In lithographic offset printing, the amount of water on the surface of the printing is transferred and overprinted. The balance of ink and water, drying, plate life, paper collection, and gloss of the ink layer all have important aspects. Therefore, how to control the amount of water in the layout to the best state has become a concern for printing operators.
The consumption of ink in offset printing is relatively fixed and easy to control, but relatively speaking, the control of the amount of water is not so easy. The main reason is attributed to the large fluidity of water and easy evaporation. There are many ways to consume water. Changes in environmental conditions. Then, there is no definite standard for the size of the layout water, and we need to understand some decisive factors that affect the amount of layout water:
1. The area and distribution of the graphic on the plate. Under normal circumstances, the size of layout water is proportional to the size of the graphic area.
2. The thickness of the imprinted ink layer and the nature of the paper. The layout water volume increases with the increase of the ink layer thickness. In addition, the alkaline paper needs more water than the acid paper, and the coated paper requires a smaller amount of layout water than the offset paper.
3. The nature of the ink and the size of the emulsification. When printing with dark ink, the amount of water on the layout is slightly larger than the light color ink. For printing color, the water consumption for the four inks is M>K>C>ä¸«. In addition, in the deployment of ink, a certain amount of dry oil is generally added as an auxiliary agent, and the amount of water should increase with the increase of dry oil addition volume.
4. Machine speed. The faster the machine speed is, the smaller the water consumption is.
5. Temperature, humidity, and ambient air flow. When the working environment humidity is less than 65:6, the water consumption can be appropriately increased; when the working environment temperature is higher than 26Â°C, the water consumption should be increased as appropriate.
6. The thickness of the grain on the surface of the plate. The coarser surface of the plate used for water consumption is slightly larger than the plate for fine sand.
7. Plate types and surface properties. When using a zinc oxide plate for printing operations, the amount of water used is higher than that of the PS plate.
Only when we know the above points well can we better control the amount of water in the layout so as to ensure the smooth operation of the printing operation. Produce high-quality prints.
In addition, because there are many variables that affect the amount of water on the layout, it is important to pay attention to the change in the amount of water on the layout and correctly identify the amount of water in the layout during the printing process. Here are some of the more practical ways to identify the size of the layout water:
1. Observe the surface of the printing plate. If the plate is bright, it indicates that the layout is too large.
2. When the amount of water in the layout is large, a certain amount of water will be transferred to the ink roller. Therefore, when water droplets are visible in the ink fountain or on the ink roller, the amount of water in the layout is excessive.
3. There is too much water on the surface of the ink film. When the ink scraper scrapes ink with water droplets, the ink is not easy to be even, and when the ink transfer roller has slippage, the amount of water in the layout is too large.
4. There is a lot of ink on the ink roller. Ink is thick. When the ink roller is separated, there is a lot of buzzing, indicating that the layout volume is too large.
5. Blot ink is light, even if the amount of ink added is not easy to deepen the ink in a timely manner, indicating the layout of water is too large.
6. Before and after printing is interrupted, the ink roller is temporarily separated from the plate. The barrier effect of the water film on the ink transfer changes. If the layout water is too large, there will be a big difference before and after the ink color.
7. The sheets absorb excess moisture, positive. The amount of water on both sides is uneven, and the large amount of water is also deformed, causing curling of the paper and difficulty in delivery.
8. The tugs have moisture retention and excessive amounts of water will drop water droplets there.
9. After the machine shuts down, the layout is not dry, indicating that the layout volume is too large.
10. Install a water film thickness gauge on the machine.
Under normal circumstances, while ensuring the printing quality, the smaller the amount of layout water, the better. However, how to control the amount of water in the layout is just right. It remains to be further explored in the subsequent production practices to find a more scientific and effective way to solve the difficult problem of layout water control.
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