that is in equilibrium with the relative humidity of the environment at room temperature. It is also called moisture content, or moisture for short. Generally, the water content of offset printing paper is between 6% and 8%. If the water content of the paper is too high, the tensile strength and surface strength are reduced, the plasticity is increased, and the ink film curing at the printing speed is delayed, which will result in tight edges, ruffles, curls or unevenness, and wrinkles and folds during printing.
(6) pH. PH refers to the acidic or alkaline nature of paper (expressed by pH). The pH of the paper is an important factor that inhibits or accelerates the drying of the ink or affects the pH value of the wetting fluid, and also affects the durability of the printed matter (ink fading).