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Precautions for printing paper and paper storage
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Thickness, tightness, smoothness, dustiness, water content, pH and impact of printing paper on lithographic offset printing
(1) Thickness. Refers to the thickness of the paper, the thickness of the paper should be uniform, otherwise the printing effect will be significantly different.
(2) Tightness. Tightness refers to the degree of looseness or tightness of the paper structure, also known as specific gravity or volume. Tightness is closely related to ink absorption and smoothness. Generally, the ink absorbing property of paper is lowered as the tightness is increased, so that a paper having a high tightness should be an oxidized conjunctiva drying type ink.
(3) Smoothness. Smoothness refers to the smoothness and smoothness of the surface of the paper. The smoothness determines the tightness of the contact between the paper and the blanket. Obviously, the sharpness of the printed text on the paper with poor smoothness will be affected.
( 4) Dust degree. Dustiness 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). Water content refers to the water content of a certain weight of paper, which is balanced with the relative humidity of the environment under normal temperature conditions, also called moisture content, referred to as moisture. Generally, the water content of offset paper is between 6% and 8%. The water content of the paper is too high, the tensile strength and the surface strength are lowered, the plasticity is enhanced, and the ink film of the printing speed is delayed, and the tight edges, the ruffles, the curls or the unevenness are formed, and wrinkles, pleats, and the like are generated during printing.
(6) pH. Acidity refers to the nature of paper that is acidic or alkaline (in pH). The pH of the paper is an important factor in inhibiting or accelerating the drying of the ink or affecting the pH of the dampening solution, while also affecting the durability of the print (ink fading).
How can I keep my paper safe? What issues should I pay attention to during the storage process?
Because paper is one of the important materials in printing production, it is very important to store and manage paper. Paper should not be thrown from high to low during transportation to avoid loose parts and damage. Do not erect storage and transportation, should be flat, should not be parked in the open air for too long, to move into the workshop or warehouse in time.
Paper that has not been subjected to humidity control should be noted when storing or storing it in the workshop or warehouse:
(1) Paper is moisture-proof. Paper is very sensitive to the humidity of the air, and the moisture content of the paper always changes with the humidity in the air. The warehouse where the paper is stored should be cleaned, dried, or placed directly in the offset shop. The pile should be off the ground and away from the wall. The indoor relative humidity of the storage area is preferably maintained at 60% to 70%, and the room temperature should be 18 to 22 °C.
(2) Paper sunscreen. The paper must be protected from direct sunlight. Otherwise, the paper will be brittle and yellow due to evaporation of water, and the paper will be warped and deformed. Even worse, it will not be used for printing.
(3) Paper heat protection. Paper should not be stored in places where the temperature is too high. When the paper is subjected to a high temperature of more than 38 °C, its strength is significantly reduced, and it is warped and deformed. In particular, the coated paper will stick to pieces and cause scrapping.
(4) Paper folding prevention. Paper storage should be flattened and stacked, absolutely avoiding the placement of one fold and three stacks. When stacking, do not make the ends of the paper staggered, otherwise the protruding parts will easily deteriorate.