The situation of the lithographic process shows that the proper size of the surface water is an important part of ensuring normal printing. The ideal printing process effect and product quality, under the condition of maintaining the ink and water balance, is to achieve the normal printing with as little water supply as possible. Therefore, accurately discerning the size of the layout and controlling the balance of ink and water are effective measures to ensure the quality of product printing.
At present, our printing industry to identify the layout of the size of the water method, are generally used visual inspection method, through the naked eye to observe the plate layout, the surface of the ink roller light intensity and print ink with or without dilute the situation to identify the layout of water is appropriate . The visual inspection method has certain limitations, and the accuracy of the judgment has a great relationship with the operator's observation ability, production experience, and skill level. The visual inspection method usually uses the illumination light source on the transmission surface of the printing machine to lean diagonally onto the printing plate layout, and according to the intensity of the reflected light brightness of the plate water film, the size of the layout moisture is judged. The production process clearly shows that the thicker the water film is, the stronger the brightness of the reflected light is, and the thinner the water film is, the weaker the reflected light brightness of the plate is. However, the same thickness of the water film, due to different conditions, the reflected light brightness will also be different, such as the layout of the text and blank area size, the strength of the light source, the thickness of the layout of the trachoma, the old and new printing plate, and visual observation The position and the angle of the station are different, which will affect the accuracy of the layout water discrimination. Therefore, when observing the layout moisture, it should stand on the other side of the light source so that the angle of incident light is equal to the angle of reflected light, so as to avoid visual errors and cause inaccurate discrimination. Throughout the daily survey method, it has certain feasibility, but it also has certain limitations, affecting the accuracy of the identification. Therefore, in production, in addition to observing some features, the layout moisture should also be checked and observed by adopting a sampling method, and the abnormal situation such as whether the layout is dirty or whether the print is pale or not is often checked. When the moisture is too small to resist the ink, dirt appears easily, and the ink has a distinctly faded visual appearance. When the plate surface water is too large, the ink emulsification value is also large, which will directly affect the viscosity, fluidity, and transfer performance of the ink. In addition, the size of water in the layout can also be determined from the following aspects in daily production:
1. The amount of water remaining on the surface of the ink roller will have a bright visual sense, and there will be accumulation of water droplets between the ink roller and the ink transfer roller.
2. When the ink on the ink roller produces a supersaturated emulsification amount, the ink will scald with the ink scoop. When the ink is added to the ink roller, due to the presence of a water film on the surface of the ink roller, it is difficult to stir the ink evenly, and slippage may easily occur when the ink roller is hem.
3. Small water droplets exuded in the ink fountain, and water droplets were visible in the ink fountain, indicating that the water was too large;
4. Before and after parking in the printing process, due to the temporary separation between the ink roller and the printing plate, the barrier effect of the water film on the ink transfer changes, too much moisture will cause the ink color of the printing product to change significantly;
5. After embossed paper, if it absorbs too much water, it appears soft and weak, and there is a lack of crisp sound in the conveying process;
6. Excessive moisture will hinder the normal application of ink, so that the ink accumulated in the ink roller, so that although the ink layer on the ink roller is thick, but the ink is still faded ink;
7. When the moisture is too large, the downtime is longer, and the plate surface moisture is not easily evaporated.
8. When there is too much water in the layout, the edge of the imprint of the printed sheet and the edge of the blank with large area are likely to show wavy voids.
9. When the moisture is too large, moisture remains in the dragged area of ​​the blanket. Excess moisture will form water droplets in the area. In addition, the blanket in the blanket cylinder and plate cylinder is also easily wetted by moisture;
10. If the printed sheet absorbs excessive moisture, the water will be deformed after being peeled off, causing downward curling, resulting in disordered delivery of the delivery table, and curling on the four sides of the printed sheet, resulting in uneven delivery;
11. When the moisture is too large, the dots of the printed product are empty, and the marks on the mouth of the mouth are wavy and pale, and the ink is dull and lacking in gloss.
To sum up, only by correctly grasping the moisture content of the lithographic printing plate, and controlling the ink and water balance conditions in the printing process can not only effectively prevent the occurrence of various printing defects, but also can improve the printing quality of the product.
Source: cpnic