Among the four printing methods of flat concave and soft hole, only one method is obviously different from the other three printing methods on the principle of ink transfer. This is lithography, which is what we usually call offset printing. The most basic printing principle in offset printing is to use the two rules of incompatibility of oil and water, and selective adsorption of the printing plate to keep the ink and water balanced on the printing plate to achieve the transfer of the dots, and to achieve clear images and full colors Effect. This is where the term ink balance is derived. 7. Water and ink balance in color newspaper printing In the process of color newspaper printing, the overall control of the blue ink, red ink, yellow ink and black ink water and ink balance will directly affect the printing quality of the color newspaper. Newsprint is coarser and more absorbent than coated paper. Normally, the water-ink balance ratio in the newspaper printing process is larger than that in the sheet-fed offset printing. In the newspaper printing process, as the printing speed continues to increase, the contact time between the paper and the rubber cylinder becomes shorter and shorter, and the paper absorbs less and less water. At this time, the water supply is mainly used to balance the ink on the printing plate. Therefore, the overall water supply will continue to decrease as the speed increases, and eventually reach a critical value. In addition, since the color newsletter is generally only pictures or a few titles with colors, most of the text and titles are still black, so the water supply of the black ink printing unit is always larger than that of the color printing unit during the printing process, but the water volume should not be too large. Subject to no lateral deformation of the paper. Newspapers printed when the amount of water is too large have a wet hand feel. Therefore, we must strictly control the water-ink balance in the printing process. The following theoretically analyzes the effect of water-ink balance on newspaper printing quality. In a sense, only when the water film on the blank surface and the ink film on the graphic surface have a very strict boundary line, that is, the water blank area and the inked graphic area are objectively seen not to invade and mix with each other. Only when the water-ink balance is reached, in fact, absolute non-mixing is impossible, and the emulsification of ink is also inevitable. Therefore, the balance of water and ink is just a relative concept. It is worth noting that when the printing press maintains high-speed and stable operation for a period of time, the water supply is not as low as possible. In the actual production, due to the high speed of the imported rotary printing press, a large amount of heat will be generated during the high-speed printing process, and it will also rely on water to dissipate the heat and cool down. Therefore, the role of the fountain solution is not only to balance the water and ink, but also to reduce the printing plate and The temperature of the blanket also plays an important role. In addition, ink emulsification is not entirely a bad thing. In fact, slight W / O emulsification is beneficial to printing. It reduces the viscosity of the ink and improves the ink transfer performance. It also prevents the ink from sticking too much and pulling too much paper powder onto the rubber roller. In view of the above reasons, the water supply in actual production is slightly higher than the critical state.
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The so-called water-ink balance refers to adjusting the supply of fountain solution under a certain printing speed and printing pressure to ensure the newspaper printing quality and normal production, so that the fountain solution contained in the emulsified ink is less than 26%. A slight W / O type emulsified ink is formed, and the minimum liquid supply is used to compete with the ink on the printing plate.
In the production process, when the prepared PS plate is printed on the machine, its graphics and text are partially inked and transferred directly to the rubber cylinder, and the graphics and text are transferred to the paper through the two rubber cylinders, and at the same time, the printed blank Partially touch the water to prevent the ink from adhering to the blank surface. This shows that there is a balance between the water supply and ink supply to the printing surface. If the amount of ink supplied to the layout exceeds the balance (ink> water), the ink will expand to the blank part after being strongly squeezed, invading the blank part, causing dirty, otherwise, if the water supply to the layout exceeds the balance (water> Ink), it will leave more water on the surface of the printing plate and text, and the strong squeeze of the water roller and the ink roller will deeply emulsify the ink layer attached to the graphic and text, causing the blot to be dull.