The printing performance of the paper determines whether the printing process can proceed smoothly and whether high quality prints can be obtained. The quality of paper is related to the quality of printed products. Therefore, correctly understanding and understanding certain properties of paper is of great significance for accurately grasping the suitability of printing technology and ensuring the quality of printed products.
Surface strength refers to the bond strength between the surface fibers of the paper, the size of the compound, between the fillers, or between the coating particles on the surface of the paper and between the coating and the paper base. It has a decisive influence on the abrasion resistance, powder drop resistance and lint resistance of the paper surface during printing. In order to obtain clearer dots during printing, some inks with higher viscosity can be used. If the surface strength of the paper is insufficient, it is prone to powder falling and lint, and adhere to the surface of the plate.
In the printing process in Shanghai, when the ink is split between the paper and the blanket, the peeling tension is generated due to the adhesive force of the ink and the adhesion between the blanket and the paper. When the bonding strength is insufficient, a paper stick phenomenon occurs during the printing process to form a powder or a lint, which may cause the paper to rupture in severe cases. On the surface where the paper is stuck, white spots are formed where ink should be present. The loose coatings, filler particles and fibers can cause adverse consequences: First, the image is partially contaminated, and more and more paper and paper powder are accumulated on the printing plate, which will lead to paste printing and printing. The writing is blurred, the picture produces spots, which seriously affects the quality of the printed product. Secondly, the number of cleaning of the blanket and the ink roller in the offset printing increases, which reduces the printing efficiency. Increased the labor intensity of the printer.
If the surface bonding strength of the paper is insufficient, the viscosity of the printing ink must be appropriately reduced before printing to reduce the adhesion of the ink to the paper, and also to prevent surface sticking during printing.
2. Ink absorption
The so-called paper absorbency refers to the ability of paper to absorb ink. The ink absorption performance of paper is an important printability index that affects the quality of printed matter. Paper absorbency is mainly determined by the tightness of the paper fibers (the size of the gap). Printing paper requires a proper porosity of the paper fiber structure.
If the paper is too slack, the fiber gap is too large, and the ink absorption of the paper is too strong. On the one hand, the paper is easily pulled, and on the other hand, the binder is excessively absorbed into the paper layer or coating, causing the ink layer on the paper surface. The lack of binder allows the pigment particles to be suspended on the paper surface. After the conjunctiva is dried, the printed matter is old or tarnished. Even if the imprint is rubbed, the pigment will peel off in a granular form, causing pulverization. Paper that is too absorbing to the ink may also cause offset.
If the paper absorbs ink too little, it will slow down the drying speed of the ink on the surface of the printed product, the printing speed will not be lifted, and the back of the printed matter will be dirty, especially for the letter-drying and high-speed printing. In addition, in printing, paper with poor ink absorption performance is used, and ink adsorption performance after inking is also poor.
In addition, the paper should also have the uniformity of ink absorption, otherwise the ink color of the writing is different.